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  • C10G3/00—Production of liquid hydrocarbon mixtures from oxygen-containing organic materials, e.g. fatty oils, fatty acids
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  • C10K3/00—Modifying the chemical composition of combustible gases containing carbon monoxide to produce an improved fuel, e.g. one of different calorific value, which may be free from carbon monoxide
  • C10K3/02—Modifying the chemical composition of combustible gases containing carbon monoxide to produce an improved fuel, e.g. one of different calorific value, which may be free from carbon monoxide by catalytic treatment
  • C10K3/023—Reducing the tar content
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  • C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
  • C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
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  • C01B2203/1205—Composition of the feed
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  • C10L2290/00—Fuel preparation or upgrading, processes or apparatus therefore, comprising specific process steps or apparatus units
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  • Y02P20/145—Feedstock the feedstock being materials of biological origin
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Definitions

• the present embodiments concern a thermochemical process for hydro- gasification of biomass feed stocks, such as lignocellulosic materials, including forestry residues or lignocellulosic waste materials, to generate higher value hydrocarbon fuels, in particular methane plus aromatic and/or phenolic compounds with low levels of depositable tars.
• biomass feed stocks such as lignocellulosic materials, including forestry residues or lignocellulosic waste materials
• thermo-chemical conversion of biomass has been under investigation for centuries but has received considerable scientific attention since the 1980's as a potential source for renewable hydrocarbon fuels.
• Preferentially useful fuel products are hydrocarbons with high energy content such as methane, alkanes, olefins and light aromatic hydrocarbons.
• Synthesis gas (CO+H2) is a less preferred fuel product but is still valued as an intermediate for further chemical processing to liquid fuels and chemicals.
• biomass gasification is the production of 'synthesis gas' (CO+H 2 ) or 'producer gas'
• Raising the temperature of reactants to achieve pyrolysis is endothermic and requires the supply of heat.
• the formation reaction for synthesis gas (H 2 +CO) from pyrolysis products is endothermic.
• the heat required for both reactions is typically supplied by the addition of superheated steam or partial oxidation using oxygen or air.
• the extension of reaction conditions beyond temperatures required for thermal pyrolysis of the biomass feedstock is to further react pyrolysis products towards synthesis gas or producer gas. This is a key differentiator between pyrolysis processes and gasification processes.
• Biomass pyrolysis produces non-condensable gas, water, condensable tars and char.
• Biopolymers such as cellulose, hemi-cellulose, lignin and others are converted by pyrolysis into gaseous compounds at elevated temperature.
• 'Tars' are not well defined in the literature despite several efforts to categorize them.
• the term 'tar' is insufficient and misleading with respect to forming deposits as not all tars compounds will tend to form deposits.
• biomass derived 'tars' are considered to be non-water chemical compounds that condense upon cooling to ambient temperature, including benzene. This grouping of tar compounds is often referred to as 'gravimetric tar' and relates to its measurement method.
• Tars produced by biomass pyrolysis are considered to be 'primary' tars.
• "Pyrolysis vapors" are produced by pyrolysis only generally contain in excess of 50% tars if the conventional definition of gravimetric tars is used. It is generally understood in the art that the 'primary tar' chemical species resulting from biomass pyrolysis are derived from fragments of the biopolymers within the biomass as observed by Evans et al [Evans, R.J. and Milne, T.A., "Molecular Characterization of the Pyrolysis of Biomass. 1. Fundamentals, " Energy & Fuels 1 (2), pp.123-138] which is incorporated by reference.
• Bio-oil is produced by the rapid cooling of pyrolysis vapors.
• pyrolysis vapors are light oxygenated compounds such as alcohols, ethers, ketones, aldehydes, carboxylic acids containing zero, one, two or three carbon atoms within their molecular structure in addition to the oxygen containing functional group.
• Another fraction of pyrolysis vapors are light oxygenated compounds such as alcohols, ethers, ketones, aldehydes, carboxylic acids containing one aromatic group within their molecular structures in addition to the oxygen containing functional group.
• These 'light oxygenates' and 'light oxygenated aromatics' are considered to be 'tars' within the definition of gravimetric tars.
• Most of the light oxygenate and light oxygenated aromatic compounds in pyrolysis gas condense to liquids at ambient temperature. Some of these compounds can condense on cooler downstream surfaces to form deposits. In addition, some of these compounds can react with other compounds present to form compounds that can condense on cooler downstream surfaces to form deposits.
• Non-monomer biomass polymeric fragments are depositable tars because of the high boiling points of these compounds. Trimers and tetramers would generally tend to have higher boiling points than monomers and dimers.
• these primary tar polymeric fragments are, at least initially, not polyaromatic hydrocarbons (PAH) typical of secondary and tertiary tars. Polyaromatic hydrocarbons containing fused aromatic rings are not naturally present in biopolymers and are formed during high temperature processing. High molecular weight heterocyclic and PAH compounds can be considered to be depositable tars because of high dew points.
• the biopolymer derived oligomers can exist as vapor or aerosols within the pyrolysis gas stream [Lede, J., Diebold, J.P., Peacocke, G.V.C, Piskoriz, J., "The Nature And Properties Of Intermediate And Unvaporised Biomass Pyrolysis Materials ", p51-65 in Bridgwater, A., Czernik, S., Diebold, J., Meier, D., Oasmaa, A., Peacocke, C, Piskorz, J., and Radlein, D. editors, Fast Pyrolysis of Biomass: A Handbook, CPL Press, Newbury, UK, 1999] which is incorporated by reference.
• oxidative gases such as steam, oxygen or carbon dioxide
• tar reduction is to remove tars after cooling the gas stream.
