Desorption Of Acetone Research Articles

Adsorption and desorption of acetone by TiO2 clusters: Transition state theory and sensing analysis

TiO2 cluster sensitivity to acetone adsorption using transition state theory is investigated. Ti10O20 cluster is used to perform the calculations using density functional theory with dispersion corrections. Adsorption state and transition state are calculated via thermodynamic energies, i.e., Gibbs free energy of adsorption and activation. Reaction rate, response, response time, and recovery time as a function of temperature and acetone concentration are calculated. Acetone burning in the air due to autoignition is considered using a logistic function. The results of the theory are compared with available experimental findings that revealed the quality of both theoretical and experimental results. The response time decreases with respect to acetone concentration. On the other hand, the recovery time in the desorption phase increases with acetone concentration. The temperature of maximum response is 356 °C, while the maximum response value is 2.9.

Sensing mechanism of acetone adsorption on charged ZnO and ZnSe surfaces: Insights from DFT calculations

Acetone sensing is meaningful for human health, food safety and animal safety. In this work, the sensing mechanism of acetone adsorption on charged II-VI semiconductor (ZnO and ZnSe) is systematically investigated by density functional theoretical calculations. It is found that compared with charged ZnO surfaces, charged ZnSe surfaces possess stronger acetone adsorption strength. Both positive and negative surface charges could enhance acetone sensing of ZnO surface while only negative surface charges could enhance acetone sensing on ZnSe surface. The appropriate charge states of ZnO or ZnSe are of significance to realize fast recovery. Because acetone desorption process could be endothermic with added energy under some charge states. Additionally, the acetone selectivity of sensing surface could be controlled by surface charge states. Moreover, acetone sensing could be effectively improved by the synergistic effect of surface charge states and ZnSe/ZnO heterostructures. Our results extend the knowledge into the acetone sensing mechanisms induced by surface charge states.

Manganese catalyzed transfer hydrogenation of biomass-derived aldehydes: Insights to the catalytic performance and mechanism

Manganese catalyzed transfer hydrogenation (CTH) of aldehydes is an attractive method for the synthesis of alcohols. Here, we report a novel and efficient MnO@C-N catalyst for the CTH of biomass-derived 5-hydroxymethylfurfural and other aldehydes to alcohols in high yields. Catalytic experimental studies showed that the MnO and nitrogen-doping are responsible for the high selectivity and high conversion, respectively. Isotopic labelling experiments demonstrated that the CTH of aldehydes to alcohols over MnO@C-N is via a route by direct hydrogen transfer. Kinetic studies revealed that the N-doping can improve the reaction rate and reduce the activation energy of the aldehydes conversion. DFT calculations also indicated that both pyridine N and pyrrolic N doping can reduce the energy barrier for acetone desorption by the interaction between N and hydroxyl-H of alcohol. Furthermore, MnO@C-N showed good recyclability for at least five reaction cycles. We anticipate that these results can drive progress in the manganese catalyzed transfer hydrogenation reaction.

Fundamental understanding of oxygen content in activated carbon on acetone adsorption desorption

To explore the effect of O-containing surface functional groups on volatile organic compounds (VOC) adsorption, three kinds of activated carbons named as PC, PH and ZC, after K2CO3, KOH and ZnCl2 activation respectively, were prepared from tobacco stem. Under room temperature (298 K), the saturated adsorption capacities towards acetone of PC, PH and ZC agree well with the resultants of specific surface area. Noteworthy that the normalized adsorption capacity (adsorption value per area) of these activated carbons display a completely different trend, but positively correlated with the O content. Moreover, acetone desorption processes on these materials were also investigated, and the activation energy of desorption were calculated with the order of PC > PH > ZC. Through density functional theory calculation, we determine the nature difference of these activated carbons with varying O content that O-containing surface groups could obviously strengthen the interaction between acetone and carbon surface via the formed hydrogen bond or van der Waals force, and hence significantly improve the adsorption strength to affect the acetone adsorption and desorption process. This study advances the mechanism of O content in the form of surface functional groups during VOC adsorption/desorption process on activated carbons.

Adsorption of acetone and cyclohexane onto CO2 activated hydrochars.

