1. Field of the Invention
The present invention relates to fluid catalytic cracking (FCC), and particularly to the manufacture of a ZSM-5/MCM-41 composite catalyst for use with FCC processes.
2. Description of the Related Art
Fluid catalytic cracking (FCC) is commonly used to produce propylene. In the FCC process, heavy feedstocks, such as vacuum gas oil or residual oil, are cracked into value-added lighter products, such as gasoline. Currently, about 28% of the world's propylene is supplied by refinery FCC operations, and 63% is co-produced from thermal steam cracking of naphtha or other feedstocks. The remainder is produced using metathesis or propane dehydrogenation processes. Special FCC process designs and catalysts have been developed to selectively increase propylene production, and ultimately to provide a technology for full light olefins and aromatics petrochemical integration.
The addition of the zeolite ZSM-5 to FCC catalysts has improved propylene yield by offering refiners a high degree of flexibility to optimize the production output of their FCC units. Recent research has indicated the importance of biporous composites for usage with FCC processes, involving both microporous ZSM-5 and MCM-41 as additives in enhancing FCC propylene output. Such biporous materials, however, are typically extremely difficult to produce and previous attempts have been highly labor intensive and cost ineffective.
Thus, a method of forming a hydrocarbon cracking catalyst solving the aforementioned problems is desired.
The method of forming a hydrocarbon cracking catalyst provides a method of varying or tuning the mesophase MCM-41 or microporous ZSM-5 properties in biporous ZSM-5/MCM-41 composites, depending on the requirements of the intended application. The method includes the steps of performing a surfactant-mediated hydrolysis of ZSM-5, through gradual heating, to form a solution, and then adjusting the pH of the solution to selectively tune the microporous and mesoporous properties of the final ZSM-5/MCM-41 catalyst product. Following tuning, soluble aluminosilicates are hydrothermically condensed to form. a mesoporous material over the remaining ZSM-5 particles to form the ZSM-5/MCM-41 composite. The ZSM-5/MCM-41 composite may be used as a hydrocarbon cracking catalyst for cracking gas, oil or the like.
The zeolitic disintegration may be single or composed of a mixture of two zeolites, such as ZSM-5 and Beta, ZSM-5 and HY, or ZSM-5 and mordenite. This leads to biporous (micro/meso) or triporous composites (micro-micro-mesoporous) after the formation of MCM-41 in the final step. The ZSM-5/MCM-41 composite produced by this method shows high hydrothermal stability.
These and other features of the present invention will become readily apparent upon further review of the following specification and drawings.
Similar reference characters denote corresponding features consistently throughout the attached drawings.
The present invention relates to a method of forming a hydrocarbon cracking catalyst that permits controlled varying or tuning of mesophase MCM-41 or microporous ZSM-5 properties in biporous ZSM-5/MCM-41 composites, depending on the requirements of the intended application. The method includes the steps of performing a surfactant-mediated hydrolysis of ZSM-5 to form a solution, and then adjusting the pH of the solution to selectively tune the microporous and mesoporous properties of the final ZSM-5/MCM-41 catalyst product. Following tuning, soluble aluminosilicates are hydrothermically condensed to form a mesoporous material over the remaining ZSM-5 particles to form the ZSM-5/MCM-41 composite. The ZSM-5/MCM-41 composite may be used as a hydrocarbon cracking catalyst for cracking gas, oil or the like.
The zeolitic disintegration may be single or composed of a mixture of two zeolites, such as ZSM-5 and Beta, ZSM-5 and HY, or ZSM-5 and mordenite. This leads to biporous (micro/meso) or triporous composites (micro-micro-mesoporous) after the formation of MCM-41 in the final step. The ZSM-5/MCM-41 composite produced by this method shows high hydrothermal stability.
