Richard G. Mallinson

Comparative investigations on plasma catalytic methane conversion to higher hydrocarbons over zeolites

Abstract Zeolites are an important class of industrial catalyst. In this investigation, the application of zeolites for plasma catalytic methane conversion (PCMC) to higher hydrocarbons at very low gas temperatures (room temperature to 200°C) has been addressed. Zeolites NaY, HY, NaX, NaA, Linde Type 5A and Na-ZSM-5 have been tested for the application in PCMC. The products contain C2 hydrocarbons (acetylene, ethane and ethylene), other carbon species including carbon deposits and trace C+3 hydrocarbons, and syngas (H2+CO), depending upon co-reactant or dilution gases added to the feed. A streamer corona discharge, a cold plasma phenomenon, has been found to be the most effective and efficient at inducing plasma catalytic activity over zeolites. The order of the zeolites tested from good to poor for sustaining the desired streamer discharges is NaY,NaOH treated Y>HY>NaX>NaA>Linde Type 5A>Na-ZSM-5 . Oxygen, carbon dioxide, hydrogen (with or without oxygen added in a small amount), steam and nitrogen have been tested as co-reactants or dilution gases for PCMC over zeolites. Experimental results showed that the selectivity to higher hydrocarbons decreases in the order H2>H2+O2>H2O>N2>N2+O2>CO2>O2, while the methane conversion decreases in the order N2+O2>N2>O2>CO2>H2+O2>H2O>H2. All the co-reactants tested here, except hydrogen, can induce high methane conversions during plasma catalytic reactions. Small amounts of oxygen added to hydrogen can improve significantly the plasma reactivity of hydrogen over zeolites. This has led to a very selective net production of hydrogen and higher hydrocarbons (especially acetylene).

Methane conversion to higher hydrocarbons in a corona discharge over metal oxide catalysts with OH groups

Abstract The gas discharge promoted oxidative conversion of methane to higher hydrocarbons over various metal oxide and zeolite catalysts was investigated over a wide range of temperatures (373–973 K). The most significant gas discharge effects were observed over catalysts containing polar OH groups. Significant methane conversions and C 2 yields were achieved at temperatures sufficiently low that no intrinsic catalytic activity for C 2 production was found in the absence of gas discharge, and the lower the gas temperature, the greater was the observed gas discharge effect on methane conversion. It is believed that the gas discharge effects depend on the gas temperature, the concentration of the OH groups and the acidity and basicity of the OH groups on the catalysts. A possible reaction mechanism for gas discharge promoted catalysis is presented.

Partial Oxidation of Methane to Form Synthesis Gas in a Tubular AC Plasma Reactor

AC plasma discharges can produce valuable products, namely synthesis gas, from the partial oxidation of methane while maintaining low bulk gas temperatures. The products for this reaction are limited to synthesis gas, ethane, ethylene, acetylene, CO2, and water. The objective of the study is to maximize the partial oxidation of methane to synthesis gas and/or C2 species using both pure O2 and air and to minimize the electrical energy required for conversion.

Decoupling HZSM‐5 Catalyst Activity from Deactivation during Upgrading of Pyrolysis Oil Vapors

The independent evaluation of catalyst activity and stability during the catalytic pyrolysis of biomass is challenging because of the nature of the reaction system and rapid catalyst deactivation that force the use of excess catalyst. In this contribution we use a modified pyroprobe system in which pulses of pyrolysis vapors are converted over a series of HZSM-5 catalysts in a separate fixed-bed reactor controlled independently. Both the reactor-bed temperature and the Si/Al ratio of the zeolite are varied to evaluate catalyst activity and deactivation rates independently both on a constant surface area and constant acid site basis. Results show that there is an optimum catalyst-bed temperature for the production of aromatics, above which the production of light gases increases and that of aromatics decrease. Zeolites with lower Si/Al ratios give comparable initial rates for aromatics production, but far more rapid catalyst deactivation rates than those with higher Si/Al ratios.

THE PRODUCTION OF HYDROGEN FROM METHANE USING TUBULAR PLASMA REACTORS

The dc plasma catalytic system is very effective in the conversion of methane to hydrogen, acetylene, and carbon monoxide. Reducing the cross sectional area of the reactor decreased the amount of gas that was bypassing the streamer discharges resulting in an increase in methane conversion. Single pass methane conversions as high as 68% and hydrogen, acetylene, and carbon monoxide yields of 52%, 47%, and 21%, respectively, have been achieved. High hydrogen yields can be achieved under different conditions. The highest conversions were obtained with an oxygen concentration of 2% and a residence time of 2.6 seconds. Further work needs to be done to reduce the energy cost. The projected cost of hydrogen may be met by increasing conversion and the throughput of methane while maintaining similar power requirements. This could be accomplished by further minimizing bypassing to increase the overall efficiency of the plasma zone.

