Adsorption Of Cyclohexane Research Articles

Ozone assisted vapor phase selective catalytic oxidation of cyclohexane on the 13X zeolite supported cobalt oxides

The present work reports the application of ozone and effect of cobalt oxide content on the vapor phase selective oxidation of cyclohexane. The catalysts with various cobalt loadings (0.5–10.0wt%) prepared by a wet impregnation method followed by microwave drying. The one wt% cobalt catalyst (Co-1) exhibited the better conversion (16.5%) as well as selectivity to cyclohexanone/cyclohexanol (K/A, 64%) among the other cobalt catalysts at 110°C, which might be due to the formation of isolated or fine cobalt particles on the surface of the catalyst and the strong Lewis acidity. Further, high moisture content (above 40%) is significantly increased the K/A selectivity from 64 to 71% on the Co-1 catalyst. The absence of cobalt oxide particles in the high resolution-transmission electron microscopy (HR-TEM) at lower cobalt loadings (<3wt%) reveal that the cobalt oxides form an isolated species or fine particles on the surface of the support. The exchange of monovalent sodium ions with trivalent cobalt atoms increased the strong Lewis acidic sites at lower cobalt loadings that are reflected in the temperature programmed desorption (TPD) of ammonia. These strong Lewis acidic sites facilitated the high amount of cyclohexane adsorption on the Co-1 catalyst, which observed in the TPD of cyclohexane. On the other hand, neither cyclohexanone nor cyclohexanol observed in the presence of air using the Co-1 catalyst.

Mechanism of Phenol Alkylation in Zeolite H-BEA Using In Situ Solid-State NMR Spectroscopy.

The reaction mechanism of solid-acid-catalyzed phenol alkylation with cyclohexanol and cyclohexene in the apolar solvent decalin has been studied using in situ 13C MAS NMR spectroscopy. Phenol alkylation with cyclohexanol sets in only after a majority of cyclohexanol is dehydrated to cyclohexene. As phenol and cyclohexanol show similar adsorption strength, this strict reaction sequence is not caused by the limited access of phenol to cyclohexanol, but is due to the absence of a reactive electrophile as long as a significant fraction of cyclohexanol is present. 13C isotope labeling demonstrates that the reactive electrophile, the cyclohexyl carbenium ion, is directly formed in a protonation step when cyclohexene is the coreactant. In the presence of cyclohexanol, its protonated dimers at Brønsted acid sites hinder the adsorption of cyclohexene and the formation of a carbenium ion. Thus, it is demonstrated that protonated cyclohexanol dimers dehydrate without the formation of a carbenium ion, which would otherwise have contributed to the alkylation in the kinetically relevant step. Isotope scrambling shows that intramolecular rearrangement of cyclohexyl phenyl ether does not significantly contribute to alkylation at the aromatic ring.

Study of the carbonization temperature for a chemically activated carbon: influence on the textural and structural characteristics and surface functionalities

This study aims at investigating the relationship between the porosity and the surface functional groups of an activated carbon during the pyrolysis process. Several activated carbons are prepared by the carbonization of a mixture of olive waste and ZnCl2 at different temperatures, which are chosen by taking into account the different phenomena occurring during this treatment. The porosity of the prepared carbons is investigated using both N2 and CO2 isotherms at 77 and 273 K, respectively. Long-range and short-range orders are studied respectively by X-ray diffraction (XRD) and Raman spectroscopy. The investigation of the carbon functionalities is carried out by Boehm titration, Fourier transformed infrared spectroscopy (FTIR) and water adsorption measurements. The effect of carbonisation temperature on the adsorption of cyclohexane provides additional information on the oxygen functional groups and especially the carboxylic proups. To summarize, the results show that a carbonisation at 573 K is sufficient to obtain a well-developed porosity and to ensure already the formation of acidic surface groups and especially the carboxylic groups.

