JP3831952B2 - Method for producing terephthalic acid - Google Patents
Method for producing terephthalic acid Download PDFInfo
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- JP3831952B2 JP3831952B2 JP00508795A JP508795A JP3831952B2 JP 3831952 B2 JP3831952 B2 JP 3831952B2 JP 00508795 A JP00508795 A JP 00508795A JP 508795 A JP508795 A JP 508795A JP 3831952 B2 JP3831952 B2 JP 3831952B2
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- JP
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- Prior art keywords
- terephthalic acid
- dryer
- purified
- acid solution
- crystals
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- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts
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- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
Description
【０００１】
【産業上の利用分野】
本発明はテレフタル酸の製造方法に関するものであり、詳しくはテレフタル酸水溶液から析出させたテレフタル酸結晶を乾燥する方法に関するものである。
【０００２】
【従来の技術】
テレフタル酸はポリエステルの原料として工業的に大規模に製造されている。その製造法はいくつか知られているが、現在では臭素およびマンガン、コバルト等の重金属から成る触媒を溶解した酢酸溶液を収容した酸化反応帯域中に、パラキシレン及び分子状酸素含有ガスを連続的に供給し、パラキシレンを酸化してテレフタル酸とする方法が主流をなしている。この方法で得られるテレフタル酸は、精密に制御された条件下で改良された工程により製造されたものはそのまま各種の用途に供することができるが、通常は更に精製して各種の用途に供されている。精製法としては、テレフタル酸を高温、高圧下で水に溶解してテレフタル酸水溶液とし、これをパラジウム等の白金族金属触媒と接触させる方法が主として用いられている。この場合、分子状水素が共存すると精製が更に良好に進行する。従って代表的な精製法では、活性炭にパラジウムを担持させた触媒を充填した精製塔にテレフタル酸水溶液と水素ガスとを２６０〜３２０℃の温度で流通させることにより、粗テレフタル酸の精製が行なわれる。精製塔から流出したテレフタル酸水溶液は、晶析装置、通常は順次降温する３〜５個の晶析槽を直列に接続した連続多段晶析装置に供給され、テレフタル酸を晶析させてテレフタル酸の水スラリーとする。次いでこのスラリーから濾過、遠心分離等の分離手段により精製テレフタル酸結晶が回収され、乾燥装置で乾燥して製品のテレフタル酸とされる。
【０００３】
【発明が解決しようとする課題】
水スラリーから分離した湿った精製テレフタル酸結晶の乾燥には、処理量が大きく、且つ連続的に乾燥できる回転乾燥器が適している。特に好適なのは、水蒸気が流通する加熱管を備えた回転乾燥器である。テレフタル酸結晶は非腐蝕性であり、かつ付着している母液は水なので、乾燥器は安価な軟鋼又は万一の腐蝕をおもんばかってステンレススチールで製作される。
【０００４】
しかし、一般に耐蝕性が高いとされているニッケル−クロム系のステンレススチールで製作しても、乾燥器に腐蝕が発生することが判明した。乾燥器に腐蝕が発生すると、腐蝕生成物（＝錆）が製品のテレフタル酸中に混入して、このテレフタル酸から製造したポリエチレンテレフタレートを紡糸する際に糸切れを起す原因となる。従って乾燥器における腐蝕は極力避けなければならない。
【０００５】
この乾燥器における腐蝕は、乾燥器のなかでもテレフタル酸結晶の乾燥が進行してテレフタル酸結晶が約１００〜１４０℃に達する部分、すなわち乾燥が完結する部分で多く発生する。また、乾燥器内を非爆発性雰囲気に保ち、かつ器内で発生した水蒸気をすみやかに器外に排出して乾燥を促進するために乾燥器には不活性ガスを導入するが、このガスとして酸化反応帯域から排出された主として窒素などの不活性ガスからなる廃ガスを用いると、腐蝕が更に促進される。
