Desulfurization experiments

Chang and co-workers isolated strain Nocardia sp. CYKS2 from a dyeing industry wastewater using DBT as the sole sulfur source [27]. This strain also desulfurized DBT to the same product 2-HBP however, it had broader substrate specificity and was reported to desulfurize thiophenes, sulfides, and disulfides (Table 3) in addition to DBT. However, it did not desulfurize trithiane, thianthrene and 4,4 -thiodiphenol. The desulfurization experiments were conducted in batch with the rate reported as 0.279 mg-sulfur/L dispersion/h for DBT conversion. 

The desulfurization experiments were run in a batch reactor designed and constructed at the Ames Laboratory. The reaction crucible (8 in. x 3.5 in. o.d.) was constructed from Inconel tubing. A basket to hold the coal was fashioned from -20 mesh stainless steel screen. The chromel-alumel thermocouple was sheathed in stainless steel. 

Benzothiophene experiments conducted at 375°C for 30 minutes with KCl-NaOH mixtures (70 30 by wt) resulted in no decomposition or desulfurization. Experiments conducted with K2C09-Na0H mixtures (70 30 by wt) resulted in complete decomposition of benzothiophene, yielding o-thiocresol and toluene as products. Relative amounts of the two products were similar to those found in experiments that used the KOH-NaOH mixture. Experiments with the KCl-NaOH mixture were repeated at longer reaction times (1 and 3 hours). After 1 hour, very little decomposition of benzothiophene had occurred. After 3-hour reaction times, the majority of benzothiophene had decomposed to toluene (4>), o-thiocresol (26 ), and tolyldisulfide (23>). While the yield of tolyldisulfide (an oxidation product of o-thiocresol) was somewhat unexpected, the longer reaction times demonstrate that KCl-NaOH mixtures can cause benzothiophene decomposition. Again, the induction or inhibition period may account for the lack of KCl-NaOH reactivity using 30-minute reaction times. 

Another slurry pipeline desulfurization experiment was conducted using Indiana 3 (Ayrshire) coal as a 25 wt% slurry in deionized water. The other process variables were carefully controlled flow rates 6-6.5 ft/sec, temperature 70-90°F, and pH 2.5 -2 8.The experiment was continued for 14 days, and the slurry samples for pyritic sulfur determination were taken daily. The desulfurization rates with Indiana 3 coal in the pipeline experiment are shown in Table 4 and are in good agreement with the laboratory data and the results with Illinois 6 coal. As observed in the laboratory experiments, the rate of desulfurization of bituminous coals is directly proportional to the pyritic sulfur content and inversely to the particle size of the coal sample. 

A major problem in the catalytic hydrodesulfurization of residual oils is the deactivation of the catalyst by metal-containing asphaltenic species in the feed. As can be seen from the results of a typical desulfurization experiment presented in Fig. 1, the catalyst shows a rapid initial decline which is attended with a fast build-up of coke on the catalyst. At a relatively low catalyst age 0, as defined in Section IV, a stationary coke level is reached. In contrast, the deposition of the inorganic remnants of the hydro-cracked asphaltenes (mainly vanadium and nickel sulfides) continues and gradually clogs the pores in the outer zone of the catalyst particles, as confirmed by electron microprobe analyses of spent catalyst samples (see Fig. 2). This causes a slow further loss in desulfurization activity over a longer period of time. Ultimately, the catalyst becomes totally inactive for desulfurization because the - still active - inner core has become completely inaccessible to the sulfur-bearing molecules. 

There are two part experiments of this new desulfurizer, one is Mg vapor production experiment the other one is hot metal desulfurization experiment. The materials in the two experiments are the same. Dolomite and 75ferrosilicon were used. The chemical chemical composition is shown in Table 1 and 2. 

ABB, 1992A, ABB Dry Flue Gas Desulfurization Experience List for Coal-fired Boilers, ABB Fiakt, Knoxville, TN. July. 

Finally the authors tested the efficiency of the best three ILs prototypes in a multistage desulfurization experiment using a real predesulfurized diesel oil sample (without additives, sulfur content 375 ppm) at 60 °C with mass ratio oil/IL = 5/1 and 15 minutes of reaction time. Lewis acid ILs showed the best performance after four extraction step (Table 1). 

