The nature of the active sites in the catalytic cracking of gas—oil

The kinetics of gasoil cracking over an HY zeolite catalyst have been studied at atmospheric pressure and temperatures of 482°, 503° and 524°C, using a fixedbed integral reactor. The total conversion of gas-oil, the yield of gasoline, of various gaseous products, and the influence of temperature on conversion, gasoline and minor product yield are presented here. The various primary reaction rate constants, the constants describing the decay of catalyst activity, and the refractoriness of the feed, have been determined for this system and are compared with those obtained using a LaY zeolite catalyst. The observed differences between these two catalysts are discussed in terms of the nature and number of active sites present on the two catalysts. We conclude that the initial reaction of a saturated gas-oil feed occurs on a range of Lewis acid sites of various strengths. Such sites are more numerous on LaY than on HY, and this disparity is larger for weak sites than it is for strong sites.     

The nature of active sites in the isomerization of 1-hexene on cracking catalysts

The molar ratio of cis/trans 2-hexene isomers formed from 1-hexene on NaY zeolites exchanged to various levels with protons or lanthanum ions can be explained by assuming that two types of sites are active for the 1–2 isomerization reaction. The first gives both isomers, while the second gives only the cis isomer. In HY zeolite, active sites for the isomerization reaction can be produced by substitution of the most easily replaced sodium ions, either by simple washing with water, or by calcination of a partially exchanged ammonium form. The catalyst activity and the observed ratio of cis/trans isomers formed on a partially exchanged LaY zeolite, has been found to depend on the degree of hydration of the catalyst. Ratios of cis/trans 2-hexene are closer to their equilibrium value when the reaction is carried out on ZSM-5, mordenite and amorphous silica-aluminas rather than on Y zeolite. This is explained in terms of the proportion of each type of site present, although diffusional limitations within the narrower pore structures of ZSM-5 and mordenite may also play a role.     

Catalytic reactions of methylcyclopentane on HY zeolite

Catalytic reactions of methylcyclopentane have been studied on HY Zeolite at 500°C. Initial reactions include ring cleavage, the formation of paraffins and the formation of methylcyclopentane. Aromatic species are formed as both primary and secondary products. In contrast to the reaction of methylcyclopentane under reforming conditions, benzene is not a dominant initial aromatic product formed under cracking conditions. Unlike the reaction of cyclopentane on HY, the cracking of methylcyclopentane produces molecular hydrogen as an initial product. This we attribute to the presence of a hydrogen atom bonded to a tertiary carbon in the methylcyclopentane molecule.     

Catalytic reactions of n-hexenes on amorphous silica-alumina

Reactions of n-hexenes on 80/100 mesh amorphous silica-alumina have been studied in a plug flow reactor at 405°C, and compared with results previously obtained using HY and H-ZSM-5. The dominant primary reaction is skeletal isomerization while the initial selectivity for cracking is very low compared to that on the zeolite catalysts. The dimerization-cracking reaction, the major cracking process on the zeolites, was not a primary reaction on amorphous silica-alumina. This and the slowness of reactions leading to paraffins and dehydrogenated species is attributed to the small number of strongly acidic sites on the amorphous material.     

Kinetics of and catalyst decay accompanying the gas phase rearrangement of cyclohexanone-oxime over a hy ultrastable zeolite

The kinetics of the rearrangement of cyclohexanone-oxime has been studied in a fixed bed, glass tubular reactor at atmospheric pressure and temperatures of 240, 270, 300 and 335°C, using ultrastable HY zeolite catalyst. Several kinetic models, including the Langmuir-Hinshelwood type, have been derived and the best statistical fit has been obtained with a pseudo-first order kinetic equation. The rate constants and activation energies for the formation of the products caprolactam, cyclohexanone and 5-cyanopent-l-ene have been calculated. Based on the evolution of the selectivity with temperature, and the I.R. spectra of the poisoned catalyst, different decay models have been deduced and discussed.     

