Reducing Byproduct Formation during Conversion of Glycerol to Propylene Glycol

Abstract

During the conversion of glycerol to propylene glycol, highly selective conversion is necessary for commercial viability. The greatest strides in achieving high selectivity are attained with catalyst and temperature. For the conversion of glycerol to propylene glycol, these parameters can be optimized to achieve selectivities of greater than 80%. This paper is on the optimization of more-subtle parameters such as concentration, water content, pressure, isothermal operation, and residence time to achieve selectivities in excess of 90%. Data reveal that low concentrations are important to reduce by-product whose formation relies on second-order reaction mechanisms. Water is important to reduce dehydration reactions and indirectly helps to maintain more-isothermal operation. An optimal hydrogen partial pressure between 5 and 15 bar minimizes the cumulative amount of by-product that results from hydrocracking versus dehydration side-reactions.

Selective Conversion of Glycerol into 1,2-Propanediol at Ambient Hydrogen Pressure

“…[5][6][7][8][9][10][11][12][13][14][15][16] In liquid-phase hydrogenolysis under hydrogen pressure, glycerol is converted into 1,2-PDO and 1,3-PDO in the presence of supported Rh, 5 Ru, [6][7][8]9 In the vapor-phase hydrogenolysis of glycerol, Cu catalyzes 1,2-PDO formation in the presence of high hydrogen pressure. [10][11][12][13] Since the hydrogenolysis requires elevated hydrogen pressure, 5-11 side reactions occur to form several by-products, including ethylene glycol (EG), propanol, lactic acid, and propanoic acid. Hydroxyacetone (HA) is an intermediate product in the conversion of glycerol into 1,2-PDO through the dehydration-hydrogenation reactions.…”

“…13,15 It is known that copper works as a dehydrogenation catalyst for polyols, such as 1,2-17 and 1,3-diols. 18 However, glycerol can be dehydrated into HA over copper metal catalysts.…”

“…[5][6][7][8][9][10][11][12][13][14][15][16] In liquid-phase hydrogenolysis under hydrogen pressure, glycerol is converted into 1,2-PDO and 1,3-PDO in the presence of supported Rh, 5 Ru, [6][7][8] or Pt. 8,9 In the vapor-phase hydrogenolysis of glycerol, Cu catalyzes 1,2-PDO formation in the presence of high hydrogen pressure.…”

“…Hydroxyacetone (HA) is an intermediate product in the conversion of glycerol into 1,2-PDO through the dehydration-hydrogenation reactions. Over Cu catalysts, however, 1,2-PDO selectivity higher than 90 mol % is attained: 12,13 low temperatures and high hydrogen pressures favor the shift of equilibrium from HA to 1,2-PDO and reduce the formation of by-products resulting from HA side reactions. 13 One effective operation is a two-step process composed of dehydration under vacuum and hydrogenation under hydrogen pressure.…”

“…Over Cu catalysts, however, 1,2-PDO selectivity higher than 90 mol % is attained: 12,13 low temperatures and high hydrogen pressures favor the shift of equilibrium from HA to 1,2-PDO and reduce the formation of by-products resulting from HA side reactions. 13 One effective operation is a two-step process composed of dehydration under vacuum and hydrogenation under hydrogen pressure. 13,15 It is known that copper works as a dehydrogenation catalyst for polyols, such as 1,2-17 and 1,3-diols.…”