Selective oxidation of light alkanes to alcohols has been a long-standing challenge, largely due to the difficulty to control secondary reactions leading to over-oxidation (to ketones, acids, COx). One concept that has been reported for improving alcohol selectivity in alkane oxidations is the Bashkirov process, which involves the use of boron compounds such as boric acid, boric oxide and borate esters. These boron species function as Lewis acids which direct the oxidation towards the formation of alcohols, and subsequently trap the alcohols in the form of borate esters to protect them from over-oxidation. Although borate-assisted alkane oxidation was performed commercially for high boiling alkanes, this concept has so far not been successfully applied to light alkanes such as n-pentane. In this work, oxidation of n-pentane with molecular oxygen to sec-pentanols was performed in the presence of a free radical initiator (di-tert-butyl peroxide) and a boron compound (sec-butyl metaborate), with in situ adsorption of water on molecular sieve 3A. Kinetics of the reaction was studied in a laboratory-scale batch reactor over a broad range of conditions (130-150°C, 20-30 bar, 5-10 vol% ) in order to establish the optimum parameters for maximizing the selectivity and yield of sec-pentanols. Results show that the initiator markedly improves the rate of oxidation, and hence yield, compared to thermal oxidation without an initiator, while the boron species enhances the selectivity to sec-pentanols. Under the conditions investigated, maximum sec-pentanol selectivity is 56% with an alcohol-to-ketone ratio of 3.6:1 for the borate-assisted oxidation compared to 33% and 1.1:1, respectively, for the oxidation without borate. This work demonstrates the feasibility of oxyfunctionalization of n-pentane with industrially relevant selectivity and yield using the borate-assisted approach.[1]

Borate-assisted liquid-phase selective oxidation of n-pentane

2019 Spring National Meeting

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