CN105836846B - Selective separation method of fluorine-containing organic acids - Google Patents
Selective separation method of fluorine-containing organic acidsDownload PDFInfo
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Abstract
Translated fromChinese
Description
Translated fromChinese技术领域technical field
本发明涉及一种含氟有机酸的选择性分离方法。The present invention relates to a selective separation method of fluorine-containing organic acid.
背景技术Background technique
含氟羧酸等含氟有机酸的拨水作用、表面活性作用等优异，在拨水喷雾、表面涂敷剂、消化剂、蜡等中被使用。目前，作为代表的含氟羧酸，广泛着使用全氟辛烷磺酸(以下，也称为“PFOS”)和全氟辛酸(以下，也称为“PFOA”)。但是，PFOS和PFOA的环境负荷大，根据与残留性有机污染物质有关的斯德哥尔摩条约等规定，其制造及使用受到限制，其使用量正在减少。Fluorinated organic acids such as fluorinated carboxylic acids are excellent in water repellent action, surface active action, and the like, and are used in water repellent sprays, surface coating agents, digestive agents, waxes, and the like. Currently, perfluorooctane sulfonic acid (hereinafter, also referred to as "PFOS") and perfluorooctanoic acid (hereinafter, also referred to as "PFOA") are widely used as representative fluorine-containing carboxylic acids. However, PFOS and PFOA have a large environmental load, and their manufacture and use are restricted according to regulations such as the Stockholm Treaty on Residual Organic Pollutants, and their usage is decreasing.
从上述的理由出发，目前，作为取代PFOS和PFOA的含氟有机酸，利用全氟己酸(以下，也称为“PFHxA”)或具有醚键的含氟羧酸，其制造及使用量增加。与其相伴，作为工业排水被排出的大量含有含氟有机酸的废液的量也增加。作为处理该废液的方法，目前进行利用反渗透膜将废液浓缩、其后焚烧的处理。例如，在专利文献1中记载有对在制造含氟聚合物的工艺中产生的、含有作为氟链烷酸的含氟表面活性剂的水溶液使用反渗透膜进行过滤处理的方法。另外，在非专利文献1中记载有用NaCl除去率为97.0％的反渗透膜除去95.5～98.5％的PFHxA的方法。For the reasons described above, perfluorohexanoic acid (hereinafter, also referred to as "PFHxA") or a fluorinated carboxylic acid having an ether bond is currently used as a fluorine-containing organic acid to replace PFOS and PFOA, and the production and use amount thereof are increasing. . Along with this, the amount of waste liquid containing a large amount of fluorinated organic acid discharged as industrial waste water also increases. As a method of treating this waste liquid, a treatment of concentrating the waste liquid by a reverse osmosis membrane and then incinerating it is currently performed. For example, Patent Document 1 describes a method of performing filtration treatment using a reverse osmosis membrane on an aqueous solution containing a fluoroalkanoic acid, which is produced in a process for producing a fluoropolymer, and contains a fluoroalkanoic acid. In addition, Non-Patent Document 1 describes a method for removing 95.5 to 98.5% of PFHxA using a reverse osmosis membrane with a NaCl removal rate of 97.0%.
现有技术文献prior art literature
专利文献Patent Literature
专利文献1：日本专利第5055652号公报Patent Document 1: Japanese Patent No. 5055652
非专利文献Non-patent literature
非专利文献1：Steinle-Darling,E.,Reinhard,M.,2008.Nanofiltration fortrace organic contaminant removal:structure,solution,and membrane foulingeffects on the rejection of perfluorochemicals.Environmental science&technoGlogy 42，5292-7Non-patent document 1: Steinle-Darling, E., Reinhard, M., 2008. Nanofiltration for trace organic contaminant removal: structure, solution, and membrane fouling effects on the rejection of perfluorochemicals. Environmental science & technoGlogy 42, 5292-7
发明内容SUMMARY OF THE INVENTION
发明所要解决的课题The problem to be solved by the invention
如上所述的利用反渗透膜的含有含氟羧酸的废液的处理方法中，由于使用的反渗透膜的孔非常小，因此，需要负载大的膜间压力。因此，现有的处理方法需要高能量。另外，在处理中需要时间，因此，存在处理效率低、难以处理大量的废液的问题。In the above-described method for treating a waste liquid containing a fluorine-containing carboxylic acid using a reverse osmosis membrane, since the pores of the reverse osmosis membrane used are very small, it is necessary to load a large intermembrane pressure. Therefore, existing treatment methods require high energy. In addition, since it takes time for the treatment, there is a problem that the treatment efficiency is low and it is difficult to treat a large amount of waste liquid.
