Enzyme Cocktail Turns Biomass Into Hydrogen

Corn stover could be a new source of hydrogen gas, thanks to a carefully selected cocktail of enzymes.

AsianScientist (Apr. 17, 2015) – A cocktail of more than 15 enzymes is able to turn corn byproducts into hydrogen cheaply and efficiently. The results, published in the Proceedings of the National Academy of Sciences, make the hydrogen economy more feasible.

The hydrogen economy envisions a future of high energy efficiency and nearly zero pollution. However, most hydrogen is currently produced from fossil fuels such as natural gas and coal, resulting in net greenhouse gas emissions. Existing hydrogen production facilities are equipped with high-temperature and high-pressure reactors that require high capital investment and large scale facilities. They cannot be scaled down to produce environmental friendly and affordable hydrogen for local users.

Although a few solutions are proposed to produce carbon-neutral hydrogen in distributed facilities, few solutions are practical considering output, production efficiency, production cost and capital investment. For example, water electrolysis is costly because of high price tags of electricity (i.e., more than 5 cents/KWh) and solar spitting powered by sunlight suffers from slow reaction rate and low photo-to-chemical energy efficiency. Producing hydrogen from less expensive and evenly distributed biomass is an attractive research subject.

Professor Zhang Yiheng affiliated with Tianjin Institute of Industrial Biotechnology of Chinese Academy of Sciences, and his co-workers in the US, have developed an enzyme cocktail containing more than 15 enzymes which can produce hydrogen from both glucose and xylose of corn stover, one of the most abundant agricultural remains in the world.

A commercial cellulase cocktail was used to hydrolyze biomass including cellulose and hemicellulose to glucose and xylose, respectively. The glucose and xylose accounted for more than 95 percent biomass sugars. This method could produce nearly 12 moles of hydrogen from one glucose and 10 moles of hydrogen from one xylose by using enzyme cocktails, three-times of the yield from hydrogen-producing microorganisms.

By using the enzyme cocktail instead of microorganism, hydrogen yield was increased two times. By using mathematical modeling and validated predictions, hydrogen production efficiency was optimized with an increase of 67 times to 54 mmole of hydrogen per L per hour. This hydrogen production reaction rate is 15 times faster than the biological hydrogen generation rate and is fast enough for industrial production.

Furthermore, instead of the complicated carbon flux regulation in microorganisms, the enzyme cocktail could utilize both glucose and xylose at the same time. This bioprocess mediated by in vitro artificial enzymatic pathway meets three biomanufacturing criteria of titer, rate and yield at the same time.

This bioprocess could become the solution to produce affordable green hydrogen from renewable energy resources, which benefits regional social and economic development. The process has advantages like low capital investment and high-purity hydrogen generation without carbon monooxide. Unlike ethanol fermentation which requires high concentration sugar solutions, this process produces and separates hydrogen from low concentration sugar solutions easily which decreases the production cost.

The article can be found at: Rollin et al. (2015) High-Yield Hydrogen Production from Biomass by in vitro Metabolic Engineering: Mixed Sugars Coutilization and Kinetic Modeling.


Source: Chinese Academy of Sciences.
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