Electroscrubbers for removing volatile organic compounds and odorous substances from polluted gaseous streams

The treatment of waste gaseous streams has become an important topic of environmental concern. One promising technology is electroabsorption which combines two important treatment processes into a single unit. In this sense, this review compiles the information available in the recent literature showing the hybridization of absorption units with electrochemical cells for treatment of gases polluted with volatile organic compounds and odorous substances. This approach is compared with other competing technologies, paying special attention to the technology readiness level. Although from the laboratory tests, it appears to be a promising methodology for the degradation of volatile organic compounds and environmental odorous gases; this critical review points out that more research is needed to raise the technology readiness level of this treatment technology in a context in which the society is demanding more and more sustainable technologies.     

CO removal by two-stage methanation for polymer electrolyte fuel cell

In order to remove CO to achieve lower CO content of below 10 ppm in the CO removal step of reformer for polymer electrolyte fuel cell （PEFC） co-generation systems, CO preferential methanation under various conditions were studied in this paper. Results showed that, with a single kind of catalyst, it was difficult to reach both CO removal depth and CO2 conversion ratio of below 5%. Thus, a two-stage methanation process applying two kinds of catalysts is proposed in this study, that is, one kind of catalyst with relatively low activity and high selectivity for the first stage at higher temperature, and another kind of catalyst with relatively high activity and high selectivity for the second stage at lower temperature. Experimental results showed that at the first stage CO content was decreased from 1% to below 0.1% at 250-300 ℃, and at the second stage to below 10 ppm at 150-185 ℃. CO2 conversion was kept less than 5%, At the same time, influence of inlet CO content and GHSV on CO removal depth was also discussed in this paper.     

Composition and major odorous compounds of the essential oil of Bifora radians,an aldehyde-producing weed

The composition of the essential oil of Bifora radians, an aldehyde-producing weed, has been investigated by capillary gas chromatography, coupled gas chromatography – mass spectrometry, on-line catalytic hydrogenation and coupled gas chromatography – infrared spectrometry. The nineteen compounds identified included eighteen aldehydes: seven alkanals (C6, C9, C10, C11, C12, C13, and C14), ten alkenals, including five (E)-2-alkenals (C12, C13, C14, C15, and C16), and one (E,E)-2,4-alkadienal (C13). Typical Bifora odors were attributed to three major (E)-2-alkenals, C12, C13, and C14.     

Use of peat-based sorbents for removal of arsenic compounds

It is important to apply sorbent materials for purification of water from arsenic contamination due to serious arsenic pollution worldwide. We have developed new sorbents based on natural materials that provide a cheap and environmentally friendly alternative. For the first time, peat modified with iron compounds and iron humates were tested for sorption of arsenic compounds. The highest sorption capacity was found in peat modified with iron compounds. We have found that sorption of different arsenic speciation forms was strongly dependent on solution pH, reaction time and temperature. Calculations of the sorption process using thermodynamic parameters indicate the spontaneity of sorption process and its endothermic nature. Sorption kinetics showed that most arsenates are removed within 2 hours, and the kinetics of arsenate sorption on modified peat can be described by the pseudo-second order mechanism.      

An evaluation of two calibration procedures using thermal desorption-gas chromatography in the analysis of odorous volatile compounds

In this study, the relative performance of gas chromatography (GC) was investigated with respect to the differences in two types of calibration approaches with a thermal desorption (TD) method: the fixed standard concentration approach (FSC: the comparison of different sample volumes for a given standard) was compared with the fixed standard volume approach (FSV: the comparison of different concentration standards at a fixed loading volume). Gaseous working standards of seven odorants, including methyl ethyl ketone (MEK), butyl acetate, methyl isobutyl ketone, isobutyl alcohol, toluene, xylene, and a reference component, benzene, were prepared at four concentration levels (10-100 ppb). They were then analyzed by controlling the TD-loading volumes at six levels (40-1200 mL). The results derived by these contrasting calibration approaches showed moderate changes in the GC sensitivity, either with an increasing concentration (i.e., FSC), or with an increasing sample loading volume (i.e., FSV). Despite an eccentric trend of MEK, the TD-based analysis was fairly predictable and can be recommended for the analysis of the selected odorants.     

