Phosphorus-modified zeolites

The activity of the phosphorus-modified zeolite was similar to that of the original catalyst, but the yield of light olefins was higher and the yield of aromatics, and subsequently of paraffins, was smaller. The changes in cataly-... 

The specifically formulated CGP-1 catalyst plays a vital role in the MIP-CGP process. Unique catalyst design, such as metal promoted MFl zeolite, phosphorus modified Y zeolite, and a novel matrix with excellent capability to accommodate coke [12] were involved to ensure the primary cracking and secondary reactions to proceed within a defined path. The commercial trial results of the MIP-CGP process in SINOPEC Jiujiang Company showed that, in combination with CGP-1 catalyst, the propylene yield was 8.96 wt%, which increased by more than 2.6% as compared with FCC process. The light ends yield and slurry yield are basically equal. The olefin content of the gasoline produced by MIP-CGP process was 15.0 v%, which was 26.1% lower than that of FCC gasoline. The sulfur content of gasoline was decreased from 400 to 270 pg/g. 

We also studied the effect of ion exchange with on the catalytic activity of acid-treated Bent (H -Bent ), sometimes called activated clay. The results are given in Table IV. H" -Bent is virtually the same as H -Bent in catalytic activity. However, the catalytic activity of Ti -Bent for methanol conversion to hydrocarbons is much higher than that of Ti -Bent. The hydrocarbon yield reaches 90%, and the products, in addition to methane, are primarily olefins lower than Ce. The selectivity for olefin formation is estimated to be 90% or higher based on C2 and C3 hydrocarbon product distribution. Ti -Bent appears to surpass the phosphorus compound-modified zeolite proposed by Kaeding and Butter (31) in selective activity for olefin formation, and has the potential to exceed H-Fe-silicate (32) and Ni-SAPO-34 (33), proposed recently by Inui et al. 

This work deals with systematic studies on the phosphorus modified ZSM-5 zeolites prepared by secondary synthesis to demonstrate relations between the structural, surface-chemical and adsorptional properties of those materials. 

These cyclization reactions are suppressed if a phosphorus-modified B-pentasil zeolite is used, as shown by comparison with the conventional silica-based catalyst. Only the silica carrier is replaced by a zeolitic carrier. The amount of cyclic compounds is reduced from 6.7 mol % to 1.4 mol %, and the yield of the desired product adipodinitrile is about 10 % higher [20]. This is evidently due to the restricted transition state shape selectivity of the pentasil zeolite the steric constrains of the zeolite framework prevent the formation of the transition state of the cyclic compounds. The reactions on the outer surface are responsible for the 1,4 mol-% yield of cyclic compounds. 

By reducing the A1 content (acidity) in zeolites, the hydrocarbon cracking efficiency is decreased while the octane number of the products is increased, giving a commercially more valuable product. Zeolites can be used to select certain molecules based on their shapes because of their small pore size (5-7 ). para-Xylene can be produced from a mixture of ortho-, meta- and para-isomers in a 1 2 97 ratio using phosphorus-modified ZSM-5 Zeolite. 

Various ways to modify ZSM-5 catalyst in order to induce para-selectivity have been described. They include an increase in crystal size (15,17,20) and treatment of the zeolite with a variety of modifying agents such as compounds of phosphorus (15,18), magnesium (15), boron (16), silicon (21), antimony (20), and with coke (14,18). Possible explanations of how these modifications may account for the observed selectivity changes have been presented (17) and a mathematical theory has been developed (22). A general description of the effect of diffusion on selectivity in simple parallel reactions has been given by Weisz (23). 

Of the processes likely to favor its production, only the one proposed by Mobil currently appears capable of industrialization. This is because, among the different forms of zeolite developed by this company, tbe catalyst HZSM5, modified by magnesium mid phosphorus, is capable of alkylating toluene by ethylene with a high para isomer selectivity. Thus, a 95/5 blend of p- and m>methylethylbenzenes can be obtained, which considerably simplifies separation problems and yields p-meth styrene by dehydrogena ... 

Apparently, phosphorus first neutralized the outer strong acid sites of the channels, whereas the inner and strongest acid sites were not modified. A similar effect on the acid sites was observed for HZSM-5 zeolite after 20 min of methanol conversion (3. 93, 170), indicating that carbonaceous residues were formed at the outer acid sites of the particles. The strongest acid sites were only neutralized for samples modified both by phosphorus and by carbonaceous residues produced by methanol conversion. 

Calorimetric Measurements of Ammonia Adsorption at 423 K on ZSM-5 Zeolite Modified with Phosphorus or Boron... 

The results of this query are plotted as a graph of the selectivity for para-xylene among xylene vs. temperature (Fig. 3). Obviously, it is observed that there is an influence of the temperature on the selectivity when ZSM-5 is modified with phosphorus the selectivity is increasing with temperature. For zeolites modified by Mg, Ni, or B, no experiments relative to the influence of temperature are reported in the literature only single values are available. Hence, one can propose that other experiments should be carry out by modifying ZSM-5 with Ni and Mg and vary the temperature. We can also observe that for experiments carried out with B or P-modified catalysts, 600°C seems to be the upper limit, probably due to deactivation of the catalyst. 

