1. Cross Canizaro condensation method Cross Canizaro condensation method is also known as sodium formate method. Aldol condensation reaction between n-butyraldehyde and formaldehyde solution under the action of alkaline catalyst to generate 2,2-dimethylolbutyraldehyde, 2,2-dimethylolbutyraldehyde then reacts with excess formaldehyde under strong alkali conditions Cross-Connizzaro reaction generates trimethylolpropane, formaldehyde is oxidized to generate formic acid, formic acid is neutralized with sodium hydroxide to generate sodium formate, and the reaction mixture is desalted and refined to obtain qualified products. The relevant reaction equation is:
Fig. 1 is the reaction equation that crosses Cannizzaro condensation method to synthesize TMP When adopting this method to produce trimethylolpropane, the used catalyst mainly contains sodium hydroxide, calcium hydroxide, calcium oxide and organic tertiary amines (such as trimethylamine, triethylamine, etc.) etc. When using sodium hydroxide as a catalyst, because it is soluble in water, the process difficulty increases when the sodium formate is finally removed, so the catalyst has been eliminated abroad; using an organic tertiary amine as a catalyst, the separation is easier, but the catalyst is expensive. As a result, the production cost of trimethylolpropane increases; calcium hydroxide (or calcium oxide) can be precipitated due to its low solubility in water, and the rest can be separated by centrifugal separation and membrane separation. Calcium can be directly used in feed additives, preservatives, etc. At present, most of the foreign trimethylolpropane is produced by this catalyst. Cross-Canizaro condensation method is a traditional method for producing trimethylolpropane. However, this method has many by-products, poor product quality, and large post-processing workload, and the product yield is only 60% to 70%. In order to reduce the formation of by-products, a large excess of formaldehyde (generally 8 to 10:1 molar ratio) is required to facilitate the completion of the reaction and to suppress the formation of some difficult-to-separate heat-sensitive substances, but a large excess of formaldehyde increases the load of the post-processing dealdehyde tower , the energy consumption increases. In addition, the post-treatment of this process is cumbersome, and 1 t of sodium formate with very low added value is by-produced for every 1 t of trimethylolpropane, resulting in a very low utilization rate of formaldehyde, an increase in production costs, and difficulty in refining trimethylolpropane. , How to effectively remove formate is the key to the preparation of high-quality trimethylolpropane. 2. Aldehyde hydrogenation reduction method n-butanol reacts with formaldehyde under the catalysis of trialkylamine (such as triethylamine) to obtain 2,2-dimethylol butyraldehyde, the aldol condensation product, and then in the presence of a catalyst, to 2,2-Dimethylolbutyraldehyde is hydrogenated to produce trimethylolpropane. The relevant reaction equation is:
Figure 2 shows the reaction equation for synthesizing TMP by the aldehyde hydrogenation reduction method. During the aldol condensation, triethylamine is mainly used as the catalyst, and triethylamine is used as the catalyst for the aldol condensation reaction, which can control the selectivity of the reaction and suppress the side effects of The occurrence of the reaction reduces the formation of formate. The aqueous hydrogenation catalyst is mainly nickel or nickel oxide distributed on the carrier, and copper chromite can also be used, and copper oxide or copper-chromium is used as a cocatalyst. The aldehyde hydrogenation reduction method has high formaldehyde utilization rate, strong hydrogenation technology, can save a lot of formaldehyde and alkali, relatively few side reaction products, good product quality, simple purification and purification, less equipment, and low production cost, but it needs to add The hydrogen unit adopts high-pressure equipment, which has high requirements on hydrogenation equipment and catalysts, as well as high production technology requirements, and is more suitable for large-scale continuous production. At present, some trimethylolpropane manufacturers in Europe and the United States mainly use this method for production.