Decomposition kinetics of dimethyl methylphospate(chemical agent simulant) by supercritical water ox

ISSN 1001-0742Jounnl of Emrironmental Sciences Vol. 18, No. 1, pp.13- 16, 2006CN 11-2629/XArticle ID: 1001-0742006)01-0013-04CIC mumber: X703Document code:ADecomposition kinetics of dimethyl methylphospate(chemical agentsimulant) by supercritical water oxidationBambang VERIANSY AH', Jae-Duck KIM', Youn-Woo LEE2(1. Supercnticat Fluid Research Laboratory, Korea lnstitute of Science and Tcchnology (KIST), 39-1 Hawolgok-dong, Seoungbuk-gu, Scoul 136-791,Korea. E-mail; jdkim@kisl.re.kr; 2. School o[ Chemical and Bivlogical Engineering. Seoul National University (SNU), San 56-1 Sllim-dong,Giwanak-gu, Seoul 151-744, Korea)Abstract: Supereritical water oxidation (SCWO) has been drawing much attention due t(0 effectively destroy a large variety ofhigb-risk wastes resulting from munitions demilitarization and complex industrial chemical. An imporant design consideration in ihedevelopment of supereritical water oxidation is the informnation of decomposition rate. In this paper, the decomposition rate ofdimethyl methylphosphonate(DMMP), which is similar to the nerve agent VX and GB(Sarin) in is struclure, was investigated underSCWo conditions. The experiments were performed in an isothermal lubular reactor with a H2O2 as an oxidant. The reactiontcmpcraturcs were ranged from 398 to 633"C at a fixed pressure of 24 MPa. The conversion of DMMP was monitored by analyzingtotal organic carbon (TOC) on the liquid efluent samples. It is found that the oxidative decomposition of DMMP proceeded rapidlyand a high TOC decomposition up to 9.99% was obtained within 11 s at 555C. On the basis of data derived from experiments, a .global kinetic cquation for the decomposition of DMMP was developed. The model predictions agreed well with the experimentalKeywords: supercritical water; oxidation kinetics; chemical agent; DMMPand Abeln, 1999; Gloyna et al., 1994; Savage el al.,lntroduction1995).Under the provisions of the 1993 InternationalKnowledge of the kinetics of the chemicalChemical Weapon Convention, all stockpiled chemi-reactions that occur during SCWO is required tocal warfare agents (CWAs) are to be irreversiblydesign and analyze SCWO reactors and process(Oh eldestroyed. Studies of supercritical water oxidational., 1996). This rcalization has motivated numerous(SCWO) for treating and destroying CWAs areprevious studies of SCWO kinetics, nearly all ofunderway in support of an international program forwhich havc conccntratcd in the kinetics of reactantthe destruction of these CWAs stockpiles. SCWO hasdisappearance. Simply making the reactant disappcar,een known as an efficient and clean technology forhowever, by converting into a sct of diffcrcnt organicthe treatment of aqueous organic wastes that derivescompounds is insufficicnt for waste treatment byits effectiveness from the unique solvent properties ofSCWO. Moreover, it is potcntially dangcrous if thewater at conditions well above its critical point ofproducts of incompletc oxidation arc more toxic OI374.3C and 22.1 MPa(Fang et al, 2005, 2004, 2000;hazardous than the starting material. [t is the oxidationVeriansyah et al, 2005; Park et al, 2003; Shaw andralc of the lotal organic carbon (TOC) to CO2, not theDahmen, 2000; Lachance et al., 1999; Rice anddisappearance ratc of the initial organic rcactant itself,Steeper, 1998). When organic compounds and oxygenwhich is of primary applicability to the commercialare brought together in supercritical water (SCW), theSCWO process (Frisch and McBrayer, 1996). Indeed,oxidation of the organic is rapid and complete todestruction and removal ofTOC is the utimate goal ofcarbonr dioxide and water. Heteroatom such as CI, S,some SCWO. Thus, the kinetics of TOCand P are converted to their corresponding mineraldisappearance assumes particular sigmificance.acids (HCl， H2SO4， and H,PO)， which can beIn this paper we describe experiments ofneutralized by using a suitable base to produce salts ofdimethyl