Q&A on Methanol Distillation

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1. What are the physical and chemical properties of methanol? Answer: Methanol is a colorless, flammable liquid that evaporates very easily; it has a slight alcohol-like odor and is readily miscible with water and most organic solvents. 2. What are the job responsibilities for this position? Answer: The crude methanol from the methanol synthesis section is fed into an ether removal tower, where it is heated by steam. Through the principle of distillation, the low-boiling hydrocarbons and some insoluble gases in the crude methanol are removed. It is then sent to a pressure tower for further distillation, also using steam for heating; the methanol vapor coming out of the top of this tower serves as a heat source for the atmospheric pressure tower. By applying the principle of distillation, high-purity methanol that meets **the specified standards is obtained from the reflux streams in each tower. 3. What is the purpose of distillation? Answer: It is to obtain high-purity methanol by using distillation and extraction processes to purify it and remove all impurities, thereby getting refined methanol that meets **the standards. 4. What is the function of the ether removal reflux tank? Answer: Allow the condensate from the dewaxing tower to stay in the tank for ten minutes; at the same time, add water from the dewaxing tower directly into the collection tank, thereby diluting the condensate there. The hydrocarbons dissolved in the concentrated methanol are extracted in this process and remain suspended on the surface of the liquid, after which the methanol oil is periodically removed from the top. 5. What is the function of a reboiler? Answer: The liquid at the bottom of the heating tower is heated to boil and vaporize, thereby continuously supplying steam. 6. What role does reflux play in the distillation process? Answer: Adding volatile components to the tray helps maintain stability of the liquid components on the tray. 7. What is extractive distillation? Answer: Extractive distillation is a process in which useful substances are extracted from an aqueous solution using a solvent; due to the presence of azeotropes during the distillation process, water is used to raise the boiling point of methanol, thereby separating out its impurities with lower boiling points. 8. What is distillation? Answer: Distillation is the process of achieving complete separation of a mixture by repeatedly allowing it to partially vaporize and partially condense. 9. Why is it necessary to drain condensate from the steam pipe while driving? Answer: After the system is shut down, some condensate water accumulates in the steam pipes. If this condensate is not removed before restarting the system, steam entering the pipes will collide with the condensate water inside, causing fluid shock that can damage the pipes and valves. 10. How are the distillation section and the stripping section defined? What is its function? Answer: The section above the feed inlet is the distillation section, while the section below the feed inlet is the stripping section. The function of the distillation section is to gradually increase the concentration of the volatile components in the gas phase from bottom to top, that is, to concentrate the light components. The function of the stripping section is to gradually increase the concentration of the less volatile components, that is, the concentrated heavy components, in the liquid phase from top to bottom. 11. What is the reflux ratio? How is its optimal reflux ratio determined? Answer: The reflux ratio refers to the ratio of the liquid flow rate back to the distillation section to the amount of liquid taken out. The optimal reflux rate during operation is adjusted based on the system’s feed rate at that time, the bottom temperature of the tower, and the quality of the product, in order to achieve a reflux ratio that is both economical and ensures product quality. 12. What is the main component of the overhead distillate from the ether removal tower? Answer: The main components of the overhead distillate from the ether removal tower are dimethyl ether, formaldehyde, methylamines, acetaldehyde, etc. 13. Describe in words the process flow diagram of this section. (With temperature control) 14. Draw the flow diagram of the pressure tower. 15. Write down at least two reaction molecular formulas for methanol. 16. Why is water added to the ether removal tower? Answer: This is because some of the impurities in methanol form an azeotrope with methanol, and this azeotrope is difficult to separate. Water, on the other hand, can dissolve in methanol in any proportion; by adding water, the boiling point of methanol increases, allowing the impurities in the azeotrope to be separated. Therefore, water needs to be added to the deethanizer, with the addition rate being around 20 percent of the feed amount. 17. What phenomena occur if the liquid level in the ether removal tower is too high or too low? Answer: An excessively high liquid level in the ether removal tower can cause liquid phase circulation, resulting in a decrease in the reflux flow ； The liquid level should also not be too low, in order to prevent the gas removed from the ether removal tower from entering the main tower at the bottom of it; meanwhile, it is necessary to ensure that the methanol from which light fractions have been removed stays in the bottom of the ether removal tower for a sufficient amount of time. 18. What are the reasons for high pressure at the bottom of the tower? How to handle it? Answer: In production, a high pressure at the bottom of the tower is generally caused by factors such as a high liquid level inside the tower, a sudden increase in steam volume, and a low throughput. Solution: If the liquid level is high but the bottom temperature of the tower is normal, the discharge rate should be increased ； If the increased steam has an adverse effect, reduce the amount of steam ； If the yield is low, it should be increased. 