Adsorption Of N-heptane Research Articles

Promotion of hydrophobic-hydrophilic separation of coal gasification fine slag through ultrasonic pre-treatment

Coal gasification fine slag (CGFS) is a solid waste byproduct generated during the coal gasification process. However, the high content of residual carbon hinders its potential for resource utilization. The urgent need for an efficient carbon extraction and ash reduction technology is evident. Hydrophobic–hydrophilic separation (HHS) is a technology that enriches hydrophobic particles in the oil phase while hydrophilic particles are in the water phase by stirring, and the different hydrophobic particles are separated by the separation of the oil and water phases. The molecular dynamics simulations revealed that the adsorption of n-heptane onto the residual carbon surface occurred spontaneously and was primarily driven by van der Waals forces. Ultrasonic pre-treatment pulp could enhance the effect of HHS. The fluctuation in tailings ash did not exceed 2% while the concentrate ash was reduced from 31.81% to 18.93% with a continual increase in ultrasonic power. The application of ultrasonic treatment on CGFS facilitated the separation of Carbon-ash molten state, as well as the elimination of ash materials particles residing within the pores of the residual carbon matrix and on its surface. Notably, many residual carbon particles are concentrated in the particle size range of 0.045–0 mm. The heightened hydrophobicity exhibited by particles within this size range enhanced the capture of oil droplets, thereby promoting the efficiency of HHS. This research aims to provide technical support and theoretical foundation for utilizing ultrasonic pretreatment as a means to enhance the HHS efficiency of CGFS.

Enhanced microwave regeneration of a polymeric adsorbent through carbon nanotubes deposition

Microwave (MW) regeneration can be an effective alternative to conventional adsorbent regeneration methods; however, regeneration of MW-transparent adsorbents can be challenging. In this study, multiwall carbon nanotube (CNT) was used to enhance the MW absorption and regeneration of Dowex Optipore V503, a commercial hypercrosslinked polymeric adsorbent with low dielectric loss factor. CNTs were dispersed in sodium dodecyl sulfate solution and physically deposited on the surface of the adsorbent at different weight percent (wt %). On average, coating the adsorbent with 0.1 to 0.3 wt% of CNT resulted in a 3 to 24% decrease in its surface area. Dielectric properties measurement revealed a sharp increase in the loss factor from 0.05 to 1.30 after coating the adsorbent with 0.3 wt% of CNT. MW energy needed to heat the adsorbent by 1 °C decreased from 722 to 13 J/g at 0.3 wt% of CNT owing to improved MW absorption by CNT-coated adsorbent. Finally, 5 cycles of n-heptane adsorption and MW-assisted regeneration were completed for CNT-coated and as-received adsorbent samples. The deposition of a very small amount of CNTs (0.1 to 0.3 wt%) on the adsorbent increased the MW-assisted desorption efficiency by 103% to 284% compared to the as-received adsorbent. These results are encouraging because they show that addition of small amounts of CNT can be effective in enhancing the MW regeneration of MW-transparent adsorbents.

Synergic role of platinum (Pt) and molybdenum trioxide (MoO3) promoted HBEA zeolite towards n-heptane isomerization

The potentiality of Pt and MoO3 loading on HBEA zeolite in enhancing n-heptane isomerization was investigated. The multiple characterization techniques revealed the engagement of Pt and MoO3 on the lattice or defect structures of the HBEA framework. Furthermore, the occurrence of dealumination was confirmed by the existence of hydrated aluminium-molybdate, Al2-(MoO4)3. These findings proposed the presence of strong metal-support interactions. The n-heptane isomerization was comparatively investigated over Pt and MoO3 modified catalysts, and significantly higher rate of n-heptane conversion (0.059 μmol/g-cat m2 s) and rate of iso-heptane formation (0.026 μmol/g-cat m2 s) were achieved with Pt/MoO3-HBEA catalyst. The catalytic performance followed the order of Pt/MoO3-HBEA > MoO3-HBEA > Pt-HBEA > HBEA. It is anticipated that the results of in-situ FTIR studies of low-temperature hydrogen adsorption and n-heptane adsorption analyses help elucidate the isomerization mechanism and indicated there was a prerequisite for the presence of both Pt and MoO3 as dissociation and adsorption active sites for enhanced n-heptane isomerization. This study sheds light on the design of new type of MoO3 based catalysts for isomerization reaction.

