A method for recovering alkali and lignin from papermaking black liquor using cationic displacement dialysis

Abstract

The present invention relates to the field of papermaking black liquor resource utilization, and specifically to a method for recovering alkali and lignin from papermaking black liquor using cationic exchange dialysis. The method comprises the following steps: 1) ammonium ion exchange dialysis: using a cationic exchange dialysis device, the papermaking black liquor is passed through the cationic exchange dialysis device and subjected to cationic exchange dialysis with an aqueous solution containing ammonium ions to obtain desalted ammoniacal papermaking black liquor; 2) ammonia recovery: recovering ammonia from the desalted ammoniacal papermaking black liquor obtained in step 1) to obtain ammonia or ammonia water and desalted and dealkalized papermaking black liquor; 3) lignin separation: separating the precipitated lignin from the desalted and dealkalized papermaking black liquor obtained in step 2) to obtain a lignin precipitate and desalted, dealkalized and delignified papermaking black liquor. The method can simultaneously recover alkali and lignin from the papermaking black liquor and achieve desalination of the papermaking black liquor, with low energy consumption, low membrane fouling, and high alkali and lignin recovery rates.

Description

Technical Field

[0001] The present invention relates to the field of papermaking black liquor resource utilization, and in particular to a method for recovering alkali and lignin from papermaking black liquor by utilizing cationic displacement dialysis. Background Art

[0002] Papermaking black liquor is the primary source of pollution in papermaking wastewater, accounting for approximately 90% of the papermaking industry's pollution. Pulping black liquor contains a large amount of lignin and hemicellulose degradation products, pigments, pentoses, residual alkali, and other dissolved substances. It is dark brown in color, has a pH of approximately 11.0 to 14.0, a BOD concentration of 5,000 to 40,000 mg / L, and COD values ​​as high as tens of thousands or even hundreds of thousands of mg / L. It is a complex system characterized by high alkalinity, high COD, high viscosity, and high color. Effective treatment and resource utilization of pulping black liquor are key to papermaking wastewater treatment.

[0003] At present, the most common method for treating black liquor in the pulp and paper industry is the alkali recovery method, which includes the extraction, evaporation, combustion and causticization of black liquor. The basic principle is to evaporate and concentrate the black liquor and then burn it in a combustion furnace to recover heat energy and obtain sodium carbonate, and then add lime for causticization to obtain sodium hydroxide. However, the alkali recovery technology uses the precious lignin resources in the black liquor as fuel at a low value, resulting in a waste of lignin resources, and the recovered heat energy is far lower than the heat energy required for black liquor concentration. In addition, the methods used at home and abroad for treating papermaking black liquor include acid precipitation, biotechnology, supercritical water gasification, membrane separation, etc. Among them, the use of membrane separation technologies such as electrodialysis and bipolar membrane electrodialysis to treat papermaking black liquor can simultaneously recover alkali (sodium hydroxide) and acidified lignin, showing good development potential in the resource treatment of papermaking black liquor.

[0004] Chinese patent application CN113563605A discloses a device and method for separating lignin from papermaking black liquor and recovering alkali. The device passes papermaking black liquor through a lignin separation and alkali recovery device (actually an electrodialysis + electrolysis device). Direct current is applied to produce a clear liquid containing lignin and an alkali solution containing sodium hydroxide or potassium hydroxide. A similar method (Process Safety and Environmental Protection, 2017, 106) also reports a method for treating papermaking black liquor using bipolar membrane electrodialysis to produce acidified papermaking black liquor and an alkali solution. The pH of the acidified papermaking black liquor is then adjusted, and the lignin solid is obtained after filtration and washing.

[0005] However, the above-mentioned existing methods all use electric fields as the driving force, which will cause serious membrane fouling when treating high-COD feed liquids such as papermaking black liquor. The reason is that a large number of charged particles (proteins, pigments, etc.) are attached to the membrane under the drive of the electric field. Therefore, the feed pretreatment requirements are extremely high, making the corresponding industrial process difficult to carry out. Summary of the Invention

[0006] In view of the problems existing in the prior art, the object of the present invention is to provide a method for recovering alkali and lignin from papermaking black liquor using cationic displacement dialysis. The method does not require an electric field, can achieve the recovery of alkali and separation of lignin in papermaking black liquor with low energy consumption and high efficiency, and greatly alleviates membrane fouling.

