Removal Rate Constants for Singlet Methylene with Oxygen-Containing Organic Species

The work described in this and the following paper is a continuation of that in parts I and II, devoted to elucidation of the mechanism of the reactions of methylene with chloroalkanes, with particular reference to the reactivities of singlet and triplet methylene in abstraction and insertion processes. The products of the reaction between methylene, prepared by the photolysis of ketene, and 1-chloropropane have been identified and estimated and their dependence on reactant pressures, photolysing wavelength and presence of foreign gases (oxygen and carbon monoxide) has been investigated. Both insertion and abstraction mechanisms contribute significantly to the over-all reaction, insertion being relatively much more important than with chloroethane. This type of process appears to be confined to singlet methylene. If, as seems likely, there is no insertion into C—Cl bonds under our conditions (see part IV), insertion into C2—H and C3—H bonds occurs in statistical ratio, approximately. On the other hand, the chlorine substituent reduces the probability of insertion into C—H bonds in its vicinity. As in the chloroethane system, both species of methylene show a high degree of selectivity in their abstraction reactions. We find that k S Cl / k S H >7.7, k T Cl / k T H < 0.14, where the k ’s are rate constants for abstraction, and the super- and subscripts indicate the species of methylene and the type of atom abstracted, respectively. Triplet methylene is discriminating in hydrogen abstraction from 1-C 3 H 7 Cl, the overall rates for atoms attached to C1, C2, C3 being in the ratios 2.63:1:0.

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Limitations in Studying the Kinetics of Fabric Detergency

Textile Research Journal ◽

10.1177/004051757604600614 ◽

1976 ◽

Vol 46 (6) ◽

pp. 459-462 ◽

Cited By ~ 3

Author(s):

Hans Schott

Keyword(s):

Rate Constants ◽

Soil Removal ◽

Removal Rate ◽

Fiber Surface ◽

Natural Soil ◽

Residual Soil ◽

Washing Process ◽

Two Factors ◽

Surface Irregularities ◽

Particulate Soil

The simplest expressions for the rate of removal of particulate soil from fabrics, including those for first-order kinetics, are described. Two factors militate against obtaining proportionality constants between a time function and a residual soil function which remain constant for long washing times, namely: redeposition, and heterogeneities in soil and fabric. Soil redeposition tends to lower the observed soil-removal rate. This effect can be eliminated by suitable experimental procedures. However, the inhomogeneities inherent in fabrics (fiber surface irregularities, variation in spaces between fibers and yarns) cause them to have sorption sites with a broad range of soil binding strengths. Variations in the size and shape of particles on artificial test fabrics and, for natural soil, in chemical composition as well, cause the particles to adhere to fabric substrates with bonds of different strengths. These heterogeneities produce a broad range of specific soil-removal rates whose values depend on the energies of adhesion of the particle-fabric complex. The most loosely held soil, with the highest removal rate constants, is washed off early so that the soil remaining on the fabric becomes progressively richer in the most tightly bound soil, with the smallest removal rate constants. Hence the average or observed rate constant for soil removal decreases during the washing process.

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Mass transfer approach and the designing of horizontal subsurface flow constructed wetland systems treating waste stabilisation pond effluent

Water Science & Technology ◽

10.2166/wst.2019.031 ◽

2018 ◽

Vol 78 (12) ◽

pp. 2639-2646 ◽

Cited By ~ 3

Author(s):

Anita M. Rugaika ◽

Damian Kajunguri ◽

Rob Van Deun ◽

Bart Van der Bruggen ◽

Karoli N. Njau

Keyword(s):

