U.S. patent application number 14/619611 was filed with the patent office on 2015-06-04 for process for the production of furfural.
The applicant listed for this patent is E I DU PONT DE NEMOURS AND COMPANY. Invention is credited to DAVID RICHARD CORBIN, PAUL JOSEPH FAGAN, STUART B. FERGUSSON, KEITH W. HUTCHENSON, PRANIT S. METKAR, RONNIE OZER, CARMO JOSEPH PEREIRA, BHUMA RAJAGOPALAN, SOURAV KUMAR SENGUPTA, ERIC J. TILL.
Application Number | 20150152074 14/619611 |
Document ID | / |
Family ID | 48695359 |
Filed Date | 2015-06-04 |
United States Patent
Application |
20150152074 |
Kind Code |
A1 |
CORBIN; DAVID RICHARD ; et
al. |
June 4, 2015 |
PROCESS FOR THE PRODUCTION OF FURFURAL
Abstract
Furfural is produced by contacting a feedstock solution
containing C.sub.5 sugar and/or C.sub.6 sugar with a solid acid
catalyst using reactive distillation. Both high yield and high
conversion are obtained, without production of insoluble char in
the reaction vessel. Degradation of furfural is minimized by its
low residence time in contact with the solid acid catalyst. Higher
catalyst lifetime can be achieved because the catalyst is
continually washed with the refluxing aqueous solution and not
sitting in high-boiling byproducts like humins, which are known to
be deleterious to catalyst lifetime.
Inventors: |
CORBIN; DAVID RICHARD; (WEST
CHESTER, PA) ; FAGAN; PAUL JOSEPH; (WILMINGTON,
DE) ; FERGUSSON; STUART B.; (KINGSTON, CA) ;
HUTCHENSON; KEITH W.; (LINCOLN UNIVERSITY, PA) ;
METKAR; PRANIT S.; (WILMINGTON, DE) ; OZER;
RONNIE; (Arden, DE) ; PEREIRA; CARMO JOSEPH;
(SILVER SPRING, MD) ; RAJAGOPALAN; BHUMA;
(WILMINGTON, DE) ; SENGUPTA; SOURAV KUMAR;
(WILMINGTON, DE) ; TILL; ERIC J.; (NEWTOWN SQUARE,
PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
E I DU PONT DE NEMOURS AND COMPANY |
Wilmington |
DE |
US |
|
|
Family ID: |
48695359 |
Appl. No.: |
14/619611 |
Filed: |
February 11, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13729445 |
Dec 28, 2012 |
9012664 |
|
|
14619611 |
|
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|
61580717 |
Dec 28, 2011 |
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Current U.S.
Class: |
549/489 |
Current CPC
Class: |
Y02P 20/10 20151101;
C07D 307/50 20130101; C07D 307/48 20130101; Y02P 20/127
20151101 |
International
Class: |
C07D 307/50 20060101
C07D307/50 |
Claims
1. A process comprising: (a) providing a reactive distillation
column comprising a top, a bottom, a reaction zone in between the
top and the bottom, and a solid acid catalyst disposed in the
reaction zone; (b) bringing a feedstock solution into contact with
the solid acid catalyst in the presence of a water-miscible organic
solvent for a residence time sufficient to produce a mixture of
water and furfural, wherein the feedstock solution comprises
C.sub.5 sugar, C.sub.6 sugar or a mixture thereof, and the reaction
zone is at a temperature in the range of 90-250.degree. C. and a
pressure in the range of 0.1-3.87 MPa; (c) removing the mixture of
water and furfural from the top of the reactive distillation
column; and (d) collecting water, unreacted sugars and nonvolatile
byproducts from the bottom of the reactive distillation column in a
reboiler, wherein the water-miscible organic solvent is
polyethylene glycol, isosorbide dimethyl ether, isosorbide,
propylene carbonate, polyethylene glycol dimethyl ether, adipic
acid, diethylene glycol, 1,3-propane diol, glycerol,
gamma-butyrolactone or gamma-valerolactone.
2. The process according to claim 1, wherein the acid catalyst
comprises a heterogeneous heteropolyacid, a salt of a heterogeneous
heteropolyacid, a natural or synthetic clay mineral, a cation
exchange resin, a metal oxide, a mixed metal oxide, a metal
sulfide, a metal sulfate, a metal sulfonate, sulfated titania,
sulfated zirconia, a metal nitrate, a metal phosphate, a metal
phosphonate, a metal molybdate, a metal tungstate, a metal borate,
or a combination of any of these.
3. The process according to claim 2, wherein the acid catalyst
comprises a cation exchange resin that is a
sulfonic-acid-functionalized polymer.
4. The process according to claim 2, wherein the acid catalyst
comprises a clay mineral that is a zeolite.
5. The process according to claim 4, wherein the acid catalyst is a
medium or large pore, acidic, hydrophobic zeolite.
6. The process according to claim 5, wherein the zeolite comprises
ZSM-5, faujasite, beta zeolite, Y zeolite, mordenite, or a
combination of any of these.
7. The process according to claim 1 further comprising: e. removing
water and unreacted sugars from the water, unreacted sugars and
nonvolatile byproducts of step (d); and f. concentrating by
evaporation at least a portion of the water and unreacted sugars
and using it as feedstock solution in step (b).
8. The process according to claim 1 further comprising separating
the furfural from the removed water and furfural of step (c).
9. The process according to claim 1 wherein the combined
concentration of C.sub.5 sugar and/or C.sub.6 sugar in the
feedstock solution is in the range of 1-99 weight percent based on
the total weight of the feedstock solution.
10. The process according to claim 9 wherein the combined
concentration of C.sub.5 sugar and/or C.sub.6 sugar in the
feedstock solution is in the range of 5-35 weight percent based on
the total weight of the feedstock solution.
11. The process according to claim 1 wherein the feedstock solution
comprises xylose, glucose, or a mixture thereof.
12. (canceled)
13. The process according to claim 1, further comprising a
steam-stripping step, comprising feeding water or steam to the
reaction zone from the bottom of the reactive distillation
column.
14. The process of claim 1 further comprising the steps of: h)
diluting at least a portion of the contents of the reboiler with
water or with the feedstock solution, thereby precipitating
water-insoluble byproducts; i) removing the byproducts precipitated
in step h); and j) feeding the precipitate-free solution remaining
after step i) back to the reaction zone.
15. A process comprising the steps of: (a) providing a reactor
comprising a reactive distillation column comprising an upper,
rectifying section; a lower, stripping section; and a reboiler,
wherein the stripping section or the reboiler is a reaction zone
containing a solid acid catalyst, (b) continuously feeding a
feedstock solution comprising C.sub.5 sugar, C.sub.6 sugar or a
mixture thereof to the column at a location between the rectifying
section and the stripping section, allowing the solution to flow
into the reaction zone into contact with the solid acid catalyst in
the presence of a water-miscible organic solvent, thereby forming a
reaction mixture, wherein (i) the water-miscible organic solvent
forms a monophasic solution with the water in the reaction zone and
the temperature of the reaction mixture is between about 90.degree.
C. and about 250.degree. C. (ii) the reaction mixture is held at a
pressure between atmospheric pressure and 3.87 MPa, and (iii) the
sugar solution and catalyst are in contact for a time sufficient to
produce water and furfural (c) drawing off a mixture of furfural
and water at the top of the column (d) collecting water, unreacted
sugars, and nonvolatile byproducts dissolved in the water-miscible
organic solvent in the reboiler; (e) removing nonvolatile
byproducts from the reboiler; and (f) removing the water and
unreacted sugars from the reboiler for further use or disposal,
wherein the water-miscible organic solvent is polyethylene glycol,
isosorbide dimethyl ether, isosorbide, propylene carbonate,
polyethylene glycol dimethyl ether, adipic acid, diethylene glycol,
1,3-propane diol, glycerol, gamma-butyrolactone or
gamma-valerolactone.
Description
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(e) of U.S. Provisional Application No. 61/580,717, filed
Dec. 28, 2011, which is herein incorporated by reference.
FIELD OF THE INVENTION
[0002] A method for the production of furfural and related
compounds from sugar streams is provided.
BACKGROUND OF THE INVENTION
[0003] Furfural and related compounds, such as
hydroxymethylfurfural (HMF), are useful precursors and starting
materials for industrial chemicals for use as pharmaceuticals,
herbicides, stabilizers, and polymers. The current furfural
manufacturing process utilizes biomass such as corn cob and sugar
cane bagasse as a raw material feed stock for obtaining xylose or
hemicellulose.
[0004] The hemicellulose is hydrolyzed under acidic conditions to
its monomer sugars, such as glucose, fructose, xylose, mannose,
galactose, rhamnose, and arabinose. Xylose, which is a pentose
(i.e., a "C.sub.5 sugar") is the sugar present in the largest
amount. In a similar aqueous acidic environment, the C.sub.5 sugars
are subsequently dehydrated and cyclized to furfural.
