PNNL

Abstract

With the increasing demand for sustainable aviation fuel, new conversion technologies are needed to efficiently process biomass, produce high quality jet fuel, and meet carbon emission targets. This study demonstrates the synthesis, conditioning, and catalytic upgrading of 2,3-butanediol (BDO) fermentation broth into sustainable aviation fuel. A high-titer 2,3-BDO fermentation broth (i.e., ~90 g/L) was successfully produced at a 100-L scale and pretreated via a nanofiltration method to effectively decrease the total impurities level in the broth from 4.6 wt.% to 0.6 wt.%. A novel four-step process for catalytic upgrading of aqueous 2,3-BDO to jet fuel was developed, and each step was efficiently demonstrated. The catalytic steps include 1) 2,3-BDO dehydration into methyl ethyl ketone (MEK) over AlPO4 (reactor R1), 2) MEK conversion into olefins over Zn1Zr10Ox (reactor R2), 3) oligomerization of olefins over a zeolite beta catalyst (reactor R3), and 4) hydrogenation over Pt/carbon (reactor R4). The unique two-step conversion of 2,3-BDO to olefins via the MEK intermediate allows the use of non-zeolite catalysts for MEK production, that are more suitable for applications with aqueous feedstocks such as 2,3-BDO fermentation broth. Both the model feed and real 2,3-BDO fermentation broth feeds were tested for upgrading 2,3-BDO to MEK for over 120 hours time on stream (TOS). With the real feed, a continuous loss of conversion (i.e., >50% loss over ~140 hours TOS) was partly attributed to reversible deactivation from coking species. However, the conversion remained stable with the model feed (5 wt.% BDO/H2O), which demonstrates the efficiency of the first step for converting aqueous 2,3-BDO without energy-intensive 2,3-BDO/water separation. For upgrading MEK to olefins, high selectivity to olefins (i.e., 82.5%) was obtained at high conversion levels (i.e., 93–98%) with stable conditions being achieved for >70 hours TOS. This level of performance shows that the Zn1Zr10Ox catalyst is suitable for this reaction. Oligomerization of light olefins, which was demonstrated for >270 hours TOS, mainly led to the formation of dimers (C8-10) and trimers (C13-14). The oligomerized product was hydrogenated and distilled to recover the jet fraction, which consists mostly of desired iso-alkanes (31.7 wt.%), n-alkanes (24.5 wt.%), and cyclo-alkanes (29.6 wt.%). Fuel properties including freezing point, density, aromatics content, and T10 were measured, and they verified ASTM D7566 criteria highlighting the potential of this process for production of jet fuel.