"De-lubrication is the first stage in a sintering operation, where the lubricants (higher weight hydrocarbons) are removed from the parts by controlled heating. Improper de-lubrication leads to defects such as blistering, sooting, micro-porosity etc in a sintered part. Most of these problems arise, as there exists a gap in the present understanding of de-lubrication. The primary motive of this work is to direct research towards the development of sensors and controls and thus, mitigate the various problems due to improper de-lubrication. Currently, there exists a myriad of lubricants being used during the process of compaction. They include metallic based lubricants, polymers and non-metallic lubricants. In this work, research was limited in understanding the de-lubrication of EBS (Ethylene Bisstearimide), as, it the most commonly used lubricant in the industry. It has replaced commonly used lubricant due to cleaner burnouts, absence of metallic residue and, cost effectiveness. The entire work is divided into three phases: • Phase 1: Ascertained the most important parameters that affect the kinetics of de-lubrication. • Phase 2: Investigated the type of gases released during the decomposition of EBS. • Phase 3: Recommended a control strategy. TGA (Thermo-gravimetric analysis) was used in the phase I, the results clearly show that the rate of heating is the most important parameter during de-lubrication. Identification of gases was performed using the FTIR (Fourier transform infrared spectroscopy) and DUV (Deep ultraviolet spectroscopy). This constituted the second phase of our experiments. The primary gases identified in Phase II were carbon dioxide and a hydrocarbon (hepta-decane). Finally, an empirical model for de-lubrication has been proposed in Phase III. The model was verified in an industrial furnace. It has been observed that there exists a very good correlation between the proposed empirical model and the experiments performed in Phase II of this study. This study lays down the following guidelines for the development of future sensors and controls: • The development of future sensors should focus in the detection of CO2 and hepta-decane. • Rate of heating determines how fast or slow the lubricant decomposes and finally escapes form the compacted part. • The empirical model may be used, as a means to determine the time a part should reside in a furnace for complete lubricant burnout at a given heating rate."

Este trabalho investigou a deposição dos filmes finos de ferritas de lantânio dopado com estrôncio e cobalto La1-xSrxCo1-yFeyO3-δ (LSCF) através da técnica de spray pirólise empregando precursores inorgânicos e silício como substrato. Foram utilizados água e etanol na proporção de (3:1) como solvente na preparação da solução a ser aspergida. As deposições foram realizadas em diferentes temperaturas: 130ºC, 150ºC, 170ºC e 200ºC. Os filmes de LSCF antes e após o tratamento térmico foram analisados por difração de raios X (DRX) e microscopia eletrônica de varredura (MEV). O spray de deposição dos filmes em função das soluções com diferentes proporções de etanol (0%, 50%, 75% e 100%) foi investigado utilizado uma câmera rápida de alta resolução e um laser com comprimento de onda 532 nm. Os resultados evidenciaram que a temperatura de ebulição do solvente e de deposição são parâmetros importantes na determinação da morfologia dos filmes. Maiores teores de etanol promovem um aumento nos valores do ângulo de cone e que a propriedade da tensão superficial exerce significativamente maior influência nos aspectos que envolvem a estrutura do spray, a atomização do líquido, formação de gotas e no ponto de ruptura das soluções Os resultados de DRX apresentaram a fase cristalina majoritária de LSCF após o tratamento térmico a 750°C por 2 horas e a fase secundária de La2O3. As imagens de MEV evidenciaram a formação de filmes para as distâncias de deposição de 120 mm, embora apenas na temperatura de 200°C apresentasse uma estrutura porosa antes e após o tratamento térmico. A presença de interdifusão e microporosidade foi observada para esse filme. Para as diferentes composições de LSCF nas condições de 120 mm e a 200°C, apenas as composições de La1-xSrxCo0,2Fe0,8 