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17 Nov 2019
Methane, CH_4, is a plentiful energy source. Methane is easily pumped to residences and its oxidation products are chemically innocuous. CH_4 + 2O_2 rightarrow CO_2 + 2H_2O Because CO_2 is a greenhouse gas, it may be desirable to capture and sequester CO_2. However, it is ambitious and inefficient to collect CO_2 from each residence's exhaust. Rather, it may be better to convert CH_4 to H_2 at a central facility. CH_4 + 2H_2O rightarrow CO_2 + 4H_2 CO_2 can be collected centrally and H_2 can be pumped to residences where it is oxidized to H_2O, which is truly innocuous. The process to form H_2 is conducted in two steps. The first step is steam reforming at 900 degree C. steam reforming: CH_4 + H_2O rightarrow CO + 3H_2 The second step is the water-gas shill reaction at 200 degree C. water-gas shift: CO + H_2O rightarrow CO_2 + H_2 Steam reforming is catalyzed by Ni, a solid that remains unchanged and is a permanent fixture in the reactor; no Ni catalyst enters or leaves the reactor. The water-gas shift is catalyzed by CuO-ZnO, also a solid, but this catalyst is deactivated by the disproportionation of CO, a side reaction. disproportionation: CuO-ZnO + 2CO rightarrow C/CuO-ZnO + CO_2 Solid C deposits on the catalyst and degrades its activity. The CuO-ZnO catalyst is continuously cycled through the water-gas shift reactor and a catalyst reactivation reactor for the following reaction at 500 degree C. catalyst reactivation: C/CuO-ZnO + H_2O rightarrow CuO-ZnO + CO + H_2 The CuO-ZnO catalyst is fine particles suspended in the reaction gas. A fraction of the catalyst dust is carried out with the effluent. Design a process to produce hydrogen from methane and water, and collect the by-product CO_2. Design Rules. Neither steam reforming nor water-gas shift completely convert reactants to products. Each has a conversion of 80% to 90%. You may assume catalyst reactivation is complete if excess H_2O is present. To maximize conversions, do not feed reactor products into a reactor. For example, do not feed H_2 into the water-gas shift reactor.
Methane, CH_4, is a plentiful energy source. Methane is easily pumped to residences and its oxidation products are chemically innocuous. CH_4 + 2O_2 rightarrow CO_2 + 2H_2O Because CO_2 is a greenhouse gas, it may be desirable to capture and sequester CO_2. However, it is ambitious and inefficient to collect CO_2 from each residence's exhaust. Rather, it may be better to convert CH_4 to H_2 at a central facility. CH_4 + 2H_2O rightarrow CO_2 + 4H_2 CO_2 can be collected centrally and H_2 can be pumped to residences where it is oxidized to H_2O, which is truly innocuous. The process to form H_2 is conducted in two steps. The first step is steam reforming at 900 degree C. steam reforming: CH_4 + H_2O rightarrow CO + 3H_2 The second step is the water-gas shill reaction at 200 degree C. water-gas shift: CO + H_2O rightarrow CO_2 + H_2 Steam reforming is catalyzed by Ni, a solid that remains unchanged and is a permanent fixture in the reactor; no Ni catalyst enters or leaves the reactor. The water-gas shift is catalyzed by CuO-ZnO, also a solid, but this catalyst is deactivated by the disproportionation of CO, a side reaction. disproportionation: CuO-ZnO + 2CO rightarrow C/CuO-ZnO + CO_2 Solid C deposits on the catalyst and degrades its activity. The CuO-ZnO catalyst is continuously cycled through the water-gas shift reactor and a catalyst reactivation reactor for the following reaction at 500 degree C. catalyst reactivation: C/CuO-ZnO + H_2O rightarrow CuO-ZnO + CO + H_2 The CuO-ZnO catalyst is fine particles suspended in the reaction gas. A fraction of the catalyst dust is carried out with the effluent. Design a process to produce hydrogen from methane and water, and collect the by-product CO_2. Design Rules. Neither steam reforming nor water-gas shift completely convert reactants to products. Each has a conversion of 80% to 90%. You may assume catalyst reactivation is complete if excess H_2O is present. To maximize conversions, do not feed reactor products into a reactor. For example, do not feed H_2 into the water-gas shift reactor.
Nestor RutherfordLv2
2 Mar 2019