• fine aerosols have proven to be difficult to remove and often an electrostatic precipitator is required in addition to conventional aqueous scrubber systems operating near ambient temperature. This approach does not mitigate problems of deposit formation on cooler system surfaces or gas cooling heat exchanger surfaces.
• aqueous scrubbers create waste streams for treatment and disposal.
• Oxygen blown, entrained flow gasifiers can operate with maximum temperatures exceeding 1200°C which is sufficient to destroy virtually all tars prior to exiting the gasifier.
• a significant disadvantage with thermal tar destruction (by raising the temperature of the gasifier or heating gasifier outlet gas) is a loss of system thermal efficiency.
• Catalysts have been used in a secondary bed in series with the gasifier for the destruction of tars contained in the synthesis gas or producer gas by oxidation or reaction with hydrogen or steam within the synthesis gas.
• a recent review of published information on catalytic tar reduction was performed by Gerber and is incorporated here by reference Gerber, M.A., "Review of Novel Catalysts for Biomass Tar Cracking and Methane Reforming", PNNL-16950, October 2007] .
• Mudge et al disclosed in U.S. Patent No.4,865,625 (Mudge-625) the use of a catalytic secondary reactor in which air, oxygen and/or steam was injected in a secondary bed to effect tar destruction over supported nickel and other catalysts operating from about 550°C to 750°C.
• producer gas containing ⁇ 10 CH 4
• Ekstrom et al disclosed in U.S. Patent No.5,213,587 (Ekstrom-587) the use of a secondary fluidized bed containing a catalyst (and absorbent) of magnesium- calcium carbonate and calcined magnesium-calcium carbonate (and mixtures) to affect the destruction of tars, ammonia, etc from a gasifier output stream with an operating temperature of the secondary stage maintained at between about 600°C and about 1000°C, preferably 700°C-900°C. Oxygen is added to maintain bed temperature by partial combustion. It is generally known in the art that alkali earth and alkali carbonates (and their corresponding oxides) catalyze biomass pyrolysis and gasification reactions.
• the Mudge-625, Simell-705 and Ekstrom-587 processes utilize catalysts to enhance the destruction of residual levels of tars contained in biomass gasifier output streams (synthesis gas or producer gas) and require the addition of oxygen or steam to oxidize residual tars and/or maintain temperatures well in excess of 600°C, preferably in excess of 700°C.
• synthesis gas or producer gas synthesis gas or producer gas
• oxygen or steam to oxidize residual tars and/or maintain temperatures well in excess of 600°C, preferably in excess of 700°C.
• Finnish Patent 76 834 and Finnish Patent Application 910 731 disclose methods for removing depositable tars from a gasifier output stream by cooling in a fluidized bed reactor to deposit tar and other compounds onto a solid material placed in a secondary reactor before they reach the cooling surfaces of the reactor.
• This 'depositable tar condensation on solid media' approach requires additional complex heat transfer systems for the cooling of solid media and the removal of deposited tars from the media.
• Boerrigter and Bergmann in U.S Patent Application 20040220285 disclosed the application of oil wash for tar removal from biomass derived synthesis gas at 600°C-1300°C. This process is also described in several research reports including [Boerrigter, H., van Paasen, S., Bergman, P., Konemann, J., Emmen, R., Wijnands, A "OLGA Tar Removal Technology Proof -of -Concept (PoC)for application in integrated biomass gasification combined heat and power (CHP) systems", Report No. ECN-C-05-009, January, 2005] which is incorporated by reference.
• tar vapors that simply condense to form low viscosity liquids do not form deposits. Exceptions can occur if condensed liquid tars interact with other compounds, particulates or aerosols present in the gas stream.
• the interactions may be physical or chemical, such as by binding of char particles in order to adhere to a surface or by chemical reaction to increase molecular weight.
• the three primary bio-polymer components of biomass are cellulose, hemi- cellulose and lignin. It is generally known that these will thermally decompose in the absence of oxygen to form gaseous or liquid intermediate oxygenated compounds plus carbonaceous char upon heating over temperature ranges depending on the biopolymer type. This thermally induced self-decomposition is typically referred to as pyrolysis as opposed to gasification.
• flash pyrolysis is considered to require ⁇ 0.1 second to heat the biomass particle to above the pyrolysis temperature and remove the pyrolysis gas from the reactor.
• Fast pyrolysis is considered to require about 0.1 to about 5 seconds while slow pyrolysis of biomass is considered to occur over about 30 seconds with rapid pyrolysis in between.
• Flash, fast, rapid and slow pyrolysis produce pyrolysis (vapor+gas) gas streams which are high in tars but differ in amounts and chemical makeup.
• Both fast and flash pyrolysis maximize pyrolysis vapor (tar plus light gas compounds) generation and minimize char formation.
• the carbon content of the pyrolysis gas/vapor is maximized with faster pyrolysis rates and this is generally desirable when producing a fuel from the gas/vapor stream.
• the speed of pyrolysis strongly affects the solid char formation rate with char formation is generally understood to be inversely related to speed of pyrolysis:
• the Scott-935 process consisted of rapid pyrolysis of solid biomass particles fed to a near- atmospheric pressure fluidized bed containing supported catalyst particles in the presence of flowing hydrogen.
• the catalyst typically nickel supported on alumina, was found to react biomass with flowing hydrogen gas to form methane and steam with minor proportions of CO, C0 2 , char and 'tars'.
• reaction to form methane was observed to occur at temperatures of 450°C to 650°C and preferably 500°C-550°C.
• Fluidizing gas hydrogen
• Hydrogen gas containing entrained wood particles was not pre-heated.
• a 'cooling finger' was incorporated within the fluidized reaction bed to avoid pre-heating of the wood particle and hydrogen feed stream.