[0005] A major difficulty with known methods for dehydration of
sugars is the formation of undesirable resinous material that not
only leads to yield loss but also leads to fouling of exposed
reactor surface and negatively impacts heat transfer
characteristics. Further, the use of solid acid catalyst could also
lead to coking issues.
[0006] A review by R. Karinen et al. (ChemSusChem 4 (2011), pp.
1002-1016) includes several commonly used methods of producing
furfural generally as described above. All of those methods involve
use of a soluble inorganic acid catalyst, such as sulfuric,
phosphoric, or hydrochloric acid. These acids are difficult to
separate from the reaction medium or product stream. Low yields can
result from formation of undesirable byproducts. Further, their use
can require increased capital costs because of associated corrosion
and environmental emission issues.
[0007] There remains a need for a process to produce furfural and
related compounds from sugars at both high yield and high
conversion.
SUMMARY OF THE INVENTION
[0008] In an aspect of the invention, there is a process
comprising: [0009] (a) providing a reactive distillation column
comprising a top, a bottom, a reaction zone in between the top and
the bottom, and a solid acid catalyst disposed in the reaction
zone; [0010] (b) bringing a feedstock solution into contact with
the solid acid catalyst for a residence time sufficient to produce
a mixture of water and furfural, wherein the feedstock solution
comprises C.sub.5 sugar, C.sub.6 sugar or a mixture thereof, and
the reaction zone is at a temperature in the range of
90-250.degree. C. and a pressure in the range of 0.1-3.87 MPa;
[0011] (c) removing the mixture of water and furfural from the top
of the reactive distillation column; and [0012] (d) collecting
water, unreacted sugars and nonvolatile byproducts from the bottom
of the reactive distillation column.
[0013] In an aspect, the process further comprises feeding a
water-miscible organic solvent to the reaction zone.
[0014] In another aspect, the feedstock solution further comprises
a water-miscible organic solvent.
[0015] In another aspect, there is a process comprising the steps
of:
[0016] (a) providing a reactor comprising a reactive distillation
column comprising an upper, rectifying section; a lower, stripping
section; and a reboiler, wherein the stripping section or the
reboiler is a reaction zone containing a solid acid catalyst;
[0017] (b) continuously feeding a solution comprising C.sub.5
sugar, C.sub.6 sugar or a mixture thereof to the column at a
location between the rectifying section and the stripping section,
allowing the solution to flow into the reaction zone into contact
with the solid acid catalyst, thereby forming a reaction mixture,
wherein [0018] (i) the temperature of the reaction mixture is
between about 90.degree. C. and about 250.degree. C. [0019] (ii)
the reaction mixture is held at a pressure between about
atmospheric pressure and about 3.87.times.10.sup.6 Pa, and [0020]
(iii) the sugar solution and catalyst are in contact for a time
sufficient to produce water and furfural;
[0021] (c) drawing off a mixture of furfural and water at the top
of the column;
[0022] (d) collecting water, unreacted sugars, and nonvolatile
byproducts in the reboiler;
[0023] (e) removing nonvolatile byproducts from the reboiler;
and
[0024] (f) removing the water and unreacted sugars from the
reboiler for further use or disposal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Various features and/or embodiments of this invention are
illustrated in drawings as described below. These features and/or
embodiments are representative only, and the selection of these
features and/or embodiments for inclusion in the drawings should
not be interpreted as an indication that subject matter not
included in the drawings is not suitable for practicing the
invention, or that subject matter not included in the drawings is
excluded from the scope of the appended claims and equivalents
thereof.
[0026] FIG. 1 is a schematic illustration of an exemplary reactor
configuration used in the production of furfural in accordance with
various embodiments of the present invention.
DETAILED DESCRIPTION
Definitions
[0027] As used herein, the term "sugar" includes monosaccharides,
disaccharides, and oligosaccharides. Monosaccharides, or "simple
sugars," are aldehyde or ketone derivatives of straight-chain
polyhydroxy alcohols containing at least three carbon atoms. A
pentose is a monosaccharide having five carbon atoms; some examples
are xylose, arabinose, lyxose and ribose. A hexose is a
monosaccharide having six carbon atoms; some examples are glucose
and fructose. Disaccharide molecules (e.g., sucrose, lactose,
fructose, and maltose) consist of two covalently linked
monosaccharide units. As used herein, "oligosaccharide" molecules
consist of about 3 to about 20 covalently linked monosaccharide
units.
[0028] As used herein, the term "C.sub.n sugar" includes
monosaccharides having n carbon atoms; disaccharides comprising
monosaccharide units having n carbon atoms; and oligosaccharides
comprising monosaccharide units having n carbon atoms. Thus,
"C.sub.5 sugar" includes pentoses, disaccharides comprising pentose
units, and oligosaccharides comprising pentose units.
[0029] As used herein, the term "hemicellulose" refers to a polymer
comprising C.sub.5 and C.sub.6 monosaccharide units. Hemicellulose
consists of short, highly branched chains of sugars. In contrast to
cellulose, which is a polymer of only glucose, a hemicellulose is a
polymer of five different sugars. It contains five-carbon sugars
(usually D-xylose and L-arabinose) and six-carbon sugars
(D-galactose, D-glucose, and D-mannose, fructose). Hemicellulose
can also contain uronic acid, sugars in which the terminal carbon's
hydroxyl group has been oxidized to a carboxylic acid, such as,
D-glucuronic acid, 4-O-methyl-D-glucuronic acid, and D-galacturonic
acid. The sugars are partially acetylated. Typically the acetyl
content is 2 to 3% by weight of the total weight of hemicellulose.
Xylose is typically the sugar monomer present in hemicellulose in
the largest amount.
[0030] As used herein, the term "solid acid catalyst" refers to any
solid material containing Bronsted and/or Lewis acid sites, and
which is substantially undissolved by the reaction medium under
ambient conditions.
[0031] As used herein, the term "nonvolatile byproduct" denotes a
reaction byproduct that either has a boiling point at one
atmospheric pressure greater than the boiling point of the
distilled product(s), or is a nonvolatile solid.
[0032] As used herein, the term "heteropolyacid" denotes an
oxygen-containing acid with P, As, Si, or B as a central atom which
is connected via oxygen bridges to W, Mo or V. Some examples are
phosphotungstic acid, molybdophosphoric acid.
[0033] As used herein, the term "high boiling" denotes a solvent
having a boiling point above about 100.degree. C. at one
atmosphere.
[0034] As used herein the term "water-miscible organic solvent"
refers to an organic solvent that can form a monophasic solution
with water at the temperature at which the reaction is carried
out.
[0035] As used herein the term "humin(s)" refers to dark, amorphous
byproduct(s) resulting from acid induced sugar and furfural
degradation.
[0036] As used herein, the term "selectivity" refers to the moles
of furfural produced, divided by the moles of xylose transformed to
products over a particular time period.
[0037] In an embodiment, there is a process for the production of
furfural comprising providing a reactive distillation column
comprising a top, a bottom, a reaction zone in between the top and
the bottom, and a solid acid catalyst disposed in the reaction
zone. FIG. 1 shows a schematic illustration of an exemplary reactor
configuration comprising a reactive distillation column 10
comprising a top 11, a bottom 12, a reaction zone 20 in between the
top 11 and the bottom 12, and a solid acid catalyst 2 disposed in
the reaction zone 20.
[0038] The solid acid catalyst is a solid acid having the thermal
stability required to survive reaction conditions. The solid acid
catalyst may be supported on at least one catalyst support.
Examples of suitable solid acids include without limitation the
following categories: 1) heterogeneous heteropolyacids (HPAs) and
their salts, 2) natural or synthetic clay minerals, such as those
containing alumina and/or silica (including zeolites), 3) cation
exchange resins, 4) metal oxides, 5) mixed metal oxides, 6) metal
salts such as metal sulfides, metal sulfates, metal sulfonates,
metal nitrates, metal phosphates, metal phosphonates, metal
molybdates, metal tungstates, metal borates, and 7) combinations of
any members of any of these categories. The metal components of
categories 4 to 6 may be selected from elements from Groups 1
through 12 of the Periodic Table of the Elements, as well as
aluminum, chromium, tin, titanium, and zirconium. Examples include,
without limitation, sulfated zirconia and sulfated titania.
