Desulfurization kinetics

Vestal, M.L. and Johnston, W.H., "Desulfurization Kinetics of Ten Bituminous Coals", Report No. SRIC 69-10. Baltimore Scientific Research Instruments Corp., 1969. 

Residuum desulfurization kinetics are generally not first order. Figure 5 illustrates this with a first-order plot for desulfurization of Arabian light residuum. On this type of plot a first-order reaction would yield a straight line with a slope corresponding to the reaction rate constant. The over-all desulfurization reaction is not therefore first order and can in fact be represented by second-order kinetics. However, the figure shows that it may also be considered as the sum of two competing first-order reactions. The rates of desulfurization of the oil and asphaltene fractions are reasonably well represented as first-order reactions whose... 

The proposed NSPS can be met by hydrotreating the coal liquids obtained by filtering the product from the coal dissolution stage. The desulfurization kinetics can be presented by two parallel first-order rate expression, and hydrogen consumption kinetics can be presented by a first-order rate expression. A linear relationship exists between total sulfur content and SRC sulfur content of the hydrotreated product. For the Western Kentucky bituminous 9/14 coal studied here, the maximum selectivity and lowest SRC conversion to oil for a fixed SRC sulfur content are obtained using the highest reaction temperature (435°C) and the shortest reaction time 7 min.). ... 

The objective of this process is the deep desulfurization of middistillate types of feedstocks. Exxon licensed hydrotreating units in the past, but decided that a new technology had to be developed for deep desulfurization of diesel oil. Main differences from the existing technology is the different desulfurization kinetics for deep desulfurization and the importance of a good... 

A new approach for desulfurization kinetics is proposed which is based on a discretization of the GC-AED spectrum. For LGO it was discretisized into 132 pseudo components... 

The spinning basket reactor was used to study the desulfurization kinetics of a model sulfur compound—dlbenzothlophene in white oil. This study is confirming data for an earlier study by Frye and Mosby (8) with a trickle bed type reactor and actual petroleum fractions. There is good agreement between the two kinetic studies. This current study has achieved a further... 

Confirm earlier desulfurization kinetics developed by Frye and Mosby on selected sulfur compounds using a trickle bed reactor refine their kinetic model if necessary. 

The Amoco annular spinning basket reactor system Is a useful tool for studying the fundamental kinetics of llquid-vapor-solid catalyzed reaction systems. We believe it is generally superior to trickle bed systems for the study of pure compound kinetics in liquid-vapor-solid catalyzed systems. A desulfurization kinetic study with dlbenzothlophene in white oil was successfully completed. The results of the study compare favorably with an earlier study performed in a trickle bed reactor by Frye and Mosby (8). 

Desulfurization kinetics were studied with a model sulfur compound system, a dlbenzothlophene in white oil. Tests on basket agitation rate indicate that mass transfer and contacting effects are small above 750 rpm. The reaction kinetics agreed well with earlier work. The Langmulr-Hlnshelwood kinetic model was further refined to account for con5)etitlve adsorption effects due to dlbenzothlophene as well as hydrogen sulfide. 

Effect of HjS, Carbon Oxides, Etc. Hydrogen sulfide in the treat gas has an inhibiting effect on the kinetics of hydrotreating. Being a product of the desulfurization reactions, HjS must diffuse from the catalyst surface into the bulk gas stream. Any HjS present beyond that formed, further slows down the rate of diffusion with a consequent decrease in the amount of desulfurization for a given amount of catalyst. Therefore, additional catalyst would be required. 

Although desulfurization is a process, which has been in use in the oil industry for many years, renewed research has recently been started, aimed at improving the efficiency of the process. Envii onmental pressure and legislation to further reduce Sulfur levels in the various fuels has forced process development to place an increased emphasis on hydrodesulfurization (HDS). For a clear comprehension of the process kinetics involved in HDS, a detailed analyses of all the organosulfur compounds clarifying the desulfurization chemistry is a prerequisite. The reactivities of the Sulfur-containing structures present in middle distillates decrease sharply in the sequence thiols sulfides thiophenes benzothiophenes dibenzothio-phenes (32). However, in addition, within the various families the reactivities of the Substituted species are different. 

