Conversion of biomass, organic waste and carbon dioxide into synthetic hydrocarbons

Abstract

A process and system for producing a synthetic hydrocarbon having a desired H/C ratio is disclosed. Organic material is biochemically digested in a two stage biodigester for separately producing a hydrogen containing biogas substantially free of methane in a first stage and a methane containing biogas in a second stage. The methane containing biogas is reformed in a first reformer to generate hydrogen gas and carbon monoxide gas, which are then combined in a mixer with the hydrogen containing biogas into a syngas in amounts to achieve in the syngas an overall H/C ratio substantially equal to the desired H/C ratio. The syngas is reacted with a catalyst in a second reformer, a Fischer-Tropsch (FT) reactor, to produce the hydrocarbon. Using a two stage biodigester allows for the generation of separate hydrogen and methane streams, a more economical generation of the FT syngas and reduced fouling of the FT catalyst.

What is claimed is: 
     
         1 . A process for producing a synthetic hydrocarbon having a desired H/C ratio, comprising the steps of
 a) subjecting organic material including biomass and microorganisms for anaerobic digestion to multiple stage anaerobic digestion for separately producing hydrogen containing biogas substantially free of methane in a first stage and methane containing biogas in a second stage, wherein to minimize growth of hydrogentrophic methanogens in the first stage, a solids retention time is decoupled from a liquid retention time in the first stage by recycling to the first stage solids separated from an effluent of the first stage,   b) reforming the methane containing biogas to generate hydrogen gas and carbon monoxide gas, and   c) combining the hydrogen containing biogas, the hydrogen gas, and the carbon monoxide gas into a syngas in amounts to achieve in the syngas an overall H/C ratio substantially equal to the desired H/C ratio; and   d) operating a Fischer-Tropsch synthesis by reacting the syngas with a catalyst to produce the synthetic hydrocarbon.   
     
     
         2 . The process of  claim 1 , wherein the biomass is lignocellulosic biomass and step
 a) comprises the further step of
 a1) subjecting the biomass to pretreatment selected from the group of extruder pretreatment for reducing particle size and cell lysis, chemical pretreatment, thermal pretreatment, thermochemical pretreatment, steam explosion pretreatment, dual stage or single stage hydrothermal pretreatment for hydrothermal liquefaction and hydrolysis of hemicellulose in the biomass, thermomechanical pretreatment, and combinations thereof. 
   
     
     
         3 . The process of  claim 1 , wherein in step a) the biomass includes one or more of cellulosic materials, lignocellulosic materials, an effluent from a lignocellulosic material processing plant, an effluent from a cellulosic material processing plant, an effluent from a paper plant, an effluent from an ethanol from biomass process, thin stillage, whole stillage, dry distillers grains, and waste water treatment sludge. 
     
     
         4 . The process of  claim 1 , wherein at least one of the hydrogen containing biogas and the methane containing biogas includes carbon dioxide. 
     
     
         5 . The process of  claim 1 , wherein the methane containing biogas is added into the syngas in step c), in an amount to achieve or maintain the overall H/C ratio in the syngas. 
     
     
         6 . The process of  claim 2 , wherein the methane containing biogas is added into the syngas in step c), in an amount to achieve or maintain the overall H/C ratio in the syngas. 
     
     
         7 . The process of  claim 1 , wherein in the first stage carbon dioxide is sequestered for rendering the hydrogen containing biogas substantially free of carbon dioxide. 
     
     
         8 . The process of  claim 1 , wherein in step b) the methane containing biogas is reacted with a catalyst to produce the hydrogen gas and the carbon monoxide gas. 
     
     
         9 . The process of  claim 7 , wherein the catalyst is a dry reforming catalyst, the methane containing biogas includes a methane component and a carbon dioxide component and both components are reacted with the dry reforming catalyst for dry reforming the methane into hydrogen and carbon monoxide. 
     
     
         10 . The process of  claim 8 , wherein additional carbon dioxide is reacted with the methane over the dry reforming catalyst, the additional carbon dioxide having been sequestered in step a), derived from another process, or captured from the atmosphere. 
     
     
         11 . The process of  claim 7 , wherein the catalyst is a wet reforming catalyst and the methane containing biogas is reacted with water in the presence of the wet reforming catalyst for wet reforming the methane into hydrogen and carbon monoxide. 
     
     
         12 . The process of  claim 1 , wherein in step b) the methane containing biogas is divided into a first portion and a second portion, the first portion is reacted with a dry reforming catalyst and carbon dioxide for dry reforming of the methane and the second portion is reacted with water and a wet reforming catalyst for wet reforming the methane. 
     
     
         13 . The process of  claim 11 , wherein a volume ratio of the first and second portions is adjusted for controlling the overall carbon monoxide/hydrogen ratio achieved by the combined dry reforming and wet reforming. 
     
     
         14 . The process of  claim 1 , comprising the further steps of sequestering carbon dioxide for producing the hydrogen containing biogas substantially free of carbon dioxide and generating additional hydrogen gas and oxygen gas by water electrolysis. 
     
     
         15 . The process of  claim 13 , wherein the additional hydrogen gas is reacted with carbon dioxide for producing carbon monoxide for use in the FT process. 
     
     
         16 . The process of  claim 13 , wherein the electrolysis uses any of excess electricity, renewable electricity and excess renewable electricity. 
     
     
         17 . The process of  claim 13 , wherein the additional hydrogen gas is added to the syngas for adjustment of the H/C ratio in the syngas directly ahead of step d). 
     
     
         18 . The process of  claim 13 , wherein the additional hydrogen gas and the oxygen gas are reacted for generating heat to be supplied to the reformer and/or the FT process.