[0039] Suitable HPAs include compounds of the general formula
X.sub.aM.sub.bO.sub.c.sup.q-, where X is a heteroatom such as
phosphorus, silicon, boron, aluminum, germanium, titanium,
zirconium, cerium, cobalt or chromium, M is at least one transition
metal such as tungsten, molybdenum, niobium, vanadium, or tantalum,
and q, a, b, and c are individually selected whole numbers or
fractions thereof. Nonlimiting examples of salts of HPAs are
lithium, sodium, potassium, cesium, magnesium, barium, copper, gold
and gallium, and onium salts such as ammonia. Methods for preparing
HPAs are well known in the art and are described, for example, in
G. J. Hutchings, C. P. Nicolaides and M. S. Scurrel, Catal Today
(1994) p 23; selected HPAs are also available commercially, for
example, through Sigma-Aldrich Corp. (St. Louis, Mo.). Examples of
HPAs suitable for the disclosed process include, but are not
limited to, tungstosilicic acid
(H.sub.4[SiW.sub.12O.sub.40].xH.sub.2O), tungstophosphoric acid
(H.sub.3[PW.sub.12O.sub.40].xH.sub.2O), molybdophosphoric acid
(H.sub.3[PMo.sub.12O.sub.40].xH.sub.2O), molybdosilicic acid
(H.sub.4[SiMo.sub.12O.sub.40].xH.sub.2O), vanadotungstosilicic acid
(H.sub.4+n[SiV.sub.nW.sub.12-nO.sub.40].xH.sub.2O),
vanadotungstophosphoric acid
(H.sub.3+n[PV.sub.nW.sub.12-nO.sub.40].xH.sub.2O),
vanadomolybdophosphoric acid
(H.sub.3+n[PV.sub.nMo.sub.12-nO.sub.40].xH.sub.2O),
vanadomolybdosilicic acid
(H.sub.4+n[SiV.sub.nMo.sub.12-nO.sub.40].xH.sub.2O),
molybdotungstosilicic acid
(H.sub.4[SiMo.sub.nW.sub.12-nO.sub.40].xH.sub.2O),
molybdotungstophosphoric acid
(H.sub.3[PMo.sub.nW.sub.12-nO.sub.40].xH.sub.2O), wherein n in the
formulas is an integer from 1 to 11 and x is an integer of 1 or
more.
[0040] Natural clay minerals are well known in the art and include,
without limitation, kaolinite, bentonite, attapulgite,
montmorillonite and zeolites.
[0041] In an embodiment, the solid acid catalyst is a cation
exchange resin that is a sulfonic-acid-functionalized polymer.
Suitable cation exchange resins include, but are not limited to the
following: styrene-divinylbenzene copolymer-based strong cation
exchange resins such as Amberlyst.TM. and Dowex.RTM. available from
Dow Chemicals (Midland, Mich.) (for example, Dowex.RTM. Monosphere
M-31, Amberlyst.TM. 15, Amberlite.TM. 120); CG resins available
from Resintech, Inc. (West Berlin, N.J.); Lewatit resins such as
MonoPlus.TM. S 100H available from Sybron Chemicals Inc.
(Birmingham, N.J.); fluorinated sulfonic acid polymers (these acids
are partially or totally fluorinated hydrocarbon polymers
containing pendant sulfonic acid groups, which may be partially or
totally converted to the salt form) such as Nalion.RTM.
perfluorinated sulfonic acid polymer, Nafion.RTM. Super Acid
Catalyst (a bead-form strongly acidic resin which is a copolymer of
tetrafluoroethylene and perfluoro-3,6-dioxa-4-methyl-7-octene
sulfonyl fluoride, converted to either the proton (H.sup.+), or the
metal salt form) available from DuPont Company (Wilmington,
Del.).
[0042] In an embodiment, the solid acid catalyst is a supported
acid catalyst. The support for the solid acid catalyst can be any
solid substance that is inert under the reaction conditions
including, but not limited to, oxides such as silica, alumina,
titania, sulfated titania, and compounds thereof and combinations
thereof; barium sulfate; calcium carbonate; zirconia; carbons,
particularly acid washed carbon; and combinations thereof. Acid
washed carbon is a carbon that has been washed with an acid, such
as nitric acid, sulfuric acid or acetic acid, to remove impurities.
The support can be in the form of powder, granules, pellets, or the
like. The supported acid catalyst can be prepared by depositing the
acid catalyst on the support by any number of methods well known to
those skilled in the art of catalysis, such as spraying, soaking or
physical mixing, followed by drying, calcination, and if necessary,
activation through methods such as reduction or oxidation. The
loading of the at least one acid catalyst on the at least one
support is is in the range of 0.1-20 weight based on the combined
weights of the at least one acid catalyst and the at least one
support. Certain acid catalysts perform better at low loadings such
as 0.1-5%, whereas other acid catalysts are more likely to be
useful at higher loadings such as 10-20%. In an embodiment, the
acid catalyst is an unsupported catalyst having 100% acid catalyst
with no support such as, pure zeolites and acidic ion exchange
resins.
[0043] Examples of supported solid acid catalysts include, but are
not limited to, phosphoric acid on silica, Nafion.RTM.
perfluorinated sulfonic acid polymer on silica, HPAs on silica,
sulfated zirconia, and sulfated titania. In the case of Nafion.RTM.
on silica, a loading of 12.5% is typical of commercial
examples.
[0044] In another embodiment, the solid acid catalyst comprises
Amberlyst.TM. 70.
[0045] In one embodiment, the solid acid catalyst comprises a
Nafion.RTM. supported on silica (SiO.sub.2).
[0046] In one embodiment, the solid acid catalyst comprises natural
or synthetic clay minerals, such as those containing alumina and/or
silica (including zeolites).
[0047] Zeolites suitable for use herein can be generally
represented by the following formula
M.sub.2/nO.Al.sub.2O.sub.3.xSiO.sub.2.yH.sub.2O wherein M is a
cation of valence n, x is greater than or equal to about 2, and y
is a number determined by the porosity and the hydration state of
the zeolite, generally from about 2 to about 8. In naturally
occurring zeolites, M is principally represented by Na, Ca, K, Mg
and Ba in proportions usually reflecting their approximate
geochemical abundance. The cations M are loosely bound to the
structure and can frequently be completely or partially replaced
with other cations by conventional ion exchange.
[0048] The zeolite framework structure has corner-linked tetrahedra
with Al or Si atoms at centers of the tetrahedra and oxygen atoms
at the corners. Such tetrahedra are combined in a well-defined
repeating structure comprising various combinations of 4-, 6-, 8-,
10-, and 12-membered rings. The resulting framework structure is a
pore network of regular channels and cages that is useful for
separation. Pore dimensions are determined by the geometry of the
aluminosilicate tetrahedra forming the zeolite channels or cages,
with nominal openings of about 0.26 nm for 6-member rings, about
0.40 nm for 8-member rings, about 0.55 nm for 10-member rings, and
about 0.74 nm for 12-member rings (these numbers assume the ionic
radii for oxygen). Zeolites with the largest pores, being 8-member
rings, 10-member rings, and 12-member rings, are frequently
considered small, medium and large pore zeolites, respectively.
[0049] In a zeolite, the term "silicon to aluminum ratio" or,
equivalently, "Si/Al ratio" means the ratio of silicon atoms to
aluminum atoms. Pore dimensions are critical to the performance of
these materials in catalytic and separation applications, since
this characteristic determines whether molecules of certain size
can enter and exit the zeolite framework.
[0050] In practice, it has been observed that very slight decreases
in ring dimensions can effectively hinder or block movement of
particular molecular species through the zeolite structure. The
effective pore dimensions that control access to the interior of
the zeolites are determined not only by the geometric dimensions of
the tetrahedra forming the pore opening, but also by the presence
or absence of ions in or near the pore. For example, in the case of
zeolite type A, access can be restricted by monovalent ions, such
as Na.sup.+ or K.sup.+, which are situated in or near 8-member ring
openings as well as 6-member ring openings. Access can be enhanced
by divalent ions, such as Ca.sup.2+, which are situated only in or
near 6-member ring openings. Thus, the potassium and sodium salts
of zeolite A exhibit effective pore openings of about 0.3 nm and
about 0.4 nm respectively, whereas the calcium salt of zeolite A
has an effective pore opening of about 0.5 nm.
[0051] The presence or absence of ions in or near the pores,
channels and/or cages can also significantly modify the accessible
pore volume of the zeolite for sorbing materials. Representative
examples of zeolites are (i) small pore zeolites such as NaA (LTA),
CaA (LTA), Erionite (ERI), Rho (RHO), ZK-5 (KFI) and chabazite
(CHA); (ii) medium pore zeolites such as ZSM-5 (MFI), ZSM-11 (MEL),
ZSM -22 (TON), and ZSM-48 (*MRE); and (iii) large pore zeolites
such as zeolite beta (BEA), faujasite (FAU), mordenite (MOR),
zeolite L (LTL), NaX (FAU), NaY (FAU), DA-Y (FAU) and CaY (FAU).
The letters in parentheses give the framework structure type of the
zeolite. Definitions of zeolite framework types may be found in the
following references: http://www.iza-structure.org/, and
Baerlocher, McCusker, Olson["Atlas of Zeolite Framework Types,
6.sup.th revised edition, Elsevier, Amsterdam].
