29-P-06-acidity characterization of dealuminated H-ZSM-5 zeolites by isopropanol dehydration

The performance of ZSM-5 as a fluid catalytic cracking (FCC) catalyst additive has been tested in a microactivity test unit for the cracking of gas oil. Laboratory-synthesized ZSM-5 samples, with various Si/Al ratios, fresh or hydrothermally dealuminated were tested. A 2 wt % ZSM-5, on total catalyst weight, found by previous investigators to be the optimum additive concentration, was used for all of the experiments. It has been found that a direct and smooth correlation exists between the product yields and the total number of ZSM-5 acid sites measured by ammonia temperature-programmed desorption tests. This is a unique function of the aluminum content of fresh samples as well as the temperature of the hydrothermal deactivation of steamed ZSM-5 zeolite samples. Previous works have been qualitatively compared to the results of this work and have been classified on the basis of different total acidity regions of the ZSM-5 used in each case. Higher total acidity results in gasoline loss, liquified petroleum gases (LPG) and ethylene increases, and research octane number gain. The C5 aliphatics are increased in the low acidity region because of cracking and isomerization of larger alkenes, while an increase of the total ZSM-5 acidity resulted in a monotonic decrease of all of the gasoline range hydrocarbons, except of n-C5 alkane, C6−C7 aromatics, and C5 naphthenes. The branched/linear (B/L) ratios for C5−C6 alkenes were found to increase with acidity, while the B/L ratios for C5−C9 alkanes decrease. The number and strength of the additive's acid sites control the contribution of the different reaction paths, through which cracking, isomerization, and aromatization occur, to the final product distribution. The sizes of the ZSM-5 particles have a strong effect on the changes in product yields and gas and gasoline compositions. Smaller particles favor a decrease in gasoline and an increase in LPG yield more than larger particles. The effect is more pronounced in the high acidity region where the decrease in the yields of C7+ isoalkanes, naphthenes, and aromatics is favored by small particle additives, while the effect of particle size on gasoline range hydrocarbons is clearly evident on the yields of gaseous products.

Section: Methodsmentioning

confidence: 99%

Performance of ZSM-5 as a Fluid Catalytic Cracking Catalyst Additive: Effect of the Total Number of Acid Sites and Particle Size

Triantafillidis¹,

Evmiridis²,

Nalbandian³

et al. 1999

“…While circulating in an FCC unit, zeolites encounter severe hydrothermal conditions, resulting in physical and chemical changes that affect the surface area, pore volume, and catalytic cracking performance of the zeolites. Several factors influencing the hydrothermal stability of Y zeolite have been reported, including the Si/Al ratio, 1 the dealumination procedure, [2][3][4][5][6] and the hydrothermal aging conditions. 7,8 Zeolites with higher hydrothermal stability can be obtained by using higher Si/Al ratios or by incorporating rare earth or noble metals into the zeolite framework to help prevent dealumination upon hydrothermal treatment.…”

Section: Introductionmentioning

confidence: 99%

An Alternative Correlation Equation between Particle Size and Structure Stability of H−Y Zeolite under Hydrothermal Treatment Conditions

Sombatchaisak

Praserthdam

Chaisuk

et al. 2004

The effect of particle size in the range of 0.16−2.01 μm on the hydrothermal stability of H−Y zeolite under hydrothermal treatment conditions similar to those used in FCC processes was investigated. The average particle size of 0.45 μm was found to be the optimum particle size of H−Y zeolite to retain a high percent crystallinity upon hydrothermal treatment. A new correlation was developed by plotting the relative crystallinity (C/C 0) against the reciprocal of the square root of the particle size (d 0) of Y zeolite. The correlation accurately predicts the hydrothermal stability of Y zeolite in small to medium particle sizes for a given temperature. For the larger particle sizes of Y zeolite (>0.45 μm), no exact correlation between particle size and hydrothermal stability was found, probably because of the presence of more structural defects in the zeolite, as shown by higher Brønsted/Lewis acid ratios.

“…Although steam is widely used in industrial operations and can be of use in the gasification of coke, 23 the hydrothermal stability of the catalyst should be taken into account when steam is selected as the regeneration gas because steam is prone to attacking the Al−O bond of the crystal under highertemperature conditions and then steadily destroying the crystal structure of zeolite, such as HZSM-5, 24 β, 25 HY, 26 and so on. Watanabe et al found that SAPO-34 zeolites were hydrothermally stable up to 1000 °C even under almost pure steam conditions.…”

Section: Industrial and Engineering Chemistry Researchmentioning

confidence: 62%

Partial Regeneration of the Spent SAPO-34 Catalyst in the Methanol-to-Olefins Process via Steam Gasification

Zhou

Zhang

Zhi

et al. 2018

The methanol-to-olefins (MTO) reaction over the SAPO-34 catalyst suffers rapid deactivation due to coke deposition. Here, partial regeneration methods with air combustion and steam gasification were investigated. The results showed that both methods could not only reactivate the spent SAPO-34 catalyst but also prompt ethylene selectivity. Whereas, steam gasification was more effective , by which the initial ethylene selectivity could reach 53%, much higher than that of 23% over fresh SAPO-34 catalyst. Several characterizations, e.g., Fourier transform infrared spectroscopy and gas chromatography−mass spectrometry, indicated that methylated benzenes, which were active hydrocarbon pool species and prompted ethylene selectivity, presented as the main species of residual coke in the SAPO-34 catalyst regenerated via steam gasification. Meanwhile, oxygenated compounds and naphthalene, which could accelerate catalyst deactivation, were observed in the SAPO-34 catalyst partially regenerated via air combustion. This finding improved our understanding of the role of residual coke in the MTO reaction and provided a potential regeneration method for the industrial MTO process.