Thesis (Ph. D.)--Ohio State University, 2009. / Title from first page of PDF file. Includes bibliographical references (p. 268-291).

The gas transport properties of side-chain crystalline poly(n-alkyl acrylate) and poly(m-alkyl acrylate) blends are determined as a function of temperature for varying side-chain lengths, n and m, and blend compositions. The side chains of poly(n-alkyl acrylate)s crystallize independently of the main chain for n [is greater than or equal to] 10 which leads to an extraordinary increase in the permeability at the melting temperature of the crystallites. The compatibility of these polymers are examined and macroscopic homogeneity is observed for a small range of n and m when the difference /n - m/ is between 2 - 4 methylene units. Thermal analysis shows that the blend components crystallize independently of one another; at the same time, the crystallization of each component is hindered by the presence the other component. The permeation responses of these blends show two distinct permeation jumps as the crystallites from each component melt at their respective melting temperatures. Blends with continuous permeation responses are found to have higher effective activation energies than observed for common polymers. Thermal analysis proved to be a useful tool to help predict the permeation response for poly(alkyl acrylates); thus the thermal behavior of poly(n-alkyl acrylate) blended with n-aliphatic materials and random copolymers of poly(n-alkyl acrylates) are briefly examined. A bulk modified atmospheric storage design is proposed where produce is stored in a rigid chamber that is equipped with both selective and non-selective membrane modules that help regulate the oxygen entering and the carbon dioxide leaving the produce compartment. The design enables control of the atmosphere inside the chamber by modulating gas flow, i.e. the gas flow rate and composition, through the non-selective membrane by delivering fresh air upstream of the non-selective membrane. The model shows that the choice of materials for the selective and non-selective membranes dictate the range of concentrations achievable; however, the air flow rate allows the control between these ranges. The method to design a practical chamber from this model is also described.

The main theme of this dissertation is the fabrication and analysis of modified mesoporous silica membranes for separation applications. Synthesis methods for mesoporous silica membranes have been developed to enhance the transport performance and quality of the membranes, such as permeability, pore volume, and surface area. Then, synthesized membranes were modified with different organic groups to tailor selectivity in separations. The collected studies of modified mesoporous silica membranes showed that appropriate functionalization on newly synthesized novel membranes leads to promising structural and permeation properties. First, a seeded growth method was developed for synthesis of MCM-48 membranes on alumina supports, thereby extending the seeded growth technique used for zeolite membranes to mesoporous silica membrane synthesis. The surface properties of the MCM-48 membranes were then modified by silylation with hexamethyldisilazane (HMDS). In comparison to MCM-48 membranes previously synthesized by the in situ growth technique, much less silica infiltration into the alumina support was observed. The pore structure of the MCM-48 membranes demonstrated that a large accessible pore volume was available for molecular permeation and pore modification to tailor selectivity. The gas permeation properties of the calcined and silylated MCM-48 membranes were consistent with a Knudsen-like mechanism, albeit with a substantial influence of gas-solid interactions in the mesopores. The silylated MCM-48 membranes were evaluated for pervaporative separation of ethanol (EtOH), methyl ethyl ketone (MEK), and ethyl acetate (EA) from their dilute aqueous solutions. The synthesized membranes exhibited high pervaporative separation factors and organic fluxes. The selective separation of organic/water mixtures with MCM-48 membranes were attributed to both the organophilic nature of the surface and the effective pore size of the silylated mesopores. Next, the synthesis and organic/water separation properties of mesoporous silica membranes supported on low-cost and scalable polymeric (polyamide-imide) hollow fibers and modified by trimethylsilylation with HMDS was studied. Thin, defect-free membranes that exhibited high gas permeances consistent with Knudsen-like diffusion through the mesopores were prepared. Silylation of these membranes did not affect the integrity of the mesoporous silica structure and the underlying polymeric hollow fiber, but led to capping of the surface silanol groups in the mesopores with trimethylsilyl groups. The silylated mesoporous membranes were evaluated for pervaporative separation of EtOH, MEK, EA, iso-butanol, and n-butanol from their dilute aqueous solutions. The membranes showed higher separation factors than those of flat membranes, along with high organic fluxes. The large increase in hydrophobicity of the membranes upon silylation allowed upgrading of the feed mixtures to permeate streams with considerably higher organic content. The selective separation of organic/water mixtures with the fiber-supported mesoporous silica membranes was attributed to both the organophilic nature of the surface (yielding good adsorption selectivity) and the effective pore size of the silylated mesopores (giving good fluxes). Comparison with other types of organic/water separation membranes revealed that the present silylated membrane platform shows good promise for use in organic/water separation applications due to its high flux, scalable and low-cost fabrication methodology, and good separation factors that can be further enhanced by tailoring the mesopore modification chemistry. Further, the gas transport properties of aziridine-functionalized mesoporous silica membranes on polymeric hollow fibers have also investigated. The mesoporous membranes were amine-functionalized with aziridine and their transport properties were studied to understand the effects of surface functionalization on gas separations. This new hybrid aminosilica membrane showed interesting and counter-intuitive N₂ selective permeation properties in dry CO₂/N₂ separations. Detailed characterization of the membrane structure and its permeation behavior showed that such behavior was due to the strong adsorption of CO₂, leading to reduced gas flux because of CO₂-induced amine crosslinking in the mesopores. This hyper-branched aminosilica membrane showed CO₂ selective properties when applied to humid gas permeation. Water molecules in the humid gas affected the adsorption of CO₂ molecules by causing a lower degree of crosslinking, allowing facilitated transport of CO₂.