methylphosphonate(DMMP) which was desrelatively low solubility at supercritical conditions. Ifigned to identify kinetic oxidation rate in supcreriticalany organic nitrogen presents the resulting product iswater. DMMP was chosen as a simulant for the nerveprimarily molecular N2 with some N2O(Killilea, 1992).agent such as yX and GB since it is structurallyNOx gases, typicalundesired byproducts ofsimil中国煤化工operties that arecombustion processes, are not formed because thcomp|YHC N M H Qe chemical structuretemperature is too low for these oxidation pathways towhich can be descnbed DMMI', VX and GB is shownbe favored. Detailed reviews of the technology arein Fig.I where R and R2 are differing functionalavailable from Brunner (Brunner, 1994; Schmiedergroups. For DMMP, R: = OCH3 and R2= CH; for GB,4Bambang VERIANSYAH et al.Vo.18R=FandR:=CH(CH);andforVX,R,=a shell and tube heat exchanger and thenSCHLCH2N (C;H) and R2 = CH2CH3 Selected physi-depressurized to ambient condition by a back-prcssurecal properties of DMMP and Agent GB are listed inregulator (Tescom Co. 26-1721-24). The productTable l(ANFC, 2002).stream was then separated into liquid and vaporphases. The liquid products were collected in agraduated cylinder, and their volumetric flow rateswere mcasured at ambient laboratory conditions.1.2 Materials and analytical methodsRORzCHsDMMP (Aldrich, 97 wt. %) was the reagent usedin the experimcnts. Hydrogen peroxide (Junsei, 35%Fig. 1 Structure of chemical agent welfarew/v aqueous solution) was used as an oxidant. Dilutedoxidant solutions were preparcd using deionizedTable 1 Physical propertes of DMMP and GBwater. .DMMPMolecular weight124.08140.1The conccntration of DMMP and liquid-phaseBoiling point,心180158reactor efluents werc analyzed by TOC AnalyzerMeclting point, cPour poinl:<-50 -56(Shimadzu TOC-VCPN), which is based on combus-Density al 25C, g/ml .1.J71.09tion catalytic oxidation method and highly sensitiveSolubility in dsited water at 25C，MiscibieMisciblcnon-dispersive infrared (NDIR) gas analysis,/100grespectively. Destruction efficiency of TOC，X,defined as follows, was used to evaluate thc cxtent of1 Experimentaloxidative decomposition.1.1 Apparatus and procedureX=1-. [TOCl(1)Theexperiments wereconducted”[TOC].laboratory-scale, continuous-flow SCWO reactorwhere [TOC] is the initial TOC and [TOC] is thesystem. The experimental set-up is similar to previousresidual TOC after reaction.published works(Veriansyah et al.. 2005). The system2 Results and discussioninvolved two parallel sets of equipment that are almostidentical, one for delivering the DMMP solution andForty-one supercritical water oxidation experi-the other for the oxidant. DMMP and oxidant solutionments were performed in an isothermal and isobaricwere pumped separately into the system by high prc-tubular reactor. Table 2 provides the cxperimentalssure pumps (Thermo Separation Product Company).ranges and variables. The oxidation reaction in thisAll hot sections of the system were insulated in boxesstudy can be represented to following stoichiometricof ceramic board and the temperature was monitoredEq. (2).directly using thermocouple. The temperature of theCII,O3P+5O2一- 3CO2+H,PO,+ 3H2O (2)systcm was controlled by a temperature controllerTable 2 Experimental variables and ranges(Hanyoung DX 7). Oxygen, the oxidant used in theseexpcriments, was prepared by dissolving hydrogenExpenimental variableRangcpcroxide with deionized water in a feed tank. In orderPressure(P), MPa2to assure all of H2O2 is dccomposed to give H2O andTemperature(T), C398- -633O2, the oxidant was pre-heated by flowing through 6 mRcsidencc time(t). s4-15coiled 1/8-in O.D. SS 316 tubing at 600C andTOC conccntration at reactor inlet, mmol/L2--32Oxidanl concentration at reactor inlet, mmo/L38- 30residence time of more than 14 s. Based on the studiesof Phenix et al.(2002) and Croiset et al.