Crystallization 结晶 - 维基百科

Crystallization is the process by which solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some ways by which crystals form are precipitating from a solution, freezing, or more rarely deposition directly from a gas. Attributes of the resulting crystal depend largely on factors such as temperature, air pressure, and in the case of liquid crystals, time of fluid evaporation.
结晶是固体形成的过程,其中的原子或分子高度有序地组织成为一种被称为晶体的结构。形成晶体的一些方式包括从溶液中沉淀、冷冻,或者更少见的直接从气体沉积。最终晶体的属性在很大程度上取决于温度、气压等因素,而在液晶的情况下,还取决于流体蒸发的时间。

Crystallization occurs in two major steps. The first is nucleation, the appearance of a crystalline phase from either a supercooled liquid or a supersaturated solvent. The second step is known as crystal growth, which is the increase in the size of particles and leads to a crystal state. An important feature of this step is that loose particles form layers at the crystal's surface and lodge themselves into open inconsistencies such as pores, cracks, etc.
结晶过程主要分为两个步骤。首先是成核,这是从过冷液体或过饱和溶剂中出现的晶体相。第二步被称为晶体生长,这是粒子大小的增加,导致形成晶体状态。这一步的一个重要特征是,松散的粒子在晶体表面形成层,并将自己嵌入到开放的不一致性中,如孔洞、裂缝等。

The majority of minerals and organic molecules crystallize easily, and the resulting crystals are generally of good quality, i.e. without visible defects. However, larger biochemical particles, like proteins, are often difficult to crystallize. The ease with which molecules will crystallize strongly depends on the intensity of either atomic forces (in the case of mineral substances), intermolecular forces (organic and biochemical substances) or intramolecular forces (biochemical substances).
大多数矿物和有机分子容易结晶,且所得的晶体通常质量良好,即没有可见的缺陷。然而,像蛋白质这样的大型生物化学颗粒往往难以结晶。分子结晶的容易程度强烈依赖于原子力(在矿物质的情况下)、分子间力(有机和生物化学物质)或分子内力(生物化学物质)的强度。

Crystallization is also a chemical solid–liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs. In chemical engineering, crystallization occurs in a crystallizer. Crystallization is therefore related to precipitation, although the result is not amorphous or disordered, but a crystal.
结晶也是一种化学固液分离技术,其中溶质从液体溶液转移到纯固态晶体相。在化学工程中,结晶发生在结晶器中。因此,结晶与沉淀有关,尽管结果不是无定形或无序,而是晶体。

The crystallization process consists of two major events, nucleation and crystal growth which are driven by thermodynamic properties as well as chemical properties. Nucleation is the step where the solute molecules or atoms dispersed in the solvent start to gather into clusters, on the microscopic scale (elevating solute concentration in a small region), that become stable under the current operating conditions. These stable clusters constitute the nuclei. Therefore, the clusters need to reach a critical size in order to become stable nuclei. Such critical size is dictated by many different factors (temperature, supersaturation, etc.). It is at the stage of nucleation that the atoms or molecules arrange in a defined and periodic manner that defines the crystal structure – note that "crystal structure" is a special term that refers to the relative arrangement of the atoms or molecules, not the macroscopic properties of the crystal (size and shape), although those are a result of the internal crystal structure.
结晶过程包含两个主要环节,即成核和晶体生长,这两个环节由热力学性质和化学性质驱动。成核是溶质分子或原子开始在溶剂中聚集成簇的步骤,在微观尺度上(在小区域内提高溶质浓度),这些簇在当前的操作条件下变得稳定。这些稳定的簇构成了核。因此,簇需要达到临界大小才能成为稳定的核。这样的临界大小由许多不同的因素(温度,过饱和度等)决定。在成核阶段,原子或分子以定义和周期性的方式排列,这定义了晶体结构 - 注意,“晶体结构”是一个特殊的术语,指的是原子或分子的相对排列,而不是晶体的宏观属性(大小和形状),尽管这些是内部晶体结构的结果。

The crystal growth is the subsequent size increase of the nuclei that succeed in achieving the critical cluster size. Crystal growth is a dynamic process occurring in equilibrium where solute molecules or atoms precipitate out of solution, and dissolve back into solution. Supersaturation is one of the driving forces of crystallization, as the solubility of a species is an equilibrium process quantified by K_sp. Depending upon the conditions, either nucleation or growth may be predominant over the other, dictating crystal size.
晶体生长是达到临界簇大小的核后续增大的过程。晶体生长是一个动态过程,在这个过程中,溶质分子或原子从溶液中沉淀出来,并重新溶解回溶液。过饱和是结晶的驱动力之一,因为物种的溶解度是一个由K _sp 量化的平衡过程。根据条件的不同,成核或生长可能会优于另一个,从而决定晶体的大小。