分子筛催化剂脱除重整油中微量烯烃的研究

以Hβ分子筛、HY分子筛和经水蒸汽处理后的HY分子筛为脱烯烃催化剂活性主体,研究了不同分子筛、分子筛酸性和水蒸汽处理时间等对催化剂的脱烯烃性能影响。结果表明,催化剂表面酸性对催化剂脱烯烃性能有重要影响,B酸是主要活性中心,L酸起辅助催化剂作用,B酸中心密度过高会加速催化剂结焦失活。水蒸汽处理可以有效改善分子筛的表面酸量和酸强度,可延长催化剂的单程寿命达到工业白土的6倍。脱烯烃催化剂有更好的容焦能力,其表面的积碳属于轻质焦碳,易于再生。     

Hydrocracking of n-heptane. Study of NiO—MoO3 catalysts supported on a HY ultrastable zeolite

The hydrocracking of n-heptane in the temperature range of 573 to 623 K and at 2.45 × 10⁶ Pa pressure has been employed as a test reaction for the study of Ni—Mo bifunctional catalysts supported on a HY ultrastable zeolite. Two groups of catalysts containing 8 and 12 wt% of MoO₃ and different amounts of NiO have been studied. In both series a maximum in the activity has been obtained for catalysts with a Ni/Mo atomic ratio of 0.8-1.0. The order of the impregnation of the oxides can have little influence on the activity. The most active catalyst has been obtained when the zeolite is exchanged with NH⁺₄ ions until the Na⁺ level is less than 2% of the original and calcined at 823 K to obtain a HY ultrastable zeolite. Using this catalyst the rate controlling step could be the transformation of the carbonium ion on the acid sites.     

Catalyst decay in the kinetics of methylcyclohexane dehydrogenation over Pt-NaY zeolite

The kinetics of the dehydrogenation of methylcyclohexane to toluene over platinum on NaY zeolite have been studied at 390°C and atmospheric pressure. Cumulative conversion data obtained at constant space velocity and various reaction times on stream was treated using the “Time on Stream” theory. In this way the rate constants for both dehydrogenation and catalyst decay have been determined. The reaction has been shown to occur via a series of consecutive partial dehydrogenations, with the first dehydrogenation as the rate controlling step. The influence of the partially dehydrogenated products as well as the influence of the toluene, on the deactivation of the catalyst is discussed.     

Effect of partial poisoning of acid sites on selectivity in the multiple reactions of mono-substituted-t-Butylbenzenes

The decomposition reaction of p–t-butylcumene and t-butylbromobenzene have been carried out over pyridine poisoned silica-alumina and HY zeolite in order to examine the effect of acid strength on selectivity. Since the catalyst deactivation rate for isomerization over the poisoned silica-alumina was greater than that of de-t-butylation in the reaction of p–t-butylcumene, the selectivity of de-t-butylation gradually improved with process time. In the reaction of t-butylbromobenzene over poisoned HY zeolite, the de-bromination rate was suppressed by the poisoning because the nature of active sites was different between silica-alumina and HY zeolite. The poisoned HY zeolite was found to be favorable for the de-t-butylation of halogenated-t-butylbenzenes.     

Catalytic enhancement of platinum supported on zeolite beta for toluene hydrogenation by addition of palladium

This work focused on the preparation, characterization and catalytic performance of a bimetallic platinum–palladium catalyst for toluene hydrogenation. A catalyst with 3 wt% loading of each metal was prepared by co-impregnation on zeolite beta in proton form and denoted as 3Pt3Pd/HBEA. The structure of HBEA was retained after catalyst preparation and the metal occupied strong acidic sites of the zeolite. Compared to monometallic 3Pt/HBEA, the 3Pt3Pd/HBEA exhibited smaller Pt particle size due to better dispersion on the support. The catalytic performance of the bimetallic catalyst at various temperatures indicated that the presence of Pd enhanced toluene hydrogenation of Pt catalyst at high temperature. The most suitable temperature for toluene hydrogenation on 3Pt3Pd/HBEA was 150 °C for which a complete toluene conversion was obtained with methylcyclohexane as the only product.     

