Naphtha was steamcracked over ZSM-5 zeolites modified by both calcium and magnesium cations in a fixed-bed quartz reactor. Calcium and magnesium cations with a constant proportion were simultaneously impregnated into the fresh ZSM-5 zeolite with Si/Al ratio 140 (mol/mol). After drying and calcination, the modified zeolites were ground into 20~40 mesh for use. Reaction conditions were: temperature 700°c, W/O (w/w) =1.1, WHSV 12h-1.
It was found that Si/Al ratios of the modified ZSM-5 zeolites incresed with the decrease of the impregnated metal contents. And all modified zeolites had higher Si/Al ratios than the fresh one. The total acid amounts of the modified zeolites raised with the Si/Al ratios when the Si/Al ratios were less than 200.86, then dropping and rising again. However, B/L values had no obvious tendency with Si/Al ratios of the modified zeolites.
It was also found that gas yields and C2=+ C3=+ C4== yields basically went up with the increase of Si/Al ratios of the modified zeolites. And a maxium also appeared when the Si/Al ratio was 200.86. Meanwhile, it was found that BTX yields basically raised with the gas yields except the Si/Al ratio with 200.86, when a minimum was seen.
In addition, it was found a distinct difference of C5+ product distributions between the modified zoelites and the fresh one. Obviously, the diffenrence was an appearance of the modified function on the steam cracking.
As above, it was obtained a direction to the preparation of modified ZSM-5 zeolites with Ca and Mg through the comparison of the characterization results with the steamcracking ones. Also it was acqiured the modification function of the Ca and Mg on the ZSM-5.
Naphtha steamcracking is an important way to produce ethylene now. Due to the increasing need to propylene, the catalytic steamcracking naphtha has been developed. Usually, the catalysts are focused on the modified MFI zeolites. And the objective of the modification is to change the acidic properties of the original zeolites. In the paper, double alkali-earth metals, calcium and magnesium, were used to modify the ZSM-5 zeolite.
The original ZSM-5 zeolite, with Si/Al ratio 140 (mol/mol), was produced by Hunan Jianchang Petrochemical Co., Ltd, China, and marked as ZRP140. The original zeolites were modified by a series of calcium and magnesium elements, with a certain proportion, through ion-exchange+immersion. After drying and calcination, the modified zeolites were ground into 20~40 mesh.
The industrial naphtha was provided by Yanshan Chemical Industrial Factory, SINOPEC. The tail gas was routinely analyzed by GC. The liquid products and Yanshan naphtha were qualitatively and quantitatively analyzed by GC-MS. The components of Yanshan naphtha were listed as Table 1.
(Table in full paper)
The catalytic steamcracking of naphtha was performed in a quartz reactor. The catalyst loading was 1g, reaction temperature 700°C, water/oil (w/w) 1.1, WHSV 12h-1.