Many compounds have the ability to crystallize with some having different crystal structures, a phenomenon called polymorphism. Certain polymorphs may be metastable, meaning that although it is not in thermodynamic equilibrium, it is kinetically stable and requires some input of energy to initiate a transformation to the equilibrium phase. Each polymorph is in fact a different thermodynamic solid state and crystal polymorphs of the same compound exhibit different physical properties, such as dissolution rate, shape (angles between facets and facet growth rates), melting point, etc. For this reason, polymorphism is of major importance in industrial manufacture of crystalline products. Additionally, crystal phases can sometimes be interconverted by varying factors such as temperature, such as in the transformation of anatase to rutile phases of titanium dioxide.
许多化合物具有结晶的能力,其中一些具有不同的晶体结构,这种现象被称为多晶型。某些多晶型可能是亚稳态的,这意味着虽然它不处于热力学平衡状态,但它在动力学上是稳定的,需要一些能量输入才能启动向平衡相的转变。每种多晶型实际上都是不同的热力学固态,同一化合物的晶体多晶型表现出不同的物理性质,如溶解速率、形状(各面之间的角度和面生长速率)、熔点等。因此,多晶型在工业生产晶体产品中具有重要意义。此外,通过改变诸如温度等因素,有时可以相互转化晶体相,如钛白粉的锐钛矿相向金红石相的转变。

Crystal formation can be divided into two types, where the first type of crystals are composed of a cation and anion, also known as a salt, such as sodium acetate. The second type of crystals are composed of uncharged species, for example menthol.
晶体形成可以分为两种类型,第一种类型的晶体由阳离子和阴离子组成,也被称为盐,例如醋酸钠。第二种类型的晶体由未带电的物种组成,例如薄荷醇。

Crystal formation can be achieved by various methods, such as: cooling, evaporation, addition of a second solvent to reduce the solubility of the solute (technique known as antisolvent or drown-out), solvent layering, sublimation, changing the cation or anion, as well as other methods.
晶体的形成可以通过各种方法实现,例如:冷却、蒸发、添加第二种溶剂以降低溶质的溶解度(这种技术被称为反溶剂或淹没法)、溶剂分层、升华、改变阳离子或阴离子,以及其他方法。

The formation of a supersaturated solution does not guarantee crystal formation, and often a seed crystal or scratching the glass is required to form nucleation sites.
超饱和溶液的形成并不能保证晶体的形成,通常需要种晶或刮擦玻璃来形成成核位点。

A typical laboratory technique for crystal formation is to dissolve the solid in a solution in which it is partially soluble, usually at high temperatures to obtain supersaturation. The hot mixture is then filtered to remove any insoluble impurities. The filtrate is allowed to slowly cool. Crystals that form are then filtered and washed with a solvent in which they are not soluble, but is miscible with the mother liquor. The process is then repeated to increase the purity in a technique known as recrystallization.
实验室常用的晶体形成技术是将固体溶解在部分可溶的溶液中,通常需要高温以获得超饱和。然后过滤热混合物以去除任何不溶的杂质。过滤液被允许慢慢冷却。形成的晶体然后被过滤并用它们不溶的溶剂洗涤,但是这种溶剂可以与母液混合。然后重复该过程以提高纯度,这种技术被称为重结晶。

For biological molecules in which the solvent channels continue to be present to retain the three dimensional structure intact, microbatch crystallization under oil and vapor diffusion methods have been the common methods.
对于溶剂通道持续存在以保持三维结构完整的生物分子,微批量在油下结晶和蒸汽扩散方法一直是常见的方法。

1. Tank crystallizers. Tank crystallization is an old method still used in some specialized cases. Saturated solutions, in tank crystallization, are allowed to cool in open tanks. After a period of time the mother liquor is drained and the crystals removed. Nucleation and size of crystals are difficult to control.^{[citation needed]} Typically, labor costs are very high.^{[citation needed]}
   储罐结晶器。储罐结晶是一种古老的方法,仍在一些特殊情况下使用。在储罐结晶中,饱和溶液被允许在开放的储罐中冷却。经过一段时间后,母液被排出,晶体被移除。晶核的形成和晶体的大小难以控制。 ^{[citation needed]} 通常,劳动成本非常高。 ^{[citation needed]}

