Changqing He

Crystallization and Si incorporation mechanisms of SAPO-34

In this study of the synthesis of SAPO-34 molecular sieves, XRD, SEM, XRF, IR and NMR techniques were applied to monitor the crystalloid, structure and composition changes of the samples in the whole crystallization process in order to get evidence for the crystallization as well as Si incorporation mechanism of SAPO-34. XRD results revealed that the crystallization contained two stages. In the first 2.5 h (the earlier stage), high up to ∼80% of relative crystallinity could be achieved and the crystal size of SAPO-34 was almost the same as that of any longer time, indicating a fast crystallization feature of the synthesis. In this stage, IR revealed that the formation of SAPO-34 framework structure was accompanied by the diminution of hydroxyls, suggesting that crystal nuclei of SAPO-34 may arise from the structure rearrangement of the initial gel and the condensation of the hydroxyls. NMR results reveal that the template and the ageing period are crucial for the later crystallization of SAPO-34. Preliminary structure units similar to the framework of SAPO-34 have already formed before the crystallization began (0 h and low temperature). Evidence from IR, NMR, and XRF shows that the formation of the SAPO-34 may be a type of gel conversion mechanism, the solution support and the appropriate solution circumstance are two important parameters of the crystallization of SAPO-34. Meanwhile, NMR measurements demonstrated that about 80% of total Si atoms directly take part in the formation of the crystal nuclei as well as in the growth of the crystal grains in the earlier stage ( 2.5 h), the relative content of Si increased slightly with a little decrease of Al and P. The increase of Si(4Al) and the appearance of the Si(3Al), Si(2Al), Si(1Al) and Si(0Al) in this stage suggest that substitution of the Si atoms for the phosphorus and for the phosphorus and aluminum pair takes place in the crystallization. The relationship among structure, acidity and crystallization process is established, which suggests a possibility to improve the acidity and catalytic properties by choosing a optimum crystallization time, thus controlling the number and distribution of Si in the framework of SAPO-34.

Dialkylation of naphthalene with isopropanol over acidic zeolites - Influence of pore structure on selectivity

The liquid phase alkylation of naphthalene with isopropanol has been studied over various large pore zeolites with intermediate aluminum content. While H-Y zeolite exhibits the best activity, and shows a high selectivity in 2,6- and 2,7-diisopropylnaphthalenes, in agreement with previous studies, H-Beta displays a peculiar behavior under the same conditions. The latter produces little diisopropylnaphthalenes; instead, a series of unexpected compounds, consisting of (cyclopentyl)naphthalene derivatives (so-called cyclizates), are formed in high yields. H-Mordenite, which features low activity, also demonstrates such an unexpected behavior towards formation of multialkylated products. The results obtained over H-Beta are more particularly reported, and the identification of the cyclizates is confirmed. A mechanism is proposed to explain the formation of these compounds depending on the various catalytic materials used, and the impact of the pore structure on activity and product distribution is discussed.

Research progress and pilot plant test on SDTO process

In the earlier of 1990s, we have proposed a new process for the synthesis oflight olefins from syngas, which was designated as SDTO method. That is to convert syngas to dimethylether and than to convert dimethylether to light olefins. The present work deals with the R&D research progress of this process. The catalysts were developed for the two reactions, scale-up preparation of the catalysts and pilot plant test were performed. Evaluation of the pilot plant data showed that 190-200 grams of DME were yielded by single-pass for each standard cubic meter of syngas. For the second reaction, material-balance data indicated that 1.880 tons of DME or 2.615 tons of methanol can produce one ton of light olefins, which constituting 0.533 ton of ethylene, 0.349 ton of propylene and 0.118 ton of butenes.

Unusual results in the liquid phase alkylation of naphthalene with isopropyl alcohol over zeolite H-beta

Unexpected compounds are formed with high selectivity in the liquid phase alkylation of naphthalene with isopropyl alcohol over large pore zeolite H-beta; these have been confirmed to be cyclized products from naphthalene derivatives.