For purposes of comparison, conventional AlMCM-41 was first synthesized by dissolving 10.6 g of sodium metasilicate and 0.95 g of aluminum nitrate in 60 g of water. This solution was then thoroughly stirred until a clear solution was obtained. 3.36 g of cetyltrimethylammonium bromide (CTAB) was then dissolved in 20.0 g of ethanol, and the mixture of sodium metasilicate and aluminum sulfate was added to the CTAB/ethanol solution drop-wise, The resultant mixture was stirred for 3.0 h, and then the pH of the resulting gel was adjusted to 11.0 with 4.0 N sulfuric acid followed by stirring for 3 h. This homogenous solution was transferred into an autoclave and heated to 140° C. in static conditions for 12 h. The product was then filtered, washed, dried and calcined at 550° C. for 6 h. The resulting AlMCM-41 was ion-exchanged three times with 0.05 M NH4NO3 solution at 80° C. for 2 h, and then calcined at 550° C. for 2 h.
The specific surface area, pore diameter and the total pore volume are shown in Table 1 of
Also for purposes of comparison, a conventional ZSM-5 zeolite sample with a Si/Al ratio of 13.5:1 that is commonly used for the formation of composite additives for fluid catalytic cracking (FCC) processes was obtained from Catal International, Ltd. The surface area and total pore volume of the ZSM-5 sample were 284 m2/g and 0.29 cm3/g, respectively.
A micro/mesoporous ZSM-5/MCM-41 catalyst with tunable porosity and a high zeolitic character was formed by disintegrating 2 g of ZSM-5 having a Si/Al ratio of 27:1 in 55 ml of 0.2M NaOH. The disintegration was performed under gradual heating (without stirring) at 100° C. for 24 hours in the presence of CTAB (4.45%). Next, the mixture was cooled down and then the pH was adjusted to 9.0 through the addition of dilute sulfuric acid (2N). The mixture was then stirred for 24 h and then aged at 100° C. for another 24 h to form a ZSM-5/MCM-41 composite.
The solid product was then filtered, washed thoroughly using distilled water, dried at 80° C. overnight, and then calcined at 550° C. for 6 h to remove the surfactant. The resultant composite was ion-exchanged three times with 0.05M NH4NO3 solution at 80° C. for 2 hours, and then calcined at 550° C. for 2 h. The resulting powder was sieved to a particle size between 0.5 mm and 1.0 mm and then used as an additive to enhance the yield of propylene from catalytic cracking of vacuum gas oil (VGO).
The mesoporous content in the ZSM-5/MCM-41 composite was found to be 19 wt %. The specific surface area, pore diameter and the total pore volume are shown in Table 1 of
A ZSM-5/MCM-41 composite with a biporous character was synthesized similar to that described above in Example 3, except that 2 g of H-ZSM-5 was disintegrated in 55 ml of 0.7M NaOH. The resulting powder was then sieved to a particle size between 0.5 mm and 1.0 mm and used as an additive to enhance the yield of propylene from catalytic cracking of vacuum gas oil (VGO). The specific surface area, pore diameter and the total pore volume are shown in Table 1 of
A ZSM-5/MCM-41 composite with a high mesoporous character was synthesized similar to that described above in Example 3, except that 2 g of H-ZSM-5 was first disintegrated in 55 ml of 1.0M NaOH. The mesoporous content in the ZSM-5/MCM-41 composite was found to be 96 wt %. The specific surface area, pore diameter and the total pore volume are shown in Table 1 of
In order to form mesoporous MCM-41 from a zeolitic seed, 2 g of ZSM-5 (with a Si/Al ratio 27:1) was dissolved completely by stirring in 55 ml of 0.7M NaOH (with a pH of 13.0) at 100° C. for 2 hours, in the presence of CTAB (4.45%). The mixture was then cooled down and the pH was adjusted to 9.0 through the addition of dilute sulfuric acid (2N). The mixture was then stirred for another 24 h and then aged at 100° C. for a further 24 h. The solid product was then filtered and calcined at 550° C. for 6 h to remove the surfactant. The resulting composite was ion-exchanged three times with 0.05M NH4NO3 solution at 80° C. for 2 hours, and then calcined at 550° C. for 2 hours. The specific surface area, pore diameter and the total pore volume are shown in Table 1 of
The resultant MCM-41 had a Si/Al ratio of 13:1, as determined by atomic absorption measurements. The XRD pattern showed the presence of three well resolved peaks at the lower angle (20) region between 2° and 5° indexed to (100), (110), and (200) reflections, thus showing the presence of characteristic long range ordered hexagonal symmetry. The absence of any Bragg peaks corresponding to the zeolitic phase at higher angles indicates that the synthesized material is in a pure mesophase. The material showed a d spacing value of 3.86 nm. The presence of intense peaks of ZSM-5 diffraction patterns, compared to MCM-41, shows the dominant zeolitic character in the composite. The surface area, pore volume and pore diameter, as measured by nitrogen adsorption, were 527 m2/g, 0.72 cm3/g and 2.2 nm, respectively.