Positron study of adsorption of n-heptane in SBA-3

The sorption of n-heptane in the SBA-3 silica was investigated using positron annihilation lifetime spectroscopy (PALS). The PALS technique allows to study in situ evolution of pore filling by the n-alkane. In the dry SBA-3, the free volumes attributed to the silica skeleton, micropores, mesopores as well as intergranular spaces can be distinguished by PALS as various ortho-positronium components. The liquid n-heptane appears as an additional component, which allows to monitor adsorption and desorption using the ortho-positronium parameters. Filling the SBA-3 silica with n-heptane leads to the rapid, already at p/p0 = 0.08, disappearance of the pore-related components. Simultaneously, a large increase in the intensity of the components attributed to liquid n-heptane is observed. The adsorption proceeds slightly faster than the desorption, which is most likely the consequence of the difference in the alkane–alkane and alkane-silica interaction forces. The pore size distributions calculated for n-heptane and water from the PALS results clearly indicate that the mechanism of sorption is different for both liquids. This can result from the different strength of the interactions between molecules of each liquid and between the liquid and the atoms of pore walls.

Nickel-containing hybrid ceramics derived from polysiloxanes with hierarchical porosity for CO2 methanation

Abstract Nickel-containing hybrid ceramics were prepared by pyrolytic conversion from either methyl or methyl-phenyl polysiloxanes mixed with bistrimethoxysilylpropylamine (BisA) as a complexing agent and nickel salt. Materials with tailorable characteristics were generated by varying the pyrolysis temperature from 400 up to 600 °C in order to evaluate their applicability in the CO2 methanation. The materials were characterized by thermogravimetric analysis (TGA), N2 adsorption-desorption isotherms (BET-BJH), water and n-heptane adsorption, X-ray diffraction (XRD) and transmission electron microscopy (TEM). In-situ X-ray diffraction analysis (in-situ XRD) was used to evaluate the Ni particle structure and size during a simulated catalytic reaction. Porous hybrid ceramics (ceramers) with high specific surface areas (100–550 m2 g−1), hydrophobic or hydrophilic surfaces and different Ni particle sizes (4–7 nm) were obtained by varying the pyrolysis temperature and polysiloxane composition. The pyrolytic conversion of polysiloxanes combined with the complexing amino-siloxane BisA not only permitted a good dispersion of the Ni nanoparticles but also enabled the formation of hierarchical porosity with micro-, meso- and macropores. Regarding the catalytic performance, ceramers prepared from methyl polysiloxane exhibited a more hydrophobic surface and improved catalytic performance compared to the ones prepared from methyl-phenyl polysiloxane. A negative effect on the catalytic performance of ceramers was observed with increasing pyrolysis temperatures, which led to an increase in Ni particle size (from 4 to 7 nm), and lower levels of conversion and selectivity. The ceramers pyrolyzed at 400 °C exhibited the best catalytic performance, showing selectivity up to ∼77% and good stability over a 10 h test, during which the Ni particle size was preserved.

Surface modification of molecular sieve fillers for mixed matrix membranes

Two requirements of a porous filler for Mixed Matrix Membranes [MMMs] are a good adhesion to the polymer and the openness of its pores. The surface of SAPO-34 has been grafted with moieties containing amino groups, aromatic rings, and fluorinated chains, for a good adhesion to glassy polyimides, aromatic polymers and perfluoropolymers. The controlled excess of the modification agent – preferably trichlorosilanes – in hydrophobic solvents and the strict control of moisture in the reaction environment prevent the growth of thick layers of grafts around the crystals. XPS confirms the success of the derivatizations and indicates a homogeneous and thin coverage of the surface. The negligible reduction of the surface area suggests that the modification of the surface does not plug the micropores. The counter-intuitive faster adsorption of n-heptane in silicalite-1 after modification with bulky fluorinated grafts indicates the openness of the pores even for large molecules, and the reduction of the resistance to the transport of mass across the surface of the molecular sieves, thanks to the reduced amount of water adsorbed on the hydrophobic outer surface of the crystals.