Despite intrinsically high separation performance, conventional polymeric membranes suffer from CO₂ induced plasticization, which reduces CO₂/CH₄ separation efficiency significantly. Covalent ester-crosslinking can improve the plasticization resistance by controlling the segmental chain mobility in the polymer; however, only relatively thick selective skin layers and lower separation productivity have been reported to date. On the other hand, the high cost of crosslinkable polymers makes the approach challenging, especially for large-scale gas separations which require large membrane areas with high feed pressures. Dual-layer hollow fiber spinning can be used to reduce the cost of membrane production by integrating a low-cost supporting core polymer with the expensive crosslinkable sheath polymer. However, the complexity of interfacial interaction between the sheath/core layers and subsequent crosslinking required can delaminate the sheath/core layers and collapse the core layer polymer. This can reduce mechanical strength and the separation productivity significantly. This work aimed to develop thin-skinned high-performing ester-crosslinked hollow fiber membranes with improved CO₂ plasticization resistance. The skin layer thickness of hollow fibers was first optimized by simultaneous optimization of the polymer dope and spinning process variables. Moreover, this study also addresses the solutions of challenging in transitioning the monolithic hollow fiber to composite hollow fiber format. The ester-crosslinked hollow fibers were subjected to high feed pressures and high-level contaminants to probe their CO₂ plasticization and hydrocarbon antiplasticization resistance, respectively. The resultant ester-crosslinked monolithic hollow fibers show significantly reduced skin layer thickness and improved separation productivity under extremely challenging operation conditions. They also demonstrate strong stability under high feed pressures and reversibility after contaminant exposure. Moreover, this study presents a newly discovered core layer material, Torlon®, which demonstrates excellent compatibility with the crosslinkable polymer and superior thermal stability during crosslinking without sheath/core layer delamination or collapse. The characterization under aggressive feed conditions clearly suggests that ester-crosslinked composite hollow fibers can achieve high separation performance and reduce membrane cost simultaneously. This provides a significant advance in state of the art for natural gas separations under realistic operation environments

It had been shown that the transport properties of CMS membranes varies as a function of H₂S exposure making the conditioning protocol an important step in identifying the steady state properties of CMS membranes. In this study the conditioning of CMS membranes with H₂S was studied for the determination of the acid gas steady state transport properties. The conditioned steady state has been shown to be the same state for both an extended conditioning protocol using high pressure mixed gas and a rapid conditioning protocol using pure H₂S. The rate of conditioning does vary between the two conditioning protocols as the rapid conditioning protocol takes 48 hours less to reach the conditioned steady state. The results of this study also show that oxygen doping during the formation of the CMS membrane affects the final, conditioned steady state transport properties.

