Acetone Pressure Research Articles

Influence of Alkalinization Over Metal Organic Frameworks MIL-100(Fe) for Enhanced Volatile Organic Compounds (VOCs) Adsorbents

Substantial attempts have been undertaken for the improvement of the air quality over decades; and Volatile Organic Compounds (VOCs) from the chemical and textile industries are truly listed as severe issue to be controlled. To come up with modus operandi for this issue, a novel composite of metal organic frameworks (MOFs) MIL-100(Fe) with salient tuned features of natrite was designed by a green and facile method. Mineralized composite MOFs exhibited enhanced crystallinity than pure MIL-100(Fe) as well showcased a higher surface area of 1300 m² g-1. Through dynamic acetone pressure swing adsorption setup, MIL-0.05Na (MIL-100(Fe) synthesized with 0.05 mM Na₂CO₃ solution) revealed an enhanced acetone adsorption of 210 mg g 1 at room temperature. Gas phase adsorption isotherms confirmed the mono layer adsorption behavior. The kinetics models evaluated that the external mass transfer was the rate limiting step for surface adsorption. The thermodynamic study manifested that the adsorption reaction was spontaneous and exothermic. The proposed mechanism of adsorption was the act of physisorption which enriched the adsorbents reusability. This research work provides a futuristic vista to design mineralized Fe-MOFs composites for an energy saving adsorbents for VOCs removal.

Extraction of astaxanthin from microalga Haematococcus pluvialis in red phase by using generally recognized as safe solvents and accelerated extraction

Solvent Extraction was tested to extract astaxanthin from Haematococcus pluvialis in red phase (HPR), by investigating effects of solvents, extraction pressure and temperature. Astaxanthin isomers were identified and quantified in the extract. The performances of acetone and ethanol, Generally Recognized As Safe (GRAS) solvents, were explored. Negligible effect of pressure was found, while with increasing extraction temperature astaxanthin recovery increased till a maximum value, beyond which thermal degradation seemed to be greater than the positive effect of temperature on extraction. Furthermore, to maximize the extraction yield of astaxanthin, mechanical pre-treatment of HPR biomass was carried out and several extraction runs were consecutively performed. Experimental results showed that after the mechanical pre-treatment the astaxanthin recovery strongly increased while a single extraction run of 20 min was sufficient to extract more than 99% of total astaxanthin extracted. After pre-treatment, maximum recovery of about 87% was found for acetone (pressure = 100 bar; temperature = 40 °C; total time = 60 min).

Selective conversion of acetone to isobutene and acetic acid on aluminosilicates: Kinetic coupling between acid-catalyzed and radical-mediated pathways

Solid Brønsted acids catalyze aldol condensations that form CC bonds and remove O-atoms from oxygenate reactants, but sequential β-scission reactions also cleave CC bonds, leading to isobutene and acetic acid products for acetone reactants. The elementary steps and site requirements that cause these selectivities to depend sensitively on Al content and framework type in aluminosilicate solid acids remain speculative. Acetone reactions on microporous and mesoporous aluminosilicates (FER, TON, MFI, BEA, MCM-41) showed highest β-scission selectivities on MFI and BEA; they increased as the Al content and the intracrystalline density of active protons decreased. The effects of acetone and H2O pressure on turnover rates and selectivities indicate that an equilibrated pool of reactive C6 ketols and alkenones are present at pseudo-steady-state concentrations during catalysis and that they act as intermediates in β-scission routes. Two distinct C6 β-scission pathways contribute to the formation of isobutene and acetic acid: (i) a minor H2O-mediated route involving β-scission of C6 ketols on protons and (ii) the predominant anhydrous path, in which H-transfer forms unsaturated C6 enols at protons and these enols propagate radical chains mediated by transition states stabilized by van der Waals contacts within vicinal microporous voids. This latter route is consistent with coupled-cluster free energy estimates for these unsaturated C6 enols and their respective free radicals. It accounts for β-scission selectivities that increase with decreasing proton density, a finding that precludes the sole involvement of acid sites and requires instead the kinetic coupling between reactions at protons and propagation steps mediated by transition states confined within proximate voids, even when such voids lack a specific binding site. These mechanistic interpretations also account for the observed effects of residence time, of the loss of active protons by deactivation, of acetone and H2O pressures, and of aluminosilicate framework structure on selectivity. These mechanistic insights also demonstrate the ability of voids to stabilize transition states that mediate homogeneous reactions by mere confinement, even in the absence of chemical binding onto specific sites, as well as the essential requirement of intimate proximity for the effective kinetic coupling between reactions on protons and in proton-free voids, a process mediated by the diffusion of very reactive and unstable intermediates present at very low local concentrations within microporous frameworks.

