U.S. patent application number 11/462207 was filed with the patent office on 2008-02-07 for moving bed biomass fractionation system and method.
This patent application is currently assigned to PureVision Technology, Inc.. Invention is credited to Kiran L. Kadam, Richard C. Wingerson.
Application Number | 20080029233 11/462207 |
Document ID | / |
Family ID | 39028013 |
Filed Date | 2008-02-07 |
United States Patent
Application |
20080029233 |
Kind Code |
A1 |
Wingerson; Richard C. ; et
al. |
February 7, 2008 |
MOVING BED BIOMASS FRACTIONATION SYSTEM AND METHOD
Abstract
Countercurrent extraction of lignocellulosic biomass such as
trees, grasses, shrubs, and agricultural residues or waste involves
the separation of cellulose fibers from other constituents, for
subsequent use in the manufacture of paper, plastics, ethanol, and
other industrial chemicals. Systems and methods involve continuous,
multiple processing steps that may include chemical reactions with
mixing at elevated temperature and/or pressure, efficient reagent
or solvent utilization, filtration at elevated temperature and/or
pressure, controlled discharge of liquid and solid products, and
energy recuperation.
Inventors: |
Wingerson; Richard C.;
(Sandpoint, ID) ; Kadam; Kiran L.; (Golden,
CO) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER, EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
PureVision Technology, Inc.
Ft. Lupton
CO
|
Family ID: |
39028013 |
Appl. No.: |
11/462207 |
Filed: |
August 3, 2006 |
Current U.S.
Class: |
162/60 ; 162/233;
162/238; 162/246 |
Current CPC
Class: |
D21C 3/24 20130101; D21C
7/00 20130101; Y02P 70/10 20151101; Y02P 70/24 20151101; D21C 3/00
20130101 |
Class at
Publication: |
162/60 ; 162/233;
162/238; 162/246 |
International
Class: |
D21C 7/00 20060101
D21C007/00 |
Claims
1. A continuous, countercurrent process of one or more stages for
the fractionation of a lignocellulosic biomass feedstock,
comprising: feeding the biomass feedstock into a first stage of a
pressurized reaction vessel; injecting a first wash liquid into the
first stage countercurrently to the biomass feedstock; discharging
the first wash liquid from the first stage; and discharging a solid
biomass product from the reaction vessel in slurry form.
2. The process of claim 1, further comprising conveying a first
stage biomass product from the first stage to a second stage of the
reaction vessel, injecting a second wash liquid into the second
stage countercurrently to the first stage biomass product, and
discharging the second wash liquid from the second stage.
3. The process of claim 1, wherein the first wash liquid comprises
water or a solution of water and a mineral acid for hemicellulose
hydrolysis, and the second wash liquid comprises water and a sodium
or ammonium hydroxide base for lignin hydrolysis.
4. The process of claim 3, wherein the second wash liquid comprises
about 40% to about 60% ethanol by weight.
5. The process of claim 1, wherein the first wash liquid comprises
a water rinse and a concentrated chemical reagent that mix to form
the first wash liquid.
6. The process of claim 1, wherein the first wash liquid provides
optimal recovery of oils, proteins, and other extractives.
7. The process of claim 1, further comprising maintaining a
temperature of at least one of the stages in a range from about
190.degree. C. to about 240.degree. C.
8. A continuous, countercurrent system of one or more stages for
the fractionation of a lignocellulosic biomass, the system
comprising: means for feeding the biomass into an elongated,
pressurized reaction vessel; means for conveying the biomass
through the length of the reaction vessel; means for discharging a
processed biomass from the reaction vessel; means for injecting a
counter-flow of pressurized wash liquid into each stage of the
reaction vessel; means for discharging the wash liquid from each
stage of the reaction vessel; means for separating liquids from
solids in each stage of the reaction vessel prior to discharging
the wash liquid; means for maintaining a desired temperature in
each stage of the reaction vessel; means for transferring heat from
the liquid being discharged to the liquid being injected; and means
for controlling pressure throughout each stage of the reaction
vessel such that boiling nowhere occurs, separate countercurrent
flows are established in each stage where desired, and mixing of
liquids between stages is minimized.
9. The system of claim 8, wherein the pressurized reaction vessel
comprises an elongated barrel accommodating twin screws for
conveying the biomass, the screws being driven by a gearbox and
motor.
10. The system of claim 8, wherein the means for discharging a
processed biomass from the reaction vessel comprises a processed
biomass discharge progressive cavity pump configured to reduce
pressure while avoiding clogging from liquid-solid separation, and
the means for discharging the wash liquid from each stage of the
reaction vessel comprises a wash liquid discharge progressive
cavity pump configured to reduce pressure while avoiding clogging
from liquid-solid separation.
11. The system of claim 8, wherein the means for separating liquids
from solids in each stage of the reaction vessel prior to
discharging the wash liquid comprises at least one twin-screw
extruder configured to force solids back into the reaction
vessel.
12. A simulated moving bed (SMB) system of one or more stages for
the countercurrent fractionation of lignocellulosic biomass, the
system comprising: a plurality of elongated, pressurized reactors
interconnected with a plumbing system for controlling and directing
one or more fluid flows; means for sequential loading of the
plurality of reactors with a biomass feedstock and for sequential
unloading of a processed biomass; means for injecting
countercurrently a pressurized wash liquid into each stage of the
simulated moving bed system; means for discharging the wash liquid
from each stage of the simulated moving bed system; means for
separating liquids from solids prior to discharging the wash liquid
and transferring the wash liquid between reactors; means for
maintaining a desired temperature in each of the plurality of
reactors of the simulated moving bed system; means for transferring
heat from the wash liquid being discharged to the wash liquid being
injected; means for controlling a pressure in each of the plurality
of reactors to prevent boiling and to maintain a desired liquid
flow throughout the simulated moving bed system; and means for
sequential switching of a plurality of valves to create a desired
countercurrent, moving bed simulation.
13. The system of claim 12, wherein the means for sequential
loading of the plurality of reactors with a biomass feedstock and
for sequential unloading of a processed biomass comprises: one or
more augurs configured to load the biomass feedstock into the
plurality of reactors; and means for slurrying and washing out the
processed biomass with water.
14. The system of claim 12, wherein the means for sequential
loading of the plurality of reactors with a biomass feedstock and
for sequential unloading of a processed biomass comprises a
plurality of baskets.
15. The system of claim 12, wherein the means for discharging the
wash liquid from each stage of the SMB comprises a wash liquid
discharge progressive cavity pump configured to reduce pressure
while avoiding clogging from liquid-solid separation.
16. The system of claim 12, wherein the means for separating
liquids from solids in each stage of the SMB prior to discharging
the wash liquid comprises at least one twin-screw extruder
configured to force solids back into the reaction vessel.
17. The system of claim 12, wherein the means for sequential
switching of a plurality of valves to create a desired
countercurrent, moving bed simulation comprises an electronic
computer.
18. The system of claim 12, wherein the plumbing system for
controlling and directing one or more fluid flows comprises a first
reactor outlet port coupled with a second reactor inlet port.
19. The system of claim 18, wherein the first reactor outlet port
is coupled with the second reactor inlet port via a heat
exchanger.
20. The system of claim 12, wherein the means for sequential
loading of the plurality of reactors with a biomass feedstock and
for sequential unloading of a processed biomass comprises a common
feedstock hopper in operative association with the plurality of
elongated, pressurized reactors.
Description
BACKGROUND OF THE INVENTION
[0001] Embodiments of the present invention relate to systems and
methods for the fractionation of lignocellulosic biomass into its
components, including extractives, hemicellulose, lignin, and
cellulose.
[0002] Natural cellulosic feedstocks typically are referred to as
"biomass". Many types of biomass, including wood, paper,
agricultural residues, herbaceous crops, and lignocellulosic
municipal and industrial solid wastes have been considered as
feedstocks for the manufacture of a wide range of goods. These
biomass materials consist primarily of cellulose, hemicellulose,
and lignin bound together in a complex gel-like structure along
with small quantities of extractives, pectins, proteins, and ash.
Due to the complex chemical structure of the biomass material,
microorganisms and enzymes cannot effectively attack the cellulose
without prior treatment because the cellulose is highly
inaccessible to enzymes or bacteria. This inaccessibility is
illustrated by the inability of cattle to digest wood with its high
lignin content even though they can digest cellulose from such
material as grass. Successful commercial use of biomass as a
chemical feedstock depends on the separation of cellulose from
other constituents.
[0003] The possibility of producing sugar and other products from
cellulose has received much attention. This attention is due to the
availability of large amounts of cellulosic feedstock, the need to
minimize burning or landfilling of waste cellulosic materials, and
the usefulness of sugar and cellulose as raw materials substituting
for oil-based products. Other biomass constituents also have
potential market values. A wide variety of biomass processing
techniques have been proposed, as further discussed below.
NREL Process
[0004] The NREL process involves biomass utilization in the
production of fuel ethanol. At the front of the NREL process, a
3-reactor train is used comprising a pre-steamer, pretreatment
reactor, and flash tank. Corn stover is steamed with low-pressure
steam in a pre-steamer at 100 C for 20 min. After the stover is
pre-steamed, concentrated H.sub.2SO.sub.4 is added to the
pretreatment reactor (Sunds hydrolyzer). The resultant acid
concentration is 1.1% and the insoluble solids loading is 30%. The
reactor operates at 190.degree. C. and 12.1 atm (177 psia), and the
residence time is 2 min. The exiting material is flash cooled to 1
atm in the flash tank. After a residence time of 15 min in the
flash tank, the hydrolyzate slurry containing about 21% insoluble
solids is filtered to yield a solid stream and a liquid stream. The
solid cake is washed, and the wash liquor is mixed with the
hydrolyzate liquor. The combined liquid stream is overlimed and the
resulting gypsum is filtered off. The solid cake and the
conditioned hydrolyzate liquor are mixed and fermented to ethanol
using a recombinant organism. A hybrid hydrolysis and fermentation
(HHF) mode is used. The NREL process does not emphasize the lignin
component of biomass as a potential marketable product.
Pretreatment, saccharification, and co-fermentation conditions are
provided in Tables 1-3, respectively.
