Industrial application of selective hydrogenation catalyst for catalytic gasoline

The 750kt·a-1 catalytic gasoline hydrogenation unit of petrochina Dagang Petrochemical Company adopts Axens Prime-G+ technology，it was put into production in May 2008 and successfully applied in China for the first time. The unit consists of two parts: selective hydrogenation and hydrodesulfurization. The main products are light gasoline and heavy gasoline. Under the condition of minimizing octane loss, the sulfur content in catalytic gasoline is reduced to 25x10-6 and the olefin content is less than 33%.

1.  Technical Principle

The raw material is catalytic cracking gasoline, which contains diolefin, sulfur, nitrogen and aromatics, etc. Under the condition of low temperature and pressure, under the action of selective hydrogenation catalyst (HR-845), the selective hydrogenation of diolefin to monolefin mainly occurs. Diolefin is unstable and easy to polymerize into colloid, so the conversion of diolefin to monolefin can improve the stability of the product. All thiols and some light sulfides were converted into heavy sulfides and olefins were isomerized. The selected hydrogenated products were treated with hydrodesulfurization catalyst (HR-806) to undergo hydrodesulfurization and nitrogen removal.

2.  Technical and Design Features

The prevulcanization catalysts HR-845S and HR-860S developed by Axens were selected. The main components were high purity alumina carrier, and the reactive components were nickel oxide and molybdenum oxide. The catalyst was loaded in nitrogen environment and oxygen-free loading was completed in two days.Omit catalyst vulcanization, protect equipment, save start-up time.

In order to prolong the operation cycle of the catalyst, the selective hydrogenation reactor was used to remove the diolefin and mercaptans. The hydrodesulfurization catalyst was protected from the rise of reactor pressure drop caused by the participation of diolefin in the HCN fraction. The raw oil is provided with filter and hydrogen protection facilities.The reaction product heating furnace is arranged at the outlet of the reaction product to avoid the furnace tube easy coking caused by the heating furnace in front of the reactor.The Axens process package stipulates that in order to ensure product quality, the temperature should be raised before the quantity is raised, and the quantity should be lowered before the temperature is lowered.By slowly raising the temperature first and then the dosage (up to 1℃ each time), there is no risk of flying temperature.

3.  Main problems in the start-up and operation of the device

3.1  Influence of design on fractionation and stabilization of two columns of pressurized nitrogen lines

Axens designed that the charging nitrogen line of the distillation column and stabilization column is on the feed line of the tower, and the operating pressure of the stabilization tower is 0.8MPa. When the low pressure nitrogen pressure is lower than the pressure of the stabilization tower, if the gate valve or check valve on the nitrogen charging line is not strict, gasoline will be backstrated to the nitrogen line, affecting the safe operation of the public engineering system.The quality of the valve must be ensured and the rigor of the process must be carefully verified.

3.2  Reboiler leakage in distillation column after starting-up

On June 20, 2008, it was found that the water in the gasoline exceeded the standard. As the distillation column reboiler used 3.5MPa steam as the heat source, it was judged that the steam from the reboiler in the distillation column was straded into the gasoline, making the product unqualified.The device was temporarily shut down for maintenance, and the water pressure test showed that three bundles were leaking, and they operated normally after plugging.

3.3  Decrease of catalyst activity

Since the start -up, the inlet temperature of R-101 has been increased by 11℃ and the population temperature of R-201 has been increased by 8℃, but the sulfur content of the product has been increasing. In order to ensure the quality of the product, the reaction temperature should be increased continuously according to the activity of the catalyst, so as to ensure that the product meets the requirement of the quality index of national Ⅳ, the sulfur content is lower than 50*10-6.

4.  Conclusion

The patent technology of selective hydrogenation of gasoline by Axens has been successfully applied in Dagang Petrochemical Company of China. After the installation was started, the control of various parameters is relatively stable and the product is qualified.