Quality control in biofuels production
Additives such as emulsion breakers and antioxidants can help to improve the product quality of biofuels and hence their profitability
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Fossil fuels are not running out yet, but bottlenecks of these natural resources are just a question of time. Biofuels are clean fuels which do not produce excessive amounts of greenhouse gases. They are sustainable and can be produced from crops and organic matter. The use of suitable additives can help to meet product quality requirements with increased production capacity and improved workflow.
The increasing use of fossil fuels leads to higher CO2 emissions into the atmosphere, resulting in a greenhouse effect with climate change and global warming. Compared to fossil fuels, renewable fuels from non-fossil sources have many advantages and are more eco-friendly. They produce fewer greenhouse gases (GHG) and are environmentally sustainable. Unfortunately, it is also true that growing plants and processing the plants into biofuels still consumes a lot of energy and that biofuels are not ‘carbon neutral’. Biofuels are not an invention of modern times and have been around for decades. Henry Ford had originally designed his famous Model T to run with ethanol and, since the 1930s, biodiesel has been available worldwide.
Biofuels are produced from organic matter in a relatively short period of time (days, weeks, months). This is a significant difference when they are compared to fossil fuels, where formation took millions of years. The first step in biofuels production is obtained through a process of biological carbon fixing. Inorganic carbon (CO2) is converted into organic compounds. The term biofuels covers a range of products such as biogas, bioethanol, biobutanol and biodiesel.
Raw materials for biofuel production are biomass from biological sources such as products of agriculture and forestry, vegetable oils, sugar, corn, starch, and so on. Biofuels can be produced by a number of commercial processes and serve as components for blending into petroleum-based fuels. Worldwide, more and more new plants are being built to produce biofuels, using well-established technologies or new concepts. Biofuels represented around 4.7% of energy used in transport in Europe during 2012. A number of European policies like the Renewable Energy Directive (RED) and the Fuel Quality Directive (FQD) have been adopted with a focus on defined greenhouse gas savings and reduction in fossil fuels.
Biomass to liquids (BTL) is a multi-step process which can be accomplished by bioprocessing technologies such as fermentation, anaerobic digestion and distillation. These processes require strong technical knowledge because the conversion of useful liquid biofuels and bioproducts is carried out by microorganisms. There are a number of effective biological/chemical technologies available, which convert any biodegradable material such as urban wastes and agricultural residues into useful chemicals.
Products which can be economically produced from biomass are:
• Primary alcohols (ethanol, propanol, n-butanol)
• Secondary alcohols (isopropanol, 2-butanol, 3-pentanol)
• Organic acids (acetic acid, propionic acid, butyric acid)
• Ketones (acetone, MEK, DEK).
For decades, Brazil has converted sugarcane into ethanol. Research facilities like the BP Biofuels Global Technology Centre in San Diego, California, are developing innovations like sugar-to-diesel technology. In the past, it was uneconomical to break the structure of cellulose to produce cellulosic ethanol from agricultural residues. Promising new biological/chemical technologies like the Sunliquid process developed by Clariant are in operation in Germany where straw is converted into bioethanol. New concepts with special microorganisms economically break the structure of cellulose and provide sugar molecules. The following fermentation with another type of microorganism produces bioethanol. Energy-saving absorption technologies, rather than distillation, are used after fermentation. Around 100 kg of bioethanol can be produced from 450 kg of straw. About 60% of the 240 million t/y of straw produced in Europe could be used for the production of bioethanol, sufficient to cover up to 25% of total fuel demand up to 2020.
Biofuels can also be produced through a thermochemical route, which is a high energy consuming process. The biomass is gasified and converted to syngas, from which high quality Fischer-Tropsch (FT) fuels can be made. Proprietary new technologies with modified versions of the Fischer-Tropsch process are available. They favour the formation of long chain waxy molecules and reduce gaseous byproducts and unwanted smaller hydrocarbons. A combined hydroisomerisation and hydrocracking step provides the desired, lighter products.
Another interesting technology which awaits the next big breakthrough is the industrial production of algae biofuels. It is a process involving algae growth, biomass extraction and post-processing. Algae production does not compete with high value foods and can yield more fuel than soy or palm oil. Nutrient rich water is pumped into a container with specially chosen algae. Wastewater or brackish water can be used as growing medium. By means of photosynthesis the algae produce high quantities of lipids. The lipids can be converted into biodiesel and related fuels. Typically, centrifuges are used to separate the biomass from solution, which is why algae biofuels are expensive.
Biodiesel is made from animal and vegetable oil feedstocks and can be used neat or blended with conventional diesel. Biodiesel offers some advantages as it is biodegradable with a high flashpoint. Less net CO2 is produced if vegetable feeds like sunflowers, soya beans, rapeseed or palm oil are used. In Europe, mainly rapeseed oil is used; this is extracted from the seeds of the rape plant (Brassica napus oleifera). These seeds have an oil content of 40 to 45%. Other plants like Jatropha (Jatropha curcas) show great promise for the future as they have high oil contents as well. They can be grown in arid regions which are otherwise incapable of being used for agricultural purposes.
In 2012 worldwide, approximately 20 million tonnes of biodiesel were produced. This covers around 1% of the planet’s total yearly fuel consumption. Production and the market for biodiesel are both expanding as oil prices remain high. In general, biodiesel can be produced by a number of commercial processes, including innovative processes for the removal of glycerin, methanol and other byproducts.
A commonly applied technology to produce fatty acid methyl ester (FAME) biodiesel is the base catalysed transesterification of triglycerides. Methanol reacts with triglycerides in the presence of a catalyst such as sodium hydroxide (NaOH). The transesterification reaction takes place at a temperature of about 60-70°C at atmospheric pressure. The free fatty acid (FFA) chain is broken off from the triglyceride molecule. The chemical reaction produces FAME and byproducts such as glycerin (glycerol) and soaps. The biodiesel is washed with mildly acidic water, which removes the neutralised catalyst, glycerin, soaps and unreacted methanol. High soap levels can result in emulsification of the soapstocks. To overcome this hurdle, an emulsion breaker such as Kurita EB-4113 can be added to provide a quick separation into oil, water and remaining fatty acids. The flushed soapstock phase contains byproducts such as phosphatides, tocopherols, sterols, waxes, free fatty acids, chlorophyll and carotene. Figure 1 shows the separation of water and remaining soapstock at ambient temperature after treatment with Kurita EB-4113. A temperature increase above 30-40°C improves the efficiency of water separation and provides pumpable soapstocks. Although fatty acids can be recovered from the soapstock with mechanical separation equipment, a residual amount has to be disposed of at high cost.
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