Adsorption of volatile organic compounds in composite zeolites pellets for space decontamination

FAU–*BEA-types zeolites pellets were elaborated with a hydraulic press in the presence of a small amount (5 wt%) of binder [methylcellulose (MC) or anhydrous sodium metasilicate (Na2SiO3)] for molecular decontamination, in particular for the space field. Nitrogen sorption–desorption revealed a small loss of micropore volume (10%) with a compression load of 6 tons (0.24 cm3/g instead of 0.27 cm3/g for the mixture of FAU and *BEA-types zeolites powders), which can be attributed to a partial amorphization. Adsorption kinetics of n-hexane, and cyclohexane showed that the optimum pellets can adsorb volatile organic compounds. For example, FAU–*BEA-type zeolite powder mixture (50 wt% of each zeolite) adsorb 130 mg of n-hexane per g of anhydrous zeolite whereas the pellets made with 5 wt% of MC or Na2SiO3 adsorb about 117–118 mg of n-hexane per g of anhydrous zeolite. These results are coherent with the ones obtained with the cyclohexane and nitrogen adsorption where a small loss of the adsorption capacities was observed.

Pore Environment Effects on Catalytic Cyclohexane Oxidation in Expanded Fe2(dobdc) Analogues

Metal-organic frameworks are a new class of heterogeneous catalysts in which molecular-level control over both the immediate and long-range chemical environment surrounding a catalytic center can be readily achieved. Here, the oxidation of cyclohexane to cyclohexanol and cyclohexanone is used as a model reaction to investigate the effect of a hydrophobic pore environment on product selectivity and catalyst stability in a series of iron-based frameworks. Specifically, expanded analogues of Fe2(dobdc) (dobdc4- = 2,5-dioxido-1,4-benzenedicarboxylate) were synthesized and evaluated, including the biphenyl derivative Fe2(dobpdc) (H4dobpdc = 4,4'-dihydroxy-[1,1'-biphenyl]-3,3'-dicarboxylic acid), the terphenyl derivative Fe2(dotpdc) (H4dotpdc = 4,4″-dihydroxy-[1,1':4',1″-terphenyl]-3,3″-dicarboxylic acid), and three modified terphenyl derivatives in which the central ring is replaced with tetrafluoro-, tetramethyl-, or di-tert-butylaryl groups. Within these five materials, a remarkable 3-fold enhancement of the alcohol:ketone (A:K) ratio and an order of magnitude increase in turnover number are achieved by simply altering the framework pore diameter and installing nonpolar functional groups near the iron site. Mössbauer spectroscopy, kinetic isotope effect, and gas adsorption measurements reveal that variations in the A:K selectivities arise from differences in the cyclohexane adsorption enthalpies of these frameworks, which become more favorable as the number of hydrophobic residues and thus van der Waals interactions increase.

Evidence for the effect of the cooling down step on activated carbon adsorption properties

Two activated carbons are prepared by chemical activation of olive residue using zinc chloride. The first sample is cooled down slowly after the carbonization in the furnace under a flow of nitrogen, while the second is directly removed from the furnace just after the carbonization and put at ambient temperature and pressure. The textural and structural characteristics of the two samples are determined by nitrogen adsorption at −196 °C and X-ray diffraction (XRD). The oxygen functional groups are characterized via Boehm's titration and Fourier transformed infrared spectroscopy (FTIR). The cooling down step at different rates is followed by thermogravimetry–mass spectroscopy analysis (TG/MS). Slow cooling down of the sample after carbonization leads to CO2, O2, and CO consumption creating more active sites, which are responsible of the formation of surface oxygen groups, and especially carboxylic groups. The latter dramatically enhance water vapor adsorption at low relative humidity. The cyclohexane adsorption on activated carbons, which is carried out by thermogravimetric analysis (TGA), shows that the cooling down step has an effect on both the initial rate of adsorption and the adsorption uptake at equilibrium.

Adsorption of benzene, cyclohexane and hexane on ordered mesoporous carbon

Ordered mesoporous carbon (OMC) with high specific surface area and large pore volume was synthesized and tested for use as an adsorbent for volatile organic compound (VOC) disposal. Benzene, cyclohexane and hexane were selected as typical adsorbates due to their different molecular sizes and extensive utilization in industrial processes. In spite of their structural differences, high adsorption amounts were achieved for all three adsorbates, as the pore size of OMC is large enough for the access of these VOCs. In addition, the unusual bimodal-like pore size distribution gives the adsorbates a higher diffusion rate compared with conventional adsorbents such as activated carbon and carbon molecular sieve. Kinetic analysis suggests that the adsorption barriers mainly originated from the difficulty of VOC vapor molecules entering the pore channels of adsorbents. Therefore, its superior adsorption ability toward VOCs, together with a high diffusion rate, makes the ordered mesoporous carbon a promising potential adsorbent for VOC disposal.

