Study On The MTO Dewaxing Extractant

After the "Eleventh Five-Year Plan",coal-to-olefins have attracted much attention as a new coal chemical project,in which Methanol to Olefins(MTO)is the core process in coal-toolefins.In recent years,with the construction and start-up of MTO industrialized plants,the market share of PE and PP produced by MTO industrialized plants has been expanding day by day.How to ensure MTO devices keep long-term operation is becoming more attractive.The MTO process mainly includes the MTO anti-re-system and the MTO water system.The main factors affecting the long-term operation of the MTO water system are the high solid content in the quench water system and the waxing in the washing water system.Among them,the issue of MTO waxing is a common problem in current MTO industrial devices.At present,the general measure for treating MTO wax is to wash it with an extracting agent such as xylene,xylene is a low-toxic chemical,this increases the risk of device operation.This paper mainly studies MTO wax removal,and it screens out the agent which can replace xylene as MTO clear wax extractant.In this paper,the MTO wax is collected by dissolving,evaporating and purifying the MTO wax block on the industrial equipment.The composition of the MTO wax is analyzed by gas chromatography.The analysis shows that the MTO wax is mainly an aromatic hydrocarbon compound.Hexamethylbenzene is the main composition,and MTO wax has the characteristics of high melting point,high boiling point,insoluble in water and slightly higher density than water.This paper also studies the reaction mechanism of MTO wax starts from two aspects: the MTO reaction mechanism and raw materials.And it compares the conditions of oil waxing,diesel waxing and methanol waxing,and finds the same and different MTO waxes.The results show that the main factors affecting the formation amount of MTO wax are MTO reaction conditions and refining materials,while the raw material composition has little influence on the formation amount of MTO wax;The main factors affecting the production rate of MTO wax are ambient temperature,particles and flow rate;The pH value has little effect on wax production and wax rate.In this paper,the similar compatibility principle is used in the laboratory,and four kinds of chemical products such as acetate,petroleum ether,heavy aromatic hydrocarbon and solvent oil are compared with xylene to dissolve MTO wax.The new clear wax extractant(aromatic solvent oil)is similar to xylene in some aspects;Then the wax removal effect of the selected clear wax extractant under different conditions is tested in the laboratory.The experimental results show that the dissolution and extraction performance of the new wax cleaning extractant C9(aromatic solvent oil)on the MTO wax decreases with the decrease of temperature,decreases with the decrease of extraction time,and decreases with the decrease of concentration.Compared with the properties of xylene,the new clear wax extractant has better operational safety,less toxicity to operators,lower cost,and it is a good extractant that can replace xylene.This paper builds a small test device to simulate the heat exchanger in industrial equipment to investigate the wax removal effect of the newly screened MTO clear wax extractant and xylene in the small test device.The test results show that the 10 % concentration of the extractant has industrial application conditions,and it can effectively remove the MTO wax by circulating washing at 40 ?.In the industrial trial process,the new clear wax extractant can effectively remove the wax in the heat exchanger tube bundle,it can improve the heat exchange efficiency of the heat exchanger,and effectively wash the wax in the washing tower tray and reduce the pressure difference of the washing tower.The external drainage meet the requirements of the subsequent water treatment system.