Hydrodesulphurization Activity Research Articles

Hydrodesulphurization activity and coking propensity of carbon and alumina supported catalysts

Co—Mo, Fe and Mo catalysts were prepared on alumina and carbon supports. The reactivity of sulphided catalysts for thiophene hydrodesulphurization and the propensity for coke deposition of nonsulphided catalysts during propylene cracking and anthracene carbonization were measured. The hydrodesulphurization activity of Co—Mo and Fe catalysts increased in the order γ- Al 2 O 3 < C-black composite < active carbon. For a given metal, considerable differences in activity were found both between the carbons and alumina and between the carbons themselves. Possible reasons for the different activities include the influence of the supports on metal dispersion and the presence of impurities in the carbons. For alumina supported catalysts there is a correspondence between hydrodesulphurization activity and coking propensity. On carbon supported catalysts, the rates of carbon deposition appear insensitive to the nature of the metal component(s) whereas hydrodesulphurization activity is not. Thus it is possible to enhance the latter without attendant increases in the susceptibility to coke-forming reactions. Increasing Mo loading from 0–12 wt% was found to substantially increase the rate of carbon deposition on alumina, whereas the effect on a carbon support was comparatively small. This behaviour appears to relate to the inherent support acidity and its modification on metal addition.

Influence of the preparation conditions on the surface properties of HDS catalysts

This work presents results on the nature of the precursor structures of active CoMo/Al 2O 3 catalysts. Catalysts with the same chemical composition prepared by different procedures and calcined at two temperatures are studied. The catalysts are characterized by gravimetrically determined reducibility in H 2, oxygen chemisorption at low temperature (LTOC), diffuse reflectance spectroscopy, infrared spectroscopy using NO as probe molecule, and thiophene hydrodesulphurization (HDS) activity measurements. The presence of ammonia and a low concentration of molybdate ions in the solution (with longer time of impregnation) favour molybdena dispersion. By using beads of alumina, molybdena profiles appeared, and they markedly depend on the subsequent incorporation of the promoter in aqueous media. Upon increasing the calcination temperature, from 670 K to 820 K, no significant variations in the HDS activity were observed, however an increase in the concentration of the tetrahedrally coordinated Co 2+ ions at the interface (with a decrease of the amount of octahedrally coordinated Co which chemisorbs NO) was found. All results indicate that the optimization of the oxidic surface species (dispersion degree of molybdena and interacting Co-Mo phase) in these hydrodesulphurization catalysts may be achieved by varying preparation conditions, i.e. low concentration of Mo with long time of impregnation or presence of ammonia in solution.

Catalytic activity of mineral matter from western Kentucky coals for hydro-desulphurization and hydrodenitrogenation

A pulse reactor was used to study the catalytic activity and selectivity of mineral matter from Kentucky No.9 and No.11 seam coals and a low calorific value gasifier ash in the hydrodesulphurization (HDS) of thiophene and hydrodenitrogenation (HDN) of pyrrole, pyrrolidene and n-butylamine. Mineral matter in its least altered state was obtained by low temperature ashing. Thiophene conversion correlated well with the iron and zirconium contents ( R > 0.95) of the catalysts, and at 450 °C all catalysts including a commercial Fe 2O 3/AI 2O 3 gave similar distributions of the butenes and <5% butane. Reactivities of N-compounds catalysed by mineral matter from Kentucky Nos.9 and 11 coals were in the order: n-butylamine > pyrrolidine > pyrrole ≈0. Nickel was found to be the important element n-butylamine conversion and 1-butene was the predominant product species for all the catalysts. Mineral acid treatment of the mineral matter from No.11 coal decreased its HDN activity but increased its HDS activity. Results of this study indicate that hydrogen consumption for removal of sulphur and nitrogen can be reduced by using dehydrogenation-type catalysts.

Correlation of catalytic activity with the amount of sulphhydryl groups in molybdenum hydrodesulphurization catalysts

The adsorption of silver ions from a pyridine solution of silver nitrate onto nine commercial sulphided hydrodesulphurization catalysts was studied. The amount of sulphhydryl groups SH was determined on the basis of the amount of protons liberated in this reaction. The reaction of catalysts with silver ions was compared with their activity in thiophene hydrodesulphurization under pressure. A dependence was found between the amount of silver ions adsorbed and the rate constant of thiophene hydrodesulphurization. For cobalt-molybdenum catalysts, a relationship exists between this constant and the amount of sulphhydryl groups. It was ascertained that the catalysts which are most active in the thiophene desulphurization probably contain, in sulphided state, a part of cobalt (nickel) in the form of sulphides.

Effect of the pretreatment conditions on the activity of an industrial Co-Mo/Al2O3 catalyst

The processes of reduction and sulphidation of an industrial Co-Mo/Al2O3 catalyst have been studied by means of gravimetric and kinetic methods at atmospheric pressure. The effect of the pretreatment temperature on the catalytic activity for ethylene hydrogenation and thiophene hydrodesulphurization has been studied. Two types of active centres, for hydrogenation and for hydrodesulphurization, have been characterized on the basis of their different properties.