Adsorption of isopropanol and cyclohexane on zinc oxide

Adsorption isotherms of isopropanol and cyclohexane are obtained in the range of 234–303 K on an initial surface of zinc oxide and after its treatment with glow-discharge plasma in O2 and high-frequency plasma in Ar. The values of isosteric heat and adsorption entropy are shown to be only slightly affected by these treatments. It is found that the acidity of the surface increases by 38 and 97%, respectively, and the acidic sites are not adsorption sites for either adsorbate. At low degrees of occupation, the adsorption isotherms of (CH3)2CHOH are described by an equation of induced adsorption whose parameters are dependent on the plasma-chemical treatments. It is concluded that adsorbed isopropanol particles exist in positively and negatively charged forms. The adsorption of cyclohexane is described by the Hill-de Boer equation for the initial ZnO surface, and by the Langmuir equation after plasma-chemical treatments.

Development of a Thin-Film Microextraction Device based on ZSM-5/Tenax TA for VOC Detection in Liquid Samples

The zeolite material ZSM-5 was combined with Tenax TA, a porous polymer adsorbent, to form a thin film microextraction (TFME) device that was used as a novel alternative tool for headspace (HS) volatile organic compound (VOC) extraction and preconcentration. The ZSM-5/Tenax TA film deposited on a cylindrical aluminium rod (AR) substrate exhibited superior properties for the adsorption and preconcentration of chloroform, hexane, cyclohexane, benzene, and toluene compared with those of a conventional Tenax TA film when applied in both the direct and HS extraction modes. The advantages of the fabricated device include its enhanced chromatographic performance and consequently lower detection limits for certain VOCs, the improved retention of compounds in the film (possibly enabling its application for both HS and direct extractions from aqueous solutions), the exceptional simplicity of its fabrication, and its robustness. The use of the film for HS extraction leads to increased application lifetime, film stability and shorter preparation times, because drying step is not necessary. Desorption of the adsorbed VOCs was achieved by heating in a conventional Curie point injector for less than 2 min. It should be noted that the catalytic properties of the zeolite can be disadvantageous at high VOC concentrations (e.g., 100 μM); abundant background peaks as a result of a range of saturated and unsaturated hydrocarbons generated via catalytic degradation of adsorbed compounds at high temperature in the presence of ZSM-5 appear in the gas chromatograph. This effect is still visible at concentrations as low as 10 μM, but does not influence the measurement results. Thus, safe and accurate analyses are achievable at the liquid VOC concentrations in the submicromalar range, which is sufficient for a number of important analytical applications (e.g., detection of VOCs in waste water).

Adsorption and separation of n-hexane and cyclohexane on the UiO-66 metal–organic framework

Adsorption and separation of n-hexane and cyclohexane on the UiO-66 metal organic framework was studied by pulse gas chromatography and vapour phase breakthrough experiments. Vapour phase breakthrough experiments were performed with mixtures of both components, diluted in helium. Experiments were carried out at temperatures between 50 and 200°C, at partial pressures between 0.0024 and 0.05bar and varying mixture composition. In all conditions, separation between both components is observed, with cyclohexane being the most strongly retained component. This unusual preference for adsorbing the more bulky cyclic alkane isomer was further studied by pulse GC measurements at low coverage, at temperatures between 200 and 300°C. These experiments confirm the inverse shape selective behaviour of UiO-66 in the adsorption of linear and cyclic alkanes. Cyclohexane fits better in the cages of UiO-66, leading to a more negative adsorption enthalpy, together with a lower loss of entropy during adsorption as compared to n-hexane.

