Method for detecting alkenyl succinic acid / anhydride compounds in paper

Abstract

The invention provides a method for detecting an alkenyl succinic acid / anhydride compound (ASA) in paper. The method comprises the following steps: performing ASA extraction by using an organic extraction agent containing methanol and inorganic acid, performing esterification reaction on the extracted ASA, and detecting the esterified ASA by using detection equipment. According to the method disclosed by the invention, combined and non-combined ASA in the paper can be efficiently and fully extracted and accurately detected so as to establish a brand new means for evaluating the performance of the paper, and in addition, the method also effectively eliminates defects caused by toxic and harmful conventional solvents such as diethyl ether and acetone.

Description

Technical Field

[0001] The present application relates to the field of analytical chemistry, and more specifically to a method for separating, extracting and detecting alkenyl succinic acid / anhydride compounds in different states in paper. Background Art

[0002] Compounds such as alkenyl succinic acid, alkenyl succinic anhydride and alkenyl succinate are collectively referred to as ASA, which is a type of chemical added to the wet end for sizing in paper production. Since ASA is easily hydrolyzed in water, only a portion of ASA can be retained in the paper to play a sizing role, and the rest of ASA is lost in the papermaking white water. The ASA retained in the manufactured paper includes two categories, one is ASA that is not bound to the fibers in the paper (bound by covalent bonds), such as alkenyl succinic anhydride, alkenyl succinic acid, or alkenyl succinate (such as alkali metal salts, alkaline earth metal salts, ammonium salts, etc.), which are collectively referred to as "unbound ASA" in this article; the other is ASA that forms a covalent bond with the cellulose in the paper through a carboxyl group, which is referred to as "bound ASA" in this article. The papermaking industry is in great need of a simple, efficient, low-cost and highly accurate technology to characterize the ASA content in paper products, especially to accurately characterize the "unbound ASA" and "bound ASA" contained therein. This way, the retention rate of ASA in the papermaking process can be tracked for each batch of specific paper products based on the characterization results, and the effects of different forms and contents of ASA on the performance of paper products can be further studied.

[0003] Unfortunately, there is no standard method for detecting ASA in paper in this field so far, and there are very few related studies. The only few detection technologies reported all require the use of methanol and dichloromethane or acetone to extract ASA from paper, esterify the extracted ASA (such as methyl esterification), and then characterize it using techniques such as gas chromatography (GC), but these existing detection technologies all have extremely serious problems. The first problem of the prior art is that it is difficult to fully extract ASA (especially bound ASA) from paper. Often, even after 4 hours or more of heating extraction operation with an organic extractant, the bound ASA in the paper cannot be completely extracted, and on this basis, the accuracy of the test results cannot be guaranteed. The second problem of the prior art is that it involves a large variety of organic reagents, which are easy to introduce impurity interference into the extracted ASA. The dosage and process conditions of these organic reagents are not well controlled, which may seriously affect the final test results; and acetone is a controlled raw material involved in the drug manufacturing process, and its large-scale purchase and use will be further subject to many restrictions. The third problem of the prior art is that the process is too complicated and lengthy, wherein the solvent drying / evaporation and solvent dissolution operations are required multiple times before and after the extraction and esterification steps, which further limits its practicality. Therefore, the art particularly hopes to develop a new technology to effectively solve the above problems.

[0004] The inventors of the present application have invested a lot of energy in conducting in-depth research and unexpectedly developed the method of the present invention, which successfully solves the long-standing problem in the prior art that needs to be solved. Summary of the invention

[0005] The present application provides a method for detecting alkenyl succinic acid / anhydride compounds (ASA) in paper, the method comprising: extracting ASA with an organic extractant containing methanol and an inorganic acid, performing an esterification reaction on the extracted ASA, and detecting the esterified ASA with a detection device.

[0006] According to one embodiment of the present application, the ASA includes bound ASA covalently bound to cellulose in paper, and unbound ASA not covalently bound to cellulose in cellulose;

[0007] The combined ASA has a structure shown in Formula 1 or Formula 2,

[0008]

[0009] The non-binding ASA has a structure shown in Formula 3, Formula 4 or Formula 5:

[0010]

[0011] In Formulae 1 to 5, R1, R2, R3 and R4 are each independently selected from one or more of the following: hydrogen, C1-C6 alkyl, C1-C6 alkoxy, C3-C8 cycloalkyl, C6-C12 aryl, C2-C8 alkenyl; M is selected from one or more of the following: ammonium ion, alkali metal ion, alkaline earth metal ion, transition metal ion.