(1997), it hasIn order to develop reliable reaction ratbeen evidenced that H2O2 completcly decomposed inexpression, data were taken under various conditions.the pre-heater even in those experiments carried out atThe global power-law reaction rate can be describedhigh flow rate and low tempcrature. DMMP solutionas follows:was pre-heated by flowing through 0.5 m 1/8-in O.D.SS 316 tubing. The solutions mixed at the reactor中国煤化工) [H201(3)entrance in a SS 316 cross and then cntcred thewher.MYHC N M H Gf reactant(mmolL);reactor, which was constructed from a 280 mm length[O] is the concentration of oxidant(mmol/L); [H2O] isof 18 mm O.D. and 9.5 mm I.D. SS 304 tubing. Uponthe concentration of watcr; t is the reactor residenceleaving the reactor, the effluent was cooled rapidly intime;a, b, and c are the reaction orders of Ca O2, andNo.1Decomposition kinetics of dimethyl methylphospate(chemical agent simulant) by supercritical water oxidation15H2O respectively. k is the rate constant, which can be1exprcssed in Arrhenius form in equation as follow:k=A cxp (-E。/RT)(4)0.9where A and E. are the pre-exponential factor andactivation energy, respectively.0.8In this study, we assumed the global oxidation of0.7DMMP depends only on the temperature, the reactantconcentration, and the oxidant concentration. The0.6water concentration was assumed to have no expliciteffect on the reaction rate, as is the case in manyreported SCwO kinetic studies, so the global0.5 0..7 0.8 0.9 1.Experimeatal conversionpower-law reaction rate can be expressed as:rate=. dLC.]= k[C,J[O2j(5)Fig.2 Parity plot for powe-aw rate equation for TOC ConversiondrSubstituting C, with [TOC] and rearranging the(perfect match), contain all data points. This modelequation with respect to the TOC decomposition Xfits very well with our experimental data.dcfined by Eq.(1), the relationship obtained is,3 Conclusions. d(1-X)，= k[TOC]。(1-X)" [01'"The decomposition kinetics of DMMP wasdtSince all of experiments were performed at veryexamined from 398 to 633C at 24 MPa, residenccshort contact time, between 4 and 15 s, the method oftime of 4-15 s with the initial concentration ofinitial rates can be uscd to all data(Fogler, 2000; Por-DMMP based on TOC was ranged from 2 to 32ela et al, 2001). If the method of initial rate is appliedmmol/L and the initial oxidant concentration rangedto Eq.(6) with the initial condition X - 0 at reactionfrom 38 to 300 mmol/L. Experimental data showedtimel = 0, it can be solved analytically to provide Eq.that TOC decomposition greater than 99.99% can be(7) as the relationship between the TOC removalobtained within 11 s at tcmperature 555C.effciency and the experiment variables.By taking into account the dependence ofb .1/01-reaction rate on oxidant and TOC concentration, allX=1-[1-(1-a)hc[TOC]" [O2" ]for a≠l (7)experimental data were used to fit the reaction rate inA multi variable non-lincar least squaresa non-linear regression analysis, assuming a zero-technique was used to estimatc the kinetic paramelersorder dependence on water concentration. ReactionA，Ea, and the rcaction orders. The best-fit valuesparameter values were determined to be 66.56土0.48were obtained by minimizing the sum o[ squares error.L'lmmol 031 sI for the prc-cxponential factor, 42.00土(8)0.41 kJ/mol for the activation energy, and for thereaction orders, 0.96 土0.02 for DMMP (based onwhere iNop is the number of expecriments, Xap is theTOC), and 0.35土0.04 for oxidant.experimental conversion and Xpa is the modelAcknowledgement: This work has been suppored bypredicted DMMP conversion， The quality of datathe National Research Laboratory Program forfitting was evaluated by R' in ANOVA routineSupercritical Fluid and the authors would like to thank(Johnson and Bhattacharyya, 2001). It has algorithmsto the Ministry of Science and Technology, Korca.to cstimate 95% confidence interval on each para-References:meter and on the predicted response. Using thisprocedure and considering all data points, the best- fitANFC (Akzo Nobel Function Chemical by), 2002. 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Catalytic supereritical water(Received lor review May 30, 2005. Accepted August 5, 2005)中国煤化工MYHCNMHG