Also known as acetylenic aldehyde method, this process is a traditional method for producing BDO, and is divided into classical method and improved method.
(1) Classical method
At high pressure (13.8-27.6 MPa) and 250-350 °C, acetylene is reacted with formaldehyde in the presence of a catalyst (usually cuprous acetylene and bismuth on a silica support), and then the intermediate is separated by Raney nickel catalyst. The typical theoretical yield of the whole process (calculated as acetylene) is 91% by hydrogenation of l,4-butynediol to BDO. The characteristic of the classical method is that the catalyst and product do not need to be separated, and the operating cost is low. However, the partial pressure of acetylene is high, and there is a danger of explosion. The safety factor of the reactor design is as high as 12 to 20 times, the equipment is large and expensive, and the investment is high; shortening and yield reduction.
(2) Improvement method
In the first step, acetylene and formaldehyde are placed in a reactor composed of several medium-slurry bed reactors in series, and an improved Cu catalyst is used to react at 79-90 ° C and 0.12-0.13 MPa to form butynediol. After filtration, the catalyst and the reactant are separated and left in the reactor, and the liquid-phase material flows out of the reactor for purification and enters the next reactor. The conversion rate of formaldehyde in this reaction was 98%, and the yield of 1,4-butynediol was 95%.
In the second step, a modified Pd/C catalyst is used in the slurry bed, and butynediol is hydrogenated at 60-70 °C and 2.0-2.5 MPa to form butenediol and BDO, and then in a packed reactor, with Ni is used as a catalyst to hydrogenate butenediol to form BDO at 120-150 ℃. Finally, BDO is purified by distillation and thin-film evaporation, and the purity of BDO is ≥99%. The technical characteristics of the improved method are:
a. Using an improved Cu catalyst, low-pressure operation, the decomposition pressure of acetylene itself does not exceed 0.14MPa, which simplifies the additional safety facilities and saves the high-pressure container and compressor;
b. The reactor is equipped with a special filtration system to facilitate the separation of catalyst and reactant in the reactor;
c. Butynediol is hydrogenated to form butenediol and BDO by using an improved Pd/C catalyst, and butenediol is converted to BDO by hydrogenation using Ni as a catalyst;
d. The feed composition is flexible, the formaldehyde content in the formaldehyde solution can be 2-10%, and the acetylene feed does not need to be diluted with inert gas. It is estimated that the operating cost and investment are reduced by 10-20% compared with the classical method.