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2013|14 Annual Report Fraunhofer IGB

124 ENZYME TECHNICAL PRODUCTION OF METHANOL AND FORMIC ACID FROM FORMALDEHYDE Dipl.-Ing. Matthias Stier, Prof. Dr. rer. nat. Dieter Bryniok Reutilizing substances from biogas Currently biogas is used mainly as an energy carrier for the production of heat and electricity. The energetic use of bio- gas is efficient when the heat is used sensibly all year round. However, this is not the case with all biogas plants. That is why for a long time there has been research into possibili- ties for reutilizing substances from biogas – which consists of approx. 40 to 75 percent methane, 25 to 55 percent carbon dioxide and 10 percent water – for example for the produc- tion of methanol. However, so far neither chemocatalytic nor biotechnological approaches have been very promising. In the joint project “ECOX – Enzymatic-chemocatalytic oxi- dation cascades in the gas phase” in cooperation with the Leibniz Institute for Catalysis LIKAT in Rostock and the Martin Luther University in Halle, chemical and biotechnological reac- tion steps are combined in such a way that biogas can be con- verted as efficiently as possible to methanol and formic acid (Fig. 1). The aim here is also to lay the foundations for further processes for the conversion of gaseous substrates. Combination of chemocatalytic and enzymatic conversion The solution is to be found in the combination of a chemo- catalytic conversion of methane to formaldehyde, which is being developed by the project partners, and the subsequent disproportionation of the formaldehyde to methanol and formic acid by means of a formaldehyde dismutase from Pseudomonas sp. in an enzyme reactor (Fig. 2). The enzyme technical step is being developed at the Fraunhofer IGB. The formic acid produced in the enzyme reactor can be used as a recoverable substance, returned to the catalytic process or converted to methyl formate. In this process, methyl formate is formed directly from methanol and formic acid in aqueous solution. If the formic acid is returned to the process, the re- sulting chemical analysis indicates 4 moles of methanol from 3 moles of methane, 1 mole of carbon dioxide and 2 moles of water. In this endothermic process the enthalpy of combustion for 4 moles of methanol is higher than that of the converted biogas with 3 moles of methane. Enzyme reactor – immobilization of the dismutase In the studies carried out so far we have succeeded in obtain- ing the formaldehyde dismutase from both the wild-type strain and from several recombinant strains as a storable enzyme with long-term stability. The enzyme was bound to various carrier materials. This resulted in enzyme activities of 0.0088 – 0.028 micromoles per minute per milligram of the carrier material. The catalytic half-life is 155 days. Enzymes were applied to the carrier with a defined spatial orientation by means of genetic modification, thus increasing the activity one hundred times. Automated pilot plant for gas phase reactions To develop the process technology, a fully automated test facility for gas phase reactions was designed and set up (Fig. 2) in which the temperature and the pressure can be precisely controlled. The concentrations of both the substrate formal- dehyde and of the products is measured with an online mass spectrometer. By means of a special membrane module it is ENERGY 1 enthalpy of combustion of methane: –890.4 kJ / mole => –2671.2 kJ enthalpy of combustion of methanol: –726.4 kJ / mole => –2905.6 kJ 3 CH4 methane 1 CO2 carbon dioxide 2 H2O water 4 HCOOH formic acid 4 CH3OH methanol 4 H2O water 8 CH2O formaldehydechemocatalysis in membrane reactor enzyme reactor material separation possible reaction to 4 H2 + 4 CO2

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