High Propylene Selectivity in Methanol-to-olefin Reaction over H-ZSM-5 Catalyst Treated with Phosphoric Acid

Abstract

H-ZSM-5 zeolite was treated with phosphorus acid by impregnating H-ZSM-5 with aqueous solutions of phosphoric acid at various concentrations. H-ZSM-5 (P-HZSM-5) modified with phosphoric acid was used as a catalyst for the methanol-to-olefin reaction. The molar ratios of P/Si and Si/Al in H-ZSM-5 and P-HZSM-5 were measured by EDX analysis. The Si/Al molar ratios of P-HZSM-5 increased with higher concentration of H3PO4 in the solution, which might be caused by partial dealumination of H-ZSM-5 by the H3PO4 treatment. The P/Si molar ratio of P-HZSM-5 after washing was proportional to the H3PO4 concentrations in the aqueous solutions. The remaining phosphorus species after the washing must be strongly adsorbed by interaction with the pore surface of H-ZSM-5 zeolite. The P-HZSM-5 catalyst showed very high propylene selectivity up to 57% with methanol conversion of 100%. Furthermore, catalyst stability was significantly improved for the P-HZSM-5 catalysts. Ammonia TPD spectra showed that the strong acid sites of H-ZSM-5 disappeared after the phosphoric acid treatment. Consequently, the formation of aromatics and coke was inhibited, resulting in higher light olefin selectivity and catalyst stability.

Synthesis of Propylene From Ethanol Using Phosphorus-Modified HZSM-5

“…Similar results were reported in the literature (Hodala et al, 2014;Takahashi et al, 2012;Lu and Liu, 2011;Song et al, 2010;Vu et al, 2010;Li et al, 2010;Ramesh et al, 2009;Zhao et al, 2007;Lercher and Rumplmayr, 1986). The addition of P up to 1.2 wt.…”

“…Phosphorus addition to HZSM-5 caused a decrease in the total acid site density. It also appears that the decrease in strong acid sites density was greater than that observed for weak acid sites, as reported previously (Takahashi et al, 2012;Lu and Liu, 2011;Ramesh et al, 2009;Song et al, 2010;Vu et al, 2010;Li et al, 2010;Zhao et al, 2007;Lercher and Rumplmayr, 1986).…”

“…Therefore, the production of propylene from ethanol has attracted considerable attention. The use of zeolites in catalytic conversion of ethanol has been reported by several authors, in particular the use of HZSM-5 for this kind of reaction (Takahashi et al, 2012;Inaba et al, 2006;Lu and Liu, 2011;Barros et al, 2007;Duan et al, 2012;Vu et al, 2010;Song et al, 2010;Ramesh et al, 2009).…”

“…To reduce the density and strength of acid sites of HZSM-5, an increase in SiO2/Al2O3 (Inaba et al, 2006;Song et al, 2010;Blasco et al, 2006), phosphorus addition (Takahashi et al, 2012;Lu and Liu, 2011;Ramesh et al, 2009;Song et al, 2010;Barros et al, 2007;Vu et al, 2010;Zhao et al, 2007) and metals impregnation (Inaba et al, 2006;Blasco et al, 2006) are current alternatives.…”

Effect of Phosphate Modification on the Brønsted Acidity and Methanol‐to‐Olefin Conversion Activity of Zeolite ZSM‐5

“…The H-form of this material was obtained by exchange with an aqueous solution of ammonium nitrate, washing in demineralized water, and calcination in air. For the phosphate impregnation of zeolite H-ZSM-5 [19], a distinct amount of ammonium dihydrogen phosphate was dissolved in 10 or 20 mL demineralized water. Up to 1.2 or 3.5 mL of this solution was used for the pore impregnation of 5 or 7 g of zeolite H-ZSM-5, respectively.…”