460057 Bioconversion of Natural Gas to Higher Value Chemicals: Engineering Considerations for Commercialization

Wednesday, November 16, 2016: 8:30 AM
Union Square 3 & 4 (Hilton San Francisco Union Square)
Christina Bodarky and Bryan Yeh, Intrexon, South San Francisco, CA

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 a developmental technology which applies synthetic biology to a naturally methane consuming bacteria, a methanotroph, to program it to produce higher value materials of interest. Intrexon has formed joint ventures to commercialize methanotrophic bioprocesses for biofuels and high value chemical intermediates. Biocatalytic processes which achieve high yields under milder processing conditions allow for reduced capital and operation expenditures while also offering greater economic viability. Currently, the production of both isobutanol and farnesene has been demonstrated in lab scale fermentation. 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, downstream processing and overall plant economics.

At any scale, aerobic natural gas fermentation must overcome the challenge of gas to liquid transfer of low solubility gases. Low gas to liquid mass transfer reduces the process productivity and yield, which in turn increases fermentor cost, process operating cost and may add additional equipment necessary to recycle gases. There are many fermentor designs currently available to increase the overall mass transfer coefficient of these gases; however, capital and operating expenditures of the reactor become a critical metric for evaluating commercialization feasibility. Unique fermentor configurations can greatly increase capital cost by raising the cost of fabrication and decreasing the ability to receive competitive bids. These unique fermentors also may not create a homogenous well-mixed reactor, which increases the cost of controls and instrumentation.

Downstream process selection for commercialization is a balance of capital cost, operating cost and the risk of cutting-edge over well-established techniques. Low fermentation broth concentrations of product increase the size and energy requirement of downstream equipment. Cutting-edge technologies can increase the efficiency of separation and reduce energy inputs, but these technologies can be capitally intensive and unproven at commercial scales. Bioprocesses also create metabolic byproducts which need to be evaluated for separation and purification to meet specifications for sale.

Favorable plant economics are necessary to move forward with commercialization of a technology. Scale is carefully selected based on a comparison of the production rate, fermentation productivity and yield targets to revenue, capital and operating costs. The plant location is also an important selection factor as costs are affected by utility rates in the area and/or co-location of the plant with shared infrastructure.

Traditional engineering workflows, such as a front-end loading strategy, were used to shape the commercial scale process design. The biologic, technical and economic commercial feasibilities of the end-to-end natural gas to isobutanol process were critical to Intrexon’s plant design. Laboratory scale learnings were applied to select technology that was commercially feasible at demonstration scale. This demonstration scale design was scaled down to pilot scale, where the operation will yield learnings into refinement of at-scale design, equipment selection, empirical data on heating and cooling, and controls strategies.

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