19. What is the impact of high or low temperatures in the atmospheric pressure tower on product quality? Answer: In a column operating at normal pressure, the high temperature at the bottom of the column allows heavier distillates to rise upward. When isobutyl oil is extracted, methanol can be carried along with it, which affects the yield of methanol as well as its oxidizing properties. If the temperature is too low, methanol may be included in the residual liquid discharged, resulting in reduced yields and increased waste and material consumption. 20. What are the hazards of an increase in the liquid level in an atmospheric pressure tower? How to handle it? Answer: The hazard of an increased liquid level at the bottom of the tower is that it causes liquid phase circulation and a decrease in the reflux flow rate. The solution is to increase steam supply, reduce the production load, and increase the discharge of residual liquid. 21. How should a fire in a vent pipe be handled? Answer: In such a situation, the steam valve on the venting system should be opened promptly to use low-pressure steam to displace and dilute the flammable gases, thereby smothering the fire. However, the plant must not be shut down, as doing so could create negative pressure inside the tower, allowing embers to enter the tower and causing serious consequences. If steam cannot be supplied, it is sufficient to continue operating normally without stopping the machine; the flame will extinguish on its own. 22. How does flooding occur? How should it be handled? Answer: It is because the rising steam inside the tower prevents the liquid from reaching the next tray, disrupting the normal operation of the tower. If temperatures at various instruments are inconsistent and the pressure inside the tower increases, it indicates flooding. The solution is to reduce the steam supply and lower the feed rate to the system; if flooding occurs severely, feeding and extraction should be stopped, and operations can resume only after the pressure at the bottom of the tower decreases and flooding is resolved. 23. How does tower flooding occur? How should it be handled? Answer: It is caused by an excessive amount of feed and a low amount of product being extracted, which leads to an increase in the liquid level inside the tower. The rising pressure within the tower prevents mass and heat transfer between the gas and liquid phases. The solution is to increase the steam supply, reduce the feed rate to the system and increase the extraction rate; in severe cases, stop both feeding and extraction, and restart the operation only after the pressure at the bottom of the tower has decreased and the phenomenon of tower flooding has been resolved. 24. How does leakage occur? How should it be handled? Answer: One reason is that the temperature at the bottom of the tower is too low, preventing the rising gas from holding back the falling liquid; the other reason is caused by the tilting or falling off of the tray plates. The solution is to increase the steam supply and shut down the tower for plate maintenance. 25. How do high and low temperatures at the top of an atmospheric distillation column occur? How should it be adjusted? Answer: A high tower top temperature is generally caused by a sudden increase in steam volume, too rapid heating, excessive processing capacity, or a fast rise in heavy distillates. Solution: The amount of steam should be reduced; production can be suspended or decreased to allow heavier fractions to move downward, thereby ensuring the quality of the pure alcohol ； If the temperature inside the tower is generally high and steam addition is normal, it indicates that the alcohol content in the tower is too low; therefore, the feed amount should be increased while reducing the amount taken out. The low tower top temperature is caused by a sudden reduction in steam addition, an increase in reflux due to excessive feed and withdrawal, as well as the overflow of the condenser. Solution: Increase steam supply, boost production volume, reduce feed input, and lower the reflux rate. 26. What causes turbidity in the water solubility of pure methanol? How should it be handled? Answer: There are mainly three reasons: first, too little extraction water is added, resulting in poor extraction ； Second, the vent pressure of the deetherification tower condenser is low ； Third, the removal of fusel oil from the atmospheric tower is not timely, causing the heavy fractions to rise. Treatment method: Add an appropriate amount of extraction water to ensure effective extraction ； Increase the vent temperature of the condenser ； Control the temperature of the sensitivity plate and discharge fusel oils in a timely manner. 27. What is the reason for no liquid level at the bottom of the ether removal tower? How should it be handled? Answer: There are four reasons: (1) low feed volume, (2) high extraction volume, (3) high steam volume, (4) faulty level indication. Treatment methods: (1) Increase the feed volume; (2) Reduce the output volume; (3) Decrease the steam supply; (4) Inspect the level gauge. 