[0052] Zeolites suitable for use herein include medium or large
pore, acidic, hydrophobic zeolites, including without limitation
ZSM-5, faujasites, beta, mordenite zeolites or mixtures thereof,
having a high silicon to aluminum ratio, such as in the range of
5:1 to 400:1 or 5:1 to 200:1. Medium pore zeolites have a framework
structure consisting of 10-membered rings with a pore size of about
0.5-0.6 nm. Large pore zeolites have a framework structure
consisting of 12-membered rings with a pore size of about 0.65 to
about 0.75 nm. Hydrophobic zeolites generally have Si/Al ratios
greater than or equal to about 5, and the hydrophobicity generally
increases with increasing Si/Al ratios. Other suitable zeolites
include without limitation acidic large pore zeolites such as H--Y
with Si/Al in the range of about 2.25 to 5.
[0053] Zeolites with a high Si/Al ratio can be prepared
synthetically, or by modification of high alumina containing
zeolites using methods known in the art. These methods include
without limitation treatment with SiCl.sub.4 or
(NH.sub.4).sub.2SiF.sub.6 to replace Al with Si, as well as
treatment with steam followed by acid. A SiCl.sub.4 treatment is
described by Blatter [J. Chem. Ed. 67 (1990) 519]. A
(NH.sub.4).sub.2SiF.sub.6 treatment is described in U.S. Pat. No.
4,503,023. These treatments are generally very effective at
increasing the Si/Al ratio for zeolites such as zeolites Y and
mordenite.
[0054] The presence of aluminum atoms in the frameworks results in
hydrophilic sites. On removal of these framework aluminum atoms,
water adsorption is seen to decrease and the material becomes more
hydrophobic and generally more organophilic. Hydrophobicity in
zeolites is further discussed by Chen [J. Phys. Chem. 80 (1976)
60]. Generally, high Si/Al containing zeolites exhibit higher
thermal and acid stability. Acid forms of zeolites can be prepared
by a variety of techniques including ammonium exchange followed by
calcination or by direct exchange of alkali ions for protons using
mineral acids or ion exchangers. Acid sites in zeolites are further
discussed in Dwyer, "Zeolite, Structure, Composition and Catalysis"
in Chemistry and Industry, Apr. 2, 1984.
[0055] Certain types of molecular sieves, of which zeolites are a
sub-type, may also be used as the catalytic material in the
processes hereof. While zeolites are aluminosilicates, molecular
sieves contain other elements in place of aluminum and silicon, but
have analogous structures. Large pore, hydrophobic molecular sieves
that have similar properties to the preferred zeolites described
above are suitable for use herein. Examples of such molecular
sieves include without limitation Ti-Beta, B-Beta, and Ga-Beta
silicates. Molecular sieves are further discussed in Szostak,
Molecular Sieves Principles of Synthesis and Identification, (Van
Nostrand Reinhold, NY, 1989).
[0056] Referring back to the process for the production of
furfural, the process also comprises, as shown in FIG. 1 bringing a
feedstock solution 1 into contact with the solid acid catalyst 2
for a residence time sufficient to produce a mixture 5 of water 7
and furfural 8 in the reaction zone 20. In an embodiment, the
feedstock solution 1 comprises C.sub.5 sugar, C.sub.6 sugar or a
mixture thereof dissolved in water, or a high boiling
water-miscible organic solvent, or a mixture thereof. In another
embodiment, the reaction zone is at a temperature in the range of
90-250.degree. C. and a pressure in the range of 0.1-3.87 MPa.
[0057] The feedstock solution comprises at least one C.sub.5 sugar,
at least one C.sub.6 sugar, or a mixture of at least one C.sub.5
sugar and at least one C.sub.6 sugar. Examples of suitable C.sub.5
sugars, pentoses include without limitation xylose, arabinose,
lyxose and ribose. Examples of suitable C.sub.6 sugars, hexoses
include without limitation glucose, fructose, mannose, and
galactose.
[0058] In one embodiment, the feedstock solution comprises xylose.
In another embodiment, the feedstock solution comprises glucose. In
another embodiment, the feedstock solution comprises comprises
xylose and glucose.
[0059] The total sugar (C.sub.5 sugar, C.sub.6 sugar, or a mixture
thereof) is present in the feedstock solution in the range of 1-99
weight % or 0.1-50 weight % or 5-35 weight % or 5-10 weight %,
based on the total weight of the feedstock solution. In an
embodiment, the feedstock solution 1 is an aqueous feedstock
solution.
[0060] As shown in the FIG. 1, the feedstock solution 1 is added to
the distillation column 10 at a location between the rectifying
section 16 and the reaction zone 20 at a rate that provides
sufficient residence time in the reaction zone 20 (which is also
the stripping section) for complete or nearly complete conversion
of sugars to furfural. The required residence time is a function of
temperature and sugar concentration and is readily determined by
one of skill in the art. In an embodiment, the residence time in
the reaction zone is in the range of 1-500 min or 1-250 min or
5-120 min. The feedstock solution 1 flows down through the reaction
zone 20 and is converted to a mixture 5 of furfural 8 and water 7
which is then partially vaporized and refluxes as part of the
distillation column 10.
[0061] The temperature of the feedstock solution in the reaction
zone 20 is in the range of 90-250.degree. C. or 140-220.degree. C.
or 155-200.degree. C.
[0062] The reaction is carried at a pressure between about
atmospheric pressure and 3.87 MPa or 0.1-3.4 MPa or 0.1-2.0 MPa. In
an embodiment, the feedstock solution is an aqueous feedstock
solution and the reaction is carried at a pressure in the range of
0.5-1.6 MPa. In another embodiment, the feedstock solution
comprises a high boiling water-miscible organic solvent, and the
reaction is carried at about atmospheric pressure.
[0063] The process for the production of furfural further comprises
removing the mixture 5 of water and furfural from the top 11 of the
reactive distillation column 10 and collecting water and/or solvent
unreacted sugars and nonvolatile byproducts into the reboiler 3
from the bottom of the reactive distillation column 10, as shown in
FIG. 1.
[0064] As the reaction proceeds, a mixture 5 of vapors comprising
one or more of furfural, water, acetic acid, acetone, and formic
acid are removed from the reaction mixture via reflux through a
multistage distillation column 10, condensed, and collected as a
solution 5 of furfural and water. The use of staging in the
distillation process allows more efficient stripping of furfural
away from the acid catalyst solution. This increases furfural yield
by driving the reaction toward completion and by minimizing
formation of byproducts.
[0065] The sugar in the feedstock solution undergoes chemical
transformation to furfural, which, along with water (from the
aqueous feedstock and water produced by the reaction), is then
drawn at the top 11 of the distillation column 10. This minimizes
the residence time of furfural in the acidic environment of the
reaction zone 20 and thereby minimizes its degradation. The
furfural 8 is separated from the water and purified by any
convenient methods known in the art, and the product furfural is
removed. The water is either recycled to the source of the
feedstock sugar solution or is released from the process.
[0066] Reaction byproducts 3, including, but not limited to, water,
unreacted sugars, and non-volatile byproducts such as humins are
collected in the reboiler 15 beneath the distillation column 10, as
shown in FIG. 1. The nonvolatile byproducts 4 are removed from the
reboiler 15 (e.g., by filtration). The solution 6 of water and
unreacted sugars can be disposed of, or at least a portion can be
concentrated by evaporation and fed as a stream 6' to be used as
feedstock solution 1, as shown in FIG. 1.
[0067] In one embodiment, with reference to FIG. 1, the feedstock
solution 1 is fed into the distillation column 10 at a location
between the rectifying section 16 of the distillation column 10 and
the reaction zone 20, above the solid catalyst 2. The catalyst 2 is
included in the bottom, stripping section, which is the reaction
zone 20. A mixture 5 of furfural and water (as steam) are drawn off
at the top 11 of the column 5. Reaction byproducts 3 such as, water
and/or solvent, unreacted sugars, and nonvolatile byproducts (e.g.,
humins and other higher boiling byproducts) are collected in the
reboiler 15. The nonvolatile materials 4 are removed from the
reboiler 15. The remaining solution 6 is concentrated by
evaporation, with evaporated water vapor removed for disposal or
reuse. The concentrated stream 6' is then fed back as the feedstock
solution 1.
[0068] In an embodiment, the process comprises feeding a high
boiling water-miscible organic solvent to the reaction zone 20,
which would dissolve water-insoluble, nonvolatile byproducts such
as humins. In one embodiment, the high boiling water-miscible
organic solvent is added to the feedstock solution before feeding
to the reaction zone 20. The nonvolatile byproducts can be removed
diluting the remaining contents of the reboiler in a mixing chamber
with water or aqueous feedstock solution, thereby precipitating
water-insoluble byproducts; and removing the precipitated
water-insoluble byproducts, e.g., by filtration or centrifugation
and feeding the precipitate-free solution remaining back to the
reaction zone 20.