[0007] To achieve this object, the present invention provides a method for recovering alkali and lignin from papermaking black liquor by using cationic displacement dialysis, such as Figure 3 As shown, the following steps are included:

[0008] (1) Ammonium ion exchange dialysis: Using a cation exchange dialysis device, the papermaking black liquor is passed into the cation exchange dialysis device and subjected to cation exchange dialysis with an aqueous solution containing ammonium ions to obtain desalted ammonia-containing papermaking black liquor;

[0009] (2) recovering ammonia: recovering ammonia from the desalted ammonia-containing papermaking black liquor obtained in step 1) to obtain ammonia or ammonia water, and desalted and dealkalized papermaking black liquor;

[0010] (3) Separating lignin: Separating the precipitated lignin from the desalted and dealkalized papermaking black liquor obtained in step 2) to obtain lignin precipitate and desalted and dealkalized delignified papermaking black liquor.

[0011] The cation exchange dialysis device in step 1) includes a cation exchange dialysis membrane and a feed liquid chamber and a drive chamber separated by the cation exchange dialysis membrane, such as Figure 1 As shown, papermaking black liquor is passed into the feed chamber, and an aqueous solution containing ammonium ions is passed into the drive chamber. Ion exchange occurs between the sodium / potassium ions in the black liquor passed into the feed chamber and the ammonium ions in the aqueous solution containing ammonium ions passed into the drive chamber via the cation exchange dialysis membrane. That is, the sodium / potassium ions migrate across the cation exchange dialysis membrane into the drive chamber, while the ammonium ions migrate across the cation exchange dialysis membrane into the feed chamber, where they combine with hydroxide ions in the feed chamber to form ammonia. The pH of the black liquor in the feed chamber decreases, causing lignin to precipitate.

[0012] The cation exchange dialysis apparatus in step 1) of the ammonium ion exchange dialysis comprises one cation exchange dialysis module or two or more cation exchange dialysis modules connected in series and / or in parallel, as well as associated pumps, pipes, and valves. The cation exchange dialysis module may be a plate-and-frame cation exchange dialysis membrane stack, a tubular cation exchange dialysis membrane module, or a spiral cation exchange dialysis membrane module.

[0013] The plate-and-frame cation exchange dialysis membrane stack includes a plurality of flat-plate cation exchange dialysis membranes and separators, as well as a feed and liquid chamber and a drive chamber separated by the plurality of flat-plate cation exchange dialysis membranes. The tubular cation exchange dialysis membrane assembly includes a plurality of tubular cation exchange dialysis membranes and a feed and liquid chamber (e.g., outside the membrane tube, shell side) and a drive chamber (e.g., inside the membrane tube, tube side) separated by the tubular cation exchange dialysis membranes. The rolled cation exchange dialysis membrane assembly includes one or more flat-plate cation exchange dialysis membranes and separators rolled into a membrane roll, as well as a feed and liquid chamber and a drive chamber separated by the cation exchange dialysis membranes.

[0014] The cation exchange dialysis membrane can be a cation exchange membrane familiar to those skilled in the art, which can be purchased from the market, such as a conventional electrodialysis cation exchange membrane, a diffusion dialysis cation exchange membrane, an alkali-resistant cation exchange membrane, a monovalent selective cation exchange membrane (i.e., an ion exchange membrane that allows monovalent cations to pass through preferentially while blocking divalent and higher valence cations from passing through), or obtained by ion exchange membrane modification (doping modification and surface modification).

[0015] The aqueous solution containing ammonium ions in step 1) includes but is not limited to aqueous solutions of ammonium sulfate, ammonium chloride, ammonium carbonate, etc.

