Electrochemical oxidation of polyethylene glycol in electroplating solution using paraffin composite

Jounal of Enirormental Sciences Vol. 16, No.5,pp. 851- 855 ,2004ISN 100742Article ID: 101-0742(2004)05-0851-05CLC number: X131Document code: AElectrochemical oxidation of polyethylene glycol in electroplating solution usingparafin composite copper hexacyanoferrate modified ( PCCHM) anodeRajesh S. Bejankiwar ”，Abir Basu, Max Cementi(Department of Civil and Environmental Engineering, University of Windsor, Windsor, Ontario N9B 3P4, Canada. E mail: bejanki @ uwindsor . ca)Abstract: Electrochemical oxidation of polyethylene glycol(PEG) in an acidic(pH 0.18 to 0.42) and high ionicstrength electroplating solution was investigated. The electroplating solution is a major source of wastewater in theprinting wiring board industry. A paraffin composite copper hexacyanoferrate modified( PCCHM) electrode was usedas the anode and a bare graphite electrode was used as the cathode . The changes in PEG and total organic carbon(TOC) concentrations during the course of the reaction were monitored. The efciency of the PCCHM anode wascompared with bare graphite anode and it was found that the former showed significant electrocatalytic property ftorPEG and TOC removal . Chlorides present in the solution were found to contribute significantly in the overall organicremoval process. Short chain organic compounds like acetic acid， oxalic acid, formic acid and ethylene glycolformed during electrolysis were identified by HPLC method. Anode surface area and applied current density werefound to infuence the electro- oxidation process, in which the former was found to be dominating. Investigations ofthe kinetics for the present electrochemical reaction suggested that the two stage first-order kinetic model provides amuch better representation of the overall mechanism of the process if compared to the generalized kinetic model .Keywords: polyethylene glycol( PEG ); paraffin composite copper hexacyanoferrate modified( PCCHM) electrode;electroplating solution; two stage first order kinetic model; generalized kinetic modelozone/UV radiation has been reported ( Chang, 2001 )，butIntroductionthis method appears to be uneconomical in both installationA highly acidic electroplating solution (pH 0.18 tond operation. Also， other advanced oxidation processes0.42) with high ionic strength is a major wastewater source in(AOP's) like Fenton's reagent, H202/03 and H2O2/UVthe printing wiring board ( PWB) industry. The chemicaloxidation, photocatalytic oxidation， gamma iradiation andcomposition of the recipe solution ( sulfuric acid of 60 g/L，ultrasound technique though scienifically feasible are noCuSO, .5H20 of 200 g/L and 0.03 g/L of chlorides) makes iteconomicaly suitable for wastewater treatment ( Gulyas ,difficult to treat with conventional treatment processes1997). The limiting factors for using conventional treatment(Suzuki，1976; Andreozi， 1996a). Also， the chemicalmethods, namely, high acidity and ionic strength can becoagulation method, presently adopted by the industries is notadvantageous for the electrochemical oxidation method. Ina viable method due to a large amount of hazardous chemicalsuch situations electrochemical oxidation technique appears tosludge ( containing very high concentration of Cu2* ions )be an ideal method for decomposition of PEG in electroplatingproduced during the treatment. Recycling or reuse of thesolution. A high salinity wastewater with 5% w/w chloridessolution is inhibited because of the low quality of organicswas treated electrochemically to remove organie pollutantspresent after electroplating and electrophoresis . Therefore,( Sheng，1998). Also， high strength wastewaters fromremoval of spent organics in order to add new additives is onedifferent industries were treated successfully at lab scale byof the very important steps for the neutralization processresearchers( Vlyssides，1997;Canozares，2002; .(Chang, 2001).Bejankiwar, 2003; Bunce, 2003 )Polyethylene glycols ( PEG: H-( 0CH2CH2).