4,4′-Dimethylbiphenyl (DMBP) can be easily transformed into diamines, diols and diacids, making it a major precursor in different organic chemicals, especially in the polymer industry. For instance, 4,4′-biphenyldicarboxylic acid, the diacid form of DMBP, is important in producing polymer products with high molecular weight without intermediate solidification. As such, it has been identified as a potential precursor in the production of engineering plastics, liquid crystal polymers and polyester fibers with excellent heat resistance and high tensile strength.
Although coupling reactions of arenediazonium salts or aryl chlorides are proven routes for synthesizing 4,4′-DMBP, they are not very selective, require costly substrates and produce waste in large amounts. Producing 4,4′-DMBP from benzene or toluene has recently emerged as an alternative and more effective route. It involves the production of (methylcyclohexyl)toluene (MCHT) via hydroalkylation of toluene and dehydrogenation of the intermediates to DMBP. However, the main challenge of this route is the difficulty in separating the mixture of several isomers (such as the 3,4′-, 3,3′-, etc.). Alternative routes involving benzene follow a similar pathway.
With the projected growth in the global polyester fiber market, developing more effective and robust routes for sustainable synthesizing 4,4′-DMBP is imperative. Producing polyesters using DMBP derived from renewable sources could reduce its overall lifecycle greenhouse gas emissions. In particular, it has already been shown that replacing oil-based toluene with biomass-derived furfural for 4,4′-DMBP manufacturing is a promising strategy for green production of polyester.
Herein, the University of Delaware researchers: PhD candidates Yuqing Luo, Mi Jen Kuo, Mingchun Ye, Professor Raul Lobo and Professor Marianthi Ierapetritou conducted a lifecycle assessment and technoeconomic analysis to compare the environmental and economic performances of two conceptual design for 4,4′-DMBP production. The first toluene-based design involved alkylation of toluene to MCHT, MCHT dehydration to DMBP and isomerization of lower-valued 3,3′-DMBP. The second renewable furfural-based design considered a three-step process: hydrogenation of furfural to 2-methylfuran (MF), oxidative coupling of MF to 5,5′-DMBF (dimethylbifuran) and tandem Diels-Alder dehydration of 5,5′-DMBF to 4,4′-DMBP. Their work is currently published in the research journal, Industrial and Engineering Chemistry Research.
The research team established that the proposed biomass-based DMBP production route is a sustainable, environmentally friendly and profitable technology. By optimizing the reaction conditions, using more robust catalysts, and shortening the reaction times, the commercial viability of this production process was improved, and the cost breakdown provided insights into the path toward profitability. Such process innovations are essential in improving further the operational and financial feasibility of biomass-based production routes. Furthermore, through sensitivity analysis, feedstock and 3,4′-DMBP isomer prices were identified as the most critical parameters for economic evaluation.
The toluene-based process benefits from inexpensive toluene feedstock and small equipment sizes, thus showing a lower 4,4′-DMBP minimum selling price ($2,488/t) than that of furfural-based process ($3,044/t) at a scale of 83 kmol/h feedstock. Nevertheless, when other factors were considered, the toluene-based process was less appealing economically. For instance, the furfural-based process was more carbon-efficient, producing significantly less greenhouse gas emission (5.00 kg CO2 equiv/kg DMBP) than toluene-based method (8.28 kg CO2 equiv/kg DMBP). Other advantages of furfural-based process included smaller plant size requirement, lower sensitivity to fluctuations in the market price of isomers and better controllability of the product quality.
In summary, this is the first study to perform process simulation and evaluate the environmental and economic feasibility of sustainable DMBP production. Optimizing the reaction conditions could further improve conversion and prevent unwanted side reactions. In a statement to Advances in Engineering, the authors explained that their new proposed biomass-based DMBP production path provides a promising alternative route for the sustainable production of high-quality, cost-effective and environmentally friendly polyesters.
Luo, Y., Kuo, M. J., Ye, M., Lobo, R., & Ierapetritou, M. (2022). Comparison of 4,4′-dimethylbiphenyl from biomass-derived furfural and oil-based resource: Technoeconomic Analysis and lifecycle assessment. Industrial & Engineering Chemistry Research, 61(25), 8963–8972.