28. What is the reason why the bottom temperature of the atmospheric pressure rectifying tower is below 100 degrees? How should it be handled? Answer: There are three reasons: (1) low steam volume, (2) low recovery rate of pure methanol with high feed volume, (3) low recovery rate of isobutyl oil. Treatment methods: (1) Increase steam volume; (2) Increase the amount of product extracted while reducing the feed amount; (3) Increase the amount of isobutyl oil extracted. 29. Why must low-boiling impurities be removed in the ether removal tower? Answer: Since the top of a atmospheric distillation column almost condenses all of the vapor and lacks the ability to remove low-boiling-point impurities, the efficiency of the degassing column often affects the performance of the main column. If the degassing column fails to remove all low-boiling-point impurities before they reach the main column, an accumulation of such impurities will eventually show up in the final methanol product. Therefore, it is necessary to remove low-boiling-point impurities in the degassing column. 30. What precautions should be taken while driving? Answer: (1) The steam condensate must be completely drained to prevent liquid slugging. (2) Maintain all liquid levels within the specified range. (3) The temperature rise in each tower should not be too rapid. (4) Control the upper limit of the ambient temperature for the condenser in the ether removal tower. (5) To ensure effective removal, the startup time of the ether removal tower should be appropriately extended. 31. How to maintain the operating equipment in this work section? Answer: (1) Strengthen inspection efforts and sense of responsibility; (2) Replace lubricant in a timely manner; (3) Keep the machine clean; (4) Ensure that the equipment operates without defects; (5) Provide enhanced maintenance for the equipment in use; (6) Rotate the shaft of the equipment before starting it up. 32. If both materials and heat are in balance, is the operation of the entire system then in balance? Why? Answer: In distillation, the operation only maintains the balance of materials and heat; the entire system is not in equilibrium. This is because material balance involves the balance between the feed rate and the withdrawal rate. If the feed rate remains constant while the alcohol content in it decreases, and the withdrawal rate stays the same, it will inevitably lead to a decrease in the alcohol content of the liquid on each tray within the tower. Over time, this will result in an empty space inside the tower, meaning that the quality balance is not properly controlled. In operations, the balance of quality is more important than the balance of quantity. 33. What are the hazardous properties of methanol? Answer: Methanol is a neurotoxin with significant effects, particularly causing severe damage to the optic nerve. Ingesting 5-10 mL of methanol can cause severe poisoning, and amounts over 10 mL pose a risk of blindness. Ingesting more than 30 mL can be fatal. The maximum allowable concentration of its vapor in the air is 0.05 mg/L. 34. What are the initial boiling point and dry point? Answer: The initial boiling point refers to the temperature at which, during the distillation process, the gas formed by the evaporation of the liquid condenses back into a liquid phase. The dry point refers to the final temperature at which, during the distillation process, the vapor phase formed by the evaporation of the liquid condenses back into a liquid state at the boiling point, and can no longer evaporate. 35. What is the distillation volume? 36. What is the purpose of conducting a water test run in the distillation section? Answer: The water test run in the distillation section is carried out to clean the equipment and pipelines, detect leaks, and familiarize oneself with the operations. 37. What causes the excessive acid value in pure methanol? Answer: The excessive acid value is mainly due to the light components in crude methanol not being completely removed in the ether removal tower, which then end up in the main distillation tower. Secondly, it is also related to the untimely discharge of fusel oil in the atmospheric pressure tower and the low vent temperature of the condenser. 38. What are the reasons for the unsatisfactory initial boiling point, dry point, and distillation volume of pure methanol? Answer: The reasons are as follows: (1) low reflux ratio, (2) high density of the reflux liquid, (3) leakage in the main column condenser, (4) leakage in the purified methanol cooler, (5) high recovery temperature. 39. What is the relationship between excessive moisture content in pure methanol and operating procedures? Answer: (1) Excessive emphasis on prognosis; (2) High top temperature of the tower; (3) Poor condensation performance of the condenser, resulting in a high temperature of the reflux liquid; (4) Low reflux ratio. 40. What aspects should be considered to increase the recovery rate of pure methanol? Answer: The temperatures of each reflux tank are controlled at their lower limits, while the temperature at the bottom of the atmospheric pressure tower is kept at its upper limit to prevent alcohols from remaining in the residue; the appropriate reflux ratios for each tower are also carefully controlled. 41. What is the temperature control in the stripping section of an atmospheric distillation column and what are the benefits? Answer: (1) The temperature in the stripping section changes sensitively, allowing for precise control. (2) It is possible to detect the trends in the material conditions in advance and make adjustments accordingly. 