[0005] Pretreatment conditions
TABLE-US-00001 TABLE 1 Parameter Value Acid concentration 1.1%
Residence time 2 min Temperature 190.degree. C. Pressure 12.1 atm
Insoluble solids loading 30%
[0006] Saccharification conditions (as part of HHF)
TABLE-US-00002 TABLE 2 Parameter Value Temperature 65.degree. C.
Initial total solids loading 20% Residence time 1.5 days Cellulose
loading 12 FPU/g cellulose
[0007] Co-fermentation conditions (as part of HHF)
TABLE-US-00003 TABLE 3 Parameter Value Organism Recombinant Z.
mobilis Temperature 41.degree. C. Initial total solids loading 20%
Residence time 1.5 days Inoculum level 10%
Solvent Extraction of Lignin
[0008] Pulping is another way of exposing the cellulose via
delignification, the Kraft process being standard industry
practice. Pulping with alcohols has also been known for several
decades. Although methanol, ethanol, propanol, isopropanol,
butanol, and glycols can be used for pulping, ethanol has been
reported to yield the highest ratio of
lignin removal carbohydrate removal . ##EQU00001##
Ethanol actually protects cellulose during delignification. Aqueous
ethanol penetrates with ease into the structure of hardwoods and
softwoods resulting in uniform delignification; however,
delignification rates of the former are much higher. The reasons
for differences in lignin hydrolysis rates are related to
variations and heterogeneity in structure and the chemical
composition of cellulosic materials. The process dissociates lignin
and xylan in the middle lamella and the primary wall of the
lignocellulosic material while substantially preserving the
structural integrity of the fiber core, also referred to as the S2
layer, which is the strongest component of the fiber. The usual
objective of pulping is to produce a strong and "pure" fiber. For
chemical applications, however, the resultant cellulose product
should be easy to digest enzymatically.
[0009] During conventional aqueous ethanol pulping, the liquor pH
drops from 7 to about 4 due to the cleavage of acetyl groups from
the hemicellulose. In most cases several hours of treatment is
required to accomplish delignification. U.S. Pat. No. 4,100,016 to
Diebold et al. ["Diebold"] describes what later became known as the
Alcell.RTM. process. Using a 40-60% (wt/wt) ethanol-water mixture,
and temperature of 190-200.degree. C. (corresponding pressure of
400-500 psig), the Alcell.RTM. process produces pulps that are
similar to kraft pulps in physical properties. However, the lignin
recovered is different from kraft lignins or lignosulfonates in
terms of containing no sulfur and very low ash. It is reported to
be "natural" lignin. Ethanol is recycled, hence, requiring only
make-up quantities, about 1% on wood.
[0010] Lignin produced from Alcell.RTM. pulping of hardwoods is a
polyphenol of high purity, low MW, low polydispersity, low glass
transition temperature, and relatively high decomposition
temperature. It can be used industrially as a partial replacement
for phenolic resins, e.g., waferboards. See Lora et al.,
"Industrial scale production of organosolv lignins: characteristics
and applications" Cellulosics: chemical, biochemical and material
aspects. Chichester, UK: Ellis Horwood Ltd. pp. 251-256 (1993).
[0011] Commercial processes for producing cellulose pulp from wood
generally depend on inorganic chemicals as the extracting agent and
do not yield lignin as a valuable byproduct. In order to yield
high-quality lignin byproduct, an organosolv type process is used,
in which the cooking liquor is an aqueous solution of an organic
solvent. U.S. Pat. No. 3,585,104 to Kleinert describes pulping with
an aqueous mixture of lower aliphatic alcohols such as methanol,
ethanol, propanol or aqueous mixtures of the lower aliphatic
ketones such as acetone, with pulping temperature of
150-200.degree. C. and a residence time of 1-2 h. Other variations
of the organosolv process are discussed below.
[0012] Diebold describes a solvent pulping process in which lignin
is extracted from fibrous plant material by a lower aliphatic
alcohol, such as ethanol, at an elevated pulping temperature and
pressure. This is an example of a simulated countercurrent system
using a batch mode. The pulping liquor is an aqueous solution of
ethanol, and several batch extractors are used in carrying out the
following sequential steps in each extractor: (1) Feeding an
initial charge of fibrous material to a first extractor. (2)
Filling the first extractor with a first used pulping liquor. (3)
Introducing a second used pulping liquor of relatively high
dissolved solids content at an elevated temperature and pressure
into first extractor so as to displace first used pulping liquor,
and recirculating second used pulping liquor without separation of
lignin at a relatively high velocity through said first extractor.
Achieving a pulping temperature of 160-220.degree. C. The second
used pulping liquor is obtained from step 5 (described below)
during pulping of another charge in a second extractor and is
supplied from second extractor to said first extractor without
separation of lignin. (4) Continuing recirculation of second used
pulping liquor without separation of lignin to effect essentially
isothermal initial extraction of first charge at desired pulping
temperature and pressure, and thereafter withdrawing second used
pulping liquor from first extractor. (5) Flowing at least one
additional used pulping liquor through first charge in first
extractor on a once-through basis, additional used pulping liquor
having a lower dissolved solids content than second used pulping
liquor and being obtained from step 6 (described below) during
pulping of still another charge in a third extractor and being
supplied from third extractor to first extractor without separation
of lignin. (6) Flowing heated fresh pulping liquor through first
charge in first extractor on a once-through basis to effect
essentially isothermal final extraction of said first charge. (7)
Discharging crude cellulose pulp from first extractor.
[0013] The solvent extraction can be carried out at ethanol
concentrations (in aqueous solution) of 40-60% by weight, at
pressures ranging from 20-35 atm, and at temperatures ranging from
180-210.degree. C. To assure maximum lignin extraction efficiency
with a minimum degree of redeposition of undesirable condensed
fractions, the extraction vessel is to be designed to minimize
channeling and/or back-mixing of the alcohol-water solvent. This
then dictates a vessel with high aspect ratio (height to diameter
ratio) of about 10:1.
[0014] U.S. Pat. Nos. 4,409,032 and 4,470,851 to Paszner et al.
["Paszner '032 and '851"] discuss organosolv delignification and
saccharification of lignocellulosic plant materials. Cellulosic
material is cooked under pressure at 180 C-220.degree. C. to
convert pentosans and hexosans to their respective sugar
constituents. The cooking is done with acetone-water solvent
mixture containing 0.05-0.25 wt % of phosphoric, sulfuric or
hydrochloric acids. A delignified pulp containing predominantly
cellulose is hydrolyzed to yield relatively pure glucose within an
elapsed time of a minute or less.
[0015] Paszner '851 reports that acetone at high concentration
forms stable complexes with sugars, thereby minimizing their
degradation. They employed an aqueous mixture containing 60-70%
acetone by volume, and hydrochloric acid at 0.05-0.25 wt % of the
mixture or phosphoric/sulfuric acids at 0.15-0.25 wt % of the
mixture. The vessel under pressure provides a retention time for
the solvent mixture of .ltoreq.7 min to minimize sugar degradation.
However, the examples provided use longer retention times: 25 min
for Douglas-Fir sawdust or Aspen wood cooked at 200.degree. C. with
60:40 acetone-water containing 0.08% by weight of HCl, with liquor
circulation to pass six times the volume of the cooking vessel
through the charge in 25 minutes. The liquor is removed from the
vessel which initially contains lignin and is separated from the
liquor collected subsequently which contains the sugars. Hydrolysis
of .beta.-glycosidic chains characterizing amorphous and
crystalline cellulose is reported.
[0016] U.S. Pat. No. 4,496,426 to Baumeister et al. describes a
two-stage process for continuous extraction of fibrous material
such as wood chips. The process comprises impregnating the fiber
with organic solvents followed by reaction at elevated
temperatures. In the first stage, extraction is conducted at
180-210.degree. C. using an aqueous mixture containing about 90%
methanol by weight with a reaction time of 40-120 min and a pH of
3.8-4.9. Additional extraction is achieved in the second stage at
150-190.degree. C. for a period of 10-80 min. The second stage is
different from the first stage in that the methanol concentration
is lower and there is addition of sodium hydroxide and
anthraquinone (5-30% by weight of sodium hydroxide to dry wood and
0.01-0.15% by weight of anthraquinone to dry wood). The extraction
liquid, which gets saturated by leached substances, is removed
continuously at each stage. In this process, the essential
constituents of the fiber material such as cellulose, hemicellulose
and lignin may all be recovered in pure form.
[0017] U.S. Pat. No. 4,746,401 to Roberts et al. describes a
delignification process using an aqueous organic solvent and an
acid neutralizing agent which yields cellulose pulp and reactive
lignin of low molecular weight as byproduct. This process comprises
degassing lignocellulosic material followed by rapidly heating in
an aqueous mixture of an organic solvent and a buffer to maintain a
neutral pH during solvent extraction. The cooked temperature ranges
from 150-280.degree. C. The mixture is rapidly cooled to a
temperature of <150.degree. C. Additional cooking can take place
in an optional third stage. A last or final stage, in which the
liquor is cooled to a temperature of <150.degree. C., should
proceed at a fastest possible cooling rate. The operating
conditions are controlled so as to maximize reactive lignin
salvation while suppressing cellulose degradation in order to
enable recovery of high quality cellulose pulp and of reactive
lignin. Using an acid neutralizing agent is thought to aid the
liquor in attaining and maintaining a mostly neutral pH (6.8-7.5)
during an early or first stage of the cooking process.
[0018] U.S. Pat. No. 4,520,105 to Sinner et al. discusses a process
for the production of sugars, cellulose, and lignin from
lignocellulosic materials. The process comprises subjecting
cellulosic materials to pretreatment with a mixture of water and
lower aliphatic alcohols and/or ketones at a temperature of
100-190.degree. C. for a period of 4 h to 2 min. This is followed
by separation of residue and subsequent chemical treatment with a
similar solvent mixture at elevated temperatures for a further
period of from 2-180 min. The cellulosic material is treated under
elevated pressure with an aqueous mixture containing 30-70% acetone
by volume and an acid catalyst in a concentration 0.001-1N at a
temperature of 170-220.degree. C. Substantially all of lignin and
hemicelluloses are dissolved in the first solution leaving a
residue of microcrystalline cellulose. After separating the residue
from the mixture, it is treated with a similar water-acetone
mixture at a temperature of 170-220.degree. C. This almost
completely hydrolyzes the microcrystalline cellulose to glucose.
