WO2010134434A1 - (メタ)アクリル酸の製造方法 - Google Patents
(メタ)アクリル酸の製造方法 Download PDFInfo
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- WO2010134434A1 WO2010134434A1 PCT/JP2010/057815 JP2010057815W WO2010134434A1 WO 2010134434 A1 WO2010134434 A1 WO 2010134434A1 JP 2010057815 W JP2010057815 W JP 2010057815W WO 2010134434 A1 WO2010134434 A1 WO 2010134434A1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D9/00—Crystallisation
- B01D9/0004—Crystallisation cooling by heat exchange
- B01D9/0013—Crystallisation cooling by heat exchange by indirect heat exchange
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/42—Separation; Purification; Stabilisation; Use of additives
- C07C51/43—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation
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- the present invention relates to a method for producing (meth) acrylic acid.
- (Meth) acrylic acid is generally purified by introducing a (meth) acrylic acid-containing reaction gas obtained by a gas-phase catalytic oxidation reaction into a condensation tower or collection tower to obtain a crude (meth) acrylic acid solution. Manufactured by. As such a purification method, crystallization is used in addition to distillation, diffusion, extraction and the like.
- Patent Document 1 in order to more easily obtain high-purity (meth) acrylic acid, a (meth) acrylic acid-containing gas obtained by catalytic gas phase oxidation is condensed, and (meth) is further obtained from the obtained solution.
- a technique for crystallizing acrylic acid is disclosed. Examples of the crystallization temperature include temperature ranges of ⁇ 25 ° C. to + 14 ° C. and 12 ° C. to ⁇ 5 ° C.
- the crude solution is cooled from room temperature to ⁇ 0.9 ° C. to form the first acrylic acid crystals, and further cooled to ⁇ 4.4 ° C. over 3 hours and 54 minutes. is doing.
- Patent Document 2 discloses a technique in which a crude solution is preliminarily cooled to a temperature below the freezing point before the crystallization step to precipitate crystals, and then a mixture of the crystals and the crude solution is supplied to the crystallization tank. Yes. According to this technique, it is said that a coarse crystal having excellent filterability and the like can be obtained, and scale formation in the crystallization tank can be suppressed.
- a crude solution having a freezing point of 8.5 ° C. is preliminarily cooled to 8.3 ° C. and supplied to the crystallization tank together with the generated crystals.
- this technique is characterized in that crystals are preliminarily obtained before the crude solution is introduced into the crystallization tank, and the purity of the crystals is not considered.
- an object of the present invention is to provide a method for stably and efficiently obtaining high-purity (meth) acrylic acid by crystallization.
- the inventors of the present invention have made extensive studies to solve the above problems. As a result, before the crude (meth) acrylic acid solution is cooled to below the freezing point and crystallized, the crude solution is cooled to such an extent that crystals do not precipitate, and then the crude solution is cooled to below the freezing point. In this state, it was found that (meth) acrylic acid with higher purity could be stably obtained, and the present invention was completed.
- the method for producing (meth) acrylic acid according to the present invention is such that the temperature of the cooling medium discharged from the crystallizer is above the freezing point of the crude (meth) acrylic acid solution in the crystallizer and the freezing point is + 5 ° C. or lower.
- a step of bringing the crude (meth) acrylic acid solution in the crystallizer into a supercooled state and a step of crystallizing (meth) acrylic acid from the crude (meth) acrylic acid solution.
- the temperature of the cooling medium supplied to the crystallizer for bringing the crude (meth) acrylic acid solution into a supercooled state is 1-10 ° C. lower than the freezing point of the crude (meth) acrylic acid solution. It is preferable that If the crude (meth) acrylic acid solution is cooled in a short time with an excessively low temperature cooling medium, crystallization proceeds rapidly after supercooling, and the purity of the crystal may be reduced. However, if the temperature of the cooling medium is set to a temperature 1 to 10 ° C. lower than the freezing point of the crude solution, the crude solution can be more reliably obtained without excessively cooling the crude solution.