-0H) areIn this study, we have carried out the electrochemicalmajor organic compounds used as brightening and stabilizingoxidation of PEG in a simulated solution( similar to the recipeagent during eletroplating process(Fang，1996). It is anof electroplating solution of PWB industry ) using parafnimportant group of non-ionic synthetic water-soluble polymerscomposite copper hexacyanoferrate modified ( PCCHM )of ethylene oxide. Several studies have been performed on theelectrode. PCCHM anode has been used extensively in electrobiodegradability of PEC' s in water since biological oxidationchromic devices, power sources, ion-selective electrodes anis generally considered the most environmentally friendly andelectro catalysis . Composite electrodes comprising of graphitecheapest method of wastewater treatment ( Haines，1975;powder中国煤化工hexaerocyanoferatesWatson, 1976， Dwyer， 1983). However, as mentionedhave alsletermination of alkaliFYHCNMH Gearlier，biological treatment cannot work in such highly acidicmetalionsand for pHand high ionic strength solutions .measurements. Narayanan and Deepa ( Narayanan，2001 )Decomposition of PEC in electroplating solution byhave explained in detail the widespread use of PCCHM* Corresponding author852Rajesh s. Bejankiwar et al .Vol. 16electrode. So far, there is no report on the use of this anodefor electro-catalytic oxidation of organics presented in theDC powersupplywastewater. The main reason for selecting PCCHM anode for田日the present study is because of the fact that this electrode isrelatively insoluble on redox cycling as charge neutrality isalways maintained via the diffusion of electrolyte ions throughthe zeolytic structure( Scoltz, 1996) .InletThe main objective of the present study is to evaluatethe eficiency of paraffin composite copper hexacyanoferratemodified electrode for oxidation of PEG and to study thekinetics of the process . Measuring PEG concentration andtotal organic carbon(TOC) concentration during the course ofElectrodereaction enabled the monitoring of the process efficiency. Theexperimental TOC concentration data was correlated to the twoElectro-chemical reactordifferent kinetic models to establish the kinetics of theprocess. Kinetie rate constants were evaluated by non-linearFig. 1 Schematic diagram of electron- chermaicalregression method using Polymath software and energyreactor set-upconsumption was evaluated in terms of kWh energy consumedH, P04): acetonitrile as an isocratic mobile phase at 1 ml/per kg of TOC removed.min and their detection was through a diode array detector atMaterials and methods200 nm. Injecting standards of the suspected compounds and1.1 Electrode preparationcomparing their chromatograms to those of the unknownGraphite powder (LOBA Chemicals Ltd., India) wascompounds with respect to peak retention times and spectralmixedwith a precipitate of copper hexaferrocyanate ( Merck,characteristics, the unknown compound is identified. 0ICGermany) in the ratio of 12:1(Narayanan, 2001) and was700 TOC analyzer (0.1. Cor.， Tex.) was used forthen added uniformly to melted paraffin to fom a paste-likedetermination of TOC concentration. The instrument uses theconsistency. This paste was then packed into a plasticUV-persulfate technique to convert the organic carbon for themould, which was removed after few minutes to get paraffinsubsequent analysis by an infrared carbon dioxide analyzercomposite electrode of the required size . Similar procedurecalibrated with potassium hydrogen phthalate standards. Allwas followed, except for the addition of hexaferrocyanate tohe samples were analyzed in triplicates to get reproducibleget bare graphite electrode.results of replication was found to be below 5% in all.2 Electrochemical reactoranalyses.Schematic of a single cell electrochemical reactor used2 Results and discussionin the study is shown in Fig. 1. The reactor was a 500 mlcapacity Plexiglas container with a sampling port at theCurrent density below 0.4 A/cm was found to be toobottom of reactor. A Testronix 35D Model Dual DC powerlow to give detectable results. Therefore， preliminaryunit( Muropye, India) equipped with digital curent- voltageelectrolysis experiments were conducted at a higher currentmeter was used as power supply source. A copper wire wasdensity of 0.5 A/em' ( anode surface area of 8 cm2 )，toused for all electrical circuits. All the experiments wereoptimize the electrolysis time, using both bare graphite anodeconducted at room temperature with the exception of those forand PCCHM anode. The variations of PEG and TOCthe kinetic study， which were conducted at 25C，35C,concentration during the course of electrochemical oxidation45C and 55C.process for both the anodes are depicted in Fig.2. It is1.3 Analysisevident from the figure that, with PCCHM anode around 78%Samples