Emulsion polymerized mixed matrix (EPMM) membranes is a new category of membranes, which incorporate silica-based inorganic nanoparticles dispersed in continuous phase of an organic polymer. The uniqueness of the EPMM membranes comes from the fact that they may combine otherwise incompatible inorganic and organic phases. This is achieved by the synthesis of the inorganic nanoparticles from a silica precursor in a stable emulsion, in which an aqueous phase is dispersed in a continuous phase of the polymer solution. More specifically, the silica precursor soluble in the polymer solution polymerizes in contact with the aqueous phase, and consequently the latter acts as finely dispersed micro reactors. The objective of this work was to optimize the previously developed protocol for the synthesis of poly (2,6-dimethyl-1,4pheneylene oxide) (PPO) based EPMM membranes, and to characterize their physical and gas transport properties. In particular, the effects of inorganic loading and the membrane post-treatment protocol on the permeability and selectivity of the membranes were of interest. However, the results showed that the obtained permeation and separation were virtually not affected by the theoretical Si loading and the post-treatment protocol. Moreover, in comparison to the base PPO membranes, the observed O2 permeability and the O2/N2 permselectivity have generally decreased. The differential scanning calorimetry (DSC) analysis of the synthesized membranes showed an important scatter of the glass transition temperatures (Tg) of the EPMM membranes with the values generally lower than the Tg of the base PPO. Moreover, the inductively coupled plasma mass spectrometry (ICP-MS) showed the silica content in selected EPMM membranes to be far below the expected theoretical level. This, in combination with the 29Si nuclear magnetic resonance (29Si NMR) results, showed that most of the already low silica content comes from the unreacted silica source (tetraethylorthosilicate) and have led to the second phase of the project in which a modified synthesis protocol has been developed. The major differences of the modified protocol compared to the original one include the replacement of a surfactant, 1-octanol, by ethanol and using greater concentrations of the reactants. To study the effect of different parameters involved in the synthesis protocol, a Gravimetric Powder experiment, in which the inorganic polymerization is carried out in an emulsion with a pure solvent rather than a polymer solution, has been designed. The Gravimetric Powder experiments have confirmed polymerization of tetraethylorthosilicate (TEOS) in the emulsion system. Using the conditions, which resulted in the maximum production of the polymerized TEOS in the Gravimetric Powder experiments, one set of new EPMM membranes has been synthesized and characterized. The new EPMM membranes have the Tg of 228.2oC, which is distinctly greater compared to the base PPO, and contain one order of magnitude more of silica compared to the old EPMM membranes. More importantly, the 29Si NMR analysis has proven that the silica content in the new EPMM membranes originates from the reacted rather than unreacted TEOS. Interestingly, the observed conversion of TEOS in the new EPMM membranes, exceeding 20%, is greater than the largest conversion in the Gravimetric Powder experiments. The oxygen permeability in the new EPMM membrane of 33.8 Barrer is more than twice that of the base PPO membrane. Moreover, this increase in O2 permeability is associated with a modest increase in the O2/N2 permselectivity (4.75 versus 4.67).

Mixed matrix membranes that comprise domains of organic and inorganic components are investigated in this research. Such materials effectively circumvent the polymeric 'upper bound trade-off curve' and show properties highly attractive for industrial gas separations. Nevertheless, lack of intrinsic compatibility between the organic polymers and inorganic fillers poses the biggest challenge to successful fabrication of mixed matrix membranes. Consequently, control of the nanoscale interface between the sieve and polymer has been the key technical challenge to the implementation of composite membrane materials. The overarching goal of this research was to devise and explore approaches to enhance the performance of mixed matrix membranes by properly tailoring the sieve/polymer interface. In an effort to pursue the aforementioned objective, three approaches were developed and inspected: (i) use of silane coupling agents, (ii) hydrophobizing of sieve surface through alcohol etherification reactions, and (iii) a two-step modification sequence involving the use of a Grignard reagent. A comparison was drawn to evaluate these methodologies and the most effective strategy (Grignard treatment) was selected and further investigated. Successful formulation and characterization of mixed matrix membranes constituting zeolite 4A modified via the Grignard treatment are described in detail. Membranes with impressive improvements in gas separation efficiency and mechanical properties were demonstrated. The basis for the improvements in polymer/sieve compatibility enabled by this specific process were proposed and investigated. A key aspect of the present study was illuminating the detailed chemical mechanisms involved in the Grignard modification. Systematic characterization and carefully designed experiments revealed that the formation of distinctive surface structures is essentially a heterogeneous nucleation process, where Mg(OH)2 crystals grow from the nuclei previously extracted from zeolites. In addition to the main work, discovery of sonication-induced dealumination of zeolites was made during the systematic exploration of Grignard chemistry. The new procedure employing sonication can potentially be applied to prepare zeolites with a variety of Si/Al ratios under relatively mild conditions. The last part of this thesis focused on development of a technique to generalize the highly specific Grignard treatment to inorganic materials other than zeolite 4A. This work delivered composite membranes with improved interfacial adhesion. Moreover, research revealed the effect of surface nuclei density on the ultimate morphology of deposited nanostructures and how different surface morphologies influence polymer/filler interaction in composite membranes. Methods were devised to tailor the morphologies of such structures in order to optimize adhesion enhancement. The acquired results demonstrated the potential of extending this modification process to a broad domain of materials and render it a general methodology for interfacial adhesion promotion.

