200530175 九、發明說明： 【發明所屬之技術領域】 本發明係關於一種製造對苯二甲酸時所使用的水溶劑 的再利用方法。 【先前技術】 高純度對苯二曱酸的製備方法為將粗對苯二甲酸放入 水中，在加壓下進行升溫溶解，並在氫的存在下使其與觸 媒（例如鈀）接觸，將屬粗對苯二曱酸中主要雜質的氧化 中間體4 -羧基苯曱醛還原為容易被結晶除去的對甲苯曱 * 酸，再以結晶除去雜質後，藉由固液分離製得。此時作為 溶劑使用的水因含有很多雜質，被作為排出水廢棄，因而 需要大型的排出水處理裝置。 作為此從水中除去雜質的方法，已在例如日本專利 2 8 9 9 9 2 7號中揭示。該方法是將對上述所結晶的對苯二曱 酸進行固液分離後的水，使用對二曱苯予以萃取的方法。 但是，在此方法中，作為用以將粗對苯二曱酸精製而再利 用的水，未能將雜質除去至必要的純度。 又，作為結晶對苯二曱酸的手段，可以使用藉由減壓使 水急驟降溫的裝置。此步驟中產生的蒸發水中，因不含有 固液分離後的4非出水中所含的高沸點雜質，因此認為冷凝 後的水可以不用回到結晶槽中進行處理而直接排出，再次 直接作為用於精製粗對苯二曱酸的水進行使用。但是，由 於蒸發水中含有大量的對曱苯曱酸，因此採用這種方法的 最終產品中，對曱苯曱酸的濃度變高。因此，必須藉由預 3 ] 2XP/發明說明書(補件)/9103/93134〇52 200530175 先降低粗對苯二曱酸中的4 -羧基苯曱醛的濃度，以保持作 為最終產品的高純度對苯二甲酸中對曱苯甲酸的濃度，從 而導致粗對苯二曱酸的製造成本增高的問題。 【發明内容】 (發明所欲解決之問題） 習知之以對二甲苯從固液分離後的排出水中萃取雜質 的方法中，即使在對二甲苯萃取後，排出水中仍含有很多 雜質，不能作為用以精製粗對苯二甲酸的水而再使用。又， 在使將粗對苯二曱酸予以結晶的步驟中產生的蒸發水冷凝 後直接循環的方法中，為維持高純度對苯二曱酸的純度， 必須降低粗對苯二曱酸中的4 -羧基苯曱醛的濃度，因此存 在粗對苯二曱酸的製造成本增高的問題。 進一步存在的問題為，這不僅造成經氧化即能成為最終 產品對笨二曱酸的對曱苯甲酸與排出水一同被丟棄，而且 還需要大型的排出水處理裝置。 本發明提供一種能夠將精製粗對苯二甲酸的步驟所排 出的排出水再利用於例如精製粗對苯二甲酸的水，進一步 提高對苯二曱酸的產率之方法。 (解決問題之手段） 本發明係關於一種對苯二曱酸之製造方法，其係將氧化 對二曱苯所得到的粗對苯二甲酸在加壓下進行升溫使其溶 解於水後，藉由減壓蒸發水分，使對苯二曱酸發生結晶， 並將此時產生的蒸發水冷凝所得到的冷凝水與對二曱苯接 觸後，將分離的冷凝水再利用於製造對苯二甲酸的任意步 6 312XP/發明說明書(補件)/94-03/93134052 200530175 驟中。 本發明還提供一種將冷凝水作為溶解粗對苯二曱酸的 水而再利用的方法；藉由將粗對苯二甲酸在5MPa-G以上的 壓力下升溫至2 2 5 T：以上而溶解後，經一級式或多級式減 壓，蒸發出3 0〜7 0重量％的用於溶解粗對苯二甲酸的水之 方法；以及在冷凝蒸發水的冷凝步驟中使冷凝溫度達到7 0 °C以上的方法。 最好使將蒸發出的水冷凝的冷凝水在4 0〜2 0 0 °C下與對 二曱苯接觸。 又，本發明還提供一種以氣體狀物質使接觸對二甲苯後 分離得到的冷凝水起泡（b u b b 1 i n g )的方法。氣體狀物質 最好使用氮氣或水蒸氣。 又，本發明還提供一種將與冷凝水接觸並分離後的對二 甲苯供給至氧化步驟，作為製造粗對苯二甲酸的原料而使 用的方法；及將起泡後的氣體狀物質中含有的對二甲苯供 給至氧化步驟，以作為製造粗對苯二曱酸的原料的方法。 (發明效果） 藉由使用屬於對苯二曱酸的原料的對二曱苯作為萃取 劑，不必進行通常需要大型設備和能量的萃取劑再生步 驟，可使習知之作為排出水而丟棄、必須用大型排出水處 理裝置處理的從粗對苯二曱酸的精製步驟中產生的排出 水，再次予以再利用於精製粗對苯二曱酸的水。 此外，可以將過去被丟棄的排出水中的對甲苯曱酸回收 為目標產物對苯二曱酸。 3 ] 2XP/發明說明書(補件)/94-03/93134052 200530175 【實施方式】 將對二曱苯在醋酸溶劑中，使用鈷化合物和錳化合物、 漠化合物作為觸媒，在反應壓力0 . 4〜5 Μ P a - G、反應溫度 1 6 0〜2 6 0 °C下，在空氣中進行氧化製造粗對苯二曱酸。此 粗對苯二曱酸中的主要雜質是氧化中間體4 -羧基苯曱醛 500〜5000重量ppm，和對甲苯甲酸100〜1000重量ppm。 其他雜質有苯曱酸、羥曱基苯曱酸、間苯二甲酸等，以及 該等以各種形式結合而成的高沸點雜質或分解而成的低沸 點雜質。 將如此得到的粗對苯二曱酸，在5 Μ P a -以上、較佳為7 〜9MPa-G的壓力下，升溫至225 °C以上、較佳為升溫至250 °C〜3 1 0 °C，使其溶解在水中。將此時水中的對苯二曱酸濃 度調整至10〜40重量％，較佳為20〜35重量％的範圍内。 如果對苯二曱酸的濃度較低，則使用的水量增多，導致下 述的裝置變大，因此較不佳。又，對苯二甲酸的濃度較高 之情況，如下所述，在將水蒸發出3 0〜7 0重量％時，未蒸 發出的母液中雜質濃度增高，成品高純度對苯二甲酸中的 雜質濃度增高，因此較不佳。 然後，在氫的存在下與觸媒（例如纪）接觸，將屬於粗 對苯二曱酸中主要雜質的氧化中間體4 -羧基苯曱醛還原 為易以結晶除去的對曱苯曱酸，然後，以一級式或多級式、 較佳以3〜7級式進行減壓，蒸發水分。 本發明中，雖然為了對蒸發後的水進行精製而再利用， 採用較大的蒸發量為佳，但蒸發量過大時未蒸發出的母液 8 312XP/發明說明書(補件)/94-03/93134052 200530175 中雜質的濃度變高，使成品高純度對苯二曱酸中雜質的濃 度增高，較為不佳。因此，調整減壓操作使蒸發量為水的 3 0〜7 0重量％ 、較佳為3 5〜6 0重量％ 。藉由蒸發的汽化 熱，使溫度降低至1 0 0〜1 7 5 t ，析出對苯二曱酸結晶。對 曱苯曱酸的5〜5 0重量％轉移至蒸發水中，而其餘幾乎所 有的雜質均殘留在母液中。又，雖然微量存在的低沸點雜 質也可能轉移至蒸發水中，但可以藉由將蒸發水在7 0 °C以 上、較佳在8 0〜1 0 0 °C的溫度下冷凝而除去這些物質。為 了除去低沸點雜質，雖然以較高的冷凝溫度為佳，但為了 可以低價的裝置在大氣壓下進行下述的萃取和起泡操作， 較佳的溫度上限為1 0 0 °C 。 如此，除去了高沸點雜質和低沸點雜質的冷凝水中的主 要雜質成為對甲苯曱酸，其濃度為100〜5 0 0 0重量ppm。 相對於1 0 0重量份之該冷凝水，使其與3〜2 0 0重量份、較 佳為5〜1 0 0熏量份、更佳為1 0〜3 5重量份的對二曱苯接 觸，以除去冷凝水中的對曱苯甲酸。對二曱苯的量越多， 對甲苯曱酸的除去率越高，因此較佳。但是，由於將對二 甲笨萃取後係作為粗對苯二曱酸的原料而使用，因此對二 甲苯量的上限必然取決於整體的平衡。 冷凝水與對二曱苯接觸的溫度通常為4 0〜2 0 0 °C ，較佳 為6 ◦〜1 5 0 °C ，更佳為8 0〜1 0 0 °C 。 因為藉由逆流式多級萃取可以提高對曱苯曱酸的除去 率，所以較佳採用2〜1 0級、更佳為2〜4級的逆流式多級 萃取。本發明中不必完全除去對曱苯曱酸，若可除去例如 9 312XP/發明說明書(補件)/94-03/93134052 200530175 7 0 %以上即可。