Abstract: By using a fixed fluidized bed device, the effect of weight hourly space velocity (WHSV), catalyst aging time and Ni content of catalyst on the coke constitution of spent catalyst under simulating DCC (deep catalytic cracking) process conditions was investigated. Test results show that under constant reaction temperature and catalyst to oil (cat/oil) ratio the coke content on spent catalyst decreases with the increase of WHSV till finally reached a minimum value (minimum coke), which is the sum of additional coke and stripping coke under this reaction temperature. The amount of additional coke is related with the carbon residue of the feedstock, about 86.7% of which was converted to coke under a reaction temperature of 565 ℃. With the increase of catalyst aging time, the specific surface area of the catalyst decreases, as well as the sum amount of additional coke and stripping coke. The yield of stripping coke has a quadratic function with the specific surface area of catalyst. Under constant WHSV, the coke content of spent catalyst increases with the increase of Ni content on catalyst, and the effect of Ni content is more significant under low WHSV. Under the conditions of a reaction temperature of 565 ℃, cat/oil mass ratio of 8 and WHSV of 4 h-1, the amount of stripping coke occupied 42.64% of the total coke on spent catalyst, which is more than 30 percentage points higher than that in the reference.

Key words: weight hourly space velocity, specific surface area, additional coke, catalyst-to-oil mass ratio, stripping coke