Application of hydrophobic silica based aerogels and xerogels for removal of toxic organic compounds from aqueous solutions

This work is devoted to the application of hydrophobic silica based aerogels and xerogels for the removal of three toxic organic compounds from aqueous solutions. These materials were tested and characterized regarding their morphology, particle size distribution, surface area and porous structure. The equilibrium tests were carried out at different adsorbate concentrations and the experimental data were correlated by means of Langmuir and Freundlich isotherms. The equilibrium data were well described by Langmuir and Freundlich in most cases. The maximum adsorption capacity by Langmuir model was observed for the adsorption of benzene onto aerogel (192.31 mg/g), though the most promising results were obtained for toluene adsorption due to the greater adsorption energy involved. Comparing these results with other reported results, the hydrophobic silica based aerogels/xerogels were found to exhibit a remarkable performance for the removal of benzene and toluene. In addition, the regeneration of previously saturated aerogel/toluene was also investigated by using an ozonation process. The adsorption/regeneration tests with ozone oxidation showed that the aerogel might be regenerated, nevertheless the materials lost their hydrophobicity and thus different methods should be evaluated in forthcoming investigations.     

Optimal control of a two-stage reactor system

Optimal operation policies were investigated for a batch reactor system with two different operation stages. At the end of the first nonisothermal stage one of the reactants was added. Since that moment the reactor was operated isothermally. In each stage behavior of the reactor was described by a set of differential equations. The maximum conversion problem was investigated subject to various operating constraints. Dynamic optimization based on the control vector parametrization was used to find the optimal control profile. Gradients of the resulting nonlinear programming problem were obtained by adjoint method based on the optimal control theory.     

Differentiation of isomeric compounds by two-stage proton transfer reaction time-of-flight mass spectrometry

We investigated a two-stage ion source for proton transfer reaction (PTR) ionization to achieve more selective mass spectrometric (MS) detection of selected volatile organic compounds (VOCs) than that achieved with commonly used PTR-MS instruments, which are based on single-step PTR ionization with H3O+. The two-stage PTR ion source generated reagent ions other than H3O+ by an initial PTR between H3O+ and a selected VOC, and then a second PTR ionization occurred only for VOCs with proton affinities larger than the affinity of the reagent VOC. Acetone and acetonitrile were useful as reagent VOCs because they provided dominant peaks as a protonated form. Using two-stage PTR-MS, we differentiated isomeric VOCs (for example, ethyl acetate and 1,4-dioxane) by means of differences in their proton affinities; protonated acetone formed the [M + H]+ ion from ethyl acetate but not from 1,4-dioxane. The PTR-MS-derived concentrations agreed quantitatively with those independently determined by Fourier transform infrared spectroscopy (FT-IR) at parts per million by volume (ppmv) levels. In addition, interfering fragment ions formed from alkyl benzenes at m/z 79 (C6H7+) could be distinguished from the m/z 79 ion arising from protonation of benzene, and therefore this method would prevent overestimation of benzene concentrations in air samples in which both benzene and alkyl benzenes are present. This two-stage PTR ionization may be useful for distinguishing various isomeric species, including aldehydes and ketones, if appropriate reagent ions are selected.     

Performance of fibrous bed bioreactor for treating odorous gas

A fibrous bed bioreactor was used for treatment of odorous volatile fatty acid (VFA). The effect of gaseous VFA (acetic, propionic, and butyric acids) mass loading on the bioreactor performance was investigated. The VFA degrading microbial culture was selected from activated sludge by the three VFAs using a shake-flask culture. The selected microorganisms were then immobilized in a biofilter using cotton fabric as packing material. In the biofiltration experiment, the inlet gas flow rates ranged from 1 to 4 L/min, the total VFA concentrations ranged from 0.10 to 0.43 g/m³, and the resulting total mass loadings of VFA studied ranged from 9.7 to 104.3 g/m³/h. At total mass loading of 104.3 g/m³/h, the VFA removal efficiency was 87.7%. Higher removal efficiencies (>90%) were achieved at mass loadings below 50.3 g/m³/h.     

