The chemistry of accelerated sulfur vulcanization is reviewed and a fundamental kinetic model for the vulcanization process is developed. The vulcanization of natural rubber by the benzothiazolesulfenamide class of accelerators is studied, where 2-(morpholinothio) benzothiazole (MBS) has been chosen as the representative accelerator. The reaction mechanisms that have been proposed for the different steps in vulcanization chemistry are critically evaluated with the objective of developing a holistic description of the governing chemistry, where the mechanisms are consistent for all reaction steps in the vulcanization process. A fundamental kinetic model has been developed for accelerated sulfur vulcanization, using population balance methods that explicitly acknowledge the polysulfidic nature of the crosslinks and various reactive intermediates. The kinetic model can accurately describe the complete cure response including the scorch delay, curing and the reversion for a wide range of compositions, using a single set of rate constants. In addition, the concentration profiles of all the reaction intermediates as a function of polysulfidic lengths are predicted. This detailed information obtained from the population balance model is used to critically examine various mechanisms that have been proposed to describe accelerated sulfur vulcanization. The population balance model provides a quantitative framework for explicitly incorporating mechanistically reasonable chemistry of the vulcanization process.

We present a model that predicts the research and motor octane numbers of a wide variety of gasoline process streams and their blends including oxygenates based on detailed composition. The octane number is correlated to a total of 57 hydrocarbon lumps measured by gas chromatography. The model is applicable to any gasoline fuel regardless of the refining process it originates from. It is based on the analysis of 1471 gasoline fuels from different naphtha process streams such as reformates, cat-naphthas, alkylates, isomerates, straight runs, and various hydroprocessed naphthas. Blends of these individual process streams are also considered in this work. The model predicts the octane number within a standard error of 1 number for both the research and motor octane numbers.

A detailed kinetic model has been developed that describes the selective hydro-desulfurization chemistry of FCC naphtha at minimal olefin saturation. The FCC naphtha is represented by 348 molecular lumps measured by different gas-chromatographic methods. The reaction chemistry is specified in terms of reaction rules using the structure-oriented lumping (SOL) framework. A total of 15 reaction rules, which describe 444 individual reaction steps, have been used to model the governing chemistry. Relative reactivity relationships among different molecular lumps within the same rule have been derived using model feeds or established results from the literature. The kinetic parameters have been estimated from a comprehensive experimental data set comprising of both pilot plant and commercial refinery data spanning a wide range of process conditions and feed compositions. The kinetic model quantitatively predicts the product composition, product properties, extent of hydro-desulfurization, olefin saturation, and the associated octane loss. The modeling framework is generic to naphtha hydroprocessing technologies, and its specific application to the Selective CAtalytic Naphtha hydrofining (SCANfining) process, a proprietary technology of ExxonMobil, is demonstrated.

A composition-based model is presented that predicts the effect of cetane improver (specifically 2-ethyl hexyl nitrate) on the cetane number of diesel fuels. A total of 206 different diesel fuels were considered in this work containing varying amounts of improver. The fuels were chosen to span a wide range of compositions, from highly paraffinic to highly naphthenic and, in some cases, highly aromatic fuels. Improver concentrations were varied between 0 to 3500 ppm (v/v), which exceeds the usual commercial application range of 500-1000 ppm. Detailed molecular composition of all the fuels was analyzed using a combination of GC-MS and supercritical fluid chromatographic techniques, while cetane number measurements were made using an Ignition Quality Tester (IQT). Molecular composition was correlated to the cetane number (CN) boost using a simple correlative equation, derived from phenomenological considerations. The model predicts CN boost with a standard error of (0.8 CN, which is within the experimental error of the measurements.

It is difficult and challenging to design high-performance fuel additi®es in an indus

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A set of adsorption energies for all the reaction intermediates completely defines the reaction thermodynamics. Hence, it is important to quantitatively predict adsorption energies for a given system. Describing desulfurization catalysis via transition metal sulfides involves numerous combinations of sulfur-containing molecules and active site geometries. For such a system, a correlative model for adsorption energy predictions would be very useful. We have calculated the η1 adsorption energies for 12 different sulfur-containing molecules on 5 different Co-MoS2 metal edge structures. These edge structures give rise to 12 different adsorption modes corresponding to different S-coverages, Co-decorations, and H-coverages. We find adsorption energies for any pair of molecules or any pair of adsorption modes are linearly correlated, confirming the applicability of scaling relationships. Natural bond orbital (NBO)-based electronic descriptors for gas phase adsorbate species are sufficient to describe the adsorption energy variation for a set of adsorbate molecules. A linear regression model indicates that occupancy of the lone pair orbitals for electrons on sulfur plays an important role in determining adsorption energy. Our analysis of the occupancy and energy level of the lone pair of electrons reveals the close relation between aromatic delocalization of the lone pair and adsorption energies of the molecule.

Hillocks of coir pith accumulate in the vicinity of coconut coir-fiber extraction units, of which disposal and management remain a major problem. Southern states of India, especially Kerala, Tamil Nadu, Andhra Pradesh, Karnataka, and Orissa, face this problem. A simple technology for accelerated composting of coir pith was developed, and on-site composting of coir pith hillocks was demonstrated. The composting of pith was complete in 21 days. The composted pith was an excellent organic manure, with a reduced C/N ratio of 20:1, pH of about 6.5, and electrical conductivity of 0.23 dS/cm, making it a more desirable soil organic manure. The composted pith did not contain or carry weeds and undesirable pathogens, thus providing a rich soil environment for plant and vegetation growth.