U.S. patent application number 14/606694 was filed with the patent office on 2015-08-13 for aromatic hydrocarbons from lignocellulose biomass.
The applicant listed for this patent is Washington State University. Invention is credited to Hanwu Lei, Lu Wang.
Application Number | 20150225652 14/606694 |
Document ID | / |
Family ID | 53774393 |
Filed Date | 2015-08-13 |
United States Patent
Application |
20150225652 |
Kind Code |
A1 |
Lei; Hanwu ; et al. |
August 13, 2015 |
AROMATIC HYDROCARBONS FROM LIGNOCELLULOSE BIOMASS
Abstract
Various embodiments of microwave-assisted systems, devices, and
associated methods of operation are described herein. In one
embodiment, a method for producing a bio-oil from a carbonaceous
material includes feeding the carbonaceous material to a pyrolysis
reactor, pyrolyzing the carbonaceous material in the reactor to
produce a raw bio-oil containing oxidized aromatic hydrocarbons,
and catalytically reducing at least a portion of the oxidized
aromatic hydrocarbons in the raw bio-oil to produce an upgraded
bio-oil having reduced aromatic hydrocarbons.
Inventors: |
Lei; Hanwu; (Richland,
WA) ; Wang; Lu; (Richland, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Washington State University |
Pullman |
WA |
US |
|
|
Family ID: |
53774393 |
Appl. No.: |
14/606694 |
Filed: |
January 27, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61938416 |
Feb 11, 2014 |
|
|
|
Current U.S.
Class: |
585/242 |
Current CPC
Class: |
C10L 2200/0469 20130101;
C10L 10/10 20130101; C10L 1/04 20130101; C10B 19/00 20130101; C10G
3/42 20130101; C10K 3/02 20130101; C10G 2300/304 20130101; C10L
2290/02 20130101; Y02P 30/20 20151101; C10G 3/50 20130101; C10B
53/02 20130101 |
International
Class: |
C10G 1/06 20060101
C10G001/06; C10L 1/04 20060101 C10L001/04; C10L 10/10 20060101
C10L010/10; C10G 1/00 20060101 C10G001/00 |
Claims
1. A method for producing a bio-oil from a carbonaceous material,
the method comprising: feeding the carbonaceous material to a
pyrolysis reactor; pyrolyzing the carbonaceous material in the
reactor to produce a raw bio-oil containing oxidized aromatic
hydrocarbons; and catalytically reducing at least a portion of the
oxidized aromatic hydrocarbons in the raw bio-oil to produce an
upgraded bio-oil having reduced aromatic hydrocarbons.
2. The method of claim 1 wherein feeding the carbonaceous material
includes feeding a carbonaceous material with a moisture content of
about 0.5% to about 20% and a particle size from about 0.4 mm to
about 5 mm.
3. The method of claim 1 wherein pyrolyzing the carbonaceous
material includes reducing formation of coke forming
precursors.
4. The method of claim 1 wherein pyrolyzing the carbonaceous
material includes producing an aromatic carbon precursor rich
pyrolytic product.
5. The method of claim 4 wherein the precursor comprises at least
one of guaiacol in an amount of about 30% to about 70%), phenol in
an amount of about 4% to about 30%, furan in an amount of about
0.5% to about 10%, esters in an amount of about 0% to about 5%, or
sugar in an amount of about 0% to about 15%.
6. The method of claim 1 wherein pyrolyzing the carbonaceous
material includes producing a syngas having about 10% to about 65%
carbon monoxide, about 0% to about 7% methane, and about 0% to
about 5% carbon dioxide.
7. The method of claim 6 wherein catalytically reducing includes
producing hydrogen in by inducing a gas shift reaction between
carbon monoxide and water.
8. The method of claim 1 wherein catalytically reducing includes
catalytically reducing at least a portion of the oxidized aromatic
hydrocarbons in the raw bio-oil in a vapor phase.
9. The method of claim 1 wherein catalytically reducing includes
producing an upgraded bio-oil containing at least one of benzene,
toluene, p-xylene, o-xylene, indene, or naphthalene.
10. The method of claim 1 wherein catalytically reducing includes
producing an upgraded bio-oil having a flash point between about
128.degree. C. to about 406.degree. C.
11. The method of claim 11 wherein catalytically reducing includes
producing an upgraded bio-oil having a carbon number distribution
in the range of C9 to C23.
12. The method of claim 1 wherein catalytically reducing includes
producing about 10% to about 40% upgraded bio-oil, about 10% to
about 50% syngas, and about 10% to about 30% bio-char.
13. The method of claim 12 wherein the syngas has a heating value
of about 100 BTU/standard cubic feet to about 400 BTU/standard
cubic feet.