Efficient Pt/Silicalite-1 catalyst for isomerization of n-heptane

The isomerization of n-heptane was studied over highly dispersed Pt/Silicalite-1 catalysts, and significantly higher n-heptane conversion and isomerization selectivity were achieved when compared with Pt/SiO2 catalysts. The outstanding performance of Pt/Silicalite-1 catalysts was attributed to the high dispersion of Pt on Silicalite-1, the strong interaction between Pt nanoparticles and Silicalite-1, and the stronger n-heptane adsorption capacity on the catalysts.

Positron Annihilation Lifetime Spectroscopy Application to <i>In Situ</i> Monitoring of <i>n</i>-Heptane Sorption in Mesopores

The dynamics of n-heptane adsorption and desorption on two silicas (Si-A and SBA-15) with different porosity was studied using positron annihilation lifetime spectroscopy (PALS). Simplified method of spectra analysis consisting in the summation of counts in the long-lived part of PALS spectra was used. It allowed to observe changes occurring in the minute time scale. The dependence of the number of counts on time could be fairly well approximated by exponential functions. It was found that the time required for reaching equilibrium in long cylindrical pores is up to ten times longer than in bell-mouthed interconnected ones. The longest time constants (ca. 5 min in Si-A and ca. 60 min in SBA-15) were observed for desorption in both samples.

N-heptane adsorption and desorption in mesoporous materials

Positron Annihilation Lifetime Spectroscopy (PALS) was used for an in situ monitoring of adsorption and desorption processes. The disordered and ordered porous silica as well as the porous polymer were used as adsorbents, while an adsorbate in all the cases was n-heptane. The lifetimes and particularly the intensities of the ortho-positronium(o-Ps) components depend strongly on the adsorbate pressure. The analysis of these dependencies allows us to identify several processes, which are taking place during sorption. At low pressure, an island-like growth of the first layers of the adsorbate on the silica, in a contrary to a swelling of the polymer, is observed. A size of the pores, which remain empty, is estimated at the subsequent stages of the adsorbate condensation and evaporation. The adsorbate thrusting into micropores is deduced at p/p0 > 0.6 whilst the mesopores are still not completely filled.

Adsorption deformation of AUK microporous carbon adsorbent at adsorption of n-heptane

Isotherms of relative linear adsorption deformation are measured on an AUK microporous carbon adsorbent for adsorption of @n-heptane in the pressure range of from 1 Pa to 5 kPa and the temperatures of 273, 293, 313, 353, and 393 K. The curves of adsorption deformation behave in a similar way in the whole range of studied temperatures: the adsorbent is practically not deformed in the range of small and medium fillings and its drastic expansion is observed in the range of high fillings. Numeric simulation of n-heptane adsorption in AUK pores is carried out using the model of slit-shaped pores equivalent to porosity parameters determined on the basis of the Dubinin’s bulk micropore filling theory for AUK. The relationship has been established between adsorption deformation of the adsorbent and adsorbate structure variation in micropores.

N-Heptane adsorption in periodic mesoporous silica by in situ positron annihilation lifetime spectroscopy

The development and testing of positron annihilation lifetime spectroscopy (PALS) – the method used for the characterization of a model pore system, is presented. The PALS technique is used to study in situ the porosity changes during n-heptane adsorption and desorption in the periodic mesoporous silica SBA-15. The results are analyzed in terms of PALS spectra as well as nitrogen and n-heptane conventional adsorption/desorption experiment. The PALS results allow to monitor character of a n-heptane multilayer at p/p0<0.45. The multilayer made of “isles” is formed during adsorption, while a much smoother layer of adsorbed n-heptane remains during desorption. In the pressure range where n-heptane capillary condensation occur (p/p0=0.45–0.55) a hysteresis of the ortho-positronium intensities is observed. A similar phenomenon is commonly registered during the nitrogen conventional adsorption and desorption isotherm for mesoporous solids. Above p/p0=0.55, when the regular pores in the SBA-15 are filled with n-heptane, a small amount of pores blocked by condensate plugs remains empty.