作为其它的问题，由于反渗透膜的孔的直径非常小(0.2nm～1nm)(参照水循环系统的构造，Natsume公司(水循環システムのしくみ，ナツメ社)，2010)，因此，存在容易发生污垢(堵塞)、膜的保养的频率增大的问题。这使得处理成本增大，保养期间需要停止处理，因此，效率也降低。As another problem, since the diameter of the pores of the reverse osmosis membrane is very small (0.2 nm to 1 nm) (refer to the structure of the water circulation system, Natsume Co., Ltd. (Water Circulation System), 2010), fouling is likely to occur ( clogging) and increased frequency of membrane maintenance. This increases the processing cost, requires stopping the processing during maintenance, and therefore reduces the efficiency.
为了提高处理能力、防止污垢，需要增大反渗透膜(半透膜)的孔的直径。但是，增大孔的直径时，表面活性剂等中所使用的含氟羧酸自身为比较小的分子，因此，含氟羧酸分子穿过膜，含氟羧酸的截留率会降低。In order to improve the processing capacity and prevent fouling, it is necessary to increase the diameter of the pores of the reverse osmosis membrane (semi-permeable membrane). However, when the diameter of the pores is increased, the fluorine-containing carboxylic acid itself used in the surfactant or the like is a relatively small molecule, and therefore, the fluorine-containing carboxylic acid molecules pass through the membrane, and the rejection rate of the fluorine-containing carboxylic acid decreases.
另外，由于反渗透膜的孔的直径非常小，因此，产生过度的分离。即，不打算分离的分子量小的物质、例如NaC1等也不能穿过孔，与含氟羧酸一起被分离、浓缩。这样，在含氟羧酸浓缩液中存在许多其它物质时，回收含氟羧酸并再利用变得困难。其结果，现状是该含氟羧酸浓缩液被焚烧处理。另外，在该焚烧处理时，由于产生氟化氢(HF)，因此，焚烧用的炉需要形成为特殊的结构，维持费用也高。In addition, since the diameter of the pores of the reverse osmosis membrane is very small, excessive separation occurs. That is, substances with a small molecular weight that are not intended to be separated, such as NaCl, cannot pass through the pores, and are separated and concentrated together with the fluorine-containing carboxylic acid. In this way, when there are many other substances in the fluorine-containing carboxylic acid concentrate, it becomes difficult to recover and reuse the fluorine-containing carboxylic acid. As a result, the present situation is that the fluorine-containing carboxylic acid concentrate is incinerated. In addition, since hydrogen fluoride (HF) is generated during this incineration process, the furnace for incineration needs to be formed with a special structure, and the maintenance cost is also high.
如果选择性地截留含氟羧酸，能够消除上述的问题，但仍未发现这样的方法。If the fluorine-containing carboxylic acid is selectively trapped, the above-mentioned problems can be eliminated, but such a method has not yet been found.
因此，本发明的目的在于提供一种能够以低能量和短时间对碳原子数为2～7的含氟有机酸溶液进行处理、进而能够选择性地分离碳原子数为2～7的含氟有机酸的处理方法。Therefore, an object of the present invention is to provide a fluorine-containing organic acid solution having 2 to 7 carbon atoms that can be treated with low energy and in a short time, and further capable of selectively separating fluorine-containing organic acids having 2 to 7 carbon atoms. Treatment of organic acids.
用于解决课题的技术方案Technical solutions for solving problems
本发明的发明人为了解决上述的问题而进行了深入研究，结果发现，通过使用截留分子量大、并且在表面具有负的电荷的膜作为过滤膜(半透膜)，由于与碳原子数为2～7的含氟有机酸的负电荷相排斥，能够选择性地分离碳原子数为2～7的含氟有机酸，进而能够提高处理效率。The inventors of the present invention have conducted intensive studies in order to solve the above-mentioned problems, and as a result found that, by using a membrane having a large molecular weight cut-off and having a negative charge on the surface as a filter membrane (semi-permeable membrane), since the number of carbon atoms is 2 The negative charges of the fluorine-containing organic acids of ~7 repel, and the fluorine-containing organic acids having 2 to 7 carbon atoms can be selectively separated, thereby improving the treatment efficiency.