ExxonMobil extended the Hydrofining technology to produce a 200 ppm diesel, with the Diesel Oil Deep Desulfurization technology, DODD. The reactor is packed with multiple beds of different catalysts. A preceding history of commercial experience provided data to build a model for deep HDS and pave the way to a new technology, MAK Fining. 

A procedure for immobilization of a P. stutzeri UP-1 strain using sodium alginate was reported [133], This strain does not perform sulfur-specific desulfurization, but degrades DBT via the Kodama pathway. Nevertheless, the report discussed immobilization of the biocatalyst cells in alginate beads with successful biocatalyst recovery and regeneration for a period of 600 h. However, the immobilized biocatalyst did decrease in specific activity, although the extent of loss was not discussed. The biocatalyst was separated after every 100 h of treatment, washed with saline and a boric acid solution and reused in subsequent experiment. The non-immobilized cells were shown to loose activity gradually with complete loss of activity after four repeat runs of 20 hour each. The report does not mention any control runs, which leaves the question of DBT disappearance via adsorption on immobilized beads unanswered and likewise the claim of a better immobilized biocatalyst. 

Desulfurization of other diesel feedstocks from Total Raffinage was also reported by EBC. In these studies, different engineered biocatalysts were used. Two different middle distillate fractions, one containing 1850 ppm sulfur and other containing 650 ppm sulfur, were tested. R. erythropolis sp. RA-18 was used in one experiment and was reported to desulfurize the diesel from 1850 to < 1200ppm sulfur within 24 hours. On the other hand, it removed sulfur from a middle distillate with 650ppm sulfur to below 200 ppm sulfur [222], Various Pseudomonas strains were also tested in this study and reported to remove less amounts of sulfur. A favorable characteristic of the Pseudomonas strains is their inability to form stable emulsions, which can be useful trait for product recovery. 

The dsz genes in ECRD-1 are expressed at a baseline level constitutively in the presence of sulfate, although their levels are presumably higher in the absence of sulfate. Studies were conducted with and without sulfate. The Rhodococcus cells are known to use alkanes as substrates, thus an alternate carbon source was used to minimize hydrocarbon degradation. The hydrocarbon profile of the oils was demonstrated to be the same before and after the desulfurization. The experiments were aimed at identifying the extent of desulfurization of these oils and so were conducted at oil to water ratio of 1 1000. The results showed 90% or higher removal of CO to C4 DBTs in fully induced cells (without sulfate). In the presence of sulfate, the extent removal was lower. 

A novel Double Draw-Off (DDO) ciystallizer has been designed in order to improve the particle size distribution in the precipitation of CaS03 V 20 simulated Flue Gas Desulfurization (FGD) liquor. The effects of DDO ratio and residence time on the mean particle size were studied. Industrial conditions were maintained in all experiments as far as practical. Significant improvement in mean particle size was achieved. The performance of an actual industrial DDO ciystallizer (DuPont) for gypsum ciystallization was reported. 

Lenz and Aicher reported the experimental results obtained with an autothermal reformer fed with desulfurized kerosene employing a metallic monolith coated with alumina washcoat supporting precious metal catalysts (Pt and Rh) [78]. The experiments were performed at steam-to-carbon ratios S/C = 1.5-2.5 and... 

It is true that completely independent experiments may be confused by subtle effects of inhibition by H2S, which is a byproduct in desulfurization reactions, but as discussed later, the magnitude of the inhibition at the levels produced in the experiments is not large enough to result in such drastic changes in the hydrogenation rates of biphenyl. A few well-chosen experiments in which competitive test reactions are conducted simultaneously can provide definitive information that can be used in setting reasonable limits on the ratios of the important rate constants. This is illustrated later. 

Satterfield s studies indicated that, as the temperature was increased, the preference for adsorption of THs becomes larger (125), but the differences between authors is far more than can be explained by the different temperatures of their experiments. The various parameters are summarized in Table XV. The report of Froment may provide the best guidelines at present (104). That report indicates the following relative preferences for adsorption on the direct desulfurization site (cr) ... 

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