- the method of the present invention it is preferable to use a falling film type crystallizer.
- the falling film type crystallizer the cold heat of the cooling medium is easily efficiently transferred to the crude (meth) acrylic acid solution through the heat transfer surface, the temperature of the crude solution is easily controlled, and high-purity crystals can be obtained. It is easy to be done.
- FIG. 1 is a schematic view showing an embodiment of a crystallization apparatus used in the method of the present invention.
- 1 is a crystallizer
- 2 is a cooling medium inlet
- 3 is a cooling medium outlet
- 4 is a pump
- 5 is a pressure gauge
- 6 is a valve
- 7 is heat exchange.
- 8 is a crude (meth) acrylic acid solution tank.
- Pre-cooling step In the method of the present invention, first, until the temperature of the cooling medium discharged from the crystallizer is stabilized above the freezing point of the crude (meth) acrylic acid solution in the crystallizer and below the freezing point + 5 ° C. The crude (meth) acrylic acid solution in the crystallizer is cooled.
- the crude (meth) acrylic acid solution is not particularly limited as long as it contains impurities in addition to the target compound (meth) acrylic acid.
- a crude (meth) acrylic acid solution obtained by bringing a (meth) acrylic acid-containing gas obtained by a catalytic gas phase oxidation reaction into contact with a collection liquid or condensing can be mentioned.
- the crude (meth) acrylic acid solution obtained by bringing the (meth) acrylic acid-containing gas into contact with the collection liquid or condensing includes water, acetic acid, propionic acid in addition to (meth) acrylic acid and unreacted raw materials.
- By-product impurities such as maleic acid, acetone, acrolein, furfural and formaldehyde are contained.
- the (meth) acrylic acid once purified by crystallization is melted and then supplied to the crystallizer instead of the crude (meth) acrylic acid solution.
- the purification may be repeated twice or more.
- crystallization purification is repeated twice or more, even if (meth) acrylic acid purified one or more times is further crystallized, it is referred to as a crude solution.
- (meth) acrylic acid is crystallized and purified using a crystallizer
- the type of crystallizer is not particularly limited.
- a crystallizing apparatus for dynamic crystallization such as a falling liquid film type or a completely poured tube type. This is because the cold heat of the cooling medium is easily transmitted to the crude (meth) acrylic acid solution via the heat transfer surface of the crystallizer, and the temperature control of the crude solution becomes easier.
- a falling film type crystallizer is suitable.
- FIG. An example of a dynamic crystallizer used in the method of the present invention is shown in FIG.
- the present invention is not limited to such an embodiment.
- the crystallization apparatus 1 shown in FIG. 1 can adjust the temperature or crystallization of (meth) acrylic acid while circulating a crude (meth) acrylic acid solution. That is, the crude (meth) acrylic acid solution supplied to the falling liquid film crystallizer 1 is supplied from the upper part of the crystallizer 1 by the pump 4. The supplied crude solution falls inside the crystallization tube in the crystallizer.
- the crystallization tube is not particularly limited, but is made of a material having excellent corrosion resistance such as stainless steel and copper, and having a high thermal conductivity. Cold or warm heat is transferred to the crude solution in the crystallization tube via the heat transfer surface.
- the crude solution stored in the tank 8 may be adjusted in temperature by the heat exchanger 7 before being supplied to the crystallizer 1, or may be supplied to the crystallizer 1 as it is and the temperature in the crystallizer 1. May be adjusted. However, if the temperature of the crude solution stored in the tank 8 is too high, cooling in the crystallizer 1 takes time, leading to a decrease in productivity. Therefore, the temperature is about 3 to 20 ° C. as the freezing point. It is preferable to do. Such temperature control can be performed by the valve 6.
- the crystallizer 1 is configured so that the heat of the heat medium can be sufficiently transferred to the crude (meth) acrylic acid.