Oligosaccharides and polysaccharides, which may still be present in
the solution after separation from fibrous materials, are subjected
to acid hydrolysis. The organic solvent and lignin are subsequently
separated.
[0019] U.S. Pat. No. 4,941,944 to Chang describes a method for
continuous countercurrent organosolv saccharification of
lignocellulosic biomass. Continuous countercurrent production of
lignins and sugars from wood and other lignocellulosic materials by
organosolv delignification or saccharification at elevated
temperatures and pressures is discussed. This method involves
continuously feeding biomass (30-70% moisture by weight) and
cooking liquor into a reaction vessel at opposite ends to achieve
countercurrent flow. The cooking liquor, consisting of ethanol,
water, and a catalytic amount of inorganic acid, is continuously
withdrawn from the reaction vessel. It contains dissolved sugars
and lignin and other substances released from the lignocellulosic
material. The reaction is conducted at the following conditions:
temperatures ranging from 150-210.degree. C., residence times of
2-5 min, and initial insoluble solids loading of 12.5%. Mainly
lignin and hemicellulosic sugars are dissolved in the first zone of
the vessel. The cooking liquor in the first zone is removed from
the vessel and rapidly cooled; lignin remains dissolved during the
cooling step. The resultant cellulose-rich solids are then
hydrolyzed in the second zone of the vessel by acid to mainly form
oligomers of glucose. The objective is to obtain pentose sugars and
lignin under relatively mild conditions in one part of the reactor,
and to yield hexoses under more severe conditions in the other part
of the reactor. This is accomplished by designing a reactor that
has different operating conditions and thus produces different
reaction products for the two stages.
Countercurrent Batch Systems
[0020] An example of a countercurrent system using a batch mode is
described in Diebold. Another such example is discussed in U.S.
Pat. No. 4,123,318 to Sherman. In this three-vessel system, fiber
material is impregnated with the liquid, sent to a separate
digesting vessel, and from the digesting vessel sent to separate
washing vessels without a significant reduction in pressure.
Countercurrent operation is simulated in the washing vessels in a
manner similar to that described in Diebold.
Continuous Countercurrent Digesters
[0021] An example of a countercurrent system using a batch mode was
discussed above. Pulping with continuous countercurrent digesters
is also possible. U.S. Pat. No. 5,716,497 to Richter et al.
describes a device for continuous production of pulp. This process
relates principally to pulp and involves impregnating the chips
with the aid of hot black liquor, which can improve the strength
properties of the fibers, due to the fiber-sparing effect of the
black liquor, i.e., a milder treatment. If a large proportion of
white liquor is used in connection with the impregnation, this
exposes fibers to the aggressive effect of the white liquor, with
carbohydrates degradation and loss of fiber strength. The aim of
the impregnation step is to thoroughly soak each chip to render it
susceptible, by diffusion, to the active cooking chemicals. In this
continuous cooking process, hot impregnated chips are fed at the
top of a countercurrent steam digester. The digester has a bottom
outlet and at least one draw-off point for discharging the black
liquor. About 70% of the cooking liquor is fed to the top of the
digester as finely divided droplets.
[0022] U.S. Pat. No. 5,882,477 to Laakso et al. describes the use
of a continuous digester with a low temperature gas phase. The
continuous pulp digester is operated so that it has the advantages
of a hydraulic digester yet has a gas-filled zone over the liquid
level. A slurry of chips and cooking liquor is introduced into the
top of the digester vessel. A gas-filled zone above the liquid
level includes compressed gas and is at a temperature of
>120.degree. C. and at a pressure of 80-150 psig. The chips are
heated by heating liquid using a recirculation loop below the chips
level, and a countercurrent flow zone is provided. Kraft pulp from
the bottom of the digester is withdrawn.
[0023] U.S. Pat. No. 5,192,396 to Backlund discusses a process for
continuously digesting cellulosic fiber material, which employs
both cocurrent and countercurrent modes. The fiber material is
impregnated with liquid in a closed system comprising a cocurrent
zone and a countercurrent zone. The liquid in the cocurrent zone
includes black liquor and possibly some white liquor, and the
liquid in the countercurrent zone is fresh white liquor. A liquid
stream is withdrawn from the impregnation system at an exit
situated between the two zones.
[0024] U.S. Pat. No. 5,401,361 to Prough et al. discusses a
completely countercurrent digester for continuous cooking. A
conventional continuous digester can be modified to achieve a
countercurrent cook throughout the entire height of the digester.
The process utilizes an upright digester, and the operation is
comprised of the following steps: (1) Continuously introducing
cellulosic material steeped in cooking liquor into the top of the
digester so that the material continuously travels downwardly in
the digester. (2) Establishing a countercurrent flow between
cooking liquor and solids throughout the entire height of the
digester, from the top where the cellulosic material is introduced
to the bottom where the pulp is withdrawn. (3) Continuously
withdrawing liquid from the digester at different points along the
height of the digester, and reintroducing the withdrawn liquid. (4)
Continuously withdrawing cellulose pulp from the bottom of the
digester.
[0025] U.S. Pat. No. 4,668,340 to Sherman discusses countercurrent
acid hydrolysis of cellulosic materials. After prehydrolysis
treatment of cellulosic fibrous material, subsequent kraft
digestion can be conducted to produce paper pulp. The material is
steeped with cooking liquor, steamed, and transferred by a high
pressure feeder to the top of a first vertical vessel. Liquid is
withdrawn from the top of the first vessel via a liquid/solids
separator. This recovered hydrolyzate contains hemicellulose,
sugars, etc. Countercurrent acid hydrolysis takes place in the top
section of the vessel, and a countercurrent wash is effected in the
bottom section of the vessel. After hydrolysis and washing, the
resultant material is withdrawn from the bottom of the first vessel
and sent to the top of a kraft digester.
Biomass Fractionation
[0026] Many steps are required in production, harvesting, storage,
transporting, and processing of biomass to yield useful products.
One step in the processing is the separation of biomass into its
major components: extractives, hemicellulose, lignin, and
cellulose. This separation process is called fractionation. Biomass
can be viewed as an intermingled structure of three complex
polymers saturated with mobile extractives. Many approaches have
been investigated for disentangling this complex structure. Once
this separation has been achieved, a variety of paths are opened
for further processing of each component into marketable products.
The separation of cellulose from other biomass constituents is
difficult, in part because the chemical structure of
lignocellulosic biomass is so complex. See, e.g., ACS Symposium
Series 397, "Lignin Properties and Materials", edited by G. W.
Glasser and S. Sarkanen, published by the American Chemical
Society, 1989, which includes the statement that "[L]ignin in the
true middle lamella of wood is a random, three-dimensional network
polymer comprised of phenylpropane monomers linked together in
different ways. Lignin in the secondary wall is a nonrandom
two-dimensional network polymer. The chemical structure of the
monomers and linkages which constitute these networks differ in
different morphological regions (middle lamella vs secondary wall)
different types of cell (vessels vs fibers) and different types of
wood (softwoods vs hardwoods). When wood is delignified, the
properties of the macromolecules made soluble reflect the
properties of the network from which they are derived." The
separation of cellulose from other biomass constituents is further
complicated by the fact that lignin is intertwined and linked in
various ways with cellulose and hemicellulose both of which are
polymers of sugars. Thus there is a need for systems and methods
for separating solid biomass, such as lignocellulosic biomass, into
its constituent components, for example by chemical fractionation,
and treating the components to make useful products. Biomass is
widely recognized as a potential raw material for the production of
transportation fuel and industrial chemicals, but an economically
competitive commercial biorefinery has yet to be devised. Much
research and development has been conducted toward this goal over
the past 30 years or more, and there is in addition a century of
experience working with biomass for the production of paper pulp at
commercial scale, yet there remains a need for an economically
viable path to a commercial biorefinery. These and other needs are
addressed by the present invention.
BRIEF SUMMARY OF THE INVENTION
[0027] Embodiments of the present invention include methods and
systems that involve the continuous countercurrent flow of biomass
and reactive liquids, and the control of degradation reactions to
increase product yields. Design features include elevated
temperature and pressure to minimize processing time, and the
efficient use of chemical reagents and/or solvents as well as heat
energy. Other features provide for the in-situ separation of
liquids and solids for discharge, and the optional linking of
multiple processing steps.
[0028] Embodiments of the present invention provide ethanol-water
mixture techniques that may differ in one or more aspects from
known approaches (e.g. Alcell.RTM. process of Diebold). For
example, in some cases, embodiments include a prehydrolysis step to
remove a desired amount of hemicellulose in a two-stage approach,
where hemicellulose can be removed in a first stage. Embodiments
may also include the use of a regime of high temperature and short
residence time during delignification. For example, the residence
time may be on the order of minutes, whereas other known approaches
may involve a residence time on the order of hours. Embodiments may
also provide the ability to produce low-hemicellulose pulp
(suitable, for example, in making dissolving pulp) using a
two-stage approach, whereas some known approaches may remove about
50% of the hemicellulose. Embodiments may also provide the ability
to produce high-yield pulp using a single-stage approach, whereas
other known approaches may remove about 50% of the hemicellulose,
thereby lowering pulp yield.
[0029] In one aspect, embodiments of the present invention provide
a continuous, countercurrent process of one or more stages for the
fractionation of a lignocellulosic biomass feedstock. The process
includes feeding the biomass feedstock into a first stage of a
pressurized reaction vessel, injecting a first wash liquid into the
first stage countercurrently to the biomass feedstock, discharging
the first wash liquid from the first stage, and discharging a solid
biomass product from the reaction vessel in slurry form. The
process can also include conveying a first stage biomass product
from the first stage to a second stage of the reaction vessel,
injecting a second wash liquid into the second stage
countercurrently to the first stage biomass product, and
discharging the second wash liquid from the second stage. The first
wash liquid can include water or a solution of water and a mineral
acid for hemicellulose hydrolysis, and the second wash liquid can
include water and a sodium or ammonium hydroxide base for lignin
hydrolysis. The second wash liquid can include about 40% to about
60% ethanol by weight. The first wash liquid can include a water
rinse and a concentrated chemical reagent that mix to form the
first wash liquid. In some cases, the first wash liquid provides
optimal recovery of oils, proteins, and other extractives. The
process can also include maintaining a temperature of at least one
of the stages in a range from about 190.degree. C. to about
240.degree. C.