因此，萃取級數在1 0級以下已足夠。又， 通常為了減少萃取溶劑的量而增加萃取級數，但由於本發 明中作為萃取劑的對二曱苯可作為粗對苯二甲酸的原料而 使用，因此不需要通常萃取操作所需要的萃取劑再生裝 置。相對於1 0 0重量份冷凝水，可使用1 0重量份以上的對 二甲苯作為萃取劑，萃取級數在4級以下便可達到充分的 除去率。例如，逆流萃取級數為2級，相對於1 0 0重量份 冷凝水使用2 5重量份對二曱苯，可除去9 0重量％以上的 冷凝水中的對曱苯甲酸。 在大型對苯二曱酸生產工廠中，冷凝水量可達到5 0 t / h r以上，為避免萃取塔中的溝流（c h a η n e 1 i n g )問題，不 採用大型的單塔結構，而是予以多塔化進行並聯處理較 好。因此，在大型對苯二曱酸生產工廠中冷凝水的量達到 5 0 t / h r以上之情況，以串聯連接由攪拌機與靜置分離器 組合構成的混合器·沉降器型裝置，進行多級式萃取較佳。 攪拌器葉片的翼端速度為0 . 2 5 m /秒以上，較佳為0 . 5〜5 m /秒。高速攪拌可提高萃取效率並實現裝置小型化，因此 較佳，但攪拌速度過快時，由於對二甲苯發生微粒化，導 致分離為2層的靜置時間延長，因此速度較佳為5 m /秒以 下。攪拌機葉片的翼端速度為0 . 5〜5 m /秒之情況的靜置 時間在逆流多級萃取的中間級為1〜3 0分鐘、較佳為2〜5 分鐘，在逆流多級萃取的兩端級為2〜6 0分鐘、較佳為5 〜1 5分鐘。 為了回收逆流多級萃取的最終級排出的水中殘留的對 10 3】2XP/發明說明書(補件)/94-03/93134〇52 200530175 二曱苯，以氣體狀物質對萃取後的水進行起泡。此時 為氣體狀物質，雖然可使用氮氣，但從氮氣中回收對 苯比較困難，最好使用水蒸氣，藉由冷凝而回收對二气 此時水蒸氣的量，相對1 0 0重量份冷凝水為0 . 0 5〜1 0 份、較佳為0 . 5〜5 . 0重量份 '更佳為1 . 0〜2 . 0重量 水蒸氣的量越多，對二曱苯的除去率越高，但即使有 殘存也不會影響到成品高純度對苯二甲酸的品質，混 9 5 %以上的對二曱苯在結晶槽中蒸發，然後返回萃取 置，因此相對1 0 0重量份的冷凝水，水蒸氣的量為0 量份以上即可。又，相對於1 0 0重量份冷凝水，水蒸 量為1.0重量份以上時，無需設置用以除去對二曱苯 的特殊通氣口 ，因此較佳。 又，為了除去對二甲苯，也可使用聚結劑（c 〇 a 1 e s c 作為聚結劑，有例如日本P a 1 1股份有限公司的屬於氟 脂、商品名為P h a s e s e p的聚結劑。此情況，由於可能 含有伴隨飛沫的對苯二甲酸的情況，因此有必要使結 蒸發面的蒸發速度為每單位平方公尺3 0 0 0 k g / h r以二 佳為2 0 0 0 k g / h r以下，藉以降低伴隨飛沫的對苯二曱 量，同時，使加入聚結劑之前的溫度在7 0 °C以上、較 9 0〜1 0 0 °C ，以使對苯二曱酸不析出。 因萃取出雜質後的對二曱苯不含有高沸點雜質，不 品質，所以可以不變更生產粗對苯二曱酸之條件地作 料使用。 以下記載本發明的實施例，但本發明並不限定於以 312XP/發明說明書(補件)/94-03/93 ] 34052 ，作 二曱 7苯。 重量 份。 少量 入的 裝 • 5重 氣的 臭味 e r ) ° 系樹 存在 晶的 F、較 酸的 佳為 影響 為原 下的 11 200530175 實施例。 〔實施例1〕 圖1示出本發明裝置的一實施例。將粗對苯二曱酸1與 水1 4和蒸餾水1 5 —起在加熱溶解步驟8中，在1 0 Μ P a - G 下升溫至3 0 0 °C進行溶解。水的總量相對於1 . 0重量份之 粗對苯二曱酸為3 . 0重量份。溶解後，在氫化步驟9中將 粗對苯二曱酸中的4 -羧基苯曱醛還原為對曱苯曱酸，在結 晶步驟1 0析出對苯二曱酸。此時，使最終的結晶槽的壓力 為0 . 5 Μ P a - G，使水的5 0重量％蒸發。將析出的對苯二甲 酸在固液分離步驟1 1中進行分離，在乾燥步驟1 2中乾燥 後，取出成品高純度對苯二曱酸2。 結晶步驟蒸發水5被運送至冷凝器3，在9 5 °C下冷凝。 此時，冷凝水中的對曱苯曱酸的濃度為7 0 0重量p p m。然 後運送至萃取步驟1 3，進行2級逆流萃取操作。即，對應 於1 0 0重量份冷凝水，使其與2 5重量份之對二曱苯在第1 級攪拌機1 3 - 1中接觸2分鐘。然後，在第1級靜置分離機 1 3 - 2中靜置3分鐘進行分離，再次使1 0 0重量份冷凝水與 2 5重量份的對二曱苯在第2級攪拌機1 3 - 3中接觸2分鐘， 在第2級靜置分離機1 3 - 4中靜置5分鐘後進行分離。此 時，對二曱苯相對於水係以逆流的方式流動。攪拌機有4 片傾斜的槳葉，葉片以翼端速度3 . 0 m /秒進行旋轉。 如此得到的水中的對曱苯曱酸濃度為3 0重量p p m，對二 甲苯的濃度為5 0 0重量p p m。將此運送至汽提塔1 6，相對 於1 0 0重量份之水，以1 . 0重量份的水蒸氣量進行起泡。 12 312XP/發明說明書(補件)/94-03/93134〇52 200530175 該起泡後的水中之對甲苯曱酸的濃度為3 0重量p p m，對二 曱苯的濃度為1重量ppm以下。 萃取後的對二曱苯與來自對二曱苯供給通路1 8的氧化 原料用對二甲苯一起運送至氧化步驟7中，作為製造粗對 苯二曱酸的原料進行使用。 藉由本操作，可以不預先降低粗對苯二甲酸中雜質的濃 度，將用於粗對苯二甲酸精製的水的5 0 %予以再利用。 (產業上之可利用性） 藉由本發明，可不消耗大量能源地精製排出水，使其處 於能夠再利用的狀態，使目前一直被廢棄的對曱苯曱酸能 夠轉化為最終產品對苯二曱酸並進行回收。 【圖式簡單說明】 圖1為示出對本發明的排出水進行精製的實施方法之一 例的說明圖。（實施例1 ) 【主要元件符號說明】 1 粗對苯二甲酸供給通路 2 精製對苯二甲酸 3 冷凝器 4 排出水 5 結晶步驟热發水 6 對二甲苯 7 氧化步驟 8 加熱溶解步驟 9 加氫步驟 13 312XP/發明說明書(補件)/94-03/93134052 200530175 10 結 晶 步 驟 11 固 液 分 離 步 驟 12 乾 燥 步 驟 13 萃 取 步 驟 13- -1 第 1 級 攪 拌 13- -2 第 1 級 靜 置 分 離 13- -3 第 2 級 攪 拌 13- -4 第 2 級 靜 置 分 離 14 水 15 蒸 餾 水 16 汽 提 塔 17 低 >弗 點 雜 質 18 對 二 曱 苯 14 312XP/發明說明書(補件)/94-03/93134052200530175 IX. Description of the invention: [Technical field to which the invention belongs] The present invention relates to a method for reusing an aqueous solvent used in the production of terephthalic acid. [Previous technology] A method for preparing high-purity terephthalic acid is to put crude terephthalic acid in water, dissolve it under elevated temperature, and