根据本发明的一个要点，提供一种通过过滤来分离碳原子数为2～7的含氟有机酸溶液中的含氟有机酸的方法，其特征在于，过滤膜具有比碳原子数为2～7的含氟有机酸的分子量大的截留分子量，具有负的表面Zeta电位。According to an aspect of the present invention, there is provided a method for separating fluorine-containing organic acid in a fluorine-containing organic acid solution having 2 to 7 carbon atoms by filtration, wherein the filter membrane has a specific carbon number of 2 to 7. The fluorine-containing organic acid of 7 has a large molecular weight cut-off and a negative surface Zeta potential.
根据本发明的一个要点，一种碳原子数为2～7的含氟有机酸溶液的过滤系统，其特征在于，该过滤系统具备过滤膜，半透膜具有比碳原子数为2～7的含氟有机酸的分子量大的截留分子量，具有负的表面Zeta电位。According to one aspect of the present invention, a filter system for a fluorine-containing organic acid solution having a carbon number of 2 to 7 is characterized in that the filter system is provided with a filter membrane, and the semi-permeable membrane has a ratio of carbon atoms of 2 to 7 to the filter system. The fluorine-containing organic acid has a large molecular weight cut-off and has a negative surface Zeta potential.
发明效果Invention effect
根据本发明，通过使用具有比碳原子数为2～7的含氟有机酸的分子量大的截留分子量、具有负的表面Zeta电位(即负的电荷)的过滤膜，即使在施加于膜的压力比较小的情况下，也能够实现高处理量，进而，由于与碳原子数为2～7的含氟有机酸的负电荷相排斥，能够选择性地分离碳原子数为2～7的含氟有机酸。即，根据本发明，能够以低能量且短时间对碳原子数为2～7的含氟有机酸的溶液进行处理。According to the present invention, by using a filtration membrane having a molecular weight cutoff larger than that of a fluorine-containing organic acid having 2 to 7 carbon atoms and having a negative surface Zeta potential (ie, a negative charge), even under pressure applied to the membrane In a relatively small case, a high throughput can be achieved, and furthermore, fluorine-containing organic acids having 2 to 7 carbon atoms can be selectively separated due to repulsion from the negative charges of fluorine-containing organic acids having 2 to 7 carbon atoms. organic acid. That is, according to the present invention, a solution of a fluorine-containing organic acid having 2 to 7 carbon atoms can be treated with low energy and in a short period of time.
附图说明Description of drawings
图1是表示实施例中的PFHxA的截留率的坐标图。FIG. 1 is a graph showing the retention rate of PFHxA in Examples.
具体实施方式Detailed ways
本发明的方法使用过滤膜来分离碳原子数为2～7的含氟有机酸溶液中的碳原子数为2～7的含氟有机酸。In the method of the present invention, the fluorine-containing organic acid having 2 to 7 carbon atoms in the solution of the fluorine-containing organic acid having 2 to 7 carbon atoms is separated using a filter membrane.
在优选的方式中，过滤通过反渗透来进行。In a preferred manner, the filtration is carried out by reverse osmosis.
碳原子数为2～7的含氟有机酸Fluorine-containing organic acids with 2 to 7 carbon atoms
利用本发明的方法进行处理的溶液中所含的碳原子数为2～7的含氟有机酸中，碳原子数优选为3～7，更优选为5～7，特别优选为6～7。Among the fluorine-containing organic acids having 2 to 7 carbon atoms contained in the solution treated by the method of the present invention, the number of carbon atoms is preferably 3 to 7, more preferably 5 to 7, and particularly preferably 6 to 7.
作为利用本发明的方法进行处理的溶液中所含的碳原子数为2～7的含氟有机酸，可以列举碳原子数为2～7的含氟羧酸及其盐、碳原子数为2～7的含氟磺酸及其盐。Examples of the fluorine-containing organic acid having 2 to 7 carbon atoms contained in the solution treated by the method of the present invention include fluorine-containing carboxylic acids having 2 to 7 carbon atoms and salts thereof, and 2 to 7 carbon atoms. ~7 Fluorinated sulfonic acids and salts thereof.