[0069] The water-miscible organic solvent has a boiling point
higher than about 100.degree. C. at atmospheric pressure. Examples
of suitable solvents include without limitation: sulfolane,
polyethylene glycol, isosorbide dimethyl ether, isosorbide,
propylene carbonate, poly(ethylene glycol) dimethyl ether, adipic
acid, diethylene glycol, 1,3-propanediol, glycerol,
gamma-butyrolactone, and gamma-valerolactone.
[0070] In one embodiment, the water-miscible organic solvent is
sulfolane.
[0071] In one embodiment of the invention, the solvent is PEG 4600,
PEG 10000, PEG 1000, polyethylene glycol, gamma-valerolactone,
gamma-butyrolactone, isosorbide dimethyl ether, propylene
carbonate, adipic acid, poly(ethylene glycol)dimethyl ether,
isosorbide, Cerenol.TM. 270 (poly(1,3-propanediol), Cerenol.TM.
1000 ((poly(1,3-propanediol)), or diethylene glycol.
[0072] In one embodiment of the invention disclosed herein, a
process is provided comprising the steps of:
[0073] (a) providing reactor comprising a reactive distillation
column comprising an upper, rectifying section; a lower, stripping
section; and a reboiler, wherein the stripping section or the
reboiler is a reaction zone containing a solid acid catalyst,
[0074] (b) continuously feeding an solution comprising C.sub.5
sugar, C.sub.6 sugar or a mixture thereof to the column at a
location between the rectifying section and the stripping section,
allowing the solution to flow into the reaction zone into contact
with the solid acid catalyst, thereby forming a reaction mixture,
wherein [0075] (i) the temperature of the reaction mixture is
between about 90.degree. C. and about 250.degree. C. [0076] (ii)
the reaction mixture is held at a pressure between about
atmospheric pressure and about 3.87.times.10.sup.6 Pa, and [0077]
(iii) the sugar solution and catalyst are in contact for a time
sufficient to produce water and furfural;
[0078] (c) drawing off a mixture of furfural and water at the top
of the column;
[0079] (d) collecting water, unreacted sugars, and nonvolatile
byproducts in the reboiler;
[0080] (e) removing nonvolatile byproducts from the reboiler;
and
[0081] (f) removing the water and unreacted sugars from the
reboiler for further use or disposal.
[0082] The combination of high yield and high conversion is
desirable for a most efficient and economical process. In the event
that a higher selectivity can be obtained at lower conversion, it
may be desirable to run at lower conversion, for example 50-80%,
and recycle unreacted sugars back to the reaction zone. The process
described above produces furfural from solutions of C5 and/or C6
sugars at both high yield and medium to high conversion, without
production of insoluble char in the reaction vessel. In an
embodiment, the furfural yield is in the range of 40-95% or 60-95%
or 65-85%. In another embodiment, the conversion of sugar to
furfural is in the range of 10-100% or 25-100% or 50-100%. In an
embodiment, the furfural selectivity is in the range of 40-95% or
60-95% or 65-85%
[0083] Degradation of furfural is minimized by its low residence
time in contact with the solid acid catalyst. Higher catalyst
lifetime can be achieved because the catalyst is continually washed
with the refluxing solution and not in contact for long periods of
time with high-boiling byproducts like humins, which are known to
be deleterious to catalyst lifetime. Solid acid catalysts have the
advantage of not inducing corrosion in the reaction vessels and
other process equipment as compared to liquid acid catalysts.
[0084] As used herein, where the indefinite article "a" or "an" is
used with respect to a statement or description of the presence of
a step in a process of this invention, it is to be understood,
unless the statement or description explicitly provides to the
contrary, that the use of such indefinite article does not limit
the presence of the step in the process to one in number.
[0085] As used herein, when an amount, concentration, or other
value or parameter is given as either a range, preferred range, or
a list of upper preferable values and lower preferable values, this
is to be understood as specifically disclosing all ranges formed
from any pair of any upper range limit or preferred value and any
lower range limit or preferred value, regardless of whether ranges
are separately disclosed. Where a range of numerical values is
recited herein, unless otherwise stated, the range is intended to
include the endpoints thereof, and all integers and fractions
within the range. It is not intended that the scope of the
invention be limited to the specific values recited when defining a
range.
[0086] As used herein, the terms "comprises," "comprising,"
"includes," "including," "has," "having," "contains" or
"containing," or any other variation thereof, are intended to cover
a non-exclusive inclusion. For example, a composition, a mixture,
process, method, article, or apparatus that comprises a list of
elements is not necessarily limited to only those elements but may
include other elements not expressly listed or inherent to such
composition, mixture, process, method, article, or apparatus.
Further, unless expressly stated to the contrary, "or" refers to an
inclusive or and not to an exclusive or. For example, a condition A
or B is satisfied by any one of the following: A is true (or
present) and B is false (or not present), A is false (or not
present) and B is true (or present), and both A and B are true (or
present).
[0087] As used herein, the term "invention" or "present invention
is a non-limiting term and is not intended to refer to any single
variation of the particular invention but encompasses all possible
variations described in the specification and recited in the
claims.
[0088] As used herein, the term "about" modifying the quantity of
an ingredient or reactant of the invention employed refers to
variation in the numerical quantity that can occur, for example,
through typical measuring and liquid handling procedures used for
making concentrates or use solutions in the real world; through
inadvertent error in these procedures; through differences in the
manufacture, source, or purity of the ingredients employed to make
the compositions or carry out the methods; and the like. The term
"about" also encompasses amounts that differ due to different
equilibrium conditions for a composition resulting from a
particular initial mixture. Whether or not modified by the term
"about", the claims include equivalents to the quantities. The term
"about" may mean within 10% of the reported numerical value,
preferably within 5% of the reported numerical value.
EXAMPLES
[0089] The methods described herein are illustrated in the
following examples. From the above discussion and these examples,
one skilled in the art can ascertain the essential characteristics
of this invention, and without departing from the spirit and scope
thereof, can make various changes and modifications of the
invention to adapt it to various uses and conditions.
Abbreviations
[0090] The meaning of abbreviations is as follows: "cm" means
centimeter(s), "g" means gram(s), "h" means hour(s), "HPLC" means
high pressure liquid chromatography, "m" means meter(s), "min"
means minute(s), "mL" means milliliter(s), "mm" means
millimeter(s), "MPa" means megapascal(s), "N" means normal, "psi"
means pound(s) per square inch, "PTFE" means
poly(tetrafluoroethylene), "rpm" means revolutions per minute, "wt
%" means weight percent(age), ".mu.L" means microliter(s), and
".mu.m" means micrometer(s).
Materials Amberlyst.RTM. A70 ion exchange resin was manufactured by
Dow Chemical's Rohm and Haas division (Philadelphia, Pa.).
[0091] Xylose, sulfolane, and dimethylsulfoxide were obtained from
Sigma-Aldrich Corporation (St. Louis, Mo.).
[0092] Zeolite CP7146 used in Example 3 was obtained from Zeolyst
International (Conshohocken, Pa.)
[0093] The following solid acid catalysts were obtained from
Zeolyst International, Conshohocken, Pa., or Conteka B. V. (now
Zeolyst, International): Product #: CBV 400, CBV 500, CBV 712, CBV
720, CBV 760, CBV 780, CP 814C, CP 814E, CP 811B-200, CP 811C-300,
CBV 3020, CBV 5020, CBV 1502, CBV 2802 (now CBV 28014), CBV 10A,
CBV 20A, and CBV 30A. The solid acid catalyst S-115 (LA) was
obtained from Union Carbide Corporation (now UOP, Des Plaines,
Ill.). The solid acid catalyst Amberlyst.TM. 70 was obtained from
Dow Chemical Company (Midland, Mich.). Amberlyst.TM. 70 is a
macroreticular polymer based catalyst primarily comprising
sulfonic-acid-functionalized styrene divinylbenzene copolymers. The
solid acid catalyst 13% Nafion.RTM. on silica (SiO.sub.2) was
obtained from E. I. du Pont de Nemours and Co. (Wilmington, Del.).
Nafion.RTM. is a registered trademark of E. I. du Pont de Nemours
and Company for its perfluorinated sulfonic acid polymer
products.
[0094] Deionized water was used unless otherwise indicated.
Analytical Methods
FOR EXAMPLE 1 (PROPHETIC), COMPARATIVE EXAMPLES A AND B
[0095] Furfural and sugar analysis is done by HPLC. Samples were
collected and passed through a 0.2 .mu.m syringe filter prior to
analysis. The samples were neutralized with calcium carbonate and
re-filtered before they were analyzed by high pressure liquid
chromatography (HPLC). The HPLC instrument employed was a HP 1100
Series equipped with Agilent 1200 Series refractive index (RI)
detector and an auto injector (Santa Clara, Calif.). The analytical
method was adapted from an NREL procedure (NREL/TP-510-42623).