Mass Transfer ◽

Constructed Wetlands ◽

Rate Constants ◽

Removal Rate ◽

Subsurface Flow ◽

Oxygen Demand ◽

Domestic Wastewater ◽

Organic Load ◽

Mass Transfer Effect ◽

Horizontal Subsurface Flow

Abstract Pilot-scale constructed wetlands (CWs) that allowed wastewater to flow with high interstitial velocities in a controlled environment were used to evaluate the possibility of using mass transfer approach to design horizontal subsurface flow constructed wetlands (HSSF-CWs) treating waste stabilisation ponds (WSPs) effluent. Since CW design considers temperature which is irrelevant in tropics, mass transfer approach could improve the design. HSSF-CWs were operated in batch recycle mode as continuous stirred tank reactors (CSTR) at different interstitial velocities. The overall removal rate constants of chemical oxygen demand (COD) at various interstitial velocities were evaluated in mesocosms that received pretreated domestic wastewater. The mean overall removal rate constants were 0.43, 0.69, 0.74 and 0.73 d−1 corresponding to interstitial velocities of 15.43, 36, 56.57 and 72 md−1, respectively. Results showed that the interstitial velocities up to 36 md−1 represented a range where mass transfer effect was significant and, above it, insignificant to the COD removal process. Since WSPs effluent has high flow rates and low organic load, it is possible to induce high interstitial velocities in a HSSF-CW treating this effluent, without clogging and overflow. The performance of these HSSF for tertiary treatment in tropical areas could be improved by considering flow velocity when designing.

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SINGLET METHYLENE FROM THERMAL DECOMPOSITION OF DIAZOMETHANE. UNIMOLECULAR REACTIONS OF CHEMICALLY ACTIVATED CYCLOPROPANE AND DIMETHYLCYCLOPROPANE MOLECULES

Canadian Journal of Chemistry ◽

10.1139/v62-218 ◽

1962 ◽

Vol 40 (7) ◽

pp. 1425-1451 ◽

Cited By ~ 56

Author(s):

D. W. Setser ◽

B. S. Rabinovitch

Keyword(s):

Thermal Decomposition ◽

Rate Constants ◽

Vibrational Energy ◽

Kcal Mole ◽

Thermal Systems ◽

Geometric Isomerization ◽

Wide Range ◽

Structural Isomerization ◽

Quantum Statistical ◽

Singlet Methylene

The thermal decomposition of diazomethane (DM) into singlet methylene radicals and nitrogen has been studied from 225° to 450° in 10:1 olefin–diazomethane mixtures. At 2.5 cm pressure, k = 1.2 × 1012 exp (−34,000/RT) sec−1. The methylene radicals have similar reactivity to methylene generated from photolytic decomposition of DM, as judged by the follow-up reactions with ethylene and cis-butene-2. The structural isomerization reactions of energized cyclopropane and the structural and geometric isomerization of 1,2-dimethyl-cyclopropane (DMC), formed from the addition of the thermally generated methylene to the olefins, were measured from 250° to 450° over a wide range of pressures. For comparison, cyclopropane formed from photolysis at 4358 Å and 25° of DM and ethylene was studied. As judged from comparison of the experimental isomerization rate constants, the energy of the cyclopropanes formed at 350° in the thermal DM system is about the same as for cyclopropanes formed by photolysis at 4358 Å of DM at 25°. The experimental rate constants obtained on the assumption of strong collisions are compared with calculated rate constants which are based on quantum statistical models for kE which fit literature data on conventional thermal isomerization of cyclopropane and DMC. From this comparison, the average energies of the formed molecules in the thermal systems are estimated to be between 107 and 115 kcal/mole, depending upon the temperature. Photolysis at 25° of the ketene–ethylene system (3200 Å) and of DM–ethylene system (4358 Å) give cyclopropane characterized as being at 103 and 111 kcal/mole respectively. These energies deduced from kinetic data are compared with available thermochemical quantities; the existing value of ΔHf0(CH2N2) is questioned. Further support for fast intramolecular relaxation of vibrational energy in DMC, relative to the relaxation process for reaction, is noted. Comparison of data in the literature on the ketene and DM photolytic systems strongly suggests that a larger fraction of the excess light energy resides with methylene from ketene (0.65–0.8) than with methylene from DM (0.3–0.5). Various approximations for the calculation of kE are examined and are compared with accurate quantum statistical evaluation.

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ChemInform Abstract: Direct Measurement of Singlet Methylene Removal Rates by Organic Species Containing the -O- and > C = O Moieties.