contact it with a catalyst (such as palladium) in the presence of hydrogen. The oxidized intermediate 4-carboxybenzaldehyde, which is a major impurity in crude terephthalic acid, is reduced to p-toluene * acid which can be easily removed by crystallization, and the impurities are removed by crystallization, followed by solid-liquid separation. In this case, the water used as the solvent contains a lot of impurities and is discarded as the drain water. Therefore, a large-scale drain water treatment device is required. As a method for removing impurities from water, this method is disclosed in, for example, Japanese Patent No. 2 8 9 9 2 7. This method is a method of extracting p-xylene with water after solid-liquid separation of the crystallized terephthalic acid. However, in this method, as water used for refining crude terephthalic acid, the impurities cannot be removed to the necessary purity. As a means for crystallizing terephthalic acid, a device for rapidly lowering the temperature of the water by reducing the pressure can be used. The evaporated water produced in this step does not contain the high boiling point impurities contained in the 4 non-effluent water after solid-liquid separation. Therefore, it is considered that the condensed water can be directly discharged without returning to the crystallization tank for treatment, and directly used again. It is used to purify crude terephthalic acid. However, since the evaporated water contains a large amount of p-benzoic acid, the concentration of p-benzoic acid in the final product by this method becomes high. Therefore, it is necessary to reduce the concentration of 4-carboxybenzaldehyde in crude terephthalic acid by pre-3XP / Invention Specification (Supplement) / 9103 / 93134〇52 200530175 to maintain high purity as the final product. The concentration of p-benzoic acid in terephthalic acid causes a problem that the production cost of crude terephthalic acid increases. [Summary of the Invention] (Problems to be Solved by the Invention) In the conventional method for extracting impurities from the discharged water after the para-xylene is separated from the solid and the liquid, even after the para-xylene extraction, the discharged water still contains a lot of impurities and cannot be used as It is reused as purified terephthalic acid water. In addition, in a method of condensing evaporated water generated in the step of crystallizing crude terephthalic acid, in order to maintain the purity of terephthalic acid with high purity, it is necessary to reduce the amount of There is a problem in that the production cost of crude terephthalic acid is increased due to the concentration of 4-carboxybenzaldehyde. A further problem is that this not only causes the p-benzoic acid, which can be the final product of p-dibenzoic acid upon oxidation, to be discarded together with the discharged water, but also requires a large-scale discharged water treatment device. The present invention provides a method capable of reusing the discharged water discharged in the step of purifying crude terephthalic acid, for example, water for purifying crude terephthalic