Abstract
Although thermal hydrolysis of digested biosolids is an extremely promising strategy for wastewater management, the process economics are prohibitive. Here, a biosolids-based material generated through thermal hydrolysis was used as a catalyst for urea glycerolysis performed under several conditions. The catalytic system showed remarkable activity, reaching conversion values of up to 70.8 ± 0.9% after six hours, at 140 °C using a catalyst/glycerol weight ratio of 9% and an air stream to remove NH3 formed during the process. Temperature played the most substantial role among reaction parameters; increasing temperature from 100 °C to 140 °C improved conversion by 35% and glycidol selectivity by 22%. Furthermore, the catalyst retained good activity even after the fourth catalytic run (conversion rate of 56.4 ± 1.3%) with only a slight decrease in glycidol selectivity. Thus, the use of a biosolids-based catalyst may facilitate conversion of various glycerol sources (i.e., byproduct streams from biodiesel production) into value-added products such as glycidol, and may also improve the economic feasibility of using thermal hydrolysis for treatment of biosolids.
Highlights
Over the last twenty years, the increased accountability of companies with regards to environmental issues has represented a formidable driving force for the development of sustainable industrial processes [1,2]
The production of glycerol carbonate is of key interest, as it could be used for the synthesis of high-performance hyperbranched polymers [8,9]
Urea glycerolysis can proceed through two different mechanisms, a radical or a non-radical pathway
Summary
Over the last twenty years, the increased accountability of companies with regards to environmental issues has represented a formidable driving force for the development of sustainable industrial processes [1,2]. The production of fuels and chemicals has started to use recycled or renewable feedstocks in place of oil-based raw materials [3,4] in an attempt to improve process sustainability while maintaining performance of traditional commodities. A one-step synthesis of glycerol carbonate has been reported by several authors through reaction of glycerol with supercritical CO2 [11], or using urea [12,13] or other reagents [14]. During urea glycerolysis, glycerol carbonate can undergo decarboxylation with the formation of glycidol, a highly reactive compound that could potentially replace glycerol carbonate in the production of polymers, leading to higher quality materials [9]. Despite the better performance of glycidol in Catalysts 2018, 8, 373; doi:10.3390/catal8090373 www.mdpi.com/journal/catalysts
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