ChemInform ◽

10.1002/chin.199227104 ◽

2010 ◽

Vol 23 (27) ◽

pp. no-no

Author(s):

W. S. STAKER ◽

K. D. KING ◽

G. J. GUTSCHE ◽

W. D. LAWRANCE

Keyword(s):

Direct Measurement ◽

Removal Rates ◽

Organic Species ◽

Singlet Methylene

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Direct measurements of methoxy removal rate constants for collisions with CH4, Ar, N2, Xe, and CF4 in the temperature range 673–973 K

Symposium (International) on Combustion ◽

10.1016/s0082-0784(89)80106-7 ◽

1989 ◽

Vol 22 (1) ◽

pp. 973-981 ◽

Cited By ~ 7

Author(s):

Paul J. Wantuck ◽

Richard C. Oldenborg ◽

Steven L. Baughcum ◽

Kenneth R. Winn

Keyword(s):

Rate Constants ◽

Removal Rate ◽

Temperature Range ◽

Direct Measurements

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Removal of Emerging Contaminants in Wastewater by Sonolysis, Photocatalysis and Ozonation

Global NEST Journal ◽

10.30955/gnj.002625 ◽

2018 ◽

Vol 21 (2) ◽

pp. 98-105 ◽

Cited By ~ 1

Keyword(s):

Rate Constants ◽

Photocatalytic Oxidation ◽

Advanced Oxidation Processes ◽

Emerging Contaminants ◽

Removal Rate ◽

Experimental Conditions ◽

Oxidation Processes ◽

First Order ◽

Performance Variation ◽

Pseudo First Order

<p>Three different advanced oxidation processes (AOPs) were applied to investigate the removal of emerging contaminants (ECs) i.e. sulfamethoxazole (SMX), diclofenac (DCF) and carbamazepine (CBZ) in synthetically prepared solutions. The degradation of these substances was carried out by ozonation, sonolysis and photocatalytic oxidation, as well as by different combinations of these processes. The objectives of this work were to evaluate the removal efficiency in each AOP and to assess the performance variation of sonolysis in combination with other AOPs. The best performances were achieved by sonocatalysis, which resulted in the removal of the selected pharmaceuticals in the range between 37% and 47%. Under similar experimental conditions, the removal of the selected ECs by single compounds by ozonation was slightly lower than the removal of respective compounds in the mixture. Moreover, pseudo first-order removal rate constants of photocatalytic mineralization were determined as 9.33×10-2, 4.90×10-3, 1.06×10-2 min-1 for SMX, DCF and CBZ, respectively.</p>

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Trace Organic Removal during River Bank Filtration for Two Types of Sediment

Water ◽

10.3390/w10121736 ◽

2018 ◽

Vol 10 (12) ◽

pp. 1736 ◽

Cited By ~ 8

Author(s):

Victoria Burke ◽

Laura Schneider ◽

Janek Greskowiak ◽

Patricia Baar ◽

Alexander Sperlich ◽

...

Keyword(s):

Rate Constants ◽

Prediction Models ◽

Removal Rate ◽

Substantial Improvement ◽

Bank Filtration ◽

Field Site ◽

River Bank ◽

Spatial Differences ◽

Trace Organic ◽

River Bank Filtration

The process of bank filtration acts as a barrier against many anthropogenic micropollutants, such as pharmaceuticals and industrial products, leading to a substantial improvement of groundwater quality. The performance of this barrier is, however, affected by seasonal influences and subject to significant temporal changes, which have already been described in the literature. Much less is known about spatial differences when considering one field site. In order to investigate this issue, two undisturbed cores from a well-investigated bank filtration field site were sampled and operated in the course of a column study. The ultimate aim was the identification and quantification of heterogeneities with regard to the biodegradation of 14 wastewater derived micropollutants, amongst others acesulfame, gabapentin, metoprolol, oxypurinol, candesartan, and olmesartan. While six of the compounds entirely persisted, eight compounds were prone to degradation. For those compounds that were subject to degradation, degradation rate constants ranged between 0.2 day−1 (gabapentin) and 31 day−1 (valsartan acid). Further, the rate constants consistently diverged between the distinct cores. In case of the gabapentin metabolite gabapentin-lactam, observed removal rate constants differed by a factor of six between the cores. Experimental data were compared to values calculated according to two structure based prediction models.

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