As an important chemical raw material, propylene glycol is widely used in many fields. Its traditional chemical synthesis route often faces problems such as environmental pollution and resource waste, so green improvement is imminent.
First, the traditional synthesis of propylene glycol often adopts the propylene oxide hydrolysis method. Although this method is relatively mature, it will produce a large amount of salt-containing wastewater, which puts great pressure on the environment. One improvement idea is to use catalytic hydrogenation. Glycerol is used as a raw material and hydrogenated under the action of a specific catalyst to produce propylene glycol. The advantage of this method is that the by-products are mainly hydrogen and water, which reduces the generation of salt-containing wastewater, and glycerol can be derived from the by-products of the biodiesel production process, realizing the comprehensive utilization of resources, which is in line with the concept of green chemistry. For example, by screening efficient copper-based catalysts, the selectivity and conversion rate of the reaction can be improved, so that the yield of propylene glycol can be improved.
Secondly, in the synthesis process, the selection of reaction solvent is also crucial. The organic solvents commonly used in traditional processes may be toxic and difficult to recover. Nowadays, supercritical carbon dioxide can be explored as a reaction solvent. Supercritical carbon dioxide has the characteristics of good solubility, non-toxicity, and easy separation and recovery. In the propylene glycol synthesis reaction, it can effectively promote the mixing and mass transfer of reactants, increase the reaction rate, and can be separated from the product by a simple pressure reduction operation after the reaction, and recycled, reducing solvent consumption and environmental pollution.
Furthermore, the development of new catalysts is a key link in improving the synthesis route. For example, some nanocomposite catalysts, which combine different active components at the nanoscale, can show unique catalytic properties. This type of catalyst can reduce the activation energy of the reaction, improve the reaction activity and selectivity, reduce the occurrence of side reactions, and thus reduce the generation of waste. At the same time, through the immobilization technology of the catalyst, it can be reused, further reducing production costs and environmental impact.
In addition, the optimization of the reaction process is also an important aspect of greening. Using a continuous reaction process instead of an intermittent reaction can improve production efficiency, reduce equipment footprint, and reduce energy consumption. In the continuous reaction process, by precisely controlling parameters such as reaction temperature, pressure, and material flow rate, the reaction is always in the best conditions, thereby improving the synthesis quality and yield of propylene glycol.
From the perspective of raw material pretreatment, refining raw materials such as glycerol to remove impurities and moisture can improve the stability of the reaction and product quality. For example, the use of membrane separation technology to purify glycerol can efficiently separate impurities, provide high-quality raw materials for subsequent catalytic hydrogenation reactions, and reduce reaction anomalies and by-product generation caused by raw material problems.
Finally, in the design of the entire synthesis route, the comprehensive utilization of energy should be fully considered. For example, the reaction heat can be used to preheat the raw materials or drive other auxiliary equipment, reduce the input of external energy, improve energy utilization efficiency, and realize the green improvement of the entire process of propylene glycol chemical synthesis route from raw materials to products.
