A method for determining the corn starch content in papermaking white water

Abstract

The present invention discloses a method for determining the corn starch content in papermaking white water. It belongs to the related technical field of pulp and paper making. In the present invention, the test value x of a blood glucose meter is pre-fitted with the starch concentration y calibrated in advance to obtain a standard curve, and then the test value of the blood glucose meter is substituted into the standard curve to calculate the corn starch content in the papermaking white water. The present invention uses a digestion bottle and a COD digester to quickly gelatinize the white water containing corn starch. The detection cost is low, and there is no need to use high-precision and expensive equipment such as chromatographs. An excessive amount of glucosidase is used to accelerate the enzymatic hydrolysis time, which can be used for rapid on-site assessment of the corn starch content in white water. The present invention has the advantages of simple operation, intuitive method, high portability, and reliable results.

Description

Technical Field

[0001] The present invention relates to the technical field of pulp and paper making, and specifically to a method for determining the content of corn starch in papermaking white water. Background Art

[0002] Corn starch is one of the important raw materials in the papermaking process. Retaining corn starch on paper can effectively improve the paper properties, improve the retention and drainage system of the paper machine, and increase the production efficiency. Corn starch in white water will breed microorganisms in the system, cause the pulp to become sour, produce peculiar smells, and affect the quality of paper products; at the same time, the residual corn starch in white water will lead to an increase in the COD concentration of white water. Excessive dissolved corn starch in the white water under the wire will affect the operation of the paper machine system, especially increase the load of the wet end dewatering system, and seriously cause a decrease in the paper machine speed or paper breakage and other serious impacts. White water is the wastewater in the paper-making section, which comes from the paper-making process in the papermaking workshop. White water mainly contains fine fibers, fillers, coatings and dissolved wood components, as well as added sizing agents, wet strength agents, preservatives, etc. It is mainly insoluble COD and has low biodegradability. The added preservatives have certain toxicity.

[0003] At present, the method for determining the content of corn starch in the white water under the wire of papermaking is complex. It requires complex pretreatment in a large laboratory and then precise optical instrument detection and analysis to determine the content of corn starch. Most paper machines on site cannot easily determine the starch content in the white water under the wire, and at the same time, production can only adjust the paper machine operation system based on production experience.

[0004] Therefore, there is a need for a method for detecting the content of corn starch in papermaking white water with portability and reliable results to solve the problem that it is difficult for paper machine technicians to quickly determine the content of corn starch in white water on site. Summary of the Invention

[0005] To solve the existing technical problems, the present invention provides a method for determining the content of corn starch in papermaking white water, including the following steps:

[0006] Ⅰ. Draw a standard curve and fit the curve equation; Ⅱ. Accurately weigh 0.100 - 0.107 g of glucosidase powder and place it in the first digestion flask for later use;

[0007] Ⅲ. Take 5 mL of white water under the wire of the paper machine, put it into a 10 mL second digestion flask, place it in a preheated digester for digestion for 0.3 - 1 h, and cool to room temperature;

[0008] Ⅳ. Pour the digested white water in the second digestion flask into the first digestion flask, add 0.1 mL of ethanol and 2.0 mL of buffer solution, shake well, and water bath at 50 °C for 0.3 - 1 h;

[0009] Ⅴ. Use a blood glucose meter to measure the test value of the white water in the first digestion flask, and then substitute it into the standard curve to calculate the corn starch content in the white water;

[0010] The steps for drawing the standard curve are as follows:

[0011] (1) Prepare a buffer solution;

[0012] (2) Accurately weigh 4 portions of 0.100 - 0.107 g of glucoamylase powder respectively, and place them in 4 10-mL first digestion flasks for later use;

[0013] (3) Add 1 g / L, 3 g / L, 5 g / L, and 7 g / L of dry corn starch to 4 portions of white water without corn starch respectively. After dissolving evenly, transfer 5 mL of the solution to 4 10-mL second digestion flasks respectively. Place the 4 second digestion flasks in a preheated Hach COD digester and digest at 95 °C for 0.3 - 1 h, and then cool to room temperature;

[0014] (4) Pour the solutions in the 4 second digestion flasks into the 4 first digestion flasks respectively, add 0.1 mL of ethanol and 2.0 mL of buffer solution, shake well, and water bath at 50 °C for 0.3 - 1 h;

[0015] (5) Use a blood glucose meter to measure the glucose content in the 1 g / L, 3 g / L, 5 g / L, and 7 g / L corn starch solutions. Draw a standard curve based on the measured values, and fit the curve to obtain the curve equation. The standard curve is the standard curve of the test value x and the starch concentration y, and the specific curve equation is y = 0.0096x 2 + 0.1316x + 0.1475.

