10 June 2011 18:51 [Source: ICB]
Rocketing acrylate prices could open the door to alternative production technologies
For more than two years, the price of acrylic acid has risen steeply. Consumers complain, but producers say margins must improve to justify the very investments that would allow output to increase and prices to soften.
|New tools change the economics of acrylic acid production|
A change may not be so bad, however. Propylene oxidation did not always dominate acrylic acid manufacturing, and the day may come when it no longer does. Complementary production technologies based on alternative feedstocks are being developed, and each penny added to the cost of propylene hastens commercialization for one or more of them.
SMOOTHING THE BUMPS
At least eight routes employ bio-based feedstocks. They offer to reduce cost and to insulate production from the ups and downs of petroleum markets.
Sourcing agricultural products such as sugar might present as many headaches as sourcing propylene, of course, but consumers would still benefit in that the cost of a feedslate comprising both bio-based and petro-based acrylic acid would be less volatile than a feedslate consisting of either by itself. By the same token, producers making both would be in a better position to absorb the variability of their own costs.
Each one of the four global majors in acrylic acid - BASF, Dow, Arkema and Nippon Shokubai - has a bio-based manufacturing process in development.
Dow made the most recent move in this direction, teaming with OPXBIO, a US biotech firm based in Denver, Colorado. Using an engineered microbe, OPXBIO can fermentatively convert corn- or cane-derived sugars to 3-hydroxypropanoic acid, or 3HP, in nearly 80% yield. Subsequent catalytic dehydration yields acrylic acid.
OPXBIO has conducted an 18-month trial of its process at pilot scale. The Dow partnership will operate the process at demonstration scale, with Dow contributing expertise in catalysis and downstream processing. "We have the objective, and it looks like we can meet it, of being able to produce and sell bio-based acrylic that is performance-equivalent without any subsidy or underwriting of the cost," says Chas Eggert, CEO of OPXBIO. "This product will compete head-to-head on a cost-and-performance basis with petro-based acrylic."
Eggert says OPXBIO should be able to make glacial acrylic acid at commercial scale from corn dextrose at 50-70 cents/lb, and from cane sugar (sucrose) at 40-60 cents/lb. This compares with producing petro-based acrylic acid, which the firm estimates at 75 cents/lb, assuming a propylene cost of 70 cents/lb. The economics would have an advantage at current propylene prices - monthly chemical-grade propylene contracts in the US hit 95 cents/lb in May.
Several other bio-based routes employ a fermentation step. Danish enzyme maker Novozymes and US agri-product giant Cargill are also pursuing the same path through 3HP. Both have extensive capabilities as well as deep pockets, but the partners do not plan to enter the acrylic acid business.
"Novozymes won't be an acrylic acid producer, but we are working with our partner Cargill to look at possibilities, including licensing the technology to another producing company," says Thomas Videbaek, executive vice president at Novozymes. "Our next milestone is to work toward development of a commercially viable process in the lab by 2012."
A licensee of the technology could have a plant operational by 2014 or 2015, he says.
US-based Metabolix does something that is similar, yet completely different. Metabolix's specialty is the engineering of microbes to make a family of bioplastics known as polyhydroxyalkanoates (PHAs). The technology is proven. Since 2007, Telles, a joint venture with US agri-product major ADM, has used it at commercial scale, producing PHAs that are marketed under the trademark Mirel.
One of the PHAs Metabolix's microbes can make is poly(3-hydroxypropanoate), or P3HP - a polymer of 3HP. A polyester, P3HP could be hydrolyzed to obtain 3HP, but Metabolix takes a shortcut that circumvents the isolation and hydrolysis of P3HP, and eliminates the dehydration of 3HP. "The whole biomass is concentrated, dried then subjected to a thermolysis process that produces acrylic acid directly," says Johan van Walsem, vice-president of strategy and commercial development.
"P3HP is converted directly to acrylic acid at essentially quantitative yield without requiring any additional chemical conversion steps," he says. "P3HP is already dehydrated, and the thermal process merely activates a molecular rearrangement without any loss or change in molecular weight, resulting in a very efficient process."