14. The method of claim 12 wherein the syngas has about 0% to about
25% hydrogen, about 0% to about 11% methane, and about 0% to about
37% carbon monoxide.
15. The method of claim 1 wherein catalytically reducing includes
catalytically reducing at least a portion of the oxidized aromatic
hydrocarbons in the raw bio-oil to produce an upgraded bio-oil
having reduced aromatic hydrocarbons at a temperature of about
100.degree. C. to about 600.degree. C.
16. The method of claim 1 wherein catalytically reducing includes
catalytically reducing at least a portion of the oxidized aromatic
hydrocarbons in the raw bio-oil to produce an upgraded bio-oil
having reduced aromatic hydrocarbons at a residence time of about
10 seconds to about 10 minutes.
17. The method of claiml wherein carbonaceous material comprises
lignin, hemicelluose, and/or cellulose.
18. The method of claim 1 wherein catalytically reducing includes
catalytically reducing at least a portion of the oxidized aromatic
hydrocarbons in the raw bio-oil to produce an upgraded bio-oil
having reduced aromatic hydrocarbons at a catalyst to carbonaceous
material ratio of about 0.15:1; about 0.25:1; about 0.3:1; about
0.35:1; about 0.4:1; about 0.45:1; or about 0.5:1.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a non-provisional application of and
claims priority to U.S. Provisional Application No. 61/938,416,
filed on Feb. 11, 2014.
BACKGROUND
[0002] Ongoing research trend suggests that catalytic fast
pyrolysis ("CFP") as one promising approach to directly convert
lignocellulose biomasses into gasoline range aromatic hydrocarbons
("AH"). A typical CFP process includes rapidly heating a solid
biomass at high temperatures (e.g., greater than about 500.degree.
C.) to decompose the biomasses into a bio-oil. Subsequently, the
bio-oil is subject to catalytic hydrocracking, for example, using
zeolite-based catalysts, to be converted into aromatics, carbon
monoxide (CO), hydrogen (H.sub.2), carbon dioxide (CO.sub.2), water
(H.sub.2O), and/or bio-char.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] FIG. 1 is a schematic block diagram of a pyrolysis system
according to embodiments of the present technology.
[0004] FIG. 2 is a graph showing example compositions of bio-oils
produced by a catalytic pyrolysis process according to embodiments
of the present technology prior to and after catalytic upgrading at
diverse reaction conditions.
[0005] FIG. 3 is a graph showing example compositions of bio-oils
produced by a catalytic pyrolysis process according to embodiments
of the present technology after catalytic upgrading at optimized
reaction conditions.
[0006] FIG. 4 is a graph showing a flash point profile (solid line)
of an example bio-oil that includes about 5% low flash point
compounds (Toluene, Ethylbenzene, p-Xylene, and o-Xylene; flash
point<38.degree. C.), 10% medium flash point compounds
(1-ethyl-3-methyl-Benzene, 1,3,5-trimethyl-Benzene, Indane, and
2-butenyl-Benzene; 38.degree. C.<flash point<60.degree. C.),
and 85% high flash point compounds (2-ethenyl-1,4-dimethyl-Benzene,
1-methyl-1,2-propadienyl-Benzene, 1-methyl-1H-Indene, Naphthalene,
1-methyl-Naphthalene, 2-ethenyl-Naphthalene, etc.; flash
point>60.degree. C.). FIG. 4 also shows another flash point
profile (dashed line) of the example bio-oil after compounds with
flash points lower than 60.degree. C. were removed by
distillation.
[0007] FIG. 5a shows a distillation profile (dash-dot line) of an
example bio-oil inclusive of compounds with distillation points
lower than 60.degree. C., a distillation profile (solid line) of
the example bio-oil exclusive of compounds with distillation points
lower than 60.degree. C., and a distillation profile (dashed line)
No 2. D diesel fuel.
[0008] FIG. 5b is a graph that shows carbon number distribution of
an example bio-oil produced by a catalytic pyrolysis process
according to embodiments of the present technology.
DETAILED DESCRIPTION
[0009] Various embodiments of microwave-assisted systems, devices,
and associated methods of operation are described below. The term
"pyrolysis" is used herein to refer to a thermochemical
decomposition or transformation of an organic material (e.g., a
lignocellulose biomass) at elevated temperatures in the absence of
oxygen (O.sub.2). The term "catalytic pyrolysis" refers to
pyrolysis facilitated by a catalyst. Also, the term "biomass"
generally refers to an organic source of renewable energy. Examples
of biomass include wood (e.g., fir, pine, etc.), wood waste
products (e.g. saw dust), agricultural products/wastes (e.g., wheat
straws, corns, fruits, and vegetables, etc.). The term "raw
bio-oil" generally refers to a bio-oil derived by direct pyrolysis
without being undergone catalytic hydrocracking and/or other
subsequent processing. In contrast, the term "upgraded bio-oil"
generally refers to a bio-oil derived by catalytic hydrocracking
and/or other suitable processing of a raw bio-oil. A person skilled
in the relevant art will also understand that the technology may
have additional embodiments, and that the technology may be
practiced without several of the details of the embodiments
described below with reference to FIGS. 1-5b.
