Zhijian Da

Liquid-phase alkylation of toluene with long-chain alkenes over HFAU and HBEA zeolites

Abstract The alkylation of toluene with 1-heptene and 1-dodecene were used as model reactions for the synthesis of long-chain linear alkylbenzenes, the precursors of biodegradable surfactants. The effect of the pore structure of large pore zeolites: HFAU (framework Si/Al=15) and HBEA (framework Si/Al=12.5) on their catalytic properties was determined in liquid phase at 90°C with a toluene/alkene molar ratio of 3. With these large pore zeolites, the main reactions are alkene double bond shift and toluene alkylation. Monoalkyltoluenes are the main reaction products, whereas bimonoalkyltoluenes and alkene dimers appear in low amount from, respectively, HFAU and HBEA. HBEA, despite the small size of its crystallite is practically inactive for the toluene alkylation by 1-dodecene. This low activity can be attributed to the slow desorption of the reaction product from the narrow pore of this zeolite and more particularly the non-desorption of the 3- to 6-monododecyltoluenes. These steric constraints lead to the formation of bulky aromatic compounds in the HBEA micropores. These components formed in larger amount than over HFAU, are responsible to the blockage of the alkenes (dodecene mixture and dimers) in the zeolite pores. However, the limitation effect of diffusion steps observed in the pore of HBEA leads to increase the selectivity to 2-phenylalkanes which are the most biodegradable isomers.

Liquid phase alkylation of toluene with 1-heptene over a HFAU zeolite : evidence for transalkylation between toluene and non-desorbed products

The liquid phase alkylation of toluene with 1-heptene was investigated over a HFAU zeolite (Si/Al=6) under the following conditions: batch reactor, 90°C, molar toluene/heptene ratio=3. Monoheptyltoluenes are rapidly formed, whereas biheptyltoluenes appear in low amount at high conversion. A large amount of mono, bi and triheptyltoluenes is shown to be trapped in the zeolite pores, suggesting that alkylation is limited by product desorption. After total consumption of heptene, there is an increase with reaction time in monoheptyltoluenes trapped in the pores and a decrease in bi and triheptyltoluenes. These observations can be explained both by a transalkylation reaction between bi and triheptyltoluenes trapped in the zeolite micropores and toluene molecules and by a slow diffusion of monoheptyltoluenes from the liquid phase to the zeolite micropores.

Alkylation of toluene with 1-dodecene over HFAU zeolite. Deactivation and regeneration

The alkylation of toluene with 1‐dodecene was carried out over a HFAU zeolite (total and framework Si/Al ratio = 25) under the following conditions: fixed‐bed reactor, 90°C, molar toluene/dodecene ratio of 3, WHSV =10 h−. Monododecyltoluenes are selectively formed, bidodecyltoluenes appearing only in low amounts at a complete conversion of dodecene. Tridodecyltoluenes are also formed inside the supercages but cannot desorb from the zeolite. These compounds, mainly located in the outer part of the crystallites are responsible for catalyst deactivation. However, tridodecyltoluenes can be completely removed by treatment under toluene flow, which allows a complete regeneration of the catalyst. This removal occurs by transalkylation between tridodecyltoluenes and toluene molecules with a final formation of monododecyltoluenes. At least, the first transalkylation steps occur between toluene in the liquid phase and tridodecyltoluenes in the zeolite pores (pore mouth catalysis).

Development of structure stabilized SSY zeolite

Abstract Structure stabilized Y (SSY) zeolite with high rare earth content was prepared by following the RE 3+ -exchange of NaY with a SiCl 4 treatment. Due to RE 3+ cation location in the zeolite lattice, migrating direction and presence state could be well controlled in processing, the SSY possesses the following characteristics: initial unit cell constant a 0 = 2.450–2.458nm, equilibrium unit cell size >2.435nm, RE 2 O 3 content could be adjusted within 6-14 wt %, sodium oxide content less than 1.0 wt%, and a differential thermal collapsed temperature, DTA >1000°C. Research results indicate that the SSY with an improved heavy oil conversion, a better coke selectivity and a higher hydrogen transfer activity and stability is suitable as an active component of cracking catalyst for clean gasoline production.

The role of manganese contained zeolite catalysts in tuning bi-/mono-molecular reaction pathway selectivity in FCC process

Abstract The gasoline quality of FCC process, especially olefin content, heavily depends on the catalyst performance in terms of bi-/mono-molecular reaction pathway selectivity. A reliable experimental protocol has been established by using m-xylene as a probe molecule to clarify the selectivity based on detailed reaction chemistry of m-xylene including the consecutive bi-molecular disproportionation and isomerization. Another pure hydrocarbon, n-dodecane, has been used as probe molecule to characterize the selective hydrogen transfer ability of catalytic materials. A novel series of FCC catalysts has been developed aiming at gasoline olefin reduction based on manganese incorporation or modification. The role of manganese in tuning bi/mono-molecular reaction pathway selectivity and hydrogen transfer selectivity in FCC process is elucidated by experimental approaches described. The results have been correlated with the practical performance of the new catalysts.