U.S. patent application number 13/037938 was filed with the patent office on 2011-09-29 for biomass conversion process.
This patent application is currently assigned to EXXONMOBIL RESEARCH AND ENGINEERING COMPANY. Invention is credited to Simon R. KELEMEN, Glen E. PHILLIPS, Michael SISKIN.
Application Number | 20110232160 13/037938 |
Document ID | / |
Family ID | 44654727 |
Filed Date | 2011-09-29 |
United States Patent
Application |
20110232160 |
Kind Code |
A1 |
SISKIN; Michael ; et
al. |
September 29, 2011 |
BIOMASS CONVERSION PROCESS
Abstract
Biomass material is converted into precursors for hydrocarbon
transportation fuels by contacting the biomass with liquid
superheated water or supercritical water to depolymerize and
deoxygenate the biomass into the transportation fuel precursors.
Temperatures above 200.degree. C. and preferably above 300.degree.
C. are preferred with supercritical water at temperatures above
374.degree. C. and pressures above 22 MPa providing a capability
for higher conversion rates.
Inventors: |
SISKIN; Michael; (Westfield,
NJ) ; PHILLIPS; Glen E.; (Goldvein, VA) ;
KELEMEN; Simon R.; (Annandale, NJ) |
Assignee: |
EXXONMOBIL RESEARCH AND ENGINEERING
COMPANY
Annandale
VA
|
Family ID: |
44654727 |
Appl. No.: |
13/037938 |
Filed: |
March 1, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61317545 |
Mar 25, 2010 |
|
|
|
Current U.S.
Class: |
44/307 ; 44/300;
44/311 |
Current CPC
Class: |
C10L 1/04 20130101; C10G
2300/1003 20130101; Y02P 30/20 20151101; C10G 3/40 20130101; C10G
2300/1014 20130101; C10G 2300/4006 20130101 |
Class at
Publication: |
44/307 ; 44/300;
44/311 |
International
Class: |
C10L 1/10 20060101
C10L001/10 |
Claims
1. A process for the conversion of biomass material into precursors
for hydrocarbon transportation fuels comprises contacting liquid
superheated water or supercritical water with the biomass material
to depolymerize and deoxygenate the biomass into the transportation
fuel precursors.
2. A process according to claim 1 in which the water is liquid
superheated water at a temperature of at least 200.degree. C.
3. A process according to claim 2 in which the water is liquid
superheated water at a temperature of at least 300.degree. C.
4. A process according to claim 1 in which the water is in the
supercritical state at a temperature of at least 374.degree. C. and
a pressure of at least 22 MPa.
5. A process according to claim 1 in which the biomass material
comprises plant matter, biodegradable wastes, byproducts of farming
including animal manures, food processing wastes, sewage sludge,
black liquor from wood pulp or algae.
6. A process according to claim 5 in which the plant matter
comprises the roots, stems, leaves, seed husks and fruits of
miscanthus, spurge, sunflower, switchgrass, hemp, corn (maize),
poplar, willow, sugarcane, and oil palm (palm oil).
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application relates to and claims priority to U.S.
Provisional Application No. 61/317,545, filed on Mar. 25, 2010.
This application is also related to co-pending U.S. patent
application Ser. No. ______, (Attorney Docket No. 2010EM098-US2),
entitled "Biomass Oil Conversion Process" filed on Mar. 1, 2011,
which claims priority to U.S. Provisional Application No.
61/317,557, filed on Mar. 25, 2010.
FIELD OF THE INVENTION
[0002] The present invention relates to a process for the
production of transportation fuels by the conversion of
biomass.
BACKGROUND OF THE INVENTION
[0003] Petroleum is currently estimated to account for over 35% of
the world's total commercial primary energy consumption. Coal ranks
second with 23% and natural gas third with 21%. The use of liquid
hydrocarbon fuels on an enormous scale for transportation has led
to the depletion of readily accessible petroleum reserves in
politically stable regions and this, in turn, has focused
attention, economically, technically and politically on the
development of alternative sources of liquid transportation fuels.
Liquid hydrocarbons are far and away the most convenient energy
sources for transportation in view of their high volumetric energy.
The energy density of gasoline, for example at about 9 kWh/litre
and of road diesel at about 11 kWh/litre, far exceeds that of
hydrogen (1.32 kWh/litre at 680 atm, or batteries, 175 Wh/kg.
Furthermore, the liquid hydrocarbon fuel distribution
infrastructure is efficient and already in place.
