Thermal stress stability of hydrocarbon fuels under supercritical environments

This study investigates the thermal stressing characteristics of hydrocarbon fuels to develop thermally stable fuels for supersonic vehicle applications. The thermal stability characteristics of two multicomponent hydrocarbon fuels, namely F-1 and F-2 fuels, under subcritical and supercritical conditions, are examined for a wide range of temperatures (30–500 °C) and pressures (15–50 bar) using a semi-batch reactor. Various analysis techniques, such as UV-Vis spectrophotometry, ASTM D86 distillation, gas chromatography, scanning electron microscopy (SEM), etc., are used to characterize the feed and product properties. The study showed that the fuels are reasonably stable up to around 400 °C and above 40 bar pressure. The stability of the fuels is relatively less under subcritical pressure at elevated temperatures. The amount of gum formation increased with the increase of both temperature and pressure parameters. Further, the SEM analysis showed oval-shaped and ribbon-like structures in the solid deposits. The present investigation may be useful in developing an appropriate fuel for regenerative cooling in supersonic applications.</p

One-Step Conversion of n‑Butanol to Aromatics-free Gasoline over the HZSM‑5 Catalyst: Effect of Pressure, Catalyst Deactivation, and Fuel Properties as a Gasoline

Sustainable production of gasoline-range hydrocarbon fuels from biomass is critical in evading the upgradation of combustion engine infrastructures. The present work focuses on the selective transformation of n-butanol to gasoline-range hydrocarbons free from aromatics in a single step. Conversion of n-butanol was carried out in a down-flow fixed-bed reactor with the capability to operate at high pressures using the HZSM-5 catalyst. The selective transformation of n-butanol was carried out for a wide range of temperatures (523–563 K), pressures (1–40 bar), and weight hourly space velocities (0.75–14.96 h–1) to obtain the optimum operating conditions for the maximum yields of gasoline range (C5–C12) hydrocarbons. A C5–C12 hydrocarbons selectivity of ∼80% was achieved, with ∼11% and 9% selectivity to C3–C4 paraffin and C3–C4 olefins, respectively, under optimum operating conditions of 543 K, 0.75 h–1, and 20 bar. The hydrocarbon (C5–C12) product mixture was free from aromatics and primarily olefinic in nature. The distribution of these C5–C12 hydrocarbons depends strongly on the reaction pressure, temperature, and WHSV. These olefins were further hydrogenated to paraffins using a Ni/SiO2 catalyst. The fuel properties and distillation characteristics of virgin and hydrogenated hydrocarbons were evaluated and compared with those of gasoline to understand their suitability as a transportation fuel in an unmodified combustion engine. The present work further delineates the catalyst stability study for a long time-on-stream (TOS) and extensive characterization of spent catalysts to understand the nature of catalyst deactivation

Pancreatic islet transplantation: utility of ductular obstruction and exocrine atrophy model?

Introduction of 'silent' exocrine atrophy (and endocrine 'enrichment') in pancreatic grafts following ductular blockade may have a role in human diabetes by circumventing currently elusive islet isolation/purification protocols. To explore this potential, pancreatic isografts were performed in 12 pairs of inbred Wistar NIN rats. Donor pancreatectomy was performed after distal clamping and canulation of common bile duct and injection of 0.5 ml. polyacrylamide gel (blocked n = 7) or normal saline (un-blocked n = 5) respectively. One to 2 m.m. fragments of the resulting mildly distended pancreases were transplanted in to 2 sites (renal capsule and iliac fossa subcutaneously) of cach recipient. Post-operative biopsies of the transplanted grafts (unilateral nephrectomy and iliac fossa biopsies) revealed macroscopic and microscopic evidence of necrotizing pancreatitis in both the groups at both the sites (histiocytic and giant cell infiltration, fat necrosis and focal calcification with destruction of exocrine and endocrine cells) as early as 1 and 3 weeks. Possible detrimental factors include: volume and pressure of ductal injection, graft sites (confined spaces), post-operative wound infection and bio-compatibility of the material used for ductular blockade