Separation and quantitation of monomeric sugars (glucose, xylose,
and arabinose), and furfural (FF) was performed by injecting the
sample (10 .mu.L) on to a Bio-Rad HPX-87P (Bio-Rad, Hercules,
Calif.) column maintained at 85.degree. C. Water was used as the
eluant, with a flow-rate of 0.6 mL/min. The reaction products in
the eluant were identified with the RI detector operating at
55.degree. C.
FOR EXAMPLES 2, 3, 4 AND COMPARATIVE EXAMPLE C
[0096] Distillates and reaction flask contents were analyzed on a
calibrated Aminex HPX-87H HPLC column (Bio-Rad Company) using a
refractive index detector, and the column wash was analyzed via gas
chromatographic analysis using a flame ionization detector and a
calibrated 30 m HP-INNOWax GC column (Agilent Technologies).
PROPHETIC EXAMPLE 1
Conversion via Reactive Distillation of Sugar Solution to Furfural
with Solid Acid Catalyst
[0097] A solution of 10 wt % pentose and pentose oligomers with
less than 1 wt % hexose and hexose oligomers is fed to a
distillation column. The 1 inch (2.54 cm) diameter stainless steel
distillation column has 5 trays located above the feed point and 5
trays with enhanced hold up time per tray loaded with Amberlyst.TM.
A70 sulfonic acid ion exchange resin beads. The column is refluxing
water upon startup at a temperature of 180.degree. C. and pressure
of 120 psi (0.827 MPa). Feed is begun at 5 grams per minute above
the stripping/reactive section of the column, and the material
reacts to produce a material comprising furfural, water and high
boilers The reboiler of the distillation column is level controlled
with a flow out of 1.33 grams per minute analyzing at, for example,
0.5 wt % in pentose and hexose and oligomers, 8.3 wt % in humins
and other high boilers (present primarily as solids), and about
91.2 wt % water. Furfural is not detectable in the reboiler
material. The distillate is removed at a rate of 3.67 grams per
minute at the top of the column with a composition of, for example,
7.0 wt % furfural, the remainder comprising primarily water. The
steady state yield to furfural from pentose and pentose oligomers
of the process as run in this example would be 70.0%.
EXAMPLE 1
Production of Furfural with Solid Acid Catalysts
[0098] Zeolites having different frameworks were used as catalysts
as indicated in Table 1, including faujasite (FAU), zeolite beta
(BEA), ZSM-5 (MFI), and mordenite (MOR). All zeolites were calcined
at 550.degree. C. for 8 h in air prior to use. All of the zeolites
are in proton form after calcining except for CBV 10A which was in
the sodium form. The polymer catalysts Amberlyst.TM. 70 and 13%
Nafion on silica were used as obtained.
[0099] The following amounts and variables were the same for all
experiments in this Example: 1) solvent was sulfolane, 2) mass of
solvent was 5 g, 3) mass of solid catalyst was 0.075 g (1.5% of the
solvent mass), 4) aqueous xylose solution concentration was 5 wt %,
5) xylose solution addition rate was 0.4 mL/min, 6) stirring rate
was approximately 500 rpm, 7) reaction run time was 40 min, 8)
average reaction temperature was 170.degree. C., 9) oil bath
temperature was 250.degree. C., and 10) the internal standard added
for analysis was dimethylsulfoxide.
[0100] The conversion of xylose to furfural was carried out in a 10
mL three-necked round bottomed flask (Chemglass, Inc. Life Sciences
Catalog No. PN CG-1507-03) containing a PTFE-coated stirring bar
(VWR Company Catalog No. 58949-010), a thermowell, a threaded
adapter with cap (Chemglass, Inc. Life Sciences Catalog No.
CG-350-01), and a PTFE-lined silicon septum (National Scientific
Catalog No. B7995-15). The flask was connected to a vacuum-jacketed
Vigreux distillation column (Chemglass, Inc. Life Sciences Catalog
No. CG-1242) loaded with 8.0 g of 4 mm diameter glass beads
(Chemglass, Inc. Life Sciences Catalog No. CG-1101-03). The beads
were held in place at the bottom of the distillation column with a
piece of 1/16'' diameter thick fluoropolymer film that was
approximately 3/4'' wide by 3'' long which was either wound up into
a coil or folded so that it contained pleats. A 20 mL plastic
syringe with Luer lock tip (Chemglass, Inc. Life Sciences Catalog
No. PN 309661) was connected to 1/16'' fluoropolymer tubing which
was pierced through the septum. Addition of the xylose solution
from the syringe to the reaction vessel was controlled with a
digital syringe pump. The reactions were carried out under an
atmosphere of nitrogen.
[0101] To the reaction flask were added 5 g of solvent and 0.075 g
of solid acid catalyst. The syringe on the syringe pump was filled
with an aqueous xylose solution which was weighed prior to
addition, and then reweighed after the completion of addition to
determine the total amount of xylose solution added to the reaction
mixture. After the flask was loaded, it was attached to the
distillation column and one end of the 1/16'' diameter
fluoropolymer tube was attached to the syringe containing the
aqueous xylose solution and the other end was inserted through the
septum and into the reactor. The flask was lowered into the hot oil
to bring the reactor contents to the desired internal temperature
and addition of the xylose solution from the syringe using the
syringe pump was started. The xylose solution was added at a
constant rate and the temperature of the reaction mixture was
maintained as constant as possible by slight adjustments to the
height of the apparatus in the oil bath. At the end of the
reaction, the syringe pump was stopped, the tube was pulled from
the reaction flask and the apparatus was raised out of the oil
bath.
[0102] The amount of distillate collected was weighed, a measured
amount of the internal standard (dimethylsulfoxide) was added for
analytical purposes, and the solution was then mixed until it was
homogeneous (additional water was added to dilute the mixture if
necessary). The reaction flask was removed from the distillation
head and was weighed to determine the mass of material in the
flask. A measured amount of internal standard (dimethylsulfoxide)
was added to the reaction flask and it was mixed well. The contents
of the reaction flask were then transferred to a 50 mL centrifuge
tube. The distillation head was washed with water and the washes
were also used to wash the reboiler. All the washes were combined
in the 50 mL centrifuge tube, and solids were centrifuged to the
bottom of the tube using the supernatant for analysis.
[0103] The distillate, reaction flask contents, and the washes were
then analyzed by HPLC on a calibrated Biorad Aminex HPX-87H column
using a refractive index detector. An aqueous 0.01 N
H.sub.2SO.sub.4 isocratic mobile phase flowing at 0.6 mL/min
through a column heated to 65.degree. C. and a refractive index
detector heated to 55.degree. C. The detected amounts of xylose and
furfural were recorded. Results for different solid acid catalysts
are presented in Table 1.
TABLE-US-00001 TABLE 1 Catalyst Mole Type or Mole Ratio Original
Zeolite Ratio (Al/Al + Si) Surface Xylose Selectivity Yield of
Catalyst Framework Si/Al in in Area Conversion to Furfural Furfural
Run Source Type Catalyst Catalyst (m.sup.2/g) (%) (%) (%) 1.1
CP814E BEA 12.5 0.074 680 99 74 73 1.2 CP814C BEA 19 0.05 710 97 74
72 1.3 CP811B- BEA 100 0.01 -- 94 67 63 200 1.4 Amberlyst .TM.
polymer -- -- -- 93 63 59 70 1.5 CP811C- BEA 150 0.007 620 91 62 57
300 1.6 CBV720 FAU 15 0.063 780 89 57 51 1.7 CBV3020 MFI 15 0.063
405 92 55 51 1.8 CBV30A MOR 15 0.063 600 91 55 50 1.9 CBV780 FAU 40
0.024 780 90 55 49 1.10 CBV760 FAU 30 0.032 720 92 52 48 1.11
CBV20A MOR 10 0.091 500 91 53 48 1.12 CBV712 FAU 6 0.143 730 87 47
41 1.13 CBV1502 MFI 75 0.013 420 86 46 40 1.14 13% polymer -- -- --
91 44 40 Nafion/ SiO.sub.2 1.15 CBV2802 MFI 140 0.007 411 88 43 38
1.16 CBV5020 MFI 25 0.038 425 87 42 37 1.17 CBV500 FAU 2.60 0.278
750 84 29 24 1,18 CBV400 FAU 2.55 0.282 730 83 25 20
[0104] The catalysts that gave the highest yields in these
experiments were the beta zeolites, particularly catalysts derived
from calcinations of CP814C and CP814E. Amberlyst.TM. 70 also gave
high yields and conversion.