com x = 0,6, 0,9 e 0,7 apresentaram estrutura porosa após o tratamento térmico. O filme de La0,8Sr0,2Co0,2Fe0,8 apresentou maior condutividade iônica/elétrica e energia de ativação. A presença de fases secundárias (La2O3, SrO2 e La2CoO3) contribuiu para a redução da condutividade elétrica e iônica e a energia de ativação. / This work investigated the deposition conditions of thin lanthanum ferrite films doped with strontium and cobalt – La1-xSrxCo1-yFeyO3-δ (LSCF) through the spray pyrolysis technique using inorganic precursors and silicon as a substrate. Water and ethanol were used in the proportion (3:1) as solvent in the preparation of the solution to be sprinkled. The depositions were carried out at different temperatures: 130°C, 150°C, 170°C and 200°C. The films of LSCF were analyzed by X-ray diffraction and scanning electron microscopy before and after thermal treatment. The XRD results showed the obtainment of crystalline phase of LSCF after thermal treatment at 750°C/2hours and secondary phase of La2O3. The sprays of solutions with different proportions of ethanol (0%, 50%, 75% and 100%) were analyzed using a fast high-resolution camera and a laser with a wavelength of 532nm.The results showed those deposition temperature and solvente boiling points are important parameters to determine the thin morphology Higher ethanol levels promote an increase in the cone angle values and that the property of the surface tension exerts significantly greater influence on issues involving the structure of the spray, the atomization of the liquid, the droplets formation and the breaking point of the solutions. The XRD results showed the obtainment of majority crystalline phase of LSCF after thermal treatment at 750°C/2 hours with the presence of secondary phase of La2O3. The SEM images showed formation of films for the distance of 120 mm, although only at the temperature of 200°C it presents porous morphology before and after thermal treatment. The presence of interdiffusion and microporosity was observed for this film. For different LSCF compositions under the conditions of 120 mm and 200°C, the films of La1-xSrx Co0,2Fe0,8 with x = 0,6; 0,9 and 0,7 presented porous morphology after thermal treatment. Otherwise, the film of La0,8Sr0,2Co0,2Fe0,8 showed the highest ionic/electrical conductivity. The presence of secondary phase (La2O3, SrO2 and La2CoO3) evidenced by XRD promoted a decrease in ionic/electrical conductivity and in the activation energy.

A kinetic study of the pyrolysis of municipal solid waste (MSW) was carried out bythermogravimetric analysis (TGA). Different runs were performed at heating rates of 5, 10and 150C/min. The effect of the N2, CO2 and O2 gas with different combination in theprocess was also evaluated. The results show that the most weight loss was obtained whenthe MSW was treated at a temperature interval of (20-750)0C which led to a weigh loss of95%. The kinetic study of the pyrolysis process showed also the gas mixture used in theprocess effect also the activation energy of the process and the presence of the CO2 in theincreased the activation energy (Ea) to 56 kJ/mol. Higher concentration of CO2 in the processlead to increase in the activation energy which is not optimal for the reaction. The treated andthe untreated samples were incubated and the biological activity was observed. The resultsshow that the pretreated samples did not have any biological activity. From these results itcould be concluded that the thermal pretreatment could be an alternative way for of waste forlong period of time, which could have significant impact in i.e. for transportation anddurability during storage. / Program: Högskoleingenjörsutbildning i kemiteknik