Preparation of Multi-Walled Carbon Nanotubes (MWNTs)/Polymethyl Methacrylate (PMMA) Hybrid Membranes and their Sorption Performance of Benzene/Cyclohexane

Novel organic-inorganic hybrid membranes of polymethyl methacrylate (PMMA) containing multi-walled carbon nanotubes (MWNTs) were successfully prepared. Then, the swelling adsorption experiments of benzene/cyclohexane mixtures were employed to evaluate the performance of these membranes. Via transmission electron microscopy (TEM), Fourier transform infrared spectrophotometry (FTIR), the effect of surface modification on the morphology and properties of carbon nanotubes and hybrid membranes were studied. The results indicated that the separation performance for benzene/cyclohexane of the hybrid membranes depended on both the polarity of carbon nanotubes and the distribution of MWNTs in PMMA. Because the dispersion of MWNTs were obviously improved after acidification and ammonization modification, the hybrid membranes including modified MWNTs showed higher performance than membranes with un-modified MWNTs. In addition, a large number of polar group were introduced in the MWNTs during modification of acidification and ammonization, which depressed obviously the physical adsorption of cyclohexane by MWNTs. Therefore, these two changes in the properties of MWNTs both improved the separation performance of hybrid membranes.

Probing hysteresis during sorption of cyclohexane within mesoporous silica using NMR cryoporometry and relaxometry

The conventional data analysis methods for obtaining a pore size distribution (PSD) from gas sorption data make several critical assumptions that impact significantly on the accuracy of the PSD thereby obtained. In particular, assumptions must be made concerning the nature of the pore-filling or emptying process in adsorption, or desorption, respectively. The possibility of pore–pore interactions is also generally neglected. In this work, NMR cryoporometry and relaxometry have been used to study the adsorption and desorption of cyclohexane within a mesoporous, sol–gel silica catalyst support pellet with the aim of assessing the impact of the aforementioned problems for gas sorption PSDs and developing solutions. The advanced melting effect makes cryoporometry a particularly sensitive probe of adsorbate ganglia spatial distribution. It has been demonstrated that utilising gas sorption scanning curves provided insufficient additional information to alleviate the aforementioned problems with interpreting gas sorption data. The NMR data has shown how the nature of the sorption hysteresis changed with amount adsorbed, due to detectable variations in the mechanisms of pore-filling and emptying along the isotherm. Hence, relating a particular condensation or evaporation pressure to a specific characteristic pore size is not as straightforward as assumed in typical pore size analysis software. However, the NMR techniques reveal the additional information required to improve pore size estimates from gas sorption for disordered solids.

Application of quasi-equilibrated thermodesorption of hexane and cyclohexane for characterization of porosity of zeolites and ordered mesoporous silicas

Quasi equilibrated temperature programmed desorption and adsorption (QE-TPDA) of hexane and cyclohexane was applied for characterization of zeolites 5A, ZSM-5, 13X, Y, NaMOR and ordered mesoporous silicas MCM-41, MCM-41/TMB, SBA-15 and HMS. Similar QE-TPDA profiles of hexane and cyclohexane with a single desorption maximum were observed for the wide pore zeolites. No adsorption of cyclohexane for zeolite 5A and a single desorption maximum for ZSM-5 were found, while two-step desorption profiles of hexane were observed for these zeolites. Similar values of the adsorption enthalpy and entropy of hexane and cyclohexane were obtained by fitting the Langmuir model functions for the zeolites X and Y. For NaMOR and ZSM-5 larger differences in these parameters were found. A single desorption peak found at low temperatures in the QE-TPDA profiles of hexane and cyclohexane for the studied silicas was attributed to the multilayered adsorption on their mesopore surface. The adsorption isobars calculated from the thermodesorption profiles were fitted with the BET function. This way values of the specific surface area and the adsorption heat were calculated. Additionally values of the initial heat of adsorption were found by fitting the Henry’s law to the high-temperature sections of the linearized isobars. The largest deviations from the BET and Henry functions and the largest values of the adsorption heats found for SBA-15 indicated the greatest heterogeneity of the adsorption sites on its surface.

Influence of Surface Acidity of Y Zeolites on the Adsorption of Organic Molecules by &lt;em&gt;In situ&lt;/em&gt; Fourier Transform Infrared Spectroscopy

