Bioconversion of natural gas to iso-butanol : Engineering considerations for commercialization
The low cost and abundant supply of natural gas have been motivators for the development of many technologies that convert this low cost carbon feedstock into compounds of greater value. Natural gas bioconversion is an example of a developmental technology which exploits a methanotroph, a methane consuming bacteria, by applying synthetic biology to program it to produce higher value materials of interest, such as biofuels or terpenes. Intrexon Energy Partners was formed as a joint venture to commercialize the production of isobutanol from natural gas using a methanotroph. Currently, the production of both isobutanol and farnesene has been demonstrated in lab scale fermentation. However, to successfully bring this technology to commercial scale, consideration must be given not only to optimizing the metabolic pathway engineered into the methanotroph, but to key issues in the fermentor design and downstream processing. Since the substrate is a gas, the design of the fermentor must be optimized for effective mass transfer of the natural gas to the liquid phase for increased bioavailability. Isobutanol is toxic to the organism above a certain level, so the process must also be designed to continuously remove isobutanol in order to maintain the fermentor concentration below the toxic threshold. Downstream processing must take into consideration purification of the isobutanol and removal of fermentation byproducts and contaminants. Process selection must weigh the efficiency and selectivity of technology options, while at the same time utilize as much mature technology as possible to minimize risk. The project team has performed numerous design reviews known as Front End Loading (FEL) to develop process criteria and scenarios that will be applied to the first demonstration plant.