July 16, 2012
Oxidize alkanes to olefinic carboxylic acids with these catalysts. Alkane activation technology is a “holy grail” for the petrochemical industry. Tremendous capital savings could be realized if the industry developed catalysts that are capable of converting alkanes such as ethane, propane, and butane directly to large-volume petrochemical intermediates. Except for butane-to-maleic anhydride technology, however, this goal has been elusive. Manufacturers must first convert these relatively unreactive hydrocarbons to their corresponding olefins via steam cracking. The capital investment for a world-scale steam cracker is more than US$1 billion.
P. N. Hazin and co-inventors disclose catalysts and operating conditions that allow the direct conversion of propane to acrylic acid in reasonable selectivity and yield. The catalysts are based on mixed metal oxides such as Mo1.0V0.03Nb0.12Te0.23Ox. In addition to the catalyst, the key to maintaining good selectivity is to ensure that the feed contains excess propane relative to oxygen. This keeps conversion per pass relatively low, but it gives good selectivity to acrylic acid.
The inventors also found that under these conditions some propane is converted to propylene. Recycling the propylene and unreacted propane to the reactor boosts productivity and maintains good selectivity.
In an example, propane diluted with steam in a 1:3.4 ratio is mixed with oxygen to give a C3H8/O2 ratio of 1:0.5. This stream is passed over the Mo1.0V0.03Nb0.12Te0.23Ox catalyst at 400 °C and 20 psig pressure with a residence time of 0.23 s. The propane conversion is 19.0%, and the selectivity to acrylic acid is 65.2%. Propylene is made in 18.1% selectivity.
In a series of experiments, the inventors found that adding propylene to the propane (to model the effect of recycling unreacted propane with propylene) leads to improved conversions per pass and a better overall yield of acrylic acid. (Saudi Basic Industries [Riyadh, Saudi Arabia]. US Patent 8,193,387, June 5, 2012; Jeffrey S. Plotkin)