[0010] Conventional catalytic fast pyrolysis techniques suffer from
certain limitations. For example, CFP processes typically have low
rates of heat transfer to a biomass with large particle sizes.
Thus, fine grinding of the biomass is typically required. Secondly,
to the best knowledge of the inventor, controlling the formation of
undesirable products (e.g., methane, aldehyde, acids, ketone, and
carbon) during the rapid heating of the biomass has not yet been
successful. Such formation may hamper the catalytic activity as the
undesirable products can act as precursor(s) for coke formation.
The formed coke may in turn block active sites on a catalyst.
[0011] Microwave-assisted pyrolysis ("MAP") is one technique that
can overcome certain disadvantages of conventional CFP processes.
For example, MAP techniques can have significantly lower processing
time and energy requirements than conventional CFP processes. In
conventional CFP processes, heat is transferred from a surface of
biomass towards the center by convection, conduction, and/or
radiation. In contrast, microwave radiation can penetrate a
material by transferring and converting electromagnetic energy
directly into thermal energy. Thus, heat transfer via microwave
radiation is more uniform throughout the volume of the material.
Also, during microwave heating, the material is at higher
temperatures than the surrounding space, which is directly opposite
to convection heating. The lower temperatures in the surrounding
space can also be useful in avoiding undesirable reactions and in
condensing bio-oil products.
[0012] Without being bound by theory, it is believed that a raw
bio-oil (sometime referred to as a "pyrolysis oil" or "bio-crude")
is a complex mixture of sugars, esters, furans, acids, ketones,
alcohols, phenols, guaiacols, and other organic compositions. A raw
bio-oil typically has a high oxygen content (e.g., 35-40%) and may
be acidic, viscous, reactive, and thermally unstable. Thus, raw
bio-oils typically cannot be directly used as a fuel or raw
material in engines or traditional refineries. The high oxygen
content may also lead to a low heating value of, for example, only
50% of a petroleum fuel. Thus, modification of raw bio-oils is
needed in order to derive a usable fuel.
[0013] Catalytic cracking is one approach that can remove oxygen in
the form of H.sub.2O, CO, and/or CO.sub.2 through de-oxygenation
using, for example, zeolite as a catalyst. Such an approach may
avoid hydrogen addition and may be operated at atmospheric
pressures. A number of catalysts (e.g., HZSM-5, silicalite,
H-mordenite, and H-Y and silica-alumina) may be used for catalytic
cracking of raw bio-oils. During such catalytic cracking, a raw
bio-oil has to be re-vaporized before catalytic conversion.
However, a raw bio-oil typically cannot be completely vaporized
once condensed. If heated to 100.degree. C. or more, the raw
bio-oil may rapidly react and produce a solid residue of around 50
wt % of the original bio-oil, and thus resulting in low yields.
Accordingly, techniques for catalytic upgrading after pyrolysis and
before condensation of raw bio-oils may be desirable to avoid or at
least reduce the risk of the foregoing disadvantages.
[0014] Several embodiments of the present technology are related to
systems, devices, and processes for pyrolysis (e.g.,
microwave-assisted pyrolysis) of a biomass coupled with a catalysis
reactor using, for example, a zeolite catalyst or other suitable
types of hydrocracking catalysts in the production of bio-oils. In
particular, the inventor has recognized that by controlling a
pyrolysis temperature during pyrolysis, a raw bio-oil with
surprisingly high aromatic concentrations (e.g., in excess of about
40% (v/v)) and rich in oxidized aromatics (e.g. guiacol, phenolics,
etc.) may be produced. Example pyrolysis temperature ranges include
about 200.degree. C. to about 300.degree. C., about 300.degree. C.
to about 400.degree. C., about 400.degree. C. to about 500.degree.
C., and about 500.degree. C. to about 600.degree. C. As used
herein, the term "oxidized aromatic" compound generally refers to a
compound with a chemical structure having a benzene ring
substituted by one or more nucleophilic groups (e.g. hydroxyl,
methoxyl, etc.) at the ortho and/or para position. Examples of
oxidized aromatic include phenol, guiacol, and cresol.