were ollcted at different time intervals andof PEC and 79% of TOC removals were achieved after 45analyzed for PEG and TOC concentration. PEG concentrationmin of electrolysis, while only 35% of PEG and 24% ofwas determined by conventional HPLC ( Beckman, USA )TOC removals were observed with that of bare graphitemethod( Aquagel-OH 40，300 x 7.5 column) using pureanode. This can be attributed to the electro- catalyticwater as mobile phase at 1 m/min. Detection was done byoxidation of PEG in solution by hexacyanoferrate. It is worth中国煤化工G and TOC at dfferentusing a Shimatzu refractive index detector at high sensitivityto norange of 2x 10~ 6 refractive index ( Mantzavinos, 1997). Atime|YHCNMHG.was equivalent. Thiscalibration curve was plotted using standard PEG samples.suggestea tnat rLus are converted into highly unstableThe intermediates ( short chain organic compounds ) formedintermediates，which further rapidly get oxidized to CO2 andduring the electrolysis were separated on a Hamilton PRP X-H20. This was supported by the presence of short chain300，7 m. 250x4.1 column using 95 :5 water( buffered withorganic compounds such as acetic acid, oxalic acid, formicNo.5Electrochemical oxidation of polyethylene glycol in electroplating solution using paraffin composite ....853acid and ethylene glycol formed during electrolysis aThe anode surface area and the applied current densityidentified by HPLC method .are very important factors in any electrochemical oxidationprocesses ; their significant effects on process eficiency have35十TOC (PCCHM anode)been reported by many researchers ( Bivyk，1980; Matis ,- PEG (PCCHM anode)301980; Cenkin, 1985; Lin, 1994; Awad， 1997; Gennaro,。PEG (Bare Rraphite anod1997). Therefore, experiments were conducted to examinehe efct of applied current density and surface area ong 2(removal of PEG and TOC. Table 1 gives the summery ol层1:esults obtained and the conditions maintained duringdiferent runs. It is evident from the table that there was a8 10significant enhancement in the rate removal of PEG withincreasing current density. The trend is expected based onthe greater ability of anodic electro- catalytic surface sites to”010203040506070mineralize, or at least partially oxidize substrate organic toElectrolysis time, minCO2. This can be also attributed to the fact that the increaseFig.2 Vriation of PEG and TOC during the letrolysis ofin current density increases the ionic transport that in turmselectroplating solutionincreases the rateof electrode reactions. This trend isparticularly evident on comparing the oxidation profiles atSince the electroplating solution was rich in chloridecurrent density of0.5 A/em', 1.0 A/cm', and 2.0 A/em2 .concentration, the indirect oxidation route in which chlorideBy increasing current density from 0.5 A/cm2 to 2.0 A/cm2 ,ions take part in oxidation cannot be denied。Therefore,the electrolysis time required was found to reduce from 45electrolysis experiments were conducted in a simulatedmin to 15 min and TOC removal was found to inerease fromelectroplating solution of similar composition without any79% to 91%。The energy consumption for 1 kg of TOCchloride ions. Fig.3 shows the variations of PEG and TOCremoval was found to increase from 7.476 x 10-3 kWh toconcentration during the course of electrolysis in9.655 x 10 3 kWh. However, the removal efciency waselectroplating solution without chlorides. It was observed thatfound to be influenced by more surface area of anode ratheraround 59% of PEG and 44% of TOC removals could bethan the current density. This can be seen by comparing theachieved in chloride- less electroplating solution after 45 minPEG removals al anode surface areas of 8 cm2 and 34 cm2 .of electrolysis. This suggested that indirect oxidation byThe reason is that the graphite surface area rather than thechloride ions contribute to around 24% in PEG removal andapplied current， limits oxidation reactions. Inerease insurface area also increases thmass transpot， which44% in TOC removals in the overall electrochemicaloxidation removal process. It is also noted that duringfacilitates the oxidation process. Increase in surface area fromelectrolysis in chloride-less solution the TOC removal8 em2 to 34 em2 was found to increase TOC removal fromobtained was lesser than that of PEG removal . This overrules79% to 93%，and also decreases the electrolysis time from45 min to 10 min. In this context, it is important