KF-Silica as a stationary phase for the chromatographic removal of tin residues from organic compounds

Through the simple expedient of using a mixture of KF and silica as the stationary phase in column chromatography, levels of organotin impurities from tributyltin hydride mediated reductions have been reduced from stoichiometric levels to approximately 30 ppm.     

Application of clathrate compounds for hydrogen storage

The review considers current works on clathrate hydrogen compounds, aimed at creating hydrogen accumulators suitable for practical application. Analysis of published data showed that clathrate hydrates formed by pure hydrogen are unsuitable for this purpose in view of their fairly low limiting hydrogen content and the necessity for their synthesis of extremely high pressures (>100 MPa) that are still industrially unfeasible. The possibilities for hydrogen storage in double (including auxiliary guest molecules along with hydrogen) clathrate hydrates are considered. It is concluded from published data that sorbents on the basis of the so-called “metal-organic frameworks” (MOFs) with a pore size of 1–2 nm hold a greater promise for hydrogen storage at temperatures of about 100 and moderately (up to 10 MPa) high pressures, but the development of all the considered methods of hydrogen storage has not yet grown out of laboratory experiments.     

Theoretical studies of bond dissociation energies for removal of the nitrile group in some nitrile compounds

The CCN bond distances and bond dissociation energies (BDEs) are estimated by utilizing quantum chemical calculations for 16 nitrile compounds. Since DFT methods have been researched to have low basis sets sensitivity for small and medium molecules in our earlier work [Jun Zhao, Xinlu Cheng, Xiangdong. Yang, J. Mol. Struct. (Theochem) 766 (2006) 87] 16 nitrile compounds are studied by employing the hybrid density functional theory (B3LYP, B3PW91, B3P86) and the complete basis set (CBS-Q) method in conjunction with the 6-311G^** basis set. The obtained results are compared with the available experimental data. It is demonstrated that CBS-Q method, which can produce reasonable BDEs for some systems, seems unable to predict accurate BDEs here. While, the B3P86 calculated results agree very well with the experimental values. So B3P86 method is suitable for computing the reliable BDEs of CCN bond for nitrile compounds.     

Application of gas chromatograph-mass spectrometer-computer system to evaluation of 14C-labelled compounds

Usefulness of gas chromatograph-mass spectrometer-computer system (GC-MS-CPU) not only for measurement of specific activities of 14C-labelled compounds in a mixture but also for evaluation of 14C-labelled compounds in terms of examining their purities and elucidating chemical structures of the impurities was proved. A sample of methyl 2-(p-chlorophenyl-14Cn)-3-methylbutylate (III) synthesized from p-chlorophenyl-14Cn-acetonitrile (VI) was analyzed by GC-MS-CPU, and it was found that the labelled compound was contaminated with a small amount of the corresponding m-isomer (IV) having a very high specific activity. Further examination suggested that the contaminating m-isomer (IV) originated from m-chlorophenyl-14Cn-acetonitrile (IX) which had already contaminated in the starting material (VI), and also that cyanomethylation of p-dichlorobenzene-14Cn (VIII) by benzene-type reaction resulted in producing a mixture of p- and m-chlorophenyl-14Cn-acetonitriles (VI, IX).     

GC-MIP-PED as an element-specific system for the determination of organomercury compounds

The application of the combination of gas chromatography and a self-developed plasma emission detector for organomercury speciation is presented. The system, basing on interference filter technology, is described briefly. The plasma and the optical system have to be optimized to reach highest sensitivity for mercury detection. Dimethyl-, methyl- and inorganic mercury as selected compounds have been separated on a GC column and calibrated to obtain the analytical performance data of the system used. Finally, the analysis of some real samples has been performed.     

Application of thermal analysis to the study of the kinetics of two-stage reactions

A method is suggested for studying the kinetic parameters of two-stage reactions from thermoanalytical experimental data. The method allows determination of the kinetic characteristics of the process on the basis of integral thermoanalytical data, without separation of the individual stages. Parallel, independent and successive reactions taking place under isothermal and non-isothermal conditions are considered.

