Cellulosic Propylene Glycol Production

Scientists continue to source different forms of biomass—i.e., plant material and animal waste—to produce renewable energy and alternative fuels. For example, biomass from corn is currently converted to glucose, then converted to fuel. Researchers would like to employ cellulose in this process since it is found in most plants but to do so becomes more challenging according to Walter Trahanovsky, PhD, a professor at Iowa State University’s department of chemistry, who may have discovered just how to do it. Trahanovsky developed a method to convert cellulose to glucose using pressure and high temperatures, but he was surprised to find the method also produced ethylene glycol and propylene glycol—two high value chemicals, one a major component in skin care products.

Cellulosic Ethanol Production

The two polymers of the monosaccharide glucose are cellulose, and while it is somewhat easier to convert starch to glucose, as is the case with corn, it is more difficult to do so with cellulose. Trahanovsky noted that glucose is already being produced from cellulose but via processes using enzymes or acids, which pose challenges.

“In making cellulosic ethanol, the procedures that use enzymes or acids to produce glucose from cellulose are expensive, or they do not produce the purity of glucose needed,” said Trahanovsky. “If someone is going to use glucose for the production of ethanol, there cannot be impurities because they will inhibit the enzyme reaction.”

As a first step toward converting cellulose to glucose, Trahanovsky’s team investigated cellulose from a number of plant sources. “We’ve used wood chips but the yields are not as good because about 30% lignin is present,” explained Trahanovsky. He added that his team tried using paper before deciding to purchase pure cellulose samples and optimize the production of cellulose from plant materials at a later time.

Trahanovsky and his team combined the cellulose sample with alcohols, which form a supercritical fluid when heated and applied with pressure. This combination was then heated to about 300°C with 150 atmospheres of pressure, and although Trahanovsky could not disclose which specific alcohols were used, he noted that nearly all the alcohol was accounted for at the end.

Separation Anxiety

After applying pressure and heat, Trahanovsky found that, as expected, 25% of resulting material consisted of alkyl glucoside and levoglucosan sugar derivatives, which could be converted to glucose for ethanol production and other uses. To his surprise, however, the reaction also produced an approximate 35% mixture of a propylene glycol and ethylene glycol. Once a separation technique is developed to divide the two materials, Trahanovsky believes they can be used by a number of industries as alternatives to their petrolatum-derived counterparts.

“One of the problems is that the ethylene glycol and propylene glycol still have to be separated and purified. It is relatively easy to get a mixture of the two but it is difficult to separate [them],” said Trahanovsky. While he was unsure of the best process to separate the materials, he did envision column chromatography could be a possibility; where a solution of propylene glycol and ethylene glycol is passed down a column containing an absorbent to separate the two.

Benefits and Ongoing Work

Trahanovsky finds there are a number of benefits to using his process to develop sugar derivatives, propylene glycol and ethylene glycol.

“[The process] does not use any additional reagents such as expensive catalysts or heavy metals,” said Trahanovsky.

This means the process does not incur added costs or produce waste; even further, the starting materials are relatively inexpensive.

“There are so many plants that contain cellulose. Someone could even convert waste paper to cellulose; they would just have to develop the extraction process.”

Finally, Trahanovsky emphasized that the reaction is not sensitive to impurities. “Enzymes do great things such as produce glucose from cellulose but they are sensitive to impurities. [This] technique is insensitive to impurities, allowing a person to deal with starting materials that are not pure,” noted Trahanovsky.

Once a separation technique is developed, the resulting propylene glycol could be formulated into skin moisturizers, where marketers could highlight the material’s petrolatum-alternative source. Trahanovsky also is working on separating the sugar derivatives, of which alkyl glucoside could be used as a surfactant in the cosmetics industry.

As work on the reaction continues, Trahanovsky concluded, “We are trying to make it more of a continuous process. The potential is there, it just needs additional engineering, and we are looking for a partnership to develop it on a larger scale.”

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