• the Scott-935 process temperature range is well below typical gasification temperatures required for synthesis gas or producer gas and is within the range of temperatures used for the pyrolysis of biomass for the production of bio-oil. Also of importance, this was performed without the addition of oxygen or air to provide heat by combustion or partial oxidation within the fluidized bed.
• Reported gas contact times were typically less than 2 seconds and preferably 0.4 to 0.8 seconds.
• Scott- 935 disclosed a gas residence time of less than 5 seconds, preferably less than 2 seconds and most preferably less than 1 second in the fluidized bed catalytic reactor.
• Scott-935 disclosed that low but significant levels of 'tar' and 'char' were produced; however, the levels of 'tar' are still above levels required for commercial use.
• the lowest levels of 'tar' disclosed ranged from 0.4wt to ⁇ lwt% but typically 5 wt to 15 wt .
• the nature of the 'tar' produced was not disclosed except that it condensed upon cooling to near ambient temperature.
• Mudge-625 disclosed that carbon on the catalyst in a secondary catalyst bed could be controlled by oxidation with oxygen or gasification with steam.
• the method disclosed here describes a hydro-gasification process in which lignocellulosic biomass is converted into methane and light hydrocarbons in a low- temperature, non-oxidative, thermochemical process operating with a hydrogen rich atmosphere at moderate pressure.
• the disclosed method reduces depositable tars without the addition of oxidative gases or superheated steam.
• low-temperature means above about 400°C and below about 650°C.
• Moderate pressure in this disclosure means above about 2 atm to about 50 atm.
• the disclosed method uses sequential steps of low-temperature biomass fast pyrolysis (or flash pyrolysis) followed by low-temperature catalysis under moderate hydrogen pressure to produce a methane, steam and hydrocarbon rich stream.
• An extended gas residence time within a catalyst bed downstream of the primary methane formation zone is utilized is to achieve low depositable tars in the methane- rich output stream prior to gas cooling.
• the disclosed method preferentially uses a supported catalyst with methane forming activity and a support material with tar (light oxygenate) cracking activity and preferably also with coke re-gasification activity.
• the fast (or flash) hydropyrolysis reaction preferentially uses a hydrogen rich sweep gas.
• the hydropyrolysis reaction may optionally also be catalytically enhanced to increase the quantity of pyrolysis gas generated and to reduce the char generated.
• a series of embodiments is envisaged which incorporate a variety of pyrolysis reactor configurations as options.
• the methane forming catalytic reactors are preferentially of a moving bed type with slow recirculation of catalyst particles from the end of the extended time exposure bed section to the methane forming section of the bed.
• a series of embodiments are envisaged which incorporate a variety of catalyst bed
• the disclosed method is a significant departure from a biomass gasification process producing synthesis gas or producer gas related to gasification processes using added oxygen (as air or oxygen).
• added oxygen as air or oxygen
• teachings of oxidative gasification are not applicable to non-oxidative gasification despite similarity of process stages because operating temperatures are required well in excess of 650°C to achieve reduced depositable tar levels in the gasifier outlet stream.
• the output of gasifiers is synthesis gas or producer gas. Contrary to other processes, air or oxygen is not used to partially combust biomass or pyrolysis products in order to provide heat to the secondary catalyst bed.
• the method disclosed also addresses several deficiencies of the single stage hydrogasification process including the direct contact of biomass ash and char with methane forming catalyst.
• FIG. 1 is a schematic flow chart illustrating an embodiment of the present invention.
• FIG. 1A is a schematic flow chart illustrating an embodiment of the present invention.
• FIG. 2 is graph illustrating calculated equilibrium light gas concentration as a function of temperature and concentration.
• FIG. 3 illustrates one embodiment of a system according to the present invention.
• FIG. 4 illustrates one embodiment of a reactor system according to the present invention.
• FIG. 5 is a graph illustrating methane, char and tar formation as a function of H 2 pressure.
• the separation of biomass pyrolysis and catalytic reaction steps allows the operation of each step at different operating temperatures, gas velocities and residence times.
• Catalyst operation at moderately elevated pressure greatly assists in achieving an extended residence time in the secondary catalytic reactor to reduce oligomeric tars to acceptable levels.
• Catalyst operation at temperatures elevated from the pyrolysis step is achieved by thermally coupled oxygenate cracking and methane formation reactions with a net exothermic reaction heat produced in the methane forming section of the catalyst bed. Flowing gas exiting the primary methane forming region within the reactor maintains
• pyrolysis gas is intended to mean a mixture of biomass pyrolysis vapors, aerosols and a hydrogen-rich gas where the pyrolysis vapors are produced by fast or flash pyrolysis of biomass.
• Biomass includes feedstocks such as wood, straw, etc.
• Pyrolysis gas may or may not include entrained char or ash particles and preferentially does not.
• Pyrolysis vapors include condensable and non- condensable hydrocarbons, oxygenated hydrocarbons, aerosols, steam and carbon oxides.
• the biomass (1) with a water content of about 5wt to about 25wt is fed to a hydropyrolysis reactor (3) with a source of heat for pyrolysis (2).
• the required hydropyrolysis heat can optionally be supplied to the hydropyrolysis reactor by superheated hydrogen-rich gas, direct heat exchange, hot solid media or other means.
• FIG 1A A simplified version of FIG 1 is depicted as FIG 1A showing only key process elements.
• Hydropyrolysis is used to thermally decompose biomass to a pyrolysis vapor (6) containing non-condensable gas, vapors and aerosols plus a solid char byproduct (5).
• the pressurized hydropyrolysis reactor (3) is operated at temperatures of about 400°C to about 550°C. Hydropyrolysis is preferentially performed above about 450°C to achieve acceptable pyrolysis gas formation rates. Operation at temperatures in the lower part of this range tends to increase char yield.
