A novel Ru–polyether sulfone catalytic membrane for hydrogenation of furfural to furfuryl alcohol

There is intensive research geared towards the development of alternative fuels of less injurious nature to the environment, when compared the prevalent fossil fuels. Pyrolysis of bio-oils or cellulose hydrolysis pathways, that lead to the production of biofuels or chemicals from biomass derivatives, are so far the most feasible alternatives that can help generate bio-based fuels of an energy output almost equal to that of fossil-based fuels. Generally, bio-oils are obtained by fast pyrolysis of lignocellulosic biomass, marine biomass and bio-waste. However, they have a high oxygen and water content that unarguably inhibit their use. Fortunately, this can be treated through the process of hydrogenation. Likewise, furfuryl alcohol is an important chemical intermediate for the production of chemical products and utilizes hydrogenation process. Unfortunately, in order to borrow from the furfuryl alcohol yielding procedure, there is need to further investigate on the specific catalytic hydrogenation that does not incorporate the use of batch reactors. Furthermore, so far, there are no published studies that have recorded the synthesis and testing of Ru-functionalized PES membranes obtained from hydrogenation reactions.

Recently, a team of researchers led by Dr. Aimaro Sanna at Heriot-Watt University developed a novel catalytic membrane reactor that would facilitate ease of selecting hydrogenate bio-oil derived compounds by reducing the amount of hydrogen used. Their work is currently published in the research journal, Journal of Material Chemistry A.

The research team synthesized the novel catalytic membrane with an active layer and modified the commercial PES membrane by photochemical graft polymerization of acrylic acid and doping its surface with Ru nanoparticles. Next, the researchers characterized the modified membranes in terms of pore size diameter, morphology, contact angle, porosity and Ru content. They then proceeded to test the catalytic membrane for the hydrogenation of furfural under mild process conditions in order to enable the evaluation of its turnover frequency. Lastly, the PES membrane was exposed to UV light and later dipped in hexaammine-ruthenium(II) chloride solution for 18 hours at room temperature.

The authors observed that the resulting turnover frequency was considerably higher than those reported in previous literature suggesting that the catalytic membrane reactor enhanced the catalytic activity of Ru in the selected reaction. Furthermore, a >99% selectivity to tetrahydro furfural was obtained by increasing the H₂/furfural molar ratio to 4:1 under the same process conditions. Additionally, the use of Catalytic Membrane Reactor also resulted in a residence time of the reactants in the membrane layer of less than 2 seconds, compared to a residence time higher than 1 hour for conventional packed bed reactors.

The study presented the addition of Ru nanoparticles onto the surface of the modified PES membrane using a UV source. The catalytic membrane was characterized with different techniques in order to evaluate the effective presence of the active layer and the Ru nanoparticles. Altogether, the work has shown that the selective hydrogenation of furfural to furfuryl alcohol can be successfully performed using Catalytic Membrane Reactors under mild conditions.