Production of Water-Soluble Hardwood Kraft Lignin via Sulfomethylation Using Formaldehyde and Sodium Sulfite

Abstract

Kraft lignin can be extracted from black liquor (i.e., spent liquor) of a kraft pulping process to produce value-added chemicals, but its limited water solubility hampers its end-use applications. The main objective of this study was to investigate the sulfomethylation of kraft lignin to produce water-soluble kraft lignin with an anionic charge density. In this work, hardwood kraft lignin was modified with formaldehyde and sodium sulfite under alkali conditions. The optimum conditions for sulfomethylation were 0.5 M NaOH(aq), 0.9 mol/mol sodium hydroxymethyl sulfonate/lignin at 100 °C for 3 h, and 20 g/L lignin concentration. The resulting lignin had a charge density of −1.60 mequiv/g and sulfonate group content of 1.48 mmol/g. The molecular weight, structure, thermal behavior, and elemental analyses of the product were also assessed. The modified lignin was used as a cement dispersant, and the dispersibility of cement was increased from 60 to 155 mm by adding 1.2 wt % of sulfomethylated lignin to cement. Unmodified lignin did not change the dispersibility of cement.

Synthesis and Characterization of Carboxyethylated Lignosulfonate

“…[103] Although an alkaline environment was necessary for the carboxyethylation reaction, it promoted the hydrolysis of LS. The experimentala nd modeling analyses confirmed that CELS with am aximum charged ensity of À3.56 meq g À1 , molecular weight of 46 493 gmol À1 ,a nd ad egree of substitution of 0.78 could be generated under the optimum conditions of 30 wt %N aOH, 2.0 mol mol À1 2-chloropropinic acid/lignosulfonates,9 0 8C, 0.5 h, and 0.03 mol of 2-chloropropinic acid.…”

“…[25,103] Hence,atotal of 16 runs was conducted based on Ta guchi orthogonal design (L 16 )t od etermine the optimum conditions to produce CELS with the maximumc harge density and molecular weight.T he selected reactionc onditions and polymerp roperties are given in Ta ble 3. [25,103] Hence,atotal of 16 runs was conducted based on Ta guchi orthogonal design (L 16 )t od etermine the optimum conditions to produce CELS with the maximumc harge density and molecular weight.T he selected reactionc onditions and polymerp roperties are given in Ta ble 3.…”

Production and Application of Lignosulfonates and Sulfonated Lignin

“…In this process, kraft lignin was reacted at 0.80:1 (w/w) sodium sulfite/lignin and 0.12:1 (w/w)f ormaldehyde/lignin for 2h at 140 8Ct op roduce sulfomethylated lignin. [28] Alternatively,s ulfomethylated kraft lignin was proposed to be produced at am olar ratio of 1:0.9 lignin/ sodium hydroxymethyl sulfonate at 100 8Cf or 3h without cross-linking. [71] The product mayb ep urified by filtration.…”

“…[71] Formaldehyde was subsequently added at a0 .6:1 molarr atio of formaldehyde/lignin and furtherr eacted for 5hat 100 8Ca nd pH 7. [28] The benefito fr eactingw ith sodium hydroxymethyl sulfonate is to avoid two reactions tages, and to develop as imple process for producings ulfonated lignin, but, in this case, the molecularw eight of the product is low relative to that of the two-step process. The anionic charge density increased from 0t oÀ1.6 meq g À1 ,t he molecular weighti ncreased from about 22 700 to 53 400 gmol À1 ,a nd the sulfonate group content increased from 0.03 to 1.48 mmolg À1 .…”

“…[13,14,[31][32][33][34] However,t he majority of pulp mills employ kraft technology forp ulp produc-Lignin is the largest reservoiro fa romatic compounds on earth and has great potentialt obe usedi nm anyi ndustrial applications. [28,32] The main objective of this review is to compare the production and modification of lignosulfonates from sulfite pulping processes and sulfonated kraft lignin from kraft pulping processes. Furthermore, options to increase the sulfonate contents of ligninbased products are outlined and the industrial attractiveness of them is evaluated.…”