La compréhension de la chimie prébiotique et la recherche de matière organique d’origine extraterrestre qui lui est associée sont parmi les thématiques fortes de la branche de l’astrobiologie qui concerne notamment la recherche de traces de vie dans notre Système Solaire. C’est avec cet objectif que nous nous sommes intéressés à deux objets du Système Solaire : le satellite saturnien Titan, pour ses aérosols organiques, et Mars, pour son habitabilité avérée et la recherche de matière organique in situ. A ces fins, nous avons mis en œuvre deux techniques permettant d’étudier la matière organique de ces objets : la simulation expérimentale qui permet de reproduire en laboratoire des conditions environnementale extraterrestres et la préparation d’analyse in situ grâce à des laboratoires entièrement automatisés implémentés sur des véhicules mobiles, à savoir les rovers Curiosity/MSL actuellement en activité à la surface de Mars et le futur rover Pasteur de la mission ExoMars. La première partie de cette étude est ainsi consacrée à la simulation expérimentale appliquée à l’étude des aérosols organiques de Titan. Nous avons synthétisé en laboratoire des analogues (tholins) de ces aérosols, puis nous avons étudié leur composition moléculaire par pyrolyse et chromatographie en phase gazeuse couplée à la spectrométrie de masse (Pyr-GC-MS). Nous avons tout particulièrement investigué l’influence de la composition du mélange gazeux permettant la synthèse de nos tholins (taux de méthane dans du diazote) sur leur composition moléculaire. Une étude systématique par Pyr-GC-MS nous a permis d’estimer les conditions optimales d’analyse dont la température de pyrolyse. Dans un second temps, nous nous sommes intéressés à l’analyse in situ du sol martien par les instruments SAM-GC-MS et MOMA-GC-MS à bord du rover Curiosity et du futur rover Pasteur respectivement. Ces deux instruments ont la possibilité de mettre en œuvre des techniques de prétraitements des échantillons par chimie humide (dérivatisation) pour faciliter l’extraction, la volatilisation, la préservation et l’identification de la matière organique présente dans le sol martien. Parmi ces techniques, nous avons optimisé les conditions analytiques de la thermochimiolyse en présence de TMAH sur un sol analogue du sol martien pour assurer le succès des futures analyses in situ du sol de Mars par les instruments SAM et MOMA. / The understanding of prebiotic chemistry, and the search for organic matter of extraterrestrial origin associated with it, are among the strong themes of the astrobiology branch, which concerns in particular the search for traces of life in our Solar System. It is with this objective in mind that we have taken an interest in two objects of the Solar System: the Saturn satellite Titan, for its organic aerosols, and Mars, for its proven habitability and research of organic matter in situ. To this end, we have implemented two techniques to study the organic matter of these objects: experimental simulation, which allows the reproduction of extraterrestrial environmental conditions in the laboratory, and preparation of in situ analysis thanks to fully automated laboratories implemented on the Curiosity/MSL rover currently in operation on the surface of Mars, and the future Pasteur rover of the ExoMars mission. The first part of this study is thus devoted to the experimental simulation applied to the study of organic aerosols from Titan. We synthesized analogs (tholins) of these aerosols in the laboratory, then studied their molecular composition by pyrolysis and gas chromatography coupled to mass spectrometry (Pyr-GC-MS). We investigated in particular the influence of the composition of the gas mixture allowing the synthesis of our tholins (methane content in nitrogen) on their molecular composition. A systematic study by Pyr-GC-MS allowed us to estimate the optimal conditions of analysis including pyrolysis temperature. In a second phase, we were interested in the in situ analysis of the Martian soil by the SAM-GC-MS and MOMA-GC-MS instruments aboard the Curiosity rover and the future Pasteur rover respectively. These two instruments have the possibility of using wet chemistry (derivatization) techniques to pre-treat samples to facilitate extraction, volatilization, preservation and identification of the organic matter present in the Martian soil. Among these techniques, we have optimized the analytical conditions of thermochemolysis in the presence of TMAH on a terrestrial analog of the Martian soil to ensure the success of future in situ analyses of the Mars soil by the SAM and MOMA instruments.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Bibliography: leaves 594-611. / Sc.D.