[0030] In another aspect, embodiments provide a continuous,
countercurrent system of one or more stages for the fractionation
of a lignocellulosic biomass. The system can include means for
feeding the biomass into an elongated, pressurized reaction vessel,
means for conveying the biomass through the length of the reaction
vessel, means for discharging a processed biomass from the reaction
vessel, means for injecting concurrently a flow of pressurized wash
liquid into each stage of the reaction vessel, means for
discharging the wash liquid from each stage of the reaction vessel,
means for separating liquids from solids in each stage of the
reaction vessel prior to discharging the wash liquid, means for
maintaining a desired temperature in each stage of the reaction
vessel, means for transferring heat from the liquid being
discharged to the liquid being injected, and means for controlling
pressure throughout each stage of the reaction vessel such that
boiling nowhere occurs, separate counter-flows are established in
each stage where desired, and mixing of liquids between stages is
minimized. The pressurized reaction vessel can include an elongated
barrel accommodating twin screws for conveying the biomass, the
screws being driven by a gearbox and motor. In some cases, the
means for discharging a processed biomass from the reaction vessel
includes a processed biomass discharge progressive cavity pump
configured to reduce pressure while avoiding clogging from settling
solids, and the means for discharging the wash liquid from each
stage of the reaction vessel includes a wash liquid discharge
progressive cavity pump configured to reduce pressure while
avoiding clogging from settling solids. The means for separating
liquids from solids in each stage of the reaction vessel prior to
discharging the wash liquid can include at least one twin-screw
extruder configured to force solids back into the reaction
vessel.
[0031] In another aspect, embodiments of the present invention
provide a simulated moving bed system of one or more stages for the
countercurrent fractionation of lignocellulosic biomass. The system
can include a plurality of elongated, pressurized reactors or
reaction columns interconnected with a plumbing system for
controlling and directing one or more fluid flows, means for
sequential loading of the plurality of reactors with a biomass
feedstock and for sequential unloading of a processed biomass,
means for injecting countercurrently a flow of pressurized wash
liquid into each stage of the simulated moving bed system, means
for discharging the wash liquid from each stage of the simulated
moving bed system, means for separating liquids from solids prior
to discharging the wash liquid and transferring the wash liquid
between reactors, means for maintaining a desired temperature in
each of the plurality of reactors of the simulated moving bed
system, means for transferring heat from the wash liquid being
discharged to the wash liquid being injected, means for controlling
a pressure in each of the plurality of reactors to prevent boiling
and to maintain a desired liquid flow throughout the simulated
moving bed system, and means for sequential switching of a
plurality of valves to create a desired countercurrent moving bed
simulation. In some cases, the means for sequential loading of the
plurality of reactors with a biomass feedstock and for sequential
unloading of a processed biomass includes one or more augurs
configured to load the biomass feedstock into the plurality of
reactors, and means for slurrying and washing the processed biomass
with water. In some cases, the means for sequential loading of the
plurality of reactors with a biomass feedstock and for sequential
unloading of a processed biomass includes a plurality of baskets.
The means for discharging the wash liquid from each stage of the
reaction vessel can include a wash liquid discharge progressive
cavity pump configured to reduce pressure while avoiding clogging
from liquid-solid separation. The means for separating liquids from
solids in each stage of the reaction vessel prior to discharging
the wash liquid can include at least one twin-screw extruder
configured to force solids back into the reaction vessel. The means
for sequential switching of a plurality of valves to create a
desired countercurrent moving bed simulation can include an
electronic computer. The plumbing system for controlling and
directing one or more fluid flows comprises a first reactor outlet
port coupled with a second reactor inlet port. In some cases, the
first reactor outlet port is coupled with the second reactor inlet
port via a heat exchanger. In some embodiments, the means for
sequential loading of the plurality of reactors with a biomass
feedstock and for sequential unloading of a processed biomass
includes a common feedstock hopper in operative association with
the plurality of elongated, pressurized reactors.
[0032] In still another aspect, embodiments of the present
invention provide a simulated moving bed system for processing a
lignocellulosic feedstock. The system can include a common
feedstock hopper to provide the lignocellulosic feedstock, a first
reactor having a first fluid inlet port, a first discharge port, a
first fluid outlet port, and a first feedstock inlet port that is
coupled with the common feedstock hopper. The system can also
include a second reactor having a second fluid inlet port, a second
discharge port, a second fluid outlet port, and a second feedstock
inlet port that is coupled with the common feedstock hopper. The
first fluid outlet port of the first reactor can be coupled with
the second fluid inlet port of the second reactor. In some cases,
the first fluid inlet port and the first discharge port are
disposed toward a distal end of the first reactor, and the first
fluid outlet port and the first feedstock inlet port are disposed
toward a proximal end of the first reactor. In some cases, at least
one of the first or second reactors includes a threaded shaft. The
system may also include a motor coupled with the threaded shaft,
wherein the motor is configured to rotate the threaded shaft. The
system may also include a positioning system coupled with the
threaded shaft. The positioning system may be configured to move
the threaded shaft into and out of the common feedstock hopper. The
first fluid outlet port of the first reactor can be coupled with
the second fluid inlet port of the second reactor via a heat
exchanger. At least one of the first or second feedstock inlet
ports can include a ball valve.
[0033] In yet another aspect, embodiments provide a method for
processing a lignocellulosic feedstock. The method can include
passing a first amount of the lignocellulosic feedstock from a
common feedstock hopper to a first reactor, passing a second amount
of the lignocellulosic feedstock from the common feedstock hopper
to a second reactor, passing a first reaction fluid to the first
reactor, reacting the first reaction fluid with the first amount of
the lignocellulosic feedstock in the first reactor to form a first
fractionate and a first discharge, and passing the first
fractionate from the first reactor to the second reactor. The first
amount of feedstock can be passed from the common feedstock hopper
to the first reactor in a first direction, and the first reaction
fluid can be passed to the first reactor in a second direction that
is countercurrent to the first direction. The first amount of the
lignocellulosic feedstock can be passed from the common feedstock
hopper to the first reactor with a threaded shaft. The first amount
of the lignocellulosic feedstock can be passed from the common
feedstock hopper to the first reactor by advancing the threaded
shaft into the common feedstock hopper, and rotating the threaded
shaft with a motor so as to draw the first amount of feedstock out
of the common feedstock hopper. In some cases, the threaded shaft
is advanced into and withdrawn from the common feedstock with a
positioning system. In some cases, the first amount of the
lignocellulosic feedstock is passed from the common feedstock
hopper to the first reactor via a first feedstock inlet port. The
second amount of the lignocellulosic feedstock can be passed from
the common feedstock hopper to the second reactor via a second
feedstock inlet port. The first reaction fluid can be passed to the
first reactor via a first fluid inlet port. In some cases, the
first discharge is passed out of the first reactor via a first
discharge port. The first fractionate can be passed from the first
reactor to the second reactor via a first fluid outlet port and a
second fluid inlet port. The method can also include reacting the
first fractionate with the second amount of feedstock in the second
reactor to form a second fractionate and a second discharge. In
some cases, the first fractionate is passed from the first reactor
to the second reactor via a heat exchanger. The method may also
include capturing particles from the first fractionate as the first
fractionate passes from the first reactor to the second reactor,
and returning the particles to the first reactor. The first
reaction fluid may include an alkaline solution. In some cases, the
reaction fluid has a pH of about 8 to about 13. In some cases, the
first reaction fluid has a temperature of about 180.degree. C. to
about 240.degree. C. The first fractionate may include lignin. The
first discharge may include cellulose.
[0034] Simulated moving bed systems for processing a
lignocellulosic feedstock are provided. The systems may include a
common feedstock hopper to provide the lignocellulosic feedstock,
and a first reactor having a first fluid inlet port, a first
discharge port, a first fluid outlet port, and a first feedstock
inlet port that is coupled with the common feedstock hopper. The
systems may also include a second reactor having a second fluid
inlet port, a second discharge port, a second fluid outlet port,
and a second feedstock inlet port that is coupled with the common
feedstock hopper. The first fluid outlet port of the first reactor
is coupled with the second fluid inlet port of the second
reactor.
[0035] Embodiments of the invention may also include methods for
processing a lignocellulosic feedstock. The methods may include the
steps of passing a first amount of the lignocellulosic feedstock
from a common feedstock hopper to a first reactor, and passing a
second amount of the lignocellulosic feedstock from the common
feedstock hopper to a second reactor. The methods may also include
passing a first reaction fluid to the first reactor, and reacting
the first reaction fluid with the first amount of the
lignocellulosic feedstock in the first reactor to form a first
fractionate and a first discharge. In addition, the methods may
include passing the first fractionate from the first reactor to the
second reactor.
[0036] Additional embodiments and features are set forth in part in
the description that follows, and in part will become apparent to
those skilled in the art upon examination of the specification or
may be learned by the practice of the invention. The features and
advantages of the invention may be realized and attained by means
of the instrumentalities, combinations, and methods described in
the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] A further understanding of the nature and advantages of the
present invention may be realized by reference to the remaining
portions of the specification and the drawings wherein like
reference numerals are used throughout the several drawings to
refer to similar components. In some instances, a sublabel is
associated with a reference numeral and follows a hyphen to denote
one of multiple similar components. When reference is made to a
reference numeral without specification to an existing sublabel, it
is intended to refer to all such multiple similar components.
[0038] FIG. 1A is a schematic representation of a pressure
controlled, two-stage, twin-screw, countercurrent apparatus
illustrating one embodiment of this invention.
[0039] FIG. 1B is a schematic representation of a cross section of
the apparatus of FIG. 1A.
[0040] FIG. 1C is a schematic illustrating a simulated moving bed
biomass fractionation system according to one embodiment of the
present invention.
[0041] FIG. 2 is a schematic detailing a reaction section of a
simulated moving bed biomass fractionation system according to one
embodiment of the present invention.
[0042] FIG. 3 is a schematic of a reaction section of a simulated
moving bed biomass fractionation system according to one embodiment
of the present invention.
[0043] FIG. 4 shows a simulated moving bed biomass fractionation
system according to one embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0044] Systems and methods for processing lignocellulosic
feedstocks are described. The feedstocks may be processed to
separate cellulose fibers from other constituents of a
lignocellulosic biomass, such as found in trees, grasses, shrubs,
agricultural waste, and waste paper. The separated cellulose fibers
may be used as a component in the manufacture of paper, plastics,
ethanol, and a variety of other materials and chemicals.