• Fast pyrolysis methods known in the art include auger, ablative, rotating cone, fluidized beds and circulating fluidized beds. Low gas-char contact times are easily achieved in fluidized bed fast pyrolysis reactors.
• a sweep gas is preferentially used to assist the removal of the pyrolysis products from the fast pyrolysis device. It is desirable to maximize char residence times to induce greater evolution of gases.
• Pyrolysis at elevated pressure reduces superficial gas velocities for the removal of pyrolysis products from the hydropyrolysis reactor and the use of a sweep gas (4) is preferred.
• Hydrogen or hydrogen plus steam (with or without CO or C0 2 ) is preferentially used as a sweep gas (4).
• Pyrolysis gas/char contact times are preferably less than 10 seconds, more preferably less than 2 seconds and most preferably less than 1 second.
• Fast (or flash) pyrolysis systems are known in the art which are suitable for adaptation to pressurized operation with hydrogen and the incorporation of a sweep gas (4) as required to maintain the desired pyrolysis gas/char contact times.
• the hydropyrolysis reaction may optionally also be catalytically enhanced to increase the quantity of pyrolysis gas generated and to reduce the char generated.
• Optional methods include the mixing of finely divided pyrolysis or gasification reaction enhancing materials with the biomass feedstock and the use of catalytic or catalyst coated media within the pyrolysis reactor.
• the pyrolysis gas (6) exiting the pyrolysis reactor contains the products of the thermal decomposition of the biopolymers within the biomass and other organic compounds within the biomass (oils, tri-glycerides, etc.) plus water and sweep gas. Aerosols are also typically present. Entrained char and ash are subsequently removed by cyclone or hot filter particulate removal (7). It is known that filtration does not reduce the aerosol content of pyrolysis gas.
• Optional intermediate treatments also include chlorine or sulfur sorption (9).
• the sorbent material is non-catalytic to the cracking of oxygenated compounds contained in the gas mixture.
• Appropriate materials known in the art include zinc oxide, alkali earth oxides, hydroxides or carbonates and related silica containing mineral compounds.
• the filtered and treated pyrolysis gas (10) contains a high concentration of gravimetric tars, including low molecular weight oxygenate hydrocarbons as vapors and high molecular weight oxygenated hydrocarbons as vapors or aerosols.
• the temperature of this stream (10) is approximately the same as the pyrolysis reactor (most preferably between about 450°C and about 500°C) and is above its dew point. Active heat exchange (not shown) is optionally used to control the inlet temperature to the secondary reactor (11).
• the filtered and treated pyrolysis gas (10) is catalytically reacted in a secondary reactor (11) with excess hydrogen gas (13) to preferentially form methane (and light hydrocarbons) while operating below about 650°C, preferably below about 600°C and most preferably about 550°C.
• the higher operating temperature of the catalytic reactor (11) is achieved without the addition of air, oxygen or superheated steam or by other means of external heating (except to overcome external heat losses).
• the exothermic catalytic reaction to form methane is thermally coupled with cracking reactions of compounds within the pyrolysis gas. Excess reaction heat causes the temperature of the gas stream to increase in the zone where most methane is formed and also transport heat downstream of this zone.
• endo thermic cracking reactions of light oxygenates are thermally coupled with exothermic methane formation reactions.
• a net excess of exothermic reaction heat results in a temperature rise above the pyrolysis temperature.
• the term 'thermally coupled' is defined here to mean that exothermic reaction heat is released locally by one reaction and is available to supply reaction heat for a second endothermic reaction which also occurs within a short proximity.
• An 'extended gas residence time' section in the catalyst bed (12) following the main 'methane forming section' is provided to reduce residual depositable tars. The decomposition rate of residual biopolymer oligomeric tars existing as vapors or aerosols is enhanced at the elevated temperature above the pyrolysis temperature.
• Extending the gas contact time assists in further decomposition of depositable tars.
• the oligomeric tars and slow reacting chemical species downstream of the main methane formation section (11) is exposed to catalyst, steam, methane, hydrocarbons and excess hydrogen (plus minor levels of carbon oxides) a temperature elevated above the pyrolysis temperature.
• H/C and O/C ratios are about same as the methanation section input ratios.
• Aerosols are difficult to deal using a solid-gas heterogeneous catalytic bed. It would be expected that a portion of the larger diameter (lignin derived) aerosols may impact and adhere to catalyst particle exterior surfaces. As such, it is desirable to maintain low gas velocities within the catalyst bed to minimize momentum impacts. Small diameter aerosols would tend to be maintained as entrained aerosols and tend to decompose faster because of higher surface area (exposure to hot steam and hydrogen gas). Once the liquid phase oligomers within aerosol particles de- polymerize to form vapors, the vapors can diffuse into the catalyst particles for reaction.
• a third reactor can be utilized using a different catalyst from that used in the methanation reactor (not shown in FIG 1).
• the catalyst in the optional third reactor can be utilised to selectively promote the hydrodeoxygenation (HDO) of substituted oxygenated aromatic compounds (such as substituted phenols) but limit ring-opening reactions so as to enhance the formation of light mono- aromatic compounds versus additional methane.
• HDO hydrodeoxygenation
• Mono-aromatic phenolic compounds are considered to be non-depositable tars.
• there is commercial benefit to de-oxygenating these compounds to substituted aromatic compounds such as benzene, toluene, ethyl benzene, xylene (BTEX) and other substituted aromatic hydrocarbons.
• HDO hydro-deoxygenate
• a moving bed in the catalytic reactor so that catalyst particles are removed from the end of the bed (14) and returned to the inlet.
• coke formed within the catalyst by some of the oxygenate cracking reactions in the first section of the bed (where cracking and methane formation reactions preferentially occur) is effectively moved to the 'extended time exposure' section of the bed.
