分步结晶法精制2，5-二甲基苯酚

对2,5-二甲酚粗品进行分步结晶,得到含量99％以上的2,5-二甲酚纯品。通过优化工艺参数,研究了分布结晶的时间、温度等对熔融结晶收率的影响,确定了获得高产率、低成本的较佳结晶工艺条件,该工艺总结晶收率可达55％以上。实验表明,此结晶工艺是可行的。     

多段熔融结晶精制技术在对二氯苯生产中的应用

介绍了一种采用套管刮刀或结晶器、离心机及降膜式结晶器等关键设备精制对二氯苯的工艺技术。结合生产实际应用情况对该技术装置进行了剖析。指出其优点及不足之处,提出相应的改进建议     

结晶精制技术进展

考虑到节能、环保等问题，结晶技术在有机混合物的分离和精制中得到广泛应用。特别是熔融结晶，已引起人们的重视。文中介绍了结晶研究和技术发展概况，以及几种新型的结晶精制装置。     

对二甲苯硝化还原法合成2,5-二甲酚

对二甲苯与混酸(硝酸/浓硫酸)经硝化反应制得 2,5-二甲基硝基苯,再经钯炭-甲酸铵催化氢转移还原反应、重氮化/水解反应,最终制得 2,5-二甲基苯酚。三步反应在后处理时均采用水蒸汽蒸馏。优化了反应条件,简化了操作,总收率达47%。     

用熔融结晶法分离有机物

熔融结晶是一种分离精制有机物的物理方法。它不用溶剂,仅耗熔解热,设备简单、动力设备少。对易聚合、难精馏、高沸点有机化合物分离与精制具有独特功能。在国外化学工业上已广泛使用,包括萘、肼类、氯苯、硝基苯衍生物、丙烯酸、氯乙酸、甲酚类、脂肪酸等的分离与精制。     

从工业二甲酚中分离3,5二甲酚的研究

采用常压精馏和溶剂重结晶相结合的方法,从工业二甲酚中分离3,5-二甲酚,精馏后可获得纯度>90%的3,5-二甲酚窄馏分,再经重结晶可获得纯度>99%的产品。     

分步结晶法精制3,5-二甲基苯酚

对3,5-二甲酚粗品进行分步结晶,可得到含量98%以上的3,5-二甲酚纯品,总结晶收率可达44%。     

熔融结晶过程的新进展

本文综述了工业结晶过程的一个主要部分,即熔融结晶过程的新进展。重点介绍了国内外各种新型塔式熔融结晶装置的研究、开发与工业应用的现况;并比较了它们的优缺点。本文对已提出两种基本传递过程的数学模型也做了简单的阐述。     

熔融结晶分离技术的开发及应用

本文简单介绍了输送移动层式及加压式结晶器的结构,以及熔融结晶分离技术及其应用。     

3,5-二甲酚的研制

介绍了对化工新产品3,5-二甲酚的研制、开发。以焦油中低附加值产品工业二甲酚后馏分为原料,用精馏的方法可以得到质量分数>95%的3,5-二甲酚高附加值产品。试验表明,通过一次精馏生产质量分数>95%的产品,在精馏分离3,5-二甲酚的同时,经结晶、抽滤还可得到质量分数>95%的3,4-二甲酚产品。     

磺化碱熔法制备2,5-二甲基苯酚

通过对二甲苯磺化、碱熔法合成2,5-二甲基苯酚,研究了影响磺化、碱熔产物收率和纯度的因素。磺化时酸性滤液回收套用,可减少三废,降低生产成本。最佳磺化条件:缓慢把硫酸往对二甲苯中滴加,硫酸与对二甲苯摩尔比为1.6∶1,反应温度125℃,反应时间2.0 h,2,5-二甲基苯磺酸钠收率为96.87%,纯度为99.30%。碱熔时,通入水蒸气、添加抗氧剂和硬脂酸钠,增加了物料的流动性,提高了收率和纯度。最佳碱熔条件:将KOH、NaOH、潮品钠盐、抗氧剂1035(2,2'-硫代双[3-(3,5-二叔丁基-4-羟基苯基)丙酸酯])和硬脂酸钠混合后投入反应釜,NaOH和KOH质量比3∶2,抗氧剂1035为4 g,硬脂酸钠为9 g,330—340℃保温2.0 h,2,5-二甲基苯酚收率为92.70%,纯度为99.45%。     

Separation and purification of two isomorphic steroids by a novel extractive drowning out crystallization

A novel extraction drowning out crystallization technology was brought forward for separation and purification of two isomorphic steroid pharmaceutical intermediates. In this process, extraction and crystallization are conducted in the same crystallizer simultaneously. The two immiscible (partial miscible) liquid phases were achieved by adding water into the toluene–DMF system. The role played by water is both as an antisolvent for a crystallization and a trigger to generate two immiscible phases for extraction. The advantage of this method is that two relative pure product can be achieved in a crystallization process. The experimental result shows a good prospect of this method for industrial separation of the studied two isomorphic steroids.     

应用降膜结晶法将十二烷二酸从同系物中分离及精制

Separation and purification of dodecanedioic acid (DDDA) from its homologous compounds were studied experimentally by falling film crystallization (FFC). The influences of various operation parameters, including crystallizing time, flow rate of melt and temperature of glycerine bath, on purity of DDDA and crystallizing rate were investigated. Over 99% (by mole) DDDA was obtained for a feed composition of 96% (by mole). The main factors affecting the separation efficiency are flow rate of melt and temperature of glycerine bath. The crystallizing layer of DDDA was further purified by sweating and blasting. A set of optimized operation data are provided for better understanding the mechanism of heat and mass transfer in FFC, and for further industrial application of DDDA purification process.     

