Catalytic Thermochemical Conversion of Glycerol to Simple and Polyhydric Alcohols Using Raney Nickel Catalyst

Abstract

The crude glycerol from biodiesel production possesses low economic values and alternative ways of converting it to valuable chemicals are needed to sustain the biodiesel industry. This study aimed to investigate the production of primary alcohols and propylene glycol from glycerol through a catalytic thermochemical process without an external supply of hydrogen. The effects of reaction time, water to glycerol ratio, and doses of catalyst on glycerol conversion and alcohol yields were investigated using a batch pressure reactor and Raney nickel catalyst. The presence of alcohols and gases in the products confirmed that hydrogen was produced and was utilized in the formation of propylene glycol through hydrogenolysis. Ethanol and propylene glycol yields of up to 10.4 ( 0.2 and 33.2 ( 1.4 mol %, respectively, were observed. It was also concluded that ethanol is formed through hydrogenolysis of propylene glycol and its yield improves at extended reaction time and increased initial water content of the feed.

Co-Production of Ethanol and 1,2-Propanediol via Glycerol Hydrogenolysis Using Ni/Ce–Mg Catalysts: Effects of Catalyst Preparation and Reaction Conditions

“…Results showed that glycerol conversion and ethanol selectivity are both improved as the reaction time was extended from 24 h to 48 h. Meanwhile, 1,2-PDO selectivity declined, which was assumed to be the result of further hydrogenolysis, as evidenced by the increase in ethanol and n-propanol selectivities. These results are in agreement with previous studies, in which 1,2-PDO is considered a precursor for ethanol and propanol production [17][18][19][20][21][22][23]44]. …”

“…The conditions were chosen to get similar glycerol conversions and allow direct comparison on the catalyst performance. Similar glycerol conversions were achieved when 5 g of catalyst was reacted for 6 h, as compared to 10 g of the 25 wt % Ni/Ce-Mg (9:1 mol/mol) catalyst reacted for 24 h, which showed Raney ® Ni's superior activity in terms of rate of conversion [44]. However, it was observed that the catalyst developed in this study led to higher 1,2-PDO, ethanol, and overall selectivity towards desired hydrogenolysis products at all temperatures tested.…”

“…In addition, glycerol is known to be hygroscopic in nature, and likely contains water in some amount [12]. As reported in our previous study, water plays a beneficial role in thermochemical conversion of glycerol to value-added products [44]. Therefore, water was included in the reaction system in this study.…”

“…It was proposed that the formation of ethanol in the hydrogenolysis is from the conversion of intermediates such as 1,2-PDO [44]. To verify this, experiments were conducted to investigate whether ethanol yield could be improved by extending the reaction time.…”

“…The catalytic activity of the 25 wt % Ni/Ce-Mg (9:1 mol/mol) catalyst prepared by DP and calcined at 350 • C was compared to a commercial Raney ® Ni (Ni ≥ 89%; 6-9% Al) catalyst (Table 4), which is known to catalyze selectively for glycerol hydrogenolysis to 1,2-PDO and ethanol [17,44]. The conditions were chosen to get similar glycerol conversions and allow direct comparison on the catalyst performance.…”