[0012] According to another embodiment of the present application, the method includes:

[0013] A) Detection of unbound ASA, which includes:

[0014] a1) extracting the paper with an organic extractant containing methanol and an inorganic acid to extract the unbound ASA from the paper, thereby obtaining an extract and a raffinate solid;

[0015] a2) separating the ASA in the extract from the organic extractant;

[0016] a3) esterifying the ASA obtained in step a2) with an anhydrous esterification agent containing methanol and hydrogen chloride;

[0017] a4) detecting the esterified ASA using a detection device;

[0018] B) Combined ASA detection, which includes:

[0019] b1) treating the raffinate solid obtained in step a1) with an anhydrous extraction-esterification agent containing methanol and hydrogen chloride to extract bound ASA therefrom and simultaneously esterify the extracted ASA;

[0020] b2) Detecting the esterified ASA using a detection device.

[0021] According to another embodiment of the present application, in step a1), the ratio of the paper to the organic extractant is 1 g:50 ml to 1 g:150 ml. According to another embodiment of the present application, in step a1), during the extraction process, the mixture formed by the organic extractant and the paper is heated at the top and bottom at the same time, the lower heating temperature is 50-75°C, the upper heating temperature is 28-40°C, and the extraction time is 2.5-3.5 hours.

[0022] According to another embodiment of the present application, in the step a2), the organic extractant in the extract is evaporated to obtain separated ASA. According to another embodiment of the present application, in the step a2), the separated ASA is dissolved with methanol and transferred to a first esterification container, and then the methanol is evaporated to remove.

[0023] According to another embodiment of the present application, in the step a3), the esterification reaction is continued at a temperature of 80-130° C. for 1.5-6 hours. According to another embodiment of the present application, in the step a3), in the step a3), the anhydrous esterification agent contains methanol and hydrogen chloride, and the content of hydrogen chloride in methanol is 0.1-3 mol / L.

[0024] According to another embodiment of the present application, in the step b1), the ratio of the raffinate solid to the anhydrous extraction-esterification agent is 1 gram: 30 milliliters to 1 gram: 150 milliliters. According to another embodiment of the present application, in the step b1), the anhydrous extraction-esterification agent contains methanol and hydrogen chloride, and the content of hydrogen chloride in methanol is 0.1-3 mol / L.

[0025] According to another embodiment of the present application, in the step b1), the mixture formed by the anhydrous extraction-esterification agent and the raffinate solid is heated simultaneously in the upper and lower parts, the lower heating temperature is 50-75°C, the upper heating temperature is 28-40°C, and the heating duration is 2.5-3.5 hours.

[0026] According to another embodiment of the present application, the detection equipment used in steps a4) and b2) is selected from the group consisting of: gas chromatography, liquid chromatography, gas chromatography-mass spectrometry, and liquid chromatography-mass spectrometry.

[0027] According to another embodiment of the present application, the organic extractant used in step a1), the anhydrous esterification agent used in step a3) and the anhydrous extraction-esterification agent used in step b1) do not contain ether, dichloromethane and acetone.

[0028] In the specific implementation section below, the detection method and specific applications of the present application are further introduced in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of a process flow according to a specific embodiment of the method of the present application is shown;

[0030] Figure 2 The gas chromatogram shows the effect of extracting bound ASA according to one embodiment of the present application;

[0031] Figure 3 ASA concentration / GC peak area standard curve obtained using a series of ASA standard solutions is shown. DETAILED DESCRIPTION

[0032] "Range" disclosed herein is in the form of lower limit and upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges that can be defined in this way are inclusive and combinable, i.e. any lower limit can be combined with any upper limit to form a range. For example, a range of 60-120 and 80-110 is listed for a particular parameter, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.

[0033] In this application, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations.

[0034] In this application, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined with each other to form a new technical solution.

[0035] In this application, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0036] In this application, if there is no special explanation, the "including" mentioned herein means open or closed. For example, the "including" may mean that other components not listed may also be included, or only the listed components may be included.