acid to further increase the yield of terephthalic acid. (Means for Solving the Problem) The present invention relates to a method for producing terephthalic acid, which comprises heating the crude terephthalic acid obtained by oxidizing paraxylene under pressure, dissolving it in water, and The water is evaporated under reduced pressure to crystallize terephthalic acid, and the condensed water obtained by condensing the evaporation water generated at this time is contacted with p-xylene, and the separated condensed water is reused for the production of terephthalic acid Any step 6 312XP / Invention Specification (Supplement) / 94-03 / 93134052 200530175 step. The present invention also provides a method for reusing condensed water as water to dissolve crude terephthalic acid; by dissolving crude terephthalic acid at a pressure of 5 MPa-G or higher to 2 2 5 T: and dissolving Then, a method of depressurizing one or more stages to evaporate 30 to 70% by weight of water for dissolving crude terephthalic acid; and in a condensation step of condensing the evaporated water, the condensation temperature is brought to 70 Method above ° C. The condensed water which condenses the evaporated water is preferably brought into contact with p-xylene at 40 ° to 200 ° C. The present invention also provides a method for bubbling (b u b b 1 i n g) the condensed water separated after contact with para-xylene with a gaseous substance. As a gaseous substance, nitrogen or water vapor is preferably used. The present invention also provides a method for supplying para-xylene after contacting and separating with condensed water to an oxidation step, and using the method as a raw material for producing crude terephthalic acid; and Paraxylene is supplied to the oxidation step as a method for producing crude terephthalic acid. (Effects of the Invention) By using p-xylene as an extractant, which is a raw material of terephthalic acid, it is not necessary to perform an extraction agent regeneration step that generally requires large equipment and energy, and it can be discarded as discharged water, which must be used. The effluent water produced from the purification step of crude terephthalic acid treated by a large-scale effluent water treatment device is reused for refining crude terephthalic acid. In addition, p-toluenic acid, which was discarded in the past, can be recovered as the target product, terephthalic acid. 3] 2XP / Invention Specification (Supplement) / 94-03 / 93134052 200530175 [Embodiment] P-xylene is used in acetic acid solvent, using cobalt compound, manganese compound, and desert compound as catalysts, at a reaction pressure of 0.4. The crude terephthalic acid is produced by oxidizing in the air at ~ 5 Μ Pa-G and a reaction temperature of 160 to 260 ° C. The main impurities in this crude terephthalic acid are the oxidation intermediate 4-carboxybenzophenal 500-5000 ppm by weight, and p-toluic acid 100-1000 ppm by weight. Other impurities include phenylarsinic acid, hydroxyarsinophenylarsinic acid, isophthalic acid, etc., and high-boiling-point impurities or low-boiling-point impurities that are combined in