Most of the volatile organic compounds (VOCs) are toxic and harmful to human health and environment. In this study, hydrochars activated with CO2 were applied to remove VOCs. Two typical VOCs, acetone and cyclohexane, were used as the 'model' adsorbates to evaluate hydrochars' performance. Specific surface areas of pristine hydrochars were small (<8m2/g), whereas activated hydrochars showed much higher values (up to 1308m2/g). As a result, the adsorption of VOCs onto the pristine hydrochars (13.24-24.64mg/g) was lower than that of the activated ones (39.42-121.74mg/g). The adsorption of the two VOCs onto the hydrochars was exothermal. In addition, there were significant correlations (R2>0.91) between the VOC removal and hydrochars' specific surface area. These results suggest that the governing mechanism was mainly physical adsorption. Increasing experimental temperature (80-139°C) desorbed the VOCs from the hydrochars. Due to its higher boiling point, cyclohexane desorption required a higher temperature than acetone desorption. The reusability of the activated hydrochars to the two VOCs was confirmed by five continuous adsorption-desorption cycles. The overall results indicated that hydrochars, particularly after CO2 activation, are sufficient for VOC abatement.

Adsorption and Photocatalytic Decomposition of Gaseous 2-Propanol Using TiO2-Coated Porous Glass Fiber Cloth

Combinations of TiO2 photocatalysts and various adsorbents have been extensively investigated for eliminating volatile organic compounds (VOCs) at low concentrations. Herein, TiO2 and porous glass cloth composites were prepared by acid leaching and subsequent TiO2 dip-coating of the electrically applied glass (E-glass) cloth, and its adsorption and photocatalytic ability were investigated. Acid leaching increased the specific surface area of the E-glass cloth from 1 to 430 m2/g while maintaining sufficient mechanical strength for supporting TiO2. Further, the specific surface area remained large (290 m2/g) after TiO2 coating. In the photocatalytic decomposition of gaseous 2-propanol, the TiO2-coated porous glass cloth exhibited higher adsorption and photocatalytic decomposition ability than those exhibited by the TiO2-coated, non-porous glass cloth. The porous composite limited desorption of acetone, which is a decomposition intermediate of 2-propanol, until 2-propanol was completely decomposed to CO2. The CO2 generation rate was affected by the temperature condition (15 or 35 °C) and the water content (2 or 18 mg/L); the latter also influenced 2-propanol adsorption in photocatalytic decomposition. Both the conditions may change the diffusion and adsorption behavior of 2-propanol in the porous composite. As demonstrated by its high adsorption and photocatalytic ability, the composite (TiO2 and porous glass cloth) effectively eliminates VOCs, while decreasing the emission of harmful intermediates.

Adsorption and desorption of binary mixture of acetone and ethyl acetate on silica gel

Adsorption and desorption of acetone and ethyl acetate (two typical oxygenated VOCs) on silica gel have been systematically studied by vacuum swing adsorption (VSA) combined with temperature swing adsorption (TSA) process. It is found that the adsorption of both the oxygenated VOC compounds on silica gel could be well described by the Langmuir-Freundlich model. Although highly dependent on the operational parameters, the adsorption of both the oxygenated VOC compounds on silica gel is found to be controlled by external diffusion. When the two compounds are mixed, the adsorbed acetone is found to be partially replaced by the ethyl acetate when the adsorption approaches the saturation due to the stronger affinity of ethyl acetate to silica gel. It also suggests that there is a competitive adsorption between ethyl acetate and acetone. Further modeling demonstrates that the whole kinetic adsorption of binary oxygenated components could be divided into three steps: the free adsorption, the competitive adsorption and the equilibrium state. The final ratio of adsorbed acetone to ethyl acetate on silica gel is dependent on the adsorption bed height. The adsorbed oxygenated VOCs on silica gel are observed to be desorbed by vacuum pumping, which is also found to be significantly enhanced by increasing temperature (by ∼30 °C), achieving over 2.5 times of concentration increase in the desorbed gas stream.

Few-Flakes Reduced Graphene Oxide Sensors for Organic Vapors with a High Signal-to-Noise Ratio

This paper reports our findings on how to prepare a graphene oxide-based gas sensor for sensing fast pulses of volatile organic compounds with a better signal-to-noise ratio. We use rapid acetone pulses of varying concentrations to test the sensors. First, we compare the effect of graphene oxide deposition method (dielectrophoresis versus solvent evaporation) on the sensor’s response. We find that dielectrophoresis yields films with uniform coverage and better sensor response. Second, we examine the effect of chemical reduction. Contrary to prior reports, we find that graphene oxide reduction leads to a reduction in sensor response and current noise, thus keeping the signal-to-noise ratio the same. We found that if we sonicated the sensor in acetone, we created a sensor with a few flakes of reduced graphene oxide. Such sensors provided a higher signal-to-noise ratio that could be correlated to the vapor concentration of acetone with better repeatability. Modeling shows that the sensor’s response is due to one-site Langmuir adsorption or an overall single exponent process. Further, the desorption of acetone as deduced from the sensor recovery signal follows a single exponent process. Thus, we show a simple way to improve the signal-to-noise ratio in reduced graphene oxide sensors.

