Production of Biodiesel from Rapeseed Oil Through Urea Clathration using AdBlu
Biodiesel is growing in popularity as an alternative liquid fuel which has a more positive profile for the environment than petroleum diesel. A critical challenge for biodiesel is cold weather performance, evident by cloud points ranging from 13°C to 0 °C.
Low temperature operability is a major concern for all diesel-like fuels operating in low temperature environments. With petroleum diesel fuels, a range of options exist to adjust the low temperature operability limits of the fuel, including varying fuel composition, and use of low temperature operability additives. The wide possible range of hydrocarbons that can be used as diesel fuel allows considerable control of low temperature properties just by controlling the type and amount of some high boiling point components — for example by controlling the high end distillation temperature of the finished fuel. The range of compounds that compose biodiesel, however, are very limited and varying fuel composition provides a much narrower range of adjustment. To add to the challenge, most biodiesel contains a significant proportion of saturated long chain fatty acids that are very similar to the long chain paraffins, whose concentration is undesirable in diesel fuels when low temperature operability range is to be extended. Thus, achieving acceptable low temperature operability limits with biodiesel blends can be a significant challenge.
There are several major sources of potential low temperature operability problems with biodiesel:
- Formation of waxes in the fuel—Long chain methyl esters, especially saturated ones, can solidify as the fuel temperature drops. These can plug filters and cause engines to have ignition failure or stall shortly after start-up.
- Formation of precipitates from fuel contaminants—Some fuel contaminants such as saturated monoglycerides, sterol glucosides and soaps can lead to the formation of filter plugging precipitates at temperatures above the fuel’s cloud point.
- Fuel system icing—At sub-zero temperatures, water from fuel contamination can freeze, causing the precipitation of ice particles (water contamination is discussed in Biodiesel Standards & Properties).
Cold flow properties vary depending on the biodiesel feedstock, as illustrated in Figure 1 using a cloud point example. It is apparent that there are significant differences in the cloud point for biodiesel derived from different sources.
Figure 1. Average Cloud Point for Palm Oil (PME), Soybeans (SME) and Rapeseed (RME) Biodiesel
While the cloud point of biodiesel can be reduced to extremely low levels through such processing as cold filtration or the formation of urea clathrates that reduce or even eliminate the saturated alkyl esters in the fuel [Bist 2007], fuel viscosity may become excessive at these low temperatures. Also, such processing can significantly reduce the yield of the final product because, in addition to saturates, some unsaturated fuel components are removed as well.
This project will investigate the fractionation of Rapeseed Oil by urea and methanol for producing modified biodiesel with significantly reduced cloud points. The process takes advantage of clathrates which form between urea and long-chain saturated methyl esters. These urea inclusion complexes (UICs) are removed through liquid-solid separation and the fractionated saturated methyl esters and the unsaturated methyl esters are recovered separately. The process is simple, uses low heat, and recycles all raw materials.
Blockaid plan to explore the use of AdBlu, a commercially available Diesel exhaust fluid (DEF), (32.5% urea and 67.5% deionized water), to reduce the cloud point of Rapeseed Oil and produce a modified low cost environmentally friendly biofuel with a low carbon footprint in a novel and innovative process. Blockaid is a growing Haulier with 18 HGV vehicles and a GOLD FORS rated status. Following success with the above project, Blockaid plan to further develop technology around an HGV on board Biodiesel/AdBlu unit, this would be a proactive advancement in this rapidly growing environmentally sensitive area.
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