Absorption Of Sulfur Dioxide By Composite Absorbent Based Sodium Humate

For the purpose of conducting desulfurization, the wet limestone-gypsum methodand circulating fluidized bed half-dry method are widely used domestically andinternationally. Though mature in practicing, they are not ideal for energy saving andcircular economy, and has become less adequate as the scale of flue gasdesulfurization equipment is enlarging and the by-product is not cyclic utilization.So the technology, which the by-product can be recycled, is becoming a hot spot incurrent research and the main direction on flue gas desulfurization. The method thatuses sodium humate in flue gas desulfurization technology is expected to become avaluable desulfurization technology in our country in the future as it is free fromcreating secondary pollution. Sodium humate desulfurization technology, after yearsof domestic and foreign research and development, will be further developed. Thefeasibility of this technology, the construction and operation in economy, and thedesulfurization by-products utilization, need to be further studied. The study on thesodium humate compound absorbent has a considerable theoretical and practicalsignificance for sodium humate desulfurization technology. In this paper, accordingto the goal of resource recovery the research in sodium humate composite absorbentto absorb sulfur dioxidehas been done. With the result of the experiment, themechanism of sodium humate compound absorbent to absorb sulfur dioxide whichprovides the theoretical foundation for its industrial application in the future isstudied. The main contents and results are summarized as follows:1. Sodium humate and ammonia loaded on α-alumina used to absorb sulfurdioxide when the simulated flue gas has nitrogen dioxide. Under this condition, thechemical reaction mechanism and absorption process have been analyzed. It is foundthat the presence of nitrogen dioxide in experimental conditions is conducive forabsorbing sulfur dioxide and the sulfur dioxide absorption efficiency can reachabove98%while the nitrogen dioxide absorption efficiency is about80%. The mainproducts are ammonium sulfate, ammonium sulfate and ammonium nitrate, etc.Through analyzing, the kinetics experimental results show that the desulfurizing process, with sodium humate and ammonia loaded on α-alumina used to absorbsulfur dioxide, is divided into two reaction sections, namely the fast reaction sectionand the slow reaction.The order of reaction on sulfur dioxide is0.291in fast reactionextents, and the order of reaction on nitrogen dioxide is0.464. Meanwhile, in theslow reaction section, either sulfur dioxide or nitrogen dioxide, the order of reactionis0.2. The sludge sodium humate absorbent had been prepared from sludge. Theexperimental research has been conducted about the absorbing process of sulfurdioxide in bubbling reactor used the sludge sodium humate absorbent. It is foundthat sodium humate sludge absorbent has better absorption effect for sulphur dioxidethan water, sodium hydroxide. Under the condition of experiment research, theconcentration of sulfur dioxide changes in the absorption process can be divided intothree sections: a rapid decline section, an approximate horizontal section, and a slowrise section. Meanwhile the pH value of sludge sodium humate absorbent in thisprocess changes from the original10.8to a constant about3.4. It is concluded thatdifferent inlet sulfur dioxide concentration and temperature on sludge sodiumhumate absorbent to absorb sulfur dioxide have little effect on the absorptionefficiency and have a significant effect on the absorption duration. The higher theinlet concentration is, the shorter the duration is. With the presence of oxygen theabsorption efficiency of sludge sodium humate absorbent on sulfur dioxide is higherbut the duration is shorter than without the presence of oxygen. Through analyze theproduct, it can be concluded that the main ingredient in product is humic acid,protein, carbohydrate, fat and other small molecule organic acids, etc.3. Phase-transfer catalysis (PTC) is a synthetic organic method and manufacturingprocess technology that is applied successfully in a wide range of organic reactions.A sulfuric acid/humic acid (HA) system with quaternary ammonium salts asphase-transfer catalysts were employed in the sulfonation of humic acid. Fourquaternary ammonium salts catalytic systems with ultrasound were carried out,tetrabutyl ammonium bromide behaved as the optimum active catalyst, and thesulfonation degree was above0.407mg-S/g-HA. In order to attain a highersulfonation degree of humic acid, orthogonal experiments of dilute sulfuric acidsulfonated humic acid system with tetrabutyl ammonium bromide as phase-transfercatalysts were carried out in the flask to investigate the effect of main factors, namely, temperature, ultrasound power, ultrasound time and catalyst dose onsulfonation degree. The results of orthogonal experiments showed that the optimalcondition for humic acid sulfonation should be A4B4C1D1, namely, temperature,ultrasound power density, ultrasound time and catalyst dose were85°C,12W ml-1,30min and0.02g, respectively. The verification experiments were carried out inflasks at the corresponding parameters. The results of verification experiments in theshaking flasks showed that sulfonation degree was0.517mg-S/g-HA. Theconclusion in the research would be beneficial for application of dilute sulfuric acidsulfonated humic acid.4. The study on the sodium humate/[CPL][TBAB] composite absorbent in thesulfur dioxide absorption process has been conducted. It is found that sulfur dioxidefrom the mixed gas first dissolve in the absorbent occurring dissolving balance andion balance in the process used sodium humate/[CPL][TBAB] composite absorbent.HSO3-, SO32-and H+generated in this process. And then H+react with carboxyl andhydroxyl groups to generate the undissolved humic acid, sodium bisulfite asnucleophilic reagent react with fragments of humic acid on the benzene ring asMichael addition reaction, which makes part of humic acid into sulfonated humicacid. The whole process of absorption curve can be divided into three stages,including the first and second stage is controlled by the gas side mass transferresistance of chemical absorption process, while in the third stage is common controlprocess for gas-liquid mass transfer. The system has not fully absorbed sulfurdioxide at the third stage.5. By means of the research of sodium humate/[CPL][TBAB] compoundabsorbent for circulation absorption of sulfur dioxide, respectively investigates thecycles of composite absorbent to absorb sulfur dioxide efficiency, absorption and thepH of composite absorbent absorption before and after the absorption. It isconcluded that the fresh composite absorbent should be supply timely to replace theused absorbent in order to maintain higher absorption efficiency. With the increase ofcycling times the amount of compound absorbent to absorb sulfur dioxide ingradually reduce, when it is used with the composite absorber cycle, lower initial pHvalue of consistent. Then on this basis, the product of this process have been testedrespectively by the FTIR, XRD, XPS and ion chromatographic analysis, etc..Products are mainly consists of sodium sulfate and sulfonated humic acid and sulfur element in sulfonated humic acid mainly exists in the form of sulfonic acid R-SO3Hin absorption products, oxygen element in the form of sulfonic acid R-SO3H andO–C O, carbon element in the form of C-C, C=O and O–C O.