Analysis of the reasons why the hydrogenation catalytic reaction process is too slow(2)

The above three points are the conventional factors affecting the reaction speed, the so-called catalytic hydrogenation reaction is too slow generally refers to the problem of slow reaction even after adjusting the above factors to the near limit, which is the focus of this problem. At these times, it is already difficult to solve the problem by theoretical inference alone, and the main influencing factors are summarized through experiments, including

Optimization of PH value

● PH is a key point that is easily ignored when optimizing the catalytic hydrogenation process. PH affects the reaction rate by influencing the catalyst activity. Raney nickel is more active under alkaline conditions and less active under acidic conditions, so the alkalinity of the reaction solution can be improved by supplementing with amines; palladium carbon is more active under acidic conditions and less active under alkaline conditions. 

So the acidity of the reaction solution can be improved by supplementing with acetic acid. The above acidity and alkalinity should not be too high, and strong acid and alkali should not be used, and the stability of the equipment and the influence on the post-treatment need to be considered.

Impurity content

●refers to toxicochemicals, insoluble substances, metal ions and tar, excluding low molecular impurities, isomers and solvent residues. Raney nickel is generally more resistant to poisoning, and the poisoning is mainly for palladium carbon. Toxic chemicals mainly sulfur phosphide compounds, including various forms of substances containing the use of sulfur phosphorus elements. Toxic chemicals introduced pathways include raw materials, solvents, reactors and gases; insoluble substances are mainly inorganic substances and polymers, etc., mainly deposited on the surface of the catalyst. 

So that the reaction site is blocked and the reaction slows down; metal ions mainly heavy metals, copper ions, mercury ions, lead ions and cadmium ions, etc., react with the catalyst, thus slowing down the reaction; the mechanism of action of tar is similar to insoluble substances, which may also be generated in the reaction. Therefore, the reaction conditions generally cannot be too high; the factor of impurities is difficult to be analyzed by instruments and must be verified by experiments to be known, which is most easily ignored in catalytic hydrogenation.

Type of stirring

● The main effect is the mixing effect of stirring on the bottom catalyst. Because of the small solubility of hydrogen in the solvent, the reaction system exists mostly in the gaseous state; the raw material is dissolved in the solvent and is in the liquid state; the catalyst is in the solid state. 

Microscopically, the reaction occurs on the catalyst surface, and good stirring enables the gaseous hydrogen and the raw material to pass and react quickly on the catalyst surface, while taking the products away. In small laboratory tests, magnetic stirring is mostly used, as the small amount combined with the magnetic force has the effect of grinding the catalyst, generally the fastest reaction; in pilot tests, the propulsive stirring paddle is used to mix the reaction system under pressure, which is more effective. 

Raney nickel because of heavier, by the stirring effect of the largest factors; palladium carbon because of palladium metal adsorption on the activated carbon, relatively small impact; industrial production, the scale is larger, stirring effect is worse, generally slower than the pilot reaction; traditional anchor stirring no direction, two-way can be normal stirring; propulsion stirring paddle has direction, the correct direction to have good stirring effect, the opposite direction effect is poor.