Vapomechanically Responsive Motion of Microchannel-Programmed Actuators.

Materials that respond rapidly and reversibly to external stimuli currently stand among the top choices as actuators for real-world applications. Here, a series of programmable actuators fabricated as single- or bilayer elements is described that can reversibly respond to minute concentrations of acetone vapors. By using templates, microchannel structures are replicated onto the surface of two highly elastic polymers, polyvinylidene fluoride (PVDF) and polyvinyl alcohol, to induce chiral coiling upon exposure to acetone vapors. The vapomechanical coiling is reversible and can be conducted repeatedly over 100 times without apparent fatigue. If they are immersed in liquid acetone, the actuators are saturated with the solvent and temporarily lose their motility but regain their shape and activity within seconds after the solvent evaporates. The desorption of acetone from the PVDF layer is four times faster than its adsorption, and the actuator composed of a single PVDF layer maintains its ability to move over an acetone-soaked filter paper even after several days. The controllable and reproducible sensing capability of this smart material can be utilized for actuating dynamic elements in soft robotics.

Steam reforming of acetone over Ni- and Co-based catalysts: Effect of the composition of reactants and catalysts on reaction pathways

The properties of Ni/Co/Co-Ni/MgAl2O4 catalysts in the steam reforming of acetone (SRA) were investigated regarding the metallic composition and nature of catalytic site. The catalysts were characterized by nitrogen physisorption, X-ray diffraction, X-ray absorption spectroscopy, transmission electron microscopy, and temperature programmed reduction and desorption of acetone. Experimental data revealed that the acetone conversion pathway on the Co, Co-Ni, or Ni catalysts was strongly dependent on the nature of the metal, reaction temperature, and the oxidation state of the metal atoms in nanoparticles surface atoms. Reaction data indicated that the acetone decomposition on reduced metal catalysts at high temperatures (>350°C) occurred mainly via the HC and CCO bonds cleavage, leading to the formation of CO, H2, and C on the metal surface. At low temperatures (200°C) and in the presence of H2 in the reactor feed, the Ni catalyst catalyzed the hydrogenation of the CO and CHx species formed from acetone activation on the metallic sites, producing CH4. For Co-containing catalysts, at low temperatures (200–350°C) the metal nanoparticles surface was in a higher oxidation degree and promoted the oxidation of acetone. At high temperatures (>350°C), the hydrogenation of CHx and CO species to CH4 was determined by the nanoparticle oxidation degree, which decreased in the order Ni>Co-Ni>Co. With increased temperature, the CHx species decomposed to C and H2, instead of being hydrogenated to CH4. The oxidation of C by H2O was favored on Co-containing catalysts. The reaction pathways are discussed based on theoretical data obtained from the literature.

Temperature Programmed Desorption of Quench-condensed Krypton and Acetone in Air; Selective Concentration of Ultra-trace Gas Components.

Selective concentration of ultra-trace components in air-like gases has an important application in analyzing volatile organic compounds in the gas. In the present study, we examined quench-condensation of the sample gas on a ZnO substrate below 50 K followed by temperature programmed desorption (TPD) (low temperature TPD) as a selective gas concentration technique. We studied two specific gases in the normal air; krypton as an inert gas and acetone as a reactive gas. We evaluated the relationship between the operating condition of low temperature TPD and the lowest detection limit. In the case of krypton, we observed the selective concentration by exposing at 6 K followed by thermal desorption at about 60 K. On the other hand, no selectivity appeared for acetone although trace acetone was successfully concentrated. This is likely due to the solvent effect by a major component in the air, which is suggested to be water. We suggest that pre-condensation to remove the water component may improve the selectivity in the trace acetone analysis by low temperature TPD.

국내 시판 중인 활성탄을 이용한 벤젠, 톨루엔, 아세톤 및 노말 헥산의 탈착 및 저장성 평가 연구

국내 시판 중인 활성탄을 이용한 벤젠, 톨루엔, 아세톤 및 노말 헥산의 탈착 및 저장성 평가 연구

Fumaric Acid Recovery and Purification from Fermentation Broth by Activated Carbon Adsorption Followed with Desorption by Acetone

To develop an economic and efficient recovery and purification method for fermentation-produced fumaric acid, an integrated process was developed by adsorption with activated carbon, followed with acetone desorption. Activated carbon possessed a high adsorption capacity for fumaric acid (∼200 mg/g) at a lower pH (<2) with high selectivity over glucose and malic acid. Acetone was applied to effectively desorb fumaric acid from activated carbon. The desorption solution was heated at 70 °C to evaporate the acetone, resulting in purified fumaric acid powders. Both activated carbon and acetone can be recovered and reused. This process was also evaluated in a fixed-bed column to recover fumaric acid from fermentation broth, achieving a high recovery yield of 93%. Finally, water sweeping successfully increased the purity of fumaric acid to ∼98%. Although this process requires additional capital investment, it reduces operational costs and is economically attractive compared to the conventional process.

