Renewable Route Beckons For Acrylic Acid

New catalysts promise efficient production from lactic acid.

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Alkali phosphates-modified NaY zeolites may spur use of a sustainable feedstock for making acrylic acid, hope researchers at Nanjing University, Nanjing, China, and Hong Kong Baptist University, Hong Kong. They have demonstrated that such catalysts can dehydrate lactic acid to acrylic acid at high yields.

Acrylic acid, which is widely used in the manufacture of paints and other products, conventionally is made by partial oxidation of petroleum-based propylene. "…The lactic acid dehydration route requires only one reactor and one type of catalyst, while the conventional route involves two separate reactors and two types of catalysts. Moreover, the lactic acid feedstock is renewable and the dehydration process is more environmentally friendly," note researchers Chak-Tong Au, a professor in the department of chemistry at Hong Kong Baptist University, and Weijie Ji, a professor in the school of chemistry and chemical engineering at Nanjing University.

"The key development challenges are 1) to further increase the selectivity to acrylic acid, 2) to perform the reaction under milder conditions, and 3) to achieve long-term stability of the catalyst."

"We are currently fine-tuning the catalyst system, especially on the aspect of the particle size of NaY zeolite. We are developing NaY-based catalyst of nano-size and optimizing the effect of particle size on catalytic performance. We are trying to increase the lactic acid concentration in feedstock and to further decrease the reaction temperature using the new catalysts. The results obtained on the nano-scale catalysts so far are very promising (with 74% yield of acrylic acid in a single-pass reaction)." They believe that yields of 80% or more are possible.

"We consider mass transfer an important factor for achieving better acrylic acid yield and avoiding side reactions. The design of reactor for better mass transfer would undoubtedly benefit the process."

Air treatment at 500°C reactivates used catalyst and fully restores its efficacy for lactic acid conversion. "So far we have not done tests on catalyst regeneration cycles," note Au and Ji.

"If everything goes smoothly, the pilot-scale testing could begin late this year or early next year," they say. "Several chemical manufacturers have contacted us concerning possible cooperation on the development." The researchers foresee industrial application in the near future, perhaps in five to eight years.

"Commercial production of such a catalyst is not a problem, [from] both [a] technical and economical point of view," Au and Ji say. "There are no particular obstacles for producing the alkali phosphates-modified zeolites on an industrial scale. Actually, the related preparation procedures are quite simple and straightforward."

More details on the catalysts appear in a recent article in ACS Catalysis.

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