The present invention relates to a method of purifying hydrochloric acid, and more specifically, to a method of producing high-purity hydrochloric acid not containing an organic substance from hydrochloric acid containing the organic substance.
In the process of producing a compound in which a chloro compound is treated, hydrochloric acid is generated as a by-product and the like. This hydrochloric acid usually contains impurities characteristic of the producing process. For example, hydrochloric acid obtained as a by-product in the process of producing allyl chloride from propylene and chlorine gas contains organic impurities having a relatively low boiling point, such as 2-chloropropane (2CP) [bp=36° C.], allyl chloride [bp=23° C.] and isopropyl alcohol (IPA) [bp=82° C.]
Furthermore, hydrochloric acid obtained as a by-product in the process of obtaining isocyanate by the reaction of amine and phosgene contains organic impurities having a relatively high boiling point, such as chlorobenzene [bp=131° C.] and dichlorobenzene [bp=180° C.] which are mainly used as solvents.
In order to effectively utilize the above-described by-product hydrochloric acid as raw materials in other synthetic processes, it is preferable that a very small amount of organic impurities contained in the by-product hydrochloric acid is removed to the maximum extent possible. For example, Japanese Patent Laying-Open No. 2003-112907 (Patent Document 1) discloses that an organic substance in hydrogen chloride is removed by activated carbon adsorption.
However, it is difficult by the activated carbon adsorption to obtain high-purity hydrochloric acid by removing organic impurities having a relatively low boiling point, from hydrochloric acid containing the organic impurities, such as hydrochloric acid produced as a by-product in the process of producing allyl chloride.
An object of the present invention is to provide a method of producing high-purity hydrochloric acid substantially not containing an organic substance having a relatively low boiling point, specifically, −25° C. to 120° C., under atmospheric pressure, from hydrochloric acid containing the organic substance.
The present invention provides a method of purifying hydrochloric acid by removing an organic substance having a boiling point of −25° C. to 120° C. under atmospheric pressure from a first organic substance-containing hydrochloric acid that contains the organic substance and has a hydrogen chloride concentration higher than an azeotropic hydrogen chloride concentration under atmospheric pressure. The method includes the step of subjecting a second organic substance-containing hydrochloric acid to distillation using a distillation tower under atmospheric pressure, to distill out the organic substance from a top of the distillation tower. The second organic substance-containing hydrochloric acid is obtained by mixing the first organic substance-containing hydrochloric acid and water or dilute hydrochloric acid and has the hydrogen chloride concentration lower than the azeotropic hydrogen chloride concentration under atmospheric pressure.
During the distillation of the second organic substance-containing hydrochloric acid, it is preferable that the organic substance is distilled out from the top of the distillation tower while reflux is performed for condensing distillate gas from the top of the distillation tower and returning a part of an obtained condensate liquid to the top of the distillation tower.
The method of purifying hydrochloric acid according to the present invention includes, in one preferable embodiment, the steps of:
(a) continuously introducing, into the distillation tower, the second organic substance-containing hydrochloric acid obtained by mixing the first organic substance-containing hydrochloric acid and water or dilute hydrochloric acid and having the hydrogen chloride concentration lower than the azeotropic hydrogen chloride concentration under atmospheric pressure; and
(b) subjecting the second organic substance-containing hydrochloric acid introduced into the distillation tower to distillation under atmospheric pressure, to distill out the organic substance from the top of the distillation tower and continuously collect hydrochloric acid substantially not containing the organic substance from a bottom of the distillation tower.
The method of purifying hydrochloric acid according to the present invention includes, in another preferable embodiment, the steps of:
(i) continuously introducing the first organic substance-containing hydrochloric acid into the distillation tower and continuously introducing water from the top of the distillation tower into the distillation tower; and
(ii) subjecting the second organic substance-containing hydrochloric acid produced within the distillation tower to distillation under atmospheric pressure, to distill out the organic substance from the top of the distillation tower and continuously collect hydrochloric acid substantially not containing the organic substance from a bottom of the distillation tower.
The organic substance removed by the method of purifying hydrochloric acid according to the present invention is an organic substance having a boiling point of −25° C. to 120° C. under atmospheric pressure and suitable examples thereof include isopropyl alcohol, 2-chloropropane, allyl chloride, and the like.
According to the present invention, organic impurities can be effectively removed from hydrochloric acid containing the organic impurities having a boiling point of −25° C. to 120° C. under atmospheric pressure, and particularly, from hydrochloric acid containing the organic impurities and having a hydrogen chloride concentration higher than an azeotropic hydrogen chloride concentration under atmospheric pressure. Consequently, high-purity hydrochloric acid can be obtained.
Furthermore, the purifying method according to the present invention allows complete or almost complete elimination of the loss of hydrogen chloride, due to purification process, that is contained in the organic substance-containing hydrochloric acid subjected to purification. Accordingly, purified hydrochloric acid containing the total or almost total amount of hydrogen chloride contained in the organic substance-containing hydrochloric acid subjected to purification can be obtained.
