Environmentally benign synthesis of amides and ureas via catalytic dehydrogenation coupling of volatile alcohols and amines in a Pd-Ag membrane reactor

Dual-Role Membrane as NH3 Permselective Reactor and Azeotrope Separator in Urea Alcoholysis

Urea methanolysis is a green alternative to synthesize dimethyl carbonate (UM-to-DMC). However, it is strongly challenged by the generated NH₃ induced thermodynamic equilibrium limitation and the azeotropic products' separation. Herein, these predicaments are well-relieved by introducing membranes in both reaction and product separation. An NH₃ permselective membrane reactor (MR) based on modified SAPO-34 membrane is successfully realized for UM-to-DMC. The permselectivity and acidity of the SAPO-34 membrane are significantly adjusted to cater the strict molecular sieving of NH₃/methanol and chemical inertness upon the reaction. The MR exhibits excellent reactant conversion and DMC selectivity, resulting in >139% higher DMC yield than that of the nonmembrane reactor, due to in situ removal of NH₃ by the membrane. The MR also demonstrates reliable chemical, thermal, and mechanical stability during >2000 h. Moreover, the regular SAPO-34 membrane with controlled thickness presents remarkable separation performance for the methanol-DMC azeotrope, in which the methanol-DMC separation factors and the methanol permeance are 1-2 orders of magnitude higher than those of the polymeric membranes. This study suggests the great potential that integration of such membranes offers for process intensification, energy savings, and efficiency improvement in a series of urea alcoholysis and even other NH₃ releasing reactions.

Nonoxidative Dehydrogenation of Methanol to Methyl Formate through Highly Stable and Reusable CuMgO-Based Catalysts

Nonoxidative dehydrogenation of methanol to methyl formate over a CuMgO-based catalyst was investigated. Although the active site is metallic copper (Cu⁰), the best reaction conditions were obtained by tuning the ratio of Cu/Mg and doping the catalyst with 1 wt % of Pd to achieve a very specific activity for methyl formate synthesis. On the basis of the CO₂ temperature-programmed desorption study, the basic strength of the catalyst plays a role in the efficient conversion of methanol to methyl formate via dehydrogenation. These CuMgO-based catalysts show excellent thermal stability during the reaction and the regeneration processes. Approx. 80% methanol conversion with constant selectivity to methyl formate was achieved even after 4 rounds of usage for a total reaction time exceeding 200 h, indicative of their potential for practical applications.

Catalytic Ionic-Liquid Membranes: The Convergence of Ionic-Liquid Catalysis and Ionic-Liquid Membrane Separation Technologies

Membrane technologies enable the facile separation of complex mixtures of gases, vapours, liquids and/or solids under mild conditions. Simultaneous chemical transformations can also be achieved in membranes by using catalytically active membrane materials or embedded catalysts, in so-called membrane reactors. A particular class of membranes containing or composed of ionic liquids (ILs) or polymeric ionic liquids (pILs) have recently emerged. These membranes often exhibit superior transport and separation properties to those of classical polymeric membranes. ILs and pILs have also been extensively studied as separation solvents, catalysts and co-catalysts in similar applications for which membranes are employed. In this review, after introducing ILs and their applications in catalysis, catalytic membranes and recent advances in membrane separation processes based on ILs are described. Finally, the nascent concept of catalytic IL membranes is highlighted, in which catalytically active ILs/pILs are incorporated into membrane technologies to act as a catalytic separation layer.