<div>The chemical complexity of hydrocarbon fuels and the fast-expanding list of potential plantderived biofuels pose a challenge to the scientific community seeking to provide a molecular understanding of their combustion. More refined spectroscopic tools and methodologies must be developed to selectively detect and characterize the widening array of fuel components and combustion reactive intermediates. The direct relationship between molecular structure and rotational frequencies makes rotational spectroscopy highly structural specific; therefore, it offers a powerful means of characterizing pyrolysis ntermediates. This thesis describes experimental work using broadband microwave spectroscopy to address a number of challenging problems in the spectroscopy of gas complex mixtures.</div><div><br></div><div>Usually, the observed rotational spectra contain contributions from many distinct species, creating a complicated spectrum with interleaved transitions that make spectral assignment challenging. To assist with the process, a protocol called “strong-field coherence breaking” (SFCB) has been developed. It exploits multi-resonance effects that accompany sweeping the microwave radiation under strong-field conditions to output a set of transitions that can confidently be assigned to a single component in a mixture, thereby reducing the spectral assignment time.</div><div><br></div><div>The broadband chirped pulse Fourier transform microwave (CP-FTMW) spectra of guaiacol, syringol, 4-methyl guaiacol, 4-vinyl guaiacol were recorded under jet- cooled conditions over the 2-18 GHz frequency range. Using data from the 13C isotopomers the r0 structure of guaiacol was determined by means of a Kraitchman analysis. The tunneling due to OH hindered rotation was observed in syringol and the V2 barrier was deduced to be 50% greater than phenol’s barrier. This is due to the intramolecular H-bonding between the hydroxy and the methoxy groups. The internal rotation barrier for the methyl group for 4-methyl guaiacol was also determined. Moreover, the spectral assignment of the two conformers of 4-vinyl guaiacol was sped-up by using SFCB. The main structural insight from these lignin-related molecules was that polar substituents dictate the magnitude and type of structural shift that occurs relative to that of the unsubstituted aromatic ring.</div><div><br></div><div>In the next part of my work, the pyrolysis of 2-methoxy furan was carried out over the 300-1600 K temperature range, with microwave detection in the 2-18 GHz frequency range, using hightemperature flash pyrolysis micro-reactor coupled with a supersonic expansion. The SFCB technique was used to analyze and speed up the line assignment. The 2-furanyloxy radical, a primary, resonance-stabilized radical formed by loss of a methyl group in the pyrolysis of 2-methoxy furan, was detected and its molecular parameters were determined.</div><div><br></div><div>Finally, a unique setup that combines the high-resolution spectroscopic data provided by chirped pulse Fourier transform microwave (CP-FTMW) spectroscopy with photoionization mass spectra from a vacuum ultraviolet (VUV) time-of-flight mass spectrometer (TOF-MS) was used to find optimal conditions to detect reactive intermediates and make full assignments for the microwave spectra of phenoxy radical and o-hydroxy phenoxy radical over the 2-18 GHz range. Phenoxy radical was generated through the pyrolysis of anisole and allyl phenyl ether. Using a combination of data from 13C isotopomers and fully deuterated phenoxy radical, in combination with high level ab initio calculations, a near-complete r0 structure for the radical was obtained. The structural data point to the radical being a primarily carbon-centered rather than oxygencentered radical. Using guaiacol as precursor, we studied the spectroscopy of the o-hydroxy phenoxy radical, whose structural data is compared with that of phenoxy to understand the role played by the hydroxyl group in modifying the resonance stabilization of the radical.</div><div><br></div>

A pirólise de aerossóis ou spray pirólise (SP, do inglês Spray Pyrolysis) é uma importante metodologia para a obtenção de luminóforos e diferentes matrizes sólidas em dimensões nano a micrométricas, desde a escala laboratorial ao nível industrial. O arranjo experimental permite o ajuste de uma ampla faixa das temperaturas de pirólise (100 a 1000 °C), possibilitando que sistemas de interesse sejam obtidos em uma única etapa. Contudo, não existe um controle eficiente do ambiente de coordenação do íon emissor e a simetria deste será consequência do ambiente imposto pela estrutura cristalina ou amorfa da matriz sólida final. O tratamento térmico rápido, característico desta metodologia, pode dificultar a total cristalização de determinadas fases e, sendo assim, uma heterogeneidade nos sítios de simetria será obtida. Este trabalho tem como objetivos estudar as propriedades luminescentes de aluminatos