Adsorptive purification processes can be applied to both feedstock and biodiesel to serve as a refining “safety net.” Employing such processes represents a cost for value consideration that should be well-understood before making this significant, but necessary investment. A biodiesel production facility must have a clear understanding of the production hurdles it will face in order to be successful. Adsorbent purification considerations are one such hurdle.

Feedstock management (including procurement, quality, and refining) contributes to more than 80 percent of the process costs for making quality fuel. Refining practices employed to purify oil can also reduce free fatty acids, soaps, trace metals, organic and inorganic phosphorus compounds, and water. Refinement of triglycerides upstream of conversion to biodiesel is often utilized to accomplish more effective purification, ease of final product separation and better final product quality for both biodiesel and glycerin products. Each stage of the classical refining process is focused on incremental improvement of oil quality. The underlying goal of the combined operations is to produce high-quality finished oil by stripping detrimental contaminants from crude oil to yield a final product as close to 100 percent triglycerides as is economically practical.

The bleaching process is one of the critical unit operations within the refining process and is responsible for removing the oil soluble impurities that tend to negatively affect production efficiency and finished oil quality. Bleaching, by simple definition, is a filtration process dependent on the physical and chemical interaction of a sorbent, usually a silica or silicate based adsorbent mineral, with an oil or fat to improve its quality.

The adsorptive process is dependent on processing conditions that impact the rate at which a sorbent finds, interacts, and locks onto a contaminant. The efficiency of an adsorption process is interdependent on variables that increase the probability of interaction between sorbent particles and contaminants and, therein, the kinetics of adsorption. The more critical of these conditions include contact time, oil temperature, oil moisture content and vacuum. More effective sorbents will have a high capacity to reduce or remove a broad spectrum of unwanted adulterants and have adequate porosity to adsorb the contaminants without impeding flow through a filter bed. Oil-Dri’s Select line of specially modified, natural silicate adsorbents can be utilized to purify the feedstock of oils and fats. These adsorbents also help minimize water usage and are used as a sorbent for “dry wash” purification of biodiesel fuel after conversion of oil or fat to methyl esters.

Beyond adsorbent purification considerations, a clear understanding of other major production hurdles is critical in order for a biodiesel production facility to succeed. Other factors that will impact success include feedstock oil quality, level of additional refining needed, process diversity in formulation options, plant optimization, and a drive toward minimal waste streams. Before making any significant investments, it is best to consider how to manage their impact on production economics. Contemporary biodiesel facilities need: 1) the flexibility to process a diverse range of feedstocks that may vary widely in fatty acid profile as well as level of contamination, and 2) the mindset to produce not one, but two quality product streams: fatty acid methyl esters and the glycerin byproduct. Proper implementation of good refining practices including adsorptive purification is key for allowing production flexibility in a demanding market.

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Author: David Brooks
Chief Research Scientist, Oil-Dri Corp.
david.brooks@oildri.com