The surface acidity of Y-type zeolites (HY and NaY) modified by solid state ion exchange (SSIE) and liquid phase ion exchange were characterized by in situ Fourier transform infrared (FTIR) spectroscopy using pyridine as the probe molecule (Py-FTIR). The adsorption of single probe molecules (thiophene, cyclohexene and benzene) and double probe molecules (thiophene and cyclohexene, thiophene and benzene) compared with sorbents were studied using in situ FTIR spectroscopy. The results indicated that the Bronsted acid (B acid) of HY (L-CeY) is the catalytic center of cyclohexene dimerized alkenyl carbenium ions and thiophene oligomerization, while the Lewis acid (L acid) is the major center of adsorption of thiophene, cyclohexene, and benzene. In addition, there is strong chemisorption and competitive adsorption of cyclohexene and thiophene, which provides evidence for the poor performance [Article] doi: 10.3866/PKU.WHXB201303183 www.whxb.pku.edu.cn 物理化学学报(Wuli Huaxue Xuebao) Acta Phys. -Chim. Sin. 2013, 29 (6), 1273-1280 June Received: January 2, 2013; Revised: March 18, 2013; Published on Web: March 18, 2013. ∗Corresponding author. Email: lsong56@263.net; Tel/Fax: +86-24-56860658. The project was supported by the National Natural Science Foundation of China (20976077, 21076100), Major Program of Petroleum Refining of Catalyst of Petro China Company Limited (10-01A-01-01-01), Innovation Team of Liaoning Province Colleges, China (200T110), and Construction Project of Liaoning Province High-end Talent Team. 国家自然科学基金(20976077, 21076100),中国石油天然气股份有限公司炼油催化剂重大专项(10-01A-01-01-01),辽宁省高校创新团队项目 (200T110)及辽宁省高端人才队伍建设项目资助 C Editorial office of Acta Physico-Chimica Sinica 1273 Vol.29 Acta Phys. -Chim. Sin. 2013 of removing sulfur. The S-CeY zeolite has abundant of weak Lewis acid sites. The sorbent is good at absorbing thiophene, while the influence of the competition adsorption of cyclohexene was not predominately. As to NaY zeolite, there is no preference for adsorption of thiophene, cyclohexene and benzene.

Efficient and Selective Photocatalytic Cyclohexane Oxidation on a Layered Titanate Modified with Iron Oxide under Sunlight and CO2 Atmosphere

Layered titanates modified with molecular level iron oxide were synthesized by a reaction between K0.7Ti1.73Li0.27O4 and Fe(III) acetylacetonate complex using the dodecylammonium-exchanged layered titanate as intermediate. The iron oxide-modified layered titanates were used as catalysts for selective oxidation of cyclohexane with molecular oxygen under sunlight irradiation. The catalysts produced cyclohexanone and cyclohexanol with high selectivity up to 100% and showed cyclohexane conversion comparable to that obtained over a commercially available TiO2 (P25), depending on the amount of the attached iron oxide. The results were explained by the molecular recognitive cyclohexane adsorption ability of the catalysts, that is, the inhibition of the successive oxidation of the formed products. The cyclohexane conversion over the iron oxide-modified layered titanates was substantially improved with 100% selectivity maintained by conducting the reaction under a CO2 atmosphere.

Characterization and Catalytic Performance of Deactivated and Regenerated TS-1 Extrudates in a Pilot Plant of Propene Epoxidation

TS-1 extrudates that were used for propene epoxidation in a pilot plant for about 1700 h deactivated partly. To study the reason for the deactivation, the deactivated and regenerated catalysts were investigated with X-ray diffraction analysis, Fourier-transform infrared, Ultraviolet–visible diffuse reflectance, thermogravimetry–differential thermogravimetry, N2 sorption, n-hexane adsorption, cyclohexane adsorption, and elemental analysis. The catalytic performance of the deactivated and regenerated TS-1 extrudates in the epoxidation of propene was evaluated in a fixed-bed reactor and in a batch reactor. The activity of the deactivated catalyst from the inlet of the pilot-plant reactor was higher than that from the outlet of the reactor in which more propene oxide oligomers were generated than in the pores of catalyst taken from the inlet of the reactor. External and in situ regeneration could reinstate the activity of the deactivated catalysts, while the in situ regeneration was preferred.

