A method and catalyst for preparing hexamethylenediamine from hexanediol and ammonia gas

A method and catalyst for preparing hexamethylenediamine from hexanediol and ammonia. In the method of preparing hexamethylenediamine from hexanediol and ammonia, the active sites of the catalyst play a key role in the selectivity of the reaction. For example, in some transition metal catalysts, the electron cloud density of the active sites is different, which affects the adsorption and reaction of hexanediol and ammonia on the catalyst surface, thereby determining the proportion of hexamethylenediamine in the product. As mentioned in the literature, under specific conditions, the specific structure of the active sites can achieve a selectivity of over 80% for hexamethylenediamine.
This preparation method involves complex reaction kinetics, where factors such as reaction temperature, pressure, and reactant concentration interact with each other. For example, under the conditions of temperature of 180-220 ℃ and pressure of 3-5MPa, as the molar ratio of ammonia to hexanediol increases from 3:1 to 5:1, the reaction rate shows a trend of first increasing and then stabilizing, which has been verified in relevant experimental studies. The stability of the catalyst is an important factor affecting the industrial production of hexamethylenediamine from hexanediol and ammonia gas. Taking loaded metal catalysts as an example, after several hundred hours of continuous reaction, their catalytic activity gradually decreases due to carbon deposition and other reasons. To improve stability, the catalyst can be surface modified by adding specific additives, such as a small amount of cerium element, which can significantly enhance the catalyst's ability to resist carbon deposition and prolong its service life. From the perspective of reaction mechanism, the process of preparing hexamethylenediamine from hexanediol and ammonia gas involves multiple intermediate steps. Firstly, hexanediol undergoes dehydrogenation reaction with aldehyde intermediates on the catalyst surface, followed by condensation reaction between aldehyde intermediates and ammonia gas, and finally hexanediamine through hydrogenation and other steps. Understanding these detailed mechanisms can help optimize reaction conditions and catalyst design. The effect of different types of catalysts on the reaction rate of preparing hexamethylenediamine from hexanediol and ammonia varies greatly. For example, molecular sieve catalysts have a unique pore structure, and the size of their pore size

matches the size of the reactant and product molecules, which affects the diffusion and reaction of substances in the pore. The appropriate pore size can accelerate the reaction rate and improve the production efficiency of hexamethylenediamine.
The choice of solvent is also crucial in the reaction system of preparing hexamethylenediamine from hexanediol and ammonia gas. Some polar solvents can improve the solubility of reactants, promote intermolecular interactions, and facilitate the progress of reactions. For example, when N, N-dimethylformamide (DMF) is used as a solvent, it can make the reaction system more uniform and to some extent improve the conversion rate of the reaction. The preparation method of the catalyst will significantly affect its performance. Catalysts prepared by impregnation method have different uniformity of distribution of active components on the carrier, which can lead to differences in the activity and selectivity of the catalyst. The crystal structure and particle size of catalysts prepared by precipitation method also have different effects on the reaction. By optimizing the preparation method, catalysts with better performance can be obtained. Research has shown that impurities in the reaction system have adverse effects on the reaction and catalyst performance of the synthesis of hexamethylenediamine from hexanediol and ammonia gas. For example, the trace metal ions contained in the raw material hexanediol may interact with the active sites of the catalyst, leading to catalyst poisoning and deactivation. Therefore, strict purification treatment of the raw material is the key to ensuring the smooth progress of the reaction. The thermal effect of the reaction between hexanediol and ammonia to prepare hexamethylenediamine is significant, and the removal or supplementation of heat needs to be reasonably considered when designing the reaction process. In large-scale production, appropriate heat exchange equipment is used to control the reaction temperature within a suitable range, ensuring the stability and efficiency of the reaction, and avoiding excessive temperature fluctuations that affect the reaction effect and catalyst life.
From an industrial application perspective, the economic feasibility of the method and catalyst for preparing hexamethylenediamine from hexanediol and ammonia gas is an important consideration factor. On the one hand, it is necessary to improve the activity and selectivity of catalysts to reduce raw material consumption; On the other hand, it is necessary to reduce the preparation cost and regeneration difficulty of catalysts, such as developing low-cost and high-performance catalyst supports, which can effectively improve the economic benefits of the preparation process.