Chemical engineers in India have found a way to produce a widely-used, non-toxic plasticiser for polymers from renewable citric acid and butanol using a simple, catalytic process.<\/p>\n
Tributyl citrate (TBC), is a non-toxic compound used as a plasticiser in the manufacture of polyvinyl chloride food wrapping film, toys, medical products, biodegradable polymers, cosmetics and in printing ink coatings. It is usually made using homogenous sulphuric acid and titanate catalysts, but these are dangerous to people and the environment and can produce many byproducts. Vijay Bokade and his colleagues at CSIR \u2013 National Chemical Laboratory, say that their heterogeneous catalyst is environmentally friendly, reusable and easy to separate. The use of bio-derived citric acid and butanol makes the process \u201ccompletely sustainable\u201d.<\/p>\n
The researchers tested two catalysts, a common zeolite catalyst, Ultra Stable Y (USY) and several phosphonated versions of USY with 1%, 2% and 4% phosphate. USY is particularly suitable as it is highly temperature stable, has a high surface area, is highly porous and is inherently acidic. The researchers added samples of each catalyst to the reaction mixture of citric acid and n-butanol in a closed batch system. The reactions were carried out at temperatures from 383\u2013423 K and stirred continually using a magnetic stirrer.<\/p>\n
Bokade and the team found that the phosphonated USY was more effective than standard USY, probably due to the increased acidity. The most effective catalyst was the 2% phosphonated USY. The 4% phosphonated USY, they say, had lower surface area and porosity. The most effective catalyst loading was found to be 20%. More than this did not affect the conversion rates, suggesting a surplus of active sites.<\/p>\n
The team also tested different ratios of citric acid to butanol and found that the best was 1:10. The best conversion rates were achieved at a temperature of 413 K, while after a reaction time of four hours, maximum conversion was achieved. With these conditions, Bokade and the team achieved a citric acid conversion rate of 100% and a yield of 93% TBC. They found the catalyst can be used six times before its activity begins to drop. By the seventh use the citric acid conversion rate dropped to 97%, but this still proves its stability.<\/p>\n
\u201cThis study opens new avenues of research in the development of a sustainable and industrial benign catalytic process for the synthesis of environmentally friendly and non-toxic TBC plasticiser from renewable sources,\u201d says the team.<\/p>\n