The present invention relates to a method of purifying hydrochloric acid by removing an organic substance having a boiling point of −25° C. to 120° C. under atmospheric pressure from a first organic substance-containing hydrochloric acid that contains the organic substance and has a hydrogen chloride concentration higher than an azeotropic hydrogen chloride concentration under atmospheric pressure. The present invention will be hereinafter described in detail with reference to the embodiments.
(a) First Step
Hydrochloric acid containing the organic substance subjected to the purifying method according to the present invention is the first organic substance-containing hydrochloric acid that contains the organic substance having a boiling point of −25° C. to 120° C. under atmospheric pressure and has a hydrogen chloride concentration higher than an azeotropic hydrogen chloride concentration under atmospheric pressure. The organic substance having a boiling point of −25° C. to 120° C. under atmospheric pressure, that can be removed according to the present invention, may include various types of organic substances including, for example, isopropyl alcohol (IPA) [bp (the boiling point at 1 atm; the same shall apply hereinafter)=82° C.], 2-chloropropane (2-CP) [bp=36° C.], allyl chloride [bp=23° C.], carbon tetrachloride [bp=77° C.], dichloromethane [bp=40° C.], chloromethane [bp=−24° C.], dichloroethane [bp=57° C.], a vinyl chloride monomer [bp=−14° C.], and the like. Particularly, the present invention allows effective removal of isopropyl alcohol, 2-chloropropane, allyl chloride, and the like in hydrochloric acid. The number of types of the organic substances contained in the first organic substance-containing hydrochloric acid may be only one or two or more. The concentration of the organic substance contained in the first organic substance-containing hydrochloric acid is not particularly limited, but is usually approximately 1 to 10000 mass ppm in the first organic substance-containing hydrochloric acid, and preferably, approximately 10 to 1000 mass ppm.
The first organic substance-containing hydrochloric acid has a hydrogen chloride concentration [(mass of hydrogen chloride)/(the total mass of hydrogen chloride and water contained in the first organic substance-containing hydrochloric acid)×100%] higher than the azeotropic hydrogen chloride concentration of hydrochloric acid under atmospheric pressure. The “azeotropic hydrogen chloride concentration under atmospheric pressure” means the concentration of hydrogen chloride on the mass basis in the azeotropic composition of hydrochloric acid under atmospheric pressure. The relationship between the pressure and the azeotropic hydrogen chloride concentration of hydrochloric acid is described, for example, in “Soda Handbook” (published by Japan Soda Industry Association in 1998) and the like. The specific numerical value of the “azeotropic hydrogen chloride concentration under atmospheric pressure” can be referred to the document. The azeotropic hydrogen chloride concentration of hydrochloric acid is 20.2 percent by mass, and the azeotropic temperature (azeotropic point) is 108.7° C. at 101.3 kPa (1 atm). The first organic substance-containing hydrochloric acid is not particularly limited. However, for example, an organic substance-containing hydrochloric acid obtained as a by-product in various processes of producing an organic compound can be used as it is. In addition, those subjected to the process required for the organic substance-containing hydrochloric acid (adjustment of the hydrogen chloride concentration, pre-purification, or the like) can also be used. Furthermore, the first organic substance-containing hydrochloric acid may be obtained by absorbing, in water or hydrochloric acid, organic substance-containing hydrogen chloride gas obtained as a by-product in various processes of producing an organic compound.
In the present step, referring to
As long as the hydrogen chloride concentration of the second organic substance-containing hydrochloric acid is lower than the azeotropic hydrogen chloride concentration under atmospheric pressure, the hydrogen chloride concentration is not particularly limited. It is preferable that, though depending on the content of the organic substance in the first organic substance-containing hydrochloric acid, the hydrogen chloride concentration of the second organic substance-containing hydrochloric acid is closer to the azeotropic hydrogen chloride concentration under atmospheric pressure since the higher the hydrogen chloride concentration of the hydrochloric acid finally obtained by the purification process is, the more the versatility is enhanced and the added value is increased. Specifically, the hydrogen chloride concentration of the second organic substance-containing hydrochloric acid is preferably about 15 to 20 percent by mass, and more preferably, about 18 to 20 percent by mass.
The method of introducing the second organic substance-containing hydrochloric acid into distillation tower 101 is selected as appropriate depending on whether distillation of the second organic substance-containing hydrochloric acid in the subsequent step is performed in a batch-wise manner or in a continuous manner. As described below, it is preferable that the second organic substance-containing hydrochloric acid is subjected to distillation in a continuous manner. In this case, the second organic substance-containing hydrochloric acid is continuously introduced into distillation tower 101. In consideration of the separation efficiency of the organic substance by distillation and the efficiency of preventing distillation of hydrochloric acid out of the top of the tower, it is preferable that the position where the second organic substance-containing hydrochloric acid is introduced into distillation tower 101 (the position of piping 102 in distillation tower 101) is located in proximity to the center section with respect to the height direction of distillation tower 101.
