PTT的等温与非等温结晶动力学研究

采用DSC方法对聚对苯二甲酸丙二酯进行等温与非等温结晶动力学研究,利用不同动力学模型对其结晶过程进行分析.结果表明,在等温结晶过程中,Avrami指数n和半结晶时间随着结晶温度的升高而增大,结晶速率常数K随着结晶温度的升高而减小;在非等温结晶的过程中,结晶动力学常数Zc和相对过冷度△Tc随着降温速率的提高而上升,Avr...     

铬酸钾电解-结晶制备重铬酸钾的工艺

利用阳离子膜,以K2CrO4电解结晶制备K2Cr2O7,考察了电流密度、温度、阴极液KOH浓度、阳极液K2CrO4浓度等因素对转化率、电流效率和直流能耗的影响;研究了K2Cr2O7不同浓度、不同转化率下的结晶纯度和收率及搅拌速率、降温速率和晶种加入量等对晶体粒度分布和形貌的影响. 结果表明,最佳电解工艺条件为：电流密度0.2 A/cm2,电解温度80℃,阴极液KOH浓度50 g/L,阳极液K2CrO4浓度400 g/L. K2Cr2O7转化率大于90%时,结晶纯度不低于99.8%. 优化的结晶条件为：溶液初始K2Cr2O7浓度500 g/L,搅拌速率300 r/min,降温速率0.5℃/min,不添加晶种. 所得产品符合GB 28657-2012要求.     

熔融结晶法提纯邻碘苯胺工艺

利用熔融结晶法对邻碘苯胺混合物进行分离提纯,考察并分析了降温速率、结晶终温、养晶时间、升温速率和发汗终温对产品收率和纯度的影响。邻碘苯胺质量分数为70. 95%时的最佳结晶工艺:以降温速率0. 3 K/5 min降温到结晶终温301. 15 K,使固体熔融液结晶,养晶时间为2 h;再升温发汗,升温速率为0. 2 K/5 min,升到发汗终温至313. 15 K结束。实验得到质量分数为99. 07%的邻碘苯胺,产品收率为61. 75%。     

KH_2PO_4-KNO_3-H_2O三元水盐体系在313.15 K条件下相图的测定和研究

采用等温溶解平衡法测定KH_2PO_4-KNO_3-H_2O三元水盐体系在313.15 K条件下的溶解度,并利用湿渣法和XRD对平衡固相进行分析和验证。根据实验数据绘制相图,相图结果表明,KH_2PO_4-KNO_3-H_2O体系的溶解度等温线有一个三元共饱和点,两条分支,将相图划分为4个区域:不饱和区、KH_2PO_4结晶区、KNO_3结晶区和KH_2PO_4-KNO_3的混合结晶区。313.15 K下的共饱和点组成为w(KH_2PO_4)7.76%、w(KNO_3)33.24%。同时,测定溶液的密度,画出三元体系溶液密度与KNO_3含量的关系图,并将实验测定的密度值与密度模型计算的密度值进行比较,验证了该密度模型的可靠性。     

甲醇-水溶剂中L-苯丙氨酸结晶热力学

在293.15～322.15 K温度范围内,研究L-苯丙氨酸无水物在甲醇-水混合溶剂中溶解度和超溶解度特性,得到L-苯丙氨酸无水物结晶介稳区,计算了成核级数及成核速率,考察了不同初始温度和降温速率对介稳区宽度的影响,并通过研究L-苯丙氨酸297.15 K和302.15 K的转晶水活度,依据溶解度特性绘制L-苯丙氨酸-甲醇-水在该温度下的三元相图。溶解度数据用Apelblat方程、λh方程关联、vant Hoff方程拟合。结果表明,L-苯丙氨酸无水物溶解度随温度的升高而增大,随甲醇体积分数的增加而减小;L-苯丙氨酸无水物结晶介稳区宽度在相同条件下,随初始温度的升高,降温速率的降低变窄;L-苯丙氨酸转晶水活度随温度的升高而增大。     

头孢拉定连续结晶工艺研究

采用三级混合悬浮混合产品出料结晶器(MSMPR),搭建了头孢拉定连续结晶实验装置。通过单因素实验研究了养晶pH值、晶种添加量、原料液浓度、停留时间、结晶系统温度及搅拌速率等结晶工艺条件对头孢拉定连续结晶产品收率及粒度分布的影响,优化了头孢拉定连续结晶工艺参数。通过实验获得优化结晶工艺参数：结晶温度293.15 K,搅拌速率180 r·min^-1,养晶pH=2.85,晶种添加量为3%(质量分数),头孢拉定原料液浓度11%(质量分数),停留时间33.3 min,此条件下可以获得平均粒径为85.3μm,收率为76.53%的头孢拉定连续结晶产品。     