[0016] Preferably or optionally, the digestion temperature in step III is 85 - 100 °C.

[0017] Preferably or optionally, the buffer solution is an acetic acid - sodium acetate buffer system.

[0018] Beneficial effects: The present invention first proposes a method for measuring the corn starch content in white water using a blood glucose meter. This method is simple and fast, with low detection costs, and does not require the use of high-precision and expensive equipment such as chromatographs. It can be used for rapid on-site assessment of the corn starch content in white water. The present invention uses an enzymatic hydrolysis method to treat papermaking white water. Compared with the direct or indirect iodometric methods commonly used to measure starch content, the present invention has higher specificity and is not affected by the volatilization of I 2 or the acidic oxidation of I - on the test results. It does not require a cumbersome titration process, and the observed results are not as easily affected by the turbidity of papermaking white water as the iodometric method. This method uses a digestion flask and a COD digester to quickly gelatinize the corn starch solution, and has the advantages of high portability and reliable results. Description of the Drawings

[0019] Figure 1 It is the measurement value - starch concentration curve of the present invention. Detailed implementation manners

[0020] In the following description, a large number of specific details are given to provide a more thorough understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present invention, some technical features well known in the art are not described.

[0021] The present invention will be further described below in conjunction with embodiments. The examples of the embodiments are intended to explain the present invention and should not be construed as limiting the present invention. For those technical and reaction conditions not specified in the embodiments, they can be carried out according to the techniques or conditions described in the literature in this field or the product specifications. For reagents, instruments or equipment not marked with manufacturers, they can all be obtained commercially.

[0022] At present, the main methods for measuring the corn starch content in the laboratory are as follows: ① One is to quantitatively analyze the corn starch content in the suspension by measuring the absorbance of the corn starch - iodine - potassium iodide complex. However, the maximum absorption wavelength of the corn starch - iodine complex is affected by many factors, including the turbidity of the water sample itself, pH value, temperature, corn starch polymerization degree, iodine - potassium iodide concentration, etc. With the infinite closed - loop recycling of the paper machine white water, the turbidity of the white water itself increases greatly, resulting in a reduction in the reliability of this method for quantitatively analyzing the corn starch content; ② Another is that the corn starch in the white water is degraded into monomer form (i.e., glucose) under acid hydrolysis or enzymatic action. The enzymatic method uses high - performance liquid chromatography (HPLC), ion - exchange chromatography analysis (IC) or spectrophotometry to quantitatively analyze the content of free glucose after hydrolysis or enzymatic degradation, and then calculate and convert it into the corn starch content. However, the whole set of instruments for this method is costly, the operation is complex, and it is inconvenient to carry it to the site for detecting and analyzing the corn starch content in the white water. Currently, it is only applicable to laboratory research. Many papermaking sites do not have the conditions for measuring the corn starch content by this method.

[0023] White water is the wastewater in the papermaking section, which comes from the paper - making process in the papermaking workshop. White water mainly contains fine fibers, fillers, coatings and dissolved wood components, as well as added sizing agents, wet - strength agents, preservatives, etc. It is mainly insoluble COD and has low biodegradability, and the added preservatives are somewhat toxic. The amount of white water is large, but the organic pollution load it contains is far lower than that of cooking black liquor and middle - stage wastewater. Almost all papermaking plants' papermaking workshops have adopted partial or fully closed systems to reduce papermaking water consumption, save power consumption, improve the white - water recycling rate, and reduce the discharge of excess white water. Based on the above problems, the present invention proposes a method for detecting the corn starch content in papermaking white water with portability and reliable results.

[0024] Configure the sample to be measured

[0025] Ⅰ. Accurately weigh 10.204 g of glucoamylase powder and place it in a 1000 mL conical flask for later use;

[0026] Ⅱ. Take the white water from the on-site of the cheese paper machine, accurately add 500 mL of white water after shaking well, and put it into the above 1000 mL conical flask to obtain the sample to be measured.

