Efficient Hydrogenation of Ethyl Lactate to 1,2-Propanediol over Ru–B/TiO2 in Aqueous Solution

Abstract

Catalyst Ru-B/TiO 2 showed an excellently catalytic performance for the hydrogenation of ethyl lactate to 1,2-propanediol (1,2-PDO) under mild conditions (90 C and 4.0 MPa H 2 ) without any additive. Especially, the activity of the catalyst was greatly improved in aqueous solution. The conversion of ethyl lactate was up to 98% and the selectivity to 1,2-propanediol was over 95%.1,2-Propanediol (1,2-PDO) is an important industrial chemical, which is widely used as the raw materials to produce polymers, resins, and functional fluids (antifreeze, deicing). A commercial route to synthesize 1,2-PDO is the hydration of propylene oxide derived from propylene by either a chlorohydrin process or a hydroperoxide process.1,2 Thus, to develop a cleanly and economically synthetic approach of 1,2-PDO is important. From renewable feedstocks, hydrogenolysis of glycerol is a useful route to prepare 1,2-PDO, but a challenging problem for this route is to look for an efficient catalyst as the reported catalysts generally show the low activity and selectivity.3-6 Thus, the direct hydrogenation of lactic acid or lactates, which are easily obtained by fermentation of renewable sources such as agricultural crops and biomass streams, is a good green route to produce 1,2-PDO. In the hydrogenation of lactates, it is found that nickel and ruthenium catalysts are effective, but the reaction conditions are drastic. For example, the hydrogenation over Raney Ni must be performed in a high H 2 pressure of 25 MPa. [7][8][9] To use unsupported ruthenium black as catalyst, the hydrogenation could be achieved at 150 C and 27 MPa and only gave a 1,2-propanediol yield of 84%.10 Over Ru/C, 1,2-propanediol was obtained at the reaction temperature of 150 C and hydrogen pressure of 14.5 MPa.11 Recently, it was found that the introduction of tin was an effective method to improve the hydrogenation activity of ruthenium-based catalyst, 12-14 but the hydrogenation was still carried out under the conditions of 150 C and 5.5 MPa. To our knowledge, an organic solvent is the best choice in order to obtain a good result for the hydrogenation of lactates to 1,2-PDO. In the present study, we first found that Ru-B/TiO 2 catalyst, prepared by the reduction impregnation method, was an excellent catalyst for the hydrogenation of ethyl lactates to 1,2-PDO. Especially, when the safe and environmentally friendly water was used as a solvent, the hydrogenation could quickly progress at the low temperature of 90 C and hydrogen pressure of 4.0 MPa.Catalyst Ru-B/TiO 2 was prepared by a reduction impregnation method. The alcohol solution of 10 mL containing RuCl 3 of 1.58 mmol was rapidly added to the flask containing TiO 2 (2.0 g), and then the mixture was reduced with an aqueous solution of NaBH 4 (a molar ratio of B to Ru was 10:1) at room temperature under the ultrasound agitation. At the end of reaction, the black precipitate was filtered, washed with distilled water, and dried under vacuum at 60 C for 10 h. The filtrate was collected to determine the composition of the ...

Hydrogenation of ethyl lactate over ruthenium catalysts in an additive-free catalytic system

“…It is worth noting that when 100 mg of Ru/SiO 2 was used, the yield of 1,2-PDO was high up to 82.1%. This was comparable to the boron-added ruthenium catalyst [1][2][3][4][5], but our catalytic system is more feasible and simpler.…”

“…Hence the conversion of ethyl lactate increased with increasing catalyst amount. Nevertheless, too much Ru/SiO 2 will promote the excessive hydrogenolysis reaction of 1,2-PDO, leading to the formation of by-products like 1-propanol and 2-propanol [1,5]. This can be responsible for the drop of the selectivity to 1,2-PDO at a higher dosage ([100 mg) of Ru/SiO 2 .…”

“…The conversion of ethyl lactate to 1,2-PDO is usually studied under heterogeneous catalytic conditions in the presence of hydrogen [1][2][3][4][5][6][7]. For example, Luo et al reported that RuB/c-Al 2 O 3 [1][2][3] and RuB/SBA-15 [4] are effective catalysts for the hydrogenation of ethyl lactate to 1,2-PDO at 423 K and 5.5 MPa; addition of suitable amounts of tin in the Ru-based catalysts is an efficient approach which can significantly increase the catalytic activity and the selectivity to 1,2-PDO.…”

“…For example, Luo et al reported that RuB/c-Al 2 O 3 [1][2][3] and RuB/SBA-15 [4] are effective catalysts for the hydrogenation of ethyl lactate to 1,2-PDO at 423 K and 5.5 MPa; addition of suitable amounts of tin in the Ru-based catalysts is an efficient approach which can significantly increase the catalytic activity and the selectivity to 1,2-PDO. Similarly, Fan et al [5] studied the hydrogenation of ethyl lactate over RuB/TiO 2 in aqueous solution; the reaction condition (\423 K, 4 MPa) seems more mild and more handy. Recently, vapor-phase hydrogenation of ethyl lactate over Co/SiO 2 and Cu/SiO 2 was performed in a fixed-bed reactor [6]; the best selectivity to 1,2-PDO was high up to 98.8%.…”

“…As reported in the previous works, using Ru-based catalysts [1][2][3][4][5]7] usually needs the introduction of some additives (boron, tin or iron, etc. ), while employing non-noble metal catalysts [6] generally requires drastic reaction conditions.…”