作为碳原子数为2～7的含氟羧酸，可以列举式(i)所示的化合物：Examples of the fluorine-containing carboxylic acid having 2 to 7 carbon atoms include compounds represented by formula (i):
X1-Rf1-COOH (i)X1 -Rf1 -COOH (i)
[式中，X1为H、F或Cl，Rf1为碳原子数为1～6的直链或支链状的氟代亚烷基、具有单氧氟代亚烷基的碳原子数为1～6的基团、或具有多氧氟代亚烷基的碳原子数为1～6的基团。][In the formula, X1 is H, F or Cl, and Rf1 is a straight-chain or branched fluoroalkylene group having 1 to 6 carbon atoms, and the number of carbon atoms having a monooxyfluoroalkylene group is A group of 1 to 6, or a group of 1 to 6 carbon atoms having a polyoxyfluoroalkylene group. ]
作为上述Rf1基中的碳原子数为1～6的直链或支链状的氟代亚烷基，例如，可以列举CF2、C2F4、C3F6、C4F8、C5F10、C5F12、CHF、C2F3H、C2F2H2、C2FH3、C3F5H、C3F4H2、C3F3H3、C3F2H4、C3FH5、C4F7H、C4F6H2、C4F5H3、C4F4H4、C4F3H5、C4F2H6、C4FH7、C5F9H、C5F8H2、C5F7H3、C5F6H4、C5F5H5、C5F4H6、C5F3H7、C5F2H8、C5FH9、C6F11H、C6F10H2、C6F9H3、C6F8H4、C6F7H5、C6F6H6、C6F5H7、C6F4H8、C6F3H9、C6F2H10、C6FH11。Examples of linear or branched fluoroalkylene groups having 1 to 6 carbon atoms in the above Rf1 group include CF2 , C2 F4 , C3 F6 , C4 F8 ,C5F10,C5F12,CHF,C2F3H,C2F2H2,C2FH3,C3F5H,C3F4H2,C3F3H3,_C3F2H4,C3FH5,C4F7H,C4F6H2,C4F5H3,C4F4H4,C4F3H5,C4F2______ H6 , C4 FH7 , C5 F9 H , C5 F8 H2 , C5 F7 H3 , C5 F6 H4 , C5 F5 H5 , C5 F4 H6 , C5F3H7,C5F2H8,C5FH9,C6F11H,C6F10H2,C6F9H3,C6F8H4,C6F7H______5.C6F6H6,C6F5H7,C6F4H8,C6F3H9,C6F2H10,C6FH11._____
进一步优选碳原子数为2～7的含氟羧酸为式(i-a)所示的全氟羧酸：More preferably, the fluorine-containing carboxylic acid having 2 to 7 carbon atoms is a perfluorocarboxylic acid represented by the formula (i-a):
X2-Rf2-COOH (i-a)X2 -Rf2 -COOH (ia)
[式中，X2为H或F，Rf2为式(a)所示的基团：[In the formula, X2 is H or F, and Rf2 is a group represented by the formula (a):
(CF2)l-(CF2OCF2)m-(CF2OCF(CF3))n (a)(CF2 )l -(CF2 OCF2 )m -(CF2 OCF(CF3 ))n (a)
上述式(a)中，l为0或1～4的整数，m为0或1～3的整数，n为0、1或2，其中，条件为：l+2m+3n不超过6；不包括m和n的两者为0的情况；并且用上述括弧括起来的各重复单元的存在顺序为任意的。]In the above formula (a), l is 0 or an integer from 1 to 4, m is an integer from 0 or 1 to 3, and n is 0, 1 or 2, and the conditions are: l+2m+3n does not exceed 6; The case where both of m and n are 0 is included; and the order of existence of each repeating unit enclosed in the above-mentioned parentheses is arbitrary. ]
在上述含氟羧酸中，碳原子数优选为3～7，更优选为5～7，特别优选为6～7。In the said fluorine-containing carboxylic acid, 3-7 are preferable, 5-7 are more preferable, and 6-7 are especially preferable.
作为优选的方式的碳原子数为5～7的含氟羧酸，例如，能够例示：As a preferred embodiment of the fluorine-containing carboxylic acid having 5 to 7 carbon atoms, for example, the following can be exemplified:
CF3OCF(CF3)CF2OCF(CF3)COOH、CF3 OCF(CF3 )CF2 OCF(CF3 )COOH,
CF3CF2OCF2CF2OCF2COOH、CF3 CF2 OCF2 CF2 OCF2 COOH,
CF3OCF2CF2CF2OCHFCF2COOH、CF3 OCF2 CF2 CF2 OCHFCF2 COOH,
CF3CF2OCF2CF2OCF2COOH、CF3 CF2 OCF2 CF2 OCF2 COOH,
CF3OCF2CF2CF2OCHFCF2COOH、CF3 OCF2 CF2 CF2 OCHFCF2 COOH,
CF3(CF2)4COOH、CF3 (CF2 )4 COOH,
CF3CF2CF2OCF(CF3)COOH、CF3 CF2 CF2 OCF(CF3 )COOH,
F(CF2)4CF2CF2COOH、F(CF2 )4 CF2 CF2 COOH,
H(CF2)6COOH、H(CF2 )6 COOH,
H(CF2)4COOH、H(CF2 )4 COOH,
CH2＝CFCF2OCF(CF3)COOHCH2 =CFCF2 OCF(CF3 )COOH
等。Wait.
