Novel Method for Conversion of Biomass to Fuel

Synthesis gas, a mixture of H2 and CO, is one of the top-ten platform chemicals produced from biomass and can be used to produce fuel-ethanol. However, existing heterogeneous catalysts have only a low selectivity for ethanol and produce too much low-value methane. As a result, the production of ethanol from syngas with heterogeneous catalysts is uneconomical. Our major breakthrough is the discovery of a homogeneous catalytic system that exhibits high selectivity for ethanol and produces one tenth the amount of methane as do heterogeneous catalysts. TDA Research has developed a homogeneous catalytic system that can produce ethanol from syngas at rates comparable to the best heterogeneous catalysts while producing less than 2-3% methane (heterogeneous catalysts produce 20-40% CH4). Our catalysts first convert syngas to methanol, which is homologized in-situ to ethanol. Acetic acid formed by CO-insertion into methanol reacts with methanol to form methyl acetate, which is subsequently hydrogenated to ethanol and methanol. The alcohols are separated downstream and the methanol is recycled. The only products exiting the reactor are ethanol, a small amount of 1-propanol, methanol (which is recycled) and a small amount of methane. At the same time, the water-gas shift reaction consumes water produced during alcohol synthesis to produce additional hydrogen. The goal of the Phase IIB project is to scale up our homogeneous syngas to ethanol process by a factor of 50 by designing and building a continuous flow reactor system. We have chosen a bubble column reactor to dissipate the large exothermic heat of reaction of ethanol synthesis. The bubble column will hold approximately 250 mL of homogeneous catalyst solution with another 250 mL in the circulation system. While obviously much smaller than an industrial reactor, this scale of reactor will sufficiently simulate a full scale bubble column so that we can make the kinetic and steady state measurements, and determine the heat and mass transfer characteristics of the system needed to perform a preliminary pilot plant design at the end of the Phase IIB project. Also, we will work with our industrial partners and perform a detailed techno-economic analysis of the process. Commercial Applications and Other Benefits: Corn based ethanol plants use a food to produce fuel. Thermochemical methods (such as our syngas-to-ethanol process) for making ethanol are attractive because they can use agricultural and other renewable (non-edible) waste streams to make ethanol.