- the diameter of the crystallization tube is about 50 mm or more and 100 mm or less, but the tube length is about 15 m or more and 25 m or less, the surface area of the heat transfer surface can be sufficiently increased.
- there may be one crystallization tube it is possible to further increase the heat transfer surface area by using a plurality of crystallization tubes.
- the crude solution before crystallizing (meth) acrylic acid from the crude solution, in the crystallizer, the crude solution is prepared so that (meth) acrylic acid does not precipitate and the temperature of the crude solution is as low as possible. Cooling. Such an operation then allows the crude solution to be brought into a well-defined supercooled state.
- the freezing point of the crude (meth) acrylic acid solution may be measured by a preliminary experiment or the like. Specifically, a part of the crude solution is collected and gradually cooled, and the temperature at which crystals are formed can be set as the freezing point.
- the melting point of acrylic acid is 13.5 ° C. and the melting point of methacrylic acid is 15.0 ° C.
- the solution derived from the catalytic gas phase oxidation reaction contains impurities, its freezing point is determined by Also lower.
- the temperature of the crude (meth) acrylic acid solution in the crystallizer may be measured before the crude solution reaches the liquid pool at the bottom of the crystallizer via the heat transfer surface in the crystallizer of FIG. .
- the solution was excessively cooled from the beginning to precipitate (meth) acrylic acid.
- the purity of the crystals obtained is not sufficient, and the number of crystallizations has to be increased in order to obtain crystals with satisfactory purity.
- the temperature of the cooling medium discharged from the crystallizer is stabilized above the freezing point of the crude (meth) acrylic acid solution in the crystallizer and below the freezing point + 5 ° C.
- the crude solution in the crystallizer is stabilized at approximately the same temperature.
- the heat of the crude solution affected the heat transfer surface of the crystallizer.
- the temperature of the cooling medium that is applied to the cooling medium and discharged from the crystallizer (the temperature at the outlet of the crystallizer of the cooling medium) is the temperature of the cooling medium that is supplied to the crystallizer (the inlet of the crystallizer of the cooling medium) Temperature).
- the overall temperature of the crude solution is sufficiently lowered according to the set temperature of the cooling medium supplied to the crystallizer, and the temperature of the crude solution when it is circulated and supplied to the cooler (the crystallizer for the crude solution)
- the cooling heat taken by the heat transfer surface becomes constant, and the temperature of the cooling medium discharged from the crystallizer is also stabilized.
- the crude solution cooled on the heat transfer surface of the crystallizer is also obtained. It shall be regarded as stabilizing at the same temperature.
- the temperature of the cooling medium supplied to the crystallizer (the temperature of the inlet of the crystallizer) is the temperature of the cooling medium discharged from the crystallizer (the temperature of the outlet of the crystallizer) or the temperature of the crystallizer. What is necessary is just to adjust suitably according to the change of the temperature (the crystallizer exit temperature of a crude solution) of a crude solution to be. For example, if the cooling medium inlet temperature of the crystallizer is set higher than the freezing point of the crude solution, it takes time until the crude solution is sufficiently cooled and the crystallizer outlet temperature of the cooling medium stabilizes. High (meth) acrylic acid crystals are obtained.
- the cooling medium inlet temperature of the crystallizer is set below the freezing point of the crude solution, and the crystallizer outlet temperature of the cooling medium or the crystallizer outlet temperature of the crude solution is changed. If the inlet temperature of the crystallizer of the cooling medium is adjusted above the freezing point of the crude solution so that a part of the crude solution does not solidify, the purity of the resulting crystals may be slightly reduced, The time required for stabilizing the outlet temperature of the crystallizer can be shortened, and more efficient crystallization can be achieved.
- the crystallization device outlet temperature of the cooling medium is stabilized at the freezing point of the crude solution + 5 ° C or less for the purpose of shortening the cooling time rather than the purification degree. If it does, you may raise gradually the crystallizer entrance temperature of a cooling medium from below the freezing point of a crude solution.
