Nitrogen Fixation And Treatment With Ultrafiltration And Modification On The Ammonia Sulfite Pulping Spent Liquor

Nitrogen fixation of the ammonia sulfite pulping spent liquor of wheat straw by using formaldehyde and the amount of ammonium lignosulfonate increased by nitrogen fixation were introduced.The results showed:formaldehyde could make the ammonium fixed in the spent liquor and the ammonium nitrogen transformed into organic nitrogen,so the spent liquor had better developmental prospect as slow release nitrogen fertilizer.The appropriate amount of formaldehyde was 10%,at this time,the residual ammonium sulfite was used up and free ammonia was basically fixed.When the reaction ended up,the pH of the spent liquor was 6.0-6.5. In order to understand the amount of ammonium lignosulfonate by the nitrogen fixation,the amount of ammonium sulfonate before and after nitrogen fixation was investigated.Experimental results indicated that the amount of ammonium sulfonate before and after nitrogen fixation was 1.474 mmol·g^-1and 1.918 mmol·g^-1,respectively.As a result,ammonium sulfonate incresed by 30.12%,in which ammonium lignosulfonate was 87.4%and Carboxymethyl ammonium sulfonate was 12.6%.Meanwhile,we found that the influence of temperature on nitrogen fixation was not obvious.The ammonia sulfite pulping spent liquor of wheat straw by ultrafiltration was introduced. In the ultrafiltration process,the effect of membrane with different cut-offs,temperature,pressure and volume concentration were researched.Experimental results indicated that the membrane with a cut-off of 10kDa was suitable for concentrating wheat straw spent liquor and had good anti-fouling property against the spent liquor.Under the operating pressure 200 kPa,temperature 25℃,following the increasing of the volume reduction,the permeability of ash was higher and the retentate was concentrated as the volume reducing during ultrafiltration of spent liquor. Ultrafiltration treatment of the ammonia sulfite pulping spent liquor of wheat straw and its influence on chemical structure characteristics and physical properties were studied.The results showed:after ultrafiltration,the molecular weight of lignin in retentate was higher than spent liquor;the content of sulfogroup,carboxyl,phenolic hydroxyl groups which are the main functional groups in retentate were all more than that in spent liquor.Meanwhile,after ultrafiltration,the retentate had better performance than spent liquor as surfactant,as additive in concrete and as dispersant,in which compared with spent liquor,surface tension at 1wt%was 54.7 mN/m,dropped 2.2 mN/m;Clean solution's fluidity improved from 70mm to 102mm.In the spent liquor,the lignin molecular weight had a very important influence to its application performance.The influence of several modified methods to the lignin molecular weight distribution and the performance were discussed.The results indicated that oxidation-degradation and oxidation-condensation took place at the same time in the process of the oxidation,The condensation reaction took place in the hydroxyl methylolation,and the higher active group contents had higher responding activeness.The oxidized reaction could enhance the surface activity of lignosulfonate as surfactant,higher molecular weight was the dominating factors influencing the increase of dispersing and strengthening performance of lignosulfonate as additive in concrete and as dispersant.In the lignosulfonate products after hydroxyl methylolation,clean solution's fluidity improved greatly.But when the major reaction was oxidation-condensation,oxidation reaction was advantageous as additive in concrete and as dispersant.In addition,higher molecular weight and higher sulfonic group content were the dominating factors influencing the increase of dispersing and strengthening performance of lignosulfonate,but under suitable sulfonic group content,the influence of improving the molecular weight to strengthen performance became much bigger.The chelating reaction and structure properties of ammonium lignosulfonate with Fe²⁺by oxidation were introduced.Experimental results indicated that the suitable chelating reaction condition of ammonium lignosulfonate and Fe²⁺was determined as follows:the pH was 3,the amount of hydrogen peroxide was 10%,the dosage of FeSO₄ was 40.93%,and the reaction was 50℃for 30 min.Under this reaction condition,the chelating rate of Fe²⁺was 15.08%,and the chelating compound of ammonium lignosulfonate with Fe²⁺was stable and no Fe(OH)₃ pricipitation in alkaline water solution.At the same time,The effects of the amount of hydrogen peroxide in the chelating reaction on structure properties of ammonium lignosulfonate were investigated.It was shown that the amount of phenolic Carboxyl group,hydroxyl group and carbonyl group in the chelating compound of oxidized ammonium lignosulfonate which could enhence the chelating performance of ammonium lignosulfonate was more than that of the no-oxidized ammonium lignosulfonate.As a result,the oxidized ammonium lignosulfonate had higher chelating efficiency than that of the no-oxidized ammonium lignosulfonate.In addition, the molecular weight of the oxidized ammonium lignosulfonate more than 4950 was higher than that of the no-oxidized ammonium lignosulfonate by Gel Chromatography.It was found that degradation and condensation took place at the same time in the process of the oxidation,but the major reaction was oxidation-condensation under the reaction condition.