(b) Second Step
In the present step, referring to
In the present invention, the operation pressure for distillation is assumed to be atmospheric pressure (usually, about −20 kPaG to 20 kPaG). The operation temperature for distillation (the temperature at the bottom of the distillation tower) depends on the operation pressure and the composition of the second organic substance-containing hydrochloric acid, but is usually approximately 103° C. to 114° C.
The type of the distillation tower is not particularly limited, and may be a commonly used distillation tower such as a packed tower or a tray tower, in which case a packed tower is preferable since it has a simplified structure. Examples of a packing agent packed into the packed tower may include, for example, a conventional agent such as Raschig ring, Paul ring, or Tellerette (registered trademark). In order to more efficiently suppress or prevent distillation of hydrochloric acid out of the top of the tower, it is preferable, as shown in
Distillation of the second organic substance-containing hydrochloric acid can be performed either in a continuous manner or in a batch-wise manner, but preferably performed in a continuous manner. In the case where distillation is performed in a batch-wise manner and the initial hydrogen chloride concentration of the second organic substance-containing hydrochloric acid is relatively high, the hydrogen chloride concentration of the second organic substance-containing hydrochloric acid in the middle of distillation may reach the azeotropic hydrogen chloride concentration under atmospheric pressure before the total amount of the organic substance is removed. Consequently, hydrogen chloride may be mixed into the mixture of the organic substance and water which are collected from the top of the tower. When distillation is performed in a continuous manner, the second organic substance-containing hydrochloric acid is continuously introduced into the distillation tower while continuously collecting the mixture of the organic substance and water from the top of the tower and also continuously collecting the purified hydrochloric acid from the bottom of the tower. Consequently, the hydrogen chloride concentration of the second organic substance-containing hydrochloric acid within the distillation tower can be kept stationary.
(i) First Step
The present step is for introducing the first organic substance-containing hydrochloric acid into the distillation tower while introducing water into the distillation tower from the top of the tower. The first organic substance-containing hydrochloric acid subjected to the purification method of the present embodiment is the same as that described in the above first embodiment.
In the present embodiment, as shown in
In the present embodiment, it is preferable that water (or hydrochloric acid) is introduced into distillation tower 201 from the top of the tower. Consequently, the same effect as that obtained by reflux can be obtained without performing the reflux operation described in the above first embodiment. In consideration of the separation efficiency of the organic substance by distillation and the efficiency of preventing distillation of hydrochloric acid out of the top of the tower, it is preferable that the position where the first organic substance-containing hydrochloric acid is introduced is located in proximity to the center section with respect to the height direction of distillation tower 201.
(ii) Second Step
In the present step, referring to
As shown in
Distillation can be performed either in a continuous manner or in a batch-wise manner, but preferably performed in a continuous manner. When distillation is performed in a continuous manner, the first organic substance-containing hydrochloric acid and water are continuously introduced into the distillation tower while continuously collecting the mixture of the organic substance and water from the top of the tower and also continuously collecting the purified hydrochloric acid from the bottom of the tower. Consequently, the hydrogen chloride concentration of the second organic substance-containing hydrochloric acid produced within the distillation tower can be kept stationary.
Purified hydrochloric acid obtained by the method according to the present invention is high-purity hydrochloric acid substantially not containing any organic substance (for example, approximately 0.1 mass ppm or lower). Furthermore, according to the method of the present invention, hydrogen chloride is hardly distilled out of the top of the tower during distillation. Accordingly, the resultant purified hydrochloric acid is to contain a total or an approximately total amount of hydrogen chloride contained in the second organic substance-containing hydrochloric acid introduced into the distillation tower or produced within the distillation tower. Therefore, the loss of hydrogen chloride caused by the purification process can be completely or nearly completely suppressed.
Since the purified hydrochloric acid obtained by the method according to the present invention is high-purity hydrochloric acid substantially not containing an organic substance, the purified hydrochloric acid can be suitably used as a raw material in the compound synthesizing process such as a hydrochloric acid oxidation process and also used as hydrochloric acid for food additives. Furthermore, in the case where the purified hydrochloric acid is used as hydrochloric acid for neutralization of alkaline waste water, the produced neutralized water can be released as waste water since it does not substantially contain any organic substance.
Although the present invention will be hereinafter described in more detail with reference to Examples, the present invention is not limited thereto.
As shown in
As shown in
It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the claims.
1, 1′ first organic substance-containing hydrochloric acid, 2, 2′ water or dilute hydrochloric acid, 3, 3′ mixture of organic substance and water, 4, 4′ purified hydrochloric acid, 101, 201 distillation tower, 102, 103, 105, 106, 108, 202, 203, 206, 208 piping, 104 heat exchanger (condenser), 107, 207 heat exchanger (reboiler).
Number | Date | Country | Kind |
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2008-308723 | Dec 2008 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2009/069767 | 11/24/2009 | WO | 00 | 6/1/2011 |