In Situ Generation of Active Sites in Olefin Metathesis

The depth of our understanding in catalysis is governed by the information we have about the number of active sites and their molecular structure. The nature of an active center on the surface of a working heterogeneous catalyst is, however, extremely difficult to identify and precise quantification of active species is generally missing. In metathesis of propene over dispersed molybdenum oxide supported on silica, only 1.5% of all Mo atoms in the catalyst are captured to form the active centers. Here we combine infrared spectroscopy in operando with microcalorimetry and reactivity studies using isotopic labeling to monitor catalyst formation. We show that the active Mo(VI)-alkylidene moieties are generated in situ by surface reaction of grafted molybdenum oxide precursor species with the substrate molecule itself gaining insight into the pathways limiting the number of active centers on the surface of a heterogeneous catalyst. The active site formation involves sequential steps requiring multiple catalyst functions: protonation of propene to surface Mo(VI)-isopropoxide species driven by surface Brønsted acid sites, subsequent oxidation of isopropoxide to acetone in the adsorbed state owing to the red-ox capability of molybdenum leaving naked Mo(IV) sites after desorption of acetone, and oxidative addition of another propene molecule yielding finally the active Mo(VI)-alkylidene species. This view is quite different from the one-step mechanism, which has been accepted in the community for three decades, however, fully consistent with the empirically recognized importance of acidity, reducibility, and strict dehydration of the catalyst. The knowledge acquired in the present work has been successfully implemented for catalyst improvement. Simple heat treatment after the initial propene adsorption doubled the catalytic activity by accelerating the oxidation and desorption-capturing steps, demonstrating the merit of knowledge-based strategies in heterogeneous catalysis. Molecular structure of active Mo(VI)-alkylidene sites derived from surface molybdena is discussed in the context of similarity to the highly active Schrock-type homogeneous catalysts.

Steam regeneration of acetone and toluene in activated carbon and dealuminated Y-zeolite beds

The dynamics of steam regeneration in activated carbon and dealuminated Y-zeolite (DAY-zeolite) beds was studied to recover acetone and toluene from effluent gases. Due to the higher adsorption capacity of acetone on both adsorbents, the desorption breakthrough of toluene was faster than that of acetone, but the breakthrough shape of acetone was steeper than that of toluene. The variation in breakthrough time as a function of steam flow rate was less in the activated carbon bed than in the DAY-zeolite bed. The inside temperature profiles during regeneration showed stepwise shapes. A temperature plateau was observed near 355 K for toluene, which is lower than its boiling temperature and azeotrope. A temperature plateau for acetone occurred near 330 K, near its boiling temperature. The duration of the temperature plateau at the bed end corresponded with the time period of high desorption concentration during acetone desorption; for toluene, plateau duration was shorter than the duration of high desorption concentration. The maximum effluent concentration of toluene reached only 80% of the feed concentration, while that of acetone was almost 100%. Therefore, the water-miscibility of the adsorbate was an important factor in steam regeneration.

Surface Chemistry of Isopropoxy Tetramethyl Dioxaborolane on Cu(111)

The surface chemistry of isopropoxy tetramethyl dioxaborolane (ITDB), tetramethyl dioxaborolane (TDB), and 2-propanol is studied on a clean Cu(111) single crystal using temperature-programmed desorption (TPD). 2-Propanol is found to have two competing reactions on the copper surface. Dehydration results in water and propene formation, and dehydrogenation results in the formation of acetone and hydrogen. ITDB directly adsorbed on the surface reacts completely and does not molecularly desorb. TDB and 2-propanol decompose desorbing mainly 2,3-dimethyl 2-butene and acetone, respectively. Both of those products desorb above room temperature and are present in TPDs of ITDB. An additional acetone desorption peak was observed for ITDB at higher temperatures than acetone desorption from 2-propanol. This higher temperature peak at ∼391 K was attributed to two acetone molecules forming from the tetramethyl end group resulting from a stronger bound surface species in ITDB compared to TDB despite their identical end groups. The copper surface seems to be reactive enough toward ITDB at room temperature that a potential boron-containing tribofilm could be produced for copper-copper sliding contacts. Despite their similarities, ITDB and TDB have different surface species present at room temperature, so their tribological properties will be investigated in the future.

