Process for the production of chemicals

Abstract

A process for producing one or more chemical compounds comprising the steps of providing a bioelectrochemical system having an anode and a cathode separated by a membrane, the anode and the cathode being electrically connected to each other, causing oxidation to occur at the anode and causing reduction to occur at the cathode to thereby produce reducing equivalents at the cathode, providing the reducing equivalents to a culture of microorganisms, and providing carbon dioxide to the culture of microorganisms, whereby the microorganisms produce the one or more chemical compounds, and recovering the one or chemical compounds.

1 . A process for producing one or more chemical compounds comprising the steps of providing a bioelectrochemical system having an anode and a cathode separated by a membrane, the anode and the cathode being electrically connected to each other, causing oxidation to occur at the anode and causing reduction to occur at the cathode to thereby produce reducing equivalents at the cathode, providing the reducing equivalents to a culture of microorganisms, and providing carbon dioxide to the culture of microorganisms, whereby the microorganisms produce the one or more chemical compounds, and recovering the one or chemical compounds. 
     
     
         2 . A process as claimed in  claim 1  wherein the microorganisms that form the one or more chemical compounds are present in the cathode compartment, and the process comprises causing oxidation to occur at the anode and causing reduction to occur at the cathode, wherein carbon dioxide is supplied to the cathode compartment, and the microorganisms produce the one or more chemical compounds, and recovering the one more chemicals from the cathode compartment. 
     
     
         3 . A process as claimed in  claim 1  wherein the bioelectrochemical system includes a power supply in the electrical circuit. 
     
     
         4 . A process as claimed in  claim 1  wherein the carbon dioxide acts as a carbon-containing feed material to the microorganisms that receive the reducing equivalents from the cathode or are present in the cathode compartment and the carbon dioxide comprises the only carbon-containing feed component supplied to the microorganisms. 
     
     
         5 . A process as claimed in  claim 1  wherein the carbon dioxide acts as a carbon-containing feed material to the microorganisms that receive the reducing equivalents from the cathode or are present in the cathode compartment and the carbon dioxide is used in conjunction with other organic materials by the microorganisms to produce the chemicals. 
     
     
         6 . A process as claimed in  claim 1  wherein the microorganisms provided to the cathode compartment or receiving reducing equivalents from the cathode compartment comprise a defined microbial culture containing one or more selected microbial species. 
     
     
         7 . A process as claimed in  claim 1  wherein the microbial species do not form methane in notable quantities when grown in the cathode. 
     
     
         8 . A process as claimed in  claim 1  wherein the microorganisms comprise a mixed, non-selected culture and the process further comprises the steps of producing the one or more chemicals in the cathode compartment and recovering the one or more chemicals from the cathode compartment whilst suppressing formation of methane in the cathode compartment. 
     
     
         9 . A process as claimed in  claim 8  wherein methane formation is suppressed by one or more of adding one or more chemicals to the cathode compartment that suppress the formation of methane or suppress the activity of the methanogenic organisms, operating the cathode compartment such that a low residence time is used in the cathode compartment, operating the cathode compartment at low pH, such as below 5.5, or periodically exposing the cathode compartment to air, oxygen or hydrogen peroxide. 
     
     
         10 . A process as claimed in  claim 1  wherein the bioelectrochemical system comprises a bioanode and a biocathode. 
     
     
         11 . A process as claimed in  claim 1  wherein one of the products formed in the anode compartment is carbon dioxide and this carbon dioxide is used as a feed to the cathode compartment. 
     
     
         12 . A process as claimed in  claim 1  wherein an anion exchange membrane separates the anode compartment from the cathode compartment. 
     
     
         13 . A process as claimed in  claim 12  wherein bicarbonate ions form in the cathode compartment and subsequently move through the anion exchange membrane to the anode compartment to thereby avoid increases in pH and/or salinity in the cathode compartment that could kill the microorganisms. 
     
     
         14 . A process as claimed in  claim 1  wherein the membrane separating the anode and the cathode comprises a porous membrane that allows liquid and ions to pass therethrough but prevents microorganisms from passing therethrough. 
     
     
         15 . A process as claimed in  claim 14  wherein the anode is operated as a bioanode and a waste stream is used as a feed material to the anode and during normal operation liquid passes through the porous membrane from the anode into the cathode chamber, and protons generated in an anode reaction are transported through the membrane to the cathode compartment and react with the hydroxyl ions generated in a cathode reaction in accordance with equation (4) to thereby avoid an undesirable increase in the pH in the cathode compartment:
   H + +OH − →H 2 O  (4)
 
 
     
     
         16 . A process as claimed in  claim 15  wherein pH and salt concentration in the cathode chamber remain stable and homeostasis is maintained. 
     
     
         17 . A process as claimed in  claim 1  wherein the bioelectrochemical system is operated with a biocathode only. 
     
     
         18 . A process as claimed in  claim 17  wherein an acid solution is provided to the anode compartment and the anode reaction comprises a proton generating reaction, and the membrane comprises a cation exchange membrane and protons migrate through the cation exchange membrane and react with the hydroxyl ions generated in the cathode reaction. 
     
     
         19 . A process as claimed in  claim 1  wherein the membrane separating the anode and the cathode comprises a bipolar membrane. 
     
     
         20 . A process as claimed in  claim 19  wherein the bipolar membrane is composed of a cation exchange layer on top of an anion exchange layer and the anion exchange layer is directed towards the anode chamber and the cation exchange layer is directed towards the cathode chamber such that when electrical current flows, water diffuses in between layers of the bipolar membrane and is split into protons and hydroxyl ions, and the hydroxyl ions migrate through the anion exchange layer into the anode chamber where they compensate for the proton production in the anode reaction and the protons migrate through the cation exchange layer into the cathode chamber where they compensate for hydroxyl ion production (or proton consumption) in the cathode reaction. 
     
