Published January 2019
This review updates and revises previous designs for the BASF process for methyl methacrylate (MMA) production from ethylene via propionaldehyde, methacrolein, and methacrylic acid, using BASF literature for each of four steps. Previous evaluations extrapolated similar process sections from other related processes without reference to a BASF technology source. The result is similar, with differences being mostly catalyst formulations and changes to heat integration. The process is a four-step sequence that converts ethylene to propionaldehyde (PA) by hydroformylation, then reacts the PA with formaldehyde to make methacrolein (MA), followed by oxidation of MA to methacrylic acid (MAA), and finally esterification of MAA to methyl methacrylate (MMA).
MMA is a monomer primarily used to make acrylic polymers for plastics, surface coating resins, emulsion polymers, and extrusion compounds. The plastics uses mainly include fabricated products such as building materials, lighting fixtures, signs, displays, sanitary items, glazing, lighting fixtures, lenses, appliances, etc. Demand for MMA is fairly tied to the economy, specifically economic cycle–sensitive applications in construction and automotive uses. Market estimates imply global MMA demand is expected to grow at a steady pace for the next five years. Capacity is expected to grow at a similar but slightly slower rate.
The BASF process consists of four steps. First, ethylene and syngas (with a 1:1 molar ratio) are hydroformylated at 185–195°F (85–90°C) and 245–275 psia to produce PA. The reaction is catalytic, using a rhodium-based homogeneous catalyst complex, similar to the Evonik process, but with a different catalyst formulation. Ethylene per-pass conversion and selectivity to propionaldehyde are high. Next, the PA is reacted with formaldehyde (FA) using a secondary amine and an acid to catalyze the conversion to MA. The liquid phase reaction occurs at 322–350°F (161–177°C) and 670–700 psia. FA and PA per-pass conversion are very high, as is MA selectivity from PA.
The MA is then oxidized with air over a heterogeneous catalyst composed of transition metals such as molybdenum, tungsten, and antimony, plus phosphorus. The reaction operates at 571–590°F (300–310°C) and 30–40 psia. MA per-pass conversion is high, but selectivity to MAA is moderate. The MAA isolation sequence is much more elaborate than the other steps. Finally, MAA esterification uses sulfuric acid catalyst to react methanol with MAA to make MMA and by-product water. The reaction uses staging to drive the reaction, which operates at 240–250°F (115–121°C) and 5–20 psia. MAA per-pass conversion and selectivity to MMA are very high, though excess methanol is used and recycled.
The conceptual design and economic evaluation of this process suggests that the BASF technology is roughly competitive at industry economy of scale, though not the market leader. Actual BASF plants are believed to be much smaller than the base case scenario, however, so economy of scale likely suffers.