Abstract
Increasing environmental awareness among the general public and legislators has driven this modern era to seek alternatives to fossil-derived products such as fuel and plastics. Addressing environmental issues through bio-based products driven from microbial fermentation of synthetic gas (syngas) could be a future endeavor, as this could result in both fuel and plastic in the form of bioethanol and polyhydroxyalkanoates (PHA). Abundant availability in the form of cellulosic, lignocellulosic, and other organic and inorganic wastes presents syngas catalysis as an interesting topic for commercialization. Fascination with syngas fermentation is trending, as it addresses the limitations of conventional technologies like direct biochemical conversion and Fischer–Tropsch’s method for the utilization of lignocellulosic biomass. A plethora of microbial strains is available for syngas fermentation and PHA production, which could be exploited either in an axenic form or in a mixed culture. These microbes constitute diverse biochemical pathways supported by the activity of hydrogenase and carbon monoxide dehydrogenase (CODH), thus resulting in product diversity. There are always possibilities of enzymatic regulation and/or gene tailoring to enhance the process’s effectiveness. PHA productivity drags the techno-economical perspective of syngas fermentation, and this is further influenced by syngas impurities, gas–liquid mass transfer (GLMT), substrate or product inhibition, downstream processing, etc. Product variation and valorization could improve the economical perspective and positively impact commercial sustainability. Moreover, choices of single-stage or multi-stage fermentation processes upon product specification followed by microbial selection could be perceptively optimized.
Highlights
The exploitation of fossil deposits for fuels and plastics has been considered a bane by succeeding generations, as these are the concerning causes of the ongoing environmental crisis, and it is believed that natural chaos is inevitable if this exploitation continues
This paper reviewed approaches that are being investigated for the production and fermentation of syngas
Insight has been provided on polymer production from the component of syngas through pure and mixed microbial colonies in single-stage and/or multistage cultures
Summary
The exploitation of fossil deposits for fuels and plastics has been considered a bane by succeeding generations, as these are the concerning causes of the ongoing environmental crisis, and it is believed that natural chaos is inevitable if this exploitation continues. The gasification strategy makes the FT process flexible towards feedstock variety, as a complex biomass including lignin could be accessed [3] Several limitations, such as the requirement of a high purity level of syngas to avoid catalyst poisoning; a strict ratio of H2:CO gases (2:1 for cobalt-based catalysts) to comply with the stoichiometry requirements of FT reactions, which may be challenging to achieve with feedstock diversity; and the poor selectivity of FT catalysts results in byproducts that require downstream attention, and high temperature and high pressure (over 7 MPa) operation, adding up the capital and operating costs of the process. The purification and composition optimization of syngas accounts for 60% to 70% of the total operational cost in the traditional FT process [2,3]
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