[0015] The inventor has recognized that by controlling the
pyrolysis temperature and/or pyrolysis reaction time, formation of
undesirable compounds in the raw bio-oil may be reduced or even
eliminated while oxidized aromatic compounds may be enriched. Such
undesirable compounds are believed to induce coke formation during
hydrocracking (e.g., during the catalytic upgrade operation) or
other further processing. Coking is one of the major challenges for
bio-oil upgrading reactions. It is believed that re-polymerization
of certain components of the raw bio-oil can lead to coking on a
catalyst surface, and thus significantly reducing a number of
active sites on the catalyst surface. For example, aldehydes can
react with oxygenated aromatics to form coke. In another example,
organic acids (e.g. acetic acid) in bio-oils may coke over the
catalyst surface. Thus, by controlling the pyrolysis temperature
and/or pyrolysis reaction time, aldehydes, organic acids, and other
types of coke-producing compounds (collectively referred to as
"coke precursors") may be significantly reduced when compared to
conventional techniques, resulting in low coke yields during the
catalytic upgrade operation.
[0016] The inventor has also recognized that surprisingly high
yields of aromatic hydrocarbons may be achieved by controlling the
mass ratio of hydrocracking catalyst to biomass. Examples of
hydrocracking catalyst to biomass ratio can be about 0.15:1; about
0.2:1; about 0.2.5:1; about 0.35:1; or about 0.5:1. As used herein,
the term "reduced aromatic" compound generally refers to a compound
with completely hydrogenated single or polycyclic aromatic rings.
Examples of reduced aromatic compound include naphthalene and
derivatives thereof, ethylbenzene and other benzene derivatives,
p-xylene, or o-xylene.
[0017] As a result, by controlling at least one of the pyrolysis
temperature, the pyrolysis reaction time, the catalysis
temperature, or the mass ratio of hydrocracking catalyst to
biomass, upgraded bio-oils with properties suitable as aromatic
supplement for high octane fuels (e.g. marine and/or jet fuels) can
be generated. Such upgraded bio-oils may be directly blended with a
range of petroleum-based fuels. As used herein, the term
"petroleum-based fuel" generally refers to a fossil fuel produced
by fractional distillation of a crude oil at temperatures between,
for example, about 200.degree. C. to about 350.degree. C. Examples
of petroleum-derived diesel fuel may contain a mixture of
hydrocarbons with carbon chain lengths between eight and twenty
one.
[0018] The physical properties of upgraded bio-oils produced in
accordance with embodiments of the present technology can be
comparable to certain grades of fossil fuels, e.g. No. 2-D diesel
fuel, Naval Distillate Fuels, F-76, Marine Gas Oil, Marine Diesel
Fuels, Jet Fuel JP-5, MIL-T-5624M, and Military Diesel Fuel Marine
(DFM). Examples of the physical properties can include a flash
point, a distillation temperature, and a carbon distribution. In
example bio-oils, the carbon distribution can be generally similar
to F-76 and No. 2-D diesel fuels. The inventor has also recognized
that removing C7 and/or C8 carbon compounds (e.g., through
distillation) can improve the carbon distribution profile of the
upgraded bio-oil. In one example, after distillation to remove low
flash point benzene derives, the resulting upgraded bio-oil had a
flash point of more than about 60.degree. C.
[0019] FIG. 1 is a schematic block diagram of a pyrolysis system
100 according to embodiments of the present technology. As shown in
FIG. 1, the pyrolysis system 100 includes an inert gas source 102,
a reactor 104, a reactor heater 106, a catalytic converter 108, a
condenser 112, and a separator 114 operatively coupled to one
another. Though only the foregoing components are shown in FIG. 1,
in other embodiments, the pyrolysis system 100 can also include
valves, buffer tanks, and/or other suitable mechanical components.
In further embodiments, the pyrolysis system 100 can also be
configured to operate as a continuous process by incorporating, for
example, a plug-flow reactor, a constantly stirred tank reactor,
and/or other suitable processing units.
[0020] The inert gas source 102 can include a tank or other sources
of nitrogen, argon, and/or other suitable inert gases. The reactor
104 can include a vessel constructed with a suitable material to
contain a biomass 101 during pyrolysis. The reactor heater 106 can
include a microwave heater, a radiant heater, a convection heater,
and/or other suitable types of heat source.
[0021] The catalytic converter 108 can include a conversion chamber
110 and a heater/cooler 112 configured to maintain the conversion
chamber 110 at a target temperature. In one embodiment, the
conversion chamber 110 may include a packed bed of catalyst pellets
(e.g., HZSM-5, silicalite, H-mordenite, silica-alumina, and a
zeolite). In other embodiments, the conversion chamber 110 may
include a substrate (not shown) carrying a catalyst. In further
embodiments, the conversion chamber 110 may have other suitable
components in any suitable arrangements.
