Process Technology Meets New Biodiesel Challenges
The biodiesel industry used to be fairly straightforward. Economical, refined soybean oil was fed into a well-known batch caustic process to produce on-spec product. High-priced diesel, high-value glycerin byproduct and a tax credit made turning a profit relatively simple. Over the past few years, however, the industry has changed dramatically. Expensive feedstock, ever-tightening specifications for biodiesel and glycerin, government mandates and no tax credit have added a new level of complexity and reduced margins.
Against this backdrop, producers turn toward process technology to remain competitive. Feedstock still represents more than 80 percent of biodiesel production costs, so as producers seek processing cheaper feedstock, high free fatty acid (FFA) levels, moisture, “heavies,” sulfur and solids must be dealt with. Many producers will use outside technology experts to help them define and implement the process technology suite that best fits their needs.
High FFA (15 to 100 percent): Many pretreatments can economically process up to 15 percent FFA, including noncaustic technologies, distillation, glycerolysis, acid esterification and ion exchange. Some technology combinations are effective up to 30 percent FFA, but only noncaustic technologies can effectively process up to 100 percent FFA. The best technology or combination of technologies will depend on the needs of each particular plant.
Moisture/water (higher than 2 percent): This is unacceptable for many pretreatment technologies and for transesterification. Further, since water separates over time, there may be periods when concentration is much higher than 2 percent. Pretreatments that are less affected by moisture include some noncaustic processes, distillation and glycerolysis.
Heavy components: Heavies, present in feedstock like DDG oil derived from corn, brown grease and some tallow, affect product quality and must be removed. Biodiesel distillation is used to remove heavy components.
Sulfur: Present in feedstock like brown grease and tall oil from the forestry industry, sulfur affects product quality, in particular with tightening sulfur specifications. Biodiesel distillation is used to reduce sulfur.
Solids and trash: Filtration is an effective way to remove solids, but many producers choose to settle solids in the feed tank over time and clean it periodically to eliminate regular solids handling.
Lower sulfur and glyceride specs and new cold filter plugging point expectations, among others, worry some biodiesel producers. Cheaper feedstocks can make transesterification more difficult, leaving mono- and diglycerides in the biodiesel. Distillation, again, can help meet tightening specs but not without cost.
Greater use of lower quality feedstock increases the likelihood of product losses throughout the plant. There are feedstock losses during filtration and tank cleaning; FFA creates emulsions in the reactor and product is lost to the glycerin stream; and biodiesel distillation to achieve tighter specifications may generate sizable product losses. While there are no silver bullets, technology choice or optimization may dramatically improve yields. Pretreatment technology should lower FFA to 0.1 percent instead of the currently accepted 1 percent to minimize emulsions. Reaction conversions can be increased to minimize glycerides. Biodiesel distillation can be upgraded to reduce biodiesel losses. Noncaustic technology can, in general, process low-quality feedstock with minimal yield losses.
Methanol losses end up in the wastewater or glycerin and become economic and environmental challenges. Two distillation columns are used to recover and dry methanol, and adding recovery systems tends to have a short payout. Even if the plant has a methanol recovery system, there are opportunities for additional methanol recovery and energy efficiency.
A newly upgraded biodiesel plant with multiple distillations (feedstock, methanol, glycerin, biodiesel) will benefit from periodic energy audits and investment in energy efficiency. Heat recovery, boiler and hot oil system efficiency improvements are a few of many opportunities.
Capacity increases will reduce fixed costs per gallon and is a fraction of new capacity capital expenses. Existing infrastructure, use of plant personnel and relationships with local suppliers make capacity increases a good way to improve competitiveness.
Finally, in addition to in-house technical staff, a producer should build a relationship with a technology company to provide technical services and support. These may include independent energy audits, yield improvement projects and technology upgrades. Using outside technology consultants for special projects such as plant optimization and technology upgrades, and ongoing technology reviews, is common practice in the refining industry to remain competitive in an ever-changing, challenging environment.
Author: Roman Wolff
President, Enhanced Biofuels LLC