Desulfurization Of Gas Oil Research Articles

Japan Energy’s technology removes more sulphur from diesel

Several series of commercial alumina supported nickel-molybdenum and cobalt-molybdenum hydrotreating catalysts were exposed to differing degrees of reaction lengths and severities using a variety of naphtha and gas-oil feeds. Fresh and used catalysts were characterized by gas-oil desulfurization and denitrogenation activity, chemical analysis of deposits, porosimetry, and high-resolution transmission electron microscopy; in addition, deposits on the catalysts were characterized by carbon-13 nuclear magnetic spectroscopy. Deactivation was primarily by suppression of active sites by carbon containing deposits on the support. Changes in MoS2 structure, as observed by HRTEM, do not appear to contribute to activity changes. Two types of carbon deposits were observed: processing with gas oils leads to deposition of a compact carbon, resulting in substantial loss in nitrogen removal activity but only slight loss in sulfur removal activity; at higher loadings this dense carbon deposit affects both sulfur and nitrogen removal activities, but nitrogen removal is reduced to a greater extent. Processing with naphthas results in deposition of less dense carbon, which reduces nitrogen and sulfur removal by the same amount, the extent of which is proportional to carbon loading. Comparison of different catalysts deactivated in the same commercial environment permits insights into those factors important to preventing activity loss.

Simulation of multicomponent gas separation in a hollow fiber membrane by orthogonal collocation — hydrogen recovery from refinery gases

Modeling of hollow fiber asymmetric membranes can provide useful guidelines to achieve desirable separations of multicomponent gas mixtures. Especially in cases of high commercial interest, such as hydrogen recovery from refinery streams, the accurate prediction of membrane separation performance is important. In this work, the appropriate model equations are solved by orthogonal collocation to approximate differential equations, and to solve the resulting system of non-linear algebraic equations by the Brown method. This technique is applied for the first time in a multicomponent gas separation by hollow fiber membranes and offers minimum computational time and effort, and improved solution stability. The predictions of the mathematical model are compared with experimental results for the separation and recovery of hydrogen from a typical gas oil desulfurization unit for various feed pressures, temperatures and stage cuts. In general, there is a very good agreement between simulation and experimental results. Further application of the developed mathematical model to various refinery gas streams of interest reveals that high permeate purity (99.95+), and high recovery (0.6–0.9), can be achieved even in a one-stage membrane unit. The reported experimental results and the theoretical analysis demonstrate the potential which polymer membrane technology has for the separation of hydrogen from refinery gas streams.

Radioactive Tracing As Aid for Diagnosing Chemical Reactors

Radioactive tracing is often the only fine and non-intrusive technique for characterising the flow of phases in chemical reactors. Provided that methodological constraints have been respected, this tracing allows to study, from a chemical engineering point of view, the flow of a phase by the measurement of local residence-time distributions (RTD) or internal ages distributions. From these distributions one can deduce the nature of the marked flow, which is required for scale extrapolation; the example of a packed column is given to illustrate this point. These distributions may validate computational fluid dynamics (CFD) codes as it is pointed out in the tracing of a crystallisation process by desublimation of a hot gas by a cold one. In this case, computed aerodynamics is confirmed by the experimental build-up of a systemic model; the reaction zone is then numerically localised with a high degree of confidence. A specific property of the radioactive tracing is that the signal monitored by a nuclear probe is inversely proportional to the volumetric flow rate near the probe. Then, modelling the enthalpic balance leads in a simple way to the local corresponding temperature as it is featured in the example of the tracing of a quenching tower. These measurements, even if they can point out maldistributions of flows, are not suitable for their localisations; this is the purpose of static or dynamical imaging techniques. Among them, the single photon emission computed tomography (SPECT) enables to reconstruct the image of the repartition of a tracer in the cross-section of a cylindrical reactor from a limited number of nuclear detectors. Advantages and limitations of SPECT are presented and an example of localisation of maldistributions is given. Finally, the correct treatment of images given by a gamma camera constitutes an interesting way for the visualisation and estimation of the repartition of a radioactive tracer in a laboratory three-phase catalytic reactor of the Mahoney-Robinson type used for the desulfurization of gas oils. The influence of the agitation speed on the local efficiency of the gas and liquid mass transfers can be pointed out.