dopados com íons terras raras. E nesse sentido, propuseram-se inicialmente metodologias para a obtenção de diferentes matrizes inorgânicas por SP visando o estudo do sítio de coordenação de íons lantanídeos. Num primeiro momento, foi proposto a metodologia para a obtenção de matrizes inorgânicas por SP mantendo a estrutura do sítio de coordenação de íons lantanídeos. Nesta estratégia foi escolhido um meio inorgânico estável, protegendo os íons terras raras ativos de perturbações externas, estável tanto do ponto de vista químico e térmico durante o processo de pirólise, YVO4:Eu3+ foi o escolhido por possuir sítios de simetria bem definidos e por ser um composto de grande interesse tecnológico. Ainda dentro dos objetivos, estudou a síntese de aluminatos dopados com íons ítrio visando à formação de sistemas compósitos (-Al2O3 / YAG). Os compostos foram primeiro obtidos pela co-dopagem com íons Eu3+ visando um estudo estrutural, e posteriormente, sistemas contendo Itérbio/Érbio e Itérbio/Túlio foram preparados, visto que são escassos os trabalhos que descrevem a síntese de partículas com propriedades de conversão ascendente de energia pela metodologia de pirólise de aerossol. A fase YAG foi obtida para diferentes proporções de Y3+/Al3+, porém também foi obtido a fase meta estável YAlO3 (YAH) em uma única etapa, sendo que essa fase é reportada na literatura como de difícil obtenção. Os compostos obtidos foram caracterizados principalmente por espectroscopia de fotoluminescência (espectros de emissão/excitação e tempos de vida), espectroscopia vibracional, Difratometria de raios X de pó, microscopia eletrônica e análise térmica / Spray Pyrolysis (SP) is an important methodology to obtain phosphors and different solid matrices in a nano-to-micrometric dimension, ranging from the laboratory scale up to the industrial level. The experimental arrangement allows the adjustment of a wide range of pyrolysis temperatures (100 up to 1000 ° C), which allows the system of interest obtention in a single step. However, there is no efficient control concerning the emitter ion coordination environment, and its symmetry will be a consequence of the environment imposed by the resultant solid matrix crystalline or amorphous structure. The rapid thermal treatment, which is the main characteristic of this methodology, it might hinder the total crystallization of certain phases and, thus, heterogeneity in the symmetry sites will be obtained. This study aims to study the luminescent properties of aluminates doped with Rare Earth (RE) ions. Under this perspective, several methodologies have been initially proposed in order to obtain different inorganic matrices using SP to study lanthanides coordination sites. At first, the methodology for obtaining inorganic matrices through SP maintaining the structure of the lanthanide ion coordination site was proposed. In this strategy, a stable (both chemically and thermally) inorganic medium was chosen, protecting the active rare earth ions from external perturbations during the pyrolysis process. YVO4:Eu3+ was selected for presenting well-defined symmetry sites and for its wide technological appeal. Moreover, the synthesis of aluminates doped with yttrium ions to form composite systems (-Al2O3 / YAG) has been carried out. The compounds were first obtained by co-doping with Eu3+ ions for a structural study. Subsequently systems containing Ytterbium / Erbium and Ytterbium / Yttrium were prepared, since there is a lack of description of these systems in the literature when its considered the synthesis of particles with energy upward conversion properties by aerosol pyrolysis methodology. The YAG phase was obtained using different proportions of Y3+/Al3+, but the stable YAlO3 (YAH) phase was also attained in a single step, even being reported as difficult to achieve in the literature. The compounds synthesized were characterized mainly by photoluminescence spectroscopy (emission/excitation spectra and lifetimes), vibrational spectroscopy, powder X-ray diffraction, electron microscopy and thermal analysis

La pyrolyse de sept molécules modèles de composés toxiques (le diéthyl éther, le bromoéthane, le chloroacétate de méthyle, le nitrométhane, le nitrate d’isopropyle, la diéthylamine, le chlorobenzène) a été étudiée lors de la thèse dans deux types de réacteur à l’échelle du laboratoire : un réacteur parfaitement agité (RPA) en silice et le réacteur tubulaire (RT) en alumine. Ce dernier pilote a été développé durant ce travail pour réaliser des études à des températures supérieures à 1200 K. Les profils axiaux de température dans le réacteur tubulaire ont été mesurés pour en tenir compte lors des simulations. Parallèlement à l’utilisation de la Chromatographie en phase Gazeuse, une nouvelle technique analytique pour notre laboratoire a été utilisée : la spectroscopie Infra-rouge à Transformée de Fourier (IRTF) pour laquelle une méthode d’analyse a été développée. Au cours de ces différentes