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Sunday, March 30, 2008 - 3:51 AM
Feedstock sources Although biodiesel can be produced from any triglyceride, the popular fats and oils most commonly used worldwide are: The predominant feedstock used in the United States is soybean oil. Other vegetable oils, such as corn, cottonseed, canola (rape seed), flax, sunflower and peanut, also can be used. These seed oils generally are more expensive than soybean oil.
However, on several days in October 2003, the cash price of soybean oil did exceed that of corn oil. Animal-derived products such as tallow, choice white grease (lard), poultry fat and yellow grease are also triglycerides and are used as a biodiesel feedstock. http://www.oilnfat.com/page002.aspx
These products, when compared to plant-derived oils, often offer an economical advantage as a feedstock. There is also some indication that these sources, which are high in saturated fats, produce less nitrous oxides compared to plant oils. However, this research is ongoing. The third main source of triglycerides is recycled oil and grease, usually from restaurants and food processing plants.
Although more pre-treatment is required for this feedstock compared to virgin vegetable oils, economically it can be a very attractive feedstock. The use of a recycled product such as used cooking oil is an environmentally friendly process since it solves a waste disposal problem.
Production from soybeans The main sources of soybean-derived biodiesel feedstocks are: 1. Solvent extraction plants that process 2,000 to 5,000 tons of soybeans per day. These plants are set up to meet both domestic and export markets for protein meal and soybean oil. Most soybean meal for export is shipped from extraction plants with good access to the Port of New Orleans via the Mississippi River and its tributaries. http://www.oilnfat.com/page0051.aspx
Many large extraction plants also incorporate a refinery operation or have reasonable transportation to a refinery at another site. 2. Mechanical extraction plants set up primarily to produce expeller-type meal, which has bypass protein advantages for ruminating animals.
These plants usually are set up to process 24 to 800 tons of soybeans per day. Most small plants do not have in-house refineries. Several new mechanical plants that have been constructed during the past several years do have their own refineries that produce specialty oils.
There is a high USA domestic production of soybean oil, compared with other vegetable oils and animal fats. Soybean oil represents almost 60 percent of the total fats and oils produced in the United States. -Many subsidies and grants in the past have been based on vegetable oils, although most of the new governmental programs are feedstock neutral. -National soybean associations have done an effective job in promoting the product.
It should be noted that any consideration of biodiesel feedstock supply should include soybean oil, since most of the biodiesel currently produced in the United States uses soybean oil as the feedstock. A potential biodiesel producer should also be aware of the changes during the past four to five years in the "soybean complex." The soybean complex is the global relationship between the various factors influencing the price of soybeans, soybean meal and soybean oil including supply, transportation, demand, alternate protein and oil sources, animal production and, sometimes, political considerations.
For a better understanding of the dynamics of supply, consumption and prices of whole soybeans and soybean products, the following tables show the changes in the soybean complex domestically and internationally since October 1999. You can be assured that market prices will change, up or down. The consumption of soybean oil for biodiesel feedstock at present is only a minor influence on the price.
It is estimated by FPRF that the amount of recycled cooking oils and fats (yellow grease) from the restaurant and food service industry exceeds 2.75 billion pounds. This supply of triglycerides should continue to increase as the restaurant industry grows. The message: A well-planned biodiesel facility should be designed to handle not only soybean oil, but multiple feedstocks, including locally available vegetable oils, fats from animal sources, and yellow and brown grease from restaurants. http://www.oilnfat.com/page0071.aspx
The method used for FAME synthesis from soapstock involves these steps: -Hydrolysis of all fatty acyl ester bonds by saponification. -Removal of water via standard industrial methods used to prepare an acid oil, a current product used in the animal feed industry. -Acid-catalyzed esterification of the resulting free fatty acids. While the above description seems complicated, the process is simple and efficient, and can operate at ambient pressure and relatively low temperature in simple equipment.http://www.oilnfat.com/page0061.aspx
This process appears to have promise, particularly if the market spread between soybean oil and products such as recycled grease continues to increase. Processing considerationsAll biodiesel feedstocks, including soybean oil, require some amount of pre-conditioning, often chemical refining, before being processed into biodiesel. For example, crude soybean oil must be degummed to remove sources of phosphorous, which degrades the catalysts employed in biodiesel production.
Free fatty acids should also be removed from the feedstock before transesterification, especially if recycled cooking oils, which are high in free fatty acids due to their exposure to high temperature during frying, are used. Free fatty acids are corrosive, and therefore hard on fuel storage facilities, fuel systems and engines. ASTM standards set forth tight tolerances on the allowable levels of free fatty acids in biodiesel.
A common approach for removing free fatty acids from the feedstock is via acid catalyzed esterification in the presence of methanol. This converts the free fatty acids to methyl esters (e.g., biodiesel). Acid esterification equipment requires the use of stainless steel equipment due to the corrosive nature of the process.
Crude oil from a crushing operation also may be pre-treated by caustic refining to remove free fatty acid. The soapstocks generated in this step are then removed by washing the oil with hot water. The oil must be dried to remove the water before transesterification, since water inhibits the biodiesel-producing reaction. In at least one large biodiesel plant, the feedstock is RBD soybean oil (refined, bleached and deodorized). http://www.oilnfat.com/page0031.aspx
As mentioned previously, soybean oil or other virgin vegetable oils are reasonably consistent. The feedstock used today will be approximately the same as the feedstock tomorrow. This usually is not the case when using recycled oil.
Recycled oil requires accurate chemical analysis to determine what pretreatment may be required. Used cooking oil may also contain sulphur compounds, often the result of frying sulphur-bearing foods such as onions. There are several proven methods to strip out any unwanted sulphur compounds during pretreatment.
Obtaining used cooking oil for use as a biodiesel feedstock involves more than just driving up to your local McDonalds and filling a tank truck. The recycling process includes not only the pickup of the cooking oil, but also the proper removal of food particles and other physical contaminants. In addition, used cooking oil contains water, and the oil must be dried.
An experienced rendering company is in the best position to do these pre-process steps and then deliver a cleaned and dried recycled product to the biodiesel plant. The use of feedstocks other than soybean oil may involve extra processing steps and more equipment. But to be financially successful, a biodiesel plant needs to be prepared to process multiple feedstocks based on regional availability, market prices and processing costs.
When processing multiple feedstocks, consideration should be given to using a blended feedstock. Instead of processing feedstock "A" for a few days and then switching to feedstock "B" for another period of time, various feedstocks can be pretreated and temporarily stored in separate agitated storage for final blending prior to transesterification. In this way, feedstocks can be analyzed and monitored, yielding a final blend that will be more consistent and result in a more efficient and controlled process. http://www.oilnfat.com/page0041.aspx
In conclusion, remember that the goal is to produce biodiesel that will help reduce America's dependence on imported oil, and at the same help the environment. To accomplish this, the primary cost of biodiesel production—the feedstock—must be carefully considered. Over the long term, economics will dictate that the use of multiple feedstocks will be a significant factor in the development of a successful alternate fuel business.
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