【０００６】
【課題を解決するための手段】
本発明者らは乾燥器における腐蝕の原因について検討した結果、これが触媒に由来する臭素に起因することを知得した。すなわち酸化工程で得られた粗テレフタル酸中には触媒に由来する臭素が微量含まれているので、精製工程に供給されるテレフタル酸水溶液には臭素が微量ではあるが溶解している。従って晶析工程で得られた精製テレフタル酸結晶に付着している水には臭素が含まれている。乾燥器中で精製テレフタル酸結晶の乾燥が進行すると、付着水中の臭素濃度が高くなり、テレフタル酸結晶と接触する部分の装置を腐蝕させるものと考えられる。また、酸化反応帯域から排出された廃ガス中には微量の臭化物が含まれているので、この廃ガスを乾燥器に供給すると臭化物が乾燥器の高温部で分解して臭素を生成し、これが腐蝕を更に助長するものと考えられる。
【０００７】
本発明者らの検討によれば、このような乾燥器の腐蝕は、腐蝕が発生する部分をニッケル基合金で製作することにより回避できる。ニッケル基合金とは、ニッケルを４５（重量）％以上含有する合金であり、ハステロイ（登録商標）として知られているニッケル−モリブデン合金やニッケル−モリブデン−クロム合金、モネル鋼などのニッケル−銅合金などがあげられる。これらのニッケル基合金は非常に高価なので、乾燥器のうち乾燥初期〜中期のテレフタル酸結晶と接する低温部分は通常のステンレススチールで製作し、乾燥が進行してテレフタル酸結晶が約１００℃以上、特に１１０℃以上に達する高温部分をニッケル基合金で製作するのが有利である。
【０００８】
本発明による精製テレフタル酸結晶の乾燥は、このような高温のテレフタル酸結晶と接触する部分をニッケル基合金で製作した乾燥器を用いる以外は常法に従って行なうことができる。例えば加熱管つき回転乾燥器を用いる場合には、乾燥器の入口端から湿った精製テレフタル酸結晶を連続的に供給し、加熱管に２〜６ｋｇ／ｃｍ2 Ｇの水蒸気を供給して加熱しながら、滞留時間が１０〜６０分間、テレフタル酸結晶の出口温度（最高温度）が約１１０〜１５０℃となるように操作すればよい。
【０００９】
【実施例】
以下に実施例及び比較例により本発明をさらに具体的に説明するが、本発明は以下の実施例に限定されるものではない。
【００１０】
比較例１
コバルト−マンガン−臭素触媒を含む酢酸溶媒（触媒濃度は、原子としてコバルト約３００ｐｐｍ、マンガン約２００ｐｐｍ、臭素約１０００ｐｐｍ）中でパラキシレンを空気で酸化して粗テレフタル酸を製造した。
この粗テレフタル酸を水と混合してテレフタル酸の約３０重量％スラリーとし、これを約２９０℃に加熱してテレフタル酸水溶液としたのち、活性炭にパラジウムを担持した触媒を充填した精製塔に供給した。精製塔にはテレフタル酸１０００ｋｇ当り３Ｎｍ3 の水素ガスを同時に供給した。
【００１１】
精製塔から流出したテレフタル酸水溶液は多段晶析装置で最終温度１５０℃まで順次降温させながら晶析を行ない、得られたテレフタル酸スラリーを１５０℃で固液分離した。
加熱管つきのＳＵＳ３１６製の回転乾燥器に、上記で得た湿ったテレフタル酸結晶を連続的に送入し、加熱管に約４ｋｇ／ｃｍ2 Ｇの水蒸気を供給しながら、平均滞留時間約３０分間、出口温度（最高温度）約１３０℃の条件で乾燥を行なった。なお、回転乾燥器には、テレフタル酸１０００ｋｇ当り窒素ガスを約４０Ｎｍ3 導入した。このようにして運転を継続したところ、約６ケ月で乾燥器に腐蝕が発生した。
【００１２】
実施例１
上記の比較例で用いた回転乾燥器のうち、テレフタル酸結晶の温度が約１１０℃に達する部分以降にハステロイ（登録商標）Ｃで厚さ２ｍｍのライニングを施した。この乾燥機を用いた以外は比較例１と全く同様にして乾燥を行なったところ、１ケ年経過しても目視による腐蝕発生は認められなかった。
【００１３】
【発明の効果】
本発明によれば乾燥が進行して高温のテレフタル酸結晶と接触する部分をニッケル基合金で製作した乾燥器を用いてテレフタル酸結晶の乾燥を行なうことにより、乾燥器の腐蝕を回避し、腐蝕生成物の混入によるテレフタル酸の品質低下を防止することができる。[0001]
[Industrial application fields]
The present invention relates to a method for producing terephthalic acid, and more particularly to a method for drying terephthalic acid crystals precipitated from an aqueous terephthalic acid solution.