• Slow moving beds are a most preferred configuration with catalyst being removed from the extended time exposure bed section exit and recirculated to the methanation bed section inlet either by mechanical means or by gas entrainment. Gas flows are preferably co-current but are optionally counter-current to catalyst movement within either of the two catalyst bed sections.
• Another preferred option is to use a circulating fluidized bed with a fluidized bed as the methane forming section which overflows catalyst into a slow moving second stage moving bed. Catalyst is returned to the fluidized bed after extended time exposure in the second stage.
• Another preferred option is a riser reactor configuration.
• the gas output from the catalytic reactor(s) is primarily composed of steam, methane and excess hydrogen with lower levels of C0 2 , CO and other gases.
• the gas output from the catalytic reactor(s) preferably contains levels of depositable tars with a dew point of less than the operating temperature of the cooling stage (14) following the reactor (12).
• the gas output from the catalytic reactor(s) (13) is preferentially cooled in a stepwise fashion using sequential gas cooling towers containing oil (14) and water (20). Compounds with boiling points above and near the operating temperature of the oil cooling tower (14) are preferentially condensed along with residual heavier oxygenated 'tar' compounds.
• the oil (15) is cooled and recycled to the tower (18). A fraction of the oil is removed from the recycle line where products and contaminants/byproducts (17) are separated from the oil by conventional processes (16) (such as atmospheric pressure distillation) and the oil returned to the oil tower cooling system.
• the cooling oil is preferably a paraffinic mineral oil with a normal boiling point range of about 200°C to about 500°C. It is preferred that the low boiling fraction of the oil be removed prior to use so as to minimize vapor carryover to the water cooling section.
• the outlet gas (19) temperature from the oil cooling step is maintained above the condensation temperature of water under process conditions to minimise water condensation within the oil cooling step.
• the bulk of the water contained in the gas output from the catalytic reactor(s) is condensed in a water cooling step (20).
• Low boiling point hydrocarbons, light oxygenates and water are preferentially condensed in the water condensing tower along with residual water soluble compounds.
• a portion of the water is chilled (23) and treated (24) for recovery of light hydrocarbons (26) and depressurized for C0 2 separation (24). Cooled water is recycled to the cooling tower (24).
• Other water soluble contaminants are optionally separated from the water by known boiler feed water treatment processes prior to being re-heated (41) and used as steam feed (42) to the reformer (31).
• Modeled mass balances indicate that a minimum initial biomass moisture content of about 7% plus water produced in the methane formation reaction is required as feed to the reformer to generate hydrogen needed by the process. This minimizes waste water discharges and reduces disposal costs.
• a single water cooling step can optionally be used in lieu of oil cooling plus water cooling steps.
• the output gas from the water cooling step (21) is preferentially near ambient temperature and is primarily a water- saturated, impure methane and hydrogen stream at near system pressure.
• this gas is further conditioned for low levels of CO and C0 2 and trace H 2 S, ammonia, alkali and chlorides by conventional means such as activated carbon bed, ZnO bed, alkali water scrubber, etc.
• the pressurized and cooled impure methane (+hydrogen+water+CO) gas stream (21) is desirably separated to produce a hydrogen-rich stream (29) for recycle to the process, a high-purity methane product stream (28) and a methane-rich waste gas stream (30).
• the separation process (27) for the output gas from the water cooling step is a two-stage pressure swing adsorption (PSA) system.
• PSA pressure swing adsorption
• the PSA system produces impure hydrogen as a high pressure product for recycle to the process and a high-purity methane stream preferably as pipeline- grade methane.
• the high purity methane stream can contain minor amounts of hydrogen which is subsequently removed to produce a 'pipeline grade' methane stream by known means such as a selective hydrogen permeable membrane device.
• the low-pressure PSA exhaust containing impure methane (30) is preferentially re-pressurized and steam reformed (31) to make at least a fraction of the hydrogen needed in the process.
• the PSA exhaust gas (30) is further conditioned prior to input to the steam reformer (31) for removal of trace H 2 S, alkali, ammonia and chloride compounds by conventional means such as activated carbon bed, ZnO bed, alkali water scrubber, etc.
• the methane-rich waste gas stream (30) is re- pressurized as required and preferentially fed to a steam reformer (31) to produce hydrogen required for the process (36).
• Steam produced from treated condensate water (42) is preferentially used for steam reforming.
• Light hydrocarbons condensed in the water condensation step are optionally removed as a by-product
• Reformer heat requirements are preferentially supplied by combustion of the char by-product from fast-hydropyrolysis (5,38) with air (39) producing a C0 2 containing flue gas (40). Reformer reactant pre-heating is preferentially performed by heat exchange with process cooling steps.
• C0 2 (37) and hydropyrolysis char (5) are optionally combusted with air (39) and the heat used in a steam reformer to make at least a fraction of the hydrogen (4,13) needed for the production of methane in the process.
• the hydropyrolysis char (5) is optionally gasified to make at least a fraction of the hydrogen (4,13) needed for the production of methane in the process.
• tars A significant fraction cannot be analyzed by gas chromato graph (GC) analysis.
• GC gas chromato graph
• the high molecular weight fraction with molecular weights in excess of 1000 Daltons are present in proportions which can form deposits within processing systems.
• Those compounds with boiling points above ambient temperature (excluding water) are generally referred to as tars.
• thermochemical biomass conversion processes It is disclosed that a series of conditions are required to reduce deposit formation within thermochemical biomass conversion processes. These conditions include:
• FIG 2 shows a typical calculated equilibrium of CH 4 , H 2 , H 2 0, CO and C0 2 at 10 bara total pressure.
• H2Stoich One metric of the excess hydrogen in the system is a H 2 stoichiometric ratio or "H2Stoich”.