冷冻共晶法结晶谷氨酸钠介稳区测定

冷冻共晶技术的最大特点是冰晶和固体盐同时结晶析出,介稳区的测定是冷冻共晶操作的关键研究之一。文中采用静态法测定了谷氨酸钠在0℃以下的溶解度。实验结果表明:随着温度的降低,谷氨酸钠的溶解度降低。利用FBRM,PVM在线监测系统测定了谷氨酸钠在不同的搅拌速率、降温速率、晶种加入量条件下的超溶解度。根据溶解度和超溶解度曲线,确定了谷氨酸钠的介稳区宽度。研究表明:在一定条件下,搅拌速率越小、降温速率越快、加入晶种量越多,谷氨酸钠介稳区越宽。测定的介稳区数据为后续谷氨酸钠冷冻共结晶实验打下基础。     

甲醇-水溶剂中L-苯丙氨酸结晶热力学

在293.15~322.15 K温度范围内，研究L-苯丙氨酸无水物在甲醇-水混合溶剂中溶解度和超溶解度特性，得到L-苯丙氨酸无水物结晶介稳区，计算了成核级数及成核速率，考察了不同初始温度和降温速率对介稳区宽度的影响，并通过研究L-苯丙氨酸297.15 K和302.15 K的转晶水活度，依据溶解度特性绘制L-苯丙氨酸-甲醇-水在该温度下的三元相图。溶解度数据用Apelblat方程、λh方程关联、van t Hoff方程拟合。结果表明，L-苯丙氨酸无水物溶解度随温度的升高而增大，随甲醇体积分数的增加而减小；L-苯丙氨酸无水物结晶介稳区宽度在相同条件下，随初始温度的升高，降温速率的降低变窄；L-苯丙氨酸转晶水活度随温度的升高而增大。     

PPS/GF复合材料非等温结晶性能研究

通过差示扫描量热法研究了聚苯硫醚(PPS)/玻璃纤维(GF)复合材料的非等温结晶过程,采用了Ozawa法和R-t法分析了GF质量分数为40%的PPS/GF复合材料的非等温结晶动力学特性。结果表明,随着GF用量的增加,复合材料的结晶度呈现先降低后增加的趋势,结晶速率加快,结晶趋于完善;当GF质量分数为40%时,随着降温速率的提高,复合材料的过冷度和结晶速率增大,结晶变得不完善。Ozawa法和R-t法能够描述GF质量分数为40%的PPS/GF复合材料的非等温结晶行为,Ozawa法计算结果表明,复合材料的Ozawa指数和结晶速率常数均随结晶温度的升高而增大,R-t法计算结果表明不同相对结晶度下降温速率与时间的自然对数间的线性关系良好。     

右佐匹克隆拆分工艺优化

利用外消旋体在溶液中溶解度相互竞争的特点,在使用结晶法拆分消旋佐匹克隆时,加入少量的右佐匹克隆或其苹果酸盐,通过与D-苹果酸成盐、冷却结晶的方法,可以简便有效地拆分出右佐匹克隆D-苹果酸盐,再经过中和、萃取、浓缩、结晶,即可得到右佐匹克隆。通过控制加入的右佐匹克隆或其苹果酸盐的量,得到了光学纯度(ee)大于99.9%的右佐匹克隆,且其收率在35%以上。     

膜辅助添加晶种的过硫酸铵冷却结晶在线监测与过程调控

冷却结晶是经典的溶液结晶过程,常用于分离溶解度随温度变化较大的物质,制备高品质晶体产品。直接进行降温会导致成核速率不可控,得到的晶体产品质量差。在工业中通常选择在溶液结晶介稳区内投放适量晶种来诱导成核,但晶种制备过程复杂,而且成功的添加晶种过程取决于晶种的粒度分布、数量、投放时机和操作人员的经验等因素,降低了产品质量的批次重复性。本文利用聚四氟乙烯（PTFE）中空纤维膜组件为结晶溶液和冷却液提供换热界面,结晶溶液温度降低,在膜界面处形成较均匀的过冷度梯度,进而在低过饱和度下发生异相成核,实现膜辅助添加晶种的过硫酸铵冷却结晶过程调控。膜组件中产生的晶种进入结晶釜中继续生长,将成核和生长过程进行解耦。在线结晶检测系统捕捉到的照片证实了通过控制膜组件使用温度和时长两个操作参数便可得到具有较好的形貌、较窄的粒度分布的晶种。相比直接冷却结晶,在相近的降温速率下,膜辅助添加晶种过程制备的晶体产品具有更大的平均粒径,且粒度分布更集中,表面更加光滑。因此,膜辅助冷却结晶呈现了良好的成核控制能力,有望实现晶种自动制备和添加功能,为高附加值晶体产品的冷却结晶过程开发提供了新方向。     

低温控温结晶法分离提纯1,8-桉叶油素的工艺

采用全结晶工艺对原料桉叶油[w(cineole)=63.24%]进行分离提纯,在无晶种添加下,降温速率4℃/h、结晶终温-30℃、发汗速率5℃/h、发汗终温-19℃时,可将原料油提纯至77.52%。添加晶种后,可有效提高操作温度,缩小结晶温度的操作范围,提高产品的纯度,在降温速率4℃/h、结晶终温-25℃、发汗速率4℃/h、发汗终温-6℃的操作条件下,将原料油提纯至89.63%。实验得到了低温控温添加晶种结晶法分离提纯1,8-桉叶油素的适宜工艺流程和操作参数,该方法相对其他分离方法具有较为明显的优势。     