[0045] Counter-flow operation provides for the efficient use of
processing reagents. Processed solids encounter fresh reagents just
before discharge, while the fresh and reactive feedstock first
meets with nearly exhausted liquid reagent about to be discharged.
Advantageously, countercurrent flow can establish a non-equilibrium
steady state in which the reacting liquids and solids experience
different histories. In combination with temperature gradients,
this permits manipulation of reaction rates for competing chemical
interactions to improve yields by minimizing degradation reactions.
Elevated temperatures reduce processing times for fractionation. As
a rough rule, every ten degrees Celsius rise in temperature reduces
processing time by a factor of two and can thus increase materials
throughput by this same factor for similarly sized apparatus. In
many cases, however, with increased temperature comes increased
pressure to prevent liquid boiling. Further, increased temperature
can result in undesirable degradation of biomass. Both of these
considerations may have an effect in the temperature range from 210
to 230.degree. C., depending on details of the fractionation
chemistry.
[0046] In a countercurrent system, it is possible to incorporate a
rinsing feature that provides in-situ recovery and full use of
reagents that might otherwise be discharged with the processed
solids. This additional processing can occur at the elevated
temperature and pressure where reaction rates are high and
mobilized components remain in solution. A rinse liquid can even be
used to cool the solid product with in-situ recuperation of the
heat energy in the solid product. Reagents and energy needed for
biomass fractionation can be costly and efficient utilization may
be required if the fractionation process is to be economically
viable. Advantageously, embodiments of the present invention
provide efficient utilization as a process feature. In-situ
separation of liquid and solid flows in a countercurrent system
provide opportunities for significant savings in downstream
processing. Processed solids can thus be discharged in a clean,
cooled condition as a fully prepared intermediate product.
Depending on the particulars of the biomass and the intermediate
products desired from the fractionation, one or more processing
steps may be involved. For example, a simple extraction of oils or
other extractables might involve only a single stage, while a more
complete fractionation might involve multiple stages for sequential
recovery of extractives, hemicellulose, lignin, and cellulose with
intermediate rinsing. Embodiments of the present invention provide
the ability to carry out such multiple processing steps while
maintaining operating temperatures and flows.
[0047] Embodiments provided herein include various implementing
devices, however, knowledgeable readers will readily see the
applicability of the techniques described herein in a broad range
of related situations depending on such factors as the particular
biomass feedstock, the marketable fractionation products to be
recovered, the scale of the operation, and the availability of
certain manufactured components. Embodiments of the present
invention involve the fractionation of biomass, and in some cases
it is assumed that certain feedstock preparation steps such as
cleaning, sizing, and wetting have already been accomplished, as
needed. Fractionation chemistry can be carried out in a sequence of
steps in a reactor configured to provide a plurality of
countercurrent zones. Although applicable for a single or
multi-stage fractionation process, the following steps would
characterize one embodiment of a two-stage, countercurrent
fractionation process: (1) Feed prepared (cleaned and/or
size-reduced) biomass into the pressurized reactor. (2) Discharge a
first liquid with dissolved extractives, hemicellulose, etc. (3)
Provide a zone for chemical reaction at elevated temperature. (4)
Inject a first reagent, liquid or solvent to mix with rinse liquid.
(5) Provide a zone for countercurrent rinsing of the solids. (6)
Input a rinse liquid (e.g. water). (7) Provide an interstage
separation zone with negligible liquid flow. (8) Discharge a second
liquid with dissolved hemicellulose, lignin, etc. (9) Provide a
zone for chemical reaction at elevated temperature. (10) Inject a
second reagent, liquid or solvent to mix with rinse liquid. (11)
Provide a zone for countercurrent rinsing of the solids. (12) Input
a rinse liquid (e.g. water). (13) Discharge the solid product. In
some embodiments, hemicellulose and extractives can be removed in
the first stage, and thus an ethanol extraction in the second stage
can be more efficient.
[0048] Further details of the fractionation chemistry are provided
herein. For aqueous based biomass processing, the first reagent
will often be either water itself or a dilute mineral acid. The
second reagent will often be a solution of water and an alkali such
as sodium or ammonium hydroxide. Some of the water may be replaced
by ethanol. Many process variations are contemplated by embodiments
of the present invention. For example, fractionation can begin with
an additional stage optimized for the recovery of extractives
before proceeding to hemi-cellulose extraction. Another example
might involve an alternative to discharging the solid product in
which an additional stage is optimized for rapid acid hydrolysis of
the cellulose and discharge of the resulting sugars for further
processing. Embodiments described herein can provide precise
control of the movement of liquids and solids in the reactor, and
maintenance of desired pressures and temperatures throughout, to
enhance the performance of the implementing apparatus.
[0049] The present systems integrate a plurality of processing
steps, which may include chemical reactions, mixing steps at
elevated temperatures and/or pressures, liquid/solid separation
steps at elevated temperatures and/or pressures, and controlled
discharge of liquid and solid products, among other steps. A
description of other apparatuses and methods for processing
lignocellulosic feedstocks are described in co-assigned, U.S. Pat.
No. 6,419,788, issued Jul. 16, 2002; U.S. Pat. No. 6,620,292,
issued Sep. 16, 2003, and U.S. patent application Ser. No.
11/158,831, filed Jun. 21, 2005, the entire contents of which are
all herein incorporated by reference for all purposes.
[0050] An exemplary implementing apparatus includes a twin-screw
conveyor with housing designed for operating pressures of 400 psi
or more and with metallurgy compatible with the reagents expected
to be used. This conveyor is the reaction vessel and is sized for
the desired throughput and reaction time. A crammer-feeder with a
safety shutoff can be used to take biomass from a feed hopper and
inject it continuously into the reaction vessel. The screw conveyor
creates a moving bed of solids while liquid is forced
countercurrently. Pressure pumps with flow sensors and pressure
gauges are required for each of the liquid inputs. Positive
displacement pumps (e.g. Moyno type pumps) run in reverse are used
for each of the liquid discharges and for the solid product
discharge. In some applications, a double valve system can be used
instead of a pump to discharge product while maintaining pressure.
Liquid/solid separators are used on each of the liquid discharge
ports to extract liquid while keeping solids in the reactor. A
heating system with temperature sensors is used to achieve
necessary reaction temperatures (up to 230.degree. C.). Heat
exchangers are used between liquid feed and discharge lines for
energy conservation and to prevent flashing of liquid discharges. A
control system is used to use temperature, flow, and pressure
information to maintain desired operating conditions throughout the
reactor.
[0051] In some embodiments, the present invention provides
continuous, countercurrent processes of one or more stages for the
fractionation of lignocellulosic biomass feedstock. Processes may
include, for example, feeding biomass into the first stage of a
pressurized reaction vessel, injecting a first wash liquid into
said first stage countercurrently to said biomass, discharging said
first wash liquid from said first stage, optionally conveying said
biomass into a second stage of said reaction vessel, injecting a
second wash liquid into said second stage countercurrently to said
biomass, discharging said second wash liquid from said second
stage, optionally conveying said biomass into additional stages of
said reaction vessel with provision for injecting and discharge
wash liquids, and finally discharging a solid biomass product in
slurry form. In some cases, one or more wash liquids are injected
into the reaction vessel as two streams; a water rinse and a
concentrated chemical reagent that mix to form the working wash
liquid. The wash liquid for the first stage may be selected for
optimal recovery of oils, proteins, and other extractives.
Embodiments encompass multi-stage processing in which the wash
liquid in one stage is water or a solution of water and a mineral
acid to emphasize hydrolysis of hemicellulose, and the wash liquid
in the following stage is a solution of water and a strong base
such as sodium or ammonium hydroxide and may include 40 to 60%
ethanol by weight to emphasize hydrolysis of lignin. The
temperature in one or more stages may be maintained in the range
190.degree. C. to 240.degree. C.
[0052] In related embodiments, continuous, countercurrent systems
of one or more stages for the fractionation of lignocellulosic
biomass may include means for feeding said biomass into an
elongated, pressurized reaction vessel, means for conveying said
biomass through the length of said reaction vessel, means for
discharging processed biomass from said reaction vessel, means for
injecting a countercurrent flow of pressurized wash liquid into
each stage of said reaction vessel, means for discharging wash
liquid from each stage of said reaction vessel, means for
separating liquids from solids prior to discharging wash liquids,
means for maintaining desired temperatures in each stage of said
reaction vessel, means for transferring heat from liquid being
discharged to liquid being injected, means for controlling
pressures throughout said reaction vessel such that boiling nowhere
occurs, separate countercurrent flows are established in each stage
where desired, and mixing of liquids between stages is minimized. A
pressurized reaction vessel may include an elongated barrel
accommodating twin screws for conveying the biomass, the screws
being driven by a gearbox and motor. The length of the barrel and
screws, the rotation rate of the screws, and the diameter of the
screws may be determined by the number of stages, the time
necessary for processing, and the biomass throughput desired.
Systems may be configured to discharge liquid and solid slurry
products by means of progressive cavity pumps operated in reverse
to reduce pressure while avoiding clogging from liquid-solid
separation. Liquids may be separated from solids prior to liquid
discharge by means of small, twin-screw extruders operated so as to
force solids back into the reaction vessel.
[0053] For various reasons (e.g. feedstock characteristics or
economics) moving bed fractionation systems may not always provide
an optimal or preferred solution. In such cases, a simulated moving
bed (SMB) system may be used to implement the fractionation
chemistry. An SMB system can be thought of as an actual moving bed
system, such as previously described herein, that is physically
divided into a series of segments (from one or two to up to more
than a dozen for each stage of the process) within which the solids
remain fixed. Liquid feed and discharge flows and liquid flows
between segments are then switched by valves from one segment to
the next such that both the solids and liquids experience a time
history similar to what would be experienced in an actual moving
bed system. The larger the number of segments in each process
stage, the more closely an SMB operation can match an actual moving
bed system, but at an increasing capital investment cost. Reactor
segments are loaded and unloaded sequentially to accompany the
switching of liquid flows. One advantage of the SMB system is that
reactor segments can be loaded and unloaded at atmospheric pressure
and temperature thereby avoiding the shear forces and physical
degradation encountered when solids must be injected, transported,
and discharged under pressure in screw based, continuous flow
apparatus. SMB fractionation systems are also advantageous because
they have great versatility and flexibility in adapting to
different feedstocks through computer-based reconfiguration. They
also can make use of previously developed product discharge
technology, and allow countercurrent operation in multiple stages
with all the benefits such operation provides in terms of process
control and product purity. What is more, SMB systems allow
operation at lower temperatures and longer residence times such as
may be needed to get sufficient chemical diffusion when processing
large feedstock chips such as are customary in wood pulping. SMB
system designs can be easily modified by addition of more reactor
sections to provide for additional processing stages (e.g. more
than two) as desired.