The route is a variation on the process, displaced by propylene oxidation in the 1970s, in which 3-propiolactone, obtained by the reaction of ketene with formaldehyde, is polymerized and destructively distilled to yield acrylic acid. Metabolix can manufacture other industrial chemicals from its PHAs, and the company plans to commercialize C4 chemicals derived from poly(4-hydroxybutanoate) such as gamma-butyrolactone (GBL) and butanediol (BDO) first, says van Walsem.
"Metabolix developed a common fermentation-and-recovery process such that acrylic acid commercialization will benefit directly from the experience gained with C4 chemicals," he notes. "Given the very [similar] equipment needs, the C4 chemicals site could be expanded to include production of acrylic acid with only relatively minor customization in the final refining section."
Van Walsem expects engineering for a C4 facility to begin later this year, with the acrylic acid technology following in about one year.
Other approaches based on fermentation include a technology patented by Genomatica, the US biotech firm that has partnered with Japan's Mitsubishi Chemical and the UK's Tate & Lyle to commercialize a microbial BDO technology. The acrylic acid process starts with the fermentative production of fumaric acid, a dicarboxylic acid, which is reacted with ethylene in the presence of a cross-metathesis catalyst to yield acrylic acid. A route based on lactic acid - a fermentation product with a large, well-developed market and production base - has been developed by the US-based Mid-Atlantic Technology, Research and Innovation Center (MATRIC). Last August, MATRIC spun off SGA Polymers to further develop and commercialize the technology.
PURE APPLIED CHEMISTRY
As the examples show, industrial biotech has taken a productive role in expanding the boundaries of chemical innovation - in each case, the usefulness of traditional chemical transformation has been extended by intermediates produced by engineered biological systems.
However, companies continue to direct considerable resources toward the development of purely chemical pathways to acrylic acid, some still embedded in petrochemical economics. For example, France-based Arkema is one of several companies to have sought a means of starting from propane. The absence of any functionality is challenging, but researchers made significant progress using highly active oxidation catalysts that could be continually regenerated in a circulating feed reactor.
"That reaction is attractive," says Jean-Luc Dubois, scientific director at Arkema. "The issue is that the price of propylene versus propane did not change as expected."
When the project began in the late 1990s, rising demand for polypropylene (PP) was expected to drive up the cost of propylene, while the cost of propane was expected to remain stable. Inevitably, a point would have arrived when producing acrylic acid from propane became more economical. Instead, rising oil prices drove up the price of propane, and the scenario never materialized.
In 2004, US-based Rohm & Haas (now part of Dow) began working with catalyst producer Engelhard to develop its own propane-based technology. There has been no word on the results of that association.
Two companies are developing pathways based on ethylene. US-based Novomer has invented catalysts capable of combining ethylene oxide with carbon monoxide to yield propiolactone, which can be processed to give acrylic acid. BASF is working to develop catalysts for producing acrylic acid from ethylene and carbon dioxide.
Perhaps the most promising, purely chemical route employs bio-based feedstock glycerol, a waste product of biodiesel manufacture. The approach is being developed by both Arkema and Japan's Nippon Shokubai.
Arkema's interest in glycerol stems from both its position in acrylic acid and its role as supplier of methyl mercaptopropionaldehyde (MMP), which is used to produce the amino acid methionine, says Dubois. Both MMP and acrylic acid can be made from the same intermediate, acrolein, which itself is accessible by the catalytic dehydration of glycerol.
Dubois says Arkema's process is well developed, running at pilot scale and producing several kilograms of acrylic acid per day. "We are testing several applications in house already, and a commercial plant is expected before five years," he said.
US-based management and technology consulting firm Nexant has analyzed the relative economics of alternative routes to acrylic acid. The glycerol route "could compete effectively in regions where there is significant and sustained biodiesel production, such as in Europe," says Alexander Coker, manager of Nexant's process evaluation and research planning (PERP) program.
He also suggests that the acetylene-based Reppe process could return in some regions where there is cheap coal, such as China.
However, fermentative routes through 3HP may be the strongest contenders, Coker says. "Nexant's analysis suggests that the bioroute could very well threaten the exclusive dominance of the propylene oxidation route."
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