Value-added uses for crude glycerol--a byproduct of biodiesel production

The dramatic increase in demand for transportation fuels and the increase in environmental concerns, coupled with diminishing crude oil reserves, have increased the emphasis on renewable energy. Biodiesel, one of the promising alternative and renewable fuels, has been viewed with increasing interest and its production capacity has been well developed in recent years. Although world biodiesel production was expected to reach a high capacity, in fact, it is less than the anticipated target and has increased at a slower rate [1]. The main reason is its relatively high production cost. Utilization of the glycerol co-product is one of the promising options for lowering the production cost.Biodiesel production will generate about 10% (w/w) glycerol as the main byproduct. In other words, every gallon of biodiesel produced generates approximately 1.05 pounds of glycerol. This indicates a 30-million-gallon-per-year plant will generate about 11,500 tonnes of 99.9 percent pure glycerin. It was projected that the world biodiesel market would reach 37 billion gallons by 2016, which implied that approximately 4 billion gallons of crude glycerol would be produced [2]. Too much surplus of crude glycerol from biodiesel production will impact the refined glycerol market. For example, in 2007, the refined glycerol's price was painfully low, approximately $0.30 per pound (compared to $0.70 before the expansion of biodiesel production) in the United States. Accordingly, the price of crude glycerol decreased from about $0.25 per pound to $0.05 per pound [3]. Therefore, development of sustainable processes for utilizing this organic raw material is imperative.Since purified glycerol is a high-value and commercial chemical with thousands of uses, the crude glycerol presents great opportunities for new applications. For that reason, more attention is being paid to the utilization of crude glycerol from biodiesel production in order to defray the production cost of biodiesel and to promote b