Elementary steps in acetone condensation reactions catalyzed by aluminosilicates with diverse void structures

The unselective nature and ubiquitous deactivation of Brønsted acids in aldol condensations have precluded their practical use and unequivocal mechanistic assessments. H2 and a Pt function are used here to confer stability by scavenging unsaturated intermediates to form stable products, thus allowing kinetic, spectroscopic, and isotopic assessments of elementary steps and their kinetic relevance, confirmed by density functional theory (DFT), for acetone condensation on microporous and mesoporous aluminosilicates (FER, TON, MFI, BEA, FAU, MCM-41). The selective titration of protons with 2,6-di-tert-butyl pyridine during catalysis shows that condensations occur exclusively on protons; the number of titrants required to suppress reactivity measures accessible sites and allows reactivity to be rigorously reported as turnover rates. Infrared spectra show that H-bonded acetone is present at saturation coverages during condensation catalysis. Taken together with rates that depend linearly on acetone pressure and with the absence of H/D kinetic isotope effects, these data indicate that condensation turnovers are mediated by the kinetically-relevant formation of a CC bond via reactions of H-bonded acetone with another acetone molecule, a conclusion confirmed by DFT-derived free energies along the reaction coordinate. Measured rate constants reflect free energy differences between this transition state and its relevant precursors, a H-bonded and a gaseous acetone. These rate constants (per H+) depend sensitively on size and shape of the confining voids among aluminosilicates of similar acid strength but diverse framework structure. Confinement effects are mediated by van der Waals contacts and are accurately described by energies derived from Lennard-Jones potentials of DFT-derived transition state structures; these energies are ensemble-averaged over all accessible configurations and T-site locations in each aluminosilicate framework. These energy descriptors replace incomplete metrics based solely on the sizes of voids and transition states, which fail to capture differences in reactivity among different confining frameworks.

Note: Characterization of CaF2/acetone bandpass photon detector with Kr filter gas

A modified design of a CaF(2)/acetone bandpass photon detector that uses Kr as a filter gas to tune the energy resolution is presented. Our design combines two standard single window detector tubes to build the Kr filter gas chamber. Synchrotron radiation has been used to determine the energy resolution of the detector, as a function of Kr pressure. The improvement in the detector energy resolution by 250 meV compared to the CaF(2)/acetone detector is better than that reported earlier. Substantial variation in the shape of the CaF(2)/acetone detector response functions is observed for different acetone pressure (≤3 mbar), and anode voltage (≤800 V). Our analysis reveals that the changes in the shape of the detector response function are associated to different regions of the detector operation.

Fabrication and operation of triode electron emitters as ion source for miniature mass spectrometer

We report the fabrication and operation of an ion source that can be incorporated into a micro-time-of-flight mass spectrometer. The ion source consists of an array of triode emitters with carbon-nanoparticle cathodes. We were able to extract an anode current as large as 94.3μA at a gate-bias voltage of 85V with a concomitant gate current of 38nA by using the triode structure having a recessed cathode with no gate overhang. Ion-generation tests with acetone molecules were carried out successfully, and we measured monotonic increases in the ion current and ratio between ion and electron currents with respect to acetone pressure. We also present simulation results that show equipotential and electric-field lines under different electrode-bias configurations.

Optimal operating conditions and characteristics of acetone∕CaF2 detector for inverse photoemission spectroscopy

Performance and characteristics of a band-pass photon detector using acetone gas and CaF2 window (acetone∕CaF2) have been studied and compared with an ethanol∕MgF2 detector. The optimal operating conditions are found to be 4mbar acetone pressure and 745±20V anode voltage. The count rate obtained by us is about a factor of 3 higher than what has been reported earlier for the acetone detector. Unlike other gas filled detectors, this detector works in the proportional region with very small dead time (4μs). A detector bandpass of 0.48±0.01eV full width at half maximum is obtained.