- “to stabilize” the temperature of the cooling medium discharged from the crystallizer means that the temperature change per hour of the cooling medium becomes 1.0 ° C./min or less.
- Subcooling step In the present invention, after the temperature of the cooling medium discharged from the crystallizer is stabilized within the above-mentioned predetermined temperature range, the set temperature of the cooling medium supplied to the crystallizer is lowered below the freezing point of the crude solution. A clear supercooling state is achieved by lowering the temperature of the crude solution in the analyzer beyond its freezing point.
- the solution immediately before the compound crystallizes is in a supercooled state.
- a clear supercooled state cannot often be confirmed.
- the crude solution is cooled and stabilized as much as possible within the range in which (meth) acrylic acid does not precipitate, and then cooled beyond the freezing point to obtain a clear supercooled state.
- the temperature of the cooling medium supplied to the crystallization apparatus is Set to a temperature 1 ° C. or more lower than the freezing point of the crude solution. If the temperature is set to a temperature lower by 1 ° C. or more than the freezing point of the crude solution, the crude solution can be clearly put into a supercooled state together with the preliminary cooling.
- the supercooled state means that the temperature of the crude (meth) acrylic acid solution is once lowered by 0.1 ° C. or more from its freezing point without forming crystals of (meth) acrylic acid. To do.
- the temperature of the cooling medium for bringing the crude solution into a supercooled state at a temperature 1 to 10 ° C. lower than the freezing point of the crude solution.
- the crude solution can be brought into a supercooled state by cooling beyond the freezing point.
- the cooling medium temperature is set to a temperature 1 to 10 ° C. lower than the freezing point of the crude solution, the Pure (meth) acrylic acid crystals can be obtained more reliably.
- (meth) acrylic acid crystals are deposited on the heat transfer surface inside the crystallization tube.
- a (meth) acrylic acid crystal grows by supplying the crude solution to the (meth) acrylic acid crystal crystallized through the supercooled state while cooling the crude solution. After sufficiently crystallization of (meth) acrylic acid from the crude solution, normal post-treatment may be performed.
- impurities may be mixed in the vicinity of the crystal surface, or impurities may adhere to the crystal surface, so a sweating process is performed to partially melt the crystal surface to remove the impurities. Also good.
- the cooling medium may be switched to the heating medium, and the crystal may be partially melted at an appropriate temperature. After a highly pure (meth) acrylic acid crystal is obtained, the temperature of the heating medium may be raised to melt the crystal and take it out of the crystallizer. In order to obtain higher-purity (meth) acrylic acid crystals, dissolved (meth) acrylic acid is supplied to a crystallizer and crystallization purification is repeated.
- Example 1 Initiation of Crystallization Purification of Acrylic Acid
- Crude acrylic acid solution Propylene was subjected to a catalytic gas phase oxidation reaction in a reactor.
- the obtained reaction gas was introduced into a collection tower and brought into contact with the collection liquid, and a crude acrylic acid solution was obtained from the bottom of the collection tower.
- the composition of the crude acrylic acid solution was acrylic acid 90.0% by mass, water 3.2% by mass, acetic acid 1.9% by mass, maleic acid 0.6% by mass, acrylic acid dimer 1.5% by mass, They were 0.07 mass% furfural, 0.27 mass% benzaldehyde, 0.06 mass% formaldehyde, 0.1 mass% hydroquinone, and 2.3 mass% other impurities.
- the freezing point of the solution was measured and found to be 8.0 to 8.5 ° C.
- the crystallization tube in the crystallization apparatus is a metal tube having a diameter of 70 mm and a length of 18 m. Further, the crystallizer can transfer the crude solution to the upper part of the tube by a circulation pump and flow the crude solution onto the wall surface of the crystallization tube in a falling film form (Falling Film).
- thermometers were installed at the inlet and outlet portions of the heating medium and the portion immediately before the crystallization tube and the portion immediately after the crystallization tube of the crude solution supply pipe.
