Effective and inexpensive gas chromatography method for detection of trace level SO2 in H2 fuel

J Shanghai Univ (Engl Ed), 2010, 14(5): 322 -325Digital Object Identifer(DOI): 10.1007/s11741-010-0652-3Efective and inexpensive gas chromatography method for detection oftrace level SO2 in H2 fuelWANG Hui(王慧)， LI Chang-shun (李长顺)，ZHOULi(周 丽)， SHI Sen(时森)， WANG Yao(王瑶),SUN Jian(孙俭)Green Chemical Engineering and Energy Research Center, School of Environmental and Chemical Engineering, ShanghaiUniversity, Shanghai 200444, P. R. China(Communicated by JIA0 Zheng)@Shanghai Universty and Springer-Verlag Berlin Heidelberg 2010Abstract Gas chromatography (GC) analysis of sulfer dioxide is challenging because SO2 is a highly mobile and chemicallyactive molecule. For the conventional GC method with flame photometric detector (FPD) and direct-injection, it is oftenineffective particularly when the SO2 level is as low as on the trace level. In this paper, a modified GC system integrated withan adsorption- desorption device was developed to detect the trace SO2 impurity in H2 fuel. Adsorbent;DX-502 is used inthe adsorber to adsorb/collect SO2 from the sample gas and desorb/release it in a concentrated fAow so that the conventionalGC at downstream could detect it with an acceptable accuracy.Keywords gas chromatography (GC) analysis, sulfur dioxide, adsorption, desorptionIntroduction(GC) has several advantages such a8 cost-effective, fairlyfast response, and reliable (at 10- 6 level for SO2 moni-Hydrogen fuel has gained a wide support from bothtoring). The purpose of this study is to develop a cost-the government and public because its utilization proeffective and accuracy-reliable method by using the con-duces almost zero emission. Among many applications,ventional GC method with fAame photometric detectorfuel cell vehicle (FCV) in the form of proton exchange(FPD) through an in-house built adsorption/ desorptionmembrane fuel cells (PEMFC) has been considered todevice.give H2 the most promising benefits in both energy con-1 Experimentservation and environmental protection!1-3).PEMFC has been the focus in the FCV industrialresearch since it is the most feasible technology in1.1 Apparatuscommercializationl4. On the other hand, the impuritiesA GC with FPD (GC-900, Shanghai Kechuang Chroin the H2 fuel produced from other fuel sources such asmatography Instruments Co. Ltd.) integrated with ancoal and natural gas present barriers in the FCV ap-in-house built adsorption-desorption device was usedplication. SO2 is one of the impurities in the H2 fuel,as the analysis instrument, which is shown in Fig.1.and it is made from fossil fuels. According to Yang,The system has three parts: gas cylinders, adsorption-et al5l, 5x10-7 SO2 can cause significant and irre-desorption device and the GC analyzer. A six-way valveversible effect on the PEMFC performancel6-7. Con-is used to switch between the adsorption-desorptionsequently, detection of trace SO2 in H2 fuel is indis-state and analysis state. Silica gel Chromosil 310pensable.(Sigma- Aldrich Co. Ltd.) was specially treated to sep-Monitoring and detecting trace SO2 has been a chal-arate trace (from 10-6 to 10-9 level) sulfur compounds.lenge due to its highly adsorbing and corrosive prop-Polytetrafuoroethylene (PTFE) pipes were used to con-erties, even with some of the expensive methods likestruct the adsorption tube. Adsorption of SO2 fromAuorescent spectrometry method.the standard gas was carried out at -18- 20 °C. TheCompared with other techniques like conductancesubzero temperature (-18-0。C) was achieved usingmethod and spectrophotometryl, gas chromatography中国煤化工salty ice water. InReceived Nov.24, 2009; Revised Jan.6, 2010Project supported by the National Natural Science Foundation of ChinMYHCNMHGCorresponding author SUN Jian, Ph D, Prof, E-mail: sunjk12@gmail.comJ Shanghai Univ (Eng! Ed), 2010, 14(5): 322 -325323desorption of SO2 at elevated temperature, a water-H2. Figure 2 indicates that carefully regulated H2 pres-bath heater was used to heat the desorption tube up tosure results in negligible peaks and relatively stable noise60。