Biochemical conversion of CO2 in fuels and chemicals: status, innovation, and industrial aspects

Carbon dioxide levels in the earth atmosphere have been rising to alarming levels over the past few decades by human activity and thus caused global climate change due to the “greenhouse effect,” which in turn brought about adverse effects on the planet. Major sources of carbon dioxide (CO2) emissions include fossil fuel combustion, land-use change, industrial processing, respiration of various life forms, and decomposition of biomass. However, over the past 20 years, there has been a continuous research effort on the reducing carbon dioxide levels, by converting into the syngas, methanol, dimethyl carbonate, epoxides, polymers, and fine chemicals through chemical catalytic or biotransformation routes. Biological conversion including microbial and/or enzymatic conversion holds high potential as an alternative to the energy-intensive chemical conversion of CO2. Besides being the low energy process, bio-conversion of CO2 offers several unique advantages such as an easy and improved production at a high scale with a better conversion rate, the possibility of a diverse product range, and hyper-production by genetic modifications with zero competition for land with food crops. To this end, products that use CO2 biotransformation by the global biotech and chemical industry are only about 11.5 million tons annually, and it is a very small fraction of the approximately 24 billion tons of annual CO2 emission. Hence, there is an enormous scope for generation of high end biorefineries through CO2 bioconversion systems. Here, we review the various production sources of CO2, the metabolic and enzymatic CO2 conversion pathways, and the commercialization potentiality of various green chemicals from CO2.