A separação de gases é um processo que está presente na grande maioria das indústrias e a utilização de membranas vem ganhando cada vez mais importância e destaque. Neste trabalho foram fabricadas membranas de carbono suportadas em um tubo cerâmico de alumina TCB99 (99 % de alumina) a partir da pirólise (atmosfera inerte de N2) do polímero poli(éter imida) (PEI). A técnica de recobrimento por imersão foi utilizada para formar uma camada de solução polimérica sobre o suporte. Os filmes poliméricos e de carbono e as membranas de carbono suportadas foram caracterizados em relação à estrutura utilizando diferentes técnicas morfológicas, químicas e de estrutura. Além disso, foram realizados testes de sorção nos filmes de carbono e permeação de gases nas membranas de carbono. Também foram realizadas simulações de dinâmica molecular para obter um melhor entendimento das etapas de degradação do polímero, da conformação das cadeias poliméricas e formação da estrutura de carbono durante o processo de pirólise. As membranas de carbono suportadas apresentaram uma camada seletiva bem definida e com pouca ou nenhuma intrusão nos poros do suporte. Os resultados das análises estruturais mostraram que as membranas de carbono são constituídas em sua maior parte por carbono amorfo, podendo conter carbono grafite. Foi observado pelos resultados de FTIR, CNS e DRX que o polímero precursor, poli(éter imida), não foi totalmente pirolisado na temperatura máxima empregada, contendo possivelmente grupamentos de amida e anéis benzênicos. Através de simulação de dinâmica molecular foi possível obter um melhor entendimento sobre o processo de formação e composição da membrana de carbono, confirmando os resultados obtidos experimentalmente em relação à morfologia e estrutura destas, isto é, a formação de uma estrutura amorfa contendo nanodomínios de grafite. A sorção dos gases pelo material da membrana de carbono (MC) seguiu um padrão prescrito pela literatura, onde o gás CO2 apresentou maior sorção, seguido pelos gases CH4, N2 e He. Além disso, verificou-se que para as membranas produzidas em maior temperatura obtiveram um aumento na sorção dos gases He e N2, o qual atribui-se a formação de uma estrutura mais porosa. Os testes de desempenho de permeação de gases (He, CO2, O2, N2, CH4, C3H6 e C3H8) para as membranas de carbono nas diferentes concentrações de polímero (10, 15 e 20 % (m/m)) indicaram a formação de uma estrutura porosa, onde os mecanismos de permeação predominantes foram difusão de Knudsen e difusão superficial, indicando a presença de poros maiores e/ou defeitos na estrutura da membrana, possivelmente causado pela grande área de suporte utilizada. Ainda foi observado que um aumento na concentração de polímero, acarretou em um aumento da permeância para todos os gases, o que pode estar relacionado com o aumento de volume livre no polímero precursor quando submetido à pirólise. Os resultados obtidos demonstram que as membranas de carbono desenvolvidas neste trabalho apresentam potencial para serem aplicadas em processos de separação de gases. / The gas separation is a process that is present in the vast majority of industries and the membranes use is gaining more and more importance and prominence. In this work carbon membranes supported on a TCB99 alumina ceramic tube (99 % alumina) were manufactured from the pyrolysis (N2 inert atmosphere) of the poly(imid ether) (PEI) polymer. The immersion coating technique was used to form a layer of polymer solution on the support. The polymer and carbon films and the supported carbon membranes were characterized in relation to the structure using techniques of microscopy and spectroscopy, among others. In addition, sorption tests were performed on carbon films and gas permeation on carbon membranes. Molecular dynamics simulations were also performed to obtain a better understanding of polymer degradation steps, polymer chain conformation and carbon structure formation during the pyrolysis process. The supported carbon membranes presented a well defined selective layer with little or no intrusion into the pores of the support. The results of the structural analyzes showed that the carbon membranes are composed mostly of amorphous carbon and may contain graphite carbon. It was observed by the FTIR, CNS and XRD results that the precursor polymer, poly(imide ether), was not completely pyrolyzed at the maximum temperature employed, possibly containing amide groups and benzene rings. By means of molecular dynamics simulation it was possible to obtain a better understanding of the formation and composition of the carbon membrane, confirming the results obtained experimentally in relation to the morphology and structure of these, this is, the formation of an amorphous structure containing graphite nanodomains. The gases sorption by the MC material followed a standard prescribed in the literature, where the CO2 gas presented higher sorption, followed by CH4, N2 and He gases. In addition, it was observed that for the gases He and N2, the membranes produced at higher temperature obtained an increase in the sorption, which is attributed to the formation of a more porous structure. The gas permeation tests (He, CO2, O2, N2, CH4, C3H6 and C3H8) for the carbon membranes at the different polymer concentrations (10, 15 and 20 % (m/m)) indicated the formation of a porous structure, where the predominant permeation mechanisms were Knudsen diffusion and surface diffusion, indicating the presence of larger pores and/or defects in the membrane structure, possibly caused by the large support area used. It was further noted that an increase in polymer concentration resulted in increased permeability for all gases, which may be related to the increase in free volume in the precursor polymer when subjected to pyrolysis. The results obtained demonstrate that the carbon membranes developed in this work have the potential to be applied in gas separation/adjustment processes.