[0037] In the present invention, the term "alkenyl succinic acid / anhydride compounds" and the abbreviation "ASA" can be used interchangeably, and its meaning includes the alkenyl succinic acid, alkenyl succinic anhydride, alkenyl succinates, alkenyl succinic acid covalently bound to cellulose in paper as described below, and also includes any other conventional derivative forms thereof that may appear in the papermaking process.

[0038] One of the inventive points of the present invention is that, by specially designing the composition of the organic extractant, sufficient and efficient extraction of unbound ASA and bound ASA in paper is achieved with a shorter extraction time, thereby achieving accurate and efficient detection of these unbound ASA and bound ASA.

[0039] In the present invention, the terms "bound ASA" and "bound ASA" are used interchangeably to refer to ASA bound to cellulose in paper through covalent bonds, for example, the bound ASA comprises the following formula 1 and

[0040] The structure shown in formula 2:

[0041]

[0042] In the present invention, the terms "unbound ASA" and "unbound ASA" are used interchangeably to refer to the following ASA that is not covalently bound to the cellulose in the paper, for example, the unbound ASA may be in the form of a carboxylic acid as shown in the following formula 3, in the form of a carboxylate as shown in the following formula 4, or in the form of an anhydride as shown in the following formula 5:

[0043]

[0044] In the above formulae 1 to 5, R1, R2, R3 and R4 are each independently selected from one or more of the following: hydrogen, C1-C6 alkyl, C1-C6 alkoxy, C3-C8 cycloalkyl, C6-C12 aryl, C2-C8 alkenyl; for example, hydrogen, C1-C4 alkyl, C1-C4 alkoxy, C3-C6 cycloalkyl, C6-C10 aryl, C2-C6 alkenyl; M represents one or more cations selected from the following: ammonium ion, alkali metal ion, alkaline earth metal ion, transition metal ion, preferably sodium ion, potassium ion or calcium ion.

[0045] According to one embodiment of the present application, the method of the present invention includes two parts, namely A) extraction and detection of non-bound ASA, and B) extraction and detection of bound ASA.

[0046] According to one embodiment of the present application, the A) extraction and detection of non-bound ASA comprises the following steps:

[0047] a1) extracting the paper with an organic extractant containing methanol and an inorganic acid to extract the unbound ASA from the paper, thereby obtaining an extract and a raffinate solid;

[0048] a2) separating the ASA in the extract from the organic extractant;

[0049] a3) esterifying the ASA obtained in step a2) with an anhydrous esterification agent containing methanol and hydrogen chloride;

[0050] a4) Detect the esterified ASA using a detection device.

[0051] According to one embodiment of the present application, the inorganic acid in the organic extractant used in step a1) is hydrochloric acid. According to another embodiment, the organic solvent used in step a1) is a mixture of methanol and hydrochloric acid, or a mixture of methanol aqueous solution and hydrochloric acid. The concentration of the hydrochloric acid is 10-38% by weight, or 20-38% by weight, and the hydrochloric acid used is preferably concentrated hydrochloric acid with a concentration of 37-38% by weight. The methanol aqueous solution can be a mixture of methanol and water in a volume ratio of 1:1 to 15:1, such as 5:1 to 12:1, or 8:1 to 10:1, preferably 9:1. The volume ratio of the methanol aqueous solution to hydrochloric acid can be 500:1 to 100:1, such as 400:1 to 200:1, or 300:1 to 220:1, preferably 250:1. It can be seen that the organic extractant used herein in the present application can contain water (such as water in concentrated hydrochloric acid, and water mixed with methanol).

[0052] According to a preferred embodiment of the present application, the organic extractant does not contain the extraction solvents commonly used in the prior art, such as ether, dichloromethane and acetone. According to another more preferred embodiment of the present application, the organic extractant is completely composed of water, methanol and the above-mentioned inorganic acid (preferably hydrochloric acid), and does not contain other intentionally added organic solvents.

[0053] According to one embodiment of the present application, in the step a1), the paper sample to be tested for ASA content is mixed with the organic extractant in a ratio of 1 g:50 ml to 1 g:150 ml, and then extracted for a period of time under heating conditions. The mixing ratio of the paper sample to the organic extractant can be 1 g:55 ml to 1 g:120 ml, or 1 g:58 ml to 1 g:100 ml, or 1 g:60 ml to 1 g:80 ml.