• the disclosed method includes an exposure of process gases and aerosols to temperatures above the hydropyrolysis temperature by at least 25 °C or preferably about 100°C or more preferably about 200°C above the pyrolysis temperature subject to a maximum temperature of about 650°C while in contact with catalyst.
• thermo gravimetric analysis TGA
• individual lignocelluosic biopolymers thermally degrade at different rates over different temperature ranges.
• thermal decomposition of biopolymers is enhanced by elevated temperatures.
• biopolymer fragments are created in the pyrolysis step most preferably in the temperature range of 400°C to 550°C.
• Those compounds existing in vapor form and aerosol form within the pyrolysis gas at pyrolysis temperatures can be expected to further degrade by (mildly endothermic) cracking on a catalyst or by self-destruction at temperatures higher than pyrolysis.
• the pyrolysis gas is heated above the pyrolysis temperature by the exothermic formation of methane within the catalyst bed.
• biopolymer pyrolysis includes reactions 2 and 3. A significant fraction of the
• biopolymers have been decomposed to light oxygenates during pyrolysis.
• the light gases tend to approach a complex equilibrium established between CO, C0 2 , H 2 , H 2 0 and CH 4 which is a function of temperature, pressure and overall gas composition.
• the reforming reaction 15 produces synthesis gas which increasingly dominates the equilibrium at temperatures above about 650°C at the expense of methane and water.
• oxygenated hydrocarbons within pyrolysis gas are catalytically cracked and reacted to preferentially form methane and water vapor with the consumption of hydrogen gas. This is preferably performed at temperatures less than about 650°C, under elevated hydrogen pressure and a H2Stoic greater than or equal to 1.
• light gases produced by oxygenate cracking and other reactions are reacted catalytically to better approach equilibrium.
• Oxygenate cracking activity and methane formation activity are both necessary characteristics of the catalyst used in the disclosed method.
• methane does not contribute to polymerization, condensation or other reactions which can increase molecular weight (and boiling points) of the compounds and oligomers remaining in the gas stream.
• the formation of methane is effectively an irreversible removal of depositable tar compounds from the gas stream.
• the pyrolysis gas reaction to from methane requires the use of a catalyst with both activity towards the cracking of light oxygenated hydrocarbons and activity towards the formation of methane.
• the oxygenated hydrocarbons are effectively de-oxygenated by hydrogen gas supplied to the process with the formation of water as a product.
• PAH compounds are known to be difficult to destroy under the mild conditions in this disclosed method.
• Catalyst bed outlet temperatures of less than about 550°C are preferred for the retention of substituted mono-aromatic or phenolic hydrocarbons in the product gas stream.
• reactions 4 and 5a,b,c are rapidly catalytically cracked primarily by reactions 4 and 5a,b,c.
• Reactions 5a and 5b produce carbon oxides in the general vicinity of methane forming reaction sites (reactions 14 and reverse 15) within the catalyst particle and serve as the source of carbon for methane production.
• coke can be produced by cracking some oxygenate compounds (as per reaction 4) or the decomposition of light olefins (e.g. ethylene or propylene).
• reactions 14 and reverse 15 which are active for multiple reactions including methane formation
• reaction 7 de- oxygenation
• steam reforming reactions 15 and 6
• forward/reverse water gas shift reaction 13
• oligomers biopolymer fragments
• pyrolysis gas the primary source for 'depositable tars' .
• the cellulose and hemi-cellulose ring structures are almost fully cracked to light oxygenated hydrocarbons and carbon oxides and decomposition is enhanced by both base and acid catalytic sites that are present on a variety of catalyst supports. These light gases rapidly catalytically reacted to form methane.
• lignin derived oligomers and large molecular fragments are more difficult to crack and fully decompose to be able to form methane or other hydrocarbons.
• Lignin is a large, complex bio-polymer consisting of linked aromatic rings often containing beta-ether bonds. Lignin is significantly different from cellulose and hemi-cellulose (which both contain oxygen within their primary repeating biopolymer rings). It is not necessary to fully decompose the lignin oligomers and lignin fragments to non-condensable gases but is sufficient to fragment multi- aromatic ring containing oligomers to form low boiling point mono- aromatic hydrocarbons or phenolic compounds which are not depositable tars.
• HDO of residual non-deposit forming oxygenates is optionally performed on the catalyst output gas stream (13).
• the optional capture and separation of condensable non-methane hydrocarbons can create a valuable byproduct stream or reduce process problems created by phenol type compounds in the condensed water stream (22).
• a desirable gas residence time within a catalytic reactor would be the gas residence time required to perform the primary reactions in order to minimize reactor volume and quantity of catalyst required.
• a gas residence time significantly in excess of the minimum required for the methane forming reaction is used to achieve low levels of 'depositable tar' compounds.
• Deposit forming tar aerosols (as well as char and coke) are exposed to hydrogen and steam for an extended period of time at temperatures elevated from the pyrolysis temperature and converted to non-deposit forming monomer, lighter hydrocarbons, oxygenates or non-condensable gases.
• the disclosed method includes an extended time of exposure of pyrolysis gases and aerosols to temperatures above the hydropyrolysis temperature at least 5 seconds, preferably greater than 1 minute, more preferably greater than 10 minutes or most preferably greater than 1 hour subject to economic efficiency and operating conditions required to reduce depositable tars to acceptable levels. It should be noted that this is achieved without the addition of oxygen to raise the gas temperature.
• additional cool hydrogen gas can be added to the catalytic reactor to reduced the operating temperature and raise the H/C ratio.
• the pyrolysis gas reaction to from methane requires the use of a catalyst with both activity towards the cracking of light oxygenated hydrocarbons and activity towards the formation of methane and water from light gases.
