April 14, 2014
An alkoxylated catalyst support improves the performance of a two-product reaction. The propylene oxide–styrene monomer (POSM) coproduct process has been a shining example of petrochemical process technology since its commercialization in the early 1970s. In this process, propylene and ethylbenzene hydroperoxide (EBHP) react in the presence of a catalyst to give two products: propylene oxide (PO) and 1-phenylethanol. The 1-phenylethanol is easily dehydrated to styrene monomer.
The two companies that dominate this method for making PO are LyondellBasell and Shell Chemical. There are about a dozen POSM plants around the world.
J.-K. F. Buijink discloses a method of preparing a POSM titanium catalyst on a support based on alkoxylated silica. This catalyst system provides longer on-stream times and/or higher selectivities because it operates at lower temperatures than existing catalysts.
The inventor prepared the catalyst support by the reaction of surfactant Pluronic P-123 (a block copolymer based on ethylene oxide and PO) with Si(OEt)4 in the presence of HCl and water in an autoclave at 100 ºC for 24 h. The reaction mixture was centrifuged, and the white powder obtained was calcined at 550 ºC for 6 h.
The calcined powder was treated with a TiCl4 gas stream. The impregnated support that contained 4.03% titanium was calcined again at 600 ºC for 7 h. It was then silylated at 185 ºC for 2 h by contacting it with 18 g hexamethyldisilazane.
This catalyst (0.4 g) was loaded into a reactor tube, and EBHP (as a 36 wt% solution in ethylbenzene) and propylene were pressurized and mixed in a propylene/EBHP mol ratio of 6:1. The temperature was maintained at 60–62 ºC at a pressure of 40 bar. After 75 h, the catalyst system activity was 1.07 g PO/(g catalyst·h). After 225 h, the activity decreased slightly to 1.04. The activity of a nonalkylated version of the catalyst degraded to 0.92 after 225 h on stream. (Shell Oil [Houston]. US Patent 8,664,412, March 4, 2014; Jeffrey S. Plotkin)