Chiral separation using a novel combination of cooling crystallization and a membrane barrier: Resolution of DL-glutamic acid

Chiral separation of racemic mixtures is essential in the production of many pharmaceutical compounds. The present work describes a novel chiral separation technique that combines cooling crystallization and a membrane separation that is used in DL-glutamic acid resolution. The process utilizes two crystallization chambers that are separated by a membrane that prevents transport of crystals from one chamber to another. Importantly, conditions must be controlled so that only a pure species crystallizes in each of the chambers. This is done by appropriate addition of seed crystals to each chamber and by restricting the formation of new crystals to secondary nucleation mechanisms. The seed crystals may grow or participate in secondary nucleation, but conditions must be controlled so as to prevent primary nucleation, which would result in the formation of both crystal species in each chamber. Experiments were conducted with different amounts of seed crystals to determine operating conditions that produce the high product yield and purity. The results show that this novel chiral separation process is promising: the product purity was over 94% (with a separation factor of 16) and the product yield was increased by as much as 56% more than could be obtained with simple cooling crystallization.     

甲钴胺溶解度的测定和关联

在甲钴胺的结晶分离纯化过程中,溶解度数据至关重要。本文采用静态法测定了273～335K范围内甲钴胺在溶剂——纯水、乙醇及丙酮：水=8：1的混合溶剂中的溶解度数据,为结晶方案的确定和结晶工艺条件的优化提供了基础的热力学数据。实验结果表明,甲钴胺在纯溶剂水或乙醇中的溶解度随着温度的升高而增加;此外,甲钴胺在丙酮：水=8：1混合溶剂中几乎不溶解。采用Apelblat模型和经验多项式方程关联测定结果,其溶解度关联值和实验值比较吻合。这为采用溶析结晶法分离甲钴胺提供了理论基础。     

Effect of initial dextrose concentration,seeding and cooling profile on the crystallization of dextrose monohydrate

A batch seeded cooling crystallizer was used to study dextrose monohydrate crystallization. Experiments were conducted to investigate how a 2% increase in the initial dextrose concentration (from 65.5 to 67.5%) would influence final crystal yield and size. The crystallizations were performed for three different seed masses and cooling profiles, consequently the influence of these parameters was also investigated. The parameters were varied in accordance with an industrial scale process. An in-line focused beam reflectance measurement probe and an in-line process refractometer were used to continuously monitor the crystallizations. The experimental results showed that the 2% increase in initial dextrose concentration had a major influence on the rate of crystallization and yield over a 24 h crystallization period, and only a minor influence on the median crystal size.     

果糖结晶过程优化

通过实验筛选得到适合果糖结晶的混合溶剂,利用中通量结晶仪器Crystalline测定了果糖在水-乙醇（水的摩尔分数为0.39）混合溶剂中的溶解度和介稳区,采用Apelblat方程拟合了溶解度数据。基于热力学数据设计了晶种引晶的果糖冷却结晶工艺,过程优化得到的产品收率可达78.2%以上,纯度可达99%以上,晶体形貌规则,表面光滑,粒度分布窄。当晶体粒径大于100 μm时,利用粒度无关生长的粒数衡算方程建立了果糖连续结晶过程的动力学模型,模型表明晶体生长级数大于成核级数。     

Effect of cooling mode on product crystal size in seeded batch crystallization of potassium alum

Potassium alum was crystallized by seeding in a batch crystallizer under controlled and natural cooling modes. Regardless of the cooling mode, the product crystal size distribution (CSD) became bi-modal at low seed concentrations because of enormous secondary nucleation. The mean mass size of the product was smaller for the natural cooling mode compared to that for the controlled cooling mode with more intensive secondary nucleation. On the other hand, at high seed concentrations, the product CSD became uni-modal with the same mean mass size for both cooling modes, where the crystallization was dominated by seed growth. The low supersaturation caused by the growth of enough seeds plays a key role to produce uni-modal size distribution with suppressed nucleation. Adhering of small crystals (secondary nuclei) to growing seed crystals is also considered to be another mechanism for generating uni-modal CSD.     

Modeling of crystal growth and nucleation rates for pentaerythritol batch crystallization

The kinetics of crystallization – nucleation and crystal growth – was determined for a seeded batch cooling process. Several experiments were done utilizing always the same condition: initial concentration, seed mass and size distribution, and cooling rate. From one experiment to other the agitation speed was varied. As the utilized reactor is able to measure torque of the impeller, the power dissipated in agitation was monitored during the crystallization, as well as reactor temperature and turbidity of the suspension. Turbidity monitoring and the measurement of particle size distribution from seeds and final product allowed obtaining the evolution of the second moment of the particles during the crystallization. The crystallization process was modeled utilizing the Method of Moments and the nucleation and crystal growth kinetics were obtained from least-square minimization of calculated second moments of the crystals. A crystal growth kinetic was determined and the secondary nucleation rate was described as a function of dissipated power and as functions of impeller tip speed. Additional experiments were done, in which cooling rate, seed mass and seed size were varied. The calculated kinetics could satisfactorily describe the results of the additional experiments, corroborating the quality of the modeling.