L’acier est produit aujourd’hui principalement en faisant appel à une technologie basée sur le procédé haut fourneau-convertisseur à l’oxygène, conduisant à trois types d’émissions principales: le gaz de haut fourneau (BFG), le gaz de cokerie (COG), et le gaz de convertisseur (BOFG). Dans le cadre du projet VALORCO, une analyse des possibilités de réduction des émissions carbonées, associée à une valorisation des émissions de la sidérurgie, a été réalisée. Une des voies étudiées est la production de composés d’intérêt industriel tel que méthanol, pouvant être produit par transformation chimique du CO et/ou CO2 contenus dans les émissions, associé à de l’hydrogène. L’objectif principal de ce travail de thèse consiste à évaluer les possibilités offertes par le procédé de perméation gazeuse, appliqué à la récupération sélective de ces composés dans les 3 types d’émissions. Dans un premier temps, un état de l’art des différents projets dédiés à la capture (CCS) et à la valorisation (CCU) des émissions dans l’industrie de l’acier est présenté, avec une attention particulière aux différentes technologies de séparation des gaz. Des mesures expérimentales de sélectivité et de perméance pour différentes conditions de température et de pression, réalisées sur banc dédié avec deux matériaux membranaires disponibles commercialement et sélectif à l’hydrogène (vitreux) et au CO2 (élastomère) ont permis une étude paramétrique systématique par simulation des performances de séparation du procédé appliqué au BFG, COG et BOFG. Une comparaison des procédés basés sur un seul ou plusieurs étages de perméation, y compris avec des boucles de recirculation, a ensuite été entreprise dans un environnement de type Process System Engineering (PSE, logiciel Aspen Plus). L’influence des paramètres opératoires (rapport de pression, température, taux de prélèvement) sur les performances de séparation a été réalisée, conduisant à une cartographie des compositions atteignables. La consommation énergétique et la surface membranaire nécessaires pour chaque configuration permettent au final une optimisation techno-économique du procédé, sur la base d’un modèle économique intégré aux conditions de simulation / Steel is produced today mainly in a blast furnace-oxygen converter process, leading to three main types of emissions: blast furnace gas (BFG), coke oven gas (COG), and converter gas (BOFG). In the framework of the VALORCO project, an analysis of the possibilities for reducing carbon emissions, combined with the valorization of emissions from the steel industry, was carried out. One of the routes studied is the production of compounds of industrial interest such as methanol, which can be produced by chemical transformation of the CO and / or CO2 contained in the emissions associated with hydrogen. The main objective of this thesis work is to evaluate the possibilities offered by the gas permeation process applied to the selective recovery of these compounds in the three types of emissions. Initially, a state of the art of the various projects dedicated to the capture (CCS) and the valorization (CCU) of the emissions in the steel industry is presented, with particular attention to the different gas separation technologies. Experimental measurements of selectivity and permeance for different temperature and pressure conditions, carried out on a dedicated bench with two commercially available membrane materials, one selective to hydrogen (glassy) and one to CO2 (rubbery), allowed a systematic parametric study by simulation of the separation performance of the process applied to the BFG, COG and BOFG. A comparison of the processes based on one or more permeation stages, including recirculation loops, was then undertaken in a Process System Engineering (PSE) environment (Aspen Plus software). The influence of the operating parameters (pressure ratio, temperature, stage cut) on the separation performance was evaluated, leading to a mapping of attainable compositions. The energy consumption and the membrane surface required for each configuration allow a techno-economic optimization of the process, on the basis of an economic model integrated to the simulation conditions