to mentionthe possibilityt of direct oxidation of PEG into CO2 and H20;that the increase in energy consumption is less in case ofrather it suggested the simultaneous double route oxidation,increase in surface area rather than the increase in currentwhich can be represented as follows:density .Via leeoidation,nVia elecr oxidation,PEGand CT mediationIntermediatesand C1- mdiation→CO23 Kinetic studies+ H2O.Referring to Fig.2, it is evident that at the initial stageTable 1 Results of electrochemical oxidation of PEG during different experimental runsAnode surfaceElectrolysisPEG, mg/LRemoval,T0C, og/LRemoval ,Energsy consumption,Runsdensity ,area, em2InitialFinal%kWh/kg TOC,x 10~A/cm2equired ,min8.0.5456.5878.0616.33.2879.267.4768.80.7578.337.4191.0203(6.50.79.886.5291.256.4678.47中国煤化工8.1348.01.509.4062.06.5278.27YHCNMHG9.65514.0.304.9883.402.5484.4212.4422.00.75 .5.552.9681.849.9553.8687.131.9288.22 .11.7734.02.0893.071.193.138.653854Rajesh s. Bejankiwar et al .Vol.16t TOC (Chlorde rich solutin)+ PEG (Chloride rich solutio)■凸TOC (Chloride-less solution)- * PEG (Chloide-less solution)0.0030 0.00310.0032 0.00330.003.0406081/Tx 000, 1I/kElectrolysis time, minFig.4 Arrbenius plots of kinetie rate eofficient of two-stagefig.3 Variation of PEG and TOC during etrolysis stfirst onder kineticsPCCHM anode in chloride rich and chloride less solution3.2 Generalized kinetic modelof electrolysis, the change in PEG and TOC concentration isThis model is based on the assumption that some of thevery fast. This pattern of PEC remnoval suggested the firstorganic pollutants are directly oxidized to the end productsorder kinetics . The intermediates formed during the course of(CO, and H20) in the electrochemical oxidation process ,the reaction are identified as acetic acid, oxalic acid, formicwhile the rest is fistly converted into intermediate productsacid and ethylene glycol. Therefore, the experimental PEGthat are then further oxidized to the final products. Thisconcentration data is correlated to two different kinetic modelsmodel was proposed by Li et al. (Li, 1991) for the wet airbased on first order kinetics namely, two-stage, first-orderoxidation of organics and supported by Lin et al. ( Lin,kinetic model and a generalized kinetic model.1998) for electrchermical oxidation of saline wastewater. The3.1 Two stage, first-order kinetic modelmodel can be represented by following reaction sequence:This kinetic model can be represented by,A +02“D,” PEG,ln|;(1)l PEG。]A+02“B+02,where PEG。 and PEG, are the initial PEC concentration andB +02-→D.that at time t respectively, and h is the kinetic rateIn the above reaction pathway, A represents the PEGcoefficient which is related to the reaction temperatureand other unstable intermediate organic compounds, B is theaccording to the Arrhenius equation,refractory intermediate product and D is the end productsk= Axexp[二AE],(2)(CO, and H20). Assuming a first order kinetics for allwhere A is the frequency factor, E is the activation energy，reaction paths, the generalized kinetic model is given byR is the gas constant and T is the reaction temperature. The[[A+ Bl[A+ B。=n+h2- Tksexp(-kg1)+observed data of the electrochemical treatment could beh-的represented by a two stage, first-order reaction kinetics后十,二r,exp1-(k,+ k)tl,(3)represented by Equation (2). The two kinetic rate constantk, and k2 were calculated from the slopes of the straight lineswhere [A] and [ B] are the concentration of species A andplotted ( not reported) according to Equation (1) for eachB, respectively, in the reaction pathway. In terms of COD,temperature and are given in Table 2. From the table we canconcentrations [ A + B] and[A+ B]。are the same assee that the first kinetic rate constant h, increases with[ PEG] and [ PEG ]。 respectively in Equation (1). Theincrease in reaction temperature, while second kinetic rateexperimental PEG removal data are computed according tconstant kz decreases. It means the increase in temperatureEquation (3) for four different reaction temperatures offavors the oxidation of PEG to internediates and inhibits the259C，35C, 45C and 55C . The ft seems to be quite good( not reported). The kinetic rate constants are calculatedconversion of intermediates to final products . The two kineticrate constants vs. the reciprocal of temperature in semi-using中国煤化工and shown in Table2. Itlogarithmic scale are shown in Fig. 4. The staight linessCHCNMHGrate efficient h isobtained for both kinetic rates constants are standardinereasea wIn ine Increase in reaction temperature. This isArhenius plots according to Equation (2). The regressionan usual trend, also observed in previous studies (Li, 1999)coefficient for the straight line of first reaction constant isand Lin et al.