This column is based on “Bio-Butanediol Production from Glucose,” a report published by Intratec. It can be found at: www.intratec.us/analysis/butanediol-production-cost.
Butanediol (BDO) refers to all butylene glycol isomers. The most common isomer — 1,4-butanediol — is a versatile intermediate chemical used in the manufacture of plastics, elastic fibers and polyurethanes. Commercial processes for producing bio-based BDO from sugars have emerged in recent years as alternatives to petroleum-derived BDO. This one-page process description outlines the production of BDO by the fermentation of glucose.
The following paragraphs describe a process for bio-butanediol production from glucose (Figure 1) similar to the process described in patents issued to Genomatica Inc. (San Diego, Calif.; www.genomatica.com).
Medium preparation. The preparation of the culture media involves dilution tanks, pumps and sterilizers. The culture media used in the batch and fed-batch phases of pre-fermentation and fermentation are prepared by mixing process water, glucose and nutrients.
Fermentation. In the fermentation area, the applied recombinant microorganism is initially propagated in inoculum fermenters, then sent to seed fermenters to promote growth until the concentration required for the main fermentation is reached.
The main fermentation is performed in fed-batch mode under aerobic process conditions in agitated, jacketed fermenters. At the batch phase, the microbe seed is fed into the fermenters, previously filled with the fermentation batch medium. After glucose exhaustion, the batch phase ends, and the fed-batch phase begins.
During the fed-batch phase, glucose and nutrients are continuously supplied. When the desired butanediol concentration is achieved, the feeding is suspended and the fermentation gradually decreases until being interrupted. The fermentation temperature is controlled by circulating cooling water through the fermenter jackets. The pH is controlled by ammonia injection.
Separation. The fermentation broth is passed through a centrifuge that separates cells and other insoluble particles. The separated biomass is discharged, while the broth is directed to ultrafiltration, used to remove soluble organic impurities, residual cell bodies and suspended solids.
The permeate is carbon-treated using a nanofiltration step for salts separation, color removal and desalination. The retained salts and sugars are discarded, while the permeate liquid is sent to an ion exchange separation step for removal of inorganic cations and anions.
The butanediol solution from ion exchange is then concentrated by water evaporation. The evaporation is carried out in falling-film evaporators and a forced-circulation evaporative crystallizer. The concentrated solution obtained is directed to a purification stage. The overhead stream (mostly water) is condensed and recycled to the fermentation stage.
Purification. The concentrated solution is fed to a distillation column for light-end impurities separation, and the light ends are discarded. The bottoms product, comprising the BDO, is fed to another column, in which high-purity 99.5 wt.% BDO is recovered as the overhead stream.
Petroleum-derived BDO is mainly produced by continuous hydrogenation of the 2-butyne-1,4-diol over modified nickel catalysts. Figure 2 presents different BDO production pathways.
The total operating cost (raw materials, utilities, fixed costs and depreciation costs) estimated to produce BDO was about $2,100 per ton in 2014. The analysis is based on a plant in the U.S. with capacity to produce 75,000 metric tons per year of BDO.
Edited by Scott Jenkins
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