[0004] Production of liquid fuels from biomass can help solve the
problem of CO.sub.2 emission from the transportation sector because
CO.sub.2 released from vehicle exhaust is captured during biomass
growth. While direct, carbon-neutral use of biomass as fuel is
established, for example, biodiesel, this route is limited because
the limited choice of source materials, e.g. vegetable oils.
Conversion of a wider variety of biomass sources into more
traditional types of fuel, principally hydrocarbons, is the more
attractive option.
[0005] Currently, there are two major routes for conversion of
biomass to liquid fuels: biological and thermo-chemical. In the
biological process, fermentation of easily fermentable plant
products, such as, for example, sugars to alcohols is achieved.
These easily fermentable plant products can be extracted from corn
kernels, sugar cane and etc. The major disadvantage of this pathway
is that only a fraction of the total carbon in biomass is converted
to the final desired liquid fuel. It has been calculated that
conversion of all corn produced in USA to ethanol can meet 12% of
entire US demand for gasoline which reduces to 2.4% after
accounting for fossil fuel input required to produce the
ethanol.
[0006] One well-established route to the production of hydrocarbon
liquids is the gasification of carbonaceous materials followed by
the conversion of the produced synthesis gas to form liquids by
processes such as Fischer-Tropsch and its variants. In this way,
solid fuels such as coal and coke may be converted to liquids. Coal
gasification is well-established, being used in many electric power
plants and the basic process can proceed from just about any
organic material, including biomass as well as waste materials such
as paper, plastic and used rubber tires. Most importantly, in a
time of unpredictable variations in the prices of electricity and
fuels, gasification systems can provide a capability to operate on
low-cost, widely-available coal reserves. Gasification may be one
of the best ways to produce clean liquid fuels and chemical
intermediates from coal as well as clean-burning hydrogen which
also can be used to fuel power-generating turbines or used in the
manufacture of a wide range of commercial products. Gasification is
capable of operating on a wide variety of input materials, can be
used to produce a wider variety of output fuels, and is an
extremely efficient method of extracting energy from biomass.
Biomass gasification is therefore technically and economically
attractive as an energy source for a carbon constrained
economy.
[0007] The conversion of biomass to hydrocarbon transportation
fuels by the gasification-liquefaction sequence has, however,
certain limitations both technically and economically. First, the
conversion of the biomass to synthesis gas requires large process
units, high in capital cost to deal with the enormous volumes of
gas generated in the process. Second, the gas-to-liquid conversion
uses catalysts which may, for optimum results, use noble metal
components and accordingly be very expensive. Third, and by no
means least is the fact that enormous biological resources are
needed to supply current consumption levels. An approximate
estimate for the land area required to support the current oil
consumption of about 2 million cubic metres per day by the US
transportation sector is of the order of 2.67 million square km
which represents 29% of the total US land area, using reasonable
assumptions for the efficiency of the conversion process, thus
suggesting that large scale production of liquid fuels from such a
biomass conversion process is impractical.
SUMMARY OF THE INVENTION
[0008] We have now devised a process for the conversion of biomass
into transportation fuel precursors which does not rely upon
gasification and which uses cheap, readily available materials in
the conversion. While not addressing any large proportion of total
transport energy needs, it does provide a route for using available
resources economically.
[0009] According to the present invention, biomass is converted
into precursors for hydrocarbon transportation fuels by the use of
superheated and/or supercritical water to depolymerize and
deoxygenate the biomass into the transportation fuel
precursors.
DETAILED DESCRIPTION
[0010] Biomass is conventionally defined as the living and recently
dead biological material that can be converted for use as fuel or
for industrial production. The criterion as biomass is that the
material should be recently participating in the carbon cycle so
that the release of carbon in the combustion process results in no
net increase averaged over a reasonably short period of time (for
this reason, fossil fuels such as peat, lignite and coal are not
considered biomass by this definition as they contain carbon that
has not participated in the carbon cycle for a long time so that
their combustion results in a net increase in atmospheric carbon
dioxide). Most commonly, biomass refers to plant matter grown for
use as biofuel, but it also includes plant or animal matter used
for production of fibers, chemicals or heat. Biomass may also
include biodegradable wastes that can be burnt as fuel including
municipal wastes, green waste (the biodegradable waste comprised of
garden or park waste such as grass or flower cuttings and hedge
trimmings), byproducts of farming including animal manures, food
processing wastes, sewage sludge, black liquor from wood pulp or
algae. It excludes organic material which has been transformed by
geological processes into substances such as coal, oil shale or
petroleum. Biomass is widely and typically grown from plants,
including miscanthus, spurge, sunflower, switchgrass, hemp, corn
(maize), poplar, willow, sugarcane, and oil palm (palm oil) with
the roots, stems, leaves, seed husks and fruits all being
potentially useful. The particular plant or other biomass source
used is not important to the product liquid transportation fuel
although the processing of the raw material for introduction to the
processing unit will vary according to the needs of the unit and
the form of the biomass. The biomass materials which are preferred
are those which contain a higher proportion of lignins relative to
celluloses and hemicelluloses since it is the lignins which, in the
water treatment, produce greater quantities of the fuel precursors.
