Cold Flow Treatment: FAME, HVO & Diesel Blends

By Werner A. Reimann and Bettina A. Siggelkow (Clariant OMS/Biodiesel Magazine) ... The major part of the biodiesel quota in Europe is still covered by first-generation fatty acid methyl ester (FAME) biodiesel, but recent fiscal legislation has made it possible for more second-generation biodiesel (HVO) to be brought into the market. Recent reconsiderations by the European council suggest capping the quota of edible vegetable oils processes to 6 percent with the gap in 2020 targets to be made up by alternative feedstock with no land use change/indirect land use change issues.
Europe embraces a wide range of climatic zones where single or combined use of FAME and HVO as a blending component is practiced. Cold flow treatment of the various kinds of biodiesel and blends with mineral diesel is of key importance for this industry.
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Vegetable oils contain certain amounts of saturated fatty acids that are mainly found in the chain length of C14, C16 and C18. Depending on the species of plant origin, the content of saturated fatty acids in the oil or fat can make up more than 50 percent.
The saturated fatty methyl esters are responsible for the cold flow and engine operability problems in the cold. Saturated fatty methyl esters, which are very similar to the linear paraffin in mineral diesel, will start to crystallize and drop out of solution upon cooling. This crystallization creates field problems similar to vehicle operability experienced in the past. During the crystallizing process, the saturated FAME molecules in the biodiesel are forming macrocrystalline structures that can block filter screens. Often this is found in internal combustion engines and can sometimes permeate through the whole of the fuel, causing it to form a solid gel.
This can create a serious problem in the distribution chain, because when B100 is transported to refineries or terminals to be used as a blending component, it often forms sediments or solidifies.
Saturated FAME crystal growth can be effectively controlled by the use of biodiesel flow improvers that hinder the crystals to form large interlocking species and produce very small crystal entities that can be readily dispersed.
Basic cold-flow properties of biodiesel are measured in the same way for mineral diesel. The cloud point (CP) is the temperature where the biodiesel gets turbid; the cold filter plugging point (CFPP) indicates the engine operability limit and the pour point (PP) reflects the solidification temperature.
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Through the carbon-carbon double bonds unsaturated compounds, the fuel stability is often negatively influenced and has to be compensated by appropriate antioxidants and stabilizers. On the other hand, cetane number and lubricity are positively influenced, which makes additives to bring sulfur-free B0 on-spec obsolete.
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The original concept of “second-generation biodiesel” and its major advantage in terms of sustainability implied the use of a nonalimental feedstock such as biomass from wood and organic waste. The main process postulated involved pyrolysis, creation of synthesis gas and finally liquefaction by Fischer-Tropsch synthesis. The resulting fuels therefore were called biomass to liquid.
Technically, the advantages for use as a fuel compared to first-generation FAME lie in the absence of functional groups and double bonds. These fuels, which are derived from biomass, resemble GTL-fuels derived from natural gas and are regarded as premium in terms of engine compatibility, fuel stability and cetane number.
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When used as a blending component, this kind of HVO has a devastating effect on the cold flow properties of winterized mineral diesel even at low concentrations. A German case study showed that the addition of 3 percent HVO to a FAME B7 to reach the 10 percent quota target was enough to seriously damage the CFPP performance of the cold flow additives ...
With biodiesel flow improvers out of the Dodiflow range, very effective cold flow additives are available. This allows refineries to treat biodiesel blends with a high content of saturated FAME for the desired low CFPP values. It also efficiently reduces pour points, which facilitates easier handling in cold climates. READ MORE