Calcium Magnesium Acetate (CMA) An Alternative Road Deicer

by H.J. Bothast, Fermentation Biochemistry Research Leader, National Center for Agricultural Utilization Research, ARS, Peoria, IL.

If calcium magnesium acetate (CMA) becomes widely used as a road deicer, the demand for starch could increase. Starch can be readily fermented to acetic acid, the major chemical used to make CMA.

An alternative road deicer is needed to replace the 9 million tons of salt (sodium chloride, or NaCI) used annually in the United States. Although salt is inexpensive (1 -2 cents/lb) and effective, it causes enormous economic losses each year from corrosion of vehicles, bridges, and underground utilities; from deterioration of concrete roads and bridges; from pollution of streams and water supplies; and from killing roadside vegetation. The average annual economic loss caused by salt damage in New York State alone was estimated recently to exceed $1 billion, caused by spreading about 1 million tons of salt. This is equivalent to an economic loss of more than 50 cents per pound of salt used.

Aside from the direct economic losses, the most potentially serious damage in some States is the pollution of water supplies; for example, in Massachusetts, the sodium content in drinking water in many communities already exceeds 20 milligrams per liter, the recommended upper limit for individuals on a sodium-restricted diet.

Research initiated by the Federal Highway Administration identified CMA as an acceptable deicer without the harmful side effects of salt. Compared with salt, CMA is essentially nontoxic, noncorrosive, and nonpolluting, and it lowers the freezing point of water by 16 C more than salt does. Widespread use of CMA would also help to alleviate the effects of acid rain by acting as a buffer and helping to neutralize sulfuric and nitric acids in the environment next to roadways and in streams and lakes that receive the runoff.

CMA is manufactured commercially from acetic acid, dolomitic lime (CaO - MgO), and magnesia (MgO) and sold for about 30 cents per pound. Most of the CMA manufacturing cost is for acetic acid, which is now typically synthesized from natural gas and lists for about 29 cents per pound plus shipping.

The price of CMA is a strong incentive to find methods to reduce the cost of production, and to find techniques that can reduce the rate of application for adequate snow and ice control. Costs could be reduced substantially by fermenting low-cost materials to acetic acid. Low-cost materials that could be used include corn starch (glucose),wood (glucose and xylose), municipal solid waste (glucose and xylose), unused whey (lactose), and possibly several single-carbon compounds (CO, CO₂ , and methanol). Two fermentation routes are possible for the production of acetic acid. One is a standard fermentation to ethanol followed by oxidation with bacteria to acetic acid (similar to vinegar production); the second is direct conversion of sugar to acetic acid by bacteria in the absence of oxygen.

Future research and development can help reduce the cost of CMA by:

Identifying the least expensive feedstocks;

Developing continuous fermentation processes that use bacteria which can produce acetic acid from broth containing as much as 10 percent CMA in solution;

Developing new and more efficient recovery techniques, and;

Recovering salable byproducts.