Purification And Property Of Lignin With Biological Technology In Corn Stalk Black Liquor

Lignin is a kind of the renewable resource. It has aromatic characteristic, side chain-aliphatic series characteristic and functional groups. These characteristics make it an important material that may replace oil resource. It is difficult to deal with the corn stalk cooking black liquor, at the same time both the lignin and the carbohydrate in the black liquor are available resources. The acidulation precipitation was used to separate and purify the lignin in the black liquor formerly, and a series of chemical treatments should be followed, and many kinds of chemicals should be used. The complexity and heavy pollution of acidulation precipitation made it hard to put into production and application. In this subject, the material is the black liquor of corn stalk, and for the purpose of improve the lignin purity, the biological method is used to degrade the carbohydrate into a kind of energy substance——ethyl alcohol. It not only can reduce the secondary pollution produced by the process of comprehensive utilization of lignin, but also make a better use of the separation and utilization of the lignin.Before the lignin purification with biological method, the methods to detect the lignin and the reducing sugar in black liquor, and some characters of the black liquor have been studied. Firstly, the method has been studied to detect the lignin content in the black liquor. It is found that the alkali lignin can be dissolved into the3,5-dinitrosalicylic acid solution(DNS), and the color of the solution gets dark with the more lignin dissolved. And there is a high linearity relationship between the absorbance and the lignin content. So lignin content in black liquor can be measured with DNS by UV-Spectrophotometry method, and it conquered the problem that it is difficult to measure the lignin content in the black liquor. Secondly, the measurement of Reducing Sugar in Black Liquor has been studied by Dual Wavelength Spectrophotometry. And the method can overcome the serious interference of lignin in the black liquor. Finally, after analyzing the phenomenons in the process of acidulation precipitation of alkali black liquor, it is found that, when the temperature is lower, the acidulation precipitation lignin in black liquor contains a part of combined water. And the percent of the combined water decreased with the rise of temperature. When using the bariums chloride to flocculate the lignin in the black liquor of different sodium sulfite dosages it is found that the content of organic material in the precipitate gradually decreased with the increasing of sodium sulfite dose. It is actually similar to the precipitate effect of hydrochloric acid.In this paper, the treatment to the black liquor with biological method has been selective analyzed. After comparing the biological degradation effects of different enzymes to the carbohydrate in two kinds of black liquor, it is found that the degradation trends generally resemble with each other. But different enzymes have different degradation effects, they are ranged:complex enzyme>cellulase>|3-glucanase>xylanase=diastase. After measuring the content of total sugar and the production of ethanol during the fermentation progress, it is proved that the trend of the production of ethanol is generally similar to the trends of decrease of the total sugar over time. And the alkali black liquor and the alkaline sodium sulfite black liquor share the same trend. The degradation ratio of total sugars in the fermented alkali black liquor is45%, with a production52.2mL ethanol per liter black liquor, while the alkaline sodium is50%and48.2mL. The proportion of lignin in organic material of fermented alkali black liquor can come to79.52%, while the alkaline sodium sulfite black liquor is79.56%.Comparing changes of the characters of the fermented black liquor of different samples, it turns out that the relative viscosity of black liquor after biological treatment reduced34.8%, the lignin content, the turbidity and the COD of centrifugal solution reduced72.1%,70.6%and73.1%respectively. And the index above of alkaline sodium sulfite black liquor reduced32.4%,32.4%,27.2%,40.1%respectively. But the value of the lignin content, the turbidity and the COD of centrifugal solution is much higher than the alkaline sodium sulfite black liquor.After the analysis of the infrared spectrum and1H-NMR,13C-NMR spectroscopy, it turns out that the lignin structure has changed. Some enzymes and bacterium with selectivity to carbohydrate have an effect to the lignin in the black liquor, and make its structure changed. After biological treatment, the non-conjugated C=O, C=C in the lignin structure changed, and the Ph-OH, Alc-OH reduced, and the ether bond increased. It is because during the biological treatment progress, some active groups may emerge, and these active groups may attack the non-conjugated C=O, C=C in the lignin structure with high reactivity, and form new connecting format. At the same time the active groups may stimulate the reactivity of the hydroxy in the lignin. And these hydroxy may react with the non-conjugated C=O, C=C with high reactivity, and form new steady ether bonds.