Single‐step Conversion of Methyl Ethyl Ketone to Olefins over Zn_xZr_yO_z Catalysts in Water

Abstract

In this study we investigated the conversion of aqueous methyl‐ethyl‐ketone (MEK) to olefin fuel precursors over ZnxZryOz mixed oxide catalysts. Experiments were carried out in water as MEK is intended to be produced from the dehydration of 2,3‐butanediol in fermentation broth which is highly diluted in water. We demonstrated that ZnxZryOz catalysts are highly effective for converting aqueous MEK to C4−C5 olefins. High selectivity to olefins equal to 85 % was reached at 92 % per pass conversion when under H2 atmosphere. Catalyst stability was demonstrated for 60 hours’ time on stream, highlighting the potential for upgrading 2,3‐butanediol contained in fermentation broth without the need for energy‐intensive water separation. Increased concentration of MEK in the aqueous feed results in increased activity towards olefin production. However, water inhibits catalyst deactivation from coking. A mechanistic investigation revealed the impact of the reaction environment (inert or reducing atmosphere) on the reaction pathways. In an inert environment, the mechanism involves consecutive aldol condensation of MEK and 3‐pentanone intermediate. Under reducing conditions two reaction pathways compete with each other as MEK hydrogenation to butenes occurs concurrently with the aldol condensation/decomposition.

Cleanup and Conversion of Biomass Liquefaction Aqueous Phase to C3–C5 Olefins over ZnxZryOz Catalyst

“…However, methyl ethyl ketone (MEK) and methyl butane (C 5 = ) are produced from the combination of propanoic acid with acetic acid as depicted in Scheme 2. This mechanism also agrees with our recent study for conversion of MEK to olefins over Zn x Zr y O z catalysts [23]. As shown in Figure 2, the ketone and olefin selectivity are directly affected by the GHSV, emphasizing that the ketones are indeed reaction intermediates for the olefin production as depicted in Schemes 1 and 2.…”

“…The CH 4 selectivity remained relatively constant at~4%, indicating that changing the gas environment does not significantly impact decomposition or methanation reactions. We speculate that cofeeding H 2 during the upgrading of the feedstocks explored in this work over the Zn x Zr y O z would cause a similar enhancement in propene production and shift the C 5 = production more towards C 4 = [23]. The mixed olefin product stream could be then oligomerized to higher value products as demonstrated by Saavedra Lopez et al [14].…”

“…Recently, a complete loop starting from syngas and ending with isobutene oligomerization to jet fuel was also demonstrated [15]. In addition, it has been demonstrated that the ZnxZryOz catalyst is able to convert larger alcohols, and also carboxylic acids and ketones, into mixed olefin streams [22][23][24]. As previously demonstrated, the reaction mechanism involves the conversion of alcohols into carboxylic acids before undergoing subsequent reaction steps [22].…”

Separation, recovery and upgrading of 2,3‐butanediol from fermentation broth

“…These co‐products have currently available markets and could potentially enable the production of cost‐competitive fuels. MEK and BDO have both been shown to have excellent potential for conversion to sustainable aviation fuel (SAF) or SAF precursors 20,23 …”

“…MEK and BDO have both been shown to have excellent potential for conversion to sustainable aviation fuel (SAF) or SAF precursors. 20,23 However, challenges remain regarding the isolation of BDO from the fermentation broth, which is essential for further upgrading. Distillation is the most traditional approach to isolate and purify simple fermentation products such as ethanol, but in the case of BDO, incurs significant energy penalties owing to the high boiling point of BDO (177°C) relative to water.…”