EXAMPLE 2
Dehydration of Xylose to Furfural via Reactive Distillation with
Solid Acid Catalyst
[0105] The reactive distillation unit used here consisted of a
jacketed glass tube reactor. The glass reactor, present inside the
outer jacket, had a length of 8.5 inch (21.6 cm) and an outer
diameter of 1.38'' (3.5 cm). The glass reactor was filled with
about 10 gm of beta-zeolite catalyst (granules). The catalyst was
provided by Zeolyst International (product #CP814E, lot #2200-42,
SiO.sub.2:Al.sub.2O.sub.3 mol ratio 25:1, Si: Al ratio 12.5:1,
surface area 680 m.sup.2/g) in a powder form. The powder was
calcined in air at 550.degree. C. for about 8 h. The calcined
powder was then charged in stainless steel die and pressed at
1.82.times.10.sup.5 kPa using a Preco hydraulic press. The
resulting slugs (25 mm diameter.times..about.25 mm thick) were
crushed and sieved to produce granules of -12/+14 mesh (1.40
mm-1.70 mm). These beta-zeolite granules were used as catalyst in
this study.
[0106] The catalyst bed was positioned in the middle of the glass
reactor and the rest of the reactor was packed with glass beads
(Chemglass Inc. Catalog No. CG-1101-01) of 2 mm diameter, placed
above (stripping section) and below the reactor. A stainless steel
mesh was placed below the glass beads (in the bottom portion of the
reactor) to support the catalyst bed and glass beads. A
thermocouple was used to monitor the catalyst bed temperature and
was placed inside a thermowell located in middle of the glass
reactor.
[0107] The inner glass reactor was surrounded by an outer jacket
(Outer diameter: 5.7 cm) through which an oil (Lauda Brinkmann LZB
222, THERM240) was circulated continuously in order to maintain the
reactor temperature at a desired value. A high temperature oil bath
(Neslab Exacal EX-250HT) was used to control the oil temperature,
and the flow rate of the oil through the outer jacket of the
reactor. The oil bath temperature was kept at 195-200.degree. C. so
that an average temperature of about 175.degree. C. was maintained
in the catalyst bed (placed inside the glass reactor).
[0108] A distillation head including a condenser was attached to
the top of the reactor, where a temperature of 15.degree. C. was
maintained constant with a continuous circulation of a coolant
mixture containing 50 wt. % ethylene glycol (VWR, BDH 2033) and 50
wt. % water. A circulation bath (Lauda Ecoline Staredition RE112)
was used for this purpose.
[0109] The reactor was connected to a continuous flow system
capable of precisely controlled liquid feed delivered by an HPLC
Pump (Lab Alliance Series I). In this particular study of catalyst
activity and stability for a beta-zeolite catalyst sample, a feed
consisting of 5 wt. % xylose (Sigma Aldrich, X1500) in a mixture
that contained 15 wt % water and 80 wt. % high boiling solvent,
sulfolane (Sigma Aldrich, T22209), was loaded to the HPLC pump. The
feed rate (to the reactor) was maintained constant at 0.75 ml/min.
A glass container filled with the above feed solution was kept on a
balance to continuously monitor the amount of feed introduced to
the reactor. The feed was introduced above the catalyst bed at the
specified feed rate. The stripping section (containing glass beads)
also aided in uniformly distributing the liquid feed to the
catalyst bed. The feed mixture reacted on the catalyst bed to form
furfural, which was the desired product of this reaction along with
some high boilers and water. Water and furfural being low boilers,
formed vapors and travelled to the distillation head containing the
condenser. The vapors were then condensed and were collected in a
glass flask (250 ml, Chemglass Inc., Catalog No. CG-1559-10)
surrounded by an ice bath (for the purpose of providing a low
temperature atmosphere for further cooling the vapors). One of the
necks of this flask was sealed with a rubber septum. A 10 ml
plastic syringe with Luer lock tip (BD, REF 309604) was connected
to a needle which was pierced through the septum. This syringe was
used to collect the distillate sample at regular intervals. The
reaction was carried out under atmospheric pressure.
[0110] The reactive distillation unit was also equipped with a
reflux valve, which was closed (reflux ratio=0), in order to avoid
the reaction between furfural (with itself, forming oligomers of
furfural) and xylose further resulting in the formation of high
boilers, commonly known as humins. The unreacted feed (containing
xylose and sulfolane) along with high boilers (humins) formed
during the reaction was collected in the reboiler located below the
reactor. The reboiler was a 3-necked round-bottom glass flask (250
ml, Chemglass Inc., Catalog No. CG-1530-01). A 20 ml plastic
syringe with Luer lock tip (BD 20 ml syringe REF 309661) was
connected to a needle, which was pierced through a rubber septum
used to seal one of the necks of the round bottom flask. This
syringe was used to collect the reboiler sample at regular
intervals. Another neck of the round bottom flask was sealed with a
rubber septum and a 1/8'' Teflon tubing (Chemglass Inc., Catalog
No. CG-1037-10) was pierced through the septum into the reboiler.
This tubing was used to introduce water to the reboiler at a
constant rate of 0.50 ml/min maintained with the help of a digital
syringe pump (KD Scientific, Model No. KDS KEGATO 270, Catalog No.
78-8270). The reboiler was kept heated at a temperature of
160.degree. C. With this sufficient high temperature and a
continuous input of water in the reboiler, there was a steady
formation of steam which traveled up through the catalyst bed and
further helped to effectively remove furfural (by forming an
azeotrope) from the reaction zone. Thus the steam stripping brings
additional advantage of effective furfural separation from the
reaction zone. N.sub.2 was also introduced in one of the necks of
the reboiler, for further removal of furfural from the reaction
zone.
[0111] The samples (both distillate and reboiler) were collected in
glass vials and weighed. The reboiler samples collected during the
reactive distillation run were analyzed by HPLC on a calibrated
Biorad Aminex HPX-87H column using a refractive index detector. An
aqueous 0.01 N H2SO4 isocratic mobile phase flowing at 0.6 ml/min
through a column heated to 65.degree. C. and a refractive index
detector heated to 55.degree. C. A measured amount of the internal
standard (dimethylsulfoxide) was added for analytical purposes, and
the solution was then mixed until it was homogeneous. The detected
amounts of xylose and furfural were recorded. The distillate
samples were analyzed by an Agilent 6890GC equipped with a 30 meter
DB-1 capillary column (J&W 125-1032). 5 microliters of solution
was injected into an injector port set to 175.degree. C. with a
split ratio of 5:1, a total helium flow of 55.2 ml/min, a split
flow of 44.4 ml/min and a head pressure of 6.25 psi. The oven
temperature was held at 50.degree. C. for 2 min and then it was
increased to 110.degree. C. at 10.degree. C./min followed by a
second increase to 240.degree. C. at 20.degree. C./min. A flame
ionization detector set at 250.degree. C. was used to detect
signal. A measured amount of the internal standard (1-pentanol) was
added for the GC analysis. The detected amounts of furfural were
recorded. Results obtained during the dehydration of xylose to
furfural using beta-zeolite catalyst have been presented in Table
2.
[0112] Table 2 below shows the result of a 3-day run (140 min on
day 1, 390 min on day 2 and 150 min on day 3) carried out for about
12 hours (under identical conditions of temperature, flow rate,
etc.). The data are reported for the steady state conditions
achieved in the reactor. As seen in the table 2, the beta-zeolite
catalyst resulted in xylose conversion of greater than 95%. The
furfural yields (and hence the selectivity towards furfural) were
nearly steady over the entire run.
TABLE-US-00002 TABLE 2 Dehydration of Xylose to Furfural via
Reactive Distillation Using beta-Zeolite Catalyst and a Feed
Containing 5 wt. % Xylose, 15 wt. % Water and 80 wt. % Sulfolane.
Time Xylose Furfural (min) Conversion Furfural Yield Selectivity 80
99.5% 66.8% 67.2% 110 99.3% 72.7% 73.2% 140 98.9% 69.2% 70.0% 290
96.9% 69.4% 71.7% 350 95.5% 69.7% 73.0% 410 94.5% 69.5% 73.6% 470
96.4% 65.0% 67.5% 680 97.8% 70.3% 71.8%
EXAMPLE 3
Xylose Reactive Distillation Using H-Mordenite Catalyst
[0113] Above experimental set up (in Example 3) was then used to
study the dehydration of xylose to furfural reaction using
H-mordenite catalyst. The H-mordenite catalyst used here was
provided by Zeolyst International (Product #CBV21A, lot #2200-77,
SiO.sub.2/Al.sub.2O.sub.3 mol ratio 20:1, Si:Al ratio 10:1, surface
area 500 m.sup.2/g) in a powder form. The powder catalyst was then
calcined and converted into granules using a similar technique
described earlier for the beta-zeolite catalyst. The rest of the
experimental conditions were the same as used earlier for the
beta-zeolite catalyst (feed composition: 5 wt. % xylose, 15 wt. %
water, 80 wt. % sulfolane; feed flow rate=0.75 ml/min; water folw
rate in the pot=0.50 ml/min; pot temperature=160 .degree. C., etc.)
The reactor temperature was maintained in the range of
175-180.degree. C. Table 3 summarizes the results for the
H-mordenite catalyst.