[0054] According to one embodiment of the present application, in the step a1, a special extraction device is used to heat the mixture of the paper sample and the organic extractant from both the top and bottom, and the top heating temperature is different from the bottom heating temperature. For example, the bottom heating temperature is 50-75°C, or 55-70°C, or 60-65°C; the top heating temperature is 28-40°C, or 29-35°C, preferably 30-31°C.

[0055] According to an exemplary embodiment of the present application, the above-mentioned extraction operation of applying different heating temperatures to the upper and lower parts may be performed using a Soxhlet extractor (B811 Soxhlet extractor).

[0056] One of the inventive points of the present invention is that by selecting the above specially designed extraction process, the unbound ASA contained in the paper can be fully extracted in a relatively short time. Specifically, the prior art often requires more than 4 hours of extraction time to completely extract the unbound ASA in the paper, while the extraction time for completely extracting the unbound ASA in step a1 of the present invention is only 2.5-3.5 hours, or 2.8-3.2 hours, or 3 hours.

[0057] In step a1, an extract and a raffinate solid are obtained through the above-mentioned extraction operation. The extract contains the above-mentioned organic extractant and the unbound ASA extracted from the paper sample, and the extract is subsequently treated in steps a2 to a4; while in the raffinate solid, the bound ASA is still in a state of being bound to the paper cellulose, and is left to be extracted and detected in part B) of the method of the present invention.

[0058] According to one embodiment of the present application, the weight ratio of the raffinate solid obtained after step a1 to the paper before step a1 (in terms of solid weight ratio) is 85:100 to 96:100, or 90:100 to 95:100.

[0059] Next, in step a2, the ASA in the extract is separated from the organic extractant. The step a2 can be performed in the following manner: the organic extractant is volatilized and dried, thereby achieving separation of ASA from the organic extractant. The volatilization can be performed at room temperature (natural volatilization and drying), or under heating conditions, for example, heating at 40-60° C. to volatilize and dry the organic extractant.

[0060] According to one embodiment of the present application, the step a2 may further include dissolving the separated solid ASA with methanol and transferring it to the first esterification container, and then evaporating and removing the methanol. For example, ASA may be dissolved with a small amount of methanol (preferably anhydrous methanol), and the obtained solution may be transferred to the first esterification container. The container in which the above-mentioned organic extractant is volatilized and solid ASA is obtained may also be washed once or multiple times with additional methanol to ensure that the ASA is completely transferred to the first esterification container, and the above-mentioned methanol solvent used for dissolving, transferring and washing is volatilized and removed, for example, volatilized and removed at room temperature or under heating conditions, and nitrogen purge may be additionally applied.

[0061] Next, in step a3, in the first esterification container, the ASA obtained in step a2) is esterified with an anhydrous esterification agent containing methanol and hydrogen chloride.

[0062] According to one embodiment of the present application, the anhydrous esterifying agent contains methanol and hydrogen chloride, and does not contain water (try to use a non-aqueous reagent for preparation, but it may contain inevitable trace amounts of water impurities). For example, the anhydrous esterifying agent can be a solution of hydrogen chloride in methanol with a concentration of about 0.1-3 mol / L, for example, a concentration of 1-2.5 mol / L, or 1.5-2.2 mol / L, preferably about 2 mol / L. The anhydrous esterifying agent can be prepared by mixing acetyl chloride with methanol in a desired proportion. According to a preferred embodiment of the present application, the anhydrous esterifying agent does not contain the organic solvents commonly used in the prior art, such as ether, dichloromethane and acetone. According to another more preferred embodiment of the present application, the anhydrous esterifying agent does not contain other intentionally added organic solvents.

[0063] According to one embodiment of the present application, the volume ratio of the anhydrous esterification agent used in the step a3 to the organic extractant used in the step a1 can be 1:500 to 1:30, for example, 1:300 to 1:40, or 1:200 to 1:50, or 1:100 to 1:700.

[0064] According to one embodiment of the present application, in the step a3, the esterification reaction is continuously carried out at a temperature of 80-130°C for 1.5-6 hours; for example, the temperature of the esterification reaction may be 90-120°C, or 100-110°C; the duration of the esterification reaction may be 2-5 hours, or 3-4 hours.

[0065] Through the esterification reaction in step a3, ASA is converted into the corresponding methyl ester. After the esterification reaction is completed, the anhydrous esterification agent is volatilized and removed again, for example, under nitrogen purge conditions and / or heating conditions, to leave the esterified ASA.