[0016] The temperature of the ammonium ion replacement dialysis in step 1) is 20°C to 60°C, that is, the temperature of the feed liquid in the feed liquid chamber and the feed liquid in the drive chamber is 20°C to 60°C.

[0017] The flow rates of the feed solution in the feed solution chamber and the feed solution in the drive chamber of the ammonium ion displacement dialysis in step 1) are conventional, preferably 0.5 cm / s to 7 cm / s.

[0018] The initial molar amount of ammonium ions in the aqueous solution containing ammonium ions in step 1) is greater than or equal to the initial molar amount of hydroxide ions in the papermaking black liquor; preferably, the ratio between the two is 1.05 to 1.50.

[0019] The step 1) is terminated when the pH value of the desalted ammonia-containing papermaking black liquor is reduced to 9-11, or when the hydroxyl ions converted into ammonia reach 80%-99% of the initial molar amount of hydroxyl ions.

[0020] The method for recovering ammonia in step 2) can be achieved by conventional methods, including but not limited to air stripping, steam stripping, ammonia distillation, membrane absorption, etc. Among them, the membrane absorption method is a membrane process that combines membrane separation technology with gas absorption technology, using a microporous membrane to allow the separated components to cross the membrane from the feed liquid side to the absorption side.

[0021] The step 2) is terminated when the pH value of the desalted and dealkalized papermaking black liquor is reduced to 7.0-10.5, or when the alkali (ammonia) recovery rate (defined as the ratio of the molar amount of recovered ammonia to the molar amount of initial hydroxide ions) reaches 70%-99%.

[0022] In step 3), the method for separating the lignin precipitate can adopt conventional solid-liquid separation methods, such as sedimentation, centrifugation, filtration, or a combination thereof. Furthermore, flocculants, filter aids, etc. can be added as needed.

[0023] Preferably, a pretreatment step is added before the papermaking black liquor in step 1) is passed into the cationic exchange dialysis device. The pretreatment method includes but is not limited to sedimentation, filtration, centrifugation, flocculation, etc. to remove water-insoluble matter such as mud, sand, and fiber in the papermaking black liquor. The pretreatment method can be selected according to actual needs to improve the quality of the lignin obtained in step 3).

[0024] The recovery of ammonia in step 2) can be performed after the completion of the cation exchange dialysis in step 1), or can be performed alternately with the cation exchange dialysis in step 1), or performed simultaneously. The alternating process is to proceed to step 2) before the ammonium ion exchange dialysis in step 1) reaches the predetermined end criterion, and then proceed to step 1) to continue the ammonium ion exchange dialysis after recovering part of the ammonia in the ammonia recovery in step 2), and the two are performed alternately until step 1) and step 2) reach the predetermined end criterion; the simultaneous process is to perform the ammonia recovery in step 2) while the ammonium ion exchange dialysis in step 1) is being performed, and the two are performed simultaneously until step 1) and step 2) reach the predetermined end criterion. The purpose of the alternating process and the simultaneous process is to separate the ammonia molecules in the papermaking black liquor in the liquid chamber in time, promote the dissociation equilibrium of ammonium / ammonia to move towards the direction of generating ammonia molecules, improve the recovery rate of ammonia, and further reduce the pH value of the papermaking black liquor in the liquid chamber to promote the precipitation of lignin.

[0025] Preferably, in the simultaneous process, the method for recovering ammonia in step 2) is an air stripping method, and the feed and liquid chamber of the cation exchange dialysis device is inflated while the ammonium ion exchange dialysis in step 1) is being performed. The inflating can be performed in the feed cylinder of the feed and liquid chamber, such as Figure 2 shown.

[0026] Further preferably, the temperature of the cation exchange dialysis during the simultaneous execution of the ammonia recovery in step 2) and the ammonium ion exchange dialysis in step 1) is 45° C. to 60° C.

[0027] Preferably, the present invention adds a hydrogen ion replacement dialysis step after step 2) to further recover the remaining lignin and sodium / potassium ions in the desalted and dealkalized papermaking black liquor obtained in step 2). The treatment process is as follows: Figure 4 shown.

