Sampling and Analysis of Emissions in the Rubber Industry, Artykuły naukowe, Polimery i ich analiza
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//-->DIK-Publikation 115, Tagungsband "Hazards in the European Rubber Industry", Manchester (1999)Autor: U. GieseSampling and Analysis of Emissions in the Rubber IndustryU. Giese, German Institute for Rubber Technology1.IntroductionDuring the manufacture and storage of rubber products various gases, vapors and aerosolsare emitted due to the complex compound compositions and the concurrent vulcanization thatoccurs at high temperatures. These emissions consist of volatile components of originalcompound ingredients such as plasticizers, antioxidants and residual monomers or polymeroligomers as well as primary and secondary reaction products from the crosslinking systems.The formulae and vulcanization conditions of individual substances as well as their origin havebeen identified in numerous examinations [1-8]. Using these results as a basis, well over ahundred substances are to be expected in the air at the workplace in the rubber industry.These substances are amines, amides, aliphatic/aromatic hydrocarbons, highly volatile sulfurcompounds, aldehydes and ketones, phenols and esters. Solvents may also be presentdepending upon the manufacturing process as these are used for assembly and cleaning.Furthermore, water may be expected in addition to aerosols dependant upon the weatherconditions and manufacturing processes. Measurement monitoring of the air at the workplacerequires implementation of a measurement method that is able to cope with the extremelycomplex situation in the rubber industry and can also satisfy the following requirements [9]:----Sampling period must represent a shift mean value.Selectivity for individual dangerous substances.Measurement range 1/10 up to 3x limit.High precision.The sampling and analysis procedure is developed from a base of approximately 50 relevantsubstances that can be expected as emissions and which also have limit values ortoxicological ratings [10].2.2.1Development of a Measurement MethodSampling SelectivityThe development and application of a measurement method has the goal of reliablymeasuring dangerous substances in the air at the workplace in the rubber industry. Thisrequires selective sampling structured on the families to be found by using solid-phaseenrichment (adsorbents) as well as considering and possibly necessarily excluding potentialnegative effects of aerosols, oil gases, cross-sensitivities arising from the complexity of thecompounds and humidity by using suitable filters and separator systems [11-14].Due to the diversity and insensitivity to disturbance effects the principle of active sampling [14]is applied to enriching gas, aerosol and vapor substances on adsorbents.Various adsorbents [15,16] (polymers, inorganic materials) are examined with regard to theiradsorption properties and selectivity for selected substances for the purpose of samplingindividual relevant single substances or substance groups.For selected model substances, inverse gas chromatography was employed to determineadsorption enthalpies and breakdown volumes [13,17] that were used to preselect thecombination of substance and adsorption material.The amount of adsorption enthalpy is dependant upon the interaction between adsorbentsand adsorbed substance, whereby the primary influencing factors are polarity and distillationcharacteristics. Thus, for instance, silica-gel and modified silica-gel in addition to activatedcarbon are particularly suited as an enrichment material for morpholine. Toluene, on the otherhand, is adsorbed excellently on activated carbon.2.22.2.1Measurement Method ValidationEffectiveness of the Sampling and Analysis MethodsThese results were used to examine the suitability of adsorbents by simulating sampling forapprox. 50 potentially expected substances, whereby not only enrichment but also therecovery of adsorbed substances using solvent desorption followed by GC or HPLC analysiswas uppermost as a simple and universal method.Simulation of sampling was achieved by using test gases and test gas compounds whichwere produced by the dynamic vapor pressure saturation process [18]. During thesesimulation experiments adsorption capacities and breakdown volumes were ascertained inaddition to retrieval rates (W) which are calculated in percent from the quotients of theanalytically determined concentration and the concentration to be expected theoretically. Theretrieval rates show the effectiveness of the enrichment and ensuing desorption.Table 1 shows a simplified form of an outline of substance groups and the sampling andanalysis method which is optimized under the aspect of effectiveness.Table 1: Determination method chartRecovery(desorption)Benzyl alcoholAnalysismethodGC-FID (MSD)Substance/substancegroupHighly volatile aliphaticand aromaticcompounds [20-22]Amines and amides [23]CollectionphaseActivatedcarbonWin %90.2 - 100Silica-gel ADS2% KOHmethanolinGC-NPD86.3 - 100Highly volatilechlorinated compounds[24]Carbon disulphide,highly volatile←sulfurcompounds [25]Aldehydes (and ketones)[26]Low volatilitycompounds [27]Aerosols [27]ActivatedcarbonBenzyl alcoholGC-ECD83.0 - 100Sampling bagAcetoneGC-FPD80.0 - 97.5Silica-gel DNPHAcetonitrileHPLC-UV87.2 - 97.5XAD-2AcetoneGC-MSD (FID)94.0 - 98.0Glass-fiber filter1,1,2-trichloro-trifluoroethaneFT-IR94.0 - 98.9Abbreviations used in Table 1:DNPHFIDNPDFPDHPLCMSDFT-IRDinitrophenylhydrazineGCFlame ionization detectorWNitrogen phosphor detectorUVFlame photometric detectorHigh-pressure liquid chromatographyMass-selective detector (mass spectrometer)Fourier transform infrared spectroscopyGas chromatographRecovery rateUltraviolet spectrometer2.3Examinations of the Effect of Cross-sensitivitiesCross-sensitivities were examined when sampling selected model substances by using multi-component test gases such as cyclohexane, cyclohexamine, toluene, dimethylformamide, n-octanol and tertiary butylamine [11,12]. The criterion applied when selecting substances wasone of representativeness, i.e. the frequency of the emissions to be expected and chemical-physical properties.Essentially no mutual displacement of substances in the groups in Table 1 occurred on thesurface of the selected adsorbents. Merely the simultaneous occurrence of highconcentrations of primary aldehydes with amines can result in low values as these substancescan react to Schiff’s base in the gas phase.2.4Effect of HumidityHigh humidity sometimes has a negative impact on the effectiveness and absorption capacityof adsorbents on substances to be determined in the air because of the displacement effect ofwater, which is shown in a low retrieval rate [22-30]. From the physical-chemical aspects aneffect is principally to be expected when polar adsorbents are used as water occupies a partof the adsorption centers and blocks them for the analytes. But other effects, such as analytesdissolving in water on the surface of adsorbents, can also have a negative effect uponmeasurement results.No negative effect is to be observed for nonpolar substances, such as toluene. The retrievaldecreases for polar compounds such as ketones, aldehydes and also for numerous amines.Apart from a few exceptions humidity can be expected to have a negative effect from approx.50% and higher relative humidity. In numerous examinations the retrieval rate as a function ofhumidity was measured for many substances (e.g. acetaldehyde, 2-butanone, cyclohexanoneand acetone) and must be taken into account for the analysis result.2.5Effect of Plasticizer Vapors and AerosolsThe effect of plasticizer vapors and aerosols upon the determination of gaseous substanceswas examined using examples of a typical mineral oil plasticizer and a synthetic plasticizer (Di-(2-ethylhexyl)-phthalate) with the aid of simulation tests (test gas compounds) [11,31].A negative effect upon the accuracy of measurement results only occurred at high aerosolconcentrations (approx. 60 mg/m3) by far exceeding those likely to be encountered in practice.This effect could be rectified by using an additional filter to protect the adsorption tubes fromthe aerosol.Overall, the negative effect of aerosols upon the results measured at the workplace is to beneglected in relevant concentration ranges.3.Sampling EquipmentThe interrelationships and extensive surveys upon the selectivity and effectiveness ofenrichment materials mentioned above were used as the basis to construct the samplingequipment. This equipment consists essentially of a central pump unit that has a total of sixindividually controlled intake ducts (defined volume flows) which contain adsorption tubesappropriate to the substances/substance groups to be collected.Thermal mass flow regulators were used to set and control individual sampling flows. Theequipment is only suitable for stationary sampling. The facility to place different adsorptionmaterials in the intake ducts and to adjust the volume flows to be controlled (samplingvolumes) individually means that the equipment is extremely adaptable and can be adjustedto match the appropriate relevant conditions.4.Test Measurements in Simulation Tests and „On Site“The check on the operation of the developed sampling equipment and the whole procedurewas carried out in three stages:1.Measurements in closed systems2.Measurements under practice-oriented conditions in the pilot plant3.Measurements „on site“Stages 1 and 2 were carried out with known rubber compounds under controlled conditions.A representative example is the vulcanization of a simple tire tread compound using theformulation shown in Table 2.Table 2: Formulation for a tire tread compoundComponentStyrene-butadiene rubberButadiene rubberCarbon black, N 339Aromatic plasticizerIso-propyl-p-phenylendiamine (IPPD)Trimethylquinoline-polymer (TMQ)Cyclohexylbenzthiazolsulfenamide (CBS)1)Diphenylguanidine (DPG)Sulfur1)Amount in phr802080251.01.01.50.52alternatively tertiary butylbenzthiazolsulfenamide (TBBS)The vulcanization time (t90) is 6.5 minutes at a temperature of 170°C.Measurements in the closed system:The examination of vulcanization fumes using the „Dynamic Headspace Method“ [3,32]resulted in the chromatogram in Fig. 1 [3,32]. In the „Dynamic Headspace Method“vulcanization is carried out in a closed system and all of the released substances are passedinto the analysis system loss-free. The analysis system is one linking gas chromatography withmass spectroscopy (GC-MS). The chromatogram shows the maximum expected emissionswhen vulcanizing the tire tread compound shown above.
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