The crystallization process appears to violate the second principle of thermodynamics. Whereas most processes that yield more orderly results are achieved by applying heat, crystals usually form at lower temperatures – especially by supercooling. However, due to the release of the heat of fusion during crystallization, the entropy of the universe increases, thus this principle remains unaltered.
结晶过程似乎违反了热力学的第二定律。虽然大多数产生更有序结果的过程是通过加热实现的,但晶体通常在较低的温度下形成 - 尤其是通过过冷却。然而,由于结晶过程中熔化热的释放,宇宙的熵增加,因此这个原则仍然没有改变。

The molecules within a pure, perfect crystal, when heated by an external source, will become liquid. This occurs at a sharply defined temperature (different for each type of crystal). As it liquifies, the complicated architecture of the crystal collapses. Melting occurs because the entropy (S) gain in the system by spatial randomization of the molecules has overcome the enthalpy (H) loss due to breaking the crystal packing forces:
在一个纯净、完美的晶体中,分子在外部热源的加热下会变成液体。这种现象在一个明确的温度下发生(每种晶体的温度都不同)。当它液化时,晶体的复杂结构会崩溃。熔化发生是因为分子空间随机化使系统的熵(S)增加,超过了由于破坏晶体堆积力而导致的焓(H)损失:

Regarding crystals, there are no exceptions to this rule. Similarly, when the molten crystal is cooled, the molecules will return to their crystalline form once the temperature falls beyond the turning point. This is because the thermal randomization of the surroundings compensates for the loss of entropy that results from the reordering of molecules within the system. Such liquids that crystallize on cooling are the exception rather than the rule.
对于晶体来说,这个规则没有例外。同样,当熔融的晶体冷却时,一旦温度降到转折点以下,分子将恢复到它们的晶体形态。这是因为周围环境的热随机化补偿了系统内分子重新排列导致的熵的损失。这种在冷却时结晶的液体是例外而不是规则。

The nature of a crystallization process is governed by both thermodynamic and kinetic factors, which can make it highly variable and difficult to control. Factors such as impurity level, mixing regime, vessel design, and cooling profile can have a major impact on the size, number, and shape of crystals produced.
结晶过程的性质受热力学和动力学因素的共同影响,这使得它具有高度的变异性和难以控制。诸如杂质水平、混合方式、容器设计和冷却剖面等因素,都会对产生的晶体的大小、数量和形状产生重大影响。

As mentioned above, a crystal is formed following a well-defined pattern, or structure, dictated by forces acting at the molecular level. As a consequence, during its formation process the crystal is in an environment where the solute concentration reaches a certain critical value, before changing status. Solid formation, impossible below the solubility threshold at the given temperature and pressure conditions, may then take place at a concentration higher than the theoretical solubility level. The difference between the actual value of the solute concentration at the crystallization limit and the theoretical (static) solubility threshold is called supersaturation and is a fundamental factor in crystallization.
以下是翻译内容: 1. 如上所述,晶体的形成遵循一个明确的模式或结构,这是由分子级别的力量所决定的。因此,在形成过程中,晶体处于一个溶质浓度达到某一临界值的环境中,然后才会改变状态。在给定的温度和压力条件下,溶解度阈值以下无法形成固体,然后可能在高于理论溶解度水平的浓度下发生。溶质浓度在结晶限度的实际值与理论(静态)溶解度阈值之间的差异被称为过饱和,这是结晶的一个基本因素。

Nucleation is the initiation of a phase change in a small region, such as the formation of a solid crystal from a liquid solution. It is a consequence of rapid local fluctuations on a molecular scale in a homogeneous phase that is in a state of metastable equilibrium. Total nucleation is the sum effect of two categories of nucleation – primary and secondary.
成核是在小区域内引发相变的过程,例如从液体溶液中形成固体晶体。这是由于在处于亚稳平衡状态的均相相中,分子尺度上的快速局部波动的结果。总成核是两类成核 - 初级和次级的总效应。

