Succinic acid is a four-carbon dicarboxylic acid that occurs naturally in plant and animal tissues. It plays a biochemical role in the citric acid cycle, or Krebs cycle, as part of cellular respiration. Today, succinic acid is commercially produced from fossil-based feedstocks via catalytic hydrogenation of maleic anhydride or as a byproduct of adipic acid production. This carboxylic acid can be used to produce acyl halides, carboxylic acid salts, anhydrides, esters, amides, imides, nitriles, butane diol and other materials for use in a number of industries, including resins, fibers, plastics, personal care, pharmaceuticals and agriculture.
Succinic acid is produced commercially from maleic anhydride via petrochemical processes; maleic anhydride in turn is derived from n-butane or coal. The refining of fossil-based feedstocks to produce petrochemicals leads to the emission of harmful gases into the environment.
In keeping with its green chemistry motif, DNP Green Technology, an industrial biotechnology company, has licensed a fermentation method from the US Department of Energy (USDE) to process succinic acid on a larger scale and in a more eco-friendly manner, which the company expects will benefit both the environment and the consumer. Dilum Dunuwila, PhD, vice president of business development for the company, is excited about the bio-based production of succinic acid. “We’ve taken the fermentation process developed by the USDE and scaled it up,” said Dunuwila.
The Lifecycle of Carbon
According to Dunuwila, nearly 50,000 metric tons of succinic acid are produced petrochemically per year. He adds that “it’s relatively expensive [to produce] and is made from a finite resource that is imported and highly susceptible to volatility driven by economic and geopolitical crisis.” To petrochemically produce succinic acid, carbon is obtained from fossil deposits. Dunuwila notes, “Refining and processing fossil-based carbon leads to CO2 accumulation in the atmosphere.” In contrast, the new bio-based process consumes CO2 rather than emitting it, providing the long-term potential to generate carbon credits for potential manufacturers. “We have a much lower carbon footprint,” continued Dunuwila. “Since we utilize renewable crops and CO2 to produce succinic acid, we complete the cycle of carbon.”
The process is based on an Escherichia coli bacteria that metabolize glucose produced from corn, wheat tapioca, sugarcane and cellulose. “We feed the glucose produced by these crops to the E. coli and succinic acid is produced as a metabolite of E. coli,” explains Dunuwila.
The bio-based process of creating succinic acid is not only better for the environment but also, according to Dunuwila, cheaper than the petrochemical route. The succinic acid produced from this process can be converted into compounds for specialty chemicals, plastics and personal care products, among other uses.
Esters from Succinic Acid
Esters produced from succinic acid have many applications in personal care. They are used as stabilizers for active ingredients in self-tanning lotions, and they can be applied to nail care products. Dunuwila’s company currently holds a patent for a succinic acid-derived ester in a nail care product. “The ester of succinic acid, diethyl succinate, in combination with another ester is suitable for removing nail polish,” explained Dunuwila. Solvents such as acetone that are commonly used in nail polish removers can be volatile, reports Dunuwila, and inhaled by consumers using the product and manufacturers creating it. Diethyl succinate, however, is reportedly a nontoxic, nonvolatile solvent.
With the influence of REACH in Europe and a global initiative to formulate with natural and organic ingredients, the personal care industry has sought bio-based raw material options. These regulatory issues in part led Dunuwila’s team to seek a bio-based alternative to succinic acid. “Because of global warming, there is a regulatory push as well as a consumer demand to reduce carbon footprints. That’s why we went to a bio-based process,” said Dunuwila.
The bio-based process for succinic acid will certainly be praised in California, where the state’s Environmental Protection Agency has issued a Green Chemistry Initiative. In addition, it will provide formulators of personal care products with bio-renewable alternatives to esters currently in use.
The reach of succinic acid extends beyond personal care. For example, there is a large market in industrial solvents. “There is a huge demand for non-chlorinated solvents,” said Dunuwila, who notes that the esters also can be added to diesel fuel to reduce particulate emissions. And as the industry is well aware, there has been a surge of media reports on the harmful effects of phthalates in toys and personal care, an area where an ester of succinic acid could serve as an alternative.
Regardless of application, Dunuwila finds that the compounds produced by succinic acid offer a more environmentally friendly alternative to the petrochemical version. As government regulation of chemicals increases, the option is surely viable.