1,720,985 research outputs found
The dynamic impact of uncertainty in causing and forecasting the distribution of oil returns and risk
Get PDFThe aim of this study is to analyze the relevance of recently developed news-based measures of economic policy and equity market uncertainty in causing and predicting the conditional quantiles of crude oil returns and risk. For this purpose, we studied both the causality relationships in quantiles through a non-parametric testing method and, building on a collection of quantiles forecasts, we estimated the conditional density of oil returns and volatility, the out-of-sample performance of which was evaluated by using suitable tests. A dynamic analysis shows that the uncertainty indexes are not always relevant in causing and forecasting oil movements. Nevertheless, the informative content of the uncertainty indexes turns out to be relevant during periods of market distress, when the role of oil risk is the predominant interest, with heterogeneous effects over the different quantiles levels.http://www.elsevier.com/locate/physa2019-10-01hj2018Economic
Catalogue des plantes médicinales de l'Himalaya.
No full textGupta Raj Kumar. Catalogue des plantes médicinales de l'Himalaya.. In: Journal d'agriculture tropicale et de botanique appliquée, vol. 9, n°1-2, Janvier-février 1962. pp. 1-54
Some useful and interesting supplementary food plants of the arid regions
No full textKanodia K. C., Gupta Raj Kumar. Some useful and interesting supplementary food plants of the arid regions. In: Journal d'agriculture tropicale et de botanique appliquée, vol. 15, n°1-3, Janvier-février-mars 1968. pp. 71-74
Plants used during scarcity and famine periods in the dry regions of India
No full textGupta Raj Kumar, Kanodia K. C. Plants used during scarcity and famine periods in the dry regions of India. In: Journal d'agriculture tropicale et de botanique appliquée, vol. 15, n°7-8, Juillet-août 1968. pp. 265-285
Some unusual and interesting food plants of the Garhwal Himalayas
No full textGupta Raj Kumar. Some unusual and interesting food plants of the Garhwal Himalayas. In: Journal d'agriculture tropicale et de botanique appliquée, vol. 9, n°11-12, Novembre-décembre 1962. pp. 532-535
Vernacular names of the useful plants of northwest indian arid regions
No full textGupta Raj Kumar, Dutta B. K. Vernacular names of the useful plants of northwest indian arid regions. In: Journal d'agriculture tropicale et de botanique appliquée, vol. 14, n°10-11, Octobre-novembre 1967. pp. 402-453
Grasses of the Rangelands in Arid Rajasthan
No full textGupta Raj Kumar, Sharma S. K. Grasses of the Rangelands in Arid Rajasthan . In: Journal d'agriculture tropicale et de botanique appliquée, vol. 18, n°1-3, Janvier-février-mars 1971. pp. 50-99
Medicinal plants of the indian arid zone
No full textMalhotra S. P., Dutta B. K., Gupta Raj Kumar, Gaur Y. D. Medicinal plants of the indian arid zone. In: Journal d'agriculture tropicale et de botanique appliquée, vol. 13, n°6-7, Juin-juillet 1966. pp. 247-288
Simulation Studies on Fluid Catalytic Cracking Riser Reactor
Get PDFM.Tech.The fluid catalytic cracking unit(FCC) is of great importance in petroleum refining industry as it treats heavy fractions from various process units to produce light ends (valuable products). The main units of FCC are riser, catalyst stripper and regenerator. Riser reactor is the most important part of this unit as the cracking reactions take place in the riser.
Modeling and simulation of riser helps in understanding the complex physical phenomena taking place in FCC riser unit. Modeling difficulties in FCC riser unit includes complex hydrodynamics, unknown hydrocarbons in the FCC feed and involvement of different type of simultaneous reactions. There has been lot of progress in the modeling of riser reactor. Most of the researchers have taken four to five lump model to avoid complexities in determining reaction rates. These models are easy to integrate with the material and energy balance equations. In the
literature two phase hydrodynamics models are used by many authors, heat and mass transfer
resistances are ignored in many studies and exponential catalyst deactivation model is used in most works.
In this work, FCC riser is simulated solving the material and energy balance equations
considering four lump reaction kinetics, deactivation based on coke concentration on catalyst, 2 phase hydrodynamics and interphase mass transfer phenomena. A computer program is developed in C for the model solution. A base case model for the FCC riser is solved assuming constant cluster size of 6mm.Various cluster size correlations are used in base model to predict the product yields. The predicted cluster size varies considerably for different correlations. The
results show significant variation in conversion, gasoline, and coke for these correlations. The correlations that predict larger cluster predict low overall conversion as compared to the correlations that predict smaller size clusters. Coke yield prediction is most influenced by the cluster size
Studies on transalkylation over modified zeolite catalysts
No full textAlkyl-transfer of alkyl aromatics like toluene and benzene were studied for the purpose of understanding the principles that governs them. Transalkylation of low valued alkyl aromatics was done so as to convert these aromatics to industrially important products like xylene, cumene and cymene. Transalkylation of aromatics ranging from mono to polyalkyl-benzenes was studied in a fixed bed reactor system on solid acid catalysts (zeolites).
In order to replace highly toxic, corrosive and non renewable traditional catalysts with nontoxic as well as renewable catalysts zeolites were used as catalysts for transalkylation of aromatics. In present thesis two different types of large pore zeolites, namely, Hbeta and NaX zeolites were modified using various rare earth metals and were used as catalysts for different transalkylation reactions in heterogeneous mode. The catalysts were refluxed with rare earth nitrate solution at specific conditions to carry out the ion exchange. The chemical analysis of catalysts was done by EDS to find the metal ion incorporated into the zeolite while the catalysts structure and crystallinity was established by powder XRD characterization technique. The surface morphology and particle size was determined by SEM studies. The quantity and strength of acidic sites present in catalysts were found using TPD results.
The rare earth metal ions chosen for the modification of Hbeta and NaX zeolites were lanthanum (La), cerium (Ce) and Praseodymium (Pr). The catalyst activity was found to be a function of its acidity which in turn depends on the rare earth metal ion type and its concentration in the catalyst. The modified zeolites were able to catalyze the transalkylation reaction more effectively than the parent zeolites. These rare earth metal ions modified zeolite catalyst have shown excellent stability on time-on-stream without significant loss in activity. However, the parent catalyst was found to be less active and stable to carry out the transalkylation of aromatics.
Transalkylation reactions were studied at temperatures up to 500°C. Results showed that alkyl-transfer reactions seemed to be dominant at higher temperatures. In transalkylation reactions, the reactant conversion depends on the type of alkyl substituent/s, ring conjugation of the aromatic moiety and the number of alkyl groups on the aromatic ring/s and the chain length. The outlined mechanism showed that the catalyst pore sizes and the type of pores as
xxi
well as the feed composition of binary mixtures play important roles in the transfer of alkyl groups between aromatic molecules. The activity of the zeolites also depends on type of ions exchanged with the H+ or Na+ ions present in the framework of the zeolite.
Besides evaluating the catalyt performance, kinetics and thermodynamic parameters of the reactions were also evaluated. A suitable kinetic model was developed following several mechanisms such as dual site, single site mechanism with surface reaction as the rate controlling step. Activation energy for various transalkylation reactions were found to be in range of 50-130 kJ/mol.
Zeolitic catalysts are deactivated through molecular retention which is dominant at lower temperatures. Bulkier alkylaromatics readily available in petroleum liquids can be transformed to commercially valuable products through transalkylation reactions with the help of a suitable catalyst. Thus, the transalkylation reactions have promising future applications in petrochemical and related industries
- …