Primary nucleation is the initial formation of a crystal where there are no other crystals present or where, if there are crystals present in the system, they do not have any influence on the process. This can occur in two conditions. The first is homogeneous nucleation, which is nucleation that is not influenced in any way by solids. These solids include the walls of the crystallizer vessel and particles of any foreign substance. The second category, then, is heterogeneous nucleation. This occurs when solid particles of foreign substances cause an increase in the rate of nucleation that would otherwise not be seen without the existence of these foreign particles. Homogeneous nucleation rarely occurs in practice due to the high energy necessary to begin nucleation without a solid surface to catalyze the nucleation.
初级成核是在没有其他晶体存在,或者如果系统中存在晶体,它们对过程没有任何影响的情况下,晶体的初始形成。这可以在两种条件下发生。第一种是均质成核,这是不受任何固体影响的成核。这些固体包括结晶器容器的壁和任何外来物质的粒子。然后,第二类是异质成核。这是当外来物质的固体粒子导致成核速率增加,否则在没有这些外来粒子的存在下不会看到这种增加。由于开始成核需要高能量,而没有固体表面来催化成核,所以实践中很少发生均质成核。

Primary nucleation (both homogeneous and heterogeneous) has been modeled as follows:
初级成核(包括均相和非均相)已经被建模如下:

n is an empirical exponent that can be as large as 10, but generally ranges between 3 and 4.
n是一个经验指数,其值可以高达10,但通常在3到4之间。

Secondary nucleation is the formation of nuclei attributable to the influence of the existing microscopic crystals in the magma. Simply put, secondary nucleation is when crystal growth is initiated with contact of other existing crystals or "seeds". The first type of known secondary crystallization is attributable to fluid shear, the other due to collisions between already existing crystals with either a solid surface of the crystallizer or with other crystals themselves. Fluid-shear nucleation occurs when liquid travels across a crystal at a high speed, sweeping away nuclei that would otherwise be incorporated into a crystal, causing the swept-away nuclei to become new crystals. Contact nucleation has been found to be the most effective and common method for nucleation. The benefits include the following:
二次成核是由于熔岩中已存在的微观晶体的影响而形成的核心。简单来说,二次成核就是当晶体生长开始接触其他已存在的晶体或“种子”时。已知的第一种二次结晶是由于流体剪切,另一种是由于已存在的晶体与结晶器的固体表面或其他晶体本身的碰撞。当液体以高速穿过晶体时,会发生流体剪切成核,这会将本来会被吸入晶体的核心带走,使被带走的核心变成新的晶体。接触成核被发现是最有效和最常见的成核方法。其优点包括以下几点:

• Low kinetic order and rate-proportional to supersaturation, allowing easy control without unstable operation.
  低动力学顺序和与过饱和度成比例的速率,允许在无不稳定操作的情况下轻松控制。
• Occurs at low supersaturation, where growth rate is optimal for good quality.
  在过饱和度较低的地方发生,此处的生长速率对于良好的质量是最佳的。
• Low necessary energy at which crystals strike avoids the breaking of existing crystals into new crystals.
  低能量的晶体撞击避免了现有晶体破裂成新的晶体。
• The quantitative fundamentals have already been isolated and are being incorporated into practice.
  定量基础已经被分离出来,并正在被纳入实践中。

The following model, although somewhat simplified, is often used to model secondary nucleation:
下面的模型,虽然有些简化,但常被用来模拟二次成核:

j is an empirical exponent that can range up to 1.5, but is generally 1,
j是一个经验指数,其范围可达到1.5,但通常为1。

b is an empirical exponent that can range up to 5, but is generally 2.
b是一个经验指数,其范围可达到5,但通常为2。

Once the first small crystal, the nucleus, forms it acts as a convergence point (if unstable due to supersaturation) for molecules of solute touching – or adjacent to – the crystal so that it increases its own dimension in successive layers. The pattern of growth resembles the rings of an onion, as shown in the picture, where each colour indicates the same mass of solute; this mass creates increasingly thin layers due to the increasing surface area of the growing crystal. The supersaturated solute mass the original nucleus may capture in a time unit is called the growth rate expressed in kg/(m²*h), and is a constant specific to the process. Growth rate is influenced by several physical factors, such as surface tension of solution, pressure, temperature, relative crystal velocity in the solution, Reynolds number, and so forth.
一旦第一个小晶体,即核心形成,它就会作为一个汇聚点(如果由于过饱和而不稳定)对于接触或邻近晶体的溶质分子,使其通过连续的层次增加自身的尺寸。生长模式类似于洋葱的环,如图所示,每种颜色代表相同的溶质质量;这种质量由于生长晶体的表面积的增加而形成越来越薄的层。原始核心在一个时间单位内可能捕获的过饱和溶质质量被称为生长速率,以kg/(m ² *h)表示,这是特定于该过程的常数。生长速率受到几个物理因素的影响,如溶液的表面张力,压力,温度,晶体在溶液中的相对速度,雷诺数等。