TABLE-US-00003 TABLE 3 Dehydration of Xylose to Furfural via
Reactive Distillation Using H-mordenite Catalyst and a Feed
Containing 5 wt. % Xylose, 15 wt. % Water and 80 wt. % Sulfolane.
Time (min) Xylose Conversion Furfural Yield Furfural Selectivity 70
99.0% 63.4% 64.0% 105 98.8% 72.7% 73.6% 165 97.7% 74.5% 76.3% 225
97.0% 74.6% 76.9% 290 98.5% 82.4% 83.6%
[0114] Example 3 gives an example of production of furfural with
reactive distillation utilizing a high boiling solvent resulting in
a higher yield than seen in the Comparative Examples. Example 4
shows an even higher yield of furfural than seen in Example 3.
[0115] Comparative Example A described below gives a comparison run
using a fixed bed reactor with an acidic ion exchange resin and no
high boiling solvent with a much poorer resulting yield and
selectivity to furfural. Comparative Example B described below
gives a comparison with a fixed bed reactor using a beta Zeolite
catalyst and a high boiling solvent, similar to that used in
example 3, with a worse result for yield.
COMPARATIVE EXAMPLE A
Lab-scale Continuous Process: Fixed Bed Reactor with Aqueous Xylose
Feed and Strongly Acidic Ion Exchange Resin Catalyst
[0116] A 5 inch (12.7 cm) long, 1/2'' (1.27 cm) outer diameter of
316 stainless steel tubing (Swagelock Corporation) was used as a
fixed bed reactor. The catalyst bed was supported by a 3/8'' (0.952
cm) steel tube at the bottom of the upflow arrangement, with a
stainless mesh supported by this tube as bed support for the
catalyst. The reactor tube was loaded with 3 cm.sup.3 of
Amberlyst.TM. A70 ion exchange resin. The reactor was then
connected to a continuous flow system capable of precisely
controlled liquid feed delivered by an ISCO D-500 Syringe Pump
(Teledyne ISCO, Lincoln Nebr., USA). The reactor was installed
within a tube furnace which allowed temperature control of the
catalyst bed as read by an internal 1/16'' (15.9 mm) stainless
steel thermocouple. The flow exiting the reactor was then pressure
controlled by a Swagelock backpressure regulator capable of up to
1000 psig (6.89 MPa-g) at the chosen liquid flows. The product from
the regulator was then collected in sample vials for analysis by
HPLC.
[0117] In the study of catalyst activity and lifetime for
Amberlyst.TM. A70, the feed was 4 wt % xylose in water, loaded to
the ISCO pump. The solution was fed through the reactor which was
loaded as described previously with 3 cm.sup.3 of Amberlyst.TM. A70
acidic ion exchange resin. The reactor was controlled at
160.degree. C. via a tube furnace and the pressure was controlled
at 200 psig (1.38 MPa-g) by a backpressure regulator. Table 4 below
shows the result of a continuous run where the flowrate was changed
to study the effect of space velocity on the xylose conversion and
furfural yield in an upflow fixed bed system. Also shown in the
table is a calculated first order rate constant (k) for xylose
conversion which permits comparison of catalyst activity as a
function of time. As seen in the table, the activity is low from
the start of the run, with a dramatic decrease over the course of
the experiment. The buildup of humins is believed to be the primary
cause of catalyst activity loss.
TABLE-US-00004 TABLE 4 Furfural Production in a Fixed Bed Solid
Acid Reactor with Time Space k % Time on velocity Xylose Furfural
Furfural (1/ Initial Stream (h) 1/h Conversion Yield Selectivity
min) Activity 2.5 16 40.4% 11.6% 28.9% 0.138 100.0% 2.7 16 40.6%
11.3% 27.8% 0.139 100.6% 3.8 32 20.2% 7.5% 37.2% 0.120 87.2% 3.9 32
23.1% 7.1% 30.9% 0.140 101.6% 22.5 4 30.4% 8.8% 29.0% 0.024 17.6%
23.0 4 31.5% 8.5% 27.1% 0.025 18.3% 27.1 8 14.7% 4.8% 32.5% 0.021
15.4% 27.3 8 11.6% 5.0% 43.0% 0.016 11.9% 29.3 16 9.4% 2.8% 29.7%
0.026 19.2% 29.5 16 9.6% 2.7% 27.8% 0.027 19.5% 35.2 2 46.6% 12.4%
26.6% 0.021 15.2% 35.4 2 46.4% 12.1% 26.0% 0.021 15.1%
COMPARATIVE EXAMPLE B
Lab-scale Continuous Process: Fixed Bed Reactor with Sulfolane
solvent. And Zeolite Beta Catalyst
[0118] The apparatus of Example 2 was used with a high boiling
water-miscible solvent. Sulfolane, in addition to being high
boiling, is an excellent solvent for biomass and humins
(by-products from furfural synthesis). It is hoped that use of such
a solvent will increase the lifetime of a solid acid catalyst used
for production of furfural from xylose.
[0119] In the study of catalyst activity and lifetime for a Zeolite
Beta sample, the feed was 4 wt % xylose in a mixture that contained
10 wt % water and 86 wt % sulfolane, loaded to the ISCO pump. CP
7146 (Zeolyst International) is an extruded form of ammonium-beta
(CP 814E (Zeolyst), Si/Al=12.5). The sample was calcined by heating
in air to 525 deg C. at a rate of 10 deg C./min, then 2 deg C./min
to 540 deg C. and finally 1 deg C./min to 550 deg C. where the
sample was held for 8 hours. 1.4935 grams of CP 7146 was loaded to
the tubular reactor of Comparative Example A. The reactor was
controlled at 160.degree. C. via a tube furnace and the pressure
was controlled at 200 psig (1.38 MPa-g) by a backpressure
regulator. Table 5 below shows the result of a continuous run where
the flowrate was changed to study the effect of space velocity on
the xylose conversion and furfural yield in an upflow fixed bed
system. Also shown in the table is a calculated first order rate
constant (k) for xylose conversion which permits comparison of
catalyst activity as a function of time. As seen in the table, the
activity is much better in sulfolane solvent than in an aqueous
system such as Comparative Example A. There is however a dramatic
decrease over the course of the experiment as seen in Comparative
Example A. The buildup of humins is believed to be the primary
cause of catalyst activity loss. The use of sulfolane solvent,
which solubilizes humins, apparently does not prevent the
deactivation of the catalyst.
TABLE-US-00005 TABLE 5 Furfural Production in a Fixed Bed Solid
Acid Reactor with Time, Sulfolane Solvent with Zeolite Beta
Catalyst Time on Space % Stream velocity Xylose Furfural Furfural k
Initial (h) 1/h Conversion Yield Selectivity (1/min) Activity 4.0 8
94.5% 44.0% 46.5% 0.386 100.0% 4.2 8 94.5% 43.9% 46.5% 0.386 100.1%
21.0 2 99.5% 50.5% 50.7% 0.174 45.1% 21.3 2 99.5% 50.5% 50.8% 0.174
45.1% 25.7 8 66.3% 30.5% 46.0% 0.145 37.6% 25.9 8 64.9% 30.1% 46.3%
0.140 36.2% 29.5 8 91.4% 46.7% 51.1% 0.328 85.0% 29.8 8 91.0% 46.3%
50.9% 0.321 83.3% 33.8 8 42.4% 8.4% 19.8% 0.074 19.1% 34.0 8 42.2%
8.4% 19.8% 0.073 19.0% 36.4 16 31.7% 2.5% 7.8% 0.102 26.3% 36.6 16
32.0% 2.6% 8.2% 0.103 26.7% 50.9 2 71.6% 22.1% 30.9% 0.042 10.9%
51.5 2 71.9% 22.3% 31.0% 0.042 11.0%
COMPARATIVE EXAMPLE C
[0120] Using an analogous procedure as described in Example 2, the
materials derived from S-115 (LA) and CBV 10A after calcination
were tested as catalysts for production of furfural. The results
are presented in Table 5.
TABLE-US-00006 TABLE 5 Mole Selectivity ratio Mole ratio Surface
Xylose to Yield of Catalyst Catalyst Si/Al in (Al/Al + Si) Area
Conversion Furfural Furfural Run Name Type Catalyst in Catalyst
(m.sup.2/g) (%) (%) (%) C.a S-115 MFI 400 0.002 411 77 1 0 (LA) C.b
CBV MOR 5 0.167 425 15 0 0 10A
[0121] The catalysts derived from S-115 (LA), a zeolite with very
low aluminum content, and CBV 10A, a zeolite with sodium cations
and few Bronsted acid sites, showed 0% yield of furfural in Run A
and Run B. This demonstrated that zeolites with a low number of
Bronsted acid sites, or low aluminum content (very high Si/Al
ratio, greater than or equal to 400) were not good catalysts for
furfural production from C.sub.5 and/or C.sub.6 sugars.
* * * * *
References