Simulating Adsorption of Organic Pollutants on Finite (8,0) Single-Walled Carbon Nanotubes in Water

Understanding the mechanism and thermodynamics of the adsorption of chemicals on carbon nanotubes (CNTs) is important to risk assessment and pollution control of both CNTs and chemicals. We computed the adsorption of cyclohexane, benzene derivatives, and polycyclic aromatic hydrocarbons (PAHs) on (8,0) single-walled carbon nanotubes by the M05-2X of density functional theory. The computed adsorption energies (E(a)) in the aqueous phase are lower than those in the gaseous phase, indicating that the adsorption in the aqueous phase is more favorable. The contribution of π-π interactions and the enhancing effect of a -NO(2) substituent on the adsorption were quantified. For a hypothetical aromatic with the same hydrophobicity (logK(OW)) to cyclohexane, π-π interactions contribute ca. 24% of the total interactions as indicated by E(a). -NO(2) enhances the π-π interactions due to its electron withdrawing effects, and contributes 24% to the value of E(a). Simple linear regression showed the computed Gibbs free energy changes for the adsorption correlate significantly with the experimental values (r = 0.97, p < 0.01). The correlation together with the computed thermodynamic parameters may be employed to predict the adsorption affinity of other chemicals. The study may pave a new way for evaluating/predicting the adsorption affinity of organic compounds on SWNTs and probing the adsorption mechanisms.

Activated Carbons Modified by Ar and CO2 Plasmas – Acetone and Cyclohexane Adsorption

Žemos temperatūros plazmos poveikis, leidžiantis valdyti daugelio rūsių medžiagų, pvz., polimerų, metalų, anglies, pavirsiaus savybes, siuo metu yra tiriamas daugelyje mokslo sricių. Aktyvintoji anglis (AC) dėl savo fizikinių ir cheminių savybių naudojama kaip struktūrinis elementas dujų filtruose, kurie adsorbuodami daugelį skirtingų garų is užtersto oro apsaugo kvėpavimo takus. Gerai žinoma, kad įvairios AC pavirsiaus funkcinės grupės lemia jų hidrofobine / hidrofiline elgseną. Same straipsnyje pristatomi pirminiai tyrimai, susije su žemos temperatūros plazmos poveikiu komercinei aktyvintajai angliai. Aktyvintoji anglis buvo granuliuojama ir dedama į žemos temperatūros plazmos rotacine bandymų kamerą. Kamera buvo užpildoma atitinkamomis reaktyviosiomis dujomis. Plazmos poveikis buvo tiriamas nustatant aktyvintosios anglies pavirsiaus dviejų pasirinktų rūsių organinių garų adsorbcijos izotermas, taip pat stebint sių garų adsorbcijos dinamiką ant dujų filtro, pagaminto is plazma aktyvintos anglies. Remiantis gautais rezultatais, galima daryti isvadą, kad žemos temperatūros plazmos technologija gali būti taikoma aktyvintosios anglies savybėms pagerinti užtikrinant geresne žemos temperatūros organinių garų adsorbciją. DOI: http://dx.doi.org/10.5755/j01.ms.18.2.1919

On the use of ethanol for evaluating microporosity of activated carbons prepared from Polish lignite

Microporous activated carbons prepared by KOH chemical activation or steam activation from lignite were characterised by adsorption of N2 at 77K and CO2 at 298K. Subsequently, the adsorption of ethanol was carried out and complemented by adsorption of benzene and cyclohexane. The isotherm analysis included application of the αs method using ethanol reference data obtained here by also studying non-porous carbon blacks. The work confirmed that ethanol is an experimentally convenient adsorptive to use and leads to results in overall agreement with those obtained using other probe molecules. Of particular interest was the observation that ethanol can gain access to the whole microporosity even in the case of samples containing constricted micropore entrances. It was also possible to show that certain furnace carbon blacks contain intrinsic microporosity which is more difficult to unambiguously detect by adsorption of N2 at 77K. On the other hand, the results also suggested that the exact shape of the ethanol adsorption isotherm on a non-porous surface is more sensitive to the nature of the surface than has previously been found with other adsorptives.

Adsorption of hexane, cyclohexane, and benzene on microporous carbon obtained by pyrolysis of hypercrosslinked polystyrene

The relationships of adsorption of hexane, cyclohexane, and benzene on a D4609 microporous carbon adsorbent obtained by the pyrolysis of hypercrosslinked polystyrene are compared. It is shown that in the range of relative pressures corresponding to the filling of ultramicropores, the adsorption behaviors of cyclohexane and benzene are essentially identical, in contrast to hexane, which is characterized by higher adsorption values and isosteric heat of adsorption. The observed relationships are explained by the steric features of the distribution of molecules of various structures in ultramicropores.