熔融结晶工艺开发

通过对熔融结晶工艺的研究,建立了5条熔融结晶选择的经验法则,从而对选择精馏或者熔融结晶工艺提供了借鉴。同时介绍了熔融结晶工艺的试验和工业化方法,从实践角度验证熔融结晶工艺的可行性。另外,对熔融结晶的发展趋势提出了观点和看法。     

盐析结晶法分离铬酸钾

关联了不同温度下K2CrO4在K2CrO4-KOH-H2O体系中的溶解度数据,分析了从K2CrO4-KOH-H2O体系中通过盐析结晶方式分离K2CrO4的可能性;通过K2CrO4-KOH-H2O体系中K2CrO4的盐析结晶实验,得出了初级成核现象发生时,体系的最大过饱和度与过饱和速率之间的动力学关系式及结晶过程中盐析剂浓度、盐析结晶终点K2CrO4收率、溶液体积等工艺参数间的关系,探讨了以KOH作为盐析剂,采用盐析结晶方法从K2CrO4-KOH-H2O体系中分离提纯K2CrO4的可行性,为K2CrO4的高效分离提供了一种新思路。     

High-pressure crystallization and melting of polyethylene in n-pentane

The fluid–solid phase separation and crystallization in relatively dilute solutions of polyethylene in n-pentane at high pressures were studied using time- and angle-resolved laser light scattering techniques. Majority of the experiments were carried out by cooling (crystallization) or heating (melting) while holding the pressure constant at selected pressures in the range from 10 to 54 MPa. Crystallizations were also carried out via two other pathways: (1) cooling without pressure adjustment and (2) first crossing the L–L phase boundary via pressure reduction at constant temperature followed by cooling. Crystallization and melting transitions were assessed from the variations of the transmitted light intensity or the scattered light intensity (averaged over all angles) with temperature. Kinetics of phase separation during both the crystallization and the melting were followed by the time evolution of the angular distribution of the scattered light intensities. The kinetics were typical of nucleation and growth processes. From the time evolution of the light scattering patterns the mean particle radii and their evolution were also followed. The polymer particles that form upon crystallization were collected and characterized using a field emission scanning electron microscope (FESEM) and differential scanning calorimetry (DSC). The results show that the PE crystals that form from these high-pressure conditions display a plate-like morphology, which tend to aggregate into ellipsoid-shape structures. DSC studies show that the PE crystals show higher crystallinity compared to the original polyethylene sample and display multiple melting peaks during the first heating scan, which however collapse to a single melting transition peak after the initial heating scan. The crystals that formed from the experiments in which L–L phase boundary was crossed first were found to display two distinct particle groups. These were attributed to crystals that form from polymer-rich and polymer-lean phases that form when L–L phase boundary is crossed.     

沉淀-吸附法分离纯化马尾松松针儿茶素

采用乙醇回流法提取马尾松松针儿茶素,获儿茶素含量为25.0%的粗提物,用金属离子沉淀-树脂吸附法分离纯化,得纯度为91.45%的儿茶素。用金属离子沉淀-树脂吸附法分离纯化松针乙醇粗提物中儿茶素,工艺简单、收率高、成本低、健康环保,有良好的应用前景。     

Separation of paraffins by membrane extraction combined with crystallization

An integrated mass-exchange process combining liquid-membrane separation with crystallization from solution is experimentally and theoretically investigated. Experiments on separation of binary mixtures of paraffins that have close properties and form mutual solid solutions are carried out. The maximal degree of separation is attained using an aqueous ethanol membrane containing 65 wt % ethanol. From hexadecane-octadecane and hexadecane-tetracosane mixtures containing 86 mol % hexadecane, crystals containing 96.3 and 99.8 mol % hexadecane, respectively, are obtained. The solubility of hexadecane, octadecane, and tetracosane in aqueous ethanol solutions of various concentrations is experimentally studied over a wide temperature range. Using the solubility data, thermodynamic calculations of the liquid-liquid and liquid-crystals equilibria are carried out for the upper and lower boundaries of the aqueous alcohol membrane. A mathematical model of the integrated process is obtained by compiling a set of equations for the diffusion fluxes of the components in the liquid membrane and expressions describing the phase equilibria at the membrane boundaries. A comparison of the experimental data on the separation efficiency with the results of the calculations shows that the diffusion model adequately describes the main features of the integrated process.Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 2, 2005, pp. 120–127.Original Russian Text Copyright © 2005 by Lipatov, Myasnikov, Kulov.     

Isothermal melt crystallization and melting behaviour of syndiotactic polypropylene

The lamellar morphological information and subsequent melting behaviour of syndiotactic polypropylene (s‐PP) samples isothermally crystallized at crystallization temperatures ranging from 30 to 95 °C have been investigated using a combination of wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS) and differential scanning calorimetry (DSC) techniques. Three known methods for determining the equilibrium melting temperature T_m°, namely the Gibbs–Thomson extrapolation, the linear Hoffman–Weeks extrapolation and the non‐linear Hoffman–Weeks extrapolation, have been employed to evaluate this important thermodynamic parameter, and the results obtained are compared. Finally, an estimate of the equilibrium melting temperature for a perfect s‐PP sample (T_m°)_100% is given. © 2000 Society of Chemical Industry