[0054] Turning now to the drawings, FIG. 1A is a schematic
representation of a pressure controlled, multi-stage, twin-screw,
countercurrent vessel or apparatus 20 according to one embodiment
of the present invention. Although from one to many-stage processes
may apply, this two-stage, countercurrent, biomass fractionation
apparatus allows both the liquid flow rate and the pressure to be
controlled in each of the two stages. FIG. 1B is a schematic
representation of a cross section of this vessel 20 that includes
an outer wall 1 for pressure containment (e.g. rated to at least
1000 psi). Additional reinforcement 2 is provided to aid in meeting
the pressure rating. This reinforcement 2 also creates passages 3
that can be used to circulate fluid for temperature regulation.
Within the pressure vessel 1 are overlapping twin screws 4 affixed
to drive shafts 5.
[0055] Embodiments of the present invention provide for the
maintenance of independent countercurrent flows of liquid in each
of the stages or processing zones. This can involve variable speed
pumps with speed controllers that respond to signals from pressure
or flow sensors. A multi-stage countercurrent system can have
pressure differentials in each stage to drive the liquid flows, in
addition to zones of constant pressure between stages to separate
flows. FIG. 1A is a conceptual schematic of a two-stage system
having a first stage 7 and a second stage 9, including a solids
feed 6 and a discharge 10. In some embodiments, the entire system
is maintained at an elevated pressure sufficient to prevent boiling
of any liquids. Solids can be transported by twin screws, which can
have a pitch equal to the screw diameter. The pitch of the screws
can be shortened (e.g. by half) in the compression zone 8 to
squeeze out some of the water and thereby minimize dilution of the
second stage liquid product. A second compression zone (not shown)
may be included as an option just before the solids discharge.
[0056] Liquid feed rate can be controlled by pumps as described
above. In some cases, the first stage is a simple, countercurrent
water wash 16 with auto-catalyzed hemicellulose hydrolysis. The
second stage ends with a countercurrent water rinse 13 before
discharge of solids 10. The countercurrently flowing rinse water is
then augmented with countercurrently flowing ethanol and alkali 14
to mobilize lignin. The flow of liquid input 13, 14, and 16 is
controlled by variable speed pressure pumps that are, in turn,
controlled by flow sensors on these input lines with manual set
points determined by the details of the chemistry desired. Solids
discharge 10 from the second stage 9 may be controlled by a
variable speed, positive displacement pump of the Moyno type whose
speed is set manually to accommodate the solids feed (after
processing) plus sufficient water to provide a manageable slurry.
Liquid discharge from the second stage 15 is controlled by a second
Moyno type pump with variable speed drive controlled by a pressure
sensor 11 having an electrical output proportional to pressure. The
pressure signal is compared to a manually set reference voltage. If
the pressure is too high, the continuous Moyno speed is increased;
if the pressure is too low, the Moyno speed is decreased. A small
"dead zone" minimizes hunting. The reference pressure (voltage) is
set manually to prevent boiling of the ethanol-water mixture at the
highest temperature in the second stage. Liquid discharge 17 from
the first stage is controlled by a third Moyno type pump with
variable speed drive controlled by a differential pressure sensor
12 having a bi-polar electrical output proportional to the
deviation from zero of the pressure differential across the
compression zone 8 This signal is then used to speed up or slow
down the Moyno type pump. In some embodiments, the goal is to have
no pressure differential across the compression zone, to prevent or
inhibit liquid flow and mixing of liquids between the two stages.
For applications involving additional chemical processing stages,
the first stage configuration (including compression zone, pumps,
and controls) can be replicated for each additional stage.
[0057] The twin-screw embodiment creates a moving bed of solids
that is then subjected to countercurrent flows of liquid. The
continuous solids feeder, the action of the screws, and the
continuous pump discharge all act mechanically to degrade the
physical structure of the feedstock. In some applications, this can
be an advantage by promoting mixing and degradation action and
increasing the rate of chemical reaction. In other applications,
however, the breakdown of the fibrous biomass structure may be
undesirable. In such cases, the advantages of multi-stage,
countercurrent flow can be achieved by use of apparatus in which
the moving bed of solids is simulated rather than actual. A
simulated moving bed (SMB) system for biomass fractionation is
similar to conventional SMB systems for separation of components of
a liquid in the sense that there are multiple reactor sections
(e.g. columns or barrels) and a complex array of valves to direct
liquid flows. It differs however in that full fractionation occurs
in a single pass and the "stationary phase" (biomass) is replaced
at an appropriate place in the processing cycle rather than being
regenerated.
[0058] FIG. 1C illustrates a layout plan view of a simulated moving
bed biomass fractionation system 100 according to one embodiment of
the present invention. Fractionation system 100 includes a common
feedstock hopper 110 and four reactors 120, 130, 140, and 150.
First reactor 120 includes a first fluid inlet port 122, a first
discharge port 124, a first fluid outlet port 126, and a first
feedstock inlet port 128 that is coupled with common feedstock
hopper 110. Second reactor 130 includes a second fluid inlet port
132, a second discharge port 134, a second fluid outlet port 136,
and a second feedstock inlet port 138 that is coupled with common
feedstock hopper 110. Third reactor 140 includes a third fluid
inlet port 142, a third discharge port 144, a third fluid outlet
port 146, and a third feedstock inlet port 148 that is coupled with
common feedstock hopper 110. Fourth reactor 150 includes a fourth
fluid inlet port 152, a fourth discharge port 154, a fourth fluid
outlet port 156, and a fourth feedstock inlet port 158 that is
coupled with common feedstock hopper 110. First fluid outlet port
126 is coupled with second fluid inlet port 132 via a second fluid
passage 131. Second fluid outlet port 136 is coupled with third
fluid inlet port 142 via a third fluid passage 141. Third fluid
outlet port 146 is coupled with fourth fluid inlet port 152 via a
fourth fluid passage 151. Fourth fluid outlet port 156 is coupled
with first fluid inlet port 122 via a first fluid passage 121.
[0059] In the embodiment illustrated in FIG. 1C, first fluid inlet
port 122 and first discharge port 124 are disposed toward a distal
end 120a of first reactor 120, and first fluid outlet port 126 and
first feedstock inlet port 128 are disposed toward a proximal end
120b of first reactor 120. Second fluid inlet port 132 and second
discharge port 134 are disposed toward a distal end 130a of second
reactor 130, and second fluid outlet port 136 and second feedstock
inlet port 138 are disposed toward a proximal end 130b of second
reactor 130. Third fluid inlet port 142 and third discharge port
144 are disposed toward a distal end 140a of third reactor 140, and
third fluid outlet port 146 and third feedstock inlet port 148 are
disposed toward a proximal end 140b of third reactor 140. Fourth
fluid inlet port 142 and fourth discharge port 144 are disposed
toward a distal end 140a of fourth reactor 140, and fourth fluid
outlet port 146 and fourth feedstock inlet port 148 are disposed
toward a proximal end 140b of fourth reactor 140. Simulated moving
bed biomass fractionation system 100 also includes a first motor
125, a second motor 135, a third motor 145, and a fourth motor
155.
[0060] FIG. 2 shows a schematic of an exemplary reaction section
200 of a simulated moving bed biomass fractionation system
according to one embodiment of the present invention. Reaction
section 200 can include any suitable combination of passages, inlet
valves, discharge valves, reagent valves, water valves, vents,
thermal units, motors, and the like. In the embodiment shown here,
reaction section 200 includes a first fluid passage 201 and a
thermal unit 202. In this embodiment, thermal unit 202 includes a
tube-in-tube heat exchanger 203 having a heat exchange inlet valve
204 and a heat exchange outlet valve 206. Reaction section 200 also
includes fluid inlet valves such as a warm water valve 208 and a
cold water valve 210, a fluid inlet port 212, a motor 214 having a
screw drive 216 and a screw positioning system 218, a reactor 220,
a discharge port 222, a vacuum stuffer 224 (to separate solids from
discharged liquid), a ball valve 225, a feedstock inlet port 226
coupled with a feedstock hopper (not shown), and a fluid outlet
port 228. Reaction section 200 also includes a stage 1 liquid
discharge valve 230, a stage 2 liquid discharge valve 232, a cold
water valve 234, an air vent 236, a base reagent valve 238, an acid
reagent valve 240, a hot water valve 242, a passage valve 244, and
a second fluid passage 246. In some embodiments, a simulated moving
bed biomass fractionation system may also include a computer 248 or
other control means in operative association with the thermal unit
or any of the valves, vents, motor components, or other reaction
section elements, where the computer includes or is configured to
implement instructions for regulating these elements as desired. A
simulated moving bed fractionation system can include any desired
number of reaction sections. As shown here, reaction section 200
can be coupled with an adjoining reaction section 270. Each of the
sections in a simulated moving bed biomass fractionation system may
be plumbed identically. The simulated moving bed can be created by
changing the settings, for example via computer control, of the
numerous valves and by sequential activation of other features.
[0061] In some embodiments, the present invention provides a
simulated moving bed system of one or more stages for the
countercurrent fractionation of lignocellulosic biomass. The system
may include a plurality of elongated pressurized reactors
interconnected with plumbing for controlling and directing fluid
flows, means for sequential loading of the reactors with biomass
feedstock and for sequential unloading of processed biomass, means
for injecting countercurrently pressurized wash liquid into each
stage of the simulated moving bed system, means for discharging
wash liquid from each stage of the simulated moving bed system,
means for separating liquids from solids prior to discharging wash
liquids and transferring wash liquids between reactors, means for
maintaining desired temperatures in each reactor of said simulated
moving bed system, means for transferring heat from liquid being
discharged to liquid being injected, means for controlling
pressures to prevent boiling and to maintain desired liquid flows
throughout the SMB system, and means for sequential switching of
valves to create the desired countercurrent, moving bed simulation.