[0028] The hydrogen ion exchange dialysis step comprises: using a cation exchange dialysis device, passing the desalted and dealkalized papermaking black liquor obtained in step 2) into the cation exchange dialysis device and performing cation exchange dialysis with an aqueous solution containing hydrogen ions to obtain acidified desalted and dealkalized papermaking black liquor;

[0029] The hydrogen ion exchange dialysis step can use the same cation exchange dialysis device as step 1), except for the feed liquids introduced into the feed liquid chamber and the drive chamber.

[0030] Specifically, the desalted and dealkalized papermaking black liquor obtained in step 2) is passed into the feed liquid chamber of the cation exchange dialysis device in the hydrogen ion exchange dialysis step, and the aqueous solution containing hydrogen ions is passed into the driving chamber of the cation exchange dialysis device to perform hydrogen ion exchange dialysis, such as Figure 5 As shown, sodium / potassium ions in the desalted and dealkalized papermaking black liquor passed into the feed chamber of the cation exchange dialysis device and hydrogen ions passed into the drive chamber of the cation exchange dialysis device undergo ion exchange through the cation exchange dialysis membrane. That is, sodium / potassium ions migrate across the cation exchange dialysis membrane into the drive chamber, and hydrogen ions migrate across the cation exchange dialysis membrane into the feed chamber, acidifying the lignin in the feed chamber and allowing the lignin to fully precipitate, thereby obtaining acidified desalted and dealkalized papermaking black liquor.

[0031] The aqueous solution containing hydrogen ions in the hydrogen ion exchange dialysis step includes but is not limited to any one of hydrochloric acid, nitric acid and sulfuric acid or a combination of at least two thereof. Accordingly, at the end of the hydrogen ion exchange dialysis step, sodium / potassium salt of acid, nitric acid or sulfuric acid is obtained in the driving chamber.

[0032] The initial molar amount of hydrogen ions in the hydrogen ion-containing aqueous solution in the hydrogen ion exchange dialysis step is greater than or equal to the molar amount of sodium / potassium ions in the desalted and dealkalized papermaking black liquor; preferably, the ratio between the two is 1.05 to 1.50.

[0033] In the hydrogen ion exchange dialysis step, the temperature of the hydrogen ion exchange dialysis is 20°C to 60°C.

[0034] The flow rates of the feed liquid in the feed liquid chamber and the feed liquid in the drive chamber in the hydrogen ion exchange dialysis step are conventional, preferably 3 cm / s to 7 cm / s.

[0035] Preferably, the hydrogen ion exchange dialysis step is terminated when the pH value of the acidified desalted and dealkalized papermaking black liquor is reduced to 2-3.

[0036] Compared with the prior art, the advantages of the present invention are:

[0037] (1) The present invention can simultaneously recover alkali and lignin from papermaking black liquor, thereby resolving the current problems of difficult papermaking black liquor treatment and waste of lignin and inorganic alkali resources, and achieving desalination of papermaking black liquor. The desalted and dealkalized papermaking black liquor contains only organic matter, facilitating subsequent biological treatment or resource utilization, such as biogas production.

[0038] (2) The method of the present invention for recovering alkali and lignin from papermaking black liquor by using cationic displacement dialysis does not use an electric field as the driving force. Compared with the electromembrane process and the pressure-driven membrane process, it has the advantages of low energy consumption and low membrane fouling, and can obtain a higher alkali recovery rate (up to 97.2%) and lignin recovery rate (up to 82.1%). BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of ion migration during the cation exchange dialysis process in the cation exchange dialysis device in step 1) ammonium ion exchange dialysis of the present invention;

[0040] Figure 2 Schematic diagram of the process of inflating the feed tank of the liquid chamber of the cation exchange dialysis device while the ammonium ion exchange dialysis in step 1) of the present invention is performed;

[0041] In the figure: the solid line represents the direction of the liquid in the liquid chamber, and the dotted line represents the direction of the liquid in the drive chamber.

