Sorption enhanced methanation of biomass

Abstract

Disclosed embodiments provide a system and method for producing hydrocarbons from biomass. Certain embodiments of the method are particularly useful for producing substitute natural gas from forestry residues. Certain disclosed embodiments of the method convert a biomass feedstock into a product hydrocarbon by hydropyrolysis. Catalytic conversion of the resulting pyrolysis gas to the product hydrocarbon and carbon dioxide occurs in the presence of hydrogen and steam over a CO 2 sorbent with simultaneous generation of the required hydrogen by reaction with steam. A gas separator purifies product methane, while forcing recycle of internally generated hydrogen to obtain high conversion of the biomass feedstock to the desired hydrocarbon product. While methane is a preferred hydrocarbon product, liquid hydrocarbon products also can be delivered.

1 . A method for converting a biomass feedstock into a product hydrocarbon, comprising:
 a. subjecting feedstock to fast pyrolysis or hydropyrolysis to generate fractions of pyrolysis gas and char;   b. converting at least a portion of the pyrolysis gas in a hydroconversion step to a product hydrocarbon and carbon dioxide over a catalyst in the presence of hydrogen and steam, while removing carbon dioxide by carbonation of a sorbent;   c. generating at least a portion of the hydrogen by steam reforming by reaction between steam and a portion of the pyrolysis gas or a product hydrocarbon;   d. separating hydrogen from the hydrocarbon product, and recycling the hydrogen so as to force hydroconversion of biomass into the hydrocarbon product; and   e. regenerating the sorbent in a regeneration step to release the carbon dioxide.   
     
     
         2 . The method of  claim 1 , in which subjecting the feedstock to fast pyrolysis or hydropyrolysis comprises hydropyrolysis. 
     
     
         3 . The method of  claim 1 , further comprising regenerating the sorbent by heating through combustion of the char and any coke deposited on the sorbent or catalyst. 
     
     
         4 . The method of  claim 1 , further comprising regenerating the sorbent by heating with superheated steam. 
     
     
         5 . The method of  claim 3 , further comprising regenerating or decoking the catalyst in regeneration step (e). 
     
     
         6 . The method of  claim 4 , further comprising regenerating or decoking the catalyst in regeneration step (e). 
     
     
         7 . The method of  claim 1 , in which the product hydrocarbon is methane, and where converting at least a portion of the pyrolysis gas includes a methanation step. 
     
     
         8 . The method of  claim 1 , in which the sorbent comprises CaO. 
     
     
         9 . The method of  claim 1 , where converting at least a portion of the pyrolysis gas occurs at a temperature in the range of from about 500° C. to about 650° C. 
     
     
         10 . The method of  claim 1 , where converting at least a portion of the pyrolysis gas occurs at a pressure in the range of from about 1 bara to about 50 bara. 
     
     
         11 . The method of  claim 1 , where regenerating the sorbent occurs at a temperature in the range of from about 700° C. to about 850° C. 
     
     
         12 . The method of  claim 1 , where separating hydrogen comprises pressure swing adsorption. 
     
     
         13 . The method of  claim 1 , where separating hydrogen comprises membrane permeation. 
     
     
         14 . The method of  claim 1 , further comprising providing the catalyst in any of the following reactor configurations so that the catalyst will cycle between distinct reaction zones for hydroconversion and regeneration steps:
 a. moving bed with granular catalyst;   b. fixed bed with granular packing or monolithic catalyst, and rotary or directional valve logic for cyclically switching beds between reaction and regeneration steps;   c. bubbling or circulating fluidized bed.   
     
     
         15 . The method of  claim 2 , further comprising providing staged reactors for hydropyrolysis and hydroconversion steps. 
     
     
         16 . The method of  claim 7 , further comprising performing hydropyrolysis and hydroconversion steps in a single bubbling fluidized bed reactor. 
     
     
         17 . The method of  claim 14 , in which hydroconversion is performed to produce liquid hydrocarbons, and a sorption enhanced reaction step is performed to generate hydrogen required for the hydroconversion step. 
     
     
         18 . The method of  claim 17 , in which the liquid hydrocarbons are produced as a first product of heavier hydrocarbons and a second product of gasoline range hydrocarbons. 
     
     
         19 . The method of  claim 17 , in which product methane is also produced in a hydroconversion step with sorption enhanced reaction. 
     
     
         20 . The method of  claim 1 , further comprising generating electrical power with an internal-reforming solid oxide fuel cell fuelled by methane and hydrogen converted from the biomass feedstock. 
     
     
         21 . The method of  claim 20 , in which substantially the entire anode exhaust of the solid oxide fuel cell is provided as the source of hydrogen and steam to hydropyrolysis step (a) or hydroconversion step (b). 
     
     
         22 . The method of  claim 1 , further comprising generating power with a gas turbine to recover heat from regenerating the sorbent. 
     
     
         23 . A system for producing hydrocarbons from biomass, the system comprising:
 f. fast pyrolysis means operating at a process temperature less than about 650° C. for producing pyrolysis gas and char;   g. catalytic conversion means operating at a process temperature less than about 650° C. for converting the pyrolysis gas to hydrocarbons and hydrogen by hydroconversion over a catalyst and in presence of a CO 2  sorbent;   h. gas separation means for purifying a hydrocarbon product and for recycling hydrogen to the catalytic conversion means; and   i. means for regenerating the CO 2  sorbent to release the CO 2 .   
     
     
         24 . The system according to  claim 23  where the fast pyrolysis means includes a hydrogen sweep gas. 
     
     
         25 . The system according to  claim 23  in which a portion of the hydrogen is produced in a steam reforming zone. 
     
     
         26 . The system according to  claim 23  in which hydrocarbons converted over the catalyst are mainly methane, and the catalyst is in a methanation zone. 
     
     
         27 . The system according to  claim 26  in which a catalyst used in the steam reforming and methanation zones is the same catalyst. 
     
     
         28 . The system according to  claim 27  in which steam reforming and methanation zones are combined within a hydroconversion reactor. 
     
     
         29 . The system according to  claim 23  further comprising regeneration means for heating and regenerating the catalyst in a regeneration zone. 
     
     
         30 . The system according to  claim 29 , further comprising means for cyclically circulating or switching the catalyst between the hydroconversion and regeneration zones. 
     
     
         31 . The system according to  claim 30 , in which the catalyst is supported in fixed beds with switching valves to establish the hydroconversion and regeneration zones to which each bed is cycled. 
     
     
         32 . The system according to  claim 31 , in which the fixed beds containing the catalyst are mounted in a rotor with rotary valve ports sealingly engaged with fixed ports to establish the hydroconversion and regeneration zones to which each bed is cycled. 
     
     
         33 . The system according to  claim 28  wherein substantially all of the hydrogen is produced in the steam reforming zone or hydroconversion reactor.