• Supersaturation value, as an index of the quantity of solute available for the growth of the crystal;
  超饱和值,作为晶体生长可用溶质量的指标;
• Total crystal surface in unit fluid mass, as an index of the capability of the solute to fix onto the crystal;
  作为溶质固定到晶体上能力的指标,单位流体质量中的总晶体表面;
• Retention time, as an index of the probability of a molecule of solute to come into contact with an existing crystal;
  保留时间,作为溶质分子与现有晶体接触的可能性的指标;
• Flow pattern, again as an index of the probability of a molecule of solute to come into contact with an existing crystal (higher in laminar flow, lower in turbulent flow, but the reverse applies to the probability of contact).
  流动模式,再次作为溶质分子与已存在晶体接触的可能性的指标(在层流中较高,在湍流中较低,但接触的可能性则相反)。

The first value is a consequence of the physical characteristics of the solution, while the others define a difference between a well- and poorly designed crystallizer.
第一个值是溶液物理特性的结果,而其他的则定义了设计良好的结晶器与设计不佳的结晶器之间的差异。

The appearance and size range of a crystalline product is extremely important in crystallization. If further processing of the crystals is desired, large crystals with uniform size are important for washing, filtering, transportation, and storage, because large crystals are easier to filter out of a solution than small crystals. Also, larger crystals have a smaller surface area to volume ratio, leading to a higher purity. This higher purity is due to less retention of mother liquor which contains impurities, and a smaller loss of yield when the crystals are washed to remove the mother liquor. In special cases, for example during drug manufacturing in the pharmaceutical industry, small crystal sizes are often desired to improve drug dissolution rate and bio-availability. The theoretical crystal size distribution can be estimated as a function of operating conditions with a fairly complicated mathematical process called population balance theory (using population balance equations).
结晶产品的外观和尺寸范围在结晶过程中极为重要。如果需要对晶体进行进一步处理,大的、尺寸均匀的晶体对于洗涤、过滤、运输和储存都非常重要,因为大晶体比小晶体更容易从溶液中过滤出来。此外,大晶体的表面积与体积比例较小,导致其纯度更高。这种更高的纯度是由于母液(含有杂质)的保留较少,以及在洗涤晶体以去除母液时,产量损失较小。在特殊情况下,例如在制药行业的药物制造过程中,通常希望得到小的晶体尺寸,以提高药物的溶解速率和生物利用度。理论上的晶体尺寸分布可以通过一个相当复杂的数学过程(使用种群平衡方程)作为操作条件的函数进行估算。

So one may identify two main families of crystallization processes:
因此,我们可以识别出两大主要的结晶过程家族:

This division is not really clear-cut, since hybrid systems exist, where cooling is performed through evaporation, thus obtaining at the same time a concentration of the solution.
这种划分并不十分明确,因为存在混合系统,其中通过蒸发进行冷却,从而同时获得溶液的浓缩。

A crystallization process often referred to in chemical engineering is the fractional crystallization. This is not a different process, rather a special application of one (or both) of the above.
在化学工程中经常提到的一种结晶过程是分级结晶。这并不是一个不同的过程,而是上述过程中的一种(或两种)特殊应用。

Most chemical compounds, dissolved in most solvents, show the so-called direct solubility that is, the solubility threshold increases with temperature.
大多数化学化合物在大多数溶剂中显示所谓的直接溶解性,也就是说,溶解度阈值随着温度的升高而增加。