[0066] Subsequently, in step a4, the esterified ASA obtained in step a3 is prepared into a solvent with a quantitative volume of a solvent (e.g., methanol), and then a detection device is used to perform quantitative characterization of ASA. The detection device is selected from the group consisting of gas chromatography, liquid chromatography, gas chromatography-mass spectrometry, and liquid chromatography-mass spectrometry, preferably gas chromatography.

[0067] The above steps achieve effective extraction and detection of unbound ASA in paper.

[0068] According to one embodiment of the present application, the raffinate solid phase obtained in step a1 is subsequently subjected to extraction and detection of bound ASA in part B of the method of the present invention, and part B includes the following steps b1 and b2.

[0069] First, in step b1, the raffinate solid obtained in step a1) is treated with an anhydrous extraction-esterification agent containing methanol and hydrogen chloride to extract bound ASA therefrom and simultaneously esterify the extracted ASA.

[0070] Another inventive point of the present invention is that a specially designed anhydrous extraction-esterification agent is used in step b1 to achieve sufficient extraction of bound ASA contained in the raffinate solid, and the extraction and esterification can be carried out simultaneously, further optimizing the process steps. The step b1 can be carried out in a second esterification container.

[0071] According to one embodiment of the present application, the anhydrous extraction-esterification agent contains methanol and hydrogen chloride, and does not contain water (it is prepared using an aqueous reagent as much as possible, but it may contain inevitable trace amounts of water impurities). For example, the anhydrous extraction-esterification agent can be a solution of hydrogen chloride in methanol with a concentration of about 0.1-3 mol / L, such as a concentration of 1-2.5 mol / L, or 1.5-2.2 mol / L, preferably about 2 mol / L. The anhydrous extraction-esterification agent can be prepared by mixing acetyl chloride with methanol in a desired proportion. According to a preferred embodiment of the present application, the anhydrous extraction-esterification agent does not contain the organic solvents commonly used in the prior art, such as ether, dichloromethane and acetone. According to another more preferred embodiment of the present application, the anhydrous extraction-esterification agent does not contain other intentionally added organic solvents.

[0072] According to one embodiment of the present application, in the step b1, the ratio of the raffinate solid to the anhydrous extraction-esterification agent can be 1 g:50 ml to 1 g:150 ml, or can be 1 g:55 ml to 1 g:120 ml, or can be 1 g:58 ml to 1 g:100 ml, or can be 1 g:60 ml to 1 g:80 ml.

[0073] According to one embodiment of the present application, in the step b1, the mixture of the raffinate solid and the anhydrous extraction-esterification agent can be heated from the upper and lower parts respectively, and the upper heating temperature is different from the lower heating temperature. For example, the lower heating temperature is 50-75°C, or 55-70°C, or 60-65°C; the upper heating temperature is 28-40°C, or 29-35°C, preferably 30-31°C.

[0074] The heating duration of step b1 may be 2-5 hours, or 3-4 hours.

[0075] Through the above treatment in step b1, the bound ASA in the raffinate solid is effectively separated, and the separated ASA is esterified at the same time.

[0076] Subsequently, solid-liquid phase separation is performed to volatilize and remove the anhydrous extraction-esterification agent in the liquid phase, for example, under nitrogen purge conditions and / or heating conditions, the anhydrous esterification agent is volatilized and removed, leaving the esterified ASA.

[0077] Subsequently, in step b2, the esterified ASA obtained in step b1 is prepared into a solvent with a quantitative volume of a solvent (e.g., methanol), and then a detection device is used to perform quantitative characterization of ASA. The detection device is selected from the group consisting of: gas chromatography, liquid chromatography, gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, preferably gas chromatography.

[0078] The above steps achieve effective extraction and detection of bound ASA in paper.

[0079] According to one embodiment of the present application, various detection techniques can be used to quantitatively detect the ASA (non-bound ASA and bound ASA from paper) extracted and esterified in the above steps. For example, a series of ASA standard solutions with different concentrations (e.g., solutions of ASA in methanol in the form of carboxylic acid or ester (e.g., methyl ester)) can be used separately, for example, the concentration can be 10-2000 mg / L, and a standard curve can be established between the signal intensity (e.g., gas chromatographic peak integrated area) and the ASA concentration of this series of samples, and then the standard curve can be used to conveniently determine the concentrations of non-bound ASA and bound ASA in the paper to be tested extracted and esterified in the above steps a1-a4 and b1-b2.

