Reaction & Synthesis / Environmental Health & Safety

Renewable Feedstocks Promise Lower-Cost p-Xylene

Catalytic process provides both high selectivity and yield.

By Chemical Processing Staff

Researchers at the University of Massachusetts (UMass), Amherst, Mass., have discovered an "ultraselective" process to make p-xylene from dimethylfuran (DMF) and ethylene derived from renewable resources such as lignocellulose. The route boasts more than 99% xylene selectivity to the para isomer, and 90% yield of p-xylene at 99% conversion of DMF.

Developed at the university's Catalysis Center for Energy Innovation (CCEI), the process involves combined cycloaddition/dehydration reactions using zeolite beta catalyst.

Led by professor Wei Fan, the team examined a number of nanoporous catalytic materials before selecting the beta zeolite. "We discovered that the performance of the biomass reaction was strongly affected by the nanostructure of the catalyst, which we were able to engineer and achieve 90% yield," Fan says. Details appear in a recent issue of Green Chemistry.

The research center has analyzed the potential cost of producing p-xylene via the process. "Our analysis evaluates the entire process, from biomass feedstock to p-xylene. This design is benchmarked against competing biomass-to-p-xylene technologies," says Paul Dauenhauer, a professor at the school. "We can report that our process is at least 20–25% cheaper than competing technologies."

"Fundamental research into the catalysis of zeolite beta for renewable p-xylene has already begun, but it will likely take three or four more years before a complete understanding of the elementary reactions and the role of the zeolite structure are understood," Dauenhauer notes.

"In particular, we aim to understand the specific elementary reactions occurring at the active site in zeolite beta. A second objective is to understand the chemistry and kinetics of all possible reaction pathways for a complete description which can be utilized in reactor and process development in the future."

Utilization of a continuous process for pilot-plant-scale studies will occur in the development phase in collaboration with industrial partners and is expected to take three years, he says. "The CCEI has several industrial members and we are continuing to talk to several companies specifically about p-xylene and renewable aromatic chemical technologies."

"Translating the basic catalysis research in our initial discovery to a pilot plant design will require understanding the reaction chemistry and relevant transport phenomena for constructing a continuous flow reactor. The reactants and catalysts associated with producing renewable p-xylene require a three-phase reactor, which is more challenging than conventional single-phase reactors," he adds.

However, because the team is using conventional zeolite catalysts, the researchers don't anticipate any issues with commercial scale-up in terms of catalyst production.

Furthermore, Dauenhauer doesn't foresee risk of isomerization of the p-xylene to ortho or meta isomers in the continuous process. "Our research shows that isomerization of p-xylene to isomers (or formation of toluene) is inhibited for all considered reaction conditions…. The inhibition of p-xylene isomerization is one of the main benefits of our process," he explains.

The discovery is part of a larger effort by the CCEI to create technologies for producing biofuels and chemicals from lignocellulosic biomass.