Direct Microwave Plasma Conversion of Methane to Higher Hydrocarbons and Carbon Materials

With the discovery of vast quantities of natural gas in shale formations in the U.S. comes the opportunity to convert this gas into value-added chemicals. Practical and cost-effective conversion technologies are needed to more wisely, cleanly (without CO2 production or water consumption) and efficiently use natural gas. As the capital cost of state-of-the art chemical plants continues to grow, smaller distributed modular plants that can be deployed closer to rural gas fields offer economic advantages. Advanced conversion concepts are especially needed to utilize "economically stranded" gas associated with oil production which is wastefully and harmfully flared. These challenges will be addressed by utilizing a novel non-thermal (microwave) plasma process to convert methane into industrial chemicals such as ethylene, acetylene, and others with virtually zero process CO2 emissions, no water consumption, high methane conversion yield, high selectivity, and lower capital costs than existing state of the art. Phase I demonstrated rapid, continuous, direct (single-step) conversion of methane to acetylene, hydrogen, and carbon, as well as the ability to catalytically hydrogenate and/or polymerize acetylene to higher hydrocarbons including C3s and C4s in an integrated reactor stage without the need for extra hydrogen. This electrically-powered process has low bulk temperatures, proceeds at ambient pressures, emits zero CO2, and can be powered by renewable electricity. The process can target different stream compositions via a change of parameters (e.g. energy inputs, gas flows, compositions, mixing patterns, residence times, and specific reactor configuration). Co-production of high-value, premium carbon products (including graphene platelets) has been demonstrated with clear economic and process advantages over existing state of the art. In the first 6 months of Phase II, a skid-mounted pilot system will be designed and built to evaluate process parameters for industrial scale-up. The system will integrate a modular microwave reactor system without microwave plasma containment (already demonstrated during Phase I) with adequately sized and powered microwave and process gas inputs. In the following 9 months, extensive testing will (i) evaluate key process parameters such as energy efficiency and product yields across a range of conditions and (ii) demonstrate the stability of the process in an industrially relevant setting. Finally, conceptual designs and techno-economics will be developed for several commercial scales, including a next scale demonstration system targeting platform chemicals and premium carbons. The pilot will support future studies and feasibility tests, and will be capable of commercial carbon production at 2 metric ton/year capacity. With lower-energy requirements than conventional thermal plasmas, reactions in microwave plasmas are driven by electron kinetics rather than thermodynamics, and their non-uniform, non-equilibrium energy distributions allow reaction pathways that are unavailable with conventional chemical or thermal plasma processes. Microwave plasmas also offer reaction intensification that enables reductions in system costs and the production of smaller, portable, modular, reactor systems that can produce industrial chemicals and premium carbons directly from natural gas with less capital and infrastructure expenditure than state of the art. This process could also displace the GHG-intensive ethane and/or naphtha-cracking and steam-methane reforming processes for industrial production of ethylene, hydrogen, and other chemicals.