[0002]
[Prior art]
Terephthalic acid is industrially produced on a large scale as a raw material for polyester. Several production methods are known. At present, paraxylene and a molecular oxygen-containing gas are continuously fed into an oxidation reaction zone containing an acetic acid solution in which a catalyst composed of bromine and a heavy metal such as manganese and cobalt is dissolved. The mainstream is to oxidize para-xylene to terephthalic acid. The terephthalic acid obtained by this method can be used as it is for various applications as it is produced by an improved process under precisely controlled conditions, but it is usually further purified and used for various applications. ing. As a purification method, a method in which terephthalic acid is dissolved in water at high temperature and high pressure to form an aqueous terephthalic acid solution, which is contacted with a platinum group metal catalyst such as palladium is mainly used. In this case, if molecular hydrogen coexists, purification proceeds even better. Therefore, in a typical purification method, crude terephthalic acid is purified by circulating an aqueous terephthalic acid solution and hydrogen gas at a temperature of 260 to 320 ° C. through a purification tower packed with a catalyst in which palladium is supported on activated carbon. . The aqueous terephthalic acid solution flowing out from the purification tower is supplied to a crystallizer, usually a continuous multi-stage crystallizer in which 3 to 5 crystallizers that are gradually cooled are connected in series. A water slurry of Subsequently, purified terephthalic acid crystals are recovered from the slurry by a separation means such as filtration and centrifugation, and dried in a drying apparatus to obtain a product terephthalic acid.
[0003]
[Problems to be solved by the invention]
For drying the wet purified terephthalic acid crystals separated from the water slurry, a rotary dryer having a large throughput and capable of continuous drying is suitable. Particularly suitable is a rotary dryer equipped with a heating tube through which water vapor flows. Since terephthalic acid crystals are non-corrosive and the mother liquor that is attached is water, the dryer is made of cheap mild steel or stainless steel with a little corrosion.
[0004]
However, it has been found that even when made of nickel-chromium stainless steel, which is generally considered to have high corrosion resistance, corrosion occurs in the dryer. When corrosion occurs in the dryer, the corrosion product (= rust) is mixed in the terephthalic acid of the product and causes thread breakage when spinning polyethylene terephthalate produced from this terephthalic acid. Therefore, corrosion in the dryer must be avoided as much as possible.
[0005]
Corrosion in this dryer occurs frequently in the portion where drying of terephthalic acid crystals proceeds to reach about 100 to 140 ° C., that is, in the portion where drying is completed, in the dryer. In addition, an inert gas is introduced into the dryer in order to keep the inside of the dryer in a non-explosive atmosphere and promptly discharge the water vapor generated in the vessel to accelerate the drying. Corrosion is further promoted by using a waste gas mainly composed of an inert gas such as nitrogen discharged from the oxidation reaction zone.
[0006]
[Means for Solving the Problems]
As a result of examining the cause of corrosion in the dryer, the present inventors have found that this is caused by bromine derived from the catalyst. In other words, the crude terephthalic acid obtained in the oxidation step contains a small amount of bromine derived from the catalyst, so that a small amount of bromine is dissolved in the terephthalic acid aqueous solution supplied to the purification step. Therefore, the water adhering to the purified terephthalic acid crystal obtained in the crystallization step contains bromine. As the drying of the purified terephthalic acid crystal proceeds in the dryer, the concentration of bromine in the adhering water increases, which is considered to corrode the device in contact with the terephthalic acid crystal. In addition, since the waste gas discharged from the oxidation reaction zone contains a small amount of bromide, when this waste gas is supplied to the dryer, the bromide decomposes at the high temperature part of the dryer to produce bromine, which is It is thought to further promote corrosion.
[0007]
According to the study by the present inventors, such corrosion of the dryer can be avoided by manufacturing a portion where corrosion occurs with a nickel-based alloy. The nickel-based alloy is an alloy containing 45% (by weight) or more of nickel and is known as Hastelloy (registered trademark), such as nickel-molybdenum alloy, nickel-molybdenum-chromium alloy, and nickel-copper alloy such as Monel steel. Etc. Since these nickel-based alloys are very expensive, the low-temperature part in contact with the terephthalic acid crystals in the drying initial stage to the middle stage of the dryer is made of ordinary stainless steel, and the drying progresses so that the terephthalic acid crystals are about 100 ° C. or higher. In particular, it is advantageous to manufacture the high temperature part reaching 110 ° C. or more with a nickel-base alloy.
