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

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.