Search

Direct nonoxidative methane conversion (DNMC) transforms CH4 to higher (C2+) hydrocarbons and H2 in a single step, but its utility is challenged by low CH4 equilibrium conversion, carbon deposition (coking), and its endothermic reaction energy requirement. This work reports a heat‐exchanged autothermal H2‐permeable tubular membrane reactor composed of a thin mixed ionic‐electronic conducting SrCe0.7Zr0.2Eu0.1O3–δ membrane supported on a porous SrCe0.8Zr0.2O3–δ tube in which a Fe/SiO2 DNMC catalyst is packed, that concurrently tackles all of these challenges. The H2‐permeation flux drives CH4 conversion. O2 from an air simulant (O2/He mixture) sweep outside the membrane reacts with permeated H2 to provide heat for the endothermic DNMC reaction. The energy balance between the endothermic DNMC and exothermic H2 combustion on opposite sides of the membrane is achieved, demonstrating the feasibility for autothermal operation using a simple air sweep gas. Moreover, the back diffusion of O2 from the sweep side to the catalyst side oxidizes any deposited carbon into CO. Thus, for the first time demonstrating all the desired attributes, a heat‐exchanged H2‐permeable membrane reactor capable of achieving single‐step auto‐thermal DNMC catalysis while simultaneously improving CH4 conversion and preventing coking is achieved. [ABSTRACT FROM AUTHOR]

Direct non‐oxidative methane conversion (DNMC) has been recognized as a single‐step technology that directly converts methane into olefins and higher hydrocarbons. High reaction temperature and low catalyst durability, resulting from the endothermic reaction and coke deposition, are two main challenges. We show that a millisecond catalytic wall reactor enables stable methane conversion, C2+ selectivity, coke yield, and long‐term durability. These effects originate from initiation of the DNMC on a reactor wall and maintenance of the reaction by gas‐phase chemistry within the reactor compartment. The results obtained under various temperatures and gas flow rates form a basis for optimizing the process towards lighter C2 or heavier aromatic products. A process simulation was done by Aspen Plus to understand the practical implications of this reactor in DNMC. High carbon and thermal efficiencies and low cost of the reactor materials are realized, indicating the technoeconomic viability of this DNMC technology. [ABSTRACT FROM AUTHOR]

Non-oxidative methane conversion over Fe©SiO2 catalyst was studied for the first time in a hydrogen (H2) permeable tubular membrane reactor. The membrane reactor is composed of a mixed ionic-electronic SrCe0.7Zr0.2Eu0.1O3−δ thin film (≈20 μm) supported on the outer surface of a one-end capped porous SrCe0.8Zr0.2O3−δ tube. Significant improvement in CH4 conversion was achieved upon H2 removal from the membrane reactor compared to that in a fixed-bed reactor. The Fe©SiO2 catalyst in the H2 permeable membrane reactor demonstrated a stable ≈30 % C2+ single-pass yield, with up to 30 % CH4 conversion and 99 % selectivity to C2 (ethylene and acetylene) and aromatic (benzene and naphthalene) products, at the tested conditions. The selectivity towards C2 or aromatics was manipulated purposely by adding H2 into or removing H2 from the membrane reactor feed and permeate gas streams. [ABSTRACT FROM AUTHOR]

[Display omitted] • CH 4 reactor/H 2 separator recycle system is studied for non-oxidative CH 4 conversion. • CH 4 reactor/H 2 separator recycle circumvents thermodynamic limit in CH 4 reaction. • High purity of H 2 product and high performance membrane separator are achieved. • >90 % selectivity and >50 % yield in aromatic product are achieved in recycle system. • Economic feasibility of CH 4 reactor/H 2 separator recycle system is simulated. Direct non-oxidative methane conversion (DNMC) is one of the most promising options to convert methane (CH 4) in natural gas in remote extraction sites to liquid aromatics, which is easier to transport compared to CH 4 gas. The main constraint of the DNMC is low CH 4 conversion, and thus aromatics product yield due to thermodynamic limitation. This work reports a gas recycle CH 4 reactor/hydrogen (H 2) membrane separator to achieve high CH 4 conversion and aromatics yield by circumventing the thermodynamic limitation. The DNMC took place over an iron/silica (Fe/SiO 2) catalyst in a packed-bed reactor to produce C 2 (i.e. ethane, ethylene and acetylene) and aromatics, along with reaction product H 2. The product stream passed through a condenser to collect aromatic products and then a H 2 -permeable membrane separator to remove H 2. The unreacted CH 4 , C 2 products and H 2 residual in the product stream were sent to the recycle loop for the next round of DNMC reaction and H 2 removal. The results demonstrated that >90 % product selectivity toward aromatics and >50 % aromatics yield are achieved in the gas recycle CH 4 reactor/ H 2 membrane separator system. [ABSTRACT FROM AUTHOR]

Direct non-oxidative methane coupling (NMC) is one of the promising pathways for methane upgrading into value-added olefin and aromatic hydrocarbons. The silica-supported iron (i.e., Fe/SiO 2) catalyst has been reported effective for NMC, but the effects of silica support on the catalyst property and NMC performance have rarely been explored. In this work, we prepared a vitreous silica-supported iron (Fe/SiO 2 -V) catalyst by flame fusion of a mixture of quartz silica and fayalite. The physicochemical properties and NMC performance of the as-prepared catalysts were measured. Compared to crystalline cristobalite support in Fe/SiO 2 catalyst that has been studied previously, vitreous silica support has disordered Si-O bonds and structural defects, enabling better iron dispersion and more vital metal-support interaction. The as-prepared Fe/SiO 2 -V catalyst had a shorter induction period in methane activation and lower coke yield in NMC. The increase in iron concentration in Fe/SiO 2 -V catalysts elongated the catalyst induction period and promoted aromatics and coke formation. The coke type of the spent Fe/SiO 2 -V catalyst is more uniform than the cristobalite-supported iron catalyst. [Display omitted] • Vitreous silica-supported iron catalysts were prepared by an oxyhydrogen flame fusion method. • The amorphous vitreous silica support contains disordered and defective Si-O bonds. • Iron has higher dispersion and more uniform bonding in the vitreous silica support. • Vitreous silica-supported iron enabled fast methane activation and low coking in NMC. • Increase in iron loading in vitreous silica support promoted aromatics formation. [ABSTRACT FROM AUTHOR]