No abstract

The occurrence of flooding phenomena (FP) on the vacuum distillation trays column (VDTC) is investigated on a refinery in the middle region of Iran. Accumulation of coke sediment that is occasionally observed in refinery processing using coal tar (CT) feeding is the main reason of the FP on VDTC. This usually occurs at the down-comer areas and the seal pans of the column. Quinolone insoluble (QI) and toluene insoluble (TI) parameters, two routine methods used to measure coke containing sediments, are employed to determine probable critical areas of FP at the down-comers and the seal pans of CT feed in this study. Analyzing the obtained results of QI and TI tests demonstrated that FP at the column is directly related to the quality of CT feeding. For instance, when the QI of the inlet CT in battery 1 increases from 0.56%W in the first sample to 6.5%W in the 25th sample, the vacuum pressure at the top of the distillation column is reduced from − 230 mbar to − 420 mbar. To prevent sediment accumulation of coke and the occurrence of FP, the CT feeds are centrifuged to reduce coke sedimentation at the down-comer areas and the seal pans of VDTC. Moreover, the seal pan trays are replaced by normal ones and all moveable valves with 25 mm diameter on trays 15 and higher in the column, where coke sediment accumulation is observed the most, are modified by installing wider fixed valve (40 mm diameter) trays.

In this work, various ternary cerium oxide/lanthanum oxide/cobalt oxide (Ce/La/Co) nanocatalysts were synthesized by co-precipitation method based on response surface methodology (RSM). The optimum predicted surface area was found to be 67.6 m 2 g −1 at calcination temperature of 650℃, La content of 10.0 wt%, and Co content of 8.0 wt%. Average crystal size of optimum ternary Ce/La/Co catalyst was estimated 11.4 nm. The confirmation tests revealed that experimental data can be predicted well by the model. Furthermore, the prepared catalysts were evaluated by Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX) and NH3 temperature programmed desorption (NH3-TPD) analyses. The characterization results confirmed that ternary Ce/La/Co catalysts were successfully synthesized. Also, the NH3-TPD result showed that total active sites of optimum ternary Ce/La(10)/Co(8) catalyst with La content of 10.0 wt% and Co content of 8.0 wt% was greater than that of single cerium oxide catalyst. The optimum synthesized catalyst was tested for SO2 reaction by methane to sulfur. SO2 conversion and selectivity of catalysts at various temperatures were determined. The better performance of Ce/La/Co optimum catalyst at different temperatures was obtained for SO2 reduction. Also the selectivity of the optimum catalyst for production of sulfur is better than other catalysts.