Methane Conversion in AC Electric Discharges at Ambient Conditions

Natural gas reserves, with methane as the primary constituent, are found in abundant quantities in different parts of the world. Industrial usage of natural gas is still limited to primarily a combustion fuel. The present industrial processes for the manufacture of methanol and other hydrocarbons from methane are economically feasible in areas where large reserves of natural gas are available. It is also not generally feasible to transport natural gas from remote places to areas of utilization. Therefore, to utilize such reserves economically, the conversion of methane to liquid products has been of great interest to many researchers.

Effects of gap and elevated pressure on ethanol reforming in a non-thermal plasma reactor

Production of hydrogen for fuel cell vehicles, mobile power generators and for hydrogen-enhanced combustion from ethanol is demonstrated using energy-efficient non-thermal plasma reforming. A tubular reactor with a multipoint electrode system operated in pulsed mode was used. Complete conversion can be achieved with high selectivity (based on ethanol) of H2 and CO of 111% and 78%, respectively, at atmospheric pressure. An elevated pressure of 15 psig shows improvement of selectivity of H2 and CO to 120% and 87%, with a significant reduction of C2Hx side products. H2 selectivity increased to 127% when a high ratio (29.2) of water-to-ethanol feed was used. Increasing CO2 selectivity is observed at higher water-to-ethanol ratios indicating that the water gas shift reaction occurs. A higher productivity and lower C2Hx products were observed at larger gas gaps. The highest overall energy efficiency achieved, including electrical power consumption, was 82% for all products or 66% for H2 only.

Plasma steam reforming of E85 for hydrogen rich gas production

E85 (85 vol% ethanol and 15 vol% gasoline) is a partly renewable fuel that is increasing in supply availability. Hydrogen production from E85 for fuel cell or internal combustion engine applications is a potential method for reducing CO2 emissions. Steam reforming of E85 using a nonthermal plasma (pulse corona discharge) reactor has been exploited at low temperature (200–300 °C) without external heating, diluent gas, oxidant or catalyst in this work. Several operational parameters, including the discharge current, E85 concentration and feed flow rate, have been investigated. The results show that hydrogen rich gases (63–67% H2 and 22–29% CO, with small amounts of CO2, C2 hydrocarbons and CH4) can be produced by this method. A comparison with ethanol reforming and gasoline reforming under identical conditions has also been made and the behaviour of E85 reforming is found to be close to that of ethanol reforming with slightly higher C2 hydrocarbons yields.

Relationships between Biomass Composition and Liquid Products Formed via Pyrolysis

Thermal conversion of biomass is a rapid, low-cost way to produce a dense liquid product, known as bio-oil, that can be refined to transportation fuels. However, utilization of bio-oil is challenging due to its chemical complexity, acidity, and instability—all results of the intricate nature of biomass. A clear understanding of how biomass properties impact yield and composition of thermal products will provide guidance to optimize both biomass and conditions for thermal conversion. To aid elucidation of these associations, we first describe biomass polymers, including phenolics, polysaccharides, acetyl groups, and inorganic ions, and the chemical interactions among them. We then discuss evidence for three roles (i.e., models) for biomass components in formation of liquid pyrolysis products: (1) as direct sources, (2) as catalysts, and (3) as indirect factors whereby chemical interactions among components and/or cell wall structural features impact thermal conversion products. We highlight associations that might be utilized to optimize biomass content prior to pyrolysis, though a more detailed characterization is required to understand indirect effects. In combination with high-throughput biomass characterization techniques this knowledge will enable identification of biomass particularly suited for biofuel production and can also guide genetic engineering of bioenergy crops to improve biomass features.

Selective hydrogenation of acetylene to ethylene during the conversion of methane in a catalytic DC plasma reactor

Plasma reactors have been found to be an effective technique for the activation of methane, the major component of natural gas, at low temperatures. The electric discharges produce energetic electrons that excite and decompose the feed gas molecules. Therefore, reactions are accomplished with relatively low power requirements. The catalyst, NaOH treated X and Y zeolite, enhances the production of electrons and the formation of methane radicals. Methane and hydrogen with oxygen as an additive are used as the feed mixture. Acetylene is the major product with hydrogen and carbon monoxide as by-products. However, the addition of metals to the catalyst can hydrogenate the acetylene to ethylene and ethane.