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(211d) A Three-Step Catalytic Pathway for the Scalable Production of 1,5-Pentanediol from Biomass-Derived Tetrahydrofurfuryl Alcohol

Barnett, K. J., University of Wisconsin-Madison
Huber, G. W., University of Wisconsin-Madison
Dumesic, J. A., University of Wisconsin-Madison
Brentzel, Z., University of Wisconsin-Madison
Maravelias, C. T., University of Wisconsin-Madison
Huang, K., University of Wisconsin-Madison
Li, L., Tianjin University
Liu, G., Tianjin University
Biomass conversion technologies focusing on the production of high value chemicals have received great interest due to the potential for improved economics compared to petroleum-derived processes, which rely on the selective oxidation of an inherently non-oxidized feedstock. One such class of high value biomass derived chemicals are α,ω-diols, such as 1,5-pentanediol (1,5-PD). Synthesis of 1,5-PD from biomass feedstocks has previously been achieved via the direct ring-opening of tetrahydrofurfuryl-alcohol (THFA) utilizing bimetallic catalysts comprised of a metal hydrogenation catalyst (e.g. Rh) and an oxophilic promoter (e.g. Re). The selective production of 1,5-PD via direct hydrogenolysis requires the use of noble metal catalysts, thus rendering this route economically unviable. However, we have developed an alternative pathway for producing 1,5-PD from THFA in ~90% yields. In this 3-step approach, 1,5-PD is produced via vapor-phase dehydration of THFA to dihydropyran (DHP), hydration of DHP to 2-hydroxytetrahydropyran (2-HY-THP) in water, and hydrogenation of the ring-opened tautomer of 2-HY-THP, 5-hydroxyvaleraldehyde (5-HVal), to 1,5-PD. This approach has been termed the dehydration-hydration-hydrogenation (DHH) pathway.

Dehydration of neat THFA in the vapor phase gave a >90% overall yield to DHP over a commercial γ-Al2O3 catalyst, which is able to be completely regenerated upon calcination at 400°C. Hydration of the DHP results in the formation of the main hydration product, 2-HY-THP, and dimers formed via etherification. While 2-HY-THP yields were limited by solid polymer formation high temperatures (>130˚C), nearly quantitative yields to 1,5-PD precursors (2-HY-THP + dimers) were achieved at 50-130˚C in the absence of a catalyst. Solid acid catalysts such as HZSM5 increase hydration rates several orders of magnitude without any decrease in yields. Additionally, HZSM5 was demonstrated to be stable for ~70h in a continuous flow reactor at a 50wt% DHP loading in water.

Hydrogenation of the product formed in the hydration step over supported Ru catalysts gave >96% yields of 1,5-PD from 2-HY-THP and dimers. At low conversions, the 1,5-PD selectivity is <60% due to a shift in equilibrium towards the dimers; however, at higher conversions, dimers are hydrolyzed to their monomers, which are then hydrogenated to 1,5-PD at near quantitative yields. Ru/C was shown to be the most active and stable monometallic catalyst for 2-HY-THP hydrogenation to 1,5-PD. A technoeconomic analysis showed that the DHH pathway presented herein has a 6.6x lower production cost compared to the direct hydrogenolysis route.



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