大学化工专业英语Lesson-5

Chlor-Alkali and Related Processes氯碱工业与相关过程Historically the bulk chemical industry was built on chlor-alkali and related processes. 纵观历史，大部分化学工业是建立在氯碱工业及其相关过程之上。The segment is normally taken to include the production of chlorine gas, caustic soda（sodium hydroxide）, soda-ash（derivatives of sodium carbonate in various forms） and, for convenience, lime-based products. 该部分通常包括氯气、苛性钠（氢氧化钠）、无水碳酸钠（以各种形式存在的碳酸钠的衍生物），以及以石灰为基础的产品。Soda-ash and sodium hydroxide have competed with each other as the major source of alkali ever since viable processes were discovered for both. 作为碱的主要来源，自从发现很多过程对于纯碱和火碱都是可行的，它们就相互竞争。The peculiar economics of electrolytic processes mean that you have to make chlorine and caustic soda together in a fixed ratio whatever the relative demand for the two totally different types of product, and this causes swings in the price of caustic soda which can render soda-ash more or less favorable as an alkali. 电解过程的特殊经济性意味着，不管对氯气和氢氧化钠这两种不同类型的产品的相对需求量如何，你只有以固定的比例同时制备氯气和氢氧化钠。这引起了氢氧化钠的价格的摇摆不定，从而使得纯碱作为一种碱或多或少有利。Both chlorine/caustic soda and soda-ash production are dependent on cheap readily available supplies of raw materials. 氯气/氢氧化钠和纯碱的生产都依赖于廉价的现成的原材料供应。Chlorine/caustic soda requires a ready supply of cheap brine and electricity, soda-ash requires brine, limestone and lots of energy. 氯气/氢氧化钠需要廉价的现成的卤水和电力的供应，纯碱需要卤水、石灰石和大量的能量。Soda-ash plants are only profitable if their raw materials do not have to be transported far. 如果纯碱厂的原材料不需要运输的话，它们是盈利的。The availability of such supplies is a major factor in the location of many of the chemical industrys great complexes. 在许多化学工业的重大复合物的位置中，这种供货的可行性是一个主要因素。1. Lime-Based Products1. 基于石灰的产品One of the key raw materials is lime. 一种重要的原料是石灰。Limestone consists mostly of calcium carbonate（CaCO3） laid down over geological time by various marine organisms. 石灰石主要由CaCO3组成，CaCO3是多种多样的海洋生物经过整个地质年代留下来的。High quality limestones are often good enough to be used directly as calcium carbonate in further reactions. 高质量的石灰石可以作为CaCO3直接用于下一步反应。Limestone is usually mined in vast open-cast quarries, many of which will also carry out some processing of the materials. 石灰石通常在大型露天采石场开采，其中，许多还将进行一些材料的处理。The two key products derived from limestone are quicklime（CaO） and slaked limeCa(OH)2. 来自于石灰石的两个主要的产品是生石灰（CaO）和熟石灰Ca(OH)2。Quicklime is manufactured by the thermal decomposition（12001500） of limestone according to the equation：石灰石在12001500下热分解即可制得生石灰，反应方程式如下：Typically limestone is crushed and fed into the higher end of a sloping rotating kiln where the decomposition takes place and quicklime is recovered from the end. 通常，将石灰石打碎，然后将它放入倾斜的旋转窑较高的末端，在那里，石灰石将会分解，从这个窑的末端将会得到生石灰。Most frequently, however, the quicklime is not isolated for further reactions, rather, other compounds are fed in with the lime to give final products at the low end of the kiln. 然而，最常见的是生石灰并不是下一步反应唯一的反应物，而是，其他的化合物也会和石灰一起放入，这样在窑的较低的末端得到最终的产品。For example, alumina, iron ore and sand can be fed in to give Portland cement. 例如，将氧化铝、铁矿石和沙子放入后，能够得到硅酸盐水泥。Soda-ash manufacture often adds coke to the limestone which burns to give extra carbon dioxide needed for soda-ash manufacture. 纯碱的生产通常是在石灰石中添加焦炭，它可以通过燃烧来提供制备纯碱所需的额外的二氧化碳。Slaked lime which is more convenient to handle than quicklimeis manufactured by reacting quicklime with water. 熟石灰的生产比生石灰的生产更方便一些，它通常是通过生石灰与水反应制得。About 40% of the output of the lime industry goes into steel-making. where it is used to react with the refractory silica present in iron ore to give a fluid slag which floats to the surface and is easily separated from the liquid metal. 