[0022] In the illustrated embodiment, the condenser 112 includes a
tube-and-shell heat exchanger. In other embodiments, the condenser
112 can also include plate-and-frame and/or other suitable type of
heat exchanger. The condenser 112 may utilize any suitable coolant
in a counter-flow, concurrent-flow, or other suitable arrangements.
Example coolants can include cooling water, thermal oil, or cooling
air. The separator 114 can include a flash tank or a vessel
sufficiently sized and shaped to separate a condensate from the
condenser 112 into syngas 116 and bio-oil 117.
[0023] The pyrolysis system 100 can also include one or more
transmitters, gauges, and/or other instruments for measuring and/or
transmitting one or more process variables to a controller 118. For
example, as shown in FIG. 1, the pyrolysis system 100 can include
an inert gas flow transmitter 122, a pyrolysis vapor flow
transmitter 124, a reactor temperature transmitter 126, a converter
temperature transmitter 128, a separator level transmitter 130, a
syngas flow transmitter 132, and a bio-oil flow transmitter 134. In
other examples, the pyrolysis system 100 may include additional
and/or different instruments than those shown in FIG. 1. The
controller 118 can include a desktop, laptop, and/or other suitable
computing device having a computing processor and a memory
containing instructions that can cause the computing processor to
perform a control process as described in more detail below.
[0024] During operation, the inert gas source 102 supplies an inert
gas as a continuous or intermittent flow to the reactor 104. The
supplied inert gas generally completely displaces any oxygen in the
reactor 104. The reactor heater 106 then heats and/or maintains the
reactor 101 at a target pyrolysis temperature to cause the biomass
101 to undergo a pyrolysis reaction and produce a raw bio-oil as a
vapor. It is believed that the raw bio-oil includes a mixture of
sugars, esters, furans, acids, ketones, alcohols, phenols,
guaiacols, and other organic compositions. As discussed above, the
target pyrolysis temperature and/or pyrolysis reaction time may be
controlled and/or otherwise adjusted based at least on a
composition of the biomass 101, a moisture content of the biomass
101, and/or other suitable parameters to achieve a high oxidized
aromatic content (e.g., at least about 40% v/v) while reducing or
even eliminating coke precursors (e.g., aldehydes, organic oils,
etc.).
[0025] The reactor 104 then supplies the raw bio-oil to the
catalytic converter 108, which in turn converts the raw bio-oil to
produce and/or increase a concentration of reduced aromatics or
aromatic hydrocarbons (e.g. ethylbenzene, toluene, etc.) in the raw
bio-oil, and thus producing a converted bio-oil. In one embodiment,
the converter temperature, as measured by the converter temperature
128, can be adjusted to achieve a target level of aromatic
hydrocarbon concentration in the converted bio-oil. For example,
the controller 118 may be configured to adjust an output to the
converter heater 112 to maintain the target converter temperature.
In another embodiment, a flow rate of the raw bio-oil, as measured
by the pyrolysis vapor flow transmitter 124, may be adjusted to
achieve the target level of aromatic hydrocarbon concentration in
the converted bio-oil based on a target ratio of raw bio-oil to
catalyst. In other embodiments, the converter temperature, the flow
rate of the raw bio-oil, and/or other suitable operating parameters
may be adjusted to achieve the target level of aromatic hydrocarbon
concentration in the converted bio-oil.
[0026] The condenser 112 then condenses the converted bio-oil, and
the condensed bio-oil is separated in the separator 114. The light
end of the non-condensed bio-oil is then withdrawn as the syngas
116, and the heavy end of the condensed bio-oil is then withdrawn
as upgraded bio-oil. As discussed above, by adjusting and/or
otherwise controlling at least one of the converter temperature or
ratio of raw bio-oil to catalyst, upgraded bio-oils with high
aromatic hydrocarbons suitable for direct blending with petroleum
based fuels may be provided.
Experiments
[0027] Several experiments were conducted to investigate the effect
of deoxygenation in catalyst reactor close coupled with pyrolysis
of a biomass. In particular, direct catalytic cracking of a biomass
pyrolysis vapor using a packed-bed catalysis close coupled with
microwave pyrolysis was investigated to convert Douglas fir sawdust
pellets to aromatics by a ZSM-5 Zeolite catalyst. The effects of
catalysis temperature and catalyst to biomass ratio on the
resulting bio-oil composition were examined. GC/MS analysis results
showed that the bio-oil contained aromatic hydrocarbons with little
or no oxygen. Aromatic hydrocarbons were enriched and become the
most abundant compounds which were about 15% to about 92.6% in
upgraded bio-oils under certain catalytic pyrolysis conditions. The
aromatic hydrocarbons mainly included benzene, toluene, xylene,
naphthalene, and derivatives thereof.