Acetone transformation over Pt/H[Al]ZSM5 and Pt/H[Ga]ZSM5 catalysts: Evidences of a Pt–Ga interaction

Acetone transformation into methyl–isobutyl ketone (MIBK) under hydrogen atmosphere, using bifunctional catalysts of the platinum supported over medium-pore zeolites (MFI)-type, was studied. This methodology offers a number of advantages; however, since it implies working at low hydrogen pressure ( P H 2 ) with respect to the acetone pressure ( P Ac), a rapid catalyst deactivation is observed. Therefore, to minimize deactivation of bifunctional catalysts, a solid with less strong acidic sites has been considered as a platinum support. In this sense, the use of an MFI-type gallosilicate has been deemed convenient to compare the results with those obtained over a catalyst of the platinum/aluminosilicate MFI-type. The H[Al]ZSM5 and H[Ga]ZSM5 solids were synthesized and evaluated by means of DRX, nitrogen adsorption at −196 °C, TPD–NH 3 and chemical analysis, and later used as a support for the metallic phase. Platinum of 0.50 wt.% was introduced by means of the exchange–impregnation method and the Pt(NH 3) 4Cl 2 salt was used as a platinum precursor. The solids were calcinated under dry air flow at 300 °C for 6 h and then reduced under dry hydrogen atmosphere at 500 °C also for 6 h. The bifunctional catalysts obtained, 0.50Pt/H[Ga]ZSM5 (Si/Ga=42) and 0.50Pt/H[Al]ZSM5 (Si/Al=40), were evaluated by means of chemical analysis, nitrogen adsorption, transmission electronic microscopy (TEM), electronic paramagnetic resonance (EPR), and the model reactions of toluene-hydrogenation and n-heptane hydrocracking under the conditions established in previous works. Acetone transformation was run in a dynamic reactor at 160 °C, atmospheric pressure, P Ac/ P H 2 =3 and variable WHSV. The results obtained with the model reactions and the acetone transformation shows that metallic centers in the Pt-gallosilicate catalysts exhibit a much lower hydro-dehydrogenating activity than that of the metallic centers in the Pt-aluminosilicate catalyst; this, together with the EPR results, seems to indicate that a strong interaction between platinum and a species of structural or extra-structural gallium (EFGS) of the support used has occurred over the Pt/H[Ga]ZSM5 catalyst.

Market Prospects

The unselective nature and ubiquitous deactivation of Brønsted acids in aldol condensations have precluded their practical use and unequivocal mechanistic assessments. H2 and a Pt function are used here to confer stability by scavenging unsaturated intermediates to form stable products, thus allowing kinetic, spectroscopic, and isotopic assessments of elementary steps and their kinetic relevance, confirmed by density functional theory (DFT), for acetone condensation on microporous and mesoporous aluminosilicates (FER, TON, MFI, BEA, FAU, MCM-41). The selective titration of protons with 2,6-di-tert-butyl pyridine during catalysis shows that condensations occur exclusively on protons; the number of titrants required to suppress reactivity measures accessible sites and allows reactivity to be rigorously reported as turnover rates. Infrared spectra show that H-bonded acetone is present at saturation coverages during condensation catalysis. Taken together with rates that depend linearly on acetone pressure and with the absence of H/D kinetic isotope effects, these data indicate that condensation turnovers are mediated by the kinetically-relevant formation of a CC bond via reactions of H-bonded acetone with another acetone molecule, a conclusion confirmed by DFT-derived free energies along the reaction coordinate. Measured rate constants reflect free energy differences between this transition state and its relevant precursors, a H-bonded and a gaseous acetone. These rate constants (per H+) depend sensitively on size and shape of the confining voids among aluminosilicates of similar acid strength but diverse framework structure. Confinement effects are mediated by van der Waals contacts and are accurately described by energies derived from Lennard-Jones potentials of DFT-derived transition state structures; these energies are ensemble-averaged over all accessible configurations and T-site locations in each aluminosilicate framework. These energy descriptors replace incomplete metrics based solely on the sizes of voids and transition states, which fail to capture differences in reactivity among different confining frameworks.

Interval kinetic gravimetric sorption of acetone in random copolymers of poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate)

Interval sorption kinetics of acetone in solvent cast films of random poly(ethylene terephthalate)-co-(ethylene 2,6-naphthalate) (PET-co-PEN) are reported at 35°C and at acetone pressures ranging from 0 to 7.3 cm Hg. Polymer composition is varied systematically from 0% to 50% poly(ethylene 2,6-naphthalate). Equilibrium sorption is well described by the dual-mode sorption model. Interval sorption kinetics are described using a two-stage model that incorporates both Fickian diffusion and protracted polymer structural relaxation. The incorporation of low levels of PEN into PET significantly reduces the excess free volume associated with the glassy state and, for these interval acetone sorption experiments in ∼ 5 μm-thick films, decreases the fraction of acetone uptake controlled by penetrant-induced polymer structural relaxation.

