Preperation Of High Performance 4A Zeolite By Continuous Synthesis

4A zeolites have been widely used in various industries such as detergent, petrochemical, environmental protection, etc. because of their unique absorbability, ion exchange character and chemical modificable property. In recent years, with the increasingly widespread application of 4A zeolite, it has been manufactured on a greater scale. Currently the general industrial production method of 4A zeolite is batch operation, in which the investment is large and the energy consumption is high, but the output is low and the quality of the product is unstable. In order to overcome these shortages, a modified method for the traditional batch operation is introduced in this paper, by the new method the process of crystallization is changed to continuous synthesis, in which the technological conditions are optimized.Under batch crystallization conditions, the rate of gel dissolution and crystallizate was accelerated, the time of induction was shortened and the average particle size was reduced by increasing alkalinity of the reaction mixture, reducing system of water (that is less-water and high-alkalinity system), and adding an appropriate amount of surfactant. This result provides possible for the continuous synthesize 4A zeolite. In our own designed and manufactured pilot-scale continuous crystallization reactor, the parameters such as slurry concentration, flow rate and so on were adjusted to obtain the optimal synthesis conditions of continuous synthesis through orthogonal experiments: the concentration of nucleation slurry 30%, flow 2L/min, the reaction mixture ratio of n (SiO2) / n (Al₂O₃) = 1.8 1.9, n (Na2O) / n (Al₂O₃) = 3.2 3.4, (n (H2O) / n (Al₂O₃) = 80 100, crystallization time t= 20min, the crystallization temperature is 90℃, add the dodecyl sulfonic sodium (SDS) by molar ratio of 0.1. Through the theoretical analysis, the deposition distance of zeolite particle is 1.998×10^-5mm in 20min. As the deposition is very slow, there is almost no effect on a continuous crystallization process, and in the actual experiment the phenomenon of pipe blockage has not been found. The synthesis of high-performance 4A zeolite was achieved in the pilot-scale continuous crystallization reactor.The performance of the synthetic 4A zeolite was characterized. And the results showed that the 4A zeolites with a high degree of crystallinity, small crystal size, narrow crystal size distribution, high calcium exchange capacity, fast calcium exchange rate can be produced with continuous method. In comparison with synthesis technique of batch operation, the Al³⁺ content in crystallization system under continuous synthesis was increased to 18.61% from 18.34%, the detergency was increased by 20%, the LCC of the product is increased to 44.2g/100g from 39.0g/100g, and it has little wear behavior according to the results from a series analysis.The energy consumption analysis results showed that in comparison with traditional technique, the solid content in slurry of continuous synthesis system is increased by more than 85%, and the consumption of water, steam, power and repair cost can be greatly reduced. If calculated as an annual output of 200,000 tons, the total cost reduction is greater than 22 million yuan per year.The thermodynamic study of continuous crystallization process showed that the nucleation activation energy En is 51.1kJ·mol-1 and the growth activation energy Ec is 5.8kJ ? mol-1. Compared to conventional batch method they reduced , the crystallization time is relatively shorter. Continuous crystallization system breaks through the typical composition of the traditional batch method. In the experiment, there is no sodalite formation was observed, thus we can speculate that the reasons for the formation of sodalite are not only the high degree of base, but also the way of crystallization.The results of our study showed that continuous synthesis mechanism was a liquid-phase transformation mechanism. The crystallization growth model was established for a continuous synthesis way, the crystallization process experiences three stages: collid, nanocrystalline and ultra-fine crystallite in continuous process, that was known as "Type II splicing growth model."The study about continuous process for preparation of 4A zeolite revealed the basic law of 4A zeolite crystal growth under the conditions, opened up a new way for study of formation mechanism and crystal growth of 4A zeolite, improved and developed the theory of zeolite crystal growth, enriched the content of zeolite synthetic chemistry. Therefore this study not only has a high practical value to reduce the synthetic cost of 4A zeolite, but also possesses important theoretical significance to carry out the guidance and predict of the preparation technique for zeolite of specific structure and properties.