在本发明中，“碳原子数为2～7的含氟有机酸的溶液”只要是含有碳原子数为2～7的含氟有机酸的液体即可，没有特别限定，并不限定于溶解有碳原子数为2～7的含氟有机酸的溶液，也可以为分散有碳原子数为2～7的含氟有机酸的悬浮液或乳浊液。在优选的方式中，碳原子数为2～7的含氟有机酸溶液为溶解有碳原子数为2～7的含氟有机酸的溶液。In the present invention, the "solution of a fluorine-containing organic acid having 2 to 7 carbon atoms" is not particularly limited as long as it is a liquid containing a fluorine-containing organic acid having 2 to 7 carbon atoms, and it is not limited to dissolving The solution containing the fluorine-containing organic acid having 2 to 7 carbon atoms may be a suspension or emulsion in which the fluorine-containing organic acid having 2 to 7 carbon atoms is dispersed. In a preferred embodiment, the fluorine-containing organic acid solution having 2 to 7 carbon atoms is a solution in which a fluorine-containing organic acid having 2 to 7 carbon atoms is dissolved.
在碳原子数为2～7的含氟有机酸的溶液中，碳原子数为2～7的含氟有机酸可以单独存在或以2种以上存在。In the solution of the fluorine-containing organic acid having 2 to 7 carbon atoms, the fluorine-containing organic acid having 2 to 7 carbon atoms may exist alone or in combination of two or more.
在碳原子数为2～7的含氟有机酸的溶液中，碳原子数为2～7的含氟有机酸可以为电离形态、非电离形态或盐的形态，或可以共存有这些形态的2种或3种形态。优选碳原子数为2～7的含氟有机酸的至少一部分为电离的形态。In the solution of the fluorine-containing organic acid having 2 to 7 carbon atoms, the fluorine-containing organic acid having 2 to 7 carbon atoms may be in an ionized form, a non-ionized form, or a salt form, or two forms of these forms may coexist. one or three forms. Preferably, at least a part of the fluorine-containing organic acid having 2 to 7 carbon atoms is in an ionized form.
碳原子数为2～7的含氟有机酸的溶液中的溶剂没有特别限定，可以为水或有机溶剂、或2种以上的溶剂的混合物。上述有机溶剂没有特别限定，可以为水性，也可以为非水性，例如，可以列举醇类(例如甲醇、乙醇、异丙醇等)、乙酸甲酯等酯、醚类(二乙醚等)、脂肪族烃(己烷、辛烷等)、酮类(丙酮等)、乙腈等。溶剂优选为水性溶剂，更优选水。The solvent in the solution of the fluorine-containing organic acid having 2 to 7 carbon atoms is not particularly limited, and may be water, an organic solvent, or a mixture of two or more solvents. The above-mentioned organic solvent is not particularly limited, and may be aqueous or non-aqueous, and examples thereof include alcohols (for example, methanol, ethanol, isopropanol, etc.), esters such as methyl acetate, ethers (diethyl ether, etc.), fats Hydrocarbons (hexane, octane, etc.), ketones (acetone, etc.), acetonitrile, etc. The solvent is preferably an aqueous solvent, more preferably water.
在碳原子数为2～7的含氟有机酸的溶液中可以存在杂质、即其它溶质。作为其它溶质，例如，可以列举金属盐(NaCI、KC1、Na2SO4等)、有机盐类等。Impurities, ie, other solutes, may exist in the solution of the fluorine-containing organic acid having 2 to 7 carbon atoms. Examples of other solutes include metal salts (NaCl, KCl, Na2 SO4 , etc.), organic salts, and the like.
碳原子数为2～7的含氟有机酸的溶液的pH没有特别限定，优选为pH4以上，更优选为pH7以上。通过将pH设为7以上，能够进一步提高碳原子数为2～7的含氟有机酸的截留率。pH的调整没有特别限定，能够通过添加盐酸溶液或氢氧化钠溶液来进行。The pH of the solution of the fluorine-containing organic acid having 2 to 7 carbon atoms is not particularly limited, but it is preferably pH 4 or more, and more preferably pH 7 or more. By setting the pH to 7 or more, the retention rate of the fluorine-containing organic acid having 2 to 7 carbon atoms can be further improved. The adjustment of pH is not particularly limited, and can be performed by adding a hydrochloric acid solution or a sodium hydroxide solution.