The ZSM-5/MCM-41 composite produced in Example 6 was further subjected to steaming (100% steam) in a fixed-bed for 4 h at 650° C. and at atmospheric pressure. The specific surface area, pore diameter and the total pore volume are shown in Table 1 of
The XRD patterns of calcined AlMCM-41, ZSM-5 and ZSM-5/MCM-41 composites with different degrees of porosity obtained from ZSM-5 (with a SiO2/Al2O3 ratio of 27:1) dissolution are shown in
When the dissolution was carried out in 55 ml of 0.2M NaOH solution (the pH of the initial solution was approximately 12.10), the XRD pattern showed the transformation of the zeolitic phase into the biporous phase containing both ZSM-5 and MCM-41. In the low angle region (2-5°), an intense (100) peak, along with a less intense higher order diffraction peaks indexed to (110), (200) corresponding to MCM-41, were observed (as shown in
When the dissolution pH increased to 13.30 with 55 ml of 1.0M NaOH, the dissolution of greater amounts of ZSM-5 occurs. The intensity of the hexagonal phase increased, whereas the characteristic peaks of ZSM-5 became less intense but were still retained in the composite (as shown in
Comparatively, the presence of three well resolved peaks at the lower angle (20) region between 2° and 5° indexed to (100), (110), and (200) reflections shows the presence of characteristic long range ordered hexagonal symmetry. The absence of any Bragg peaks corresponding to the zeolitic phase at higher angles indicates that the synthesized material is in pure mesophase. The dissolution of ZSM-5 in the presence of a cationic surfactant stabilizes the zeolitic subunits through ion pairing and also serves as a structure-directing agent for the mesostructure formation. Thus, the present dissolution technique is useful in avoiding excessive dissolution of ZSM-5, which leads to the controlled formation of soluble aluminosilicate species, as well as unsolvable smaller ZSM-5 zeolite particles, which are subsequently used for the formation of mesoporosity.
A triporous ZSM-5/mordenite/MCM-41 was also prepared by first dissolving ZSM-5 and mordenite, by hydrothermal heating, in 0.7M NaOH solution in the presence of CTAB. Following pH adjustment, a triporous composite was formed. The XRD of this composite sample is shown in
The samples of Example 1, Example 2, Example 4, Example 6 and Example 7 were tested as FCC catalyst additives to investigate the effect on the yield of propylene from catalytic cracking of Arabian Light hydrotreated vacuum gas oil (VGO) in a fixed-bed microactivity test (MAT) at 520° C. Their catalytic performance was assessed using a 10 wt % blend of the additives and a commercial equilibrium USY FCC catalyst (E-Cat) at various catalyst/oil ratios. Table 2 of
The MAT results show that the VGO cracking activity of E-Cat did not decrease by using these additives. The highest propylene yield of 12.2 wt % was achieved over the steamed biporous ZSM-5/MCM-41 composite of Example 7, compared with 8.6 wt % over the conventional ZSM-5 of Example 2 at similar gasoline yield penalty. Ethylene yield also increased to 2.4 wt % for the steamed biporous ZSM-5/MCM-41 composite compared with 0.5 wt % for base equilibrium catalyst. Steamed ZSM-5/MCM-41 gave a lower hydrogen transfer coefficient of 0.8. The enhanced production of propylene was attributed to the suppression of secondary and hydrogen transfer reactions and offered easier transport and accessibility to active sites. Gasoline quality was thus improved by the use of steamed ZSM-5/MCM-41.
It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.