萘在煤焦油中含量約為8%~12%，工業(yè)萘中除含有萘以外，還含有硫雜茚、酚類、喹啉類及其他不飽和化合物。要想得到精萘，就需要將工業(yè)萘進一步精制。傳統(tǒng)的工業(yè)萘精制工藝技術(shù)方法是酸洗精餾法，逐漸發(fā)展起來的工藝方法有溶劑法、催化加氫法、區(qū)域熔融結(jié)晶法和分步結(jié)晶法。

The content of naphthalene in coal tar is about 8% ~ 12%. In addition to naphthalene, industrial naphthalene also contains azaindene, phenols, quinolines and other unsaturated compounds. In order to obtain refined naphthalene, industrial naphthalene needs to be further refined. The traditional industrial naphthalene refining process is pickling distillation. The gradually developed process methods include solvent method, catalytic hydrogenation method, regional melting crystallization method and step-by-step crystallization method.

（1）酸洗精餾法

(1) Pickling distillation

酸洗精餾法一般用濃硫酸為原料，使工業(yè)萘中的硫雜茚、其他不飽和化合物與硫酸發(fā)生磺化反應(yīng)，聚合成樹脂（酸焦油），酚類經(jīng)堿洗而去除。堿洗后的液體萘經(jīng)真空蒸餾，從塔頂采出精萘。在酸洗過程中，由于發(fā)生磺化反應(yīng)而使萘的損失率較高，一般高達10%以上。酸洗精餾法對硫雜茚的去除率并不高，所生產(chǎn)的精萘一般只能達到國家二級精萘質(zhì)量標準。酸洗設(shè)備因腐蝕嚴重需要采用特殊鋼材，投資較大。另外，酸洗產(chǎn)生的廢液和污水難以處理。

Pickling distillation generally uses concentrated sulfuric acid as raw material to sulfonate azaindene and other unsaturated compounds in industrial naphthalene with sulfuric acid to polymerize into resin (acid tar), and phenols are removed by alkali washing. The liquid naphthalene after alkali washing is distilled in vacuum to extract refined naphthalene from the tower top. In the pickling process, the loss rate of naphthalene is high due to sulfonation reaction, which is generally more than 10%. The removal rate of azaindene by pickling distillation is not high, and the refined naphthalene produced can only meet the national secondary refined naphthalene quality standard. The pickling equipment needs to use special steel due to serious corrosion, and the investment is large. In addition, the waste liquid and sewage produced by pickling are difficult to treat.

（2）溶劑法

(2) Solvent method

溶劑法是利用硫雜茚與萘在溶劑中的溶解度差異而加以分離，完成萘的提純過程。溶劑法需要選擇一種選擇性良好的溶劑，一般通過二次萃取就可以得到二級精萘。若需進一步精制，還需要進行精餾或白土處理。其缺點是所采用的溶劑具有一定的毒性，生產(chǎn)設(shè)備較龐雜，精制效果較差。

Solvent method uses the solubility difference between azaindene and naphthalene in solvent to separate and complete the purification process of naphthalene. Solvent method needs to choose a solvent with good selectivity. Generally, secondary refined naphthalene can be obtained by secondary extraction. If further refining is required, rectification or clay treatment is also required. The disadvantage is that the solvent used has certain toxicity, the production equipment is complex and the refining effect is poor.

（3）催化加氫法

(3) Catalytic hydrogenation

催化加氫法是由美國環(huán)球石油公司和聯(lián)合石油公司開發(fā)的聯(lián)合精制工藝，是石油化工中常用的方法，也可用于萘的精制。目前在美、英等國建有這種裝置。

Catalytic hydrogenation is a combined refining process developed by global petroleum company and United Petroleum Company. It is a common method in petrochemical industry and can also be used for the refining of naphthalene. At present, such devices are built in the United States, Britain and other countries.

催化加氫法是將工業(yè)萘氣化，在高溫、常壓下與氫混合并通過催化劑層進行催化加氫，萘中的主要雜質(zhì)硫雜茚發(fā)生氫解反應(yīng)，轉(zhuǎn)化為硫化氫與烴類，其它非萘雜質(zhì)在加氫過程中，也轉(zhuǎn)化為易分離的氨、水和烴類。同時萘也發(fā)生副反應(yīng)，生成四氫萘等副產(chǎn)物。該工藝的特點是：產(chǎn)品質(zhì)量高，含硫低于300ppm,但由于工藝較復雜，基建及操作費用較高，推廣應(yīng)用較困難。生產(chǎn)過程中有副產(chǎn)物四氫萘生成，限制了這種萘產(chǎn)品應(yīng)用的范圍。

Catalytic hydrogenation method is to gasify industrial naphthalene, mix it with hydrogen at high temperature and atmospheric pressure, and carry out catalytic hydrogenation through the catalyst layer. The main impurity in naphthalene, azaindene, is hydrogenated and converted into hydrogen sulfide and hydrocarbons. Other non naphthalene impurities are also converted into easily separated ammonia, water and hydrocarbons in the hydrogenation process. At the same time, naphthalene also has side reactions to produce by-products such as tetrahydronaphthalene. The process is characterized by high product quality and sulfur content less than 300ppm. However, due to the complex process and high capital construction and operation costs, it is difficult to popularize and apply. Tetrahydronaphthalene, a by-product, is produced in the production process, which limits the application range of this naphthalene product.