[0008]
The purified terephthalic acid crystal according to the present invention can be dried in accordance with a conventional method except that a dryer in which a portion in contact with the high-temperature terephthalic acid crystal is made of a nickel-based alloy is used. For example, when using a rotary dryer with a heating tube, wet purified terephthalic acid crystals are continuously supplied from the inlet end of the dryer, and 2 to 6 kg / cm 2 G of steam is supplied to the heating tube and heated. However, the operation may be performed such that the residence time is 10 to 60 minutes and the outlet temperature (maximum temperature) of the terephthalic acid crystal is about 110 to 150 ° C.
[0009]
【Example】
EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples below, but the present invention is not limited to the following examples.
[0010]
Comparative Example 1
Crude terephthalic acid was produced by oxidizing paraxylene with air in an acetic acid solvent containing a cobalt-manganese-bromine catalyst (catalyst concentration was about 300 ppm cobalt, about 200 ppm manganese, and about 1000 ppm bromine).
This crude terephthalic acid is mixed with water to make a slurry of about 30% by weight of terephthalic acid. This is heated to about 290 ° C to form an aqueous terephthalic acid solution, and then supplied to a purification tower packed with a catalyst supporting palladium on activated carbon. did. The purification tower was simultaneously supplied with 3 Nm 3 of hydrogen gas per 1000 kg of terephthalic acid.
[0011]
The aqueous terephthalic acid solution that flowed out of the purification tower was crystallized while being gradually cooled to a final temperature of 150 ° C. by a multistage crystallizer, and the resulting terephthalic acid slurry was solid-liquid separated at 150 ° C.
The wet terephthalic acid crystal obtained above was continuously fed into a SUS316 rotary dryer with a heating tube, and an average residence time of about 30 minutes while supplying about 4 kg / cm 2 G of water vapor to the heating tube. Then, drying was performed under conditions of an outlet temperature (maximum temperature) of about 130 ° C. In the rotary dryer, about 40 Nm 3 of nitrogen gas was introduced per 1000 kg of terephthalic acid. When the operation was continued in this way, corrosion occurred in the dryer in about 6 months.
[0012]
Example 1
In the rotary dryer used in the above comparative example, a lining having a thickness of 2 mm was applied with Hastelloy (registered trademark) C after the portion where the temperature of the terephthalic acid crystal reached about 110 ° C. When drying was performed in the same manner as in Comparative Example 1 except that this dryer was used, no visual corrosion was observed even after one year.
[0013]
【The invention's effect】
According to the present invention, the drying of the terephthalic acid crystal is performed using a dryer made of a nickel-based alloy at the portion where the drying progresses and comes into contact with the high-temperature terephthalic acid crystal, thereby avoiding the corrosion of the dryer. It is possible to prevent the quality of terephthalic acid from being deteriorated due to the mixing of the product.
Claims (1)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP00508795A JP3831952B2 (en) | 1995-01-17 | 1995-01-17 | Method for producing terephthalic acid |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP00508795A JP3831952B2 (en) | 1995-01-17 | 1995-01-17 | Method for producing terephthalic acid |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH08193048A JPH08193048A (en) | 1996-07-30 |
| JP3831952B2 true JP3831952B2 (en) | 2006-10-11 |
Family
ID=11601618
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP00508795A Expired - Lifetime JP3831952B2 (en) | 1995-01-17 | 1995-01-17 | Method for producing terephthalic acid |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3831952B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP4402119A4 (en) * | 2021-09-16 | 2025-10-15 | Circ Llc | Process for aging regenerated diacid crystals |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP4206270A4 (en) * | 2021-07-19 | 2025-04-09 | Lg Chem, Ltd. | MONOMER COMPOSITION FOR SYNTHESIZING RECYCLED PLASTIC, METHOD FOR PREPARING SAME, AND RECYCLED PLASTIC, MOLDED ARTICLE AND PLASTICIZER COMPOSITION USING SAME |
-
1995
- 1995-01-17 JP JP00508795A patent/JP3831952B2/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP4402119A4 (en) * | 2021-09-16 | 2025-10-15 | Circ Llc | Process for aging regenerated diacid crystals |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH08193048A (en) | 1996-07-30 |
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