Acetone solubility and diffusivity in poly(ethylene terephthalate) modified with low levels of 2,6-naphthalene dicarboxylic acid, isophthalic acid, and 2,5-bis-(4-carboxyphenyl)-1,3,4-oxadiazole

A series of random copolyesters was prepared by replacing up to 10 wt.% of the dimethyl terephthalate (DMT) in poly(ethylene terephthalate) (PET) with dimethyl 2,6-naphthalene dicarboxylate (NDC), isophthalic acid (IPA), or 2,5-bis-(4-carboxyphenyl)-1,3,4-oxadiazole (ODCA). Solution cast films of the resulting copolymers were prepared and characterized. Modification of PET with NDC and ODCA led to copolymers with glass transition temperatures higher than that of PET, while modification with IPA decreased the glass transition temperature. Copolymerization decreased crystallinity levels in all cases. The acetone solubility and acetone diffusion coefficient were determined by integral kinetic gravimetric sorption experiments at 35°C and 5.4 cm Hg acetone pressure. PET containing low levels of NDC had lower amorphous phase acetone diffusivity and solubility than PET, while PET modified with IPA had amorphous phase acetone diffusivity and acetone solubility similar to that of PET. PET modified with 5% ODCA had amorphous phase acetone diffusivity similar to that of PET, while PET modified with 10% ODCA had an amorphous phase acetone diffusivity value slightly lower than that of PET. Copolymers containing ODCA had somewhat higher acetone solubilities that PET, due mainly to the lower levels of crystallinity in the ODCA-containing polymers than in PET.

Chemistry at and near the Surface of Liquid Sulfuric Acid: A Kinetic, Thermodynamic, and Mechanistic Analysis of Heterogeneous Reactions of Acetone

The interactions of gas-phase acetone with liquid sulfuric acid solutions are described. The solutions were prepared as 0.05−0.10 μm thick films deposited on single-crystal metal substrates. Experiments were carried out over broad ranges of acid composition (70 − >96 wt % H2SO4), temperature (180−220 K), and acetone pressure (10-7−10-3 Pa). Two types of measurements are reported: the time-dependent acetone uptake probability, and the infrared spectra of absorbed acetone and its reaction products. From the infrared measurements, a reaction scheme is identified in which gas-phase acetone is taken up by sulfuric acid to form protonated acetone. In solutions containing more than 70 wt % H2SO4, protonated acetone undergoes a self-condensation/dehydration reaction to form mesityl oxide. In films that contain 85 wt % or more H2SO4, a second reaction sequence occurs, ultimately resulting in the formation of trimethylbenzene. The uptake probability measurements are consistent with the infrared data. In 70 wt % H2SO4, the acetone uptake probability rapidly decreases from an initial value near unity to a steady-state value of zero, due to the formation of a saturated acetone + sulfuric acid solution. The Henry's law solubility constants of acetone in 70 wt % H2SO4 were obtained from the integrated uptake measurements. The temperature dependence of the measurements implies that the standard-state enthalpy and entropy changes of acetone solution in 70 wt % sulfuric acid are −66 kJ mol-1 and −249 J mol-1 K-1, respectively. In the more concentrated films, the steady-state uptake probability is never measured to be zero, since absorbed acetone goes on to form the condensation/dehydration products. A two-step kinetic scheme is proposed to account for the reactions of acetone in sulfuric acid. By fitting the data to the model predictions, the Henry's law solubility constants and the reaction rate constants may be estimated.