• a supported metal catalyst One catalyst taught in Scott-935 to perform this function is nickel supported on moderately high surface area alumina. The lighter oxygenated compounds within the pyrolysis gas were quickly cracked and reacted to form methane as inferred by the ⁇ 1 second gas residence times in fluidized beds described in Scott-935. It is known that alumina alone does not possess methane forming catalytic activity although it does perform oxygenate cracking very rapidly.
• Preferred catalyst substrate materials have lower oxygenate cracking activity than moderately high surface area alumina but still sufficiently active towards oxygenate cracking to keep metallic catalytic sites sufficiently supplied with light gases for methane formation.
• Preferred catalyst substrate materials include slightly lower surface area alumina as well as high surface area silica, aluminosilicates, aluminophosphates and zeolites.
• Catalyst support materials with high oxygenate cracking activity are preferred with surface areas >10 sq.meters/gram and most preferred with surface areas from about 50 to 150 sq.meters/gram.
• Catalyst support materials which enhance char gasification rates (reactions 11 and 12) at about 500°C to 650°C include calcia, magnesia, zirconia, hafnia, ceria, titania and their mixtures plus alkali earth zirconates, titanates, hafniates, ceriates plus zirconia, hafnia, ceria and titania rich aluminates.
• Catalyst support materials with high steam-coke gasification activity are preferred with surface areas >10
• the catalyst support materials noted do not have sufficient catalytic activity for the formation of methane. Finely divided metals dispersed upon the catalyst support materials are required to enhance the methane formation rate. A sufficiently high methane formation rate is required to provide excess reaction heat to raise the temperature of the catalyst and catalyst bed to a temperature sufficiently to enhance the thermal destruction of aerosols within the pyrolysis gas.
• Group VIII metals known to have high catalytic activity for the formation of methane from light gases include Ni, Pt, Ru, Rh, and Pd with the most common being nickel.
• Metal promoted or dual metal catalysts include nickel or Pt plus Co, Mo, Cr, W, La and Fe. These dual metal catalysts can be used to impart additional thermal stability or sulfur tolerance to the nickel crystallites on the support material. Nickel and other metals can also be promoted with alkali and alkali earths such as K, Ca and Mg to enhance steam-coke gasification and oxygenate cracking.
• Catalyst substrates are preferred in a physical form which imparts sufficient crush strength and abrasion resistance for operation within a moving bed while allowing gas flow.
• a particle shape is desired which avoids 'hang-up' and channeling within the catalyst bed.
• most preferred catalysts are nickel supported on alumina, aluminosilicate or zirconia with Mo or W additions for increased sulfur tolerance and promoted by calcia.
• typical, dry, lignocellulosic biomass has an approximate molecular formula of C 6 H 9 O 4 which corresponds to H/C ratio of about 1.5 and O/C ratio of about 0.7. It is known that all forms of biomass pyrolysis result in oxygen within the biomass being preferentially partitioned to the gas/vapor phase. It is known from published literature that pyrolysis vapor from fast pyrolysis of lignocellulosic biomass typically has an H/C ratio of near 1.8 and an O/C ratio of near 0.8. The H/C and O/C ratios of both compositions are calculated to be well within the thermodynamic coke stability region for light gases.
• Calculations of the coke stability region for the disclosed process based on light gases indicate that coke stability region can be avoided by maintaining a H/C ratio greater than about 4 and more preferably greater than about 5 and most preferably above about 5.5 for operation using pyrolysis gas with O/C ratios of less than about 2 at temperatures less than about 650°C and total pressure less than about 50 atm.
• Coke steam- gasification requires at least some coke to be present within the catalyst, however, the level of coke in the catalyst must not be so high as to restrict mass transfer of gaseous reactants and products to and from catalytic sites within the catalyst particles. It is generally known that low levels of coke on catalysts, such as nickel on alumina, are acceptable for catalyst activity, however, coke levels in and above the range of 6-10% can significantly inhibit catalyst activity by pore plugging.
• the rate of biopolymer oligomer decomposition or the rate of coke steam-gasification which determines the minimum extended gas residence time in the 'extended exposure time' reactor.
• Extended gas residence time is greatly enhanced by operation above atmospheric pressure.
• Both biopolymer oligomer decomposition and catalyst coke re-gasification are enhanced by elevating temperatures above the pyrolysis temperature. Catalyst which as been deactivated by carbon deposition or sulfur poisoning can be regenerated in an off-line process and returned to the catalyst bed. At some point catalyst regeneration is no longer effective in restoring activity and fresh catalyst is required.
• the bio-oil was input to the top of the reactor onto hot glass wool and glass beads with a flowing 95 vol% H 2 -5 vol% Ar gas mixture. Vaporized bio-oil and gas flowed over a 1.7 cm diameter/25 cm volume catalyst section consisting of -1 mm/+0.5 mm crushed Sud Chemie Meth-134 catalyst (nickel on alumina).
• Thermocouples were placed in the glass bead vaporization section, near the middle of the catalyst section and near the exit of the catalyst section as per FIG 4.
• Bio-oil vaporization temperatures of about 430°C and a catalyst mid-point temperature of about 460°C did not result in the detection of napthalenic compounds in condensate water.
• Initial traces of naphthalenic compounds were detected in Run F which operated with a catalyst mid-point temperature of about 570°C and bio-oil vaporization temperatures of about 548°C.