（4）區(qū)域熔融結(jié)晶法

(4) Zone melting crystallization

區(qū)域熔融法制取精萘主要是以工業(yè)萘為原料，利用固體萘與其他雜質(zhì)熔點的差別，于精制機內(nèi)用區(qū)域熔融法進行提純，再將已提純的萘送蒸餾塔去精餾，進一步除去高沸點及低沸點雜質(zhì)后，即得精萘產(chǎn)品。該方法為連續(xù)生產(chǎn)過程，產(chǎn)品質(zhì)量穩(wěn)定。但是，因其基建投資和操作費用高，操作條件要求較嚴，所以在中國還沒有得到普遍應(yīng)用。

Refined naphthalene produced by regional melting method mainly takes industrial naphthalene as raw material, uses the difference of melting point between solid naphthalene and other impurities, purifies it in the refining machine by regional melting method, and then sends the purified naphthalene to the distillation tower for rectification. After further removing the impurities with high boiling point and low boiling point, the refined naphthalene product is obtained. This method is a continuous production process with stable product quality. However, it has not been widely used in China because of its high infrastructure investment and operation costs and strict requirements for operation conditions.

（5）分步結(jié)晶法

(5) Fractional crystallization

分步結(jié)晶法是利用熔融的粗萘在冷卻結(jié)晶時發(fā)生組分在液固兩相間重新分布的原理，經(jīng)過多次熔融結(jié)晶來提純萘的工藝過程，是對萘油餾分加工得到的粗萘進行精制的工藝之一。粗萘中的雜質(zhì)一般會降低萘的熔點，所以當液態(tài)粗萘緩慢冷卻時萘首先結(jié)晶析出，而雜質(zhì)則聚集在液相中。若析出的萘再次熔融和結(jié)晶，則再次析出的萘結(jié)晶純度又進一步提高。嚴格控制熔融和結(jié)晶過程的溫度和速度，可得到純度很高的精萘產(chǎn)品。萘分段結(jié)晶精制可以連續(xù)進行，也可半連續(xù)或間歇進行。工業(yè)萘中的主要雜質(zhì)是硫茹，硫茹的沸點與萘的沸點只差2℃，很難用蒸餾方法除去，而它們的結(jié)晶點相差達48℃，所以更宜用分段結(jié)晶法把它們分離而使萘得到精制。分步結(jié)晶法制取精萘的特點如下：

The step-by-step crystallization method is a process of purifying naphthalene through multiple melting crystallization based on the principle that the components of molten crude naphthalene are redistributed between liquid and solid phases during cooling crystallization. It is one of the processes for refining crude naphthalene obtained from naphthalene oil fraction. Impurities in crude naphthalene generally reduce the melting point of naphthalene, so when the liquid crude naphthalene cools slowly, naphthalene first crystallizes and precipitates, while impurities accumulate in the liquid phase. If the precipitated naphthalene melts and crystallizes again, the crystallization purity of the precipitated naphthalene will be further improved. By strictly controlling the temperature and speed of melting and crystallization process, refined naphthalene products with high purity can be obtained. The fractional crystallization refining of naphthalene can be carried out continuously, semi continuously or intermittently. The main impurity in industrial naphthalene is thioru. The boiling point of thioru is only 2 ℃ different from that of naphthalene, which is difficult to be removed by distillation, and the phase difference of their crystallization point is up to 48 ℃, so it is better to separate them by segmented crystallization to refine naphthalene. The characteristics of refined naphthalene prepared by fractional crystallization are as follows:

a）原料單一，不需要輔助原料。

a) The raw materials are single and no auxiliary raw materials are required.

b）工藝流程、設(shè)備及操作都比較簡單，設(shè)備投資少。

b) The process flow, equipment and operation are relatively simple, and the equipment investment is less.

c）操作時僅需泵的壓送、冷卻結(jié)晶、加熱熔融，操作費用和能耗都比較低。

c) During operation, only the pressure of the pump, cooling crystallization, heating and melting are needed, and the operation cost and energy consumption are relatively low.

d）產(chǎn)品質(zhì)量可用結(jié)晶循環(huán)次數(shù)加以調(diào)節(jié)，比較靈活。

d) The product quality can be adjusted by the number of crystallization cycles, which is more flexible.

e）生產(chǎn)工藝較成熟，產(chǎn)品質(zhì)量穩(wěn)定a。

e) The production process is mature and the product quality is stable a.

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