- the crude solution was extracted from the bottom, and circulation supply was started at a supply rate of 0.34 m 3 / hr.
- a cooling medium set at 25 to 30 ° C. was started to be supplied to the crystallizer at a supply rate of 0.82 m 3 / hr.
- the inlet temperature of the cooling medium was lowered by ⁇ 1.5 ° C. (difference from the freezing point of the crude solution: ⁇ 9.5 to ⁇ 10 ° C.).
- the outlet temperature of the crude solution once decreased to 7.5 ° C. and then increased to the above freezing point, and then the freezing point gradually decreased due to the concentration of impurities and the decrease in the purity of acrylic acid.
- the inlet temperature of the cooling medium was lowered to ⁇ 1.5 ° C. and then the temperature was gradually lowered.
- the circulation was stopped and the crude solution at the bottom of the crystallizer was extracted.
- the cooling medium was switched to a heating medium having a temperature near the freezing point to perform a sweating process, and then the melted portion was extracted from the bottom of the crystallizer. Further, the temperature of the heating medium was raised to completely melt the crystal, and the crystal was extracted from the bottom of the crystallizer.
- Example 2 Acrylic acid was obtained in the same manner as in Example 1 except that the inlet temperature of the cooling medium was changed to ⁇ 5.0 ° C. (difference from the freezing point of the crude solution: ⁇ 13 to ⁇ 13.5 ° C.) in the supercooling step. Manufactured. At this time, the outlet temperature of the crude acrylic acid solution once decreased to 7.5 ° C. due to the supercooled state. Thereafter, the measured value of the pressure gauge installed in the crystallizer during crystallization slightly increased, and it was confirmed that the upper part of the crystallization tube was clogged.
- Example 1 When the purity of the obtained acrylic acid was measured in the same manner as in Example 1, the acetic acid content was 1.06% by mass, the hydroquinone content was 0.028% by mass, and the purity was slightly lower than in Example 1. Was. The reason is considered that the crystallization progressed rapidly by changing the temperature of the cooling medium at the time of supercooling from ⁇ 1.5 ° C. to ⁇ 5 ° C., and the state of crystal attachment to the crystallization tube deteriorated.
- Comparative Example 1 The temperature of the cooling medium for cooling the crude acrylic acid solution was consistently 1 ° C (difference from the freezing point of the crude solution: -7 to -7.5 ° C), and the crystallization tube temperature of the crystallizer was crude acrylic.
- Acrylic acid was produced in the same manner as in Example 1 except that the circulation of the crude acrylic acid solution was started from the state where the acid was below the freezing point. At this time, the heat transfer surface temperature of the crystallization tube is below the freezing point, and since crystallization starts immediately after the start of circulation of the crude solution, no clear supercooling state is observed, and the crude solution temperature continues to drop to the freezing point. It was only.
- Example 3 Initiation of Crystallization Purification of Acrylic Acid (1) Acrylic Acid Melt Propylene was subjected to a catalytic gas phase oxidation reaction in a reactor. The obtained reaction gas was introduced into a collection tower and brought into contact with the collection liquid, and a crude acrylic acid solution was obtained from the bottom of the collection tower. The crude acrylic acid solution was purified several times with a crystallizer under normal conditions. The impurities contained in the obtained acrylic acid were acetic acid at 1500 mass ppm and hydroquinone at 1 mass ppm. When the freezing point of the melt was measured, it was 13 to 14 ° C.
- the inlet temperature of the cooling medium was lowered by 7 ° C. (difference from the freezing point of the crude solution: ⁇ 6 to ⁇ 7 ° C.).
- the outlet temperature of the melt once decreased to 12.8 ° C. and then increased to the above freezing point, and then the freezing point gradually decreased due to concentration of impurities and a decrease in acrylic acid purity.
- the inlet temperature of the cooling medium was lowered to 7 ° C. and then gradually decreased.
- the circulation was stopped and the melt at the bottom of the crystallizer was extracted.
