Catalytic Cracking of Pentene to Ethene and Propene over ZSM-5 zeolite

Abstract

Ethene and propene are two crucial raw materials used as building blocks to manufacture plastics, fibers and anti-freeze solutions and solvents. Owing to high market demand and an increasing 5% annual demand along with a production shortage more ways to produce ethene and propene are vital. One way of addressing its shortage is to use the surplus in less valuable pentene and its abundance in FCC feeds, the pentene cracking reaction is ideal for increased production. Identifying the best industrially applicable operating conditions was crucial for the enhancement of the ZSM-5 catalyst used as an FCC additive. A fixed bed reactor was used to identify the best reaction temperature of 550 ᵒC, feed concentration of 2.8 mol% and WHSV= 1.9 h-1. Varying Si/Al ratios (Si/Al=15, 25, 58.5 and 140) for ZSM-5 catalyst identified the highest conversion of 99.9 mol% for Si/Al=15, highest C2= selectivity of 55 mol% for Si/Al=15 and highest C3= selectivity of 44 mol% for Si/Al=58.5. Deactivation studies proved that the ZSM-5 catalyst was stable throughout 1400 minutes on stream. The ZSM-5 catalysts acidity was altered to enhance its performance via a post synthetic modification of Ni and P loading. P was loaded on the Si/Al=70 in three different loadings (0.75, 1.5 and 3 wt. % P) only to achieve a 20 mol % drop in conversion. The C2= selectivity was slightly increased with 0.75 wt. % P then decreased dramatically with higher P loadings. The C3= selectivity significantly decreased with the increased P loading to reach a low of 1 mol% at 3 wt. % P loading. Loading of 0.75 wt. % of P on Si/Al=140 at 550 ᵒC and WHSV=1.9 h-1 had an negative effect by decreasing conversion from 98 to 84 mol%), C2= selectivity from 43 to 23 mol% and C3= selectivity from 40 to 25 mol%). Ni was also loaded onto the Si/Al=70 and 140 in 2 wt. % Ni at a reaction temperature of 550 ᵒC and a WHSV=1.9 h-1. The conversion of Si/Al=70 increased by 2% from 95 mol% while the conversion of the Si/Al=140 was unchanged. The C2= selectivity for the Si/Al=70 increased 3% from 38 mol% while it remained unchanged for Si/Al=140 at 43 mol%. The C3= selectivity for the Si/Al=70 increased by 3% from 36 mol% while the C3= selectivity for the Si/Al=140 decreased from 41 to 32 mol%. A combination loading of P followed by 2 wt. % Ni was investigated only to find Ni had increased the performance of the catalyst back to its original performance after the P had decreased it. The catalysts shape selectivity was investigated by manufacturing ZSM-5 larger crystals. Four crystal sizes were tested (0.2-5, 30, 65 and 100 μm) to conclude that there was an increase in conversion with an increase in crystal size up to 65 μm from 96 to 99 mol % at 550 ᵒC and WHSV= 1.9 h-1. C2= selectivity increased from 40 to 46 mol % while C3= selectivity increased from 35 to 43 mol%. Silylation was carried out in an attempt to supress surface side reaction and direct the catalyst towards increasing C2= and C3= selectivity by forcing the reactions to take place on acid sites within the catalyst pores. A single silylation of 10 wt. % TEOS and a double cycle silylation of 20 wt. % TEOS on Si/Al=58.5 with crystal size 2 μm had very little effect on conversions as well as C2= and C3= selectivities. However with increased reaction time the C3= was increased to 43 mol % while C2= slightly decreased to 44 mol%. The silylation carried out on large crystal 30 μm also proved undesirable by decreasing conversion as well as C2= and C3= selectivity. In summary, positive improvements were identified in reaction temperature, Si/Al ratio and feed concentration as well as changes in crystal size and Ni loading that improved conversion as well as C2= and C3= selectivities for pentene cracking.

Date of Award	1 Aug 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Arthur Garforth (Supervisor) & Philip Martin (Supervisor)