甲苯甲醇烷基化制对二甲苯催化剂中试反应性能研究

经过多步改性制备了负载二氧化硅（SiO₂）、氧化镁（MgO）、五氧化二磷（P₂O₅）、贵金属铂（Pt）的纳米ZSM-5分子筛催化剂,并在六段固定床反应器上分段装填该催化剂720 g进行甲苯、甲醇烷基化制对二甲苯反应活性评价。实验结果表明,通过调变甲醇和甲苯物质的量比可以使甲苯转化率在22%~30%可调,烷基化液相产物中二甲苯选择性保持在95%以上,二甲苯中对二甲苯选择性保持在95%以上;催化剂单程寿命达到1 300 h,随着反应时间延长催化剂的活性有所下降。通过X射线衍射（XRD）、热重分析（TG-DTG）和氮气吸附-脱附等手段对参加反应前后的催化剂进行了表征,结果表明反应中生成的积炭堵塞了分子筛的孔道或覆盖了催化剂的活性位;经过在反应器内原位再生,催化剂的反应活性基本恢复到新鲜催化剂水平。     

Reactions of cyclopentane on HY Zeolite

The reaction of cyclopentane has been studied on HY zeolite at 500°C. Initial reaction processes included ring cleavage to acyclic C₅ species, and cracking to produce fragments in the range C₁ - C₄. Hydrogen transfer accompanied those processes, so that paraffins as well as olefins were observed as initial products. Cyclopentene was formed as an unstable initial product by the dehydrogenation of the feed, although molecular hydrogen was not found as a primary product. Other dehydrogenated species initially formed included coke and aromatics in the range C₆ - C₁₀.     

Xylene isomerization by ZSM-5 zeolite catalyst

The larger pore LaY zeolite catalyst resembles homogeneous metal chloride and heterogeneous silica-alumina acid catalysts since the results are consistent with isomerization being a series of intramolecular 1,2 shifts. On the other hand, isomerization with the smaller pore zeolite, ZSM-5, is very different and the relative rate constants appear to be influenced by diffusion and/or shape selectivity. Disproportionation is a significant reaction with LaY but not with ZSM-5 in the temperature range used for the present study. The small amount of trimethylbenzene formed at low conversions using ZSM-5 is 1,2,4-trimethylbenzene, also providing evidence of shape selectivity influencing the reaction products.     

芳烃精制脱烯烃分子筛催化剂的研究

本研究以铝胶、硅铝胶及钛铝胶为粘合剂,以HY分子筛为主要活性组分制备了芳烃脱烯烃分子筛催化剂.采用NH3-TPD、BET、TG和活性评价等方法对催化剂的酸性、脱烯烃活性、失活原因及再生性能进行了研究.结果表明,含有不同粘合剂的HY分子筛催化剂的脱烯烃活性均明显高于工业使用的NC-01颗粒白土催化剂,分子筛催化剂表面具有较多的弱酸中心是其性能良好的重要原因.积碳是分子筛催化剂表面失活的主要原因,经焙烧再生处理后分子筛催化剂仍具有较好的脱烯烃性能.经823 K焙烧的硅铝胶质量分数为20%的分子筛催化剂具有较佳的反应性能.     

Disproportionation and Methylation of Toluene with Methanol Over Zeolite Catalysts

Zeolites TNU-9, SSZ-33, mordenite (MOR) and ZSM-5 were evaluated for their activities in toluene disproportionation and methylation reaction of toluene with methanol. The medium-pore zeolite TNU-9 was found to possess the highest conversion in toluene disproportionation as compared with SSZ-33, mordenite and ZSM-5 based catalyst. Zeolite mordenite with the highest Si/Al ratio of 135.9 (the lowest concentration of active sites) exhibited the highest toluene conversion and maximum xylene yield in toluene methylation. On mordenite, the presence of channel intersections allows more reaction space for the formation of bulky intermediates and/or products and the 12-ring channels on the other hand, allow diffusion without trapping, since the channel diameter is large enough. In toluene methylation, xylene selectivity at the same conversion level follows the order: ZSM-5 > TNU-9 > MOR > SSZ-33, which implies that xylene selectivity is directly related to the size of channels from medium to large pore zeolites. The medium-pore zeolite ZSM-5, with 10-ring channels, shows the lowest reactivity for further alkylation of xylene, while mordenite with 12-ring channel shows the highest reactivity for further alkylation of xylene.     