- the cooling medium was switched to a heating medium having a temperature near the freezing point to perform a sweating process, and then the melted portion was extracted from the bottom of the crystallizer. Further, the temperature of the heating medium was raised to completely melt the crystal, and the crystal was extracted from the bottom of the crystallizer.
- Example 4 Acrylic acid was produced in the same manner as in Example 3 except that in the supercooling step, the inlet temperature of the cooling medium was changed to 2 ° C. (difference from the freezing point of the crude solution: ⁇ 11 to ⁇ 12 ° C.). At this time, the outlet temperature of the crude acrylic acid solution once decreased to 12.8 ° C. due to the supercooled state. Thereafter, the measured value of the pressure gauge installed in the crystallizer during crystallization slightly increased, and it was confirmed that the upper part of the crystallization tube was clogged.
- Comparative Example 2 The temperature of the cooling medium for cooling the crude acrylic acid solution was consistently 7.5 ° C. (difference from the freezing point of the crude solution: ⁇ 5.5 to ⁇ 6.5 ° C.).
- Acrylic acid was produced in the same manner as in Example 3 except that the circulation of the crude acrylic acid solution was started from the state where the temperature was not higher than the freezing point of the crude acrylic acid. At this time, the heat transfer surface temperature of the crystallization tube is below the freezing point, and since crystallization starts immediately after the start of circulation of the crude solution, no clear supercooling state is observed, and the crude solution temperature continues to drop to the freezing point. It was only.
- Example 5 Start of Crystallization Purification of Acrylic Acid (1) Precooling Step After supplying the same acrylic acid melt as obtained in Example 3 (1) above to the tank and adjusting the temperature to 22 ° C., 68.6 kg was supplied to the bottom of a falling film crystallizer as shown in FIG.
- thermometers were installed at the inlet and outlet portions of the heat medium, the portion immediately before the crystallization tube, and the portion immediately after the crystallization tube.
- the melt was extracted from the bottom, and circulation supply was started at a supply rate of 0.34 m 3 / hr.
- a cooling medium set at 25 to 30 ° C. was started to be supplied to the crystallizer at a supply rate of 0.82 m 3 / hr.
- the temperature of the cooling medium was gradually lowered, and when the melt reached 20.2 kg, the circulation was stopped and the melt at the bottom of the crystallizer was extracted.
- the cooling medium was switched to a heating medium having a temperature near the freezing point to perform a sweating process, and then the melted portion was extracted from the bottom of the crystallizer. Further, the temperature of the heating medium was raised to completely melt the crystal, and the crystal was extracted from the bottom of the crystallizer.
- the impurity content in the obtained acrylic acid was measured by liquid chromatography (manufactured by Shimadzu Corporation)
- the content of acetic acid was reduced to 500 ppm by mass, and was also measured by liquid chromatography (manufactured by Shimadzu Corporation).
- the hydroquinone content was reduced to less than 0.1 ppm by mass.
- the supercooled state of the crude acrylic acid solution is the same as in Examples 1-2 and Comparative Example 1 above.
- NO was observed, the impurity concentration of the obtained acrylic acid was high, while when the supercooled state was clearly recognized, the impurity concentration of acrylic acid was low.
- the purity is further increased when the cooling condition for creating the supercooled state is mild.
- the method of the present invention even from a crude (meth) acrylic acid solution containing a large amount of impurities such as those derived from a catalytic gas phase oxidation reaction and having a composition that can vary greatly depending on the reaction conditions, high purity ( Meta) acrylic acid can be obtained stably and efficiently. Therefore, the method of the present invention is extremely useful industrially as contributing to industrial mass production of (meth) acrylic acid.