[0027] Example 1

[0028] In this example, a blood glucose meter is used to measure the corn starch content in white water.

[0029] I. Draw a standard control curve

[0030] (1) Prepare the buffer solution: 3.86 parts of anhydrous acetic acid, 2.93 parts of sodium acetate solid, and 993 parts of deionized water;

[0031] (2) Accurately weigh 0.102 g of glucoamylase powder and place it in a 10 mL first digestion flask for later use;

[0032] (3) Add 1 g / L, 3 g / L, 5 g / L, and 7 g / L of absolute dry corn raw starch to 4 parts of white water without corn starch respectively. After dissolving evenly, transfer 5 mL of the solution to 4 10 mL second digestion flasks respectively. Place the 4 second digestion flasks in a preheated HACH COD digester and digest at 95 °C for 30 min, then cool to room temperature;

[0033] (4) Pour the solutions in the 4 second digestion flasks into the 4 first digestion flasks respectively, add 0.1 mL of ethanol and 2.0 mL of acetic acid - sodium acetate buffer solution, shake well, and heat in a water bath at 50 °C for 30 min;

[0034] (5) Use a blood glucose meter to measure the glucose content in the 1 g / L, 3 g / L, 5 g / L, and 7 g / L corn starch solutions, hereinafter referred to as the "blood glucose" value (unit: mmol / L);

[0035] (6) Draw a standard curve based on the measured values and fit the curve to obtain the curve equation. The standard curve of the corn starch concentration in the (white water in the wrapping paper) wrapping paper system has been drawn: y = 0.0096x 2 + 0.1316x + 0.1475.

[0036] II. Measure the corn starch content in white water

[0037] (a) Take 10 mL of the sample to be measured in a second digestion flask, place it in a preheated HACH COD digester for digestion at 95 °C for 30 min, and cool to room temperature;

[0038] (b) Pour the digested white water in the second digestion flask into the first digestion flask, add 0.1 mL of ethanol and 2.0 mL of acetic acid-sodium acetate buffer solution, shake well, and water bath at 50 °C for 30 min;

[0039] (c) Measure the indicated value of the white water in the first digestion flask with a blood glucose meter, which is 1.4 mmol / L;

[0040] (d) Substitute into the standard curve equation y = 0.0096x 2 + 0.1316x + 0.1475 to calculate that the corn starch content in the white water is 0.705916 g / L.

[0041] Example 2

[0042] In this example, the corn starch content in white water was measured by high performance liquid chromatography (HPLC method).

[0043] (a) Take 200 mL of the sample to be tested, slowly heat it up to 95 °C, and maintain this temperature for 15 min to obtain a transparent and homogeneous starch paste solution, and cool it to 60 °C;

[0044] (b) Place the conical flask containing the starch paste solution in a constant temperature water bath shaker at 65 °C, add a mixed enzyme solution of α-amylase and glucoamylase to enzymatically hydrolyze the starch for 12 h. After the enzymatic hydrolysis is completed, heat up to 100 °C to inactivate the enzyme and obtain an enzymatic hydrolysate;

[0045] (c) Adjust the pH of the enzymatic hydrolysate to about 2 with 0.1 mo1 / L H 2 S0 4 solution, take 15 mL of the enzymatic hydrolysate for centrifugation, take 1 mL of the supernatant and dilute it with deionized water, and filter it with a 0.22 μm ultrafiltration membrane.

[0046] (d) Measure the sugar content of the filtrate filtered through the 0.22 μm membrane by HPLC, and the measured result is 0.7294 g / L.

[0047] Example 3

[0048] In this example, the corn starch content in white water was measured by the absorbance method.

