| The non-hydrodewaxing technique of diesel distillate oils is one of key technologies for the upgrade of diesel products in the current petrochemical field. Non-hydrodewaxing reactions in essence are isomerization and cracking of long paraffinic hydrocarbons in diesel distillate oils. Therefore, an adequate improvement on the isomerization and cracking activities of zeolite-based catalysts can decrease the yield of gaseous hydrocarbons and increase the total liquid yield, particularly, the diesel oil yield. With regard to this scientific proposition the disquisition on the zeolite-based catalysts and relevant catalytic processes has been developed in present work.Zeolites ZSM-35 and MCM-22 with submicron sizes as well as their intergrowth zeolites, were hydrothermally synthesized in the Na2O-SiO2-Al2O3-H2O-CHA (HMI) system, herein the CHA and HMI refer to structure-directing agents of cyclohexylamine and hexamethyleneimine, respectively. Several factors, i.e. the gel composition, crystallization temperature and time, additive sodium dodecyl benzene sulfonate (SDBS), and the rotate speed of autoclavers, were examined, which were found to effect on the crystal phase, morphology and particle size. Crystallinity and phase purity of ZSM-35 and MCM-22 are fine powder, which were obtained with average particle diameters of 590 and 770 nm, respectively under the proper synthesis conditions while samples of MCM-22/ZSM-35 have average particle diameters of 1500-2500 nm.Zeolite such as ZSM-5, MCM-22, MCM-22/ZSM-35, ZSM-35, MOR, p, and Y are respectively as the body of catalyst. Zeolite pore structures impacting on the reactions of 1-hexene as a model compound were investigated by preparing and applying various zeolite catalysts. For the zeolites with 12-membering pores, the mordenite with 1-dimensional channels shows the higher catalytic activity to 1-hexene cracking reaction whereas the hexane isomerization activity is lower. Secondly, zeolites β and Y with 3-dimensional pore structures exhibit higher catalytic activities for both the hexene cracking and polymerization but the activity of hexane isomerization is also lower. However, for the zeolites with 10-membering pore structures, submicron zeolites ZSM-35 and MCM-22 (as well as MCM-22/ZSM-35 intergrowth zeolite) with 2-dimensional channels promotes isomerization reactions of 1-hexene; zeolite ZSM-5 with the known 3-dimensional pore system presents highly initial activities both for the 1-hexene isomerization and cracking reactions. In conclusion, under the reaction condition of temperature 270 ℃, pressure 0.2 MPa, weight hourly space velocity (WHSV) 1.0 h-1 and n(H2)/n(1-C6H12)= 8,1-hexene isomerizes more active in the sequence of ZSM-5, MCM-22, MCM-22/ZSM-35 and ZSM-35. Thus, zeolite ZSM-35 may be a potential active component to improve the catalytic performance of ZSM-5 catalysts in 1-hexene isomerization reactions.The catalyst composed of ZSM-5(99.0%) and ZSM-35(1.0%) were prepared, and the catalytic performance of the composite zeolite catalyst for diesel non-hydrodewaxing processes was evaluated in a 500 mL reactor by feeding different diesel distillate oils; moreover, reaction conditions were optimized and validated further. The evaluation results indicated that the composite catalyst reveals the considerably high catalytic performance for diesel non-hydrodewaxing compared with commercial ZSM-5 catalyst. For the catalytic cracking diesel oil, the optimum reaction conditions were temperature 327℃, pressure 0.2 MPa, WHSV=1.5 h-1, and under the optimum reaction conditions the diesel yield of 94.02% was obtained, diesel condensation point was-21℃ followed a drop of 26℃ as compared with the feedstock. For the diesel distillate oil from third atmospheric side-stream, the optimum reaction conditions:temperature 310℃, pressure 0.2 MPa, WHSV=1.0 h"1, the diesel yield was 94.61%, diesel condensation point arrived at-21℃ and condensation point dropped about 43℃. For the diesel fraction from first vacumm side-stream, the optimum reaction conditions:temperature 353 "C, pressure 0.2 MPa, WHSV=1.5 h-1, diesel yield of 93.92% was obtained followed condensation point at-21 ℃ and a condensation point drop about 30 ℃. For the hydrocracking tail oil, the optimum reaction conditions:temperature 400 ℃, pressure 0.2 MPa, WHSV=1.2 h"1, the yield and condensation point of basic oil separately achieved 93.92% and lower than-20 ℃,and a condensation point drop was more than 52℃.The ZSM-5(99.0%)/ZSM-35(1.0%) catalyst for diesel non-hydrodewaxing processes was evaluated under individual optimum conditions on pilot test scale. The pilot scale testing results demonstrated that the developed zeolite-based catalyst displayed the preferable non-hydrodewaxing performance for the processes of various diesel distillate oils, viz., the catalytic cracking diesel oil, the third atmospheric side-stream diesel oil, and the first vacumm side-stream diesel oil. Considerably high yields of diesel fractions were achieved while quite low yields of gas products were obtained, nevertheless the higher fractions of light olefins were observed in the gaseous hydrocarbons. Furthermore, the corresponding catalyst was substantiated to be a more potential option for non-hydrodewaxing processes of hydrocracking tail oil.Apparent first-order reaction kinetic equations to deal with the non-hydrodewaxing reaction temperature and residence time were established based on the bench test data of the above feedstock oils, and the analysis and prediction for yields of the both gas and distillate oils formed were performed by the first-order kinetic model. It can be see that the kinetic models with magnitude-reasonable apparent activation energies and pre-exponential factors were simple and available for predicting the yields of various gas and distillate oils due to that the simplified group compositions facilitate the parameter estimation. In general, this set of kinetic model equations were confirmed to be more available for the prediction of heavier liquid fractions but the fitting precisions were found lower for the lighter fractions. |
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