i-Chao Hu

Rapid determination of hydrogen peroxide in pulp bleaching effluents by headspace gas chromatography

A headspace gas chromatographic (HS-GC) method has been developed for the determination of residual hydrogen peroxide in pulp bleaching effluents. The method is based on the reaction of hydrogen peroxide and permanganate in an acidic medium (0.1 mol/L), in which hydrogen peroxide is quantitatively converted to oxygen within 10 min at 60°C in a sealed headspace sample vial. The released oxygen is then determined by GC equipped with a thermal conductivity detector. The method is robust, sensitive, and accurate, with reproducibility characterized by a relative standard deviation of <0.5%, a sensitivity whose limit of quantification (LOQ) is 0.96 μmol, and a demonstrated recovery ranging from 98 to 103%. Further, the method is simple, rapid, and automated.

Determination of methanol in pulp washing filtrates by desiccated full evaporation headspace gas chromatography.

This paper reports on a desiccated full evaporation headspace gas chromatographic (FE HS-GC) technique for determination of the methanol content in dilute mill effluents. Anhydrous K(2)CO(3) was selected as the preferred salt for eliminating the water in the sample in the headspace sample vial. The results showed that the addition of 12 g K(2)CO(3) made it possible to introduce a larger sample size (up to 1 mL) into the FE HS-GC measurement, thereby increasing the sensitivity of the technique. At the given equilibration temperature (105°C), a near-complete mass transfer of methanol from the liquid phase to vapor phase (headspace) was achieved within 10 min. Replicate samples showed that the relative standard deviation of the method was less than 1.5%. Further, the limit of quantification (LOQ) was 0.12 μg and the recovery ranged from 95 to 104%. The present method greatly improves the methanol detection sensitivity in the FE HS-GC method and has the added advantage of being simple, rapid and accurate.

Increasing the sensitivity of headspace analysis of low volatility solutes through water removal by hydrate formation

This paper reports on the development of a new headspace analytical technique that is based on water removal by hydrate formation (WRHF). By adding anhydrous salt, the liquid water in an aqueous sample will be removed leaving behind volatile analytes that are fully vaporized at temperatures well below their boiling points. With WRHF, the amount of sample in the headspace can be significantly increased, thereby dramatically improving the detection sensitivity. The technique reduces the risk of possible column damage in gas chromatography (GC) systems. The technique was applied to the determination of phenol at different stages of a coking wastewater treatment plant. The results showed that up to mL-levels of sample solution can be used in WRHF HS-GC analysis when 5g of CaCl2 were used as the anhydrous salt. The detection sensitivity for phenol content was 500 times greater than that in earlier HS-GC work that did not incorporate hydrate formation. The proposed WRHF headspace analysis technique is simple and practical, making it a useful tool for quantifying low concentrations of volatile analytes in aqueous samples.

A novel method for the determination of black liquor viscosity by multiple headspace extraction gas chromatography

This work demonstrates a novel method for the determination of viscosity in the concentrated black liquors from pulp mill recovery process. The method is based on the kinetic release of methanol (a vapor tracer) to the headspace in a sample closed vial by a multiple headspace extraction gas chromatographic technique. Both theoretical and empirical models were proposed for establishing the correlation with the reference method. The results showed that the correlation using either of the models is excellent for the tested black liquor samples (at 110°C). The presented method is simple and practical and can be a valuable tool for black liquor viscosity related research and applications.

A new headspace gas chromatographic method for the determination of methanol content in paper materials used for food and drink packaging.

This study reports on a method for determination of methanol in paper products by headspace gas chromatography (HS-GC). The method is based on the hydrolysis of the pulp or paper matrix, using a phosphoric acid solution (42.5%) as the medium at 120 °C in 5 h (excluding air contact) in order to release matrix-entrapped methanol, which is then determined by HS-GC. Data show that, under the given conditions of hydrolysis, no methanol was formed from the methoxyl groups in the material. Reproducibility tests of the method generated a relative standard deviation of <3.5%, with recovery in the range of 93.4-102%. The present method is reliable, accurate, and suitable for use in batch testing of the methanol content in paper-related materials. The method can play an important role in addressing food safety concerns that may be raised regarding the use of paper materials in food and beverage packaging.

