Question of the Week 2.7 Issue 14: Ethanol content in synthetic crude methanol

The main reason is still the side reactions caused by high local temperatures; the catalysts inside the Cassali cannot be distributed evenly

This post was last edited by Shouhou on 2011-2-8 21:44. Synthesis process: Shell-and-tube type used by East China University of Science and Technology. Load on the synthesis tower: 100,000 units of fresh gas. Designed crude methanol content: 800 ppm (for a certain catalyst), 300 ppm (for catalysts from another manufacturer). Actual crude methanol content: 800 ppm, with peaks reaching 3200 ppm; in other cases it was 200 ppm, with peaks at 800 ppm. The level of 800 ppm was caused by too low a CO2 concentration (only 0.5%). Reasons: Low CO2 content in the syngas and poor cleanliness of the pipelines (the fresh gas pipes are made of carbon steel). Solution: Increase the CO2 concentration. Therefore, I believe the most important factor is the influence of the catalyst, followed by a low CO level and an appropriate CO2 concentration at the inlet of the synthesis tower; equipment material is the least important factor.

Reply 1# wawjia: Can ethanol be formed easily even with low levels of carbon dioxide? Why?

Reply to 4# Qingfeng Liushui: I saw this in some books, and the supplier in Casale said the same thing

The factors affecting the ethanol content in crude methanol include: 1. CO/CO2 ratio: High CO concentrations promote the formation of ethanol, while water inhibits its formation. Since all the water comes from the reaction of CO2 and H2 to produce methanol, CO2 has an indirect inhibitory effect on the production of ethanol. 2. Reaction temperature: Generally, the higher the reaction temperature, the more ethanol is produced; as the temperature needs to be increased during the later stages of catalyst operation, the ethanol content also increases accordingly. Therefore, under the condition of achieving full production capacity, the reaction temperature should be reduced as much as possible. 3. Loop pressure: High loop pressure promotes the formation of methanol and significantly inhibits the production of ethanol. 4. Space velocity: Theoretically, reducing the volume space velocity (i.e., increasing the residence time of the reactants in the catalyst) promotes the formation of by-products, but compared to the factors mentioned above, volume space velocity has a lesser impact on ethanol production.

In crude methanol, methanol accounts for about 80%, while water makes up nearly 20%; the remaining impurities are other organic alcohols, ethers, aldehydes, acids, etc. (such as formic acid and ethanol, in very small proportions, ranging from a few hundred to several dozen PPM).

Reply to 7# Yan Nan Fei wl: Why is the water content in crude methanol so high? The carbon dioxide content in fresh gas is already very low, and moreover, the reaction rate between carbon dioxide and hydrogen is much slower than that between carbon monoxide and hydrogen; as a result, the water content in crude methanol rarely exceeds 5%.

According to the catalyst manufacturers, low CO2 levels increase the ethanol content. However, based on my own experience, adjusting the CO2 level has little actual effect on the ethanol content; in fact, the ethanol content keeps rising as the catalyst temperature increases. It changes from around 10% at the inlet of the tower to around 4%, then returns to around 7%; there isn’t much actual change, but the ethanol content keeps rising steadily as the bed temperature increases. Up to 7000; analysis errors cannot be ruled out. I use the tower of Casale.

When the CO content in the gas at the inlet of the synthesis tower is high, variations in the amount of CO2 added result in only minor changes in the ethanol content. I wonder what the fresh hydrogen-to-carbon ratio is where you are?

The flow rate of low-pressure syngas is 60,000; the carbon monoxide content is 4.5%, carbon dioxide content is 0.9%, and the pressure is 4.8 MPa. Anchol tower, with a catalyst loading of 32 cubic meters; the ethanol content in crude methanol is 2000 ppm. What is the reason?