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Basic Studies on the Absorption of Toluene Exhaust Gas under the Condition of High Gravity

Author: ZhangZiDu
Tutor: LiuYouZhi
School: University of North
Course: Chemical Engineering
Keywords: rotating packed bed surfactant compound toluene exhaust gas Henry’sconstant
CLC: X701
Type: Master's thesis
Year: 2014
Downloads: 3
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Abstract

Toluene is a typical volatile organic compounds(VOCs)， the environmental pollutioncaused by emission of toluene attracts great concern. Currently combustion and adsorption arecommon technologies used for the treatment of toluene. But for some special occasions (lowconcentration, high flow, particles contained in the exhaust gas, unfixed times of emission,and factory don’t have enough space for equipment), combustion and adsorption are noteconomical and efficient approach for treatment of toluene. In these occasions, absorption isthe suitable approach for treatment of toluene exhaust gas, but limits primarily by absorbentand absorption equipment. The micelles’ solubilization is an important function of surfactantwhen its concentration exceed the critical micelle concentrations. Solubilization can increasethe apparent solubility of toluene in absorbent. Therefore, surfactant solution is used to absorbtoluene, while rotating packed bed is used as absorption equipment which it has many meritsof high mass transfer efficiency、small equipment volume、non-blocking in packing and easyfor start-up and shut-down.According to the analysis of the solubilization methods and influence factors, Tweenseries surfactants were selected as the main surfactant. By studying the absorption property ofdifferent compound surfactants solutions what absorb toluene exhaust gas, it can obtainoptimum formulation of compound absorbent. Results show that, it is feasible to use thesurfactant solution for absorption of toluene exhaust gas; Tween-20was superior to otherTween surfactants, and absorption rate was improved with the increase of the mass fraction ofsurfactant; Absorption effect of toluene by mixed surfactant solution is better than by thesingle surfactant solution. In Span series surfactants, Span-20was the best one which is mixedwith Tween-20, and the absorption efficiency of toluene increased with the increase of concentration of the Span-20, but when the concentration of the Span-20increased to a certainlevel, the absorption no longer increased. The highest increment of absorption rate is about15%mixed with Span-20; The absorption efficiency of toluene increased with theconcentration of the TBP, but when the concentration of TBP increased to a certain level, theabsorption no longer increased and some may decrease. When the mass fraction of TBP is0.578%, the highest increment of absorption rate is about25%; Surface tension haveundergone obvious change after compound, and the decrease of surface tension would be infavor of absorption of toluene.Vapor-liquid equilibrium between toluene and absorbent and the effect of temperature onHenry’s constant were analyzed by headspace analysis. Results show that, the compound ofsurfactant have obvious effect to Henry’s constant of toluene; Henry’s constant of toluene incompound surfactant solution decreased obviously than in single surfactant solution; Theeffect of temperature on Henry’s constant of toluene in compound surfactant solution wassignificantly less than single surfactant solution.The effects of process operating parameters, such as high-gravity factor、liquid-gas ratioand gas flow in rotating packed bed were discussed and the optimal operating parameterswere determined. Results show that, it is feasible to use rotating packed bed for absorption oftoluene exhaust gas. The absorption efficiency of toluene firstly increase and then decreasewith the increase of high-gravity factor and gas flow, and firstly increase and then keepconstant with the increase of liquid-gas ratio. The wetness degree has important influence onabsorption operation. The optimal operating parameters was that: high-gravity factor was33.42, the liquid-gas ratio was5~6.67L/m3, gas flow was6m3/h, when the inletconcentration of toluene was500ppm, the absorption rate can reach74.2%or so.The results show that the absorption of toluene exhaust gas by the surfactant solutionwas feasible. Surfactant solution can overcome disadvantages of traditional absorbent, such asthe high cost, large solvent volatilization loss and secondary pollution, because the water wasthe highest content component of the absorbent. Rotating packed bed used as absorptiondevice can overcome disadvantages of conventional columns, such as the large equipment volume and inconveniency for start-up and shut-down. The technology of absorption oftoluene exhaust gas under the condition of high gravity has very broad application prospectsfor some special occasions (low concentration, high flow, particles contained in the exhaustgas, unfixed times of emission, and factory don’t have enough space for equipment).

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