(421a) A General Framework for the Evaluation of Direct Nonoxidative Methane Conversion Strategies

Natural gas is a versatile and clean chemical
feedstock. The majority of natural gas is currently used for electricity
generation, heating and cooking, and it is underutilized as a feedstock for the
production of liquid transportation fuels and chemicals, including synthetic
materials and plastics. The development of natural gas conversion technologies
has recently attracted significant attention due to the
increase of natural gas supply in the United States and low natural gas prices
relative to crude oil. The conversion of natural gas into chemicals presents a
promising mean of utilizing an abundant resource, while achieving energy
security and mitigating pollutant emissions. Yet, the direct conversion of
methane to olefins and higher hydrocarbons is still at the basic research level
and it is unclear which, and to what extent, these technologies must be
improved to develop a commercial process.

In
this work, we study single-step natural gas conversion technologies that
directly convert methane to olefins and higher hydrocarbons. Despite the
relative simplicity of these technologies, the development of processes based
on these approaches remains challenging. Accordingly, we utilize process
synthesis and modeling to assess the economic feasibility of direct nonoxidative methane conversion strategies. We first
develop an integrated strategy, which is a significant undertaking because any
strategy employing a nonoxidative catalytic system
must include compression and separation sections for product recovery and
purification as well as recovery and recycle of unreacted methane, along with
refrigeration, power generation, and utility sections. We then develop a
flexible approach that allows for the systematic evaluation of various
technology alternatives and for the identification of the key technology gaps
that must be overcome. The key variables we considered include conversion
temperature, methane one-pass conversion, hydrocarbon products selectivities, and natural gas feed rate. We also develop
surrogate unit models and a database that allows to easily calculate key flows.
The results of our analyses (see Figure 1) demonstrate that an economically feasible
direct methane conversion process is contingent upon fundamental research
advances in the area of catalytic conversion to increase methane conversion to
hydrocarbon products (e.g., coke formation less than 20% and a minimum
conversion to products of 25%). Upon this development, further efforts can be
devoted to improve ethylene selectivity as well as reduce catalyst cost and
overall capital costs.

Figure 1. Impact of Key Process
Variables on Process Economics. Impact of methane one-pass
conversion and (a) conversion temperature on NPV, (b) hydrocarbon products
selectivity/coke selectivity on NPV, (c) ethylene selectivity in hydrocarbon
products on NPV, and (d) ethylene selectivity in hydrocarbon products on MESP.

References

Huang, K.; Miller, J.B.; Huber, G.W.;
Dumesic, J.A.; Maravelias, C.T.; 2018. A General Framework for Evaluation of
Direct Nonoxidative Methane Conversion Strategies. Joule 2, 349-365.