A lignin content of at least 35 percent would produce greater
amounts of fuels while at least 50 percent lignin would be
preferred. Since lignin plays a significant role in the carbon
cycle, sequestering atmospheric carbon into the living vegetable,
the use of the lignin derivatives as fuels will be
carbon-neutral.
[0011] In the present process, the biomass, after any necessary
comminution and necessary pre-drying to improve handling and
amenability to the treatment with the water, is brought into
contact with superheated or supercritical water. Organic compounds,
including the lignocellulosic material typically found in solid
biomass will readily dissolve in superheated and supercritical
water. Once the biomass is dissolved under these conditions, water
will efficiently break cellulose and other bonds as described
below; at supercritical temperatures cellulosic material will form
coke extremely rapidly.
[0012] When superheated but below the critical point, the water is
still in the liquid state rather than the supercritical
characteristic state in which the properties are intermediate those
of the vapor state and the liquid. Above the critical point,
supercritical fluids generally possess unique solvating and
transport properties compared to liquids or gases. Supercritical
fluids can have liquid-like densities, gas-like diffusivities, and
compressibilities that deviate greatly from ideal gas behavior.
Solid solubility often is enhanced greatly with respect to
solubility in the gas or liquid solvent. Supercritical water in
particular has the ability to dissolve materials not normally
soluble in liquid water or steam and also promotes certain chemical
reactions. The critical point of water is at 374.degree. C. and
about 22 MPa (3190 psi), at which it has a relative density of
0.322. When heated at the requisite pressure above this point, the
superheated water becomes supercritical and, as such, has been
found to provide faster reaction rates for the conversion of the
biomass although at the expense of maintaining higher pressure.
[0013] Superheat to a temperature of at least 300.degree. C. and
preferably at least 374.degree. C. at appropriate pressures,
typically autogeneous pressures, to maintain liquidity is preferred
in order to secure satisfactory reaction rates in the biomass
reaction. Pressures at temperatures of this order will typically be
at least 15 MPa (2175 psi) and may be at least as high as 20 MPa
(2900 psi).
[0014] High temperature water superheated under autogenic or higher
pressure provides a significantly more favorable reaction medium
for insoluble organic compounds than does water up to its boiling
temperature. The solvent properties of liquid water (density,
dielectric constant) at high temperature are similar to those of
polar organic solvents at room temperature, thus facilitating the
solubility of organic compounds and their reactions. At 300.degree.
C., for example, water exhibits a density and polarity similar to
those of acetone at room temperature: the solubility parameter
decreases from 23.4 to 14.5 cal/cm.sup.3. The dielectric constant
drops rapidly with temperature, and at 300.degree. C. has fallen
from 80 (at 20.degree. C.) to 2. Therefore, as the water
temperature is increased, the solubility of non-polar organic
compounds increases much more than expected for the natural effect
of temperature and the reactions with the biological materials are
facilitated to this extent.
[0015] When superheated liquid water is used in the range from
above about 200.degree. C. to below the critical temperature of
water, 374.degree. C., more preferably from about 250.degree. C. to
about 350 or 370.degree. C., the pressures will be autogenous or
higher. The corresponding vapor pressure needed to maintain water
in the liquid state at these temperatures ranges from 1550 kPa (225
psi) at 200.degree. C. to about 10.6 MPa (1532 psi) at 350.degree.
C. to about 22 MPa (3200 psi) at 374.degree. C. Vapor pressure
values are readily determinable by reference to standard texts such
as the CRC Handbook of Chemistry and Physics and Steam Tables by J.
H. Keenan, F. G. Keyes, P. G. Hill and J. G. Moore,
Wiley-Interscience, New York, 1969.
[0016] The water employed in the process is preferably neutral,
i.e. about pH 7 and substantially free of dissolved oxygen to
minimize the occurrence of undesirable free radical reactions. The
contacting is normally for a period of time ranging from about 0.1
second to several hours with shorter contact times being possible
at higher temperatures; typically, contact times will be from 5
seconds to about 4 hours, and preferably 1 minute to 2 hours.
Certain weight ratios of water to organic resource material drive
the reaction at faster rates. Therefore, a weight ratio of water to
biomass material in the range from about 0.5 to about 10 is
preferred, and more preferably from about 0.5 to 5.0, most
preferably 0.5 to 2.