大约40%的石灰工业的产品用于钢铁制造业。在钢铁制造业中，纯碱用来与铁矿石中难溶的硅酸盐反应，生成流态矿渣，矿渣漂浮于表面上，很容易从液态金属中分离。Smaller, but still significant, amounts are used in chemical manufacture, pollution control and water treatment. The most important chemical derived from lime is soda-ash. 较少量但重要的石灰工业的产品用于化学品的制造、污染控制和水处理。从石灰石得到的最重要的化学品是纯碱。2. Soda Ash2. 纯碱The Solvay Process. The process, which was perfected by Ernest Solvay in 1865, is based on the precipitation of NaHCO3 when an ammoniated solution of salt is carbonated with CO2 from a coke-fired lime kiln. 索尔维工艺。该工艺发现于1865年由ES优化：工艺是以当氨化的盐溶液经来自于石灰窑中焦炭燃烧产物CO2碳化时，NaHCO3沉淀析出为基础。The NaHCO3 is filtered, dried, and calcined to Na2CO3. NaHCO3经过滤、干燥和煅烧生成Na2CO3。The filtered ammonium chloride process liquor is made alkaline with slaked lime and the ammonia is distilled out for recycle to the front end of the process. 过滤后的NH4Cl溶液与熟石灰反应后，呈碱性，为了循环利用，蒸馏出的NH3放回到该过程的前端。The resultant calcium chloride is a waste or by-product stream. 生成物CaCl2是废弃物或副产物。For a simple basic product the Solvay process appears exceedingly complicated. 对于一个简单基本产品来说，索尔维工艺是极其复杂的。The basic principle of the reaction is to take salt（NaCl） and calcium carbonate（CaCO3） as inputs and to produce calcium chloride and sodium carbonate as outputs. 反应的基本原理是盐（NaCl）和碳酸钙（CaCO3）作为原料，氯化钙和碳酸钠作为产物。However, the reactions occurring between input and output are not remotely obvious and involve the use of ammonia and calcium hydroxide as intermediate compounds. 然而，反应物和产物之间的反应是很不明显的，主要涉及到了中间产物氨和氢氧化钙的使用。The essential principle is that, by carefully controlling the concentration of the components（especially ammonia and salt）, sodium bicarbonate can be precipitated from solutions containing salt, carbon dioxide and ammonia. 该过程的基本原理为：利用准确的控制组分（尤其是NH3和NaCl）的浓度，NaHCO3能够从含NaCl、CO2和NH3的溶液里沉淀析出。The key to making the process work is controlling the strength of the solutions and rates of crystallization. 该过程的关键是控制溶液的酸碱强度和结晶的速度。The essential steps of the process are as follows. 这一过程的基本步骤如下。Ammonia is absorbed in an ammonia absorber into brine which has previously been purified to reduce the amount of calcium and magnesium ions（which tend to precipitate during the process in all the wrong places, blocking pipe-work）. 将氨吸收在氨吸收器中并倒入卤水中，为了减少钙离子和镁离子的含量（钙离子和镁离子将会在不合适的地方沉淀，堵塞反应管），卤水在之前已经被提纯。The solution（nominally containing sodium chloride and ammonium hydroxide） is then passed down a tower where it absorbs carbon dioxide（passing up the tower） to form ammonium carbonate at first and later ammonium bicarbonate. 然后将所得溶液（通常包含NaCl和NH4OH）通过吸收塔，起初它将会吸收二氧化碳（离开塔）形成碳酸铵，随后变成碳酸氢铵。By the next stage of the plant sodium chloride and ammonium bicarbonate have metathesised to sodium bicarbonate（which precipitates） and ammonium chloride. 在车间的下一个阶段，氯化钠和碳酸氢铵会发生复分解反应，形成碳酸氢钠（沉淀）和氯化铵。Filtration separates the solid bicarbonate from the remaining solution. 通过过滤将碳酸氢钠从剩下的溶液中分离出来。The bicarbonate is passed to a rotary dryer where it loses water and carbon dioxide to give a fluffy crystalline mass known as light soda-ash which is mostly sodium carbonate. 碳酸氢钠通过旋转干燥器，脱去水分和二氧化碳，得到了蓬松的晶体，它是轻质纯碱，成分主要是碳酸钠。The fluffy mass is light because the original crystal shape is retained on the loss of carbon dioxide, leaving many voids. 蓬松状的物质是轻的，由于它最初的晶体形状仍然保持着失去二氧化碳的空位。It is usually more convenient to make a more dense material and this is achieved by adding water（which causes recrystallization in a denser form） and further drying. 