Environmental impacts of valorisation of crude glycerol from biodiesel production – A life cycle perspective

• Published in: Waste management (Elmsford) 2024-04, Vol.179, p.55-65
• Main Authors: Tomatis, Marco, Kumar Jeswani, Harish, Azapagic, Adisa
• Format: Article
• Language: English
• Subjects: Biodiesel; Biofuels - analysis; Climate change; Crude glycerol; Environment; Environmental sustainability; Glycerol - chemistry; Glycerol purification; Incineration; Life cycle assessment; Technology
• ISSN: 0956-053X; 1879-2456
• DOI: 10.1016/j.wasman.2024.03.005

•Three acid-based physico-chemical processes for glycerol purification are assessed.•H2SO4-based process is the best option with net-savings in 17 out of 18 impacts.•Credits for the purified glycerol and co-products offset the impacts of the process.•H2SO4-based treatment performs better than incineration in ten out of 18 impacts.•The results are sensitive to the crude glycerol composition and other assumptions. Biodiesel production produces significant quantities of impure crude glycerol as a by-product. Recent increases in the global biodiesel production have led to a surplus of crude glycerol, rendering it a waste. As a result, different methods for its valorisation are currently being investigated. This paper assesses the life cycle environmental impacts of an emerging technology for purification of crude glycerol – a multi-step physico-chemical treatment – in comparison to incineration with energy recovery commonly used for its disposal. For the former, three different acids (H3PO4, H2SO4 and HCl) are considered for the acidification step in the purification process. The results suggest that the H2SO4-based treatment is the best option with 17 net-negative impacts out of the 18 categories considered; this is due to system credits for the production of purified glycerol, heat and potassium salts. In comparison to incineration with energy recovery, the H2SO4-based process has lower savings for the climate change impact (−311 versus −504 kg CO2 eq./t crude glycerol) but it performs better in ten other categories. Sensitivity analyses suggest that that the impacts of the physico-chemical treatment are highly dependent on crude glycerol composition, allocation of burdens to crude glycerol and credits for glycerol production. For example, treating crude glycerol with lower glycerol content would increase all impacts except climate change and fossil depletion due to the higher consumption of chemicals and lower production of purified glycerol. Considering crude glycerol as a useful product rather than waste and allocating to it burdens from biodiesel production would increase most impacts significantly, including climate change (22–40 %), while fossil depletion, freshwater and marine eutrophication would become net-positive. The findings of this research will be of interest to the biodiesel industry and other industrial sectors that generate crude glycerol as a by-product.