碳原子数为2～7的含氟有机酸的溶液例如可以为作为工业排水被排出的溶液或在实验室等中被排出的溶液。The solution of the fluorine-containing organic acid having 2 to 7 carbon atoms may be, for example, a solution discharged as industrial waste water or a solution discharged in a laboratory or the like.
过滤膜filter membrane
本发明的方法中所使用的过滤膜(含有半透膜)具有比碳原子数为2～7的含氟有机酸的分子量大的截留分子量，具有负的表面Zeta电位。The filtration membrane (including a semipermeable membrane) used in the method of the present invention has a molecular weight cutoff larger than that of a fluorine-containing organic acid having 2 to 7 carbon atoms, and has a negative surface zeta potential.
“截留分子量”作为表示膜的孔径的指标，在本领域技术人员中为众所周知的，使用指标物质进行膜过滤，求出各自的截留率，将截留率相当于90％的分子量设为截留分子量(molecular weight cut off)(参照膜过滤技术(膜ろ過技術)，p.54，工业调査会，2006)。"Molecular weight cut off" is well known to those skilled in the art as an index representing the pore size of a membrane. Membrane filtration is performed using an index substance, and the respective rejection ratios are obtained. molecular weight cut off) (refer to membrane filtration technology (membrane filtration technology), p.54, Industrial Research Society, 2006).
“表面Zeta电位”作为表示膜的带电性的指标，在本领域技术人员中为众所周知的，测定在使电解质溶液流动时在膜表面产生的电位差，利用下述Helmholtz-Smo1uchowski的式子算出。"Surface Zeta potential" is well known to those skilled in the art as an index showing the chargeability of a membrane. The potential difference generated on the membrane surface when an electrolyte solution is flowed is measured and calculated by the following Helmholtz-Smoluchowski formula.
ζ＝(ηε)×(1/ρ)×(E/P)ζ=(ηε)×(1/ρ)×(E/P)
ζ：表面Zeta电位ζ: Surface Zeta potential
η：电解质的粘度(poise，泊)η: viscosity of electrolyte (poise, poise)
ε：电解质的导电率(S/cm)ε: Conductivity of the electrolyte (S/cm)
ρ：溶液的电阻率(Ω·cm)ρ: Resistivity of solution (Ω·cm)
E：测得的电位E: Measured potential
P：膜间压力P: intermembrane pressure
本发明所使用的过滤膜(半透膜)的截留分子量只要比碳原子数为2～7的含氟有机酸的分子量大即可，优选为5000Da以上、50000Da以下，更优选为8000Da以上、30000Da以下，进一步优选为15000Da以上、25000Da以下。通过使截留分子量比碳原子数为2～7的含氟有机酸的分子量大，膜的处理能力提高。即，膜的每单位面积的溶剂透过量变大。截留分子量越大，处理能力越高。另外，过滤(代表而言为反渗透)中所需要的压力也变小。进而，能够抑制不期望分离的其它杂质与碳原子数为2～7的含氟有机酸一起被分离。另外，通过将截留分子量设为20000Da以下，能够进一步提高碳原子数为2～7的含氟有机酸的截留率。The molecular weight cut-off of the filter membrane (semi-permeable membrane) used in the present invention should just be larger than the molecular weight of the fluorine-containing organic acid having 2 to 7 carbon atoms. Hereinafter, it is more preferably 15000 Da or more and 25000 Da or less. By making the molecular weight cut off larger than the molecular weight of the fluorine-containing organic acid having 2 to 7 carbon atoms, the handling capacity of the membrane is improved. That is, the amount of solvent permeation per unit area of the membrane increases. The higher the molecular weight cut-off, the higher the processing capacity. In addition, the pressure required for filtration (typically reverse osmosis) is also reduced. Furthermore, it is possible to suppress the separation of other impurities that are not desired to be separated together with the fluorine-containing organic acid having 2 to 7 carbon atoms. In addition, by setting the molecular weight cutoff to be 20,000 Da or less, the cutoff of the fluorine-containing organic acid having 2 to 7 carbon atoms can be further improved.