[0017] Organic molecules containing oxygen functionalities such as
are commonly found in biomass undergo a wide range of chemical
reactions in neutral superheated or supercritical water. In
superheated water, below the critical temperature of water, these
reactions proceed mainly via ionic vs. thermal free radical
pathways. Above the critical temperature, a competition between
ionic and thermal free radical pathways would be expected, with
radical pathways catching up and finally predominating as
temperature increases. Condensation type polymers, polymers
containing, e.g., ester, ether, and amide linkages are likely to be
cleaved to their starting materials at 300.degree. C. and above and
esters, ethers, sulfides, amines and even diaryl ethers cleave
rapidly, carboxylic acids are decarboxylated (--CO.sub.2) and
aldehydes are decarbonylated (--CO). Such reactions effect cleavage
of cross-links containing oxygen, nitrogen and sulfur moieties with
the concurrent loss of much of these heteroatoms. These as well as
many others, are facilitated by changes in the chemical and
physical properties of water as temperature increases.
[0018] Superheated water at 350.degree. C. and .about.2400 psi
(Hydrothermal Liquefaction (HTL) conditions) is in the liquid state
and will react with e.g., lignin, to hydrolytically cleave linkages
such as those typically found in biomass materials, including
ethers and esters (including carbonate esters) and amides. Under
these conditions, ester linkages in the biomass are cleaved into an
acid and an alcohol; the acid formed is then decarboxylated with
the water acting as an acid, base or acid-base bi-catalyst (--log
Kw=11.3 vs. 13.99 at 25.degree. C.). The alcohol dehydrates under
the same conditions to form an olefin. Amide bonds cleave to form
amines and diols; the diols can subsequently dehydrate to olefins
while the amines lose ammonia to form alkanes or olefins. These
reactions are strongly catalyzed by the acidity of the water at
high temperature and autocatalyzed by acidic reaction products.
Depolymerization and deoxygenation of biomass are therefore
efficient under these conditions to form a product, typically in
the form of a viscous, oily mass which can subsequently be worked
up by conventional refining procedures as a precursor of liquid
transportation fuels,
[0019] An increase in the dissociation constant by three orders of
magnitude allows water at temperatures of 200.degree. C. or higher
to act as an acid, base, or acid-base bi-catalyst without the need
for costly and cumbersome neutralization and catalyst regeneration
steps. The negative logarithmic ionic product of water [pKw] at
250.degree. C. is 11, as compared to 14 at 20.degree. C., which
means that water becomes both a stronger acid and a stronger base
as the temperature increases. Therefore, in addition to the natural
increase in kinetic rates with temperature, both acid and base
catalysis by water are enhanced at higher temperatures. Accordingly
the water/biomass conversion may be carried out in the absence of
any additional catalyst although trace amounts of acid can be added
to facilitate these reactions while acidic species generated during
the conversion process can autocatalyse the cleavage and
deoxygenation reactions as described above. Also, since water
soluble conversion products (i.e., hydrolysis products) may include
acidic products, basic products, reducing agents and oxidizing
agents, that effect further conversion and upgrading of the biomass
resource material, recycle enrichment of these materials presents
another viable processing option.
[0020] The fuel precursors which result from the reaction are
characterized by a lower molecular weight and lower oxygen content
than most biomass products. This is a result of the unique
conversion properties of the superheated/supercritical water when
applied to biological materials. Depolymerization will result in
the formation of liquid or semi-liquid products of varying
viscosities which will combine with solids present in the mass to
dissolve or disperse them and produce a rather viscous, reaction
product which can be worked up in the same or similar manner to a
petroleum crude following a filtration which is optional depending
on how the product is eventually processed, of any remaining
solids. For example, it may be used as coker feed or visbreaker
feed. Feed to an FCC unit is preferably hydrotreated to remove
sulfur and nitrogen compounds which may remain and which, if not
removed, will adversely affect catalyst performance and longevity
in the cracking process. Hydrocracking is also an option.
[0021] The reaction with the water can be carried out in a reactor
with walls suitably thick to withstand the pressures generated and
fitted with a gas/liquid circulation system to permit the
continuous circulation of the superheated/supercritical water as
well as removal of gases such as oxygen, carbon monoxide and carbon
dioxide which are evolved in the various reactions. Typically, the
reactor will allow for contact times between the water and the
biomass mentioned above, following which the reaction mass is
withdrawn from the reactor, the water separated for recirculation
and the water and residue de-gassed. Any sludge-like residue which
remains can be sent to a coker or burned as fuel for the
process.
* * * * *