Acetone sorption and uptake kinetic in poly(ethylene terephthalate)

The sorption and kinetics of acetone uptake in solvent cast films of poly(ethylene terephthalate) are reported at 35°C for acetone pressures ranging from 0 to 7.3 cm Hg. The equilibrium sorption isotherm is well described by the dual-mode sorption model with the following parameters: k D=61 cm 3(STP)/(cm 3·atm), C ′ H =7.2 cm 3( STP)/cm 3 , and b=50 atm −1. Sorption kinetics are described using a two-stage model which incorporates both Fickian diffusion and protracted polymer structural relaxation. The characteristic time associated with the relaxation process is essentially independent of acetone concentration and has an average value of approximately 15 hours. The fraction of sorption associated with polymer relaxation increases linearly with acetone concentration in the equilibrium-densified matrix of the polymer. Acetone diffusion coefficients increase with increasing acetone concentration. The concentration dependence of the acetone diffusion coefficient is well described by the dual-mobility model if the assumption of constant diffusion coefficients in the two modes is relaxed.

Synthesis, physical characterization, and acetone sorption kinetics in random copolymers of poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate)

Random copolymers of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalate) (PEN) were synthesized by melt condensation. In a series of thin, solvent cast films of varying PEN content, acetone diffusivity and solubility were determined at 35°C and an acetone pressure of 5.4 cm Hg. The kinetics of acetone sorption in the copolymer films are well described by a Fickian model. Both solubility and diffusivity decrease with increasing PEN content. The acetone diffusion coefficient decreases 93% from PET to PET/85PEN, a copolymer in which 85 weight percent of the dimethyl terephthalate in PET has been replace by dimethyl naphthalate 2,6-dicarboxylate. The acetone solubility coefficient in the amorphous regions of the polymer decreases by approximately a factor of two over the same composition range. The glass/rubber transition temperatures of these materials rise monotonically with increasing PEN content. Copolymers containing 20 to 80 wt % PEN are amorphous. Samples with 80% PEN contain measurable levels of crystallinity. Estimated fractional free volume in the amorphous regions of these samples is lower in the copolymers than in either of the homopolymers. Relative free volume as probed by positron annihilation lifetime spectroscopy (PALS) decreases systematically with increasing PEN content. Acetone diffusion coefficients correlate well with PALS results. Infrared spectroscopy suggests an increase in the fraction of ethylene glycol units in the trans conformation in the amorphous phase as the concentration of PEN in the copolymer increases. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2981–3000, 1998

Chemometric approach to evaluate the parameters affecting the determination of reaction rate constants by ion trap mass spectrometry

The effects of experimental parameters on kinetic measurements performed with an ion trap mass spectrometer have been investigated by a chemometric approach using Experimental Design techniques. The selected experiment was the determination of the rate constant of the reaction CH 3CO ++CH 3COCH 3 → CH 3CO(H)CH 3 ++CH 2CO. In a first step, eight variables were studied: temperature, acetone pressure, buffer gas pressure, method of ion selection, ionization start mass, ionization time, mass range, and reaction time. The results show that isolation method and reaction time were the only parameters affecting rate constants determination, although temperature may be considered a “borderline” factor. The remaining parameters and their interactions do not significantly affect the kinetic measurements. A second series of runs was performed to check again the effect of reaction time, temperature, and ionization time in experiments with or without ion selection in order to compare the results of the present work with those obtained in a similar study on a Fourier transform-ion cyclotron resonance instrument.

Pure and mixed gas acetone/nitrogen permeation properties of polydimethylsiloxane [PDMS

The permeability of polydimethylsiloxane [PDMS] to acetone, nitrogen, and acetone/nitrogen mixtures has been determined at 28°C. In pure gas experiments, the permeability of PDMS to nitrogen was 245 × 10−10 cm3(STP) · cm/cm2 · s · cmHg and was independent of pressure. The permeability of PDMS to acetone vapor increased exponentially with increasing acetone pressure. PDMS is much more permeable to acetone than to nitrogen; acetone/nitrogen selectivity increases from 85 to 185 as acetone partial pressure in the feed increases from 0 to 67% of saturation. In mixed gas permeation experiments, the nitrogen permeability coefficient is independent of acetone relative pressure and is equal to the pure gas permeability coefficient. The acetone permeability coefficient has the same value in both mixed gas and pure acetone permeation experiments. Average acetone diffusivity in PDMS, determined as the ratio of permeability to solubility, decreases with increasing acetone concentration due to mild clustering of acetone in the polymer (because acetone is a poor solvent for PDMS) and changes in the polymer–penetrant thermodynamic interactions which influence diffusion coefficients. A Zimm–Lundberg analysis of the acetone sorption isotherm is also consistent with acetone clustering in PDMS. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 289–301, 1998

Fiber-Optic Probe for Laser-Induced Fluorescence Measurements of the Fuel-Air Distribution in Gas-Turbine Combustors