[0049] (a) Take 10 mL of the sample to be tested, and accurately measure its mass m by the peeling method to be 9.9022 g, add 0.2 mL of alcohol (75%), and 4 mL of sodium acetate buffer ((200 mmol / L, pH = 4.5), and mix well;

[0050] (b) Add 0.1 mL of glucosidase at 200 U / mL, mix well, and ripen in a water bath at 50 ºC for 30 min;

[0051] (c) Transfer the contents of the beaker to a centrifuge tube, dilute to 15 mL with distilled water, and mix well;

[0052] (d) After separating for 20 min at 3500 r / min, take 0.1 mL of the supernatant and put it into a beaker, then add 3 mL of GOPOD reagent to the beaker, and place the beaker in a water bath at 50 °C for 20 min of ripening;

[0053] (e) Prepare a glucose control sample (consisting of 0.1 mL of 1000 μg / mL standard glucose solution and 3 mL of GOPOD reagent), and a reagent blank sample (consisting of 0.1 mL of distilled water and 3 mL of GOPOD reagent). Measure the absorbance of each sample at a wavelength of 510 nm. Let ΔE represent the absorbance of the sample to be measured, F represent the absorbance of the glucose control sample. 162 / 180 is the correction coefficient from free glucose to anhydroglucose.

[0054] The absorbance ΔE and the starch content W are related as follows:

[0055]

[0056] Therefore, the content of corn starch in the white water measured in Example 3 is 0.7724 g / L.

[0057] Comparing Examples 1 to 3, in Example 1, a blood glucose meter was used to measure the corn starch content in white water, and its test results were similar to those of the HPLC method and the absorbance method. However, obviously, compared with Examples 2 and 3, Example 1 has lower equipment requirements and faster detection results. Compared with the existing direct or indirect iodometric method, a series of titration operations are not required, and the disadvantages of easy volatilization of I 2 and easy oxidation of I - are avoided, ensuring the effectiveness of the detection results. In Example 1, a digestion flask and a COD digester were used to quickly gelatinize the corn starch solution, which is more rapid and portable, and easier to operate on-site. There is no longer a need to use a conical flask and an electric furnace for heating. Using the method of this study is safer, and the temperature required for detection is easier to control. And in Example 1, due to the use of a digestion flask, the sample treatment volume is only 5 mL, and the demand for enzymes is very low. This method uses an excessive amount of enzymes to shorten the enzymatic hydrolysis time from the original 24 h to 30 min, greatly improving the test efficiency.

[0058] In addition, it should be noted that in the various specific technical features described in the above specific embodiments, without contradiction, they can be combined in any suitable manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

Claims

1. A method for determining the corn starch content in papermaking white water, comprising the following steps: Ⅰ. Plot a standard curve and fit a curve equation; The steps for plotting the standard curve are as follows: (1) Prepare a buffer solution; (2) Accurately weigh 4 portions of 0.102 g of glucosidase powder and place them in 4 10-mL first digestion flasks for standby; (3) Add 1 g / L, 3 g / L, 5 g / L, and 7 g / L of absolute dry corn raw starch to 4 portions of white water without corn starch respectively. After dissolving evenly, transfer 5 mL of the solution to 4 10-mL second digestion flasks respectively. Place the 4 second digestion flasks in a preheated Hach COD digester and digest at 95 °C for 0.3 - 1 h, then cool to room temperature; (4) Pour the 4 second digestion flasks into the 4 first digestion flasks respectively, add 0.1 mL of ethanol and 2.0 mL of buffer solution, shake well, and water bath at 50 °C for 0.3 - 1 h; (5) Measure the glucose content in 1 g / L, 3 g / L, 5 g / L, and 7 g / L corn starch solutions using a blood glucose meter, plot a standard curve based on the measured values, and fit the curve to obtain a curve equation. The standard curve is a standard curve of the test value x and the starch concentration y, and the specific curve equation is y = 0.0096x 2 + 0.1316x + 0.1475; Ⅱ. Take 5 mL of white water under the paper machine wire and put it into a 10-mL second digestion flask. Place it in a preheated digester and digest for 0.3 - 1 h, then cool to room temperature; Ⅲ. Pour the digested white water in the second digestion flask into the first digestion flask, add 0.1 mL of ethanol and 2.0 mL of buffer solution, shake well, and water bath at 50 °C for 0.3 - 1 h; Ⅳ. Use a blood glucose meter to detect the test value of the white water in the first digestion flask, and then substitute it into the standard curve to calculate the corn starch content in the white water.

2. The method for determining the corn starch content in papermaking white water according to claim 1, wherein, the digestion temperature in step Ⅱ is 85 - 100 °C.

3. The method for determining the corn starch content in papermaking white water according to claim 1, wherein, the buffer solution is an acetic acid - sodium acetate buffer system.

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