Biomass feedstock can be loaded into reactors by means of one or
more augers and processed biomass can be unloaded by slurrying and
washing with water. In some instances, biomass feedstock may be
loaded into and unloaded from reactors while contained in
full-length baskets. Liquid products can be discharged by means of
progressive cavity pumps operated in reverse to reduce pressure
while avoiding clogging from liquid-solid separation. Liquids can
be separated from solids prior to liquid discharge by means of
small, twin-screw extruders operated so as to force solids back
into the reactors. In some cases, an electronic computer can be
used to configure an SMB for a particular application and to
automate the sequential switching of valves.
[0062] FIG. 3 provides a schematic view of a reaction section 300
having valves 1'-13'. The valves shown in FIG. 3 correspond to
certain reaction section elements of FIG. 2 as described in Table 4
below.
TABLE-US-00004 TABLE 4 Valve Number (of FIG. 3) Reaction Section
Element (of FIG. 2) valve 1' cold water valve 210 valve 2' warm
water valve 208 valve 3' hot water valve 242 valve 4' heat exchange
inlet valve 204 valve 5' acid reagent valve 240 valve 6' base
reagent valve 238 valve 7' passage valve 244 valve 8' stage 1
liquid discharge valve 230 valve 9' stage 2 liquid discharge valve
232 valve 10' discharge port 222 valve 11' ball valve 225 valve 12'
cold water valve 234 valve 13' air vent 236
[0063] In the FIG. 3 schematic, simple shutoff valves are shown for
clarity and ease of description. Embodiments of the present
invention also encompass fractionation systems having multi-port
valves as well, which may reduce the number of valve units. FIG. 4
shows a layout plan of an exemplary simulated moving bed biomass
fractionation system 400 having eighteen reaction sections 401-418
arranged in a radial constellation similar to that shown in FIG.
1C, such that the distal end of each of the reactors is coupled
with and radiates from a common feedstock hopper 419. Each of the
reaction sections includes a screw and drive, and each section is
linked to an adjoining section, for example via liquid discharge
units to the outer ends of the barrels. Hoppers can receive
finished solid product. Valves, connections to common features, and
other details are not shown in this simplified layout view. In
practice, the barrels of the SMB system can be mounted vertically
around the central feed hopper. The horizontal arrangement shown
here is merely for clarity in illustrating the interconnections,
which may be vertical, horizontal, or any combination thereof. In
some embodiments, each of the repeating sections is identical.
Operation of fractionation system 400 can be described in terms of
sequential valve settings for various valves in the reaction
sections as provided in Table 5. Thus, the simulated moving bed can
be created by changing the settings of the various valves and
activating other features. Often, operation of these system
components is controlled by a computer. Although only three steps
are shown, it is appreciated that a fractionation progression can
be continued for any number of steps.
TABLE-US-00005 TABLE 5 Section No. (of FIG. 4) Valve No. Step No.
(of FIG. 3) 1 2 3 1' 2' 3' 4' 5' 6' 7' 8' 9' 10' 11' 12' Action 401
418 417 C C C C C C C C C C O C Load Feedstock 402 401 418 C O C C
C C C C C C C C Soak Feedstock 403 402 401 C C C O C C C O C C C C
Stage 1 Liquid Discharge 404 403 402 C C C O C C O C C C C C
Counter-Flow Fractionation 405 404 403 C C C O C C O C C C C C
Counter-Flow Fractionation 406 405 404 C C C O C C O C C C C C
Counter-Flow Fractionation 407 406 405 C C C O O C O C C C C C
Stage 1 Reagent In 408 407 406 C C C O C C O C C C C C Counter-Flow
Rinse 409 408 407 C C C O C C O C C C C C Counter-Flow Rinse 410
409 408 C C O O C C C C O C C C Stage 2 Liquid Discharge 411 410
409 C C C O C C O C C C C C Counter-Flow Fractionation 412 411 410
C C C O C C O C C C C C Counter-Flow Fractionation 413 412 411 C C
C O C C O C C C C C Counter-Flow Fractionation 414 413 412 C C C O
C O O C C C C C Stage 2 Reagent In 415 414 413 C C C O C C O C C C
C C Counter-Flow Rinse 416 415 414 C C C O C C O C C C C C
Counter-Flow Rinse 417 416 415 O C C C C C O C C C C C Stage 2 Cold
Rinse In 418 417 416 C C C C C C C C C O C O Cellulose
Discharge
[0064] Table 5 describes the action occurring in each reaction
section and the settings of the valves in each reaction section at
each step. The valves can be described as open (O) or closed (C).
The valve settings for each step can be maintained for any desired
period of time. For example, Step 1 may involve maintaining valve
settings for a period of three minutes. Similar time periods may be
maintained for Step 2, Step 3, and so on. This progression may be
continued continuously, or for any desired length of time or number
of steps. With reference to FIG. 4, the reaction sections can be
numbered clockwise in accordance to with "Step 1" in Table 5. In an
exemplary lignocellulosic feedstock processing method embodiment,
Step 1 involves loading feedstock into reaction section 401,
carrying out various processing steps in reaction sections 402-417,
and discharging cellulose from reaction section 418. Step 2
involves loading feedstock into reaction section 418, carrying out
various processing steps in reaction sections 401-416, and
discharging cellulose from reaction 417, and so on. A detailed
status of each of the reaction sections (401-418) at Step 1 can be
described as follows, where specific elements of the reaction
sections are described by reference numerals as provided in FIGS. 2
and 3. It is appreciated that in some embodiments, each of the
reaction sections is identical. The description below discusses a
sequential processing of the feedstock, following the solids in a
clockwise manner through the fractionation system. Typically,
however, all section descriptions occur simultaneously or in
parallel in the various reaction sections of the fractionation
system.
[0065] Step 1: Reaction Section 401--Load Feedstock: When loading
feedstock from the common feedstock hopper into reactor 220, an
adjustable closure such as a ball valve 225 (valve 11'), which
typically has an inner diameter that matches an inner diameter of
the reactor, is opened to create a passage between the feedstock
hopper and reactor 220. All other valves are closed, so that no
other materials are introduced into reactor 220. Screw drive 216 is
turned on to enable screw penetration, and screw positioning system
218 pushes at least a portion of a screw or threaded shaft (not
shown) into the feedstock hopper. The screw continues to turn and
draws feedstock from the hopper into reactor 220. After an
appropriate time, the screw rotation is stopped and screw
positioning system 218 withdraws the screw from the hopper back
into reactor 220. Ball valve 225 is then closed.
[0066] In an alternative vertical configuration, feedstock can be
loaded into baskets (e.g. in a loading operation external to the
simulated moving bed) to be inserted into the reactors by opening
and then closing covers on the reactors. At the end of processing,
the cover can be opened, the basked of finished product removed,
and a new basket of feedstock inserted, in an endless cycle. In
some embodiments, ball valves, screws, motors, or positioning units
may not be included or involved.
[0067] Step 1: Reaction Section 402--Soak Feedstock: Warm water
valve 208 (valve 2') and air vent 236 (valve 13') are opened and
reactor 220 of reaction section is filled with warm or heated water
which mixes with the feedstock. In some embodiments, air vent 236
may include a liquid sensor that can trigger closure of valve 208
and vent 236. Optionally, warm water can be obtained via a heat
exchange process involving liquid discharge originating from
reaction section 403.
[0068] Step 1: Reaction Section 403--Stage 1 Liquid Discharge:
Stage 1 liquid discharge valve 230 (valve 8') is opened to allow
stage 1 liquid discharge (e.g. with mobilized biomass constituents
including extractives and hemicellulose) to exit reactor 220. Heat
exchange inlet valve 204 (valve 4') is opened so as to heat
material that is being transferred from reaction section 404 as it
passes through thermal unit 202. In some embodiments, heat exchange
inlet valve 204 may be coupled with a steam source. Optionally,
operation of heat exchange inlet valve 204 may be modulated with a
thermocouple control. In one example, the temperature of contents
passing through thermal unit 202 are heated to a temperature of
about 2300C. It may be desirable to avoid high pressure regulatory
requirements. For example, in some embodiments pressure is
maintained below 600 psi. Relatedly, the temperature of reactors
containing ethanol may be limited to 220.degree. C. or lower. Other
reactors may operate at 230.degree. C. or more to meet chemical
processing requirements, limited primarily by destructive
degradation of the material being processed. Prior to solid product
discharge, a reactor is often cooled below 100.degree. C. to avoid
flashing. This cooling can be accomplished with full recovery of
heat values by countercurrent rinsing with cold water in the step
just prior to discharge. The screw motor can be started in an
oscillating mode, to provide a turning of the screw. In some
embodiments, this may involve, for example, a turn or two of the
screw in one direction and a turn or two in the other direction,
for perhaps a duration of two seconds in each direction. This
action can generate some stirring and can prevent channeling or
uneven fluid flow at certain points within reactor 220. A steam
jacket or other thermal device may be coupled with reactor 220 or
any other appropriate element of the fractionation system to
achieve a desired temperature control.
[0069] Step 1: Reaction Section 404--Countercurrent Fractionation:
Heat exchange inlet valve 204 (valve 4') is opened so as to heat
material that is being transferred from reaction section 405.
Passage valve 244 (valve 7') is opened to provide countercurrent
fractionate from reactor 220 to the adjacent reaction section 403.
In some embodiments, this countercurrent fractionate comprises
hemicellulose. The term countercurrent or counter-flow can be used
to describe the flow of fractionate from a reactor containing more
processed solids into a reactor containing less processed solids.
Specifically, feedstock is passed from the common feedstock hopper
into reactor 220 in a radially outward direction, via feedstock
inlet port 226, passing from proximal end 220b toward distal end
220a of reactor 220. In contrast, fractionate from section 404
passes into reactor 220 in a radially inward direction, via fluid
inlet port 212, passing from distal end 220a toward proximal end
220b of reactor 220.
