Control of ethanol in methanol production

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Control of ethanol in methanol production: We have encountered the issue of ethanol accumulating in the system before, and it was resolved by increasing the side-stream extraction from the distillation atmospheric tower; it’s not a serious problem at all! The problem lies in the distillation system; it has little to do with the synthesis system. The selectivity of current methanol synthesis catalysts is quite good. Even in catalysts from lower-quality manufacturers, impurities such as dimethyl ether and paraffin are present in larger amounts, while ethanol content is relatively low. Therefore, distillation alone is sufficient to address this issue. When the distillation product does not meet the required standards, the common solutions are to increase the reflux rate and the heat load. Controlling the ethanol content in methanol is a matter that requires comprehensive consideration. For example, in methanol synthesis, when the H2:C ratio is low, the system’s energy consumption is high and the one-pass conversion rate decreases; whereas when the H2:C ratio is high, the one-pass conversion rate increases, but side reactions also increase. Moreover, an excessively high H2:C ratio can lead to carbon deposition, thereby shortening the catalyst’s lifespan. Therefore, it is necessary to adjust the H2:C ratio to an appropriate level during methanol synthesis. The purity of the recycle gas is also an important factor affecting ethanol production; hence, it is essential to regularly clean the methanol water coolers, reduce the temperature of the recycle gas, and improve the separation efficiency of the methanol separator. All these measures can help reduce the ethanol content in crude methanol, thus lowering its content in purified methanol as well. To reduce the ethanol content in methanol, the focus is on methanol distillation; by increasing the reflux rate based on the load of the distillation tower, efforts are made to keep the area where ethanol is concentrated in the middle and lower parts of the distillation tower ； Increase the recovery of fusel oils and control the temperature in the middle section of the atmospheric distillation column, so that the ethanol-enriched zone is concentrated at the outlet for fusel oils ； Water is added to the pre-distillation tower to reduce the concentration of crude methanol; by diluting the ethanol present in the concentrated crude methanol with water, it is possible to control the upward movement of ethanol into the refined methanol during the distillation process. Due to the varying specific parameters of different systems, it is necessary for each system to optimize itself based on its own characteristics by focusing on the aspects mentioned above; this will lead to a significant reduction in the ethanol content in methanol within those systems. These are all my experiences from working in methanol distillation; I’m glad to discuss them with you all, as it may be helpful to you. According to the American AA standards, the ethanol concentration in methanol must be kept below 10 ppm; for crude methanol, where the ethanol content is above 1000 ppm, three-column distillation is used, yet it is difficult to meet the AA standards! Pressure towers are very ineffective for separating ethanol! Separation in a atmospheric pressure column is easier compared to that in a pressurized column. Meanwhile, the domestic quality standards for methanol do not specify any limits on the ethanol content! (Negotiations for buying and selling) Therefore, in the design of many methanol projects in China, the AA standards from the United States are often adopted, which ends up tying those projects down and restricting their development. Further investigation reveals that a 200,000-ton methanol production facility in China uses natural gas as raw material; the ethanol concentration in the crude methanol is around 200 ppm. Through careful control and increased processing costs, it is possible to reduce the ethanol concentration in the refined methanol product to around 30 ppm. However, during normal production, the ethanol concentration in the methanol product remains above 100 ppm. Methanol with an ethanol concentration of 30 ppm has a selling price that is 500 yuan per ton higher than that of methanol with an ethanol concentration of 100 ppm. It’s because the processing cost is much higher. When methanol is produced using coal as a raw material, the ethanol concentration in the crude alcohol is above 1000 ppm, and the ethanol content in the final methanol product is typically between 600 and 800 ppm. In any case, the quality level of 10 ppm cannot be achieved. Call: Domestic design institutes should stop deceiving themselves by citing the American AA standards.