本发明所使用的过滤膜(半透膜)的表面Zeta电位具有负的值，优选为-10mV以下，更优选为-30mV以下，进一步优选为-50mV以下，更进一步优选为-80mV以下。表面Zeta电位的下限没有特别限定，优选为-300mV以上，例如为-200mV以上或-150mV以上。通过使过滤膜具有负的表面Zeta电位，即使在使用具有比碳原子数为2～7的含氟有机酸的分子量大的截留分子量的膜的情况下，由于碳原子数为2～7的含氟有机酸的负电荷与膜的负表面电荷相排斥，也能够以高的截留率分离碳原子数为2～7的含氟有机酸。负的表面Zeta电位越大(即膜表面的负电荷越大)，则能够使用更高的截留分子量的膜。The surface zeta potential of the filter membrane (semipermeable membrane) used in the present invention has a negative value, preferably -10 mV or less, more preferably -30 mV or less, still more preferably -50 mV or less, and still more preferably -80 mV or less. The lower limit of the surface zeta potential is not particularly limited, but is preferably -300 mV or more, for example, -200 mV or more or -150 mV or more. By making the filtration membrane have a negative surface Zeta potential, even when a membrane having a molecular weight cutoff larger than that of a fluorine-containing organic acid having 2 to 7 carbon atoms is used, the The negative charge of the fluoroorganic acid repels the negative surface charge of the membrane, and the fluoroorganic acid with a carbon number of 2 to 7 can also be separated with a high rejection rate. The greater the negative surface Zeta potential (ie the greater the negative charge on the membrane surface), the higher molecular weight cut-off membranes can be used.
膜的表面Zeta电位能够通过选择形成膜的材料来适当变更。另外，膜的表面Zeta电位也能够通过调整溶液的pH来进行调整。The surface zeta potential of the film can be appropriately changed by selecting the material for forming the film. In addition, the surface zeta potential of the membrane can also be adjusted by adjusting the pH of the solution.
在优选的方式中，本发明所使用的过滤膜具有5000Da以上50000以下、优选8000Da以上30000Da以下、更优选15000Da以上25000Da以下的截留分子量，具有-30mV以下、优选-50mV以下、更优选-80mV以下的表面Zeta电位。In a preferred embodiment, the filter membrane used in the present invention has a molecular weight cutoff of 5000 Da or more and 50000 Da or less, preferably 8000 Da or more and 30000 Da or less, more preferably 15000 Da or more and 25000 Da or less, and has -30mV or less, preferably -50mV or less, more preferably -80mV or less the surface Zeta potential.
构成本发明所使用的过滤膜的材料只要可以具有负的表面Zeta电位即可，没有特别限定，例如，可以列举全芳香族聚酰胺系树脂、聚乙烯醇系树脂、哌嗪酰胺系树脂、磺化聚醚砜等。The material constituting the filter membrane used in the present invention is not particularly limited as long as it can have a negative surface Zeta potential, and examples thereof include wholly aromatic polyamide-based resins, polyvinyl alcohol-based resins, piperazinamide-based resins, sulfonic acid Polyethersulfone, etc.
本发明所使用的过滤膜例如能够从日东电工株式会社、作为NTR7450和NTR7410获得。The filtration membranes used in the present invention are available, for example, from Nitto Denko Co., Ltd. as NTR7450 and NTR7410.
就本发明的方法中的条件(膜间压力、温度等)而言，只要是本领域技术人员，就能够根据处理的溶液的组成、使用的膜的种类等各种因素来适当设定。The conditions (intermembrane pressure, temperature, etc.) in the method of the present invention can be appropriately set by those skilled in the art according to various factors such as the composition of the solution to be treated and the type of membrane to be used.
根据本发明的方法，尽管过滤膜具有比碳原子数为2～7的含氟有机酸的分子量大的截留分子量，仍然能够良好地选择性地分离碳原子数为2～7的含氟有机酸。According to the method of the present invention, although the filter membrane has a molecular weight cut-off larger than that of the fluorine-containing organic acid having 2 to 7 carbon atoms, the fluorine-containing organic acid having 2 to 7 carbon atoms can be selectively separated with good selectivity. .
因此，本发明还提供一种碳原子数为2～7的含氟有机酸溶液的过滤系统，其特征在于，具备过滤膜，半透膜具有比碳原子数为2～7的含氟有机酸的分子量大的截留分子量，具有负的表面Zeta电位。Therefore, the present invention also provides a filtration system for a solution of a fluorine-containing organic acid having a carbon number of 2 to 7, characterized by comprising a filter membrane, and the semipermeable membrane has a fluorine-containing organic acid having a ratio of 2 to 7 carbon atoms to the fluorine-containing organic acid. A large molecular weight cut-off has a negative surface Zeta potential.
