Sunil Ashtekar - Academia.edu (original) (raw)

Papers by Sunil Ashtekar

Proceedings / Indian Academy of Sciences, 1994

Silicon-substituted aluminophosphates with different framework structures SAPO-5,-11,-34 and-44 h... more Silicon-substituted aluminophosphates with different framework structures SAPO-5,-11,-34 and-44 have been synthesized by the hydrothermal method using organic templates. The extent of silicon substitution in these materials has been investigafed by chemical analysis, measurement of acidity through temperature-programmed desorption of ammonia and silicon MAS-NMR spectroscopy. It has been found that for SAPO-5, and SAPO-11 a small amount of silicon substitution takes place at the phosphorus sites and most of the silicon atoms are present either as silica-rich regions in the structure or as amorphous silica. The amount of silicon in them is quite low. For SAPO-34 and-44, on the other hand, the major part of the silicon randomly substitutes the phosphorus atoms and the rest of it forms small silica patches in the structure. The last two structures cannot be prepared in pure form unless the concentration of the silica source in the synthesis gel is quite high. Keywords. Silicon-substituted aluminophosphates; MAS-NMR; temperature-programmed desorption of ammonia.

La presente invention porte sur une composition bitumineuse comprenant de 20 % en poids a 99,9 % ... more La presente invention porte sur une composition bitumineuse comprenant de 20 % en poids a 99,9 % en poids de bitume, de 0,01 % en poids a 10 % en poids d'un compose de maleimide et de 0,5 a 75 % en poids de soufre, par rapport au poids de la composition bitumineuse. La presente invention porte egalement sur une composition d'asphalte comprenant ladite composition bitumineuse et une charge et/ou un granulat. Les compositions bitumineuse et d'asphalte de la presente invention presentent des emissions d'H 2 S considerablement reduites.

Journal of the Chemical Society, Chemical Communications, 1994

Silicon substitution for phosphorus at crystallographically distinct sites resulting in the creat... more Silicon substitution for phosphorus at crystallographically distinct sites resulting in the creation of two silicon environments has been observed in SAPO-46 molecular sieves.

Energy & Fuels, 2018

Asphaltene deposition is one of the major flow assurance problems that can potentially deteriorat... more Asphaltene deposition is one of the major flow assurance problems that can potentially deteriorate due to the current tendencies to produce from the deep-water environment or as a result of enhanced oil recovery operations based on miscible gas injection. The deposited asphaltenes in the wellbores and on the surface of the oilfield pipelines can impede the productivity of the wells significantly. The comprehensive understanding of the mechanisms and the techniques to control asphaltene deposition at high temperature and under dynamic conditions can help resolve this critical issue. Thus, it is imperative to develop reliable, straightforward, and inexpensive tools to investigate the asphaltene deposition tendency and the performance of asphaltene inhibitors in the laboratory. In this work, a new stainless steel packed bed column deposition system that was inspired by the work of Vilas Boas Favero et al. was successfully developed. The packed bed design allows the feasibility of investigating a variety of f...

Abu Dhabi International Petroleum Exhibition & Conference, 2018

Restriction or blockage of flow path due to waxy deposits is a global issue in the oil and gas pr... more Restriction or blockage of flow path due to waxy deposits is a global issue in the oil and gas production. This undesirable flow assurance issue leads to increase in production deferment and OPEX for mitigation and frequent intervention. It may also result in huge CAPEX for pipeline sections replacement due to untreatable blockages. Despite the current prevention and mitigation strategies in place, wax deposition cannot be fully eliminated. Existing remediation technologies can be broadly classified to mechanical, thermal, and chemical-based treatments. These also have some limitations such as availability, cost, deferment and effectiveness. Today, most effective solutions are often a combination of mechanical and chemical which are expensive in terms of cost and may result in additional deferment time. As such, the development of more effective remediation strategies is of great importance. Solvent-based cleaning can be relatively less expensive if it is a viable option. However, e...

Offshore Technology Conference, 2017

To ensure proper selection of reservoir completion, subsea and topside production materials of co... more To ensure proper selection of reservoir completion, subsea and topside production materials of construction and production chemicals, it is imperative to accurately assess the Hydrogen Sulfide (H2S) concentration in produced reservoir fluids. At high reservoir pressures (>10,000 psi), H2S concentration as low as 50 ppm (mole) or less must be quantified. If an offshore production well test cannot be performed, these assessments must be made based on the analysis of open-hole formation testing samples. Open-hole sampling with formation testing equipment only allows for the production of a relatively small amount of reservoir fluid and exposes the reservoir fluid to potential sites for H2S adsorption/reaction during the sampling process. Sites for potential H2S loss include the contact of the reservoir fluid with oil or water based drilling fluids, the formation tester flowline, and within the formation tester sample chamber after isolation downhole. This work focuses on evaluating ...

SPE International Conference on Oilfield Chemistry, 2017

Hydrogen sulfide poses significant challenges to develop oil and gas fields and manage risks in t... more Hydrogen sulfide poses significant challenges to develop oil and gas fields and manage risks in terms of personal and process safety. There is a great need to accurately interpret a measured H2S concentration from a gas/oil/water sample for material selection and design during development stage and for sulfide scale/corrosion control after water breakthrough. The objective of this work was to develop an integrated tool comprising ionic chemistry and hydrocarbon thermodynamics in a single and easy to use spreadsheet based tool that is also applicable at HPHT (High Pressure High Temperature) and high saline brine conditions. The tool must account for evaporation of water from brine phase and also have the capability to estimate CO2 and H2S partitioning and speciation, bubble points and density calculations, H2S fugacity and pH of the aqueous phase. A simulation tool for ionic chemistry has been developed to model the H2S distribution with Pitzer ion interaction model to account for th...

contacting a mixture comprising dihydroxy aromatic compound, water and an alkylating agent with a... more contacting a mixture comprising dihydroxy aromatic compound, water and an alkylating agent with a catalyst system in the presence of a flowing carrier gas, to form a mono alkylated dihydroxy aromatic compound, wherein the catalyst system is obtained by the calcination of a catalyst precursor system comprising a metal oxide precursor, a transition metal element and a pore former. ® KIPO & WIPO 2007

Metal oxide catalyst precursor composition of this invention comprises a void-forming agent and t... more Metal oxide catalyst precursor composition of this invention comprises a void-forming agent and the catalytic reagent.

Journal of the Chemical Society, Faraday Transactions, 1998

... Sunil Ashtekar,a Jeremy J. Hastingsb and Lynn F. Gladdena* a Department of Chemical Engineeri... more ... Sunil Ashtekar,a Jeremy J. Hastingsb and Lynn F. Gladdena* a Department of Chemical Engineering, University of Cambridge, Pembroke Street, Cambridge, UK ... to in the discussion of results are reported in Table 1, together with the corresponding data for the pure liquid sorb ...

Microporous Materials, 1996

Medium pore molecular sieves SAPO-11, SAPO-31 and SAPO-41 have been synthesized using din -propyl... more Medium pore molecular sieves SAPO-11, SAPO-31 and SAPO-41 have been synthesized using din -propylamine as the organic template. They have been characterized by various methods such as X-ray powder diffraction, solid state MAS NMR spectroscopy, thermal analysis, chemical analysis and temperature programmed desorption (TPD) of ammonia. Catalytic activities of these materials in the alkylation of toluene with methanol have been studied. While SAPO-I1 and SAPO-31 showed moderate activity, very high catalytic activity was shown by SAPO-41. All the catalysts showed varying degrees of shape selectivity towards p-xylene. SAPO-41 gave a large amount of 1,2,4-trimethylbenzene in addition to the xylenes.