Study On Purification Of Bht With Melt Crystallization

The chemical name of BHT is butylated hydroxytoluene, which can be used as anti-aging agent in rubber plastic industry, antioxidant in products of oil-bulk-ore and annexing agent in the food industry. In the paper, a new melt crystallization technology was developed to purify butylated hydroxytoluene, which can provide the basic data and theoretical instruction for industrialization and engineering design.Firstly, the melting point, melting heat of vaporization and melting and the specific heat of solid and liquid BHT were determined. Especially, the data of specific heat was related with temperature and the parameters of the proposed equation were regression out by the least square method. At last, straightline equation was obtained which can be used to calculate the Cp. All the work above can provide the basic data and theoretical instruction for industrialization and engineering design.Due to the ethanol as solvent in the solution crystallization, in this paper the specific heat capacity(Cp) of mixtures of butylated hydroxytoluene(BHT) with alcohol solution were measured with a differential canning calorimeter at temperature from293.15K to323.15K over the concentration of BHT from0to20%(w). At the same time, Cp were correlated as function of content of BHT and the temperature((). The coefficients in the correlated equations were obtained by a least-squares regression method. The result showed Cp of BHT-ethanol solution increased with the rise of temperature and decreased with the rise of BHT content. A equation for calculating the Cp were derived, which was composed of the temperature and BHT content. By this equation, Cp can be calculated at different temperatures and BHT contents. The calculated values were compared with experimental data. The average relative errors of35data points was0.79%. So the proposed equation can be used for solution crystallization to purify BHT and calculation of heat balance in correlative system.Considering that paracresol is inevitable in the product of BHT, differential scanning calorimeter (DSC) was used to measure the solid-liquid phase diagram of butylated hydroxytoluene/paracresol system which is appeared as binary eutectic system according to the experimental result. What’s more, Wilson model and Margules mode were introduced to simulate the experimental data combined with generalized equilibrium relationship. At last, contrasted with DT. RDT and R2. the two modes presented that Wilson equation is the better model of simulating the solid-liquid equilibria of BHT system according to the comparison of the calculated and experimental temperatures It is more reliable to use Wilson equation to simulate the equilibrium relation of this system. Based on the above fundamental researches, the melt crystallization process for manufacturing BHT was systemically investigated. The effects of the cooling rate, the final crystallization temperature, keep crystal time, the final sweating temperature and the sweating time of the melt crystallization process on the yield and purity of BHT were studied. Finally, an optimal melt crystallization technology for manufacturing BHT was developed. By using of the new developed technology, the BHT product with ratio of more than99.9%can be obtained without adding any solvent.