[0080] The present invention can achieve the following advantages:

[0081] 1. In the above step a1, the use of a specially designed organic extractant can complete the extraction of unbound ASA in paper in a shorter time. In contrast, the prior art requires a much longer time to extract unbound ASA, and even after such a long extraction operation, it may not be possible to completely extract the unbound ASA in paper.

[0082] 2. The above a1-a4 and b1-b2 of the present invention do not use organic solvents such as diethyl ether, acetone, and dichloromethane commonly used in the prior art, which effectively avoids the interference of these organic solvents on the test results and eliminates the defect that acetone affects the life of the gas chromatography column.

[0083] 3. The above step b1 of the present invention uses a specially designed hydrogen chloride / methanol mixed system, which can fully extract the bound ASA in the paper sample in a relatively short time, and complete the esterification of the extracted ASA at the same time of extraction, thereby simplifying the process steps and saving time.

[0084] The present application is described below in the form of specific embodiments, the purpose of which is to better understand the content of the present application. It should be understood that these embodiments are merely illustrative and not restrictive.

[0085] Example

[0086] In the following examples, glassine paper and copy paper (weight 80 gsm) used as test objects are commercially available products. Unless otherwise specified, other reagents used in the examples are analytically pure reagents purchased from the market and used without further purification.

[0087] Example 1

[0088] In this embodiment, if Figure 1 As shown in the flow chart of FIG. 1 , the following steps are used to extract, esterify and detect ASA on the paper sample (glassine paper) to be tested.

[0089] Step A. Extraction, esterification and detection of unbound ASA.

[0090] a1) Weigh 2.5 g of the paper sample to be tested and tear it into small pieces of about 1 cm×1 cm in size. Add these small pieces and an extractant (a mixture of 150 ml of methanol and 0.6 ml of concentrated hydrochloric acid with a concentration of about 37 wt %) into a B811 Soxhlet extractor, respectively. Adjust the Soxhlet extractor to warm mode, with a lower heating temperature of about 63° C. and a right upper heating temperature of 30.9° C., and continue the extraction operation for 3 hours.

[0091] a2) After the extraction is completed, the material in the Soxhlet extractor is transferred out, the solid-liquid separation is performed by filtration, the solid phase is washed with a small amount of methanol, and the Soxhlet extractor is washed with a small amount of methanol. The washing liquids from the above two washing operations are combined with the separated liquid phase, and the washed solid phase is retained for the extraction of bound ASA in step B.

[0092] The combined liquid phases were placed in a beaker, and the beaker was placed open on a hot plate, and slowly evaporated to dryness at 40° C. in a fume hood.

[0093] Use a pipette to add 5 ml of methanol to the beaker for rinsing, and collect the rinsing liquid into a threaded test tube. Take another 5 ml of methanol and repeat the above steps to rinse the beaker, and collect the rinsing liquid into the above threaded test tube. Use a gentle stream of nitrogen at 40°C to dry the methanol in the threaded test tube.

[0094] a3) 8 ml of acetyl chloride is mixed with 100 ml of anhydrous methanol to prepare a hydrogen chloride / methanol solution, which is used as an esterification agent in step A and as an extraction / esterification agent in step B. 2 ml of the hydrogen chloride / methanol solution is added to the above threaded test tube and the cap is tightly closed. The test tube is transferred to an oven and kept heated at 100° C. for 3 hours. The test tube is then taken out and, after cooling, the liquid in the threaded test tube is completely dried with a gentle stream of nitrogen.

[0095] a4) Add 1 ml of anhydrous methanol to the threaded test tube using a pipette, shake thoroughly to dissolve the esterified ASA completely, and then quantitatively detect the ASA methanol solution using gas chromatography.

[0096] Step B. Extraction, esterification and detection of unbound ASA.

[0097] b1) The solid phase obtained after filtration and washing in step A and 150 ml of the above-mentioned hydrogen chloride / methanol solution are respectively added to a B811 Soxhlet extractor, and the Soxhlet extractor is adjusted to warm mode, with the lower heating temperature of about 63°C and the upper right heating temperature of 30.9°C, and the extraction / esterification operation is continued for 3 hours.