[0070] Step 1: Reaction Sections 405 and 406--Countercurrent
Fractionation: All valves retain their settings. Heat exchange
inlet valve 204 (valve 4') of reaction section 405 is opened so as
to heat material that is being transferred from reaction section
406. Passage valve 244 (valve 7') of reaction section 405 is opened
to provide countercurrent fractionate from reaction section 405 to
reaction section 404. In some embodiments, the fractionate may
contain hemicellulose. Heat exchange inlet valve 204 (valve 4') of
reaction section 406 is opened so as to heat material that is being
transferred from reaction section 407. Passage valve 244 (valve 7')
of reaction section 406 is opened to provide countercurrent
fractionate from reaction section 406 to reaction section 405. In
some embodiments, the fractionate may contain hemicellulose. More
reaction sections can be added here with the same valve settings if
desired for additional processing.
[0071] Step 1: Reaction Section 407--Reagent Feed: Acid reagent
valve 240 (valve 5') may be opened to provide acid or another
reagent to enhance hydrolysis in countercurrent fractionation
reaction sections 406, 405, and 404. Heat exchange inlet valve 204
(valve 4') is opened so as to heat material that is being
transferred from reaction section 408. Passage valve 244 (valve 7')
is opened to provide transfer of material to adjacent reaction
section 406. The contents of this material, in some cases, is
similar to that as described above except that it contains less
hemicellulose and more acid. In some embodiments, the acid reagent
has a pH within the range from about 2 to about 4. In some
embodiments, the acid reagent has a temperature within the range
from about 210.degree. C. to about 230.degree. C.
[0072] Step 1: Reaction Section 408--Countercurrent Rinse: Acid
reagent valve 240 (valve 5') is closed. Heat exchange inlet valve
204 (valve 4') is opened so as to heat material that is being
transferred from reaction section 409. Passage valve 244 (valve 7')
is opened to provide transfer of material to adjacent reaction
section 407. In some cases, this involves a water rinse that
contains residues from what was section 408 in the previous step.
All other valves retain their settings for a countercurrent
rinse.
[0073] Step 1: Reaction Section 409--Countercurrent Rinse: Passage
valve 244 (valve 7') is opened to provide transfer of material to
adjacent reaction section 408. In some cases, this involves a water
rinse that contains residues from what was section 409 in the
previous step. All valves retain their settings as the
countercurrent rinse continues. Heat exchange inlet valve 204
(valve 4') may be opened, and water coming from valve 3 of section
410 can be heated. Although valve 3' is for "hot" water, in some
cases this water may not be hot enough for the desired process.
[0074] Step 1: Reaction Section 410--Stage 2 Liquid Discharge: Heat
exchange inlet valve 204 (valve 4') is opened so as to heat
material that is being transferred from reaction section 411.
Passage valve 244 (valve 7') is closed, thus preventing passage of
material to reaction section 409. Hot water valve 242 (valve 3') is
opened to provide Stage 1 rinse flow (replacing valve 7' flow).
With valve 7' closed, water can pass to the previous section 409.
Stage 2 liquid discharge valve 232 (valve 9') is opened to allow
stage 2 liquid discharge, which may contain for example primarily
lignin in addition to stage 2 wash chemicals, to exit reactor
220.
[0075] Step 1: Reaction Section 411--Countercurrent Fractionation:
Heat exchange inlet valve 204 (valve 4') is opened so as to heat
material that is being transferred from reaction section 412. Hot
water valve 242 (valve 3') and Stage 2 liquid discharge valve 232
(valve 9') are closed. Passage valve 244 (valve 7') is opened to
provide transfer of countercurrent fractionate to adjacent reaction
section 410. This fractionate may contain, for example, primarily
lignin along with stage 2 wash chemicals. Progressing from section
410 through section 413, the lignin concentration may become lower
and the chemical concentration may become higher.
[0076] Step 1: Reaction Sections 412 and 413--Countercurrent
Fractionation: All valves retain their settings as fractionation
continues. Heat exchange inlet valve 204 (valve 4') of reaction
section 412 is opened so as to heat material that is being
transferred from reaction section 413. Passage valve 244 (valve 7')
of reaction section 412 is opened to provide countercurrent
fractionate from reaction section 412 to reaction section 411. Heat
exchange inlet valve 204 (valve 4') of reaction section 413 is
opened so as to heat material that is being transferred from
reaction section 414. Passage valve 244 (valve 7') of reaction
section 413 is opened to provide countercurrent fractionate from
reaction section 413 to reaction section 412. More reaction
sections can be added here with the same valve settings if desired
for additional processing.
[0077] Step 1: Reaction Section 414--Stage 2 Reagent Feed: Heat
exchange inlet valve 204 (valve 4') is opened so as to heat
material that is being transferred from reaction section 415.
Passage valve 244 (valve 7') is opened to provide transfer of
material to adjacent reaction section 413. Base reagent valve 238
(valve 6') is opened to provide alkali or another reagent for Stage
2 processing in the countercurrent fractionation reaction sections
413, 412, and 411. In some embodiments, the alkali or base reagent
has a pH within the range from about 8 to about 13. In some
embodiments, the base reagent has a temperature within the range
from about 180.degree. C. to about 240.degree. C. In some cases,
the maximum may be about 220.degree. C. when 50% ethanol is
used.
[0078] Step 1: Reaction Section 415--Countercurrent Rinse: Heat
exchange inlet valve 204 (valve 4') is opened so as to heat
material that is being transferred from reaction section 416.
Passage valve 244 (valve 7') is opened to provide transfer of
material to adjacent reaction section 414. This may involve a water
rinse that contains residues from section 414 in the previous step.
Base reagent valve 238 (valve 6') is closed. All other valves
retain their settings for a countercurrent rinse.
[0079] Step 1: Reaction Section 416--Countercurrent Rinse: Heat
exchange inlet valve 204 (valve 4') is opened so as to heat
material that is being transferred from reaction section 417.
Passage valve 244 (valve 7') is opened to provide transfer of
material to adjacent reaction section 415. This may involve the
continued washing out of residual chemicals. All other valves
retain their settings as the countercurrent rinse continues.
[0080] Step 1: Reaction Section 417--Stage 2 Cold Water Rinse In:
Passage valve 244 (valve 7') is opened to provide transfer of
material to adjacent reaction section 416. Heat exchange inlet
valve 204 (valve 4') is closed so as to reduce the temperature in
reactor 220. Cold water valve 210 (valve 1') is opened allowing
cool water to enter and cool reactor 220, in preparation for the
cellulose discharge. At the same time, this water is heated for
energy recuperation and further use in the Stage 2 counter-flow
rinse. In some cases, as the cold water flows into the section, the
hot water in the section is forced out the other end as rinse for
section 416. At the same time, the cold water is cooling the solids
and being warmed. This process may continue, for example, until the
temperature at the top or inner section of section 417 falls below
100.degree. C.
[0081] Step 1: Reaction Section 418--Cellulose Discharge: Passage
valve 244 (valve 7') to reaction section 417 is closed to retain
pressure downstream. Discharge port 222 (valve 10') is opened to
discharge cellulose product from reactor 220. Cold water valve 234
(valve 12') is opened to flush the cellulose with cold water. The
screw drive is activated to move cellulose toward discharge port
222. In some embodiments, cold water valve 210 (valve 1') is opened
for additional washing action. At the end of the cellulose
discharge period, reactor 220 can be emptied and made available for
filling with feedstock in Step 2.
[0082] In some embodiments, a vacuum stuffer operates at all times
except when a section is being emptied and filled. The vacuum
stuffer can retain solids within a section while allowing liquid to
discharge. In a vertical configuration using a basket system for
filling, a vacuum stuffer may be replaced by a large, washable
filter.
[0083] In one embodiment, a simulated moving bed fractionation
system includes reactors having an inside diameter of 4 inches and
a length of 80 inches (L/D=20). The empty volume of an individual
reactor of the system is about 1000 cubic inches, less the screw
volume or about 0.5 cubic feet or about 14 liters. The bulk density
of corn stover, a source of cellulose, is about 76 grams per liter.
Thus, a single reaction section will contain about one kilogram of
corn stover feedstock. If the SMB is on a two minute cycle, this
would result in a processing throughput of about 720 kilograms of
corn stover per day, or about 0.8 English tons per day. With the
reactor utilization shown in Table 5, a two minute cycle time would
give about 8 minutes of maximum severity processing (for example
sections 404-407 and 411-414) in each of the two stages. In
contrast, a 100 ton/day commercial system with an L/D of 20 and the
same two minute cycle time would require reactor sections of about
20 inches in diameter and 400 inches (33.3 feet) long. This
illustrates the feasibility of a simulated moving bed system for
scale-up to a small commercial configuration having similar
proportions and reaction times. Although an L/D of 20 may be
arbitrary, a slender reaction vessel may have advantages in
handling expected pressures and minimizing undesirable mixing and
channeling of the countercurrent liquid flow.
[0084] Having described several embodiments, it will be recognized
by those of skill in the art that various modifications,
alternative constructions, and equivalents may be used without
departing from the spirit of the invention. Additionally, a number
of well known processes and elements have not been described in
order to avoid unnecessarily obscuring the present invention.
Accordingly, the above description should not be taken as limiting
the scope of the invention.
[0085] Where a range of values is provided, it is understood that
each intervening value, to the tenth of the unit of the lower limit
unless the context clearly dictates otherwise, between the upper
and lower limits of that range is also specifically disclosed. Each
smaller range between any stated value or intervening value in a
stated range and any other stated or intervening value in that
stated range is encompassed. The upper and lower limits of these
smaller ranges may independently be included or excluded in the
range, and each range where either, neither or both limits are
included in the smaller ranges is also encompassed within the
invention, subject to any specifically excluded limit in the stated
range. Where the stated range includes one or both of the limits,
ranges excluding either or both of those included limits are also
included.
[0086] As used herein and in the appended claims, the singular
forms "a", "an", and "the" include plural referents unless the
context clearly dictates otherwise. Thus, for example, reference to
"a process" includes a plurality of such processes and reference to
"the electrode" includes reference to one or more electrodes and
equivalents thereof known to those skilled in the art, and so
forth.
[0087] Also, the words "comprise," "comprising," "include,"
"including," and "includes" when used in this specification and in
the following claims are intended to specify the presence of stated
features, integers, components, or steps, but they do not preclude
the presence or addition of one or more other features, integers,
components, steps, acts, or groups.
* * * * *