A e ber‐ optic probe has been developed for spatially and temporally resolved measurements of the equivalence ratio in actual gas-turbine combustors. The measurement is based on laser-induced e uorescence, where acetone is used as a e uorescence seed. The effects of acetone concentration, temperature, and pressure on the e uorescence signal have been characterized in a steady e ow test cell at temperatures (up to 400&C) and pressures (up to 12 atm) representative of real-gas-turbine combustors. The capabilities of the e ber-optic probe have been demonstrated by making measurements in a turbulent axisymmetric airjet. Under typical measurement conditions it has been shown that the mean and rms e uctuation of the equivalence ratio can be determined with an accuracy of better than 65%.

Gas phase photolysis of acetone in the far ultra-violet

The photolysis of acetone (pressure: 2 to 25 Torr, T: 300 K) was investigated at 147 nm (8.4 eV), 123.6 nm (10 eV) and 106.7-104.8 nm (11.6–11.8 eV). The quantum yields of the products H 2, CO, CH 4, C 2H 6, C 2H 4, C 2H 2, C 3H 8, C 3H 6, C 3H 4, and CH 3COC 2H 5 were measured both in the presence and absence of free radical scavengers (C 2H 4 or NO). These data, in conjunction with the results of deuterium-labelling experiments, demonstrated the occurrence of the following primary processes: ▪ It is also suggested that the primary process: ▪ occurs with a quantum yield of ≈ 0.02. The quantum yield of “molecular” methane (process d) is 0.02 (147 nm), 0.028 (123.6 nm) and 0.043 (104.8–106.7 nm). The quantum of “molecular” hydrogen is 0.03 (147 nm) 0.26 (123.6 nm) and 0.28 (104.8–106.7 nm). The quantum yield of process (a) is 0.7 ± 0.1 at 147 nm. At shorter wavelengths the quantum yield of the latter process could not be estimated because of the uncertain fate of the cations [Φ(CH 3COCH 3 + ) = 0.25 at 123.6 nm and 0.21 at 104.8–106.7 nm] and the extensive dissociation of the internally excited species formed in the primary processes.

The Catalytic Decomposition of Isopropyl Alcohol Vapor on Manganese (II) Oxide

The vapor phase decomposition of isopropyl alcohol has been studied from 210 to 365 °C on manganese(II) oxide. Rates of conversion to acetone and propylene were measured with partial pressures of isopropyl alcohol from 0.3 to 22 mm. The catalyst selectivity towards dehydrogenation was around 0.80 between 320 and 365 °C while at 306 °C it was somewhat less and depended on the alcohol partial pressure. Propylene and hydrogen additions had no effect on the reaction rate while the reaction order with respect to isopropyl alcohol partial pressure was 0.4 to 0.6 except at 306 °C when it decreased with increase in the alcohol partial pressure. The effects of acetone and water additions were shown respectively to be exerted mainly on the dehydrogenation and dehydration reactions while at acetone pressures above 4 mm, considerable amounts of by-products including mesityl oxide and heavier ketones were clearly detected. The apparent activation energy of the overall decomposition as calculated from the experimental rates was 26 ± 0.5 kcal mol−1. The results have been interpreted to be in general agreement with the concept that the rate-limiting step is linked to the direct interactions on the catalyst surface and it has been established that the reaction is significantly more complex than previously recognized. The physical properties of the manganese(II) oxide were determined by X-ray and nitrogen adsorption techniques while infrared, n.m.r., and gas chromatographic methods were used to analyze the products of catalysis.

Wall reactions in acetone photolysis

The photolysis of acetone has been re-examined at temperatures between 107 and 225°C, and pressures between 0.13 and 133 mbar. In a Pyrex reaction vessel the wall reaction, CH3·+(CH3COCH3)ads→ CH4+ CH3COCH2·, contributes significantly to methane formation at acetone pressures below 10 mbar. The rate of this reaction is proportional to the methyl radical concentration in the gas phase, and varies markedly with the nature of the surface. On PTFE and PbO surfaces the rate of reaction appears independent of acetone pressure in the range 0.13–2.7 mbar, but on Pyrex it increases slowly with increasing acetone pressure. On Pyrex surfaces the reaction has an activation energy of 6.6 ± 1.0 kcal mol–1 and is always faster on a per collision basis than the analogous reaction in the gas phase.