For each ton of MMA, an MMA plant produces about three tons of spent acid, explained Dr. Steffen Krill, who is responsible for Acrylic Monomers Innovation Management at Evonik. While the actual MMA production is slightly larger than a multi-family dwelling, the sulfuric acid facility is as big as a ship. “That was the motivation behind our engineering vision. Was there any possibility of eliminating the need for concentrated sulfuric acid?”
Ideas along that line existed as far back as the 1970’s, but all attempts at large-scale implementation failed. The acetone, hydrocyanic acid and methanol based ACH sulfo process is still used for two-thirds of MMA production worldwide. There are alternatives, but they are only economically viable under certain conditions. Might an ACH process without sulfuric acid be a possibility?
Plant Innovation Breaks New Ground
In 2007, Evonik started pilot production with the intention of breaking new ground. Like the traditional ACH sulfo process, the Aveneer process is based on hydrocyanic acid, acetone and methanol feedstock. There is however no need for sulfuric acid. By eliminating the costly acid regeneration, the Aveneer process offers an increased feedstock efficiency. In addition, the ammonia is recovered for use in the process instead of having to be removed via the ammonium salt in the dissociating acid as useless off-gas nitrogen.
It may sound simple but it is actually the result of a protracted development process. “The reaction would not be possible without state-of-the-art heterogeneous catalysis,” explained Krill. Lab tests demonstrated the basic feasibility of the technique, but in pilot trials during the early development stage the catalysts lost their effectiveness quickly. “That is when the rubber hit the road and the detective work got underway,” reported Krill. “Contamination, by-products and catalytic poisons led to rapid aging of the catalysts.”
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