So, whenever the conditions are favorable, crystal formation results from simply cooling the solution. Here cooling is a relative term: austenite crystals in a steel form well above 1000 °C. An example of this crystallization process is the production of Glauber's salt, a crystalline form of sodium sulfate. In the diagram, where equilibrium temperature is on the x-axis and equilibrium concentration (as mass percent of solute in saturated solution) in y-axis, it is clear that sulfate solubility quickly decreases below 32.5 °C. Assuming a saturated solution at 30 °C, by cooling it to 0 °C (note that this is possible thanks to the freezing-point depression), the precipitation of a mass of sulfate occurs corresponding to the change in solubility from 29% (equilibrium value at 30 °C) to approximately 4.5% (at 0 °C) – actually a larger crystal mass is precipitated, since sulfate entrains hydration water, and this has the side effect of increasing the final concentration.
因此,只要条件有利,晶体的形成就是通过简单地冷却溶液而产生的。这里的冷却是一个相对的概念:在钢中的奥氏体晶体在1000°C以上就能形成。这个结晶过程的一个例子是格劳伯盐的生产,这是硫酸钠的一种晶体形式。在图中,平衡温度在x轴上,平衡浓度(饱和溶液中溶质的质量百分比)在y轴上,可以清楚地看到硫酸盐的溶解度在32.5°C以下迅速减少。假设在30°C时有一个饱和溶液,通过将其冷却到0°C(注意,这是由于冰点降低而成为可能),相应的会有一部分硫酸盐沉淀出来,这部分硫酸盐的质量对应了从29%(30°C时的平衡值)到大约4.5%(0°C时)的溶解度变化 - 实际上,沉淀出来的晶体质量更大,因为硫酸盐带走了水合水,这会增加最终的浓度。

There are limitations in the use of cooling crystallization:
冷却结晶法的使用存在一些限制:

• Many solutes precipitate in hydrate form at low temperatures: in the previous example this is acceptable, and even useful, but it may be detrimental when, for example, the mass of water of hydration to reach a stable hydrate crystallization form is more than the available water: a single block of hydrate solute will be formed – this occurs in the case of calcium chloride);
  许多溶质在低温下以水合物形式沉淀:在前面的例子中,这是可以接受的,甚至是有用的,但是当例如,达到稳定的水合物结晶形式所需的水分质量超过了可用水分时,这可能是有害的:将形成一个水合物溶质的单一块体 - 这在氯化钙的情况下会发生
• Maximum supersaturation will take place in the coldest points. These may be the heat exchanger tubes which are sensitive to scaling, and heat exchange may be greatly reduced or discontinued;
  最大过饱和通常会发生在最冷的地方。这些地方可能是对结垢敏感的热交换器管道,热交换可能会大大减少或中断。
• A decrease in temperature usually implies an increase of the viscosity of a solution. Too high a viscosity may give hydraulic problems, and the laminar flow thus created may affect the crystallization dynamics.
  温度的降低通常意味着溶液的粘度会增加。过高的粘度可能会导致液压问题,由此产生的层流可能会影响结晶动力学。
• It is not applicable to compounds having reverse solubility, a term to indicate that solubility increases with temperature decrease (an example occurs with sodium sulfate where solubility is reversed above 32.5 °C).
  这不适用于具有反向溶解性的化合物,这个术语指的是溶解度随着温度的降低而增加(例如在钠硫酸盐中,溶解度在32.5°C以上反转)。

The simplest cooling crystallizers are tanks provided with a mixer for internal circulation, where temperature decrease is obtained by heat exchange with an intermediate fluid circulating in a jacket. These simple machines are used in batch processes, as in processing of pharmaceuticals and are prone to scaling. Batch processes normally provide a relatively variable quality of the product along with the batch.
最简单的冷却结晶器是配备了内部循环混合器的储罐,通过与夹套中循环的中间流体进行热交换来降低温度。这些简单的机器在批量生产过程中被使用,如在制药过程中,且容易产生结垢。批量生产过程通常会导致产品质量随批次的变化相对不稳定。

The Swenson-Walker crystallizer is a model, specifically conceived by Swenson Co. around 1920, having a semicylindric horizontal hollow trough in which a hollow screw conveyor or some hollow discs, in which a refrigerating fluid is circulated, plunge during rotation on a longitudinal axis. The refrigerating fluid is sometimes also circulated in a jacket around the trough. Crystals precipitate on the cold surfaces of the screw/discs, from which they are removed by scrapers and settle on the bottom of the trough. The screw, if provided, pushes the slurry towards a discharge port.
Swenson-Walker结晶器是一种模型,由Swenson公司在1920年左右特别设计,它有一个半圆形的水平空心槽,其中有一个空心螺旋输送器或一些空心盘,冷却液体在其中循环,在纵向轴线上旋转。冷却液体有时也在槽周围的夹套中循环。晶体在螺旋/盘的冷表面上沉淀,然后被刮刀去除并沉积在槽底部。如果提供了螺旋,它会将浆料推向排放口。

