Solid phosphoric acid catalyst for propene oligomerization: Effect of silicon phosphate composition

• Appropriate proportion of silicon phosphates is the guarantee of catalyst having high catalytic performance.
• The decomposition of silicon phosphate in oligomerization maintained the activity of the catalyst.
• A catalyst with more silicon pyrophosphate shows a better crushing strength.

Solid phosphoric acid catalysts have been industrially used for propene oligomerization to improve the gasoline quality. However, solid phosphoric acid catalysts will lose their mechanical strength in the presence of water which is used to hydrolyze silicon phosphates to produce free phosphoric acids for maintaining the catalytic activity. In this case, to harmonize the catalyst lifetime and activity of solid phosphoric acid catalysts, the properties of silicon phosphate were investigated to achieve the maximum catalytic performance. A solid phosphoric acid catalyst was prepared with kieselguhr and concentrated phosphoric acid. Trace water was used to promote the release of active components from silicon phosphates during the reaction. Free phosphoric acid content, as a vital property of a solid phosphoric acid catalyst, was measured by ammonia temperature-programmed desorption. The crystal phase composition of silicon phosphates in a solid phosphoric acid catalyst was analyzed by X-ray diffraction. The catalytic performance was evaluated in a fixed bed under the conditions of 210 °C and 4 MPa. A solid phosphoric acid catalyst with relative content of 51% Si5O(PO4)6 and 49% SiP2O7 showed the best performance in improving catalytic activity and lifetime, and the conversion of propene was above 99% for nearly 70 h.

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