[0028] The effect of catalysis temperature on bio-oil chemical
composition was analyzed with a fixed ratio of catalyst to biomass
(0.25). The results show that the aromatic hydrocarbons were
increased from 0.72% in raw bio-oil (no catalyst) to about 92.6%
with a catalysis temperature of about 500.degree. C. At a
temperature of about 375.degree. C., the aromatic hydrocarbon
content was increased from 0.72% to about 78.1% with the increase
of catalyst to biomass ratio from 0 to 0.39, as discussed in more
detail below.
Materials.
[0029] The feedstock used was Douglas fir sawdust pellets (Bear
Mountain Forest Products Inc., USA) which were approximately 5 mm
in diameter and 20 mm in length with moisture content of 8%. ZSM-5
(Zeolyst International, USA; SiO.sub.2/Al.sub.2O.sub.3 Mole Ratio:
50) was dried at 105.degree. C. for 12 h and calcined at
550.degree. C. for 5 hours.
Pyrolysis Apparatus
[0030] A pyrolysis apparatus generally similar to that shown in
FIG. 1 was used for the pyrolysis tests. For example, a Sineo
MAS-II batch microwave oven (Shanghai, China) with a rated power of
1000 W was used at the 700 W power setting. This power setting gave
a heating rate of 100.degree. C./min. 20 g Douglas fir pellets were
placed in a 500 mL quartz flask inside of the microwave oven. The
pyrolysis volatile vapor from the flask went through a packed bed
catalysis reactor which was filled with catalysts; and then after
the condensation system, the condensable liquid was collected as
bio-oils. The non-condensable volatiles escaped as syngas at the
end of the condensers where they were either burned or collected
for analysis. The bio-char was left in the quartz flask. The weight
of syngas was calculated using the following equation:
Weight of syngas=initial biomass mass-bio-oil mass-bio-char mass
(1)
Experimental Design
[0031] A central composite experimental design (CCD) was used to
study the product yields (bio-oil and syngas). Two independent
variables, catalyst to biomass ratio (X.sub.1) and packed-bed
temperature (X.sub.2, .degree. C.) were chosen and are shown at
various levels in Table 1 below. Yi was used as the dependent
output variable. The reaction time was set as 9 minutes. The
packed-bed catalytic reactor temperature was from about
268.9.degree. C. to about 481.1.degree. C. The catalyst to biomass
ratio was chosen from 0.11 to 0.39 with a fixed loading of biomass
(20 g).
TABLE-US-00001 TABLE 1 X.sub.1: Catalyst to X.sub.2: Packed-bed
level biomass ratio temperature (.degree. C.) -1 0.15 300 1 0.35
450 -r = -1.41 0.11 268.9 r = 1.41 0.39 481.1
[0032] For statistical calculations, the variables Xi was coded as
xi according to Equation 2 below:
x.sub.i=(X.sub.i-X.sub.0)/.DELTA.X (2)
where x.sub.i is the dimensionless value of the independent
variable while X.sub.i is the real value. X.sub.0 is the real value
of the variable at the center point and .DELTA.X is the step
length. A 22-factorial CCD, with 4 axial points (a=1.41) and 5
replications at the center points (n.sub.0=5) leading to a total
number of 13 experiments were used to study the reaction
conditions. A second order polynomial equation (Equation 3) was
used to describe the effect of independent variables in terms of
linear, squared, and interaction. The predicted model for the
response (Y.sub.i) was:
Y i = b 0 + i = 1 2 b i X i + i = 1 2 b ii X i 2 + i = 1 2 j = i +
1 2 b ij X i X j + ( 3 ) ##EQU00001##
Where Y.sub.i is the predicted response; b.sub.0 is the
interception coefficient, b.sub.i, b.sub.ii, and b.sub.ij are
coefficients of the linear, quadratic, and interaction effects;
X.sub.i is the independent variables; and .epsilon. is the random
error. The statistical analysis of the model was performed by
Design Expert 8 software. The coefficient of determination
(R.sub.2) and F test were used to determine the quality of fit of
the second order equation. The effect of each independent variable
and their interactions were determined. F test was used to
determine the model parameter's significance (.alpha.=0.05).
Analysis of Bio-Oil and Syngas
[0033] The chemical compositions of bio-oils were determined using
Agilent 7890A GC/MS (GC-MS; GC, Agilent 7890A; MS, Agilent 5975C)
with a DB-5 capillary column. The GC was first maintained at
45.degree. C. for 3 min and then increased at 10.degree. C./min to
300.degree. C. The injector temperature was 300.degree. C. and the
injection size was 1 .mu.L. The flow rate of the carrier gas
(helium) was 0.6 mL/min. The ion source temperature was 230.degree.
