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Abstract
A series of gas-oil hydrotreating experiments were carried out under different operating conditions; reaction temperatures of 300, 325, 350, 375, 400 & 425°C, hydrogen pressures of 15, 35, 50 & 65 bar and liquid hourly space velocities of 0.5, 0.75, 1.00, 1.25 & 1.50 h-1; while H2 / feed ratio and time of products collection were kept constant at 250 L/L and 9 hours respectively.The runs were conducted in a fixed bed cata-test unit. 100 cc of
a catalyst under investigation was used and divided to three zones each is separated from another by glass beads/ glass wool. The effect of operating conditions on the hydrodesulfurization (HDS) activity of the catalyst and products quality was studied using heavy vacuum gas oil (HVGO) as a feedstock. The total weight percent of coke deposited on the catalyst was also studied in each catalyst zone inside the reactor after carrying the runs with each of the operating variables (reaction temperature, hydrogen pressure, liquid hourly space velocity). The results indicated that the effect of reaction temperature on the coke formation was higher than that of hydrogen pressure and liquid hourly space velocity.
The deactivation of a Co-Mo/ γ – alumina hydrotreating catalyst was investigated in a cata – test micro reactor unit by using heavy vacuum gas oil (HVGO) and a blend of 40: 60 % HVGO and heavy vacuum residue (HVR) as feed stocks at the following fixed operating conditions: temperature of 350°C, pressure of 50 bar, H2 / oil ratio of 250 L/L and LHSV 0.5 h-1 with different durations time ranging from 3 - 24 h. The results showed that a rapid coke build up on the catalyst surface is very fast during the first 3 hours of runs reaches as
high as 3.9 wt. % and 10.2 wt. % in case of HVGO and feed blend, respectively, then tends to level off or reaches an equilibrium value within 24 h.The DROPs in catalyst surface area were particularly high (28.57 % and 41.71 % for HVGO and feed blend, respectively) during the first 3 h of operation. Pore size distribution analysis indicated that the coke, which formed during the first hours, was deposited predominantly in the narrow pores < 50 Å of the catalyst.
The coke removal on using the burn off method was increased with TOS from 3 to 24 h for both HVGO and feed blend, while in case of THF extraction method the coke removal was decreased. The improvement of surface area after regeneration is very important to reuse the catalyst again in case of HVGO rather than the feed blend.