Browsing by Author "Shakeel Ahmed"

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Adsorption of surfactants on Saudi Arabian limestone.
(Saudi Digital Library) Shakeel Ahmed
Static adsorption experiments were conducted to investigate the adsorption and precipitation properties of various surfactants including petroleum sulfonate (TRS10-410), ethoxylated sulfonates (v2880, v3348, B1083, B1139) and nonionics (T150) onto Saudi Arabian limestone. The effect of parameters such as solid to liquid ratio, salinity, pH, temperature, surfactant type, ethoxylation number, sacrificial agents, oil and alcohol has been investigated. The adsorption data for limestone/TRS10-410 system and v2880/system at different salinities show that the increase in ionic strength generally increases the surfactant adsorption on limestone at higher sulfonate concentrations. The dependence of adsorption on pH shows marginal sulfonate adsorption above ZPC (pH=8.3) where limestone is negatively charged and extremely high adsorption below pH of 8.3, where the surface of limestone acquires positive charge. Temperature data at three different levels (25, 50 and 90 degree C) show that adsorption drastically increases with increasing temperature. Increasing the ethoxylation number of surfactants decreases the adsorption but concurrently increases the CMC of surfactants. The results also indicate that adsorption of surfactants on limestone can be reduced with addition of silicates as sacrificial agents and n-butanol as co-surfactant. Adsorption data in the presence of crude oil show that adsorption of ethoxylated sulfonates increases significantly in the oil. The adsorption tests for nonionics (T150) show about five-fold higher adsorption than the anionic surfactant (B1083) of the same ethoxylation number under the same experimental conditions. Precipitation behavior of TRS10-410 in the presence of NaCI and CaCl2 indicates that the surfactant is not tolerant to even as low as 1% NaCl and 0.15
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Synthesis, modification and catalytic evaluation of high-silica zeolites
(Saudi Digital Library) Shakeel Ahmed
High-silica zeolites of MFI type were synthesized by rapid crystallization method. The major factors affecting the hydrothermal synthesis were screened using Plackett-Burman experimental design. The pH of the crystallizing mixture was found to be most important factor. A pH of 10.0+0.5 was found to be the optimum for the crystallization method were compared with that of conventional method. A narrow particle size distribution was found in the case of rapid crystallization method. This finding was rationalized on the basis of nucleation rate ralative to the crystallization rate. The synthesized zeolites were modified by varying Si/A1 ratio, metal incorporation and steaming. A quantitative relationship was found between the Si/A1 ratio of the gel and that of the zeolite product. The least square fit to the data gave: (Si/A1)zeolite = 3.53 + 0.777(Si/A1)gel with a correlation coefficient of 0.999. This was consistent with the silica having higher solubility than aluminosilicate species and that the pH of the hydrogel, within the range of Si/A1 ratios investigated, was constant. The synthesized and modified zeolites were characterized by FTIR, XRD, SEM, ESR, thermal analysis and particle size distibution analysis. Acidity measurements of some of the synthesized and modified zeolites were performed by TPD of ammonia and FTIR of absorbed pyridine. A bench scale high-pressure flow reactor system was designed and fabricated for the catalytic evaluation of the high-silica zeolites. Some of the selected zeolite catalysts were evaluated for MTBE synthesis and methanol to olefins (MTO) conversion. In the case of MTBE, the effect of temperature, Si/A1 ratio, space velocity and methanol to isobutene molar ratio was investigated for the conversion of isobutene. Higher yields of MTBE were obtained at 80°C for lower Si/A1 ratio. The space velocity and molar ratio had minor effect. The acidity of the zeolite was correlating with the conversion of isobutene. Steam-modified zeolite performed better in term of selectivity for MTBE than commercial Amberlyst-15 resin catalyst. The yield of MTBE was comparable for both catalysts. The higher activity of the steamed catalyst was explained on the basis of enhanced acidity. Steaming at higher severity caused reduction in activity resulting from excessive loss of acid sites. The results of catalytic evaluation for MTO showed that Fe-containing synthesized zeolite gave highest selectivity for the C₂ - C₄ olefins. This was attibuted to the dilute acidity of the catalyst.
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