Questions regarding methanol cracking
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This post was last edited by jordan569 on 2013-1-6 at 21:54. The original plan was to conduct a blank test for the MTP reaction, using methanol plus water as the feed, with a temperature below 500 degrees, without using a catalyst; instead, high-alumina ceramic packing was used to examine the cracking of methanol. After several days of investigation. The test results showed that CO2 was the most abundant in the gas phase; other gases included H2, CO, CH4, etc. Based on material balance calculations, the conversion rate of methanol was over 20%. However, it was found online that methanol requires temperatures above 800 degrees to undergo thermal pyrolysis. There are three possible reasons for this suspicion. First, the ceramic filler may be active and catalyze the thermal cracking of methanol; however, I think this is unlikely, as such materials are commonly available on the market and are generally used as inert fillers. Secondly, our stainless steel reactors are newly manufactured, and there may be certain substances such as chromium and manganese inside them that can catalyze the cracking of methanol. Thirdly, the addition of water vapor changes the partial pressure of methanol, resulting in easier cracking of methanol; well, I’m not sure if that makes sense. In any case, a 20% methanol conversion rate seems too high. Friends who have conducted related experiments, please help analyze this from a theoretical or practical perspective! :P. Note $ # , $ $
I haven’t conducted this experiment, but based on the observed phenomena, it seems that a catalyst is at work. There are two possible sources: one is certain metals present in the stainless steel reaction tube itself, an issue that can be ruled out by using quartz tubes; the other possibility is ceramic fillers, as these typically contain kaolin, and kaolin contains aluminum oxide, silicon oxide, and other substances that have acidic properties, thus acting as catalysts. Try using a different filler, such as quartz sand or glass beads. I lean towards the second possibility, that is, the ceramic filler has a catalytic effect.
Ceramics also tend to have a catalytic effect. Experiments were conducted previously involving methanation, also using stainless steel reactors; ceramic beads were used as controls, and the temperature was not as high as that used in your experiments. Upon opening the reactor, it was found that there was a lot of carbon buildup on the balls. Given the high level of CO2 in your product, a carbon deposition reaction is likely to have occurred; it is recommended to open the reactor and check the surface of the pellets. Wish you success with your experiment.
I am also concerned about this issue. Personally, I think the CO2 you detected may come from the methanol and water vapor reforming reaction (MEHTNAOL STEAM REFORMING). Please check the Internet; there should be many articles. Especially in the presence of a methanol synthesis catalyst at lower temperatures (200-300 degrees Celsius? ) it can produce carbon dioxide and hydrogen. This method is used in many places to produce hydrogen (for industrial applications; it is more cost-effective than methane reforming for hydrogen production, especially when the amount of hydrogen required is not large). The suggestions put forward by Zhang and others are worth trying – using inert tubes as reactors to see if there are any differences in the results. If you have new experimental results, please share them. Thank you!
It seems that everyone still thinks it’s a problem with the filler, but even if such a filler has some level of activity, it shouldn’t be that high, right? It’s even more effective than a catalyst; it’s been in use for almost a week now, and there’s not the slightest sign of deactivation! Quartz tubes cannot be made for now – there is no raw material available – and it’s unlikely that quartz tubes will be used in industry in the future either. As for the third possibility, although there is methanol and water present, there is no catalyst; 20% of cracking seems a bit high But it could also be the result of a combination of several factors, haha! I wonder if there are any other possibilities? The pressure is less than 1 MPa. As for replacing the packing, wait until next week when the reaction stops, then take it apart to check if there is any carbon buildup inside.
I think it’s still because of your stainless steel reactor – the surface of stainless steel may contain iron-containing compounds, and iron is likely to catalyze the reaction between methanol and water. The formulas for the reactions might be: CH3OH=CO+H2, CO+H2O=CO2+H2, 2CO=CO2+C, CO+H2=H2O+C, CO+3H2=CH4+H2O. It’s best to open the reactor to check if there is any carbon buildup.
We have conducted similar experiments using glass tubes filled with magnetic ring fillers, and carbon deposition occurred. It is suspected that the filler plays a catalytic role. Once your results are available, could you upload them to share them together? Thank you first!
On the 7th, Zhaofy took the reactor apart to take a look; indeed, there was a lot of carbon residue, and the inert filler was also black. However, it could be washed away by using clean water, so I think carbon buildup is not caused by the filler. The mass ratio of CO2 to H2 as a result of the reaction is approximately 7:1, so I think it corresponds well to the ratio used in the methanol steam reforming reaction. However, the specific cause of this phenomenon has not yet been identified. Well, I guess this kind of situation will also occur in future formal experiments. I don’t know what to do.
Consider using superalloy steel for the reactor. Ordinary stainless steel doesn’t seem to work well; it cannot withstand such high temperatures. It’s unlikely that the porcelain balls will react; they probably don’t have any crystal structure, so the possibility of a catalytic reaction is low. I’m an amateur when it comes to catalysts; please point out any mistakes I may have.
9# decity2007 But the MTP reactors for large-scale installations seem to use stainless steel as well, right? Why aren’t there any problems in this regard? Is it because, with a larger device, the contact time between the material and the substances is shorter?
Start by looking at the materials of the reactor itself as well as the filler. Check what the nickel content is in the stainless steel material you are using. On the other hand, break the filler apart to see if there is any darkness inside it; if it is dark inside as well, then the filler itself likely has a catalytic effect.