Chementator: A direct route to TPAL promises to be less expensive and greener
By Chemical Engineering |
LG Chem, Ltd. (Seoul, South Korea; edlinks.chemengonline.com/5826-545) has developed a direct oxidation process for making terephthalaldehyde (TPAL; terephthalic aldehyde), a key intermediate for dyestuffs, pharmaceuticals, specialty polymers, and other fine chemicals. Because the conversion requires only one reaction step and avoids the use of chlorine, it is expected to be a more economical and greener route to TPLA than conventional methods. TPLA is currently made by a two-step reaction: first the methyl groups of para-xylene are chlorinated photochemically, using Cl2 and ultraviolight, then the chlorinated product is catalytic hydrolyzed into TPAL; this process generates hydrochloric acid as a byproduct, and suffers from high production costs, says LG Chem. As a result, the current market for TPAL is relatively small, says the firm.
In the new process, the p-xylene is selectively oxidized by air over a proprietary (mixed metal oxides) catalyst at 500–600°C and atmospheric pressure. The reaction is performed in a multi-tubular, fixed-bed reactor with a shell-and-tube configuration. In laboratory trials, the process achieves a single-pass conversion of p-xylene to TPLA of approximately 70–78%, and a molar selectivity…