制备更致密的材料通常是更方便的，这将会通过添加水（这将会引起更致密形式上的重结晶）和进一步的干燥来实现。It is debatable whether the actual chemistry given above is a good description of the process, but it certainly aids understanding. 仍值得商榷的是上面给出的实际化学是否是对一个过程的很好的描述，但是它肯定有助于理解。For a detailed understanding, a great deal needs to be known about solubility products of multicomponent systems. 对于详细理解来说，需要知道许多关于多组分体系溶度积的知识。The important thing to know is that the system is complex and requires careful control at all parts of the process in order for it to operate effectively. 要知道的重要的事情是体系是复杂的，需要仔细控制过程的各个方面，才能够有效进行操作。One disadvantage of the process is the amount of calcium chloride produced. 这个过程的一个缺点是产生氯化钙的数量。Far more is produced than can be used, so much of the production is simply dumped（it is not a particularly noxious or nasty product）. 比起使用的数量来说，更多的氯化钙将会产生，所以大部分产品是被简单地丢弃（由于它不是特殊有毒的或极脏的产品）。It would be advantageous to use all the input material in this process, for example producing hydrogen chloride from the chloride. 它将有利于使用这个过程中的所有原始物料，例如，采用氯来制备氯化氢。Use of Soda Ash. Of all soda ash, 50% is sold to the glassmaking industry as it is a primary raw material for glass manufacture. 纯碱的利用。由于纯碱是制造玻璃的主要原材料，所以50%的纯碱将被卖到玻璃厂。The fortunes of the industry are therefore strongly tied to glass demand. 因此，行业的命运将与玻璃需求紧紧联系在一起。Soda ash also competes directly with sodium hydroxide as an alkali in many chemical processes. 作为一种碱，纯碱在许多化学领域与火碱直接竞争。Sodium silicates are another important class of chemicals derived from soda ash by reaction with silica at 12001400. 硅酸钠是来自于纯碱的另一种重要的化学物质，它是纯碱与二氧化硅在12001400下反应得到的。Silica-gel is a fine sodium silicate with a large surface area and is used in catalysts, chromatography and as a partial phosphate replacement in detergents and soaps. 硅胶是一种较细的硅酸钠，有较大的比表面，它通常被用作催化剂领域、色谱法与洗涤剂和肥皂中偏磷酸盐的替代物。3. Electrolytic Processes for Chloride/Caustic Soda3. 氯气/苛性钠的电解过程Introduction. Both chlorine and caustic soda have, at various times in the history of the chemical industry, been greatly in demand, but unfortunately for operators of electrochemical plants, not always at the same time. 介绍。在化学工业的不同时代，氯气和苛性钠都有很大的需求。但是不幸的是，在当时电化学工厂的操作者并不多。Chlorine has been valued as a bleach, or a raw material for the production of bleaching powder, as a disinfectant in water supplies and as a raw material for plastics and solvents manufacture. 氯被作为漂白剂或者生产漂白剂的原料、供水时的消毒剂及塑料和溶剂生产中的原料。Caustic soda has been used in the production of soda ash, soap, textiles, and as a very important raw material in an incredible variety of chemical processes. 烧碱已经被用于生产纯碱、肥皂、纺织物和各种各样化学过程中的一个非常重要的原材料。All the electrolytic processes have in common the electrolysis of salt to give chlorine and sodium hydroxide. 所有的电解过程都有共同点，盐电解生成氯气和氢氧化钠。The vast majority of production electrolyses a solution of salt, but there are some significant plants that electrolyze molten salt to give liquid sodium and chlorine. 绝大多数生产电解盐溶液，但是有一些重大的工厂电解熔融盐生成液体钠和氯气。These are used by industries that need the liquid sodium, mainly in the production of tetra-alkyl lead petroleum additives, though the petroleum additive companies are diversifying and other uses may appear. 这种方法主要被需要液体钠的工业使用，主要有四烷基铅石油添加剂的生产，但石油添加剂公司是多种多样的，其他的用法可能出现。There are essentially three different types of cell used for aqueous electrolysis: mercury cells, diaphragm cells and membrane cells. 基本上有三种不同类型的电池应用于水的电解：甘汞电池、隔膜电池和膜电池。Membrane cells are really the only technology that is viable for new capacity in modern plants, but a large amount of old capacity still exists and many companies have not found it economical to replace even their mercury cells, despite the environmental implications. 