A novel method for the determination of adsorption partition coefficients of minor gases in a shale sample by headspace gas chromatography

A novel method has been developed for the determination of adsorption partition coefficient (Kd) of minor gases in shale. The method uses samples of two different sizes (masses) of the same material, from which the partition coefficient of the gas can be determined from two independent headspace gas chromatographic (HS-GC) measurements. The equilibrium for the model gas (ethane) was achieved in 5h at 120°C. The method also involves establishing an equation based on the Kd at higher equilibrium temperature, from which the Kd at lower temperature can be calculated. Although the HS-GC method requires some time and effort, it is simpler and quicker than the isothermal adsorption method that is in widespread use today. As a result, the method is simple and practical and can be a valuable tool for shale gas-related research and applications.

Determination of degree of substitution in succinic anhydride modified cellulose by headspace gas chromatography

This paper reports on a headspace gas chromatographic method (HS-GC) for rapid determination of degree of substitution in succinic anhydride (SA) modified celluloses. The method is based on the reaction between the carboxyl groups in SA modified cellulose and bicarbonate solution in a closed headspace sample vial. The CO(2) released from the reaction was measured by HS-GC. The completion of the reaction was achieved within 25 min at 80 °C when a small sample size (<20 mg) was used. The relative standard deviation (RSD) measurement of precision was less than 4.1%, and the results were within 8.0% of those obtained with the traditional titration for determining the degree of substitution. The present method is simple, practical, automated, and suitable for use in anhydride modified cellulose research.

A novel headspace gas chromatographic method for in situ monitoring of monomer conversion during polymerization in an emulsion environment.

This paper describes a novel multiple-headspace extraction/gas chromatographic (MHE-GC) technique for monitoring monomer conversion during a polymerization reaction in a water-based emulsion environment. The polymerization reaction of methyl methacrylate (MMA) in an aqueous emulsion is used as an example. The reaction was performed in a closed headspace sample vial (as a mini-reactor), with pentane as a tracer. In situ monitoring of the vapor concentration of the tracer, employing a multiple headspace extraction (sampling) scheme, coupled to a GC, makes it possible to quantitatively follow the conversion of MMA during the early stages of polymerization. Data on the integrated amount of the tracer vapor released from the monomer droplet phase during the polymerization is described by a mathematic equation from which the monomer conversion can be calculated. The present method is simple, automated and economical, and provides an efficient tool in the investigation of the reaction kinetics and effects of the reaction conditions on the early stage of polymerization.

Experimental data and kinetic models in terms of methanol formation during oxygen delignification processes of alkaline pulps

Abstract This paper reports on the formation of methanol (MeOH) during conventional oxygen delignification (OD) of four typical alkaline pulps, namely, southern pine kraft pulp (SP-KP), wheat straw soda pulp (WS-SP), and eucalyptus kraft pulp (E-KP) with κ numbers (KN) of 32.8 and 16.9 (E-KP32.8 and E-KP16.9). Based on the mass transfer effect of MeOH and a proposed demethoxylation reaction pathway of lignin, two kinds of kinetic models were proposed to predict MeOH formation. The results show that the two-stage pseudo kinetic model with a first-order rate equation is adequate, which was further modified to a first-order kinetic model by means of which MeOH formation during OD of the pulps can be effectively predicted. Finally, the single set of kinetic parameters for the WS-SP, E-KP32.8, and E-KP16.9 pulps was calculated. The proposed kinetic model is considered as a valuable tool for the prediction and control of MeOH formation during OD of various alkaline pulps.

A novel method for rapid determination of total solid content in viscous liquids by multiple headspace extraction gas chromatography.

This work demonstrates a novel method for rapid determination of total solid content in viscous liquid (polymer-enriched) samples. The method is based multiple headspace extraction gas chromatography (MHE-GC) on a headspace vial at a temperature above boiling point of water. Thus, the trend of water loss from the tested liquid due to evaporation can be followed. With the limited MHE-GC testing (e.g., 5 extractions) and a one-point calibration procedure (i.e., recording the weight difference before and after analysis), the total amount of water in the sample can be determined, from which the total solid contents in the liquid can be calculated. A number of black liquors were analyzed by the new method which yielded results that closely matched those of the reference method; i.e., the results of these two methods differed by no more than 2.3%. Compared with the reference method, the MHE-GC method is much simpler and more practical. Therefore, it is suitable for the rapid determination of the solid content in many polymer-containing liquid samples.