Abstract
Ru-Sn/TiO2 is an effective catalyst for hydrogenation of aqueous acetic acid to ethanol. In this paper, a similar hydrogenation process was investigated in a flow-type rather than a batch-type reactor. The optimum temperature was 170 °C for the batch-type reactor because of gas production at higher temperatures; however, for the flow-type reactor, the ethanol yield increased with reaction temperature up to 280 °C and then decreased sharply above 300 °C, owing to an increase in the acetic acid recovery rate. The selectivity for ethanol formation was improved over the batch process, and an ethanol yield of 98 mol % was achieved for a 6.7 min reaction (cf. 12 h for batch) (liquid hourly space velocity: 1.23 h−1). Oxidation of ethanol to acetic acid (i.e., the reverse reaction) adversely affected the hydrogenation. On the basis of these results, hydrogenation mechanisms that include competing side reactions are discussed in relation to the reactor type. These results will help the development of more efficient catalytic procedures. This method was also effectively applied to hydrogenation of lactic acid to propane-1,2-diol.
Highlights
Bioethanol has drawn attention as a means of reducing our dependence on fossil fuels [1,2,3,4,5].Currently, commercial bioethanol production involves alcoholic fermentation with yeast, which releases two carbon atoms from glucose as CO2 [6,7], resulting in low carbon conversion efficiency.we have proposed a new ethanol production process based on acetic acid fermentation that can theoretically convert all carbon atoms into acetic acid [8]
Acetic acid is a useful industrial chemical, and the global market size is 16.3 million tons in 2018 [9,10]. This new bioethanol production process consists of three steps: a hot-compressed water treatment to hydrolyze lignocellulosics, acetic acid fermentation, and hydrogenation of acetic acid [8]
We have reported Pt [18] and Ru [19] supported on TiO2 as potential hydrogenation catalysts for aqueous acetic acid to ethanol, by activating acetic acid with Lewis acid site (Ti)
Summary
Bioethanol has drawn attention as a means of reducing our dependence on fossil fuels [1,2,3,4,5]. Acetic acid is a useful industrial chemical, and the global market size is 16.3 million tons in 2018 [9,10] This new bioethanol production process consists of three steps: a hot-compressed water treatment to hydrolyze lignocellulosics, acetic acid fermentation, and hydrogenation of acetic acid [8]. Hydrogenation of aqueous acetic acid over 4wt%Ru-4wt%Sn/TiO2 was investigated with the use of a commercially available flow type reactor system, H-Cube. Side reactions that compete with hydrogenation to ethanol were closely examined to better understand the reactions occurring and the role of the flow reactor. This catalytic system was applied to hydrogenation of lactic acid to propane-1,2-diol
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