Optimization of the parameters of obtaining potassium sulphate from sodium-potassium solutions in the acid-alkaline method of kraft pulp production

In the classic black liquor processing method for kraft pulp production, the mineral residue after burning the organic component of the black liquor in the recovery boiler is a mixture of sodium carbonate and sodium sulfate. The resulting soda solution is treated with lime coming from the decarbonization shop and a caustic alkali solution is obtained, which is subsequently used for pulping pulp in white liquor. As a result of the experiments, it becomes possible to improve the environmental safety of the black liquor processing process and diversify the production of sulfate cellulose, as well as simplify the hardware and technological scheme of the alkali regeneration process. The developed method is based on the distribution of potassium alkali between the solution and solid sodium sulfate by converting sodium sulfate with a KOH solution, depending on the change in the molar fraction of potassium alkali from the sum of potassium and sodium alkalis in the solution. Based on the considered patterns of distribution of potassium alkali between the sodium-potassium solution and sodium sulfate, a conversion method of potassium sulfate and sodium sulfate is proposed. The essence of the method lies in the exchange reaction between sodium sulfate contained in a solid mixture of sulfates with a potassium alkali solution. The work determined the optimal technological parameters for the separation of potassium sulfate from sulfate solutions and investigated the influence of individual technological parameters on the yield of potassium sulfate in the sediment. To set up the experiment, a rotatable central compositional plan was chosen. Evaluation of the research results makes it possible to come to the conclusion that the yield of potassium sulfate is affected not only by variable parameters, but also by their combination. Similar yields of potassium sulfate can be obtained with a reaction time of 60 minutes, but with different variations in the parameters. For the practical application of the presented scheme, the following optimal parameters were chosen: – the molar fraction of potassium alkali from the sum of potassium and sodium alkalis in the suspension – 60%, the mass ratio of liquid/solid in the suspension – 4.7, reaction duration – 60 minutes. Experimental data on the parameters for producing potassium sulfate as a fertilizer are scientifically substantiated. At the same time, it is proposed to obtain an additional commercial product when processing black liquor from sulfate pulp production.

1. Akim E.L. Bio-refining of wood. Chemical fibers, 2016, no. 3, pp. 34–41. (In Russ.)

2. Cardoso M., Dominigos de Oliveira E., Passos M.L. Chemical composition and physical properties of black liquors and theier effects on liquor recovery operation in Brazilian pulp mills. Fuel, 2009, no. 88, pp. 756–763.

3. Demin V.A. Chemistry and technology of sulphate liquor. Syktyvkar: SLI, 2013, 96 p. (In Russ.)

4. Fedorova O.V, Lukanin P.V., Kazakov V.G., Subbotina K.O., Samoilenko D.E. Influence of technological parameters on the extraction of organic compounds from black liquor solutions of sulphate pulp production. Vestnik SPGUTD, 2016, no. 4, рр. 49–52. (In Russ.)

5. Fedorova O.V., Lukanin P.V., Kazakov V.G., Samoylenko D.E. Modernization of the technological process of processing black sulphate cellulose liquors, 2016, vol. 89, iss. 5. pp. 654–659. (In Russ.)

6. Gioia F., Astarita G.A. general solution to the problem of hydrogen sulfide absorption in alkaline solutions. Environmental Technology, 1967, no. 6, pp. 370–375.

7. Grace T.M., Fraderick W.J., Salcudean M., Wessel R.A. Black liquor combustion validated recovery boiler modeling final year report. Atlanta: The Institute of Paper Science and Technology, 1998. 198 p.

8. Muryantoa, Triwahyunia E., Hendarsyaha H., Abimanyua H. Reuse black liquor of alkali pretreatment in bioethanol production. 2nd International Conference on Sustainable Energy Engineering and Application, 2015, pp. 236–243.

9. Nepenin Yu.N. Production of sulphate pulp. M.: Forest industry, 1990, 600 p. (In Russ.)

10. Pat. 2617569 Russian Federation IPC D21C11 / 00. Method for acid-base processing of black liquor sulphate pulp production / Kazakov V.G., Lukanin P.V., Smirnova O.S. Applicant and rightholder SPbGTURP No. 2014108629; announced 05.03.2014; publ. 25.04. 2017. Bull. No. 25. (In Russ.)

11. Pat. 2696636 Russian Federation IPC D21C11/00. Preparation of white liquor for the production of sulfate pulp / Fedorova O.V., Kazakov V.G., Lukanin P.V. Applicant and copyright holder SPbGUPTD No. 2018131321; dec. 08/30/2018; publ. 08/05/2019. Bull. No. 22. (In Russ.)

12. Sidnyaev N.I., Vilisova N.T. Introduction to the theory of experiment planning. M.: Bauman Moscow State Technical University, 2001. 32 p. (In Russ.)

13. Wertz, J.L., Deleu M., Coppee S., Richel A. Hemicelluloses and Lignin in Biorefineries, Taylor & Francis Group, 2018. 330 р.