A common practice is to cool the solutions by flash evaporation: when a liquid at a given T₀ temperature is transferred in a chamber at a pressure P₁ such that the liquid saturation temperature T₁ at P₁ is lower than T₀, the liquid will release heat according to the temperature difference and a quantity of solvent, whose total latent heat of vaporization equals the difference in enthalpy. In simple words, the liquid is cooled by evaporating a part of it.
一种常见的做法是通过闪蒸来冷却溶液:当一个给定温度T ₀ 的液体被转移到一个压力P ₁ 的腔室中,使得液体在压力P ₁ 下的饱和温度T ₁ 低于T ₀ 时,液体会根据温差释放热量,并且一定量的溶剂,其总潜热等于焓差。简单来说,就是通过蒸发部分液体来冷却液体。

In the sugar industry, vertical cooling crystallizers are used to exhaust the molasses in the last crystallization stage downstream of vacuum pans, prior to centrifugation. The massecuite enters the crystallizers at the top, and cooling water is pumped through pipes in counterflow.
在糖业中,垂直冷却结晶器被用于在真空锅后的最后结晶阶段排出糖蜜,然后进行离心。糖浆从结晶器顶部进入,冷却水通过管道以逆流方式泵送。

Another option is to obtain, at an approximately constant temperature, the precipitation of the crystals by increasing the solute concentration above the solubility threshold. To obtain this, the solute/solvent mass ratio is increased using the technique of evaporation. This process is insensitive to change in temperature (as long as hydration state remains unchanged).
另一种选择是在大致恒定的温度下,通过提高溶质浓度超过溶解度阈值,来获得晶体的沉淀。为了实现这一点,我们会使用蒸发技术来增加溶质/溶剂的质量比。只要保持水合状态不变,这个过程对温度变化不敏感。

All considerations on control of crystallization parameters are the same as for the cooling models.
所有关于控制结晶参数的考虑与冷却模型的考虑是一样的。

Most industrial crystallizers are of the evaporative type, such as the very large sodium chloride and sucrose units, whose production accounts for more than 50% of the total world production of crystals. The most common type is the forced circulation (FC) model (see evaporator). A pumping device (a pump or an axial flow mixer) keeps the crystal slurry in homogeneous suspension throughout the tank, including the exchange surfaces; by controlling pump flow, control of the contact time of the crystal mass with the supersaturated solution is achieved, together with reasonable velocities at the exchange surfaces. The Oslo, mentioned above, is a refining of the evaporative forced circulation crystallizer, now equipped with a large crystals settling zone to increase the retention time (usually low in the FC) and to roughly separate heavy slurry zones from clear liquid. Evaporative crystallizers tend to yield larger average crystal size and narrows the crystal size distribution curve.
大多数工业结晶器都是蒸发型的,例如非常大的氯化钠和蔗糖单元,其生产占全球晶体总产量的50%以上。最常见的类型是强制循环(FC)模型(参见蒸发器)。一个泵送设备(泵或轴流搅拌器)保持整个罐内的晶体浆料均匀悬浮,包括交换表面;通过控制泵流量,实现了对晶体质量与过饱和溶液接触时间的控制,以及在交换表面上的合理速度。上述的奥斯陆,是蒸发强制循环结晶器的改进,现在配备了一个大的晶体沉降区,以增加滞留时间(在FC中通常较低)并大致分离重浆区与清液。蒸发结晶器倾向于产生较大的平均晶体尺寸,并缩小晶体尺寸分布曲线。