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Abstract
Description
本発明方法では、先ず、晶析装置から排出される冷熱媒の温度が、晶析装置中の粗(メタ)アクリル酸溶液の凝固点超で且つ当該凝固点+5℃以下に安定化するまで、晶析装置中の粗(メタ)アクリル酸溶液を冷却する。
本発明では、晶析装置から排出される冷熱媒の温度が上記所定温度範囲で安定化した後、晶析装置へ供給する冷熱媒の設定温度を粗溶液の凝固点以下まで下げ、晶析装置内の粗溶液の温度を、その凝固点を超えて低下させることにより明確な過冷却状態にする。
本発明方法においては、粗(メタ)アクリル酸溶液を過冷却状態にした後、(メタ)アクリル酸を晶析させる。但し、図1に示す様な動的晶析装置の場合には、基本的に特別な処理をする必要は無い。粗溶液は常に流動しているため、いったん過冷却状態になれば、(メタ)アクリル酸は自然に晶析する。
(1) 粗アクリル酸溶液
反応器内でプロピレンを接触気相酸化反応に付した。得られた反応ガスを捕集塔に導入し、捕集液と接触させ、捕集塔の塔底より粗アクリル酸溶液を得た。当該粗アクリル酸溶液の組成は、アクリル酸90.0質量%、水3.2質量%、酢酸1.9質量%、マレイン酸0.6質量%、アクリル酸二量体1.5質量%、フルフラール0.07質量%、ベンズアルデヒド0.27質量%、ホルムアルデヒド0.06質量%、ハイドロキノン0.1質量%、その他の不純物2.3質量%であった。当該溶液の凝固点を測定したところ、8.0~8.5℃であった。
上記(1)で得た粗アクリル酸溶液をタンクへ供給し、温度を22℃に調節した後、図1に示すような流下液膜式晶析パイロット装置の底部へ55kg供給した。当該晶析装置中の晶析管は、直径70mm、長さ18mの金属管である。また、当該晶析装置は、循環ポンプにより粗溶液を管上部へ移送し、粗溶液を晶析管壁面へ落下被膜状(Falling Film)に流すことができるようになっている。当該晶析装置においては、熱媒の入口部分と出口部分および粗溶液供給管の晶析管直前部分と晶析管直後部分に温度計を設置した。当該粗溶液を底部から抜き出し、0.34m3/hrの供給速度で循環供給を開始した。また、同晶析装置へ、25~30℃に設定した冷熱媒を0.82m3/hrの供給速度で供給し始めた。
次いで、冷熱媒の入口温度を-1.5℃(粗溶液の凝固点との差:-9.5~-10℃)下げた。その結果、粗溶液の出口温度は7.5℃までいったん下がった後、上記凝固点まで上がり、次いで、不純物の濃縮とアクリル酸純度の低下により凝固点は徐々に降下していった。
過冷却工程において、冷熱媒の入口温度を-5.0℃(粗溶液の凝固点との差:-13~-13.5℃)に変更した以外は上記実施例1と同様にして、アクリル酸を製造した。この際、粗アクリル酸溶液の出口温度は過冷却状態によりいったん7.5℃まで下がった。その後、結晶化中において晶析装置に設置された圧力計の測定値が若干上昇し、晶析管上部が閉塞気味であることが確認されたが、最後まで運転することができた。
粗アクリル酸溶液を冷却するための冷熱媒の温度を一貫して1℃(粗溶液の凝固点との差:-7~-7.5℃)とし、晶析装置の晶析管温度が粗アクリル酸の凝固点以下となった状態から粗アクリル酸溶液の循環を開始した以外は上記実施例1と同様にして、アクリル酸を製造した。この際、晶析管の伝熱面温度が凝固点以下となっており、粗溶液の循環開始直後から結晶化が始まるため、明確な過冷却状態は認められず、粗溶液温度は凝固点まで下がり続けたのみであった。
(1) アクリル酸溶融液