[0042] Figure 3 This is a process flow chart for recovering alkali and lignin from papermaking black liquor using cationic displacement dialysis according to the present invention;

[0043] Figure 4 This is a process flow chart of the present invention for recovering alkali and lignin from papermaking black liquor by adding a hydrogen ion exchange dialysis step after step 2);

[0044] Figure 5 It is a schematic diagram of ion migration during the cation exchange dialysis process in the cation exchange dialysis device in the hydrogen ion exchange dialysis step of the present invention. DETAILED DESCRIPTION

[0045] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials, reagents, etc. used in the following examples are all commercially available unless otherwise specified.

[0046] Example 1

[0047] The cation exchange dialysis device of this embodiment adopts a plate-and-frame cation exchange dialysis membrane stack and Astom's CT-4 alkaline-resistant cation exchange membrane. The total effective area of ​​the membrane is 264 cm 2. 200 mL of papermaking black liquor (obtained by the sulfate process of Juntai Pulp and Paper in Hunan Province) containing a solid content of 24%, a pH of 13.5, 107 g / L of lignin, and 64 g / L of sodium ions was passed into the feed liquid chamber of the cation exchange dialysis device, and an ammonium sulfate solution with an initial ammonium ion molar amount that was 1.2 times the initial hydroxide ion molar amount in the papermaking black liquor was passed into the drive chamber of the cation exchange dialysis device to perform ammonium ion exchange dialysis. The feed liquid temperature in each chamber was 20°C, and the flow rate was 3 cm / s. The feed liquid chamber of the cation exchange dialysis device obtained desalted ammonia-containing papermaking black liquor with a pH of 10.2 and a sodium ion of 30 g / L. According to calculation, the sodium ion removal rate was 53.1%, and the membrane flux was 1.6 mol / m 2 / h.

[0048] Ammonia distillation is used to recover ammonia from desalted, ammonia-containing papermaking black liquor. The liquor is heated to 75°C, reducing the pH of the resulting desalted, dealkalized papermaking black liquor to 8.0, achieving an alkali (ammonia) recovery rate of 95%. Lignin precipitate is recovered from the desalted, dealkalized papermaking black liquor by centrifugation, achieving a lignin recovery rate of 34.0%.

[0049] Example 2

[0050] The cation exchange dialysis device is the same as that in Example 1. 200 mL of papermaking black liquor (obtained by the sulfate process of Juntai Pulp and Paper in Hunan Province) containing 24% solid content, pH 13.8, 110 g / L lignin, and 63 g / L sodium ions is passed into the feed liquid chamber of the cation exchange dialysis device, and an ammonium sulfate solution whose initial molar amount of ammonium ions is 1.5 times the initial molar amount of hydroxide ions in the papermaking black liquor is passed into the driving chamber of the cation exchange dialysis device to perform ammonium ion exchange dialysis. The feed liquid temperature in each chamber is 50°C, and the flow rate is 2 cm / s. Inflate the feed liquid chamber of the cation exchange dialysis device, as shown in FIG. Figure 2 As shown. The feed liquid chamber of the cation exchange dialysis device obtained desalted and dealkali-treated papermaking black liquor with a pH of 8.3 and a sodium ion content of 26.1 g / L. Calculations showed that the alkali (ammonia) recovery rate reached 93%, the sodium ion removal rate was 59.2%, and the membrane flux reached 2.2 mol / m 2 / h. Lignin precipitate in desalted and dealkalized papermaking black liquor was recovered by centrifugation, with a lignin recovery rate of 49.3%.

[0051] Example 3

[0052] The cation exchange dialysis apparatus was the same as in Example 1. 200 mL of papermaking black liquor (obtained by laboratory KOH alkaline cooking) containing 30% solids, a pH of 12.2, 141 g / L lignin, and 62 g / L potassium ions was passed into the feed chamber of the cation exchange dialysis apparatus. An ammonium chloride solution containing an initial ammonium ion molarity 1.5 times the initial hydroxide ion molarity in the papermaking black liquor was passed into the drive chamber of the cation exchange dialysis apparatus to perform ammonium ion exchange dialysis. The feed temperature in each chamber was 45°C, the flow rate was 1 cm / s, and air was introduced into the feed chamber of the cation exchange dialysis apparatus. The feed chamber of the cation exchange dialysis apparatus produced desalted and dealkalized papermaking black liquor with a pH of 8.7 and 36.2 g / L potassium ions. Calculations showed an alkali (ammonia) recovery rate of 71%, a potassium ion removal rate of 41.6%, and a membrane flux of 2.0 mol / m 2 / h. Lignin precipitate from desalted and dealkalized papermaking black liquor was recovered by centrifugation, with a lignin recovery rate of 28.6%.

