CN112030591A - A new method of acid-base recycling for alkali recovery from straw pulp black liquor - Google Patents

Abstract

Aiming at the problem that the black liquor is difficult to evaporate and burn due to the high content of silicon cells and the existence of sodium silicate in the conventional straw pulp black liquor, the invention provides a novel method for recycling acid and alkali from the straw pulp black liquor. The method adopts phosphoric acid as acid precipitation liquid, and lignin is precipitated by adjusting the pH value of the black liquid, so that the lignin is extracted from the black liquid. Phosphoric acid is used as a medium strong acid, the pH required for completely depositing lignin can be reached, sodium dihydrogen phosphate generated in a filter liquor is subjected to causticization treatment by calcium hydroxide, the products are calcium phosphate and sodium hydroxide, wherein the sodium hydroxide can be recycled as a cooking white liquor, the phosphoric acid and the calcium hydroxide can be obtained by a phosphogypsum recycling way, substances in the whole process are completely recycled, no harmful wastewater is generated, and clean production of non-wood fiber pulping and papermaking can be really realized.

Description

A new method of acid-base recycling for alkali recovery from straw pulp black liquor

technical field

The invention belongs to a new method for acid-base regeneration and circulating alkali recovery of papermaking black liquor, relates to the pollution control of straw pulp black liquor of alkali pulping, and is especially suitable for the technological transformation of black liquor acid precipitation method.

Background technique

The silicon cells of non-wood raw materials contain a large amount of silicon. During the traditional alkaline pulping and cooking process, the silicon cells are dissolved by the alkaline solution, and the silicon is dissolved in the form of sodium silicate and exists in the black liquor, resulting in the viscosity of the black liquor. The extraction rate of black liquor is low, and the subsequent alkali recovery and reuse of black liquor is difficult, which is the so-called "silicon interference problem". The lignin in black liquor can make degradable and renewable polymers, and hemicellulose can be used as a raw material for the production of chewing gum. If these useful components can be separated from black liquor and turned waste into treasure, significant environmental, economic and social benefits can be obtained.

In recent years, many new black liquor treatment methods have also appeared, such as treating lignin components with a combined method of catalytic conversion of ionic liquids. With the help of the super solubility of ionic liquids, the phenolic lignin is separated from the black liquor, and then the phenolic lignin is separated from the black liquor. Catalytic hydrolysis into petroleum products. The supercritical fluid method is a new method of recovering hydrogen from black liquor. The separated gas product is supplied with natural gas to heat energy for pulping production. However, using air as an oxidant will generate nitrogen oxides in the gas discharge process, which is harmful to the production of carbon dioxide. The environment causes secondary pollution. Because of the complicated requirements on equipment, instruments and experimental conditions, these methods have been stuck in the laboratory stage, and it is difficult to carry out large-scale industrialization. The traditional black liquor evaporation and combustion technology is relatively mature, and it has always been a commonly used black liquor treatment method in factories. The method of producing lignin by acid deposition in black liquor is the most studied. The key lies in the choice of acid. It is easy to use strong acids such as sulfuric acid and hydrochloric acid. The required pH is reached, but the concentration of sodium sulfate and sodium chloride in the filtrate is too low, making it difficult to recycle, resulting in secondary pollution. Passing carbon dioxide into the black liquor can also reduce the pH, but carbonic acid is a weak acid and cannot reach the pH required for complete deposition of lignin. Therefore, it is crucial to find a safe, effective and recyclable acid treatment method.

The process of the invention adopts the concept of acid-base circulation, and adopts two acid-base treatment processes of phosphoric acid acidification and calcium hydroxide causticization, which can not only effectively extract the organic matter of the black liquor, but also realize the water circulation and alkali circulation of the black liquor. The macromolecular substances in the two treatment processes of acid and alkali effectively bind small molecules such as sugar and phenolic acid, so that the COD of circulating lye is in a stable state, which provides a feasible theoretical basis for the cooking cycle of lye.

SUMMARY OF THE INVENTION

The purpose of the present invention is to design a new type of straw pulp black liquor alkali recovery technology mainly aiming at the problems such as difficult treatment and serious pollution of non-wood pulp and papermaking black liquor, aiming to solve the key problem of black liquor treatment and realize straw pulp. cleaner production. On the one hand, to solve the problem of shortage of papermaking raw materials in my country, we no longer rely on imported waste paper and make full use of local straw resources; on the other hand, based on the concept of biorefinery, the components of straw resources are separated, and the separated cellulose can not only be used Pulp and paper can also be used to produce other cellulose products, and lignin extracted from black liquor can be used to produce humic acid and other fertilizers. Making full use of straw fiber resources can not only bring economic benefits, but also alleviate the energy crisis and achieve sustainable development.