études, des modèles cinétiques détaillés ont été développés à l’exception de la diethylamine. Globalement, ces modèles cinétiques reproduisent bien dans chaque étude la décomposition du réactif en fonction de la température et la formation des produits majoritaires déterminés expérimentalement. Etant donné le manque de données cinétiques dans la littérature pour la pyrolyse ou l’oxydation de composés bromés, chlorés et azotés, de nombreux paramètres cinétiques ont été estimés dans la plupart des modèles cinétiques développés / The pyrolysis of seven surrogates of toxic compounds (diethyl ether, bromoethane, methyl chloroacetate, nitromethane, isopropyl nitrate, diethylamine and chlorobenzene) was studied during the thesis in two different types of reactors at the laboratory scale: a silica jet-stirred reactor (JSR) and an alumina tubular reactor (TR) to carry out studies at temperatures above 1200 K. Axial temperature profiles were measured and were used to take into account the temperature gradient in the TR. In addition to gas chromatography, a new analytical technique for our laboratory was used: The Fourier Transform InfraRed Spectroscopy (FTIR), for which an analysis method has been developed. As part of the study, detailed kinetics models were developed except for the diethylamine. Overall, these kinetics models well predict the reactivity temperature dependence and the formation of the major products determined experimentally. Since there is a lack of kinetic data in the literature for the pyrolysis and oxidation of brominated, chlorinated and nitrogen compounds, many kinetic parameters were estimated in most of the kinetic models developed

Lignocellulosic biomasses are considered promising feedstocks for the next generation of biofuels and chemicals; however, the recalcitrance of lignocellulose remains a barrier to its utilisation over conventional sources. Pyrolysis is the heating of biomass to several hundred degrees Celsius in the absence of oxygen, which can thermally depolymerise lignocellulose. Products of pyrolysis are a solid biochar, liquid bio-oil and syngas. Biochar has roles in both carbon sequestration and soil amendment however bio-oil has no defined use, despite a high concentration of fermentable sugars. Bio-oil is a complex organic microemulsion with a host of biocatalyst inhibitors that makes its microbial degradation a challenge. In this work, the use of aerobic cultures using microbial communities isolated from natural environments saw limited potential; however, the use of anaerobic digestion (AD) successfully generated a higher volume of biogas from reactors with bio-oil than controls. Biogas yield test reactors were set up with anaerobic digestate from a wastewater treatment plant as the substrate for degradation and conversion of bio-oils. Next-generation 16S rRNA gene sequencing was utilised to characterise the communities in the reactors while the ultrahigh resolution mass spectrometry technique of Fourier transform ion cyclotron resonance (FT-ICR) was used for characterisation of the chemical changes occurring during AD. Both sets of high-resolution data were additionally combined for multivariate analysis and modelling of the microbial genera that correlated best with the changes in digestate chemistry. This represents a novel analysis method for the microbial degradation of complex organic products. Bio-oil from common lignocellulosic feedstock was the most easily degradable by the AD communities, with significant inhibition observed when bio-oils from anaerobic digestate and macroalgae were used. Additionally it was found that the inclusion of biochars that were pre-incubated in anaerobic digestate prior to use in AD were capable of significantly reducing the lag time observed for biogas production in bio-oil-supplemented reactors. The addition of biochars that were not pre-incubated had no effect on biogas production. Specific inhibition of methanogenesis was also capable of causing the digestates to accumulate volatile fatty acids (VFAs) as a product of greater value than biogas. Scale-up experiments will be required to confirm the precise practicalities of the addition of bio-oil to AD as well as to establish the potential for isolation and purification of VFAs.

Made available in DSpace on 2014-12-17T15:42:13Z (GMT). No. of bitstreams: 1 FrancielAB_DISSERT.pdf: 3637529 bytes, checksum: 50d6de8b3a00a0b045a5b17d540f59d2 (MD5) Previous issue date: 2014-01-20 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Catalytic processes are widely present in everyday life. This results in large number of studies seeking materials that may combine the low cost catalytic efficiency. Based on this assumption, the clays have long been used as catalysts, with its huge availability, diversity and possibility of improving their properties from structural changes, primarily responsible for this great use. Among the natural clays, vermiculite due to their characteristic properties (