various forms. The crude terephthalic acid thus obtained is heated to a temperature of 225 ° C or more, preferably 250 ° C to 3 1 0, at a pressure of 5 MPa-or more, preferably 7 to 9 MPa-G. ° C to dissolve in water. The concentration of terephthalic acid in the water at this time is adjusted to 10 to 40% by weight, preferably 20 to 35% by weight. If the concentration of terephthalic acid is low, the amount of water used is increased, resulting in a larger apparatus as described below, which is less favorable. In addition, when the concentration of terephthalic acid is high, as described below, when water is evaporated to 30 to 70% by weight, the concentration of impurities in the unevaporated mother liquor increases, resulting in high purity terephthalic acid in the finished product. The impurity concentration is increased, so it is less favorable. Then, in the presence of hydrogen, it is contacted with a catalyst (for example, Koji) to reduce the oxidized intermediate 4-carboxybenzaldehyde, which is the main impurity in crude terephthalic acid, to p-phenylbenzoic acid, which is easily removed by crystallization. Then, the pressure is reduced in a single-stage or multi-stage mode, preferably in a 3 to 7 stage mode, and the water is evaporated. In the present invention, although the evaporated water is used for refining and reusing the evaporated water, it is better to use a large evaporation amount, but the mother liquor that does not evaporate when the evaporation amount is too large 8 312XP / Invention Specification (Supplement) / 94-03 / The concentration of impurities in 93134052 200530175 becomes higher, which makes the concentration of impurities in the high-purity terephthalic acid of the finished product higher, which is not good. Therefore, the pressure reduction operation is adjusted so that the evaporation amount is 30 to 70% by weight of water, and preferably 35 to 60% by weight. The temperature of the vaporization was reduced to 100 to 175 t by the heat of vaporization, and terephthalic acid crystals were precipitated. 5 to 50% by weight of p-benzoic acid is transferred to evaporated water, while almost all the remaining impurities remain in the mother liquor. In addition, although trace amounts of low-boiling impurities may be transferred to the evaporated water, these substances can be removed by condensing the evaporated water at a temperature of 70 ° C or higher, preferably 80 to 100 ° C. In order to remove low boiling point impurities, although a higher condensing temperature is preferred, in order to allow a low-cost device to perform the following extraction and foaming operations under atmospheric pressure, the preferred upper temperature limit is 100 ° C. In this way, the main impurity in the condensed water from which high-boiling impurities and low-boiling impurities have been removed is para-toluenic acid, and its concentration is 100 to 5000 ppm by weight. With respect to 100 parts by weight of the condensed water, it is mixed with 3 to 200 parts by weight, preferably 5 to 100 parts by weight, and more preferably 10 to 35 parts by weight of p-xylene. Contact to remove para-benzoic