1, a kind of acid-base cycle is used for the new method of straw pulp black liquor alkali recovery, it is characterized in that comprising the following steps:

(1) Preparation of black liquor: cut the straw into 3cm-10cm, add it into the cooking pot, the solid-liquid ratio is 1:3-1:10 (mass ratio), and the cooking conditions are: the alkali used for cooking is NaOH, and the The amount accounts for 15%-25% of the quality of the dry straw raw material, the cooking temperature is 150°C-170°C, and the cooking time is 1h-3h. After the cooking is completed, the obtained slurry is filtered, and the solid material is fully washed until the pH of the solid material is 6-9, and all the filtrate and the washing liquid are collected to obtain the required black liquor;

(2) Black liquor phosphoric acidification treatment: add NH ₄ H ₂ PO ₄ to the black liquor obtained in step (1) to adjust the pH to 5-6, and precipitate a part of lignin. After removing the precipitate by centrifugation, continue adding to the supernatant Phosphoric acid is adjusted to pH less than 2, and the extracted lignin and NaH ₂ PO ₄ red liquor are obtained by centrifugation;

(3) causticization reaction of NaH ₂ PO ₄ red liquor: the NaH ₂ PO ₄ red liquor obtained in step (2) is added with calcium hydroxide at normal temperature, and the reaction time is 30min-60min, and the reaction is uniformly stirred with constant stirring. After the reaction is finished Carry out solid-liquid separation to obtain calcium phosphate solid and NaOH lye;

(4) circulation of cooking liquor: after measuring the concentration and volume of the NaOH alkali liquor obtained in step (3), add a certain amount of solid NaOH and cooking water consumption to the cooking alkali consumption described in step (1), The supplemented cooking lye is dissolved and mixed, and the operation of step (1) is repeated, that is, the cycle of cooking lye is realized;

(5) Calcium phosphate regeneration NaOH and H ₃ PO ₄ cycle: the calcium phosphate solid produced in step (3) is used to recycle NaOH and H ₃ PO ₄ , and the calcium phosphate solid and NH ₄ H ₂ PO ₄ are more than 1:1.5 The molar ratio of CaHPO ₄ and NH ₄ HCO ₃ were added to the reactor at 600 ℃ in a molar ratio greater than 3:1 to obtain CaHPO ₄ to obtain NH ₄ H ₂ PO ₄ solution and CaCO ₃ solid, NH ₄ H ₂ PO ₄ solution is fed with the same mass of CO ₂ at 250°C to obtain H ₃ PO ₄ required for the cycle process, and the CaCO ₃ solid is calcined at high temperature to obtain CaO. CaO further obtains Ca(OH) ₂ , which is used to supplement the consumption of Ca(OH) ₂ in the causticization process;

The reaction principle is as follows:

Detailed ways

The present invention will be further illustrated by the following examples.

Example 1

(1) Preparation of black liquor: cut the straw into 3cm, add it into the cooking pot, the solid-liquid ratio is 1:5 (mass ratio), and the cooking conditions are: the alkali used for cooking is NaOH, and the amount of alkali accounts for the absolute dry straw raw material. 15% of the mass, the cooking temperature is 150℃, and the cooking time is 1.5h. After the cooking is completed, the obtained slurry is filtered, and the solid material is fully washed until the pH of the solid material is 6, and all the filtrate and the washing liquid are collected to obtain the required black liquor;

(2) Phosphoric acidification treatment of black liquor: adding NH ₄ H ₂ PO ₄ to the black liquor obtained in step (1) to adjust the pH to 5, precipitating a part of lignin, and removing the precipitate by centrifugation, adding phosphoric acid to the supernatant to adjust the pH The pH is less than 2, and the extracted lignin and NaH ₂ PO ₄ red liquor are obtained by centrifugal separation;

(3) causticizing reaction of NaH ₂ PO ₄ red liquor: the NaH ₂ PO ₄ red liquor obtained in step (2) was added with calcium hydroxide at normal temperature, and the reaction time was 30min, and the reaction was made uniform by constant stirring, and solidification was carried out after the reaction finished. Liquid separation to obtain calcium phosphate solid and NaOH lye;