&lt;i&gt;In Situ &lt;/i&gt;Monitoring of Adsorption and Desorption of &lt;i&gt;n&lt;/i&gt;-Heptane on Porous Silica by Positron Annihilation Lifetime Spectroscopy

Positron annihilation lifetime spectroscopy study of n-heptane adsorption and desorption on silica gel Si-60 gives insight into a free volume evolution during those processes. Analysis of the lifetime distribution allows to ascribe particular ortho-positronium components to silica walls, mesopores and n-heptane. Hysteresis loop of the intensities of the mesopore and n-heptane related components similar to classic adsorption/desorption isotherms is observed. Transition from an adsorbate multilayer structure to liquid when pores become completely filled, manifests itself as an intensity change. Kinetics of desorption and adsorption studies allows to determine the time of reaching the equilibrium by the Si 60–n-heptane system at various pressures.

N-Heptane hydroconversion over nickel-loaded aluminum- and/or boron-containing BEA zeolites prepared by recrystallization of magadiite varieties

Phase-pure [Al]BEA and [Al,B]BEA zeolites, prepared by solid-state recrystallization of synthetic aluminum-containing magadiites and conventionally synthesized [B]BEA, were tested, after ion exchange with nickel, as bifunctional catalysts for hydroconversion of n-heptane. The reducibility of nickel ions incorporated into BEA zeolites by ion exchange was investigated by temperature-programmed reduction (TPR). The acidity of the samples was characterized with strong (pyridine (Py) and ammonia (NH3)) and weak (nitrogen) bases. The adsorbed bases were studied by transmission FT-IR (Py), diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy (N2), and temperature-programmed ammonia evolution (TPAE, NH3). Over Ni/H-[B]BEA the reactants were completely converted via fast hydrogenolysis, whereas this reaction pathway plays only a negligible role in the hydroconversion over Ni/H-[Al]BEA and Ni/H-[Al,B]BEA zeolites. Boron-containing BEA zeolites were less active catalysts than the boron-free catalyst in the principal unimolecular hydroconversion reactions. However, incorporation of boron into the framework of BEA zeolite results in a considerable selectivity shift toward isomerization. Results suggest that the acid strength of bridged hydroxyls, probed with weak (N2) and strong basis (pyridine), was found to be similar in the boron-free and boron-containing BEA samples. The decrease in the isomerization rate and the increase of the apparent activation energy upon incorporation of boron may be attributed to the decrease in the heat of n-heptane adsorption.

N-Heptane adsorption and desorption on porous silica observed by positron annihilation lifetime spectroscopy

Many papers are devoted to interpretation of adsorption of gases on solids. A complete understanding of the mechanism of pore filling and emptying by adsorbate molecules is a fundamental meaning for obtaining the accurate parameters characterizing the pore structure. The present article deals with application of positron annihilation lifetime spectroscopy (PALS) for determination of free volumes dimensions in pores upon adsorption process. On the basis of PALS spectra a comprehensive insight into adsorption mechanism of n-heptane in silica gel is presented.

Towards predictive molecular simulations of normal and branched alkane adsorption in carbonaceous engine deposits

Engine deposits are complex carbonaceous materials that tend to accumulate on the inner surfaces of the car engine. The presence of these deposits leads to adverse engine performance through a variety of mechanisms that strongly depend on the porous nature of the deposits. The two objectives of this study are to characterize these materials and elucidate their interactions with representative components of the fuel at various conditions. Previously, we used experimental data from a single ethane adsorption isotherm at 278 K to develop a model of engine deposits, based on simple slit pore geometry, and obtained representative pore size distributions for two samples of the deposits. Here we extend this approach to another type of engine deposit, compare simulation predictions to experimental results for ethane adsorption at various conditions, and explore adsorption of more complex species such as n-butane and isobutane. Finally, we provide predictions for the adsorption of n-heptane and isooctane and demonstrate that substantial amounts of these species would be adsorbed in engine deposits in the equilibrium limit under typical engine conditions. Although the simulation predictions most likely overestimate the amount adsorbed, it is clear that the adsorption processes can not be ignored in the engine operation optimization.