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Zusammenfassung Eine Methode zur Untersuchung der kinetischen Parameter von Zweistufenreaktionen unter Verwendung experimenteller thermoanalytischer Daten wird vorgeschlagen. Die Methode ermöglicht, die kinetischen Kennwerte des Prozesses basierend auf integralen thermoanalytischen Werten ohne Trennung der individuellen Schritte zu bestimmen. Unter isothermen und nichtisothermen Bedingungen parallel, unabhängig voneinander und nacheinander verlaufende Reaktionen werden diskutiert.

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Dynamic system for the calibration of semi-volatile carbonyl compounds in air

A dynamic calibration system designed for generating accurate and precise concentrations of semi-volatile carbonyls in the ppb (v/v) (ppbv)-ppt (v/v) (pptv) range has been developed and tested. Alkanals from C6 to C9 were used as test compounds. Diffusion rates of their vapours from capillary tubes were determined theoretically and with two methods whose accuracy was independently evaluated with liquid standard solutions. Methods selected for testing the calibration system were those commonly used for the selective quantification of carbonyls in air. One is based on the well-known reaction with 2,4-dinitrophenylhydrazine (DNPH), followed by the analysis of formed hydrazones by HPLC-UV. The other is based on the retention of carbonyls on graphitic carbon adsorbents, followed by MS detection of the sample injected into a capillary column by thermal desorption. A good consistency was found between the values of the diffusion rates determined by the two methods. The scatter between the two methods was in the range of +/-10% when diffusion rates of ca. 1 ng/s were attained. Experimental values closely approached those calculated by applying the equation describing the diffusion of a vapour in equilibrium with the liquid through a capillary tube.     

Cleavable dicationic surfactant micellar system for the decomposition of organophosphorus compounds

A dimeric (gemini) surfactant containing cleavable ester groups has been synthesized and studied. The new surfactant has a low critical micelle concentration (2.7∙10^–5 mol/L) and Krafft temperature (≤0°C). Alkaline hydrolysis of 4-nitrophenyl diethyl phosphonate and 4-nitrophenyl diethyl phosphate in the presence of micelles of gemini surfactant I proceeds 30-144 times more rapidly than in water. Chemical cleavage of gemini surfactant I in an alkaline medium is achieved in 96 h.     

固体碱对油品中有机硫化物的脱除性能及分析

预碱洗（电精制）是轻质油品精制中的重要环节,通过氢氧化钠水溶液预碱洗可除去油品中的硫化氢、低分子硫醇等酸性物质,但大量含硫废碱液的排放给环保造成很大压力。以固体碱代替液体碱预碱洗,是减少甚至消除废碱液产生和排放的最有效措施。近十几年来,许多学者致力于固体碱对轻质油品中硫醇、硫化氢的脱除研究。     

Adsorptive removal of nitrogen-containing compounds from fuel by metal-organic frameworks

The adsorptive denitrogenation from fuels over three metal-organic frameworks(MIL-96(Al),MIL-53(Al)and MIL-101(Cr))was studied by batch adsorption experiments.Four nitrogen-containing compounds(NCCs)pyridine,pyrrole,quinoline and indole were used as model NCCs in fuels to study the adsorption mechanism.The physicochemical properties of the adsorbents were characterized by XRD,N2physical adsorption,FT-IR spectrum and Hammett indicator method.The metal-organic frameworks(MOFs),especially the MIL-101(Cr)containing Lewis acid sites as well as high specific surface area,can adsorb large quantities of NCCs from fuels.In addition,the adsorptive capacity over MIL-101(Cr)will be different for NCCs with different basicity.The stronger basicity of the NCC is,the more it can be absorbed over MIL-101(Cr).Furthermore,pore size and shape also affect the adsorption capacity for a given adsorbate,which can be proved by the adsorption over MIL-53(Al)and MIL-96(Al).The pseudo-second-order kinetic model and Langmuir equation can be used to describe kinetics and thermodynamics of the adsorption process,respectively.Finally,the regeneration of the used adsorbent has been conducted successfully by just washing it with ethanol.