Depolymerization Performance Of Lignite Low Ru Catalyst And Separation Of Different Components In Depolymerized Products

Benzene polycarboxylic acids（BPCAs）were prepared by ruthenium ions catalyzed oxidation（RICO）depolymerization of lignite.It was an effective way to achieve value-added utilization of lignite.However,due to the high cost of Ru catalyst used in RICO depolymerization of lignite,the amount of ruthenium catalyst should be reduced.In addition,the depolymerization products are complex.Besides BPCAs chemicals,they also contain inorganic components such as sodium iodate and sodium periodate,which hinder the separation of high value-added polycarboxylic acid chemicals.As BPCAs are important chemical raw materials,they are first separated and reused from the lignite depolymerization products,which can able to leverage the high value-added characteristics of depolymerized products and improve their utilization rate.In this paper,the depolymerization effect of RICO on lignite with low dosage of Ru catalyst was investigated.The inorganic salts and BPCAs in the depolymerization products were separated by butanone solvent extraction and crystallization method.Then different BPCAs were separated by alkaline earth metal ion coordination separation using water and organic solvent as separation medium.In order to further improve the separation effect,an anti-solvent method was established to separate different BPCAs from lignite depolymerization products,and the separation selectivity was regulated by optimizing the separation conditions.The research content and main conclusions of this paper are as follows:（1）In order to reduce the use of catalyst in RICO depolymerization of lignite,RICO depolymerization of lignite was carried out under low dosage of RuCl₃catalyst,study on the effect of RuCl₃catalyst dosage on the depolymerization degree of lignite and the yield of BPCAs.The inorganic and organic components of the depolymerization products were separated by extraction of acidified BPCAs with butanone and crystallization of salt at different temperatures.The results show that,compared with the condition of RuCl₃/lignite mass ratio of 1/10.0,the depolymerization degree and BPCAs yield do not decrease significantly under the condition of RuCl₃/lignite mass ratio of 1/1000.0 by extending the reaction time,the depolymerization degree can reach 87.0%,and the total yield of BPCAs can reach 8.9%,which indicates that the depolymerization effect can still be maintained under the condition of low RuCl₃dosage.The extraction yield of BPCAs in aqueous phase was about 91.0%.The results showed that the content of inorganic salts（mainly NaIO₃）in the extraction phase of butanone was about 0.19 mg/mL,and the desalination efficiency could reach 98.5%.The crystallization desalination efficiency at 4℃ was 52.8%,and a small amount of BPCAs was included in the precipitated salt.Butanone extraction can achieve the enrichment of BPCAs,and the desalination efficiency of inorganic salts is significantly higher than that of low temperature crystallization,which is an effective way for the preliminary separation of lignite depolymerization products.（2）In view of the selective separation of different BPCAs in depolymerization products,the separation route of metal ion coordination separation of BPCAs in organic solvent was established based on the characteristics of alkaline earth metal ion selective binding with different BPCAs in depolymerization products.The effects of alkaline earth metal ion type,organic solvent,reaction time,metal ion dosage and reaction temperature on the separation yield and selectivity were investigated.The results showed that under the optimal separation conditions,namely,the amount of BaCl₂·2H₂O was 0.02 g/mL,the reaction temperature was 120℃,and the reaction time was 8 h,the extraction yield of1,2,4,5-BTA reached the maximum value of 27.5%;the extraction yield of 1,2,3,4-BTA reached the maximum of 65.6%;the extraction yield of 1,2,3,5-BTA reached the maximum74.9%;the extraction yield of 1,2,3-BTA reached the maximum value of 37.3%;the extraction yield of BPCAs were 21.6%,36.0%,64.7%,and 32.3%higher than those of BPCAs separated with water as solvent,respectively,the separation of 1,2,4-BTA was almost non-existent.（3）Ba²⁺was used to separate BPCAs from lignite depolymerization products.Although the separation yield achieved a good effect,the regulation of selectivity was still not ideal.This paper further explored the separation route of BPCAs by anti-solvent method.The depolymerization product was dissolved in ammonia water to combine into carboxylate ammonium salt,and then some carboxylate ammonium salt crystallized out by adding anti-solvent.By adjusting the addition method and volume ratio of anti-solvents,the separation effect can be improved.The results show that all types of carboxylic acids can be precipitated when the volume ratio of anti-solvent acetonitrile to NH₄⁺-BPCAs solution reaches 5:1.When the volume ratio of anti-solvent ethanol to NH₄⁺-BPCAs solution was 3:1,it showed high selectivity for BPCAs with carboxyl group number≥4.When the volume ratio of anti-solvent methanol to NH₄⁺-BPCAs was 5:1,the main BPCAs with carboxyl group number≥5 had high selectivity.The extraction yield of benzene hexacarbonic acid and benzene pentacarbonic acid was 44.1%and 32.6%.The extraction yield could be improved by adding anti-solvent in batches,and the extraction yield of benzene hexacarbonic acid and benzene pentacarbonic acid could reach 54.8%and 50.8%,respectively.This paper provides basic data and technical reference for the separation of BPCAs,inorganic salts and different BPCAs in the depolymerization products of lignite,which is of great significance for the utilization of depolymerization of lignite.