[0053] Example 4

[0054] The cation exchange dialysis device is the same as that in Example 1. 200 mL of papermaking black liquor (obtained by the sulfate process of Juntai Pulp and Paper in Hunan Province) containing a solid content of 24%, a pH of 13.8, 110 g / L of lignin, and 62 g / L of sodium ions was passed into the feed liquid chamber of the cation exchange dialysis device, and an ammonium sulfate solution with an initial molar amount of ammonium ions that was 1.1 times the initial molar amount of hydroxide ions in the papermaking black liquor was passed into the driving chamber of the cation exchange dialysis device to perform ammonium ion exchange dialysis. The feed liquid temperature in each chamber was 60°C, the flow rate was 3 cm / s, and air was added to the feed liquid chamber of the cation exchange dialysis device. The feed liquid chamber of the cation exchange dialysis device obtained desalted and dealkalized papermaking black liquor with a pH of 8.3 and 24.3 g / L of sodium ions. According to calculations, the alkali (ammonia) recovery rate reached 95%, the sodium ion removal rate was 60.9%, and the membrane flux of the ammonium ion exchange dialysis reached 2.9 mol / m 2 / h.

[0055] The desalinated and dealkalized papermaking black liquor obtained is passed into the feed liquid chamber of the cation exchange dialysis device, and a sulfuric acid solution with an initial molar amount of hydrogen ions that is 1.2 times the molar amount of sodium ions in the desalinated and dealkalized papermaking black liquor is passed into the drive chamber of the cation exchange dialysis device to perform hydrogen ion exchange dialysis. The feed liquid temperature in each chamber is 20°C and the flow rate is 5 cm / s. The hydrogen ion exchange dialysis is stopped when the pH value of the feed liquid chamber of the cation exchange dialysis device drops to 2.0. According to calculations, the membrane flux of the hydrogen ion exchange dialysis reaches 1.0 mol / m 2 / h, after ammonium ion exchange dialysis and hydrogen ion exchange dialysis, the total sodium ion removal rate reached 81.6%. The lignin precipitate in the acidified desalted and dealkalized papermaking black liquor was recovered by centrifugation, and the lignin recovery rate reached 76.1%.

[0056] Example 5

[0057] The cation exchange dialysis device is the same as that in Example 1. 200 mL of papermaking black liquor (obtained by KOH alkaline cooking in the laboratory) containing a solid content of 30%, a pH of 12.2, 140 g / L of lignin, and 64 g / L of potassium ions is passed into the feed liquid chamber of the cation exchange dialysis device, and an ammonium sulfate solution with an initial molar amount of ammonium ions that is 1.3 times the initial molar amount of hydroxide ions in the papermaking black liquor is passed into the drive chamber of the cation exchange dialysis device to perform ammonium ion exchange dialysis. The feed liquid temperature in each chamber is 45°C, and the flow rate is 3 cm / s. The feed liquid chamber of the cation exchange dialysis device obtains desalted ammoniacal papermaking black liquor with a pH of 9.7 and 35.8 g / L of potassium ions. According to calculation, the membrane flux of the ammonium ion exchange dialysis is 1.9 mol / m 2 / h, with a potassium ion removal rate of 44.1%. Ammonia distillation is used to recover ammonia from desalted ammonia-containing papermaking black liquor. The liquid temperature is heated to 80°C, and the pH value of the desalted and dealkalized papermaking black liquor is reduced to 7.5, with an alkali (ammonia) recovery rate of 75%.