[0098] After the extraction / esterification operation is completed, the material in the Soxhlet extractor is transferred out, solid-liquid separation is performed by filtration, the solid phase is washed with a small amount of methanol, and the Soxhlet extractor is washed with a small amount of methanol, and the washing liquids of the above two washing operations are combined with the separated liquid phase. The washed solid phase is tested in the subsequent step D to determine whether ASA is completely extracted.

[0099] Place the combined liquid phase in a beaker, place the beaker open on a hot plate, and slowly evaporate to dryness at 40°C in a fume hood. Use a pipette to add 5 ml of methanol to the beaker for rinsing, and collect the rinsing liquid and transfer it to a threaded test tube. Take 5 ml of methanol again, repeat the above steps to rinse the beaker, and collect the rinsing liquid and transfer it to the above threaded test tube. Blow dry the methanol in the threaded test tube with a gentle stream of nitrogen at 40°C.

[0100] b2) Add 1 ml of anhydrous methanol to the threaded test tube using a pipette, shake thoroughly to dissolve the esterified ASA completely, and then quantitatively detect the ASA methanol solution using gas chromatography.

[0101] Step C. Establishment of ASA-methanol solution standard curve

[0102] In step C, ASA standard samples were dissolved in anhydrous methanol to prepare ASA / methanol standard solutions with concentrations of 100, 200, 500, 1000, and 1500 mg / L, respectively. For each standard sample, 1 ml of standard sample was accurately pipetted with a pipette, added to a threaded test tube, and the liquid in the threaded test tube was completely dried with a gentle nitrogen gas stream. 2 ml of the above-mentioned hydrogen chloride methanol solution was added to the threaded test tube and the bottle cap was tightly closed. The test tube was transferred to an oven and kept heated at a temperature of 100 ° C for 3 hours. The test tube was then taken out, and after cooling, the liquid in the threaded test tube was completely dried with a gentle nitrogen gas stream. 1 ml of anhydrous methanol was added to the threaded test tube with a pipette, fully shaken so that the esterified ASA was completely dissolved, and then the ASA methanol solution was quantitatively detected by gas chromatography. Anhydrous methanol injection was also used as a blank sample. The actual peak area of ​​sample ASA was obtained by subtracting the blank peak area from the peak area of ​​each ASA standard sample, and a standard curve was established using the series of standard samples, such as Figure 3 As shown, R=0.9967.

[0103] Each time the above steps A and B are tested, according to Figure 3 The ASA concentration was determined by the standard curve shown, and the concentrations of unbound ASA and bound ASA in the paper sample were calculated according to the following formula: Unbound ASA% = Unbound ASA content / Absolute dry weight of paper sample*100%, Bound ASA% = Bound ASA content / Absolute dry weight of paper sample*100%.

[0104] In this Example 1, a total of 7 paper samples were taken for experimentation, and the experimental results are summarized in the following Table 1.

[0105] Table 1: ASA content of 7 glassine papers

[0106]

[0107] Step D. Verification of complete extraction of ASA.

[0108] In this step, the solid phase after extraction / esterification and washing in step b1 is subjected to the operations of steps b1 and b2 again to verify whether there is any residual ASA in the solid phase. The gas chromatogram of the sample obtained in step B is as follows: Figure 2 As shown in the figure above, the gas chromatogram of the sample obtained in step D is as follows Figure 2 As shown in the figure below. Figure 2 It can be seen that the extraction operation in step B can effectively extract the bound ASA in the paper sample, while the repeated extraction operation in step D can no longer extract any ASA from the solid phase sample, thus proving that the complete extraction of bound ASA in the paper has been achieved through step B.

[0109] It can be seen that the method of the present invention can effectively realize the extraction and detection of unbound ASA and bound ASA in glassine paper samples, and accurately and efficiently grasp the ASA content in different states in glassine paper samples.

[0110] Example 2

[0111] In this example, the steps of Example 1 were completely repeated to perform ASA extraction, esterification and detection on the paper sample to be tested (copy paper). A total of 3 paper samples were taken for the experiment. The experimental results are summarized in Table 2 below.

[0112] Table 2: ASA content of 3 copy papers

[0113] Sample name Sample-1(%) Sample-2(%) Sample-3(%) Unbound ASA mass 0.020 0.014 0.015 Combined with ASA quality 0.012 0.012 0.014

[0114] It can be seen that the method of the present invention can effectively realize the extraction and detection of unbound ASA and bound ASA in copy paper samples, and accurately and efficiently grasp the ASA content in different states in copy paper samples.