• One aspect of the present embodiment concerns a method for converting biomass to methane and light hydrocarbons with low levels of depositable tars, comprising:
• step b) passing the hot pyrolysis gas mixture containing hydrogen through a first section of a catalytic reactor to form a methane, steam and light hydrocarbon enriched gas stream at a temperature above step a) and less than about 650°C without the addition of air or oxygen to induce the temperature rise;
• step c) providing an extended gas residence time within a second section of the catalytic reactor and at temperatures above the temperature of step a) and below about 650°C;
• Another aspect of the present invention comprises using an extended gas residence time in the catalytic conversion reactor of from about 10 seconds to about 10 hours. Another aspect of the present invention comprises using an extended gas residence time in the catalytic conversion reactor of from about 1 minute to about 1 hour.
• Another aspect of the present invention comprises maintaining hydrogen gas in the catalytic conversion reactor.
• Another aspect of the present invention comprises recovering and recycling hydrogen back to the process.
• Another aspect of the present invention comprises performing thermal pyrolysis of biomass using flowing hydrogen gas as a sweep gas.
• Another aspect of the present invention comprises using an impure hydrogen sweep gas containing significant fractions of hydrogen, steam, methane, carbon oxides or other non-oxygen gas.
• Another aspect of the present invention comprises performing thermal pyrolysis under conditions considered to be flash pyrolysis, fast pyrolysis or rapid pyrolysis.
• Another aspect of the present invention comprises performing thermal pyrolysis in an auger fast pyrolysis reactor.
• Another aspect of the present invention comprises inducing thermal pyrolysis by contacting pre -heated solid particles with biomass particles in an oxygen deficient atmosphere.
• Another aspect of the present invention comprises performing thermal pyrolysis using fluidized bed, bubbling fluidized bed or circulating fluidized bed pyrolysis processes.
• Another aspect of the present invention comprises performing thermal pyrolysis using ablative or rotating cone processes.
• Another aspect of the present invention comprises enhancing pyrolysis vapor production by using finely divided catalytic materials mixed with the input biomass feed.
• Another aspect of the present invention comprises enhancing pyrolysis vapor production by using catalytic or catalyst-coated media within the pyrolysis reactor. Another aspect of the present invention comprises performing one or more non-catalytic process steps between steps a) and b) to chemically remove impurities in the hot pyrolysis gas mixture.
• Another aspect of the present invention comprises performing one or more non-catalytic process steps between steps a) and b) to physically remove impurities such as char and ash entrained in the hot pyrolysis gas mixture.
• Another aspect of the present invention comprises using a catalyst comprising nickel on an alumina support.
• Another aspect of the present invention concerns using catalysts that are supported catalysts incorporating metals, metal oxides or metal sulfides having enhanced methane forming activity and a support active for the cracking of oxygenated hydrocarbons.
• Another aspect of the present invention comprises using catalysts that contain metals, metal oxides or metal sulfides with activity towards the formation of methane, where the metal is selected from Ni, Pt, Rh, Ru, Pd, La, Co, Mo, Cr, Fe, W or mixtures thereof.
• Another aspect of the present invention comprises using catalysts promoted with alkali or alkali earth oxides, ceria, zirconia, hafnia or mixtures thereof with enhanced activity for coke gasification by steam.
• Another aspect of the present invention comprises using a catalyst wherein the catalyst support is alumina, aluminosilicate, titania, zirconia, hafnia, ceria, zirconium silicate, aluminum phosphate, silica or zeolites with activity towards cracking oxygenated hydrocarbons.
• the catalyst support is alumina, aluminosilicate, titania, zirconia, hafnia, ceria, zirconium silicate, aluminum phosphate, silica or zeolites with activity towards cracking oxygenated hydrocarbons.
• Another aspect of the present invention comprises using a catalyst where the catalyst support is alumina, aluminosilicate, titania, zirconia, hafnia, ceria, zirconium silicate, aluminum phosphate, silica or zeolites with activity towards coke re- gasification with steam.
• the catalyst support is alumina, aluminosilicate, titania, zirconia, hafnia, ceria, zirconium silicate, aluminum phosphate, silica or zeolites with activity towards coke re- gasification with steam.
• Another aspect of the present invention comprises cooling after step b) to maintain reaction temperatures below about 650°C.
• Another aspect of the present invention comprises performing steps b) and c) with an H/C ratio of greater than about 5.5 to reduce coke formation.
• Another aspect of the present invention comprises performing steps b) and c) with an O/C ratio of less than about 2.5.
• Another aspect of the present invention comprises performing steps b) and c) with an O/C ratio of less than about 2.
• Another aspect of the present invention comprises performing steps b) and c) with an O/C ratio of less than about 1.8.
• Another aspect of the present invention comprises performing steps b) and c) in a single reactor.
• Another aspect of the present invention comprises performing b) and c) in separate reactors.
• Another aspect of the present invention comprises circulating catalyst from reactor sections performing step c) to reactor sections performing step b).
• Another aspect of the present invention comprises circulating catalyst from a reactor performing step c) to a reactor performing step b).
• Another aspect of the present invention comprises performing step b) in a circulating fluidized bed or riser reactor.
• Another aspect of the present invention comprises circulating catalyst by mechanical or gas entrained flow means.
• Another aspect of the present invention comprises employing an additional catalyst bed after step c) to perform additional hydrodeoxygenation of residual oxygenated aromatic or oxygenated hydrocarbon compounds remaining in the gas stream after step d).
• Another aspect of the present invention comprises employing an additional catalyst bed after step c) to perform partial steam reforming of the methane product with subsequent shift reaction to create hydrogen for recycle back to the process after product separation.
• Another aspect of the present invention comprises inputting hydrogen to step a) and/or step b), wherein the hydrogen is:

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• 2013
  • 2013-02-26 EP EP13876228.1A patent/EP2961720A4/de not_active Withdrawn
  • 2013-02-26 CA CA2901767A patent/CA2901767A1/en not_active Abandoned
  • 2013-02-26 WO PCT/US2013/027804 patent/WO2014133486A1/en active Application Filing

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