Reaction order and role of hydrogen sulfide in deep hydrodesulfurization of gas oils: consequences for industrial reactor configuration

Deep desulfurization of gas oils to sulfur levels below the currently legislated 0.05 wt.% is rendered difficult by the presence of refractory species as part of a spectrum of sulfur compounds that have widely differing reactivities. This distribution of reactivities is reflected in a high apparent order (approximately 2) in total sulfur for a plug–flow reactor. The consequences of this apparent kinetic behaviour for required catalyst volumes and axial profiles of hydrogen sulfide in a reactor for deep desulfurization are examined. Hydrogen sulfide proved to strongly suppress the conversion rate of sulfur compounds, including that of the refractory alkyl substituted dibenzothiophenes crucial for deep desulfurization. A number of process configurations are discussed that avoids or reduces the problem of hydrogen sulfide inhibition. These include several variants of a two-step process in which the bulk of sulfur is removed in a first step, followed by further desulfurization down to low sulfur levels in a second step with fresh, H 2S-free hydrogen gas. The theoretically most ideal option, that of operation with countercurrent flow of oil and gas, is not possible in packed beds of the usual catalyst particles because of the occurrence of flooding at industrially relevant fluid velocities. Some novel reactor concepts based on special structured packings or monoliths that allow such countercurrent operation are presented.

Kinetics of individual sulfur compounds in deep hydrodesulfurization of Kuwait diesel oil

This paper deals with the factors influencing deep desulfurization of Kuwait diesel oil. Systematic experiments were conducted to optimize the process conditions for deep desulfurization of gas oil to low-sulfur (500 ppmw max.) diesel fuel. Particular attention was paid to the effect of operating conditions on the conversion of various types of individual sulfur compounds present in the gas oil feed. Overall kinetics of gas oil desulfurization and the HDS kinetics of some important individual sulfur compounds present in the gas oil, such as dibenzothiophene and its alkyl derivatives, were also determined.

Characterization and aging of hydrotreating catalysts exposed to industrial processing conditions

Several series of commercial alumina supported nickel-molybdenum and cobalt-molybdenum hydrotreating catalysts were exposed to differing degrees of reaction lengths and severities using a variety of naphtha and gas-oil feeds. Fresh and used catalysts were characterized by gas-oil desulfurization and denitrogenation activity, chemical analysis of deposits, porosimetry, and high-resolution transmission electron microscopy; in addition, deposits on the catalysts were characterized by carbon-13 nuclear magnetic spectroscopy. Deactivation was primarily by suppression of active sites by carbon containing deposits on the support. Changes in MoS 2 structure, as observed by HRTEM, do not appear to contribute to activity changes. Two types of carbon deposits were observed: processing with gas oils leads to deposition of a compact carbon, resulting in substantial loss in nitrogen removal activity but only slight loss in sulfur removal activity; at higher loadings this dense carbon deposit affects both sulfur and nitrogen removal activities, but nitrogen removal is reduced to a greater extent. Processing with naphthas results in deposition of less dense carbon, which reduces nitrogen and sulfur removal by the same amount, the extent of which is proportional to carbon loading. Comparison of different catalysts deactivated in the same commercial environment permits insights into those factors important to preventing activity loss.

Effect of Flue Dust on the Vanadium Oxide Catalyst Utilized by the Contact Oxidation Process

Concepts for controlling SO2 from fossil fuels can be separated into two main categories: (1) Residual and vacuum gas oil desulfurization and (2) Flue gas desulfurization. The Kiyoura-T.I.T. process confines itself to the desulfurization of flue gas. It employs vandium oxide as a catalyst which oxidizes the sulfur dioxide to trioxide, followed by a gaseous phase reaction of ammonia. The end product, ammonium sulfate is removed by an electrostatic precipitator. (The details were presented at annual meetings of APCA in 1966 and 1967 as 1 and II.) Flue gas is passed through cyclone and dust filter to remove dust. Under normal operating conditions almost all of the dust is removed at the filters. The author carried out experiments to determine whether there was any effect on the activity of the catalyst, assuming that a portion of the dust escapes into the stream along the flue. It has been generally accepted that in fuel oil firing steam power plants, about 100 mg./nm3 of dust including carbon, hydrocarbon, and ash are normally contained in the flue stream. The carbon and hydrocarbon is oxidized readily at the filters and exists only as ash. An amount of ash equivalent to the amount assumed to have settled on the catalyst over a period of 3–12 months, was placed on the catalyst, and experiments were carried out. The SO2 conversion efficiency was measured and found to be over 93%. The results showed that at the actual operational temperature of 450°C, ash had practically no effect at all.