C within one minute.background. In this study, the H2 pressure of 0.065 MPa(corresponding to approximately 70 mL/min in flow) isInjection port 2Tnjection pont卫set a8 the operating condition.Toair 1Six way vavlel门2.0rColumn: Chromosil 310Oven: 50 CC ....0.060 MPa”Ghromos1 310 cohmm.5Det: FPDGas chromatograplyCarrier gas: Nitrogen.00.5一号昌| Adsorption-desorption device0.0一Carier gasFig1 Schematic drawing of upgraded GC system12一15Time/min.2 MaterialsFig.2 Infuence of the H2 gas pressure on the backgroundCarrier gas for GC operation was N2 of 9.999% pu-noiserity from Shanghai Qingda Gas Ltd. High purity H2for GC operation was made by an on-site generator. Aseries of adsorbents (GDX-101, GDX-401, and GDX-2.2 Operating conditions in adsorption502) with various degree of adsorption polarity wereAdsorption of SO2 from the sample gas was the keytested for the adsorption/ desorption device. GDX-502for an enhanced GC signal and therefore an acceptablewas a porous polymer microsphere with strong adsorp-accuracy in analysis. Three operating parameters af-tive powerl9-10]. H2 with 5x 10-6 SO2 was used asfect the GC measuremnent most. They are the choicethe standard gas (Shanghai Jiliang Reference Gas Ltd.).of adsorbent, adsorption volume of sample gas, and theThe sample gas in our work was supplied by the Auto-temperature of adsorption and desorption.motive Institute, Tongji University.2.2.1Effect of adsorbent1.3 ProceduresIn general, selected adsorbents must meet two pre-Prior to analysis, the GC and adsorption desorptionrequisites: First, it has strong adsorption capacity ofdevice should be conditioned at high temperature forSO2; Second, it can easily desorb SO2 at a reasonablyabout 2 h. A stable GC background baseline was thenelevated temperature. From commercially available ad-obtained through adjusting the H2 to air ratio. After-sorbents for GC application, three adsorbents with var-wards, some sample gas (10-50 mL) was introducedious surface polarity are tested. Based on the resultinginto the adsorption tube at the adsorption temperature.GC readouts in Fig.3, GDX-502 is chosen as the bestFollowed by the completion of sample adsorption at pre-candidate for our application.determined temperature (-18 - 20 °C), adsorbed trace2.2.2 Efect of adsorption volumeSO2 was desorbed at reasonably elevated temperatureFPD is a mass sensitive detector and therefore the(40- 60 °C). The routine GC analysis began by switch-sample injection volume determines the analysis sensi-ing the six-way valve to GC system.tivity. Four volumes of the standard gases are tested2 Results and discussionto study the efect of sampling volume. As is shown inFig.4, signals with sharp peaks are obtained when the2.1 Minimizing the effect of backgroundsampling volume ranged from 10 mL to 40 mL. Over-saturated signal with a cutoff peak is observed in theIn trace gases (10 6 to 10-9) analysis, matrix effect,case of the 50 mL of sampling volume. It appear thatcaused by the main constituent gas in large amount,the adsorbent fails to soak up all the gas when excessiveseverely affects the signal generated by the trace gases.amount of sample gas is injected. On the other hand,It is too strong to be neglected. Therefore the reductiontoo中国煤化工. reactor would caluseof background noise is our top priority. Liang川 pro-theheight of which basedposed that regulating the flow of the carrier gas couldon t:YHCN M H G. Therefore, the gasminimize the background noise effectively. In this work,sampling volume 18 set trom 1U mL to 40 mL in thiswe control the fAow rate by regulating the pressure ofstudy.324J Shanghai Univ (Engl Ed), 2010, 14(5): 322 -325350一GDx-502GDX-502 gives good performance in the adsorption of300SO2 from sample gas at 20。