Novel chromatographic process for the recovery and purification of hydroxy acids from alkaline spent pulping liquors

Abstract

In this study, an efficient sequential chromatographic process for recovering hydroxy acids (HAs) from soda and kraft black liquors (BLs) has been developed. Lignin and pulping chemicals are also recovered and can be recycled back to the pulping process. A weak cation exchange resin in Na + form separates lignin from BL. Up to 95% lignin yield was obtained, with over 50% yield for HAs as Na salts. A cellulose-based resin is used to separate HAs from NaOH. Complete separation, and thus 100% yield for HAs and NaOH, was achieved. The HAs in soda BL are liberated by ion exchange. In case of kraft BL, the solution is acidified with H 2 SO 4 and subjected to ion exchange and ion exclusion chromatography to recover the remaining pulping chemicals. It was found that fouling, which limits the efficiency of membrane-based processing of BLs, is avoided with the appropriate choice of chromatographic separation materials.

Green is the new black – a review of technologies for carboxylic acid recovery from black liquor

“…Nevertheless, the viability of sizeexclusion gels exposed to the harsh conditions in a long-term use has not been established. 97,98 J. Heinonen et al 43 proposed a consecutive chromatographic separation process to recover hydroxy acids but at the same time allowing spent chemicals and lignin to be recycled. Kraft and soda spent cooking liquors were used as feed.…”

“…Even though the final purification was more complicated, the recovery of the acid fraction was accomplished for both case scenarios, not single acid isolation was achieved. 43 J. Heinonen and T. Sainio 42 carried out a four-step sequential chromatographic separation process. In this case, the fractionation of the hydroxy acids mixture led to the complete isolation of some of the main acids in high purity.…”

A process combination of ion exchange and electrodialysis for the recovery and purification of hydroxy acids from secondary sources

“…Recently, chromatography-based methods for the production of pure mixtures of HAs with simultaneous recycling of lignin and spent pulping chemicals [19] and pure individual HAs [20] have been presented. HAs are present in BLs as sodium (Na + ) salts, and although HA mixtures can be produced with the HAs in salt form [19], the production of pure individual HAs requires the HAs to be free acids (in H + form) [20]. Thus, the HAs should be liberated.…”

“…With soda BL, HA liberation by ion exchange can be carried out after the separation of lignin and NaOH [19,21]. However, this is not possible with kraft BL because of the presence of sodium 4 thiosulfate (Na2S2O3), which decomposes to elemental sulfur and sulfur dioxide under acidic conditions [19]. Sulfur, especially, is problematic as it would precipitate into the resin pores and, thus, render it as waste.…”

“…Sulfur, especially, is problematic as it would precipitate into the resin pores and, thus, render it as waste. In [19], the removal of S2O3 2was achieved by acidification, but, as mentioned, this process is characterized by high chemical consumption as the chemicals cannot be recycled. Thus, alternatives should be found.…”