The Study On Heterogeneous Catalytic Oxidation At Low Temperature And Atmospheric Pressure In Wastewater Treatment

With the development of the modern industry, people have paid moreattention on the treatment of the industrial wastewater. To treat the industrialwastewater which is poisonous, harmful, nonbiodegradable and has highorganic content and complex composition, the biochemical method is hardto reach the demand of effluent.The advanced oxidation processes (AOPs) based on producing theradical utilize the radical to attack the giant molecule of hard degradedorganic and remove the contaminant and treating high concentrations ofhard degraded organic waste water.But AOPs often have difficulty topopularize and application in practice, due to the cost very expensive.Because some oxidant have more strong selectivity, then more and moreoxidant have been needed for get some better oxidation effects.Catalytic oxidation technology is the advanced and enforcedtechnology of AOPs. The catalysis of the catalyst can lower the temperatureand pressure of reaction, shorten the time of reaction and prevent the erosionon equipment, so the rate of oxidation reaction have increased and the costhave reduced. The disadvantages of the homogeneous catalyst are as follow:(1) the catalyst is dissoluble to the water, it can not be reused, (2) the cost ofthe reagent is higher, (3) other impurities are brought into the wastewaterduring the treatment process, etc. The separation of catalyst and wastewateris simpler in the heterogeneous catalytic oxidation. Beside this, theheterogeneous catalyst also has high activity and good stability. All of theseadvantages simplify the treatment process greatly. However, theheterogeneous catalytic oxidation technology still has some problems, forexample the high reaction temperature and pressure, the hardness of treatingthe large flux wastewater and expensive reagent etc.However the technology of heterogeneous catalytic oxidation at lowtemperature and atmospheric pressure can catalyzed the oxidant to degradedthe hard degraded organic pollutant at low temperature (T<100℃) andatmospheric pressure.Heterogeneous catalytic oxidation processes base on the Langmuirkinetics of the adsorption and desorption of single molecule layer, theHougen and Watson theory of the control and analysis of velocity, the theorywhich concluded by Carberry of Langmuir-Hinshelwood-Hougen-Watson(LHHW) and the modern surface science theory. The theory of reaction isthe pollutants and oxidant molecule permeate to around the activity centerand be absorbed by the activity center, then catalytic oxidation reactionbetween pollutant and oxidant occurs on/at the surface of the catalyst., atlast the products of reaction desorbed to solution.The reaction process can be conclude as followed,Adsorption: A(the oxidant molecule) + σ(the active center) Aσ B(the pollutant molecule) + σ(the active center) Bσ Catalysis: Aσ+ BσPσ(the products on surface)+ σDesorption:PσP(the products in liquid) + σThe velocity of reaction be controlled by the slowest reaction of theabove.This trial make the active component loaded on the multiaperturecatalyst carrier to prepare the heterogeneous catalyst and utilize the catalystto catalyzed the oxidant degrading the organic pollutants to CO2 and H2O atlow temperature and atmospheric pressure. There are some results havebeen found after the experiments as followed:(ⅰ) The adsorption performance of catalyst has been studied. It isfound that the CODcr removal ratio of C-catalyst is higher than 20% and theratio of others catalyst are between 15~17%. The NH3-N removal ratio ofF-catalyst is higher than the others catalyst , and the ratio of Cu/F and Co/Fare 47.57% and 35.08%. The ratio of C-catalyst and Al-catalyst are lowerthan 20%. The data are useful to study the catalytic performance of catalyst.(ⅱ)The cuprum loaded catalyst has a better remove ratio of CODcrand NH3-N than the cobalt loaded catalyst. The CODcr removal ratio ofCu/Al reach 88.7% and is 34.73% higher than Co/Al; the removal ratio ofCu/C reach 77.14% and is 10.59% higher than Co/C; the removal ratio ofCu/F and Co/F are 51.76% and 45.88%. The NH3-N removal ratio of Cu/Alreach 70.67% and is 14.57% higher than Co/Al; the removal ratio of Cu/Creach 63.59% and is 3.93% higher than Co/C; the removal ratio of Cu/F andCo/F are 50.65% and 49.96%.As the data has shown, we choice Cu/C 和Cu/Al2O3 as the catalyst of the catalytic oxidation at low temperature andatmospheric pressure.(ⅲ) The study found that when the concentration of impregnant is 8%,the catalyst prepared in this solution has excellent catalytic activity. Theremove ratio of CODcr and NH3-N reach 84.97% and 64.39%.(ⅳ) The optimal reaction conditions of Cu/Al2O3 catalytic oxidation atlow temperature and atmospheric pressure has been ascertained. Whentemperature is 75℃, the pH value is 3, the dosage of catalyst is 0.1kg/L, thedosage of oxidant is 80ml/L and the reaction time is 0.5 hour, the removal ofcatalytic oxidation is optimum. The remove ratio of CODcr and NH3-N are92.4% and 67.82%.(ⅴ) The optimal reaction conditions of Cu/ Al2O3catalytic oxidationat low temperature and atmospheric pressure has been ascertained also.When temperature is 80℃, the pH value is 4, the dosage of catalyst is120g/L, the dosage of oxidant is 100ml/L, the removal of catalytic oxidationis optimum. The remove ratio of CODcr is 92.24%.The reaction temperature is the most important factor of the removal.The dosage of oxidant is secondary. The dosage of catalyst and the pH valuehave litter impact on the removal. In dynamic experiment, it is found thatthe catalyst's catalytic performance decreased fast. So Cu/C catalyst hasbeen eliminate through selection.(ⅵ) The catalyst activity in dynamic reaction has also been studied byusing Cu-Al2O3 catalyst as filling of the catalytic oxidation reactor. Whenthe reaction time added, he remove ratio of CODcr and NH3-N increased.The CODcr of wastewater decreased from 4540 mg/L to1206.49mg/L, thento 409.17mg/L, and the NH3-N of wastewater decreased from 552.28 mg/L...