Effects of Sulfur Coverage. The kinetic results reported in the previous section are from reactions performed on surfaces that are initially clean. The surfaces after reaction were examined by AES and shown to be covered with carbon and sulfur at coverages close to a monolayer. It is interesting to note that although this is the case even after reaction times on the order of minutes the reaction rate is constant for a period of approximately one hour. Either the reaction is occurring on top of this oarbon/sulfur layer or these species are present as sulfur containing hydrocarbon fragments that are intermediates in the desulfurization process. 

Wang P, AE Humphrey, S Krawiec (1996) Kinetic analysis of desulfurization of dibenzothiophene by Rhodo-coccus erythropolis in continuous cultures. Appl Environ Microbiol 62 3066-3068. 

A strain P. delafeildii R-8 was reported to desulfurize DBT giving 2-HBP as the end product [92], This strain was isolated from sewage pool of Shanghai oil field. The report described the effect of cell density, oil/water phase ratio, which was very similar to that of IGTS8. These parameters will be discussed in Section 2.2.10. A Michaelis-Menten model was used to describe the kinetics and the Vmax and Km were reported for DBT to be 13mmol/kg dcw/h and 1.3 mM, respectively. 

The study did model and fit all data using a kinetic model given in Eqn. (5). The experimental data was fit to obtain values of a and (3. The utility of this model is limited because it is not based on independent parameters. However, the model does show how the desulfurization activity depends on the growth rate and cell density for various experimental conditions. 

Use of a N. globerula R-9 strain was demonstrated for desulfurization of straight run diesel oils. Sulfur reduction from 1807 to 741 mg/dm3 was reported at a desulfurization rate of 5.1 mmol/Kgdcw/h. The desulfurization of model oils containing DBT and 4,6 dimethyl DBT was studied and Michaelis-Menten kinetic parameters were reported. 

Wang, P., and Krawiec, S., Kinetic analyses of desulfurization of dibenzothiophene by Rhodococcus erythropolis in batch and fed-batch cultures. Applied and Environmental Microbiology, 1996. 62(5) pp. 1670-1675. 

Kobayashi, M. Horiuchi, K. Yoshikawa, O., et al., Kinetic analysis of microbial desulfurization of model and light gas oils containing multiple alkyl dibenzothiophenes. Bioscience Biotechnology and Biochemistry, 2001. 65(2) pp. 298-304. 

Marcotrigiano, G. Peyronel, G. Battistuzzi, R. 1972. Kinetics of desulfuration of S-35-labeled thiourea in sodium hydroxide studied by chromatographic methods. /. Chem. Soc., Perkin Trans. 2 1539-1541. 

It was observed that the overall kinetics for the desulfurization could be described by lumping the rate constants for the individual sulfur species into four reactivity groups as shown in Fig. 6. These groups are listed in decreasing order of reactivity in Fig. 7. The relative contributions of the four groups were 39, 20, 26, and 15% for groups 1, 2, 3, and 4, respectively. Thus, if the new sulfur standards are to be met with this feed, groups 1, 2,... 

Fig. 7. Kinetic reactivity groups in desulfurization (360°C, 2.9 MPa). Reprinted with permission from Ref. 14, Ma et at. (1994). Copyright 1994 American Chemical Society.

The theoretical calculations described have recently been supported by an extraordinary kinetic analysis conducted by Vanrysellberghe and Froment of the HDS of dibenzothiophene (104). That work provides the enthalpies and entropies of adsorption and the equilibrium adsorption constants of H2, H2S, dibenzothiophene, biphenyl, and cyclohexylbenzene under typical HDS conditions for CoMo/A1203 catalysts. This work supports the assumption that there are two different types of catalytic sites, one for direct desulfurization (termed a ) and one for hydrogenation (termed t). Table XIV summarizes the values obtained experimentally for adsorption constants of the various reactants and products, using the Langmuir-Hinshelwood approach. As described in more detail in Section VI, this kinetic model assumes that the reactants compete for adsorption on the active site. This competitive adsorption influences the overall reaction rate in a negative way (inhibition). 

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