acid in condensed water. The larger the amount of p-xylene, the higher the removal rate of p-toluene acid, and therefore, it is preferable. However, since the para-xylylene is extracted as a raw material of crude terephthalic acid, the upper limit of the amount of para-xylene necessarily depends on the overall balance. The temperature at which the condensed water is in contact with p-xylene is usually 40 to 200 ° C, preferably 6 to 150 ° C, and more preferably 80 to 100 ° C. Since the removal rate of p-benzoic acid can be improved by countercurrent multistage extraction, countercurrent multistage extraction of 2 to 10 grades, more preferably 2 to 4 grades, is preferably used. In the present invention, it is not necessary to completely remove p-phenylbenzoic acid, and if it can be removed, for example, 9 312XP / Invention Specification (Supplement) / 94-03 / 93134052 200530175 70% or more. Therefore, the number of extraction stages below 10 is sufficient. In addition, the number of extraction stages is generally increased in order to reduce the amount of extraction solvent. However, since p-xylene which is an extractant in the present invention can be used as a raw material of crude terephthalic acid, the extraction required for ordinary extraction operations is not required. Agent regeneration device. Relative to 100 parts by weight of condensed water, more than 10 parts by weight of para-xylene can be used as an extractant, and a sufficient removal rate can be achieved if the number of extraction stages is 4 or less. For example, the number of countercurrent extraction stages is two. Using 25 parts by weight of p-xylene relative to 100 parts by weight of condensed water can remove more than 90% by weight of p-benzoic acid in condensed water. In large terephthalic acid production plants, the amount of condensed water can reach more than 50 t / hr. In order to avoid the problem of cha η ne 1 ing in the extraction tower, a large single tower structure is not adopted, but instead Multi-tower parallel processing is better. Therefore, when the amount of condensed water in a large terephthalic acid production plant reaches 50 t / hr or more, a mixer-settler type device composed of a combination of a stirrer and a stationary separator is connected in series to perform a multi-stage Extraction is preferred. The blade tip speed of the agitator blade is 0.25 m / sec or more, preferably 0.5 to 5 m / sec. High-speed stirring can improve extraction efficiency and reduce the size of the device, so it is better, but when the stirring speed is too fast, the para-xylene will be micronized and the separation time will be extended. Therefore, the speed is preferably 5 m / Below seconds. In the case where the blade tip speed of the mixer blade is 0.5 to 5 m / sec, the standing time is 1 to 30 minutes, preferably 2 to 5 minutes in the middle stage of the countercurrent multistage extraction. The two-stage stages are 2 to 60 minutes, preferably 5 to 15 minutes. In order to recover the leftover water from the final stage of countercurrent multi-stage extraction, 10 3] 2XP / Invention Specification (Supplement) / 94-03 / 93134〇52 200530175 Dioxin was used as a gaseous substance to extract the extracted water. bubble. This is a gaseous substance. Although nitrogen can be used, it is difficult to recover p-benzene from nitrogen. It is best to use water vapor to recover the amount of water vapour at this time by condensation. Relative to 100 parts by weight of condensation The amount of water is 0.5 to 10 parts, preferably 0.5 to 5.0 parts by weight, more preferably 1.0 to 2.0 parts by weight. The greater the amount of water vapor, the greater the removal rate of xylene. High, but even if there is residue, it will not affect the quality of the high-purity terephthalic acid. More than 95% of the p-dioxobenzene will be mixed in the crystallization tank to evaporate, and then returned to the extraction unit. The amount of condensed water and water vapor may be 0 parts by weight or more. In addition, when the water vapor amount is 1.0 part by weight or more with respect to 100 parts by weight of condensed water, it is not necessary to provide a special vent for removing p-xylene. Therefore, it is preferable. In addition, in order to remove para-xylene, a coalescing agent (coa 1 esc) may be used as the coalescing agent. For example, there is a coalescing agent belonging to Fluoroester, trade name P hasesep of Japan Pa 1 1 Corporation. In this case, since terephthalic acid with droplets may be contained, it is necessary to set the evaporation rate of the junction evaporation surface to 3 0 0 0 kg / hr per square meter, and 2 to 2 0 0 kg / hr. In the following, the amount of terephthalic acid accompanying droplets is reduced, and at the same time, the temperature before adding the coalescing agent is 70 ° C or higher and 90 ° to 100 ° C, so that terephthalic acid does not precipitate. Para-xylene after extraction of impurities does not contain high-boiling impurities and has no quality, so it can be used without changing the conditions for producing crude terephthalic acid. Examples of the present invention are described below, but the present invention is not limited thereto. Based on 312XP / Invention Specification (Supplements) / 94-03 / 93] 34052 as dioxin 7 benzene. Parts by weight. Small amount of filling • 5 heavy gas odor) ° F, crystal The best effect of acid is the original 11 200530175 example. [Embodiment 1] Fig. 1 shows an embodiment of the device of the present invention. The crude terephthalic acid 1 was dissolved together with water 14 and distilled water 15 in a heating and dissolving step 8 at a temperature of 10 MPa-G to 300 ° C. The total amount of water was 3.0 parts by weight relative to 1.0 part by weight of crude terephthalic acid. After the dissolution, the 4-carboxybenzaldehyde in the crude terephthalic acid was reduced to p-phenylbenzoic acid in the hydrogenation step 9, and the terephthalic acid was precipitated in the crystallization step 10. At this time, the pressure of the final crystallization tank was set to 0.5 MPa-G, and 50% by weight of water was evaporated. The precipitated terephthalic acid is separated in the solid-liquid separation step 11 and dried in the drying step 12 and then the