Modeling of zeolite 4A synthesis with different particle morphology from kaolin via response surface methodology

Zeolite 4A has numerous established and advanced applications. Using kaolin instead of conventional SiO 2 and Al 2 O 3 sources makes its synthesis relatively green and low-cost. The best performance requires zeolite 4A to have high purity and specific particle size and morphology. However, fine-tuning these parameters is challenging due to the many influencing factors, and kaolin as a raw material only increases their number. Here, we modeled the dependence of zeolite 4A properties (relative crystallinity, yield, water vapor capacity, average size of particles and zeolite 4A cubic crystals, average number of cubes in agglomerate) on four synthesis parameters (temperature, time, stirring speed, Na 2 O: Al 2 O 3 ) via response surface methodology (RSM), namely the Box-Behnken design (BBD). Products were synthesized in two steps: metakaolinization and hydrothermal crystallization. We applied powder X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), scanning electron microscopy with energy dispersive X-ray (SEM-EDX), differential thermal and thermogravimetric analysis (DTA-TGA), laser diffraction analysis (LDA) and other techniques to characterize the samples. As a result, we obtained response surfaces and used them to synthesize zeolite 4A with high relative crystallinity. In addition, it was found that at a high alkali content in the reaction mixture, e.g. Na 2 O: Al 2 O 3 = 5, the product particles are identical in shape to precursor ones but consist of tiny zeolite crystals with an average size of 0.94–1.83 μm. We also observed several previously known crystallization mechanisms. The obtained models, observations, and experimental data expand the toolbox for producing zeolites from kaolin, and may become the basis for relatively green and low-cost technology.