(Lin, 1998)，while no order was observed insecond kinetic rate cofficient k2. It is also observed that0.988 and that of the second is 0. 998.No.5Electrochemical oxidation of polyethylene glycol in electroplating solution using paraffin composite ....55there was no significant change in the second kinetic rate .electro-oxidation mechanism. The electrochemical oxidationcoefficient with the change in reaction temperature .proces was found to be influenced by applied curent densityTable 2 Kinetics rate parameters of the electrochemical oxidation of PEGand surface area of the anode; the latter is more dominant .ReactionKinetic rate eofficient, min~Kinetic investigations ( including computations of kinetic ratetemperature,knconstants) using two different kinetics models suggest thatTwo-stage first order kinetic modelboth models provide reasonable fit to the experimental data.2:0.0345 0.988 0.0091 0.988However, two-stage first-order kinetic model appears to be a3s0.0408 0.978 0.0033 0.958much better representation of the overall reaction mechanism .0.0479 0.968 0.0031 0.9665:0.0571 0.955_ 0.0022 0.966References :Generalized kinetic modelAndreom R，Caprio V， Insola A，1996a， Kinetics and mechanism of250.0197 0.968 0.0176 0.982 0.0019 0.987350.0216 0.988 0.0183 0.984 0.0004 0.997R2011.9955_700”0zone in aqueous sgolution [J].， Water4:0.0244 0.994 0.0173 0.978 0.0003 0. 994Bejankiwar Rs, 2002. Electrochemical reatnent of cagrtte0.0267 0.956 0.0174 0.955 0.0002 0 986Biwyk A, 1980. lectrocoagulation of biologically treated sewage{C]. In: 35thPurdue industrial waste conference. Lafayette. Indiana.The Arhenius plots for the two kinetic rate coefficientsBuneeN J, Keech P G, 2003. Electrochemical oxidation of simple indoles atof generalized kinetic model are shown in Fig.5. It is evidentPbO2 anode[J]. Journal of Applied Electrochemistry, 33: 79- -83.that the straight line obtained for first kinetie rate coefficientCanoxers P, Martinez F, Gomez GJ et al., 2002. Combined electrooxidation andasisted etrochemical coagulation of aqucoues phenal wastes[]. Joumal ofk, is a standard Arrhenius plot as per Equation (2)， whileApplied Electrochenistry, 32: 1242- 1246.that of second kinetic rale coefficient is not. The regressionCenkin V E, Belevstev A N，1985. Electrochemical treatment of industrialwastewater[J]. 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Wet oxidation 册s aprelreatment method for wastewalers contaminated by bioresistant organice0.0030 0.0031 0.0032 0.0033 0.0034[J]. Water Science Technology, 36(2- -3): 109- 114.1/Tx 100, 1/kNarayananaSS, Deepa P N, 2001. Paraffn composite copper hexferocyanatemdifed electrode for catalytie oxidation and armperomet'ic determination ofFig.5 Arhenius plots for kinetic cofficients of generalizedhydraine[J] . Res Jourmal of Chemistry and Environment, 5(3): 67- -75.Suwuki J, 1976. Study on ozonation of waler soluble polymers, ozone degradationkinetiesof polyethylene glycol in water[J]. Joumal of Applied Palymer Science, 20SolarF,MeyrB,1996. Electochemical chemistry--A series of araces[M]4 ConclusionsSheng H L, Ching T s. Mei C s, 1998. Saline wastewater treatment byIn this study， we have evaluated the efficiency ofparaffin composite copperhexaferrocyanate modified anode forVlyseides A G，Israilides C J，Loizidou M et ad.. 1997. Electrochemicaltreatment of vinasse from beet molasses[J]. Water Science Technology, 36electrochemical removal of polyethylene glycol. The PCCHM(2- -3): 271- 278.anode was found ffcient in PEG and TOC removals fromWatson G中国煤化工! polyethylene elycols byelectroplating solution of high acidity and ionic strength. PECsewaYousef Mical treatment of phenolicand TOC concentrations are found to be reduced to 2.08 mg/wastewMYHC N M H Gd enom elautio[J].Joumal of Environmental Science and Health, A 32(5): 1393- 1398.L and 1.18 mg/L respectively, after 10 min using 34 cmanode and applying 0.75 A/cm' current density . Chlorides( Received for review September 11, 2003. Accepted October 24，2003)present in electroplating solution contribute to the removal ofPEG and TOC concentrations in overall process via mediated