How is bio-based isoprene typically produced from renewable feedstocks?

Bio-based isoprene is typically produced from renewable feedstocks through a multi-step process involving microbial fermentation and chemical conversion. The most common approach involves using sugars, such as glucose or xylose, derived from biomass like corn starch, sugarcane, or lignocellulosic materials. These sugars are fermented by genetically engineered microorganisms, often bacteria or yeast, to produce isopentenol (3-methyl-3-buten-1-ol) or other intermediate compounds. Metabolic engineering is used to enhance the production of these specific intermediates. The isopentenol is then chemically converted to isoprene through dehydration or other catalytic processes. This conversion step typically involves passing the isopentenol vapor over a solid acid catalyst at elevated temperatures. Another route involves the direct fermentation of sugars to isoprene using metabolically engineered microorganisms. While this direct route is more efficient in theory, it often suffers from lower isoprene yields and requires more complex metabolic engineering strategies. The produced bio-based isoprene can then be polymerized using conventional polymerization techniques to produce synthetic natural rubber (polyisoprene). For example, companies are using genetically modified E. coli bacteria to ferment sugars into isopentenol, which is then converted to isoprene using a metal oxide catalyst.