42. List the causes of abnormal phenomena in the dewaxing tower and the methods for dealing with them (Not less than 5 types) Answer: (1) Tower flooding: excessive feed volume, low steam volume, low output volume ； Reduce the feed amount, increase the steam volume, and raise the extraction rate. (2) Difficulty in feeding: high steam volume causes gas blockage in the preheater ； Reduce the steam volume and discharge the steam from the preheater. (3) No liquid level at the bottom of the tower: low feed rate, high extraction rate, high steam volume, and malfunctioning level indicator ； Increase the feed volume, reduce the output volume, reduce the steam volume, and service the level gauge. (4) High or low prognosis weight: Reduce or increase the amount of soft water. (5) High condenser vent temperature: high steam volume, unstable liquid level at the bottom of the tower, poor performance of the condenser, low circulation water volume or high temperature ； Reduce steam volume, stabilize liquid level, clear the condenser, increase water flow or lower temperature. 43. What is the significance of controlling the temperature at various points in the deetherification tower? Answer: Controlling the temperature at various points within the tower is necessary in order to regulate the vent temperature of the condenser, as the condensation temperature serves as a critical factor; light components can only be removed in the ether removal tower. Poor temperature control can directly result in inferior quality of purified methanol. 44. List the causes of abnormal phenomena in atmospheric distillation columns and their treatment methods. (Not less than 5 types) Answer: (1) Tower flooding: large feed volume, low steam volume, low output volume ； Reduce the feed amount, increase the steam volume, and increase the extraction rate. (2) Foaming: high steam volume, low extraction rate, high reflux rate, and high feed amount ； Reduce steam volume, increase the amount of product extracted, reduce the reflux volume, decrease the feed amount; in severe cases, shut down the system (3) If the temperature at the bottom of the tower is below 100 degrees: low steam volume, low amount of pure methanol extracted, low amount of isobutyl oil extracted ； Increase steam volume, increase the amount of purified methanol extracted, and increase the amount of isobutyl oil extracted. (4) The distillation yield of pure alcohol is unsatisfactory: low reflux ratio, high density of the reflux liquid, cooler leaks, and high extraction temperature ； Increase the reflux rate, service the condenser, service the cooler, and reduce the recovery volume. (5) Poor oxidizing property of the pure alcohol: low reflux ratio, high recovery temperature, and low recovery amount of isobutyl oil ； Increase flow rate, reduce production volume, and increase the production of isobutyl oil. 45. List the causes of abnormal phenomena in pressure distillation columns and their treatment methods. (Not less than 5 types) Answer: (1) Low bottom temperature: Reboiler leakage, low vapor volume, low specific gravity of the liquid ； Overhaul the reboiler, increase the steam volume, and raise the proportion of the product phase (2) No liquid level at the bottom of the tower: low feed volume, high steam volume, faulty level gauge ； Increase the feed volume, reduce the steam volume, repair the level gauge. (3) Low pressure at the top of the tower: low alcohol content, low steam volume, low reflux volume ； Increase the feed amount, increase the steam volume, increase the return flow rate. (4) Excessive moisture in the refined alcohol: low return flow rate, cooler leakage ； Increase the reflux flow rate; inspect the cooler (5) – the value of the glycidic acid content is above the specified limit: the discharge temperature of the pre-tower condenser is low, and the specific gravity after treatment is low ； Increase the vent temperature and raise the proportion of prognosis. 46. List the specifications for the dewaxing tower, pressure tower, and atmospheric pressure tower. Answer: Deethanizer diameter Ф1000*19239, pressurized tower diameter Ф1000*27380, atmospheric pressure tower diameter Ф1400*31835. 47. What are the characteristics of triple-column distillation? Answer: (1) Save steam, (2) improve the quality of methanol, (3) increase the yield of methanol. 48. What is the operating range of the bottom pressures of the three towers during normal production? Answer: 0.06–0.08 MP for the dewaxing tower, 0.6–0.65 MP for the pressure tower, and 0.07–0.08 MP for the atmospheric pressure tower. 49. From what aspects can tube leaks in the reboiler of the dewaxing tower be detected? (1) The kettle temperature cannot be increased. (2) The proportion of residue is high. (3) The liquid level at the bottom of the tower rises rapidly. 50. What is the impact on production when there is a severe leak in the reboiler of the ether removal tower? Answer: (1) An inability to raise the temperature at the bottom of the tower affects product quality; (2) In severe cases, it disrupts the three balances. 51. How can one determine tube leaks in the reboiler of a pressurized tower? Answer: (1) The temperature in the pressure column bottom cannot be increased; (2) There is a strong methanol odor in the condensate water; (3) The yield of pure alcohol in the atmospheric pressure column has decreased. 52. What is the impact on production when there is a severe leak in the reboiler of the pressure tower? Answer: (1) In cases of severe leakage, the temperature of the bottom reactor drops, which in turn lowers the temperature of the atmospheric pressure tower and affects the quality of the pure alcohol. (2) Methanol leaking into the condensate water reduces the recovery rate and results in financial losses. 