Determining operating parameters for Reverse Water Gas Shift reaction with respect to carbon formation and methanation for syngas production

Abstract

CO2 is the major contributor of green houses gases in the atmosphere. Two notable branches that revolutionized the approach toward reducing the CO2 in the atmosphere are Carbon Capture Storage (CCS) and Carbon Capture Utilization (CCU). CCS has its shortcomings in the long run, a study from MIT shows that the united states have an adequate land area to store CO2 for 100 years [64]. The important question is, what about after 100 years? The need for efficient methods to utilize the stored or captured CO2 is a reasonable solution; therefore successful development of efficient methods in utilizing CO2 is the need for the hour. This work comprises of using reverse water gas shift that utilizes CO2 as raw material and H2 produced via electrolysis using renewable electricity from wind or solar energy to produce syngas replacing gasification of coal or natural gas that produces CO2. Syngas is a major raw material for producing useful chemicals such as methanol, dimethyl ether, acetic acid, hydrocarbons and other valuable chemicals.

On this wide field of syngas production technology, this work aims in determining the optimal operating condition of the reverse water gas shift reactor to produce hydrocarbons. Hydrocarbon heavier than C5+ are used to produce liquid fuels, reverse water gas shift reaction followed by Fischer Tropsch (FT) synthesis is utilized to achieve liquid fuels. FT synthesis requires a particular composition of syngas for effective operation and high selectivity. The challenges faced are side reactions such as Boudouard and CO hydrogenation that produces carbon and methane in the reactor that are undesired. Carbon deactivates the catalyst and carburization causes ineffective conversion of CO2 resulting in high operational costs. Methane is hazardous side product that needs to be minimized in the outlet stream of the reverse water gas shift reactor before feeding the same stream into the Fischer Tropsch reactor.

Less to no literatures are available on reverse water gas shift with respect to carbon formation and methanation. The above mentioned objective is countered by modelling a plug flow tubular reactor. A nickel on calcium alumina catalyst is used in the reactor. The model is used to determine the operating conditions for the reverse water gas shift reactor to minimize carbon formation and methanation in the reactor. The parameters such as inlet conditions, pressure, inlet temperature, heat input to the reactor are all determined for a desired syngas composition, with no carbon formation inside the reactor and minimum methane in the reverse water gas shift reactor outlet.