[0115] Example 3

[0116] In this example, a paper sample (hand sheet) to which no ASA was added during the preparation process was used, and 1 ml of a standard solution (the standard solution was a solution of alkenyl succinic anhydride dissolved in methanol, with a concentration of 500 mg / L) was dropped onto 2.5 g of the paper sample to obtain a paper sample containing ASA in a non-bound state.

[0117] Repeat steps a1-a4 of Example 1 to extract, esterify and detect the unbound ASA in the paper sample to characterize the extraction ability of the method of the present invention for unbound ASA. The test results show that more than 90% of ASA was successfully extracted.

Claims

1. A method for detecting alkenyl succinic acid / anhydride compounds (ASA) in paper, characterized in that: The method comprises: extracting ASA with an organic extractant containing methanol and inorganic acid, performing an esterification reaction on the extracted ASA, and detecting the esterified ASA with a detection device.

2. The method according to claim 1, characterized in that The ASA includes bound ASA that is covalently bound to cellulose in the paper, and unbound ASA that is not covalently bound to cellulose in the paper; The combined ASA has a structure shown in Formula 1 or Formula 2, The non-binding ASA has a structure shown in Formula 3, Formula 4 or Formula 5: In Formulae 1 to 5, R1, R2, R3 and R4 are each independently selected from one or more of the following: hydrogen, C1-C6 alkyl, C1-C6 alkoxy, C3-C8 cycloalkyl, C6-C12 aryl, C2-C8 alkenyl; M is selected from one or more of the following: ammonium ion, alkali metal ion, alkaline earth metal ion, transition metal ion.

3. The method according to claim 2, characterized in that The method comprises: A) Detection of unbound ASA, which includes: a1) extracting the paper with an organic extractant containing methanol and an inorganic acid to extract the unbound ASA from the paper, thereby obtaining an extract and a raffinate solid; a2) separating the ASA in the extract from the organic extractant; a3) esterifying the ASA obtained in step a2) with an anhydrous esterification agent containing methanol and hydrogen chloride; a4) detecting the esterified ASA using a detection device; B) Combined ASA detection, which includes: b1) treating the raffinate solid obtained in step a1) with an anhydrous extraction-esterification agent containing methanol and hydrogen chloride to extract bound ASA therefrom and simultaneously esterify the extracted ASA; b2) Detecting the esterified ASA using a detection device.

4. The method according to claim 3, characterized in that In step a1), the ratio of the paper to the organic extractant is 1 g:50 ml to 1 g:150 ml; and During the extraction process, the mixture formed by the organic extractant and the paper is heated at the upper and lower parts simultaneously, the lower heating temperature is 50-75° C., the upper heating temperature is 28-40° C., and the extraction time is 2.5-3.5 hours.

5. The method according to claim 3, characterized in that In the step a2), the organic extractant in the extract is evaporated to obtain separated ASA; and The separated ASA was dissolved with methanol and transferred to the first esterification vessel, and the methanol was then removed by evaporation.

6. The method according to claim 3, characterized in that In the step a3), the esterification reaction is continued at a temperature of 80-130° C. for 1.5-6 hours; The anhydrous esterification agent contains methanol and hydrogen chloride, and the content of hydrogen chloride in methanol is 0.1-3 mol / L.

7. The method according to claim 3, characterized in that In the step b1), the ratio of the raffinate solid to the anhydrous extraction-esterification agent is 1 g:30 ml to 1 g:150 ml; and The anhydrous extraction-esterification agent contains methanol and hydrogen chloride, and the content of hydrogen chloride in methanol is 0.1-3 mol / L.

8. The method according to claim 3, characterized in that In the step b1), the mixture formed by the anhydrous extraction-esterification agent and the raffinate solid is heated simultaneously in the upper and lower parts, the lower heating temperature is 50-75°C, the upper heating temperature is 28-40°C, and the heating duration is 2.5-3.5 hours.

9. The method according to claim 3, characterized in that The detection equipment used in the steps a4) and b2) is selected from the group consisting of: gas chromatography, liquid chromatography, gas chromatography-mass spectrometry, and liquid chromatography-mass spectrometry.

10. The method according to claim 3, characterized in that The organic extractant used in step a1), the anhydrous esterification agent used in step a3) and the anhydrous extraction-esterification agent used in step b1) do not contain ether, dichloromethane and acetone.

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