Desulphurization rate

Initial rates and product distributions in thiophen hds and in reaction of possible intermediates over sulphided M0/AI2O3 and C0-M0/AI2O3 catalysts (521 K, < 1 atm) were also consistent with reaction via tetrahydro-thiophen according to Scheme 4 butane-1-thiol was not an intermediate. Relative initial rates were (i), 1 (ii), 5-10 (v), to butenes 20, and then to butane 0.1. Co promoted the desulphurization rate and, to a lesser extent, the olefin hydrogenation rate. Desulphurization [C-S scission, step (zY)] occurred on a site involving Co and Mo and hydrogenation on a Mo site. 

The hds of thiophen, benzothiophen, and dibenzothiophen and their methyl-substituted derivatives were compared in pulse experiments (623-723 K) over a sulphided CoO(5.6)-Mo03(11.2)/Al203 catalyst. Reactivities at 1 atm pressure were roughly the same but at hi er pressures, reactivity decreased with the number of rings. For benzothiophen, methyl substituents did not affect the reactivities, but for dibenzothiophen methyl substituents in the 4- or 4 - and 6- positions caused a decrease of desulphurization rate. Aromatic ring hydrogenation was not a prerequisite of C-S scission, which was the slow step. 

The feed desulphurization rate of reaction (1) is determined by the following relation ... 

Since the lead smelter owned by OAO Kazzinc has ten years of experience in smelting lead-zinc sulphide concentrates by the Kivcet technology, a method of comparing physical and chemical properties of the bulk concentrate to the characteristics of typical lead-zinc raw materials has been developed. This method was used to decide on the feed composition and process operating conditions. Two major features of the bulk concentrate that affect the results of the smelting in the Kivcet unit were examined the calorific value and the desulphurization rate. 

Once the charge was made up to generate the calorific value desired, the opportunity was taken to compare the desulphurization rate of the charge to that of the lead-zinc concentrate charge. As expected, the duration of the desulphurization ]5rocess turned out to be nearly the same. If half of the lead-copper-zinc concentrate is substituted for lead sulphate middlings (for example, lead residue or lead dust), the desulphurization rate noticeably increases. This can be explained by the fact that the rate of the exchange reactions between sulphides and sulphates. 

The influence of the desulphurization degree on the recovery of copper to matte and the matte composition was investigated. As one might expect, a too high desulphurization rate caused the enhanced solubility of copper in lead, and the copper recovery to matte decreased. The best results were realized for a desulphurization rate within the range of 80-83%. The proportion of copper passed to matte ranged from 87 to 94%. 

Tetrahydrothiophen was also detected during thiophen hds over a commercial C0-M0/AI2O3 catalyst (523-586 K, 1 atm). The rate of disappearance of tetrahydrothiophen was twice that of thiophen, but the rate of butene formation from each compound was about the same. Therefore, the greater rate of disappearance of tetrahydrothiophen was attributed to dehydrogenation to thiophen [reverse step (/)] rather than to more facile desulphurization. 

Scheme 6 Dibenzothiophen desulphurization over a sulphided Co-MolAl O catalyst (57 K, 7( 2atm) ref. 198). Reaction network including pseudo-first-order rate constants as log (k/[m (kg catalyst)" s" ] ...

Radial flow fixed bed reactors were developed to handle large gas flow rates with minimum pressure drop and are most suitable for processes in which fluids need to be contacted with solid particles at high space velocity (Chang and Calo, 1981). Radial flow fixed bed reactors are used for a variety of processes including catalytic synthesis of ammonia, xylene isomerization and desulphurization. 

Of the several applications of the desulphurization of disulphides, that of alkyl allyl disulphides seems particularly interesting. From the evidence cited it would seem that these disulphides readily rearrange to thiosulphoxides (26) which are desulphurized by the phosphine. The rate enhancement caused by increasing the size of the substituents R and R ... 

The partial desulphurization occurred successfully in the presence of many common functional groups, and was accelerated in polar solvents the rate-controlling step was probably the nucleophilic cleavage of the sulphur-sulphur bond. In accord with these mechanistic conclusions, desulphurization of (132) did not give the thietan derivative (133) but gave (134),... 

Basket centrifuges with plough discharge often have a hydraulic, variable speed drive, are of three-point support or overdriven construction (e.g. Broad-bent or Mirlees) and their diameters vary from 260 to 1500 mm (filtration areas from 0.13 to 2.9 m ). Applications of all types of basket centrifuges include separation of crystals (such as sugar where throughput rates up to 36 t/h have been reported ), nitro-cellulose, metal swarf or enamel frit, and lately also gypsum from gas desulphurization processes at coal-fired power stations. ... 

Whilst the rate of this reaction appears faster with B-type sulphides than for the A-type, the extent of reaction with the B-type is less since these desulphurate far more rapidly than the A-type so that there is little of such B-type material available for the thermal decomposition reaction. It is to be noted that not only does the reaction cleave a cross-link but also that conjugated dienes are produced. 

Show graphically that silicon does not affect the first-order kinetics of desulphurization and calculate the rate constant in both cases. 

Ruan Jianbo, and Zhang Fengshan. Factors Influencing the Rate of Hot Metal Desulphurization with Granulated Magnesium, Wuhan University (Natural Science), 27(3)(2004), 48-60. 

---