Experimental and Simulation Study of n-Heptane Adsorption on Rutile

The adsorption of n-heptane on microcrystalline rutile has been studied experimentally by thermodynamic techniques (adsorption isotherms and microcalorimetry) over a wide range of coverage at 303 K and complemented by Grand Canonical Monte Carlo simulations. The differential heat of adsorption exhibited three descending segments corresponding to the adsorption of n-heptane on three types of surfaces. The mean molar adsorption entropy of n-heptane in the monolayer was less than the entropy of the bulk liquid by ca. −23 J/(mol K), thus revealing a hindered state of motion for the n-heptane molecules on the surface of rutile. Simulations of the adsorption of n-heptane were performed on the three most abundant crystallographic faces of rutile. The adsorption isotherm obtained from the combination of the isotherm for each face weighted by the respective abundance was found to be in good agreement with experimental data. A structural characterization of n-heptane near the surface was also conducted which indicated that the substrate strongly perturbed the distribution of the n-heptane conformations relative to the situation found for the gaseous phase. Adsorbed molecules are predominantly orientated with their long axes, with the zig-zag planes of their backbones parallel to the surface and preferentially aligned along the five-fold cus Ti4+ ions of the faces. Fewer gauche conformations were observed for molecules near the surface than was characteristic of the bulk phase.

Adsorption of n-Heptane and 2-Methylheptane in the Gas Phase on Polyvinylidene Chloride-Based Microporous Activated Carbon

The selective adsorption of n-heptane and 2-methylheptane was tested on polyvinylidene chloride-based microporous carbon (CMS-IMP12) prepared from pyrolysis of poly(vinylidene chloride-co-vinyl chloride) (PVDC-PVC) copolymer. CMS-IMP12 was characterized by textural analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) and Raman spectroscopies. These results indicate the presence of graphene subunits inside the amorphous carbon and great quantity of sp2 carbon type in CMS-IMP12. It was found that 2-methylheptane is better adsorbed than n-heptane on the carbon sample by an inverse gas chromatography (IGC) adsorption study at 275−350 °C. Structural features of the carbonaceous material, entropy restrictions by steric parameters, diffusion conditions, and cooperative CH/π interactions between CH in n-heptane and 2-methylheptane and π electrons in the carbon walls determine the selective adsorption.

Effect of Pt and Sn on the adsorption of n-heptane in γ-Al2O3 catalyst models

The Grand Canonical Monte-Carlo (GCMC) method has been used to carry out simulations of the adsorption of n-heptane in models of naphtha-reforming catalysts. Models used in the study differed in the number and distribution of metal atoms-Pt and Sn. The number of adsorbed n-heptane molecules grows linearly with increasing number of metal atoms. The effect of Pt content on the adsorption of n-heptane molecules is most distinct at approximately 100 kPa and within the lower range of the temperatures investigated. In the models of bimetallic catalysts, the effect of the two metals is additive. [Figure: see text]. Effect of Pt and Sn on number of n-heptane molecules adsorbed in Al2O3 catalyst in 773 K and 1000 kPa.

Simulating adsorption of n-heptane in the Pt/Al 2O 3 model: Influence of platinum

The molecular modeling method refered to in the literature as Grand Canonical Monte Carlo was used to analyze the phenomenon of n-heptane adsorption on the Pt/γ-Al 2O 3 catalyst. In order to describe relevant interactions, use was made of the forcefield methods (UFF and CVFF). With the conditions adopted for the purpose of the study, Pt was found to exert an advantageous effect on the adsorption of n-heptane. The number of adsorbed molecules was related to the content of the noble metal, and the relation was directly proportional, when temperature and pressure were constant. The contribution of Pt was most distinct at 573 K and 100 kPa.

Adsorption of petroleum organic compounds on natural Wyoming montmorillonite

Adsorption of petroleum organic compounds on natural Wyoming montmorillonite clay is an irreversible process, as most of organic species still remain adsorbed on mineral after aging. The process is conditioned by the petroleum paraffinic content and by molecules containing alkane chains, as only these type of compounds easy intercalate within the clay interlayer. Such adsorption also involves an irreversible displacement of part of the clay interlayer water. The partial dissolution of the clay matrix is indicated by XRD as an irreversible modification of the clay structure. On the contrary, adsorption of n-heptane or toluene molecules on the same clay are reversible processes, since the clay mineral recover its original crystalline structure after aging and evaporation of the organic species.