本发明并不受任何理论限制，尽管使用具有比碳原子数为2～7的含氟有机酸的分子量大的截留分子量的膜，仍然能够分离碳原子数为2～7的含氟有机酸，其理由可以如下考虑。本发明中所使用的过滤膜在表面具有负电荷。另一方面，碳原子数为2～7的含氟有机酸也具有负电荷。其结果，可以认为，由于相互的负电荷排斥，利用该电的排斥力，碳原子数为2～7的含氟有机酸难以接近膜。The present invention is not limited by any theory, although a membrane having a molecular weight cut-off larger than that of a fluorine-containing organic acid having 2 to 7 carbon atoms is used, the fluorine-containing organic acid having 2 to 7 carbon atoms can still be separated, The reason for this can be considered as follows. The filter membrane used in the present invention has a negative charge on the surface. On the other hand, fluorine-containing organic acids having 2 to 7 carbon atoms also have negative charges. As a result, it is considered that the fluorine-containing organic acid having 2 to 7 carbon atoms is difficult to approach the film due to the mutual repulsion of negative charges and the repulsive force of the electricity.
实施例Example
使用crossflow型的平膜试验装置对全氟己酸(以下，也称为PFHxA)水溶液(初期浓度100ng/L)进行膜过滤试验。作为膜，使用日东电工制的NTR7450(截留分子量：10000Da，表面Zeta电位-33mV；标称NaCl截留率：50％)和NTR7410(截留分子量＝20000Da，表面Zeta电位-99mV；标称NaC1截留率：10％)。处理条件如下所述。pH从初始值没有进行调整。A membrane filtration test was performed on a perfluorohexanoic acid (hereinafter, also referred to as PFHxA) aqueous solution (initial concentration: 100 ng/L) using a crossflow type flat membrane test apparatus. As membranes, NTR7450 (molecular weight cut-off: 10000 Da, surface Zeta potential -33 mV; nominal NaCl rejection: 50%) and NTR7410 (molecular weight cut-off = 20000 Da, surface Zeta potential -99 mV; nominal NaCl rejection: 50%) manufactured by Nitto Denko were used; : 10%). The processing conditions are as follows. The pH was not adjusted from the initial value.
膜间压力：0.700MPaIntermembrane pressure: 0.700MPa
循环流量：1.0±0.lL/分钟Circulating flow: 1.0±0.lL/min
水温：20±2℃Water temperature: 20±2℃
在0、6、12、24、48及72小时后，采取透过液500mL，在透过液采取开始时和结束时各采取原液50mL，分析PFHxA浓度。就浓度而言，利用固相提取法将试样浓缩之后，使用HPLC/MS/MS进行测定。基于得到的结果，利用以下的式(1)算出各试验中的PFHxA的截留率。After 0, 6, 12, 24, 48, and 72 hours, 500 mL of the permeate was collected, and 50 mL of the stock solution was collected at the start and end of the permeate collection, and the PFHxA concentration was analyzed. The concentration was measured using HPLC/MS/MS after concentrating the sample by the solid phase extraction method. Based on the obtained results, the retention of PFHxA in each test was calculated by the following formula (1).
Cp：透过液浓度(ng/L)Cp: Permeate concentration (ng/L)
Cs1：透过液收集开始时浓缩液浓度(ng/L)Cs1 : Concentration of concentrate at the beginning of permeate collection (ng/L)
Cs2：透过液收集结束时浓缩液浓度(ng/L)Cs2 : Concentration of concentrate at the end of permeate collection (ng/L)
在图1表示各膜的PFHxA截留率的推移。72小时后的截留率分别为99.0％(NTR7450)和98.3％(NTR7410)，确认了尽管为低的NaC1截留率(分别为50％和10％)，仍然可以得到高的PFHxA截留率。这些膜为磺化聚醚砜膜，在膜表面具有负电荷，因此，可以认为与PFHxA的负电荷排斥，截留了PFHxA。The transition of the PFHxA rejection rate of each membrane is shown in FIG. 1 . The rejections after 72 hours were 99.0% (NTR7450) and 98.3% (NTR7410), respectively, confirming that high PFHxA rejections could be obtained despite the low NaCl rejections (50% and 10%, respectively). These membranes are sulfonated polyethersulfone membranes and have a negative charge on the membrane surface, so it can be considered that the negative charge repels PFHxA and traps PFHxA.
工业上的可利用性industrial availability
本发明的方法处理能力高，能够选择性地分离碳原子数为2～7的含氟有机酸，因此，能够用于含有碳原子数为2～7的含氟有机酸的废液的处理等。The method of the present invention has high processing capacity and can selectively separate fluorine-containing organic acids having 2 to 7 carbon atoms. Therefore, it can be used for the treatment of waste liquids containing fluorine-containing organic acids having 2 to 7 carbon atoms. .
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