53. What should be done if the computer suddenly shuts down during normal production? 54. Under what circumstances should distillation be shut down urgently? Answer: Emergency shutdown is carried out in the event of a power outage, water outage, steam outage, or when a sudden leak in the equipment occurs and cannot be repaired. 55. What is the function of the main distillation tower? Answer: Remove Reorganization components and isobutyl oil to obtain high-purity pure methanol. 56. Describe the relationship among the three equilibria in the distillation process? 57. Briefly describe the normal shutdown process of distillation. 58. How to ensure the quality of refined alcohol when there are frequent adjustments to the amounts added or removed? 59. How should an emergency shutdown in the distillation section be handled? Answer: (1) First, close the main steam valve to cut off the steam supply. (2) Open the steam backflow valve. (3) Close the fine alcohol extraction valve to the full reflux position. (4) Close the inlet and outlet valves of each pump. 60. How to ensure long-term effective extraction performance in the ether removal tower? Answer: (1) Ensure that the vent temperature of the condenser remains within the specified range. (2) Control the specific gravity properly. (3) Regularly discharge fusel oils. (4) Maintain stable temperatures in the stabilizer tower to avoid significant fluctuations. 61. What is the difference between a normal shutdown and an emergency shutdown in the distillation section? 62. What aspects should be considered to reduce the startup time of distillation? 63. The process parameters such as temperature and pressure at various points in the main distillation tower are normal, so what is the reason why the quality of the refined alcohol is not up to standard? Answer: (1) Improper timing of fusel oil discharge; (2) Low reflux rate, resulting in excessive moisture content and unsatisfactory oxidizing properties; (3) Leaks in the cooler. 64. How are the several national standards for pure alcohol determined? (Moisture, water solubility, oxidation time) 65. What are the hazards of the top temperature of a distillation column under normal pressure remaining high for an extended period of time? :Answer: If the top temperature remains high for an extended period, it causes the heavier components to move upward, affecting the quality of methanol. This disrupts the equilibrium within the tower and prevents continuous distillation. 66. How are the initial boiling point, dry point, and distillation volume of pure methanol determined? 67. How should gas blockage caused by crude methanol upon entering the tower be resolved? Answer: (1) Reduce the temperature at the bottom of the tower; (2) Reduce the preheating temperature; (3) Vent gas appropriately. 68. What are the reasons for the high temperature of the atmospheric pressure distillation reflux liquid? How should it be adjusted? Answer: (1) Poor condensation effect; (2) High temperature at the bottom of the tower; (3) Uneven regulation of the first and second cooling stages; (4) Excessive feed rate resulting in too high gas flow velocity. 69. What should be done if a leak is detected in a root valve in a methanol irrigation area? 70. What impact does the prolonged retention of fusel oil in the ether removal reflux tank have on product quality? Answer: Fusel oils are not recycled back into the dewaxing tower; as more of them accumulate, the efficiency of removal decreases, and this has an impact on the water solubility of methanol, as well as its acid value and oxidation time. 71. Under what circumstances should the non-condensable gases from the pressure tower condenser be released? Answer: (1) The temperature and pressure at the top of the pressurized tower cannot be increased; (2) The temperature at the bottom of the atmospheric tower is low and cannot be raised; (3) The quality of the pure alcohol obtained from within the pressurized tower is unstable. 72. How is the prognostic index determined? 73. Under what circumstances is it necessary to increase the discharge of isobutyl oil? Answer: (1) The acid value of the refined alcohol in the atmospheric pressure tower is above the specified limit; (2) The oxidation time does not meet the requirements; (3) The temperature in the tower cannot be raised low enough. 74. What are the hazards of high vent temperature in an atmospheric pressure tower? How to handle it? Answer: High vent temperature leads to energy waste, increases consumption per unit, and raises costs ； Solution: Reduce the bottom temperature of the tower, improve cooling efficiency, and appropriately decrease the feed rate. 75. What is flooding? Answer: The phenomenon of material surging during the production process is called flooding. 76. What is a submerged tower? Answer: The phenomenon of an increase in the liquid level at the bottom of the tower and a rise in pressure inside the tower during the production process is called tower flooding. 77. What is fluid leakage? Answer: It refers to the phenomenon in which the rising gas inside the tower is unable to hold back the liquid on the upper trays, causing it to flow back to the lower trays. 78. What precautions should be taken when parking? Answer: (1) The alcohol recovery valve must be set to the full reflux position. (2) The liquid levels in each reflux tank must be within the controlled range. (3) Close the inlet and outlet valves of each pump. (4) Close the drain valve on the main steam pipe.