反応器内でプロピレンを接触気相酸化反応に付した。得られた反応ガスを捕集塔に導入し、捕集液と接触させ、捕集塔の塔底より粗アクリル酸溶液を得た。当該粗アクリル酸溶液を晶析装置で通常の条件で数回精製した。得られたアクリル酸に含まれる不純物は、酢酸が1500質量ppmであり、ハイドロキノンが1質量ppmであった。当該溶融液の凝固点を測定したところ、13~14℃であった。
上記(1)で得たアクリル酸溶融液をタンクへ供給し、温度を22℃に調節した後、図1に示すような流下液膜式晶析装置の底部へ68.6kg供給した。当該晶析装置においては、熱媒の入口部分と出口部分および晶析管直前部分と晶析管直後部分に温度計を設置した。当該溶融液を底部から抜き出し、0.34m3/hrの供給速度で循環供給を開始した。また、同晶析装置へ、25~30℃に設定した冷熱媒を0.82m3/hrの供給速度で供給し始めた。
次いで、冷熱媒の入口温度を7℃(粗溶液の凝固点との差:-6~-7℃)下げた。その結果、溶融液の出口温度は12.8℃までいったん下がった後、上記凝固点まで上がり、次いで、不純物の濃縮とアクリル酸純度の低下により凝固点は徐々に降下していった。
過冷却工程において、冷熱媒の入口温度を2℃(粗溶液の凝固点との差:-11~-12℃)に変更した以外は上記実施例3と同様にして、アクリル酸を製造した。この際、粗アクリル酸溶液の出口温度は過冷却状態によりいったん12.8℃まで下がった。その後、結晶化中において晶析装置に設置された圧力計の測定値が若干上昇し、晶析管上部が閉塞気味であることが確認されたが、最後まで運転することができた。
粗アクリル酸溶液を冷却するための冷熱媒の温度を一貫して7.5℃(粗溶液の凝固点との差:-5.5~-6.5℃)とし、晶析装置の晶析管温度が粗アクリル酸の凝固点以下となった状態から粗アクリル酸溶液の循環を開始した以外は上記実施例3と同様にして、アクリル酸を製造した。この際、晶析管の伝熱面温度が凝固点以下となっており、粗溶液の循環開始直後から結晶化が始まるため、明確な過冷却状態は認められず、粗溶液温度は凝固点まで下がり続けたのみであった。
(1) 予備冷却工程
上記実施例3(1)で得たものと同様のアクリル酸溶融液をタンクへ供給し、温度を22℃に調節した後、図1に示すような流下液膜式晶析装置の底部へ68.6kg供給した。当該晶析装置においては、熱媒の入口部分と出口部分および晶析管直前部分と晶析管直後部分に温度計を設置した。当該溶融液を底部から抜き出し、0.34m3/hrの供給速度で循環供給を開始した。また、同晶析装置へ、25~30℃に設定した冷熱媒を0.82m3/hrの供給速度で供給し始めた。
次いで、冷熱媒の入口温度を降温速度0.8℃/分で下げた。その結果、冷熱媒の入口温度が9℃となった時点で、溶融液の出口温度は12.8℃までいったん下がった後、上記凝固点まで上がり、次いで、不純物の濃縮とアクリル酸純度の低下により凝固点は徐々に降下していった。
Claims (3)
- (メタ)アクリル酸を製造するための方法であって;
晶析装置から排出される冷熱媒の温度が、晶析装置中の粗(メタ)アクリル酸溶液の凝固点超で且つ当該凝固点+5℃以下に安定化するまで、晶析装置中の粗(メタ)アクリル酸溶液を冷却する工程;
次いで、晶析装置へ供給する冷熱媒の温度を、粗(メタ)アクリル酸溶液の凝固点から1℃以上低い温度とし、晶析装置中の粗(メタ)アクリル酸溶液を過冷却状態にする工程;および、
粗(メタ)アクリル酸溶液から(メタ)アクリル酸を結晶化させる工程;
を含むことを特徴とする方法。 - 粗(メタ)アクリル酸溶液を過冷却状態にするための、晶析装置へ供給する冷熱媒の温度を、粗(メタ)アクリル酸溶液の凝固点から1~10℃低い温度とする請求項1に記載の方法。
- 流下液膜式の晶析装置を用いる請求項1または2に記載の方法。
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