C. for the mass selective detector. The compounds were identified
by comparing the spectral data with the NIST Mass Spectral library
(Lei, et al., 2011). The water content of the bio-oils was
determined by Karl Fischer Titrator (Mettler Toledo V30). The
chemical compositions of syngas were determined by a Carle 400 gas
chromatography (Chandler Engineering, Broken Arrow, Okla., USA)
system with a thermal conductivity detector (TCD).
Results and Discussion
[0034] The experiment design and product yields are shown in Table
2 below. The bio-oil yields were from 32.20 to 37.75 wt %, while
the syngas and bio-char yields were from 40 to 46.55 wt % and from
19.70 to 23.35 wt %, respectively. Comparing with conventional
combined pyrolysis and cracking upgrading processes, from which a
wide range of yields were resulted (28.45-40.83 wt % for bio-oil
yields, 39.04 wt %-65.95 wt % for syngas yields, and 3.27-32.51 wt
% for bio-char yields), the products yield variation of the
experiments was in a smaller range because of mild pyrolysis
conditions.
TABLE-US-00002 TABLE 2 Packed-bed Bio-oil Bio char Syngas Catalyst
to Temperature yield yield yield Run Biomass Ratio (.degree. C.)
(wt %) (wt %) (wt %) 1 0.15 300 35.60 22.95 41.45 2 0.35 300 35.40
23.35 41.25 3 0.15 450 35.10 19.70 45.20 4 0.35 450 32.65 22.60
44.75 5 0.11 375 37.75 22.25 40.00 6 0.39 375 32.20 21.25 46.55 7
0.25 268.9 37.15 20.65 42.20 8 0.25 481.1 32.90 21.50 45.60 9 0.25
375 35.00 22.00 43.00 10 0.25 375 34.35 21.65 44.00 11 0.25 375
34.75 20.75 44.50 12 0.25 375 35.25 21.85 42.90 13 0.25 375 34.05
20.95 45.00
[0035] Equation (3) was reduced by using backward statistical
analysis, and parameters were sequentially removed based on the
coefficient's p-value until all remaining were significant
(p<0.05). Using the results of the experiments, the first order
equations were obtained showing the yields of bio-oil (Equation 4)
and syngas (Equation 5) as a function of the catalyst to biomass
ratio (Xi) and packed-bed catalytic reactor temperature (X.sub.2,
.degree. C.):
Y.sub.bio-oil=43.85-13.12X1-0.02X2 (4)
Y.sub.syngas=33.34+10.77X1+0.02X2 (5)
[0036] The P value of Equation 4 was 0.0005<.alpha.=0.05, and
thus the linear model was believed to be significant to describe
the bio-oil yield. The coefficient of determination (R.sub.2) for
Equation 4 was 0.78, which suggests that the model was finely
representing the relationships among the independent variables. The
model term b.sub.0, X.sub.1, and X.sub.2 were significant because
the P values for such model terms were 0.0005, 0.0011, 0.0027,
respectively, all smaller than .alpha.=0.05.
[0037] The P value of Equation 5 was 0.0097<.alpha.=0.05, and
thus the liner model was significant to describe the syngas yield.
The coefficient of determination (R.sub.2) for Equation 5 was 0.60,
which suggests that the model was fairly representing the
relationships among the independent variables. And the model term
b.sub.0, X.sub.1, X.sub.2 were significant because the P values for
these model term were 0.0097, 0.046, and 0.0098, respectively, all
smaller than .alpha.=0.05.
GC/MS Characterization of Bio-Oil
[0038] GC/MS was used to characterize the bio-oil chemical
compounds which were categorized into ten functional groups, as
shown in FIG. 2. Without catalysis, bio-oils from microwave
pyrolysis of Douglas fir pellets were mixtures of acid, ketones,
alcohols, phenols, guaiacols, furans, esters, and sugars. With
catalysis close coupled with microwave pyrolysis, aromatic
hydrocarbons not containing oxygen were enriched and became the
most abundant compounds in the upgraded bio-oils. Aromatic
hydrocarbons were about 15.4-86.5% in upgraded bio-oils under
various catalytic pyrolysis conditions. Such aromatic hydrocarbons
were mainly composed of benzene, toluene, xylene, naphthalene, and
derivatives thereof. Phenols became the second abundant compounds
which were from 8 to 39% with five main phenols: phenol,
2-methyl-phenol, 3-methyl-phenol, 2,4-dimethyl-phenol, and
3,4-dimethyl-phenol in bio-oils depending on reaction conditions.
Guaiacols were significantly decreased by close coupled catalysis
from 45% in raw bio-oils to 0-26% in upgraded bio-oils depending on
reaction conditions. The guaiacols were mainly composed of
2-methoxy-phenol, 2-methoxy-4-methyl-phenol,
4-ethyl-2-methoxy-phenol.