C and desorption at 50 °C.GDX-401250200180F--20C .Column: Chromosil 31060 t150Oven: 50 C-- -76Det: FPD40 FCarrier gas: Nitrogen50100 t800012345678910Time/min20Fig.3 Comparison among GC readouts of SO2 desorptionfrom three porous polymer microsphere with various二45678surface polarityFig.5 Efect of adsorption temperature on GC readouts1300with GDX-502500[450 f1200元10mL-40“400 t.... 50Ci 500- . Standard Gas i 40 mL350f.---60 C。Sandard Gas i, 50 mL芳300250 t防200100Adsorbent: GDX-502150 F100 F50 to 1234567 802Fig.4 Infuence of different standard gas volume on ad-sorption performanceFig.6 Desorption lines of standard gas at different temper-atures2.2.3 Efect of adsorption-desorption tempera-tureTable 1 Selected operating conditions and GC readoutsZhaol12] reported that porous polymer microsphereAdsorptionAdsorptiveDeeorptivePeak area(like GDX-502) had adsorption capacity at low tempera-volume/mL temperature/°C temperature/9C/(uv.)ture. Besides gas volume, the adsorbability is inverselyproportional to the temperaturel3). In this work, we9141 186study the effects of different temperatures on GDX-5027 543 777in the process of adsorption and desorption respectively.405 729 649Figure 5 shows the adsorption at different temperature.10o301299672.The results are obtained in accordance with Zhao's.773 287From Fig.5, 20 °C is considered as the optimal adsorp-l0386 702tion temperature.In the desorption process, the speed of desorption2.3 Detection of sample gas (10- 9 SO2)is also determined by the temperature[101]. Desorp-Under the optimal condition, we analyze the sam-tions at diferent temperature (40 °C, 50。C, 60。C)ple gas (10-9 SO2) which is provided by the Automo-are observed. 40 mL standard gas is injected into thetive Institute, Tongji University. We use the externaladsorption-desorption device. Then the six- way valve isstandard method for quantitative analysis. General onswitched to GC system when the predetermined tem-routine operations is as follows: Some volume (10-perature is achieved. In Fig.6, the desorption line of40 mL) of standard gas or sample gas is injected into the50。C shows the highest peak. Thus this temperature isadsorption-desorption device; The adsorptive and des-chosen for desorption.orption temperature are 20。C and 50 °C, respectively.For further selecting the adsorbents and the oper-Finall中国煤化工as shown in Fig.7.ating conditions, analysises of the sample gas are car-For areadout for direct-ried out. Table 1 summarizes the GC results under sixinjectiYHCNMH(3sented in Fig.7. Nooperating conditions. From the table, we can see thatSO2 signal is observed for direct injection, while clearJ Shanghai Univ (Engl Ed), 2010, 14(5): 322 325325400rsignal is observed for the adsorption-desorption method.The experiment is repeated with different adsorptive300 |volume. With the adsorption- desorption method, wework out that the concentration is 31 x 10-9, which is- Sample gasDirect-injection of standard gasin accordance with data gained by fuorescent spectrom-- Standard gasetry method conducted by Tongji University.Results in Table 2 confirm that our modifed GC100method coupled with adsorption-desorption can detectthe 10-9 SO2 in H2 fuel efectively.3 ConclusionsTime/minDetection of 10-9 level SO2 in H2 for PEMFC hasFig.7 Detection of sample gas containing trace SO2 whosepeak is corrected by standard gasbeen a focus of many studies. Our data indicates thatTable 2 Detection of sample gas result compared with the standard gas'sStandard gasSampleAdsorptive volume/mL Peak area/(uv.s) Adsorptive volume/mL Peak area/(uv.a)Concentration of sample gas/(10- 9)4(34 543 2001 000833 1253128 135 182500153 20334direct-injection method to the conventional GC with[6] LOUCKA T. 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