finished high-purity terephthalic acid 2 is taken out. In the crystallization step, the evaporated water 5 is transported to the condenser 3 and condensed at 95 ° C. At this time, the concentration of p-benzoic acid in the condensed water was 700 weight p p m. It is then transported to the extraction step 1 3 for a 2-stage countercurrent extraction operation. That is, corresponding to 100 parts by weight of condensed water, it was brought into contact with 25 parts by weight of para-xylene in a first-stage mixer 1 3-1 for 2 minutes. Then, stand still in the first-stage static separator 1 3-2 for 3 minutes to perform separation, and again make 100 parts by weight of condensed water and 25 parts by weight of p-xylene to the second-stage mixer 1 3-3 After 2 minutes of medium contact, it was allowed to stand for 5 minutes in the second-stage static separator 1 3-4 and then separated. At this time, p-xylene is flowing countercurrently with respect to the water system. The mixer has 4 inclined blades, and the blades rotate at a wing tip speed of 3.0 m / sec. The concentration of p-benzoic acid in the water thus obtained was 30 weight p p m, and the concentration of p-xylene was 500 weight p p m. This was transported to a stripping column 16 and foamed in an amount of 1.0 part by weight with respect to 100 parts by weight of water. 12 312XP / Invention Manual (Supplement) / 94-03 / 93134〇52 200530175 The concentration of p-toluenic acid in the foamed water is 30 weight p p m, and the concentration of p-xylene is 1 weight ppm or less. The extracted p-xylene and the oxidation raw material from the p-xylene supply channel 18 are transported together with p-xylene to the oxidation step 7 and used as a raw material for the production of crude p-xylene acid. With this operation, 50% of the water used for the purification of crude terephthalic acid can be reused without reducing the concentration of impurities in the crude terephthalic acid in advance. (Industrial Applicability) With the present invention, the discharged water can be refined without consuming a large amount of energy, so that it can be reused, so that the p-phenylenedicarboxylic acid, which has been discarded at present, can be converted into the final product, p-phenylenedihydrazone. Acid and recycle. [Brief description of the drawings] Fig. 1 is an explanatory diagram showing an example of an implementation method for purifying the discharged water of the present invention. (Example 1) [Description of main component symbols] 1 Crude terephthalic acid supply path 2 Refined terephthalic acid 3 Condenser 4 Discharge water 5 Crystallization step hot water 6 Paraxylene 7 Oxidation step 8 Heating dissolution step 9 Add Hydrogen step 13 312XP / Invention specification (Supplement) / 94-03 / 93134052 200530175 10 Crystallization step 11 Solid-liquid separation step 12 Drying step 13 Extraction step 13- -1 Stage 1 stirring 13- -2 Stage 1 standing separation 13- -3 2nd stage stirring 13- -4 2nd stage standing separation 14 water 15 distilled water 16 stripper 17 low > pf point impurities 18 p-xylene 14 312XP / Invention Manual (Supplement) / 94- 03/93134052