Whichever the form of the crystallizer, to achieve an effective process control it is important to control the retention time and the crystal mass, to obtain the optimum conditions in terms of crystal specific surface and the fastest possible growth. This is achieved by a separation – to put it simply – of the crystals from the liquid mass, in order to manage the two flows in a different way. The practical way is to perform a gravity settling to be able to extract (and possibly recycle separately) the (almost) clear liquid, while managing the mass flow around the crystallizer to obtain a precise slurry density elsewhere. A typical example is the DTB (Draft Tube and Baffle) crystallizer, an idea of Richard Chisum Bennett (a Swenson engineer and later President of Swenson) at the end of the 1950s. The DTB crystallizer (see images) has an internal circulator, typically an axial flow mixer – yellow – pushing upwards in a draft tube while outside the crystallizer there is a settling area in an annulus; in it the exhaust solution moves upwards at a very low velocity, so that large crystals settle – and return to the main circulation – while only the fines, below a given grain size are extracted and eventually destroyed by increasing or decreasing temperature, thus creating additional supersaturation. A quasi-perfect control of all parameters is achieved as DTF crystallizers offer superior control over crystal size and characteristics. This crystallizer, and the derivative models (Krystal, CSC, etc.) could be the ultimate solution if not for a major limitation in the evaporative capacity, due to the limited diameter of the vapor head and the relatively low external circulation not allowing large amounts of energy to be supplied to the system.
无论结晶器的形式如何,为了实现有效的过程控制,控制滞留时间和晶体质量是非常重要的,以便在晶体比表面和最快可能的生长方面获得最佳条件。这是通过将晶体与液体质量分离(简单地说)来实现的,以便以不同的方式管理这两种流动。实际的方法是进行重力沉降,以便能够提取(并可能单独回收)(几乎)清晰的液体,同时管理结晶器周围的质量流动,以在其他地方获得精确的浆料密度。一个典型的例子是DTB(Draft Tube and Baffle)结晶器,这是理查德·奇瑟姆·贝内特(Richard Chisum Bennett,Swenson的一位工程师,后来成为Swenson的总裁)在1950年代末的一个想法。DTB结晶器(见图片)有一个内部循环器,通常是一个轴流混合器 - 黄色 - 在导管中向上推,而在结晶器外部有一个在环形区域内的沉降区;在这个区域,排气溶液以非常低的速度向上移动,使得大的晶体沉降 - 并返回到主循环 - 而只有细小的颗粒,低于给定的粒度大小被提取出来,并最终通过增加或降低温度而被破坏,从而产生额外的过饱和。由于DTF结晶器提供了对晶体大小和特性的优越控制,因此实现了所有参数的几乎完美控制。这种结晶器和衍生模型(Krystal,CSC等)可能是最终的解决方案,如果不是由于蒸发能力的主要限制,由于蒸汽头的直径有限,以及相对较低的外部循环不允许大量的能量供给到系统。

1. ^ Lin, Yibin (2008). "An Extensive Study of Protein Phase Diagram Modification:Increasing Macromolecular Crystallizability by Temperature Screening". Crystal Growth & Design. 8 (12): 4277. doi:10.1021/cg800698p.
   ^林一斌 (2008). "蛋白质相图修改的广泛研究:通过温度筛选提高大分子的结晶性". 晶体生长与设计. 8 (12): 4277. doi: 10.1021/cg800698p.
2. ^ Chayen, Blow (1992). "Microbatch crystallization under oil – a new technique allowing many small-volume crystallization trials". Journal of Crystal Growth. 122 (1–4): 176–180. Bibcode:1992JCrGr.122..176C. doi:10.1016/0022-0248(92)90241-A.
   ^Chayen, Blow (1992). "油下微批结晶 - 一种新技术,允许进行许多小体积的结晶试验". 晶体生长杂志. 122 (1–4): 176–180. Bibcode: 1992JCrGr.122..176C. doi: 10.1016/0022-0248(92)90241-A.
3. ^ Benvenuti, Mangani (2007). "Crystallization of soluble proteins in vapor diffusion for x-ray crystallography". Nature Protocols. 2 (7): 1633–1651. doi:10.1038/nprot.2007.198. PMID 17641629.
   ^Benvenuti, Mangani (2007). "溶解性蛋白质在蒸气扩散中的结晶化以进行X射线晶体学研究". 自然协议. 2 (7): 1633–1651. doi: 10.1038/nprot.2007.198. PMID 17641629.

• Geankoplis, C.J. (2003) "Transport Processes and Separation Process Principles". 4th Ed. Prentice-Hall Inc.
  Geankoplis, C.J. (2003) "运输过程与分离过程原理". 第四版. Prentice-Hall Inc.
• Glynn P.D. and Reardon E.J. (1990) "Solid-solution aqueous-solution equilibria: thermodynamic theory and representation". Amer. J. Sci. 290, 164–201.
  Glynn P.D. 和 Reardon E.J. (1990) "固溶体-溶液平衡:热力学理论与表示". 美国科学杂志. 290, 164–201.
• Jancic, S. J.; Grootscholten, P.A.M.: “Industrial Crystallization”, Textbook, Delft University Press and Reidel Publishing Company, Delft, The Netherlands, 1984.
  Jancic, S. J.; Grootscholten, P.A.M.: "工业结晶", 教科书, 德尔夫特大学出版社和Reidel出版公司, 荷兰德尔夫特, 1984年。