In order to find/design porous materials that could be used in practical applications involving adsorption, it is important to investigate the basic properties (i.e. isosteric heat, specific surface area, binding energy, pore size, pore volume, etc.) of each material. With this aim in mind we have looked at three different types of materials: single-walled carbon nanotubes (prepared by the HiPco and laser methods), single-walled nanohorns (dahlia-like and bud-like) and metal-organic frameworks (Cu-BTC and RPM-1). For these substrates we have measured volumetric adsorption isotherms using several gases such as neon, argon, tetrafluoromethane (CF4), xenon, and methane (not all gases for all substrates). Experimental adsorption isotherms were measured using methane, argon, xenon, and neon gases on unpurified single-walled carbon nanotubes prepared by the HiPco method. The main idea behind these experiments was to investigate, using different size gas molecules, the sites available for adsorption on this type of porous material. We found that surface area occupied by these adsorbates on the sample is the same, regardless of their size. This means that all the gases have access to the same group of adsorption sites. Since the biggest adsorbate in this experiment was Xe, and since it is unlikely that it could penetrate the interstitial channels in the nanotube bundles, we conclude that none of the gases, including the smallest one - Ne, are able to adsorb in the interstitial channels in bundles of single-walled carbon nanotubes. For the case of argon on laser produced single-walled carbon nanotubes we measured 21 adsorption isotherms using argon gas temperatures between 40 and 153 K that were used to determine the isosteric heat of adsorption for this system. Our experimental results were compared to the ones from computer simulations performed by J. K. Johnson (from the University of Pittsburgh) for the same gas on heterogeneous and homogenous bundles. It was observed that the isosteric heat data matches better with data computed for heterogeneous nanotube bundles. This indicates that at the lowest pressure and coverages argon might be adsorbing in the defect-induced interstitial channels. We studied Cu3(Benzene-1,3,5-tricarboxylate)2(H2O)3 (abbreviated as Cu-BTC) metal-organic framework with argon to determine the sites available for adsorption on this material. Volumetric adsorption isotherms were measured at temperatures between 66 and 143 K. We found two substeps in the isotherm data, indicating that there are two types of pores present in the material: tetrahedrally-shaped side pockets and the main channels. Our experimental results were compared with data from simulations conducted using the Grand Canonical Monte Carlo method. We determined that the theoretical results match reasonably well with ours if the coverage is scaled down by a factor of 1.6. We explored the potential of two different metal-organic framework materials (Cu-BTC and RPM-1) for gas separation application. We used argon and tetrafluoromethane (CF4) gases to check if this can be achieved through kinetic and steric mechanisms. We found that Cu-BTC has excellent potential in gas separation using a steric mechanism, since argon easily adsorbs into the small pores present in the sample, while CF4 is excluded from them. Adsorption properties of RPM-1 showed that it could be employed in gas separation using a kinetic mechanism - argon gas adsorbs and reaches equilibrium in the pores of the sample more than the order of magnitude faster than CF4. Closed-ended dahlia-like nanohorns were studied with neon and tetrafluoromethane gases. In the first layer of neon and tetrafluoromethane adsorbed on dahlia-like nanohorns we found two substeps. These results were compared with results of computer simulations performed by Prof. M. Calbi. We determined, after comparison with the simulation isotherms, that the lower pressure substeps correspond to adsorption of Ne and CF4 in the narrowest parts of interstitial channels of the aggregates. Surface area calculated from neon isotherms was found to be higher than the one obtained using CF4, meaning that the smaller Ne molecule has the access to the parts of the interstitial channels that are not accessible for the bigger CF4 molecule. Features that appeared in neon adsorption isotherms on bud-like nanohorn aggregates were quite different from the ones on dahlia-like aggregates. We measured neon adsorption isotherms on this type of sample at temperatures between 22 and 49 K. In the monolayer regime we observed one single substep whose origin we can not definitely identify, because the structure of the bud-like nanohorns is not well-known. The binding energy value that was calculated from the isotherm data was lower than the value for neon adsorbed in the grooves of nanotube bundles but higher than for neon on graphite.