膜电池是真正唯一的技术，它对于现代工厂新的生产力是可行的，但是，大量的旧的生产力仍然存在，许多工厂还没有发现它甚至可以从经济上替代他们的甘汞电池，尽管受环境的影响。All electrolytic reactions are based on the idea of using electrons as a reagent in chemical reactions. The basic reactions of brine electrolysis can be written as follows: 所有的电解反应都是基于采用电子作为化学反应试剂的想法。卤水电解的基本反应为以下两个方程式：The overall reaction is: 总的电解反应为：This reaction has a positive free energy（） and needs to be driven uphill by electricity. 这个反应的自由能变为正值，需要通过电力来使它向右进行。Like many basic chemical processes, though the reaction appears to be gloriously simple, there are some significant complications. 像许多基本化学过程一样，虽然反应看起来是非常简单，但是存在一些重要的复杂性。For a start, the reaction products need to be kept apart: hydrogen and chlorine will react explosively if they are allowed to mix. Chlorine reacts with hydroxide to give hypochlorous acid（HOCl） and chloride（both wasting product and creating by-products）. 首先，反应产物需要分开：如果氢气和氯气混合的话，它们将会激烈地反应。氯和氢氧化物反应生成次氯酸（HOCl）和氯化物（都浪费了产品，产生了副产品）。The hypochlorous acid and hypochlorite（ClO-） in turn react to give chlorate（ClO3-）, protons and more chloride. 次氯酸和次氯酸盐轮流反应生成了氯酸盐、电子和更多的氯化物。Hydroxide reacts at the anode to form oxygen, which can contaminate the chlorine. 氢氧化物在阳极反应生成氧气，它能够腐蚀氯气。All the reactions reduce efficiency and/or create difficult separation of contamination problems that need to be sorted out before any products can be sold. 所有的反应降低了效率，并创造了分离污染难题，这些难题在出售产品之前需要被挑出来。The key to understanding the various types of process used for the electrolysis is the way they separate the reaction products. 理解电解中各种类型过程的关键是他们分离反应产物的方法。There are basically three types of electrolytic cell for brine electrolysis, though there are many variations of detail among the cells from different manufactures. 虽然不同的厂家所使用的电解池之间有许多不同的详细信息，但是对于卤水电解基本有三种类型的电解池。4. The Uses of Chlorine and Sodium Hydroxide4. 氯气和氢氧化钠的使用Sodium hydroxide has so many chemical uses that it is difficult to classify them conveniently. 氢氧化钠有太多用途以至于难以归类。One of the largest uses is for paper-making, where the treatment of wood requires a strong alkali. 氢氧化钠的最大的用途之一是造纸，在造纸业中对木头的处理需要一个强碱。In some countries this consumes 20% of production. Another 20% is consumed in the manufacture of inorganic chemicals such as sodium hypochlorite（the bleach and disinfectant）. 在一些国家，这种用途消耗了20%的氢氧化钠。另外20%是消耗在无机化学平的制造中，例如次氯酸钠（漂白剂和消毒剂中）。Various organic syntheses consume about another fifth of the production. The production of alumina and soap uses smaller amounts. 各种有机合成，消费了氢氧化钠产量的1/5，氧化铝和肥皂的生产也使用了少量的氢氧化钠。Chlorine is widely used in a variety of other products. 氯气是广泛应用于各种其他的产品。About a quarter of all production world-wide goes into vinyl chloride, the monomer for making PVC. 世界上大约1/4的氯气用于制备氯乙烯，氯乙烯是生产PVC的单体。Between a quarter and a half goes into a variety of other products. 第二个1/4的氯气是走进了其他各种产品领域。Depending on the country, up to 10% goes into water purification. 根据国家的情况，多于10%的氯气用于水的净化。Up to 20% goes into the production of solvents（methychloroform, trichloroethene, etc. ）though many of these are being phased out because of the Montreal Protocol. 20%的氯气用于溶剂（ ，三氯乙烯等）的生产，虽然它们中的许多都由于蒙特利尔议定书被淘汰。About 10% world-wide goes into the production of inorganic chlorine-containing compounds. 全球大约10%的氯气用于无机氯化物的制备。A very significant use in some countries is for the bleaching of wood pulp, though this is another use coming under environmental pressure. 在一些国家，一个非常重要的用途就是木浆的漂白，虽然这是又一个在环境压力下的用途。