Lance L. Lobban

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.

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.

Multistage torrefaction and in situ catalytic upgrading to hydrocarbon biofuels: analysis of life cycle energy use and greenhouse gas emissions

A well-to-wheel life cycle assessment (LCA) model is developed to characterize the life cycle energy consumption and greenhouse gas emissions profiles of a series of novel multistage torrefaction and pyrolysis systems for targeted thermochemical conversion of short rotation woody crops to bio-oil and in situ catalytic upgrading to hydrocarbon transportation fuels, and to benchmark the results against a base-case fast pyrolysis and hydrodeoxygenation (HDO) platform. Multistage systems utilize a staged thermal gradient to fractionate bio-oil into product streams consisting of distinct functional groups, and multi-step chemical synthesis for downstream processing of bio-oil fractions to hydrocarbon fuels. Results at the process scale reveal that multistage systems have several advantages over the base-case including: (1) ∼40% reduction in process hydrogen consumption and (2) the product distribution for multistage systems are skewed towards longer carbon chain compounds that are fungible with diesel-range fuels. LCA reveals that the median Energy Return On Investment (EROI) and life cycle greenhouse gas (GHG) emissions for multistage systems range from 1.32 to 3.76 MJ-fuel/MJ-primary fossil energy and 17.1 to 52.8 gCO2e/MJ-fuel respectively, over the host of co-product scenarios and allocation schemes analyzed, with fossil-derived hydrogen constituting the principle GHG and primary energy burden across all systems. These results are compelling and indicate that multistage systems exhibit comparatively higher gasoline/diesel-range fuel yield relative to current technology, and produce a high quality infrastructure-compatible hydrocarbon transportation fuel capable of achieving over 80% reduction in life cycle GHG emissions relative to baseline petroleum diesel.

Combined steam reforming and dry reforming of methane using AC discharge

Publisher Summary This chapter discusses the combined dry and steam reforming of methane using the non-equilibrium plasma generated by an AC discharge. In the low temperature plasma combination of steam and dry reforming, H, OH, and O radicals help activate more methane molecules and increasing hydrogen abstraction from hydrocarbon species, prolonging the chain reactions. The O and OH radicals also help convert carbon to carbon oxides, preventing the hydrogenation of coke to produce methane and removing solid carbon from the discharge space. As a result, methane conversion in the combined steam and dry reforming of methane are much higher than that in the pure methane discharge or in the steam reforming discharge under similar experimental conditions. The results show a significant reduction in power consumption over either steam or dry reforming on their own. At the same consumed power, higher conversion is observed than in steam reforming alone, despite further dilution of methane. The lowest power consumption is 8eV per molecule of C converted, which is 50% lower than observed in combined steam reforming with partial oxidation of methane. An investigation of the bottom electrode configuration suggests an improvement to produce more H2 and CO which can further reduce energy consumption to an estimated 5eV per molecule of H2 produced, if the water gas shift reaction is taken into account. In addition, net production of CO2 is lowered from such a process and the requirement for CO2 removal from natural gas may be eliminated.

The effects of gas composition and process conditions on the oxidative coupling of methane over Li/MgO catalyst

Abstract The effects of CO2, steam, C2H6, and C2H4 partial pressures on oxidative methane coupling over a Li/MgO catalyst were studied under low conversion conditions in a fixed bed catalytic reactor. CH4:O2 ratios from 0.5 to 35 and temperatures from 973 K to 1073 K were used in the experiments and modeling. Results indicate CO2 has a poisoning effect on both COx and C2 formation rates, while selectivity to the C2 hydrocarbon was not significantly affected. Rate expressions rigorously derived from proposed mechanisms were obtained. The rate expressions agree well with the measured rates and predict well the high conversion experimental results under various reaction conditions. Results also indicated that addition of H2O to the feed enhanced the deactivation rate. The deactivation rate increased with increasing PH2O in the feed, and/or with increasing temperature. The deactivation rate was decreased by adding small amounts of CO2 to the reaction mixture. Results indicate that both CH4 conversion and C2 selectivity decrease with increasing C2H6 and C2H4 partial pressures in the feed.