Optimization Of Crystallization Process And Spherulites Preparation Of L-Valine

L-valine is one of natural essential amino acids for human body which is widely used in food and feed additives,nutritional supplements and other fields,and has great market demand.At present,L-valine sold in the market is mainly in flaky form,which leads to the problems of low bulk density and poor fluidity,and high purification cost.Aiming at these problems,this study measured the basic crystallization data of L-valine,optimized the crystallization method and screened additives to improve the crystal behavior.Based on this,the preparation methods of high bulk density L-valine and L-valine spherulites are proposed.First,we measured the solubility of L-valine in pure water,aqueous solutions of different p H and water-miscible organic solvents,as well as the metastable zone of cooling and evaporation crystallization to provide the basis data for the selection of crystallization methods.Considering the purification and downstream-processing factors,including product yield,bulk density,moisture content,particle size distribution,energy efficiency,operating cost,etc.We determined that evaporative crystallization is more suitable method for the crystallization and purification process of L-valine.Second,in view of the low bulk density of L-valine,this study proposes two methods for preparing L-valine with high bulk density by evaporative crystallization.One is the optimization method by adding seed crystals.In other words,it can also be said that the seed crystal cycle process.Products obtained by adding seeds are used as seeds of a new round of crystallization process.Thus,the morphology of crystals can be improved continuously,and the growth process of crystals can be regulated to obtain crystals with high bulk density and good dispersion.The other method is the p H control method.The p H of the initial solution was adjusted to be acidic at about 5,and then concentrated Na OH solution was continuously added to adjust the p H of the solution to neutral,which can achieve the preparation of high bulk density L-valine of 0.7g/cm~3.Finally,in order to modify the morphology of flaky L-valine crystals and improve the fluidity,this research conducted a screening of additives.We investigated the effects of additives such as amino acids,organic macromolecules,and high molecular polymers on the crystal habit of L-valine and found that the polymer hydroxypropyl methylcellulose can promote the high bulk density spherulites of L-valine formation.The suitable additive amount is 0.25%to 1%,the evaporation temperature is 55°C to65°C,and the effective viscosity range of the additive is 40 to 50 m Pa·s.At the same time,the effects of operating conditions such as evaporation rate,temperature,and additive content on product quality were investigated.In addition,we characterized the partical properties and revealed the formation process of L-valine spherulites.It has undergone a process of spontaneously nucleates to form sheet-like crystals,grows in layers,gradually evolve into petal-like shapes,and finally forms complete spherulites.The characterization analyses of powder X-ray diffraction,thermogravimetric analysis,Fourier Transform infrared spectroscopy,Raman microscopy and,etc.,together with molecular dynamics simulation results,provided an explaination of the mechanism of the additive to promote the L-valine spherulites.In conclusion,this study proposes two methods for preparing high bulk density L-valine by optimizing the crystallization method and conditions.Meanwhile,with the addition of HPMC additives,L-valine spherulites are successfully prepared.To sum up,the above research could provide reference for the preparation and industrial production of L-valine.