High temperature CO2 sorbents and their application for hydrogen production by sorption enhanced steam reforming process

This review is focused on Sorption Enhanced Steam Methane Reforming (SESMR), an emerging process intensification of traditional Steam Methane Reforming (SMR), to produce H2 by a more environmental friendly exploitation of natural gas, thanks to in-situ CO2 capture. Ni and CaO are respectively the most investigated materials for SMR catalysis and CO2 capture, used either on separated particles or in Combined Sorbent Catalyst Materials (CSCM); the latter is potentially more advantageous from the process point of view. Preferential conditions for SESMR based on Ni and CaO are about 650 °C and 1 atm, allowing to obtain H2 with high purity (more than 95 vol% vs. 76 vol% in industrial SMR, both on dry dilution-free basis). For a continuous process, multicycle CaO regeneration is needed, by means of high temperature calcination (800–950 °C). The exploitation of Solid Oxides Fuel Cells (SOFC) flue hot gases, as well as oxy-fuel combustion, are suggested as regeneration strategies in studies concerning SESMR industrial scale-up, in combinations of packed beds or fluidised bed reactors with solid recirculation. Future studies should investigate materials stability in relevant industrial conditions, e.g. more severe regenerations under highly concentrated CO2 at high temperatures, or in presence of steam.

Sorption enhanced steam methane reforming based on nickel and calcium looping: a review

A review of CO2 sorbents for promoting hydrogen production in the sorption-enhanced steam reforming process

Experimental investigation on the CO2 transcritical power cycle

CaO is an important catalyst in biomass gasification and pyrolysis. However, CaO can stem from many precursors. And, the effect between different precursors has still not been studied. Calcined natural limestone, natural dolomite, calcium oxide, calcium carbonate, calcium acetate, and calcium propionate were used to investigate their pyrolysis reactivity of biomass (peanut shells and pine sawdust) at high temperature (>800 °C). Experiments were conducted using a thermogravimetric apparatus and a fixed-bed pyrolysis system. Pine sawdust displayed higher pyrolysis reactivity than peanut shells. During pyrolysis, Ca-based additives fixed carbon dioxide mainly in the temperature range of 300–700 °C. By addition of Ca-based additives, the concentrations of hydrogen and carbon monoxide were increased and the concentrations of methane and carbon dioxide (over 18 vol%) were decreased. De-carbonation started around 700 °C. The emission of CO2 by de-carbonation promoted the reduction of char by the Boudouard reaction and methane by the dry reforming reaction. The total pyrolysis conversion decreased as PI-Dol > PI-CaA > PI-Lime > PI-Ca > PI-CaP > PI Raw > PI-CaC. The excellent pyrolysis reactivity of biomass in the presence of calcined calcium acetate can be ascribed to its preeminent physical structure. Addition of Ca-based additives increased the activation energy of the main devolatilization region. The activation energy of biomass with calcined natural dolomite, about 110 kJ mol−1, was much lower than that of other Ca-based additives studied at high temperatures. Pyrolysis of the pure biomass sample can be simply hypothesized as a first order reaction, but it varied significantly with the addition of additives.

Qibin Zhou

Papers

Carbon Dioxide Captured from Flue Gas by Modified Ca-based Sorbents in Fixed-bed Reactor at High Temperature