A study of relationships between pore size distribution, hydrogen chemisorption, and activity of hydrodesulphurisation catalysts

A series of commercial catalysts was tested for hydrodesulphurisation (HDS) activity using an atmospheric gas oil. The pore volume distribution in the radius range 10–300 Å and the hydrogen uptake at 350 °C were measured for each catalyst. A correlation was found between relative HDS activity and the pore volume contained in the radius range 37.5–55 Å. The hydrogen uptake was also found to correlate with the same pore volume. The significance of the correlation between hydrogen uptake, a chemical property, and pore volume distribution, a physical property, is discussed.

Importance de la sulfuration dans l'apparition de l'effet promoteur du cobalt des catalyseurs d'hydrodésulfuration Mo-Co-Al 2O 3

The effect of cobalt on the hydrodesulphurization (HDS) activities of alumina-supported Co-Mo catalysts in reduced and reduced-sulphided forms was investigated using various [Co]/([Co] + [Mo]) ratios. In the reduced form, cobalt has an inhibitory influence on the HDS activity and the synergetic effect of cobalt appears only in the sulphided form. Experiments with Mo-A1 2O 3 samples mechanically mixed with Co-Al 3O 3 show similar effects of cobalt on the activity as a result of the sulphuration. However, the HDS yields are much lower. The results appear to support simultaneously the synergy by contact model and the intercalation model that contribute together to the HDS activity. Their relative importance must depend on experimental conditions and mainly on catalyst preparation mode.

Dispersion of molybdena and hydrodesulphurization activity of Mo/γ-Al 2O 3, AND Co (or Ni) Mo/γ-Al 2O 3 catalysts

Oxygen chemisorption and catalytic activity for hydrodesulphurization of gas-oil on a series of Mo/γ-Al 2O 3 and Co (or Ni) Mo/γ-Al 2O 3, oxide catalysts were studied. A linear relationship between molybdena loading, up to about 15 wt % MoO 3, and equivalent molybdena area suggests a high molybdenum dispersion on the alumina surface. Similar behaviour for hydrodesulphurization activity versus equivalent molybdena area was observed, except for the highest molybdena content where a slightly higher activity was found. The equivalent molybdena area in Co (or Ni) promoted molybdena catalysts was slightly smaller than that found in non-promoted molybdena catalysts. However, catalytic activity for hydrodesulphurization was much higher in Co (or Ni) promoted catalysts. These results indicate clearly that Co (or Ni) in Mo containing catalysts does not increase molybdenum dispersion.

Defect structure of Co-Mo sulphide catalyst and hydrodesulphurisation activity

Defect structure of Co-Mo sulphide catalyst and hydrodesulphurisation activity

Cobalt- and nickel-molybdenum catalysts: Their properties and applications for hydrodesulphurisation

Sulphur compounds in crude oil cuts can be divided into those which are easy and those which are difficult to desulphurise owing to steric effects. When the degree of desulphurisation is plotted against the reciprocal volume hourly space velocity we obtain a curve which may be regarded as being composed of several straight lines with different gradients. Their slopes correspond to the different rates with which the two groups of sulphur compounds are removed. For technical catalyst tests, such conversion-throughput graphs are used to determine the activities (by volume or by weight) of different catalysts. The industrial manufacture of hydrodesulphurisation catalysts can be divided into the following steps: preparation of the carrier, addition of the active compounds, calcination and sulphiding. Each step influences the activity. The usual starting material for the carrier is gelatinous boehmite which is converted to γ-Al 2O 3 by heat treatment. η-Al 2O 3 is less suitable as a carrier. The chemical and physical properties of the carrier are important in determining the way in which the metal oxides are incorporated and hence the chemical activity. The pore size distribution also has to be adjusted to the particular hydrodesulphurisation problem. A precise prediction of the most favourable Co(Ni):Mo ratio is not possible. The ratio depends mainly on the properties of the carrier and the way in which the metal oxides are added. The most active catalysts are those prepared by impregnation of alumina with solutions of molybdate and cobalt (or nickel) salts. The influence of promoters has been investigated but efficient promoters for the Co-Mo catalyst have not been found. The activity of the Ni-Mo catalyst can, however, be increased by phosphoric acid. The oxide catalyst is activated by pre-heating in an atmosphere of hydrogen and hydrogen sulphide. The sulphiding must be started at low temperatures (about 250 °C) in order to avoid reduction of the oxides before conversion to the sulphides or more likely to oxysulphides. A partial reduction to the metals before sulphiding results in a considerable loss of activity. Compared with Co-Mo catalysts, Ni-Mo catalysts possess. at a given level of hydrodesulphurisation activity, a higher activity for the reduction of nitrogen compounds and the hydrogenation of unsaturated compounds; they are preferred for hydrogenation of aromatics and removal of nitrogen.