The Study Of Lignosulfonate Property In Reed Pulping Red Liquor

The Mg-sulfite red liquid will generate precipitate in alkali and produce glue-like substances,most of which are lignosulfonate after the centrifuge separation.Maximum precipitation will be produced if the red liquid pH value changed to 13 with NaOH,pH value to 12 with KOH and pH value to 13 with NaOH,with 20mL Ca(NO3)2 added to each group.Not only the reaction temperature,but also the amount of precipitation reagent(Ca(NO3)2)could affect the generation of precipitation.With the optimum pH value,every group will get the maximum precipitation when the temperature reaches 40?;the precipitation will increase as the amount of Ca(NO3)2 increases;and the ash content increases as the precipitation increases.However,the CODcr value of liquid decrease to about 35 times as the pH value increase after centrifuge separation and the turbidity changes obviously.Comparing the UV spectrum of liquid and precipitate,it can be found that there exist lignin absorption and the absorption peak varies as the pH value changes;the adding of Ca(NO3)2 and alkali could not have the lignosulfonate precipitate completely,but always keeps some lignosulfonate at the top level of the liquid.Through the analysis of sample IR spectra,it is proved that the chemical structure of lignin changes greatly under different sedimentation conditions:abrupt absorption appears at 3700cm-1 which indicates the presence of free hydroxyl groups;the absorption peak at 1120cm-1 is generated by C-O-C bond;a new absorption appears at aliphatic C=C 835cm-1 because of aliphatic C=C;absorption at 810cm-1 and 440cm-1 caused by benzene substitution;the absorption at 550cm-1 is likely to be granted to the deformation vibration of N-H,C-H and O-H.After adding 20mL Ca(NO3)2 and pH value reaches up to 13 by NaOH,the precipitation will show a new absorption in 2430cm-1,which is resulted from triple bond or accumulating double bond.Comparing the different reactions of lignosulfonate,we can found that the change of the fingerprint region by adding Ca(NO3)2 to the liquid is much less than that of purely adding alkali to deposit.The measurement method of acid soluble lignin can be used directly in the determination of lignin sulfonate content.If there is no precipitation and no calcium added,the lignin content in precipitation changes not much;while as the increase of the precipitation amount,the lignin content will relatively reduce and the lignin content increase;adding Ca(NO3)2 and NaOH,the lignosulfonate content will decrease to some extent at the very beginning,but with the increase of precipitation content,the final content of the lignin sulfonate will be much more than the other series:the final pH=13,the lignin content is 25.21%,which are 3.7%and 5.25%respectively higher than that of NaOH and KOH titration.In the determination of the functional groups,Ca(NO3)2 series is the one with maximum sulfonic acid and titration series with the minimum;the NaOH titration series with maximum phenol-hydroxy and Ca(NO3)2 series with the minimum owing to the added calcium which protects the alcohol-hydroxyl group of the lignin sulfonate.Ca(NO3)2 in methoxyl is conducive to the formation of methoxy and its content is more than the original red liquid.The added Ca(NO3)2 protects the functional groups of lignin sulfonate,avoiding the hydrolysis of sulfonic acid groups and alcohol-hydroxyl group and generating methoxy.