[0058] The desalinated and dealkalized papermaking black liquor obtained is passed into the feed liquid chamber of the cation exchange dialysis device, and a sulfuric acid solution with an initial molar amount of hydrogen ions that is 1.1 times the molar amount of potassium ions in the desalinated and dealkalized papermaking black liquor is passed into the drive chamber of the cation exchange dialysis device to perform hydrogen ion exchange dialysis. The feed liquid temperature in each chamber is 40°C and the flow rate is 7 cm / s. The hydrogen ion exchange dialysis is stopped when the pH value of the feed liquid chamber of the cation exchange dialysis device drops to 2.5. According to calculations, the membrane flux of the hydrogen ion exchange dialysis reaches 1.5 mol / m 2 / h, after ammonium ion exchange dialysis and hydrogen ion exchange dialysis, the total potassium ion removal rate reached 97.2%. The lignin precipitate in the acidified desalted and dealkalized papermaking black liquor was recovered by centrifugation, and the lignin recovery rate reached 77.9%.

[0059] Example 6

[0060] The cation exchange dialysis device is the same as that in Example 1. 200 mL of papermaking black liquor (obtained by KOH alkaline cooking in the laboratory) containing a solid content of 30%, a pH of 12.5, 145 g / L of lignin, and 65 g / L of potassium ions is passed into the feed liquid chamber of the cation exchange dialysis device, and an ammonium sulfate solution with an initial molar amount of ammonium ions that is 1.1 times the initial molar amount of hydroxide ions in the papermaking black liquor is passed into the drive chamber of the cation exchange dialysis device to perform ammonium ion exchange dialysis. The feed liquid temperature in each chamber is 60°C, and the flow rate is 4 cm / s. The feed liquid chamber of the cation exchange dialysis device obtains desalted ammoniacal papermaking black liquor with a pH of 9.3 and 28.5 g / L of potassium ions. According to calculation, the membrane flux of the ammonium ion exchange dialysis is 2.6 mol / m 2 / h, with a potassium ion removal rate of 56.1%. Ammonia distillation is used to recover ammonia from desalted ammonia-containing papermaking black liquor. The liquid temperature is heated to 85°C, and the pH value of the desalted and dealkalized papermaking black liquor is reduced to 7.1, with an alkali (ammonia) recovery rate of 97.2%.

[0061] The desalinated and dealkalized papermaking black liquor obtained is passed into the feed liquid chamber of the cation exchange dialysis device, and a sulfuric acid solution with an initial molar amount of hydrogen ions that is 1.2 times the molar amount of potassium ions in the desalinated and dealkalized papermaking black liquor is passed into the drive chamber of the cation exchange dialysis device to perform hydrogen ion exchange dialysis. The feed liquid temperature in each chamber is 60°C and the flow rate is 5 cm / s. The hydrogen ion exchange dialysis is stopped when the pH value of the feed liquid chamber of the cation exchange dialysis device drops to 2.2. According to calculations, the membrane flux of the hydrogen ion exchange dialysis reaches 2.5 mol / m 2 / h, after ammonium ion exchange dialysis and hydrogen ion exchange dialysis, the total potassium ion removal rate reached 98%. The lignin precipitate in the acidified desalted and dealkalized papermaking black liquor was recovered by centrifugation, and the lignin recovery rate reached 82.1%.

