New Theory And Technology Of Static Headspace Analysis And Its Application In Pulp And Paper Related Researches

As a vapor-phase extraction technique, static headspace gas chromatography （HS-GC） isan indirect detection technology with high accuracy, sensitivity and automaticity. HSextraction is not only successful in eliminating the effects of solvent and non-volatilecomponents in sample matrix on GC analysis or the possible damage to instrument system,but also greatly simplifies the steps of sample pretreatment, saves time, and avoids the analyteloss during sample preparation. It is very suitable for the determination of analytes in processsamples with high complexity of matrices, such as raw materials, waste effluents, andproducts in pulp and paper industry. However, as a relatively new technology, there is still agreat potential to explore some new theories and techniques for the headspace based analysis,from which the quantification for many difficult industrial samples can be performed byHS-GC.In order to improving the accuracy and detection sensitivity in headspace analysis, wehave established some new theories of headspace sampling based on mass balance, pressurebalance, and pressure and temperature effects at the equilibrium states. The relations ofanalyte evaporation rate and detection sensitivity with the solvent saturated vapor pressure,temperature, gas-liquid partition coefficient, and sample loop volume have been investigatedfor the typical headspace analysis’ techniques, i.e., phase equilibrium, solvent fullvaporization-full evaporation technique （FET）, solvent partial vaporization-FET,non-volatile solvent-FET. Several methodologies have developed for improving the detectionsensitivity in headspace analysis. Moreover, a tracing （using oxygen in sample vial air）detection method that is able to measure the sample’ density/volume has been established.In order to improve detection sensitivity for trace amount of volatile analytes andovercome the water-vapor problem met in HS-GC-MS analysis for aqueous samples, asolvent full solidification full evaporation technique （SFS-FET） has been developed. Thistechnique can avoid the dilution of solvent vaporization on analytes in vapor, reduce theexpansion coefficient of gas phase in headspace vial during venting, and eliminate the effectof gas-liquid coefficient of analytes on its evaporation rate. The SFS-FET could not onlygreatly increase the detection sensitivity （from2to6orders of magnitude）, but also avoid theimpacts of solvent on GC detector and its column separation, which makes it possible toconduct a HS-GC-MS analysis at high temperature for aqueous samples. The limits ofquantification in the new method were60ppb, which is1800times low of the traditional FETmethod in methanol testing. This technique has been successfully applied to the determination of methanol in oxygen delignification （OD） effluents and pulp washing filtrate.Based on the above method for methanol, we conducted series of investigations on themethanol formation during OD processes of wheat straw, southern pine, and eucalyptus pulpwith high and low kappa number, respectively, from which a modified first-order kineticmodel was developed and it is suitable to describe the methanol formation in these processes.Combined the kinetic model for lignin removal with the variation of pulp viscosity, weproposed the methanol control strategies at these processes. For the processes of wheat strawand eucalyptus pulp, their kinetic parameters are uniform. The reaction conditions of ODprocess have no influence on the linear relationship between the amounts of methanol and thekappa number of pulps. For southern pine pulp, the improvement of the reaction efficiencycould also significantly reduce the methanol amount （>50%） generated in the process.Based on phase reaction conversion headspace analysis, a batch testing method for theresidual hydrogen peroxide （with potassium permanganate） and oxalate （with potassiumiodate）, respectively, in bleaching effluents were developed. Moreover, an indirect detectionmethod for formaldehyde in the tissue paper and microcapsules latex, using sodiumborohydride as reducing agent in both cases, was also developed. The results showed thatthese methods could meet the testing requirements in these sample analyses, in which theaccuracies of the method were better than95%and LOQ for H₂O₂, C₂O₄^-, CH₂O, and CH₂Owere2.8,13,7.7, and5.7ppm respectively. It was found that using42.5%phosphoric acid asa pretreatment reaction medium could completely dissolve the paper fibers, thus the methanolentrapped in paper products could be released and quantitatively measured by the HS-GCmethod mentioned above.Based on the tracing headspace analysis technique, the viscosity of a concentrated fluidsample at high temperature was determined, in which a two-phase unsteady-state model wasderived. The tracing headspace analysis technique was also used for measuring the averageparticle size of nano-particles of a polymer latex, according to the solid adsorptionequilibrium constant of volatile components from a three-phase steady-state model.Based on high pressure SFV-FET, a detection method was established for measuring theproportional coefficients between analytes’ concentration in gas phase and GC signal. It wasapplied to the study of the air emission of methanol from paper products. A similar approach（coupled with a multiple headspace extraction technique） was also used for in-situ detectionof oxygen formation during the degradation of hydrogen peroxide.