Effect of Reaction Temperature
[0039] The effect of catalysis temperatures on chemical
compositions of upgraded bio-oils was analyzed with a fixed ratio
of catalyst to biomass (0.25) as shown in FIG. 3. The aromatic
hydrocarbons were increased from about 0.72% in raw bio-oil to
about 92.6% when the catalysis temperature was increased to about
500.degree. C. Thus, the results showed that high temperatures
favored the production of aromatic hydrocarbons. The phenols
content was first increased from 5.5% in raw bio-oil to 39% at
375.degree. C. then decreased to 5.9% when the temperature was
increased to 500.degree. C. The guaiacols content was decreased
from 44.7% in raw bio-oil to 0% when the temperature was higher
than 481.degree. C. The furans content was decreased from 9.8% in
raw bio-oil to around 1% when the catalysis temperature was higher
than 375.degree. C. The sugar content was decreased from 4 to 0% as
the temperature was increased to more than 375.degree. C.
Effect of Catalyst to Biomass Ratio
[0040] It was observed that when the catalysis temperature was
fixed at 375.degree. C., the aromatic hydrocarbon content was
increased from 0.72% in raw bio-oil to 78.1% with the increase of
catalyst to biomass ratio from about 0 to 0.39 (FIG. 4). The
content of phenols was first increased from 5.5% (raw bio-oil) to
39.3% (catalyst to biomass ratio of 0.25) then decreased to 18.2%
with the increase of catalyst to biomass ratio from 0 to 0.39.
Thus, the results indicated that high ratios of catalyst to biomass
favored aromatic hydrocarbons production as phenols were cracked to
produce aromatic hydrocarbons. The guaiacols content was decreased
from 44.7% in raw bio-oil to 0% when the catalyst to biomass ratio
was increased to 0.39.
Mechanism Analysis for Close Coupled Catalysis Process
[0041] In this test, the highest aromatic hydrocarbon content
(92.6%) was achieved when the catalysis temperature was about
500.degree. C. and the ratio of catalyst to biomass was about 0.25.
The content of acids, ketones, alcohols, phenols, guaiacols,
furans, esters, sugars were 0.1%, 0%, 0.05%, 5.95%, 0%, 0.5%, 0%,
and 0%, respectively in the upgraded bio-oil. Raw bio-oil produced
by pyrolysis at 500.degree. C. contained 0.71% aromatic
hydrocarbons, 2% acid, 0.89% ketones, 1.5% alcohols, 5.46% phenols,
44.7% guaiacols, 9.8% furans, 2.51% ester, and 4.05% sugars. Thus,
the aromatic hydrocarbons in the upgraded bio-oil were
significantly increased while other compounds except phenols all
decreased to about 0% when compared to the raw bio-oil.
[0042] The disappearance of these oxygenated compounds after
catalysis was believed to be associated with dehydration,
decarboxylation, and decarbonylation reactions. In particular,
Douglas fir is a soft wood which contains about 21% hemicelluloses,
about 44% cellulose, and about 32% lignin. In the close coupled
catalysis with microwave pyrolysis of Douglas fir sawdust pellets,
it is believed that furfural was first produced through the bond
cleavage between O--C.sub.5 and ring forming between
C.sub.2-C.sub.5 positions of the main chain of xylan. Furans may
then be formed from decarbonylation of furfurals. Cellulose was
believed to decompose and dehydrate to form anhydrosugars such as
levoglucosan and furans. Such furans may be first converted to
intermediates (e.g., cyclohexene and 3,4-dimethylbenzaldehyde) and
then transformed into aromatics, light olefins, and carbon oxides.
It is further believed that lignin was primarily depolymerized and
dehydrated to produce propenyl-guaiacols. Then phenols were
generated from demethoxylation reactions of propenyl-guaiacols. The
cleavage of O--CH.sub.3 bond in guaiacols was indicated by the
increased CH4 in the syngas observed by the GC analyzer and mainly
contained H.sub.2, CO.sub.2, CO, CH.sub.4, C.sub.2H.sub.4, and
C.sub.2H.sub.6. Aromatic hydrocarbons such as toluene may then be
obtained from catalyzed deoxygenation of phenols during
catalysis.
[0043] From the foregoing, it will be appreciated that specific
embodiments of the disclosure have been described herein for
purposes of illustration, but that various modifications may be
made without deviating from the disclosure. In addition, many of
the elements of one embodiment may be combined with other
embodiments in addition to or in lieu of the elements of the other
embodiments. Accordingly, the technology is not limited except as
by the appended claims.
* * * * *