Dehydroisomerization reaction in a membrane reactor: Thermodynamic analysis

A study of a dehydroisomerization reaction in a membrane reactor has been carried out and the n-butane deydroisomerization was chosen for its industrial relevance of the iso-butene, a useful product in MTBE and polymers production. The dehydroisomerization converts n-butane in iso-butene with hydrogen production; therefore this reaction occurs with a mole number increase. The equilibrium conversion shift in a membrane reactor was evaluated taking into account the chemical equilibrium and the permeative equilibrium , through a 100% hydrogen-selective membrane. In fact, the equilibrium in a membrane reactor also depends on the permeative equilibrium. This study focuses on the effect of the reaction pressure on the equilibrium conversion in a membrane reactor. In a traditional reactor, the equilibrium is thermodynamically not favored by the pressure increase owing to the increase of the moles number. In a membrane reactor, the reaction pressure driving the hydrogen permeation leads conversions four-five times higher than those achievable in a traditional reactor. When the hydrogen equilibrium partial pressure is set, the equilibrium conversion in a membrane reactor does not change changing the reaction pressure. This effect is related to the hydrogen stoichiometric coefficient and the moles number variation. For this reaction, the reactive equilibrium depends on both the reaction pressure and the hydrogen partial pressure with the same power of order equals one. When, moles number variation and hydrogen stoichiometric coefficient are equal each other, the hydrogen removal from reaction volume by permeation exactly balances the negative reaction pressure effect. Actually, the hydrogen equilibrium partial pressure sets the membrane reactor equilibrium conversion which depends only on it and not on the reaction pressure.