A Catalyst for Change

With all of its drawbacks, sodium hydroxide (or potassium hydroxide) for chemical ester conversion is by far the most commonly used catalyst in the industry today. Steve Howell, technical director for the National Biodiesel Board (NBB), told Biodiesel Magazine why sodium hydroxide has become the "catalyst of choice." He succinctly said, "It's effective and it's cheap."

The disadvantages of using sodium hydroxide for biodiesel catalysis are known all too well. Some of these shortcomings include the formation of soaps or salts through saponification when inordinate amounts of free fatty acids (FFAs) and/or water react with the base catalyst. When methanol is mixed with sodium hydroxide to form sodium methoxide or sodium methylate, it presents a whole new set of problems.

For starters, sodium methoxide is highly explosive; its formation is the most perilous part of biodiesel production. Even without combustion, the mix can be a serious health hazard to humans upon contact. From a process perspective, separating the methanol from its sodium hydroxide emulsions illustrates one more hoop that producers need to jump through to achieve proper ester conversion.

On top of that, add the growing movement to "clean up" industrial chemistry to curtail byproducts from chemical conversions, minimizing the disposal of hazardous and non-hazardous pollutants from various processes. It's called "green chemistry," and utilizing its potential could align the catalytic process used to refine biodiesel with the environmentally friendly reputation its end product already enjoys.

The realm of research
Since 1992, researchers at Iowa State University's Center for Catalysis (CFC) have been working toward the goal of developing more environmentally affable and process-efficient biodiesel catalysts, according to Dr. George Kraus, the center's director.

For the environmentally conscious, the CFC's mission is a necessary one. "In essence, we're dedicated to developing useful, practical catalysts and what we call sustainable, green chemistry methods in agriculture, the environmental sciences and various industries," Kraus said. "Green chemistry basically is trying to do chemistry without creating byproducts or pollutants." He said the driving cause of the organization is the pursuit to find chemical reactions that are as mild as possible.

A solid, or heterogeneous, catalyst would alleviate both the environmental aspects of dealing with sodium methoxide as well as the issues concerning the separation of the catalyst from the reactant for later reuse.
Kraus said the sodium hydroxide/methanol solution is a homogeneous catalyst, meaning it completely dissolves in the medium. "The removal of the catalyst from biodiesel has been an issue in the past," Kraus explained. "Often times there's a water wash, and sometimes that leads to some problems. So we thought heterogeneous catalysts would be a good answer there, because we could just fish them out later on and, if necessary, reuse and recycle them. In other words, reactivate them."

Chief NREL engineer Robert McCormick explained in simple terms what a heterogeneous catalyst is and why its use might benefit the industry. He said, "A heterogeneous catalyst is usually a solid whose surface is catalyzing reactions of gases and/or liquids," McCormick said. "The main advantage of a heterogeneous catalyst is that the catalyst is easily separated from the reactants and products. A common approach is to have a reaction vessel packed with catalyst particles � with the reactants just flowing past." The trouble-free removal of the heterogeneous catalyst from the "reaction product" is where the economic advantage would lie along with the elimination of sodium deposits in the biodiesel.

The physical structure of such a catalyst provides a massive surface area-packed with catalyst particles like non-noble metals, McCormick said-in a relatively small amount of space in order to efficiently convert the triglycerides to methyl esters and glycerin. McCormick said some heterogeneous catalysts made from aluminum oxide develop a "large pore network" gained through firing and drying during their production, after which the catalyst's surface area can reach an impressive 100 square meters per gram.

Intermediate steps toward commercialization
Howell cited three process changes that could potentially revolutionize the industry: Michael Haas' in situ transesterification process (profiled in the June 2005 issue of Biodiesel Magazine), a cost-effective solid catalyst and, lastly, easier mechanisms to handle low-quality feedstocks with high levels of FFAs. "If a solid catalyst could be found that would handle both taking the triglyceride to a methyl ester as well as the fatty acid to a methyl ester, that would be a significant step change forward in process technology," Howell said.

With almost three-fourths of the cost of producing biodiesel stemming directly from the cost of its feedstock, the cheaper FFA-laden feedstocks would be ideal if the right catalysts were developed. Traditionally, a homogeneous acid catalyst is used in a pretreatment esterification process to convert the FFAs to esters before basic transesterification. This necessitates an additional process step plus adding more hazardous chemicals to the already caustic cocktail of chemicals.

To tackle these acidic and basic catalysis problems, Kraus and others at the CFC have been working with Ralston, Iowa-based West Central Co-op to bring a couple of research initiatives to commercial fruition. Kraus said the CFC and West Central received a $1.2 million grant from the USDA's Industry Lead Program to fund their progressive research.

"We've been working with Iowa State's Center for Catalysis for about a year now, and we've gone through several iterations," said Jeff Stroburg, CEO of West Central. He said the CFC-West Central team is working on heterogeneous catalysts for both acidic and basic requirements. "One thing we're looking at is whether or not they can be used together," Stroburg said. "We just don't know at this point."
Stroburg said they hope to have the catalysts ready for commercial-scale testing within a year. The alternative, solid catalysts initially would be implemented in West Central-designed facilities.

Production ready: Axens' Esterfip-H catalyst
Across the pond in Europe, Paris-based Axens has a 13-year history in biodiesel research and development. With assistance from Axens' technical experts in France, including Michel Bloch and Jean-Alain Chodorge, Axens' North American technology marketer Joseph Ross told Biodiesel Magazine, "Over the last three to four years, we developed a solid catalyst system to reduce the high catalyst and chemicals cost of the original process. This resulted in the Esterfip-H process."

Ross said the first commercial-scale plant to use the Esterfip-H catalyst technology is currently under construction in S�te, France, for Diester Industries. The S�te plant will boast a remarkable 50 mmgy capacity.

Exemplifying the previously described benefits of heterogeneous catalysis, Esterfip-H represents a technological marvel. "Without caustic present and [with the] elimination of water washes, the product separation scheme is more simple and clean with less effluent to treat and dispose of," Ross said. An added bonus is the resulting glycerin's 98 percent purity.
Ross explained that the Esterfip-H catalyst is composed of cylindrical extrudates "that are treated and transformed into the solid catalyst."

The catalyst is a spinel-mixed oxide of two non-noble metals. "Many catalysts are composed of a solid support with an active metal deposited on the support," Ross said. "In the case of a spinel, one co-mixes the alumina support material with the non-precious metal." Of course, he imparted that the exact formulation is proprietary and not up for disclosure.

In operation, Esterfip-H will require slightly higher operating temperatures to perform, but Ross said the catalyst's stability and longevity-several years worth of use-cut conventional biodiesel catalysis costs by two-thirds. The solid catalysts' cost-efficiency represents one more plus to its already long list of advantages.

Axens and the West Central-CFC team are possibly on the forefront of a process revolution in the biodiesel industry, and as this technology marches forward with vigor, these advancements are sure to be catalysts for change.

Ron Kotrba is a Biodiesel Magazine staff writer. Reach him by e-mail at rkotrba@bbibiofuels.com or by phone at (701) 746-8385.