Conversion of 4-Methylanisole Catalyzed by Pt/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and by Pt/SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>: Reaction Networks and Evidence of Oxygen Removal

Abstract  

The conversion of 4-methylanisole, a prototypical bio-oil compound, was catalyzed by Pt/Al₂O₃, Pt/SiO₂-Al₂O₃, or HY zeolite at 573 K and atmospheric pressure. More than a dozen products were formed with each catalyst, the most abundant being 4-methylphenol, 2,4-dimethylphenol, and 2,4,6-trimethylphenol; toluene was also a major product when the catalyst was supported platinum with H₂ as a co-reactant. 4-Methylphenol was the only methylphenol isomer formed in significant yields, which indicates that migration of the methyl group on the aromatic ring is not significant under the selected reaction conditions. The data determine approximate reaction networks including reactions forming 4-methylphenol, 2,4-dimethylphenol, and toluene as primary products. The kinetically significant reaction classes were transalkylation, observed with all three catalysts, and hydrogenolysis (including hydrodeoxygenation) and hydrogenation, observed only with the platinum-containing catalysts operating in the presence of H₂. Data such as those reported here provide a starting point for predicting the conversion of whole bio-oils for removal of oxygen and upgrading of fuel properties.     

Catalytic cracking and skeletal isomerization of n-hexenes on HY zeolite

The catalytic cracking and skeletal isomerization of n-hexenes on 80/100 mesh HY zeolite has been studied in the temperature range 350–405°C, and compared with results previously obtained on ZSM-5 zeolites. Species with less than three carbon atoms were not observed as primary cracking products, with traces of ethylene formed only as a secondary product. Although propylene and propane may be formed partially by monomolecular cracking of n-hexenes, the dominant cracking process is bimolecular. Dimerization, followed by disproportionation gives stable C₃, C₄ and C₅ species, in addition to C₉, C₈ and C₇ fragments. The probability of these larger fragments undergoing further cracking before desorption increases with temperature, but is significantly less than found on ZSM-5 zeolites. The main products of skeletal isomerization were monomethylpentenes, with those isomers which can originate from tertiary carbonium ions dominant. Dimethylbutenes were formed mainly as secondary products. The rate of the dimerization-cracking process in which two n-hexene species participate is ? six times slower than the reaction involving a monomethylpentene species and a linear hexene. The increase in the rate of the latter process with respect to the former is reduced on ZSM-5, and this can be attributed to the narrower pore size within this zeolite. In contrast to ZSM-5, there is significant formation of alicyclics, paraffins and aromatic species. The residual coke was found to be considerably poorer in hydrogen content than comparable material formed on ZSM-5.     

Study on Olefin Alkylation of Thiophenic Sulfur in FCC Gasoline Using La2O3-Modified HY Zeolite

HY zeolite modified by La₂O₃ on olefin alkylation of thiophenic sulfur in fluid catalytic cracking (FCC) gasoline was studied in the micro fixed-bed reactor. Reaction pressure 1.5 MPa, reaction temperature 180 °C, WHSV 3.5 h^?1, using HY zeolite modified by 2% La₂O₃, the conversion of thiophene sulfur promoted nearly 10% with good selectivity, comparing with no-modified by La₂O₃. Acidity of modification of HY zeolite with La₂O₃ was tested in Pyridine–IR, it showed that increasing the amount of weak Bronsted (B) acid and the ratio of total B acid with total Lewis (L) acid could strengthen the hydrogen transfer activity of the catalyst, which leaded to improving the capacity of thiophene alkylation. The X-ray diffraction (XRD) results showed that the structure of catalysts could be optimized by loaded proper amount of La₂O₃ for promoting the acidic properties of HY zeolite.     

The products of cumene cracking on an amorphous silica alumina

A detailed analytical study of the products of cumene cracking over amorphous silica alumina shows that the mechanism of cracking over these catalysts is identical to that observed over crystalline LaY and HY at various levels of exchange. Additional analytical details are developed in this work and are used to elaborate on the previously proposed reaction network for this reaction. In particular we find that hydrogen and propane appear as secondary products in the cracking reaction network. We also find that within the limits of our measurement all the observed coke is formed from product propylene.     

HY/BAPO-5的制备及其在二芳基乙烷合成中的应用

采用水热合成法制备HY/BAP0-5复合分子筛催化剂,并通过XRD、IR和NH_3-TPD进行表征。IR吸附和NH_3-TPD脱附程序升温显示,HY/BAPO-5分子筛的弱酸位数量增加,而强酸位数量相对减少。XRD表明,HY/BAPO-5含有HY沸石和BAPO-5两种晶相。由于HY/BAPO-5分子筛上的弱酸位,HY/BAPO-5分子筛可以取代H_2SO_4成为环境友好型催化剂用于苯乙烯和二甲苯合成二芳基乙烷。