Hydrotreating

Question 1

Basic Process

Answer 1

SO the feed is preheated and the mixed with the hydrogen feed. The mixture is then introduced to the top of the reactor containing metal oxide catalysts. In the reactor, desulphurisation, denitrogenation, metal deposition and oxygen removal all take place. The metals are deposited on the catalysts while the products from hydro treating like ammonia and h2s leave with the exit stream. The exit stream is then cooled and further cooled and then passes though a separator to separate the hydrogen gas from the mixture. The light gases also leave with the hydrogen stream. The liquid outlet stream then goes to a stripping column where H2S is stripped from the mixture hence giving a desulphurised oil product.
Catalysts used are nickel or cobalt mixed with molybdenum. The main one is cobalt and molybedum sulphide on alumina catalysts. If the removal of nitrogen is important, then nickel and molybdenum sulphide is used.
Can use tungsten instead of molybdenum but it is more expensive but can use a mixture of both tungsten and molybdenum

Question 2

Effect of process variables

Answer 2

• Increasing temperature increases rate of S and N removal but if increased too much we can shift the equilibrium. Also, if excessive temps are present we can get carrying hence causing more coke formation
• Increasing space velocity means that there is less contact time hence conversion is lover along with coking and h2 reaction
• Increasing hydrogen concentration increases hydrogen saturation and hence S and N removal
• Increasing partial pressure increases H2 formation and reduces coking