Effects of solvent,supersaturation ratio and silica template on morphology and polymorph evolution of vanillin during swift cooling crystallization

Swift cooling crystallization of vanillin was investigated in water, ethanol, isopropanol and ethyl acetate. Morphology and polymorph evolution of vanillin were discussed in terms of solvent, supersaturation ratio and silica template. PXRD, DSC, FTIR and microscope were used to identify polymorphs of vanillin. Results showed that the nucleated polymorphs of vanillin depended largely on the solvent, supersaturation ratio and silica template. Low supersaturation ratios favor the nucleation of stable form I in water, and high supersaturation ratio exceeds 7 generating 100% metastable form II. However, if the supersaturation ratio is too high (S>8), liquid–liquid phase separation will occur, and no crystals could be obtained. In other solvents such as ethanol, isopropanol and ethyl acetate, only form I was obtained. However, it should be noted that the morphology of form I prepared in ethanol, isopropanol and ethyl acetate is distinct from that obtained in water, the former is flake-like and the latter is rod-like. The nucleation of vanillin from different solution was also studied with the presence of SiO₂, SiO₂–NH₂ and SiO₂−COOH templates, which did not change the nucleated polymorph of vanillin, but changed the nucleation and growth rate of stable form I.     

Supersaturation,the Spinodal,and Their Prediction Using Equations of State

Abstract

The equations of state of Redlich-Kwong, Soave, BWR, Schmidt-Wenzel, and Harmens-Knapp have been tested and compared in their ability to predict the spinodal and the experimental limits of superheat of pure liquids. The results indicate that only the Peng-Robinson, Soave and BWR equations are capable of predicting reduced kinetic limits of supersaturation above the experimental ones.     

Application of Rosin–Rammler model for analysis of CSD in sugar crystallization

Crystal‐size distribution (CSD) is one of the most important parameters in sugar production. The objective is to grow crystals of uniform sizes or narrow CSD. CSD appears to be determined by the growth‐rate history of the crystals and the relative supersaturation (SS) of the solution from which crystals growth takes place. Three methods for preparation of nucleation seeds were described and used for industrial crystallization of raw and white sugars; these are wet milling filtered sugar (ML), agitating saturated solution (AS) and powdered sugars (PD). Rosin–Rammler (RR) and mathematical models were adopted to investigate CSD and the uniformity of the produced crystals. Higher uniformity coefficients were reported for the AS seeded crystals than the other two seeding methods. Furthermore, higher crystal contents were obtained for the AS seeded white sugar batches in comparison.     

电导法评定阻垢剂的阻垢性能

介绍了一种评价阻垢剂阻垢性能的新方法。这种方法基于溶液电导率的测定原理，是通过在加入阻垢剂和不加阻垢剂的特定水环境下测定各种成垢化合物的过饱和度来实现。此法能对各种阻垢剂的阻垢性能进行良好的区分。通过与评定阻垢剂性能的国家标准——鼓泡法的比较，证明此法简便、快捷、重现性好，可信度高。