The Marangoni convection induced by acetone desorption from the falling soap film

By means of the falling soap film tunnel and the Schlieren optical method, the Marangoni convection were observed directly in the immediate interfacial neighborhood during the desorption process of acetone from the falling soap film. Moreover, the hydraulic characteristics of the falling soap film tunnel, the acetone concentration, the surface tension of the soap liquid and the mass transfer has been investigated in details through the experimental or theoretical method.

Estimation of Volatile Organic Compound Mass Transfer Coefficients in the Vacuum Desorption of Acetone from Activated Carbon

The export concentrations of acetone desorption from activated carbon at different temperatures, vacuum degrees, and saturated adsorption capacities were measured. The results showed that the greater the desorption vacuum degree and the initial adsorption capacity, the smaller the desorption rate. Given the adsorbent microporous capillary effect and the mass transfer in the process of desorption, the concentration curve reflects three phases, which are the vacuum-concentrated phase, fast attenuation phase, and slow attenuation phase. Through theoretical analysis and a coupled model of the desorption process, numerical simulation of the acetone desorption from activated carbon was carried out. Experimental and theoretical analysis showed that small temperature changes were caused by desorption; therefore, the change of the mass transfer coefficient and concentration caused by the temperature change is also small. In different desorption phases, a coupled effect on the mass transfer coefficients have differ...

Role of Coverage and Surface Oxidation Degree in the Adsorption of Acetone on TiO2(110). A Density Functional Study

A systematic study of the adsorption of acetone on a TiO2 (110) surface by means of plane-wave pseudopotential density-functional theory calculations is presented. The relationship between the binding energy of acetone and the degree of surface coverage (up to 0.5 ML) is established on the basis of a partial reduction of the surface by the incoming acetone molecules. This allows one to explain the observed displacement toward lower temperature of the temperature-programmed desorption (TPD) maximum with increasing acetone loading. Adsorption at the bridge oxygen vacancies on supercell models of the reduced surface shows similar properties to that of regular Ti channel sites, in agreement with experimental data that do not indicate a preferential binding at vacancy sites. A high dependency between the degree of reduction of the surface and the acetone binding energies is found, implying that surface models with an excessive mean number of vacancies per unit cell may result in altered properties of this surface. Models of the oxidized TiO2 (110) surface show that coadsorbed oxygen stabilizes acetone via the formation of acetone/O-adatom complexes that, in contrast to acetone, present a barrier for desorption. This barrier allows one to explain the high temperature feature observed in the TPD spectrum for acetone desorption from the oxidized TiO2 (110) surface.

Acetone Reactions over the Surfaces of Polycrystalline UO2: A Kinetic and Spectroscopic Study

The reaction of acetone is studied on the surfaces of polycrystalline UO2, prepared by hydrogen reduction of U3O8 at 770 K. The study is conducted by in situ Fourier transform infrared (FTIR) and temperature-programmed desorption (TPD). Acetone adsorption does not fit the simple Langmuir model, and adsorbate-adsorbate interactions are found to be significant. Acetone adsorbs molecularly on UO2 as evidenced by the nuCO of the eta1(O) mode at 1686 cm(-1). Part of acetone is reduced to the isopropoxide species ((CH3)2HC-O-U4+) upon heating (nu(CC), rho(CH3) at 1167 cm(-1) and nu(CO), rho(CH3) at 980 cm(-1)), and upon further heating, acetates (CH3COO(a), (a) for adsorbed) are observed. Detailed TPD studies indicated that the main reaction of acetone on UO2 is the deoxygenation to propene, driven by the oxophilic nature of UO2. Other reactions were also observed to a lesser extent, and these included reductive coupling to 2,3-dimethylbutene and condensation to mesityl oxide. An attempt to extract kinetic parameters from TPD data was conducted. Three models were studied: variation of heating rate, leading edge analysis (Habenschaden-Kuppers method), and complete analysis. The complete analysis provided the most plausible results, in particular, at low coverage. With this method, at nearly zero coverage the activation energy, Ed, for desorption was found to be close to 140 kJ/mol with a prefactor of 10(13) s(-1). Ed dropped sharply with increasing coverage, theta, to ca. 35 kJ/mol at theta=0.15 with a prefactor of 10(11) s(-1). The activation energy for the desorption of acetone on UO2(111) single crystals, at saturation coverage, was previously found to be equal to 65 kJ/mol using the leading edge analysis.