[0062] Comparative Example

[0063] This comparative example uses diffusion dialysis to recover alkali from papermaking black liquor. The cation exchange dialysis device uses a plate-and-frame cation exchange dialysis membrane stack and a diffusion dialysis cation membrane produced by Shandong Tianwei Membrane Technology. The total effective area of ​​the membrane is 264 cm 2 . 200 mL of papermaking black liquor (obtained by the sulfate process of Juntai Pulp and Paper in Hunan Province) containing a solid content of 24%, a pH of 13.5, 105 g / L of lignin, and 64 g / L of sodium ions was passed into the feed liquid chamber of the cation exchange dialysis device, and 200 mL of deionized water was passed into the driving chamber of the cation exchange dialysis device for diffusion dialysis. The feed liquid temperature in each chamber was 30°C, and the flow rate was 3 cm / s. The feed liquid chamber of the cation exchange dialysis device obtained desalted and dealkalized papermaking black liquor (NaOH removed) with a pH value of 12.5. At this time, the alkali (sodium hydroxide) recovery rate (the ratio of the molar amount of hydroxide ions in the driving chamber to the initial hydroxide ions) was 38%, and the membrane flux of the diffusion dialysis was 0.8 mol / m 2 / h. Centrifugation of desalted and dealkalized papermaking black liquor results in virtually no lignin precipitate recovery. The alkali recovery rate, lignin recovery rate, and membrane flux of diffusion dialysis are far lower than those of the method described in the present invention.

[0064] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and are intended to be encompassed by the claims of the present invention.

Claims

1. A method for recovering alkali and lignin from papermaking black liquor using cationic displacement dialysis, comprising the following steps: 1) Ammonium ion exchange dialysis: Using a cation exchange dialysis device, the papermaking black liquor is passed through the cation exchange dialysis device and subjected to cation exchange dialysis with an aqueous solution containing ammonium ions to obtain desalted ammonia-containing papermaking black liquor; 2) recovering ammonia: recovering ammonia from the desalted ammonia-containing papermaking black liquor obtained in step 1) to obtain desalted and dealkalized papermaking black liquor; 3) Separating lignin: Separating the precipitated lignin from the desalted and dealkalized papermaking black liquor obtained in step 2) to obtain lignin precipitate and desalted, dealkalized and delignified papermaking black liquor.

2. The method according to claim 1, characterized in that The cation exchange dialysis device in step 1) includes a cation exchange dialysis membrane and a feed and liquid chamber and a drive chamber separated by the cation exchange dialysis membrane.

3. The method according to claim 2, characterized in that The cation exchange dialysis device includes one cation exchange dialysis module or two or more cation exchange dialysis modules connected in series and / or in parallel.

4. The method according to any one of claims 1 to 3, characterized in that: The aqueous solution containing ammonium ions in step 1) includes one or more of aqueous solutions of ammonium sulfate, ammonium chloride and ammonium carbonate.

5. The method according to any one of claims 1 to 4, characterized in that: The initial molar amount of ammonium ions in the aqueous solution containing ammonium ions in step 1) is greater than or equal to the initial molar amount of hydroxide ions in the papermaking black liquor.

6. The method according to any one of claims 1 to 3, characterized in that: The temperature of the ammonium ion replacement dialysis in step 1) is 20°C to 60°C.

7. The method according to claim 1, characterized in that The method for recovering ammonia in step 2) includes one or more of air stripping, steam stripping, ammonia distillation and membrane absorption.

8. The method according to claim 7, characterized in that The method for recovering ammonia in step 2) is air stripping method, and the recovery of ammonia is carried out simultaneously with the ammonium ion exchange dialysis in step 1), and the temperature of the cation exchange dialysis is 45°C to 60°C.

9. The method according to any one of claims 1 to 3, characterized in that: In step 1), a pretreatment step is added before the papermaking black liquor is passed into the cationic exchange dialysis device.

10. The method according to any one of claims 1 to 9, characterized in that: Between step 2) and step 3), the desalted and dealkalized papermaking black liquor subjected to hydrogen ion exchange dialysis treatment in step 2a) is added, and step 2a) comprises the following steps: A cation exchange dialysis device is used to pass the desalted and dealkalized papermaking black liquor obtained in step 2) into the cation exchange dialysis device for cation exchange dialysis with an aqueous solution containing hydrogen ions to obtain acidified desalted and dealkalized papermaking black liquor, and then the acidified desalted and dealkalized papermaking black liquor is sent to step 3) for treatment.

11. The method according to claim 10, characterized in that The aqueous solution containing hydrogen ions is one or more of hydrochloric acid, nitric acid and sulfuric acid.

12. The method according to claim 10, characterized in that The temperature of hydrogen ion exchange dialysis is 20°C to 60°C.

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