MTBE product turns yellow
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Our C4 feedstock is supplied directly via catalysis. A few days ago, the C4 turned yellow, which caused MTBE to turn yellow as well. What is the reason for the C4 turning yellow? We have a C4 washing tower; after washing, C4 remains yellow, so it’s probably not alkaline.
The factors that may cause MTBE to turn yellow could include: 1) The C4 feedstocks used in MTBE production have a yellow color, and these yellow substances end up in the MTBE product, affecting its color. 2) The C4 feedstock entering the etherification reactor contains a high amount of dienes, which polymerize on their own to form yellow polymers; these polymers end up in the MTBE product, affecting its color. 3) A low amount of methanol leads to the auto-polymerization of isobutylene; the color of this polymer is yellow, and when it enters the MTBE product, it affects its color. 4) Decolorization of the etherification catalyst; this color is brown, and it may be carried over into the MTBE product, affecting its color.
There are relevant threads in the forum; the original poster can search for them to learn a bit more as well. I think the yellowing of MTBE is mainly due to the desulfonation of the catalyst in the early stages of driving.
1. The sulfur content in C4 is relatively high; it is necessary to enhance the desulfurization effect, and the raw material methanol must also meet the required standards. 2. A high content of butadiene in C4 can cause MTBE to turn yellow. 3. A high C5 content in C4 can also cause MTBE to turn yellow. 4. In the reaction, whether due to the feed ratio or operational factors, an elevated level of dimeres can also cause MTBE to turn yellow. 5. Catalyst damage and the loss of thioglycolate ions can also cause MTBE to turn yellow.
The literature states that the compounds with higher boiling points are primarily multi-ring aromatic compounds. It is believed that some of these multi-ring compounds possess color, which is responsible for the yellowish appearance of the final product.
If larger molecules are present in M, or if sulfides are present, yellow coloration induced by olefins is generally more common.