The modification of high silica zeolite of a pentasil type by boron and phosphorus compounds is conducted and the conclusions about structure of the modifier and its localization are made. 

Further changes adsorption characteristics of high-silica zeolite of pentasil type and ultrastable form Y zeolite modified by boron and phosphorus, both from aqueous solutions of appropriate acids and by treating of organic derivative vapors were consideration. 

The Insertion of phosphorus was investigated for ZSM-5 zeolite (S1/A1=15) from template-free synthesist which were modified by thermlcal. combined thermical-mechanical and ultrasonic pretreatment. For this reason the parent zeolite was calcinated for 16 hrs at 600°c and taken into a vibration box for 10 hrs. Furthermore a sample treated with ultrasound was also used. 

For application of zeolites as catalysts in industrial processes, high activity and easy removal of coke deposits are required. To meet these requirements, small crystals of zeolites (0.5-1.0 (im) should be advantageously used. On the other hand, the para-shape selectivity of zeolites in alkylaromatic transformations is connected especially with large crystals of the ZSM-5 zeolite structure, modified by silicon, boron, magnesium and phosphorus [1-5], However, no definite conclusion has been drawn on the contribution of various species to restricted transport of the bulkier isomers through the zeolite crystals, selectivity of the initial... 

Using infrared and microcalorimetric techniques led Vedrine et al. to propose that phosphorus neutralizes medium and strong acid sites at the entrance of the zeolite channels. The strongest acid sites, however, would not be modified. As a result, the activity of the modified catalyst was comparable to that of the parent ZSM-5. The increased olefin selectivity was then assigned to the increased... 

Balkrishnan et al. suggested that, even though the tortuosity in the zeolite channels is increased, the observed higher selectivity toward Cj-C olefins in the methanol conversion on P-modified ZSM-5 is due more to a change in the acidity than to any steric effect. According to Cai et al., ° phosphorus affects both Bronsted and Lewis sites of various acid strength. As a result, an increased ethylene selectivity was attained. 

Dimethylether. Several strategies for the production of dimethyl ether (DME) are described, e.g. direct synthesis from syngas according to equation (8.5) or via dehydration of methanol according to equation (8.6). From a mechanistic point of view direct synthesis proceeds also via methanol formation and subsequent release of water but without procedural isolation of methanol. The process can also be designed to yield both methanol and DME. Established methanol catalysts are employed for methanol formation and typical dehydration catalysts are solid-acid catalysts, e.g. alumina, silica-, phosphorus- or boron-modified alumina, zeolite, (sili-co)aluminophosphates, tungsten-zirconia or sulfated-zirconia. " ... 

By using solid-state NMR, the hydrothermal stabilities (under 100% steam at 1073 K) of HZSM-5 zeolites modified by lanthanum and phosphorus have been studied. They are excellent zeolite catalysts for residual oil selective eatalytic cracking processes. It was indicated that the introduction of phosphorus to the zeolite via impregnation with orthophosphoric acid led to dealumination as well as formation of different A1 species, which were well distinguished by Al 3Q MAS NMR and P MAS NMR spectra. " ... 

H-ZSM-5 zeolite modified by phosphorus was studied by means of adsorption microcalorimetry of ammonia for acidity characterization [255]. It was foimd that phosphorus neutralizes acidic sites primarily at the entrance of the channels of the zeolite particles. However, the strongest acid sites remained immodified, which suggested that the aluminum distribution and consequently the distribution of acid site strengths along the zeolite channels was heterogeneous. 

The catalyst in MOI contains only ZSM-5 and/or ZSM-11 without any large pore zeolites. The ZSM-5 and/or ZSM- 11 preferably have a high initial silica/aliunina molar ratio and are modified by phosphorus and metals such as gallium. 

The shape selectivity of ZSM-5 is modified significantly by treatment with a variety of chemical reagents. For example, modification with phosphorus or boron was made by impregnating the zeolite crystals with aqueous phosphoric acid or orthoboric acid, followed by calcination in air to convert the acid into the oxides. Selected results are summarized in Table 4.3. Though the selectivity iorpara isomer in alkylation with ordinary ZSM-5 is close to that expected from the thermal equilibrium, selectivity as high as 97% is achieved with the modified ZSM-5. 

Modification of ZSM-5 zeolites with various compounds is also effective. Kaeding and Butter reported that ZSM-5 modified by treatment with phosphorus compounds showed high (70%) selectivity to Ci — C4 olefin formation from methanol. This could also be ascribed to decrease in stronger acid sites by the treatment. 

Because ZSM-5 normally may exhibit high selectivities to aromatics and paraffins, the zeolite and the process conditions have been modified to improve selectivity to light olefins. The effective shape selectivity was increased by the deposition of silica in the channel system [175]. Phosphorus modification [121] with trimethylphosphite (PCOCHj) ) followed by air calcinations improved olefin selectivity by lowering acid site strength and probably also by reducing the effective pore size. Ion exchange with + [176], and higher SiO/Al Oj ratios (lower site density) [39] were all reported to improve olefin selectivities. 

---