     
         21 . A process as claimed in  claim 1  wherein the effluent of the anode contains carbon dioxide and the effluent from the anode is sent to a stripping column or membrane unit to recover gaseous carbon dioxide for supply to the cathode as a gas. 
     
     
         22 . A process as claimed in  claim 21  wherein effluent from the anode is passed through a membrane unit to allow separation of carbon dioxide from the anode effluent, the membrane unit having a liquid flow on the other side of the membrane such that the separated carbon dioxide goes into solution in the fluid on the other side of the membrane and the carbon dioxide is provided to the cathode in dissolved form. 
     
     
         23 . A process as claimed in  claim 22  wherein the fluid passing through the membrane unit on the other side of the anode fluid comprises cathode fluid. 
     
     
         24 . A process as claimed in  claim 22  wherein the anode effluent is sent through a membrane unit to allow carbon dioxide together with organic constituents of the anode effluent to pass to a second liquid and the second fluid is sent to the cathode where reduction of the organics occurs. 
     
     
         25 . A process as claimed in  claim 1  wherein a mixture of chemicals is formed in the cathode compartment and the process further comprises the steps of removing a mixture of chemical compounds from the cathode compartment and separating the mixture of chemical compounds into two or more streams. 
     
     
         26 . A process as claimed in  claim 1  wherein the cathode compartment is filled with the microbial culture and the microbial culture is part of an aqueous mixture in the cathode compartment, or the microbial culture grows on the electrode surface or the cathode compartment is filled with part of the microbial culture and another part of the microbial culture grows on the electrode surface. 
     
     
         27 . A process as claimed in  claim 1  wherein the cathode compartment comprises a first compartment housing the cathode, the first compartment including a redox shuttle, and a second compartment containing one or more microorganisms, wherein the redox shuttle is reduced in the first compartment and a reduced redox shuttle is provided to the second compartment, the second compartment containing microorganisms that use the reduced redox shuttle as an electron donor to facilitate formation of the one more chemicals. 
     
     
         28 . A method as claimed in  claim 27  wherein the reduced redox shuttle is converted to an oxidised redox shuttle in the second compartment and the oxidised redox shuttle is returned to the first compartment. 
     
     
         29 . A process as claimed in  claim 1  wherein the chemical compounds that are formed include:
 alcohols such as methanol, ethanol, propanol, butanol, isobutanol 
 carboxylic acids, such as formic acid, acetic acid, propionic acid, butyric acid, lactic acid, 
 diols such as 1,3-propanediol and 1,2-propanediol, 
 biopolymers such as poly-β-hydroxybutyrate (PHB). 
 
     
     
         30 . A process as claimed in  claim 1  wherein the chemical compound being formed comprises butanol and the bioelectrochemical system includes chemolithoautotrophic bacteria at the cathode that produce butanol according to equation (2):
   4CO 2 +24H + +24 e   − →C 4 H 9 OH+7H 2 O  (2)
 
 
     
     
         31 . A process as claimed in  claim 1  wherein the carbon dioxide stream being fed to be cathode compartment is derived from an offgas stream or a flue gas stream from a burner or a boiler. 
     
     
         32 . A process as claimed in  claim 1  wherein a voltage is applied between the anode and the cathode of between 0 and 10 V, preferably between 0 and 1.5 V, more preferably between 0 and 1.0 V and a volumetric current density in the bioelectrochemical cell of between 0 and 10,000 A/m 3  of bioelectrochemical cell, preferably between 10 and 5,000 A/m 3  of bioelectrochemical cell, more preferably between 100 and 2500 A/m′ of bioelectrochemical cell and/or an area specific current density of between 0 and 1,000 A/m 2  membrane surface area, preferably between 1 and 100 A/m 2  membrane surface area, more preferably between 2 and 25 A/m 2  membrane surface area, is obtained. 
     
     
         33 . A process as claimed in  claim 1  wherein the carbon dioxide stream being fed to the cathode compartment comprises biogas containing a mixture of methane and carbon dioxide or the carbon dioxide being fed to the cathode is be derived from a coal seam or layer, in which carbonate rich fluid is pumped from the coal seam through the cathode compartment. 
     
     
         34 . A process as claimed in  claim 1  wherein carbon dioxide is provided to the cathode compartment via diffusion or transport from the anode of the bioelectrochemical system. 
     
     
         35 . A process as claimed in  claim 1  wherein the cathode is also provided with organic molecules to assist in the production of the biochemicals. 
     
     
         36 . A process as claimed in  claim 35  wherein the organic molecules are selected from glycerol, glucose, lactate, propionate and butyrate. 
     
     
         37 . A process as claimed in  claim 36  wherein glycerol is added and product formation includes 1,3-propanediol or butanol, and glycerol is added to the cathode compartment, to the anode compartment or to both. 
     
     
         38 . A process as claimed in  claim 37  wherein the glycerol can also be partly converted to propionate prior to entry in the bioelectrochemical system, and subsequently added to the cathode as a mixture of glycerol and propionate. 
     
     
         39 . A process as claimed in  claim 1  wherein redox mediators are added to the cathode fluid, allowing transport of electrons from the cathode to the microorganism. 
     
     
         40 . A process as claimed in  claim 39  wherein the redox mediators are selected from methyl viologen, neutral red, phenazine carboxamide, amido black or mixtures of two or more thereof.