A Dry Wash Approach to Biodiesel Purification

By Jonathan Dugan | November 01, 2007
As global warming moves onto the domestic and international agendas, and the U.S. government pursues its "Twenty in Ten" initiative to reduce carbon emissions and reliance on foreign imports, the United States is certain to remain a world leader in the production and use of biofuels. While the relatively small number of diesel vehicles in the United States currently presents limited opportunities for biodiesel, such vehicles are far more prevalent in Europe, providing a much greater biodiesel platform.

Biodiesel is produced through a chemical process called transesterification, where glycerin is separated from the fat or vegetable oil, leaving behind methyl esters and glycerin, which is detrimental to engines but valuable in soap manufacturing. To be considered "fuel-grade," biodiesel must be produced to strict industry standards in order to guarantee proper performance. Only biodiesel that meets ASTM D 6751 and is legally registered with the U.S. EPA can be sold and distributed as a legal motor fuel.

Unlike traditional diesel fuel, biodiesel offers considerable advantages, especially in terms of environmental benefits. B100 typically produces 60 percent less net carbon dioxide emissions than petroleum-derived diesel fuel.

Biodiesel clearly offers environmental, commercial and performance benefits that are only beginning to be realized. However, it should be emphasized that the fuel's performance heavily depends on the purity of the final product and the complete absence of particulates or contaminants.

The industry is answering the call by implementing programs designed to enhance fuel quality. BQ-9000 is a voluntary quality assurance program that includes procedures for fuel storage, handling and management with the goal of ensuring fuel quality throughout the biodiesel distribution system. Impure fuel may degrade engine oil, corrode fuel injectors with water and catalyst, block fuel injectors with soaps and glycerin, and cause seal failure due to methanol.

There are two generally accepted methods to filter and purify biodiesel: wet and dry washing. The more traditional wet washing method is widely used to remove excess contaminants and leftover production chemicals from biodiesel. In this process a fine water mist is sprayed over the fuel. The fuel's impurities are removed as the water settles to the bottom of the tank. However, the inclusion of additional water to the process offers many disadvantages, including increased cost and production time.

Conversely, dry washing replaces water with a magnesium silicate powder to neutralize fluid contaminants. An example is The Dallas Group of America Inc.'s trademarked Magnesol XL. The dry wash process offers myriad advantages over the wet wash system and is quickly becoming the method of choice among biodiesel producers for several reasons.

First, the dry wash process decreases production time. With biodiesel becoming increasingly attractive to end users because of its environmental and cost-saving advantages, producers are looking at streamlining production to cope with growing demand. Dry washed biodiesel can be ready for use in a few hours and is significantly quicker to produce than wet-washed fuel.

The dry wash process can also lower costs. In addition to the ever-increasing cost of water and the significant expense of water removal equipment, disposal of effluent water is often the single largest cost during production. Environmental agencies are vigorously pursuing illegal disposal of effluent waste. Hefty fines and imminent closure await those found breaking the law.

Less space is required to conduct the dry wash process. Settling is the key to effective water removal. Numerous large wash tanks and additional water settling tanks are usually required in the wet wash process. Plant space can be used more effectively with dry washing.

The dry wash process creates high-quality fuel. Since water isn't added in the dry wash process, it's possible to achieve less than 500 parts per million (ppm) water content in accordance with ASTM D 6751. In wet washing, the fuel's water content is usually more than 1,000 ppm, making it expensive, difficult and time-consuming to effectively remove.

Another advantage to the dry wash process is magnesium silicate can be reused. Magnesol used in the dry wash process has commercial use as compost and an animal feed additive. It also holds fuel source potential.

As with any growing industry, biodiesel production technologies continue to evolve. A variation of the dry wash process uses resin instead of magnesium silicate. However, this system is vulnerable and open to premature exhaustion; the resin doesn't produce the same yield of "clean" biofuel as the magnesium silicate procedure. Some resin manufacturers claim that a kilogram of resin will clean between 900 and 1,600 liters of biodiesel, but it's actually closer to 250 to 380 liters.

Companies considering a switch from wet wash to dry wash equipment may be surprised to learn it's possible. Many wet washing tanks can be relatively quickly and cost-effectively retrofitted to a dry wash system.

Schroeder Industries, a Leetsdale, Pa.-based filtration and fluid conditioning products provider, was recently selected as the exclusive U.S. distributor for UK-based Filtertechnik's line of dry wash purification products. Filtertechnik's system works on a proven method of removing production residues and soaps from fatty acid methyl esters, which is derived from vegetable oil feedstock through its absorption in magnesium silicate compound.

Schroeder's line of biofuel products employs purification units fitted with a laser particle counter to measure performance and provide users with a continuous detailed analysis of the particulate contamination and moisture content of the biodiesel. Customers can view results in real-time and store them in order to document batch cleanliness. This is particularly helpful to producers making fuel to ASTM D 6751 specification.

Regardless of which purification system is used, monitoring the contamination levels in the biodiesel is highly advisable. The measurement-and ultimately the removal-of particulates is crucial to maintaining engine life. When fuel is dirty, it quickly advances equipment wear and tear.

Biodiesel offers a wide range of benefits that makes it a highly viable alternative fuel source for the foreseeable future. The fuel's quality rests in large part on the purity and cleanliness of the final product.

Jonathan Dugan is a product specialist with Schroeder Industries LLC, a fluid conditioning technology company based in Leetsdale, Pa. Reach him at (800) 722-4810.

The claims and statements made in this article belong exclusively to the author(s) and do not necessarily reflect the views of
Biodiesel Magazine or its advertisers. All questions pertaining to this article should be directed to the author(s).
 
 
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