(4) circulation of cooking liquid: after measuring the concentration and volume of the NaOH lye obtained in step (3), add 50% of solid NaOH and 20% of cooking water to the cooking alkali described in step (1) amount, dissolve and mix the supplemented cooking lye, repeat the operation of step (1), i.e. realize the cycle of cooking lye;

(5) Calcium phosphate regeneration NaOH and H ₃ PO ₄ cycle: the calcium phosphate produced in step (3) is used to recycle NaOH and H ₃ PO ₄ , and the solid calcium phosphate and NH ₄ H ₂ PO ₄ are in a ratio of 1:1.5 It was added to the autoclave at 250°C for 2h to obtain CaHPO ₄ . The solid CaHPO ₄ and NH ₄ HCO ₃ were added to the reactor at 600° C in a ratio of 3:1 to obtain NH ₄ H ₂ PO ₄ solution and solid CaCO ₃ . , the NH ₄ H ₂ PO ₄ solution is fed with the same mass of CO ₂ at 250℃, the H ₃ PO ₄ required for the cycle process can be obtained, the CaCO ₃ solid is calcined at high temperature to obtain CaO, and the Ca(OH ) ₂ , used to supplement the consumption of Ca(OH) ₂ in the causticizing process;

Example 2

(1) Preparation of black liquor: cut the straw into 5cm, add it to the cooking pot, the solid-liquid ratio is 1:6 (mass ratio), and the cooking conditions are: the alkali used for cooking is NaOH, and the amount of alkali accounts for the absolute dry straw raw material. 20% of the mass, the cooking temperature is 160℃, and the cooking time is 2h. After the cooking is completed, the obtained slurry is filtered, and the solid material is fully washed until the pH of the solid material is 7, and all the filtrate and the washing liquid are collected to obtain the required black liquor;

(2) Phosphoric acidification treatment of black liquor: adding NH ₄ H ₂ PO ₄ to the black liquor obtained in step (1) to adjust the pH to 5, precipitating a part of lignin, and removing the precipitate by centrifugation, adding phosphoric acid to the supernatant to adjust the pH The pH is less than 2, and the extracted lignin and NaH ₂ PO ₄ red liquor are obtained by centrifugal separation;

(3) causticization reaction of NaH ₂ PO ₄ red liquor: the NaH ₂ PO ₄ red liquor obtained in step (2) was added with calcium hydroxide at normal temperature, the reaction time was 45min, and the reaction was uniformly stirred with constant stirring. Liquid separation to obtain calcium phosphate solid and NaOH lye;

(4) circulation of cooking liquid: after measuring the concentration and volume of the NaOH lye obtained in step (3), add 60% of solid NaOH and 30% of cooking water to the cooking alkali described in step (1) amount, the supplemented cooking lye is dissolved and mixed, and the operation of step (1) is repeated, that is, the cycle of cooking lye is realized;

(5) Calcium phosphate regeneration NaOH and H ₃ PO ₄ cycle: the calcium phosphate produced in step (3) is used to recycle NaOH and H ₃ PO ₄ , and the solid calcium phosphate and NH ₄ H ₂ PO ₄ are in a ratio of 1:2 It was added to the autoclave at 250°C for 2.5h to obtain CaHPO ₄ . The solid CaHPO ₄ and NH ₄ HCO ₃ were added to the reactor at 600° C. in a ratio of 4:1 to obtain NH ₄ H ₂ PO ₄ solution and CaCO ₃ The solid, NH ₄ H ₂ PO ₄ solution is fed with the same quality of CO ₂ at 250 ° C, the H ₃ PO ₄ required for the cycle process can be obtained, the CaCO ₃ solid is calcined at high temperature to obtain CaO, and CaO is further obtained from Ca ( OH) ₂ , used to supplement the consumption of Ca(OH) ₂ in the causticization process;

Example 3

(1) Preparation of black liquor: cut the straw into 10cm, add it into the cooking pot, the solid-liquid ratio is 1:7 (mass ratio), and the cooking conditions are: the alkali used for cooking is NaOH, and the amount of alkali accounts for the absolute dry straw raw material. 25% of the mass, cooking temperature 170 ℃, cooking time 3h. After the cooking is completed, the obtained slurry is filtered, and the solid material is fully washed until the pH of the solid material is 8, and all the filtrate and the washing liquid are collected to obtain the required black liquor;

(2) Phosphoric acidizing treatment of black liquor: adding NH ₄ H ₂ PO ₄ to the black liquor obtained in step (1) to adjust the pH to 6, precipitating a part of lignin, centrifuging to remove the precipitate, and adding phosphoric acid to the supernatant to adjust the pH The pH is less than 2, and the extracted lignin and NaH ₂ PO ₄ red liquor are obtained by centrifugal separation;

(3) causticization reaction of NaH ₂ PO ₄ red liquor: the NaH ₂ PO ₄ red liquor obtained in step (2) was added with calcium hydroxide at normal temperature, and the reaction time was 60min, and the reaction was uniformly stirred with constant stirring. Liquid separation to obtain calcium phosphate solid and NaOH lye;

(4) Circulation of cooking liquid: after measuring the concentration and volume of the NaOH lye obtained in step (3), add 80% of solid NaOH and 50% of cooking water to the cooking alkali described in step (1) amount, the supplemented cooking lye is dissolved and mixed, and the operation of step (1) is repeated, that is, the cycle of cooking lye is realized;

(5) Calcium phosphate regeneration NaOH and H ₃ PO ₄ cycle: the calcium phosphate produced in step (3) is used to recycle NaOH and H ₃ PO ₄ , and the solid calcium phosphate and NH ₄ H ₂ PO ₄ are in a ratio of 1:3 It was added to the autoclave at 250°C for 3 hours to obtain CaHPO ₄ . The solid CaHPO ₄ and NH ₄ HCO ₃ were added to the reactor at 600° C. in a ratio of 5:1 to obtain NH ₄ H ₂ PO ₄ solution and solid CaCO ₃ . , the NH ₄ H ₂ PO ₄ solution is fed with the same mass of CO ₂ at 250℃, the H ₃ PO ₄ required for the cycle process can be obtained, the CaCO ₃ solid is calcined at high temperature to obtain CaO, and the Ca(OH ) ₂ , which is used to supplement the consumption of Ca(OH) ₂ in the causticizing process.

Claims (1)

1. an acid-base cycle is used for the new method for recovery of grass pulp black liquor alkali, it is characterized in that comprising the following steps: (1) Preparation of black liquor: cut the straw into 3cm-10cm, add it into the cooking pot, the solid-liquid ratio is 1:3-1:10 (mass ratio), and the cooking conditions are: the alkali used for cooking is NaOH, and the The amount accounts for 15%-25% (mass ratio) of the absolutely dry straw raw materials, the cooking temperature is 150℃-170℃, and the cooking time is 1h-3h. After the cooking is completed, the obtained slurry is filtered, and the solid material is fully washed until the pH of the solid material is 6-9, and all the filtrate and the washing liquid are collected to obtain the required black liquor; (2) Phosphoric acidizing treatment of black liquor: adding NH ₄ H ₂ PO ₄ to the black liquor obtained in step (1) to adjust the pH to 5-6, and precipitating a part of lignin, after centrifugation to remove the precipitate, the supernatant is added Phosphoric acid is adjusted to pH less than 2, and the extracted lignin and NaH ₂ PO ₄ red liquor are obtained by centrifugation; (3) causticization reaction of NaH ₂ PO ₄ red liquor: the NaH ₂ PO ₄ red liquor obtained in step (2) was added with calcium hydroxide at normal temperature, the reaction time was 30min-60min, and the reaction was uniformly stirred by constant stirring. Carry out solid-liquid separation to obtain calcium phosphate solid and NaOH lye; (4) circulation of cooking liquor: after measuring the concentration and volume of the NaOH alkali liquor obtained in step (3), add a certain amount of solid NaOH and cooking water consumption to the cooking alkali consumption described in step (1), The supplemented cooking lye is dissolved and mixed, and the operation of step (1) is repeated, that is, the recycling of the cooking lye is realized; (5) Calcium phosphate regeneration NaOH and H ₃ PO ₄ cycle: the calcium phosphate solid produced in step (3) is used to recycle NaOH and H ₃ PO ₄ , and the calcium phosphate solid and NH ₄ H ₂ PO ₄ are more than 1:1.5 The molar ratio of CaHPO ₄ and NH ₄ HCO ₃ were added to the reactor at 600 ° C according to the molar ratio of more than 3:1 to obtain CaHPO ₄ to obtain NH ₄ H ₂ PO ₄ solution and CaCO ₃ solid, NH ₄ H ₂ PO ₄ solution is fed with the same mass of CO ₂ at 250°C to obtain H ₃ PO ₄ required for the cycle process, and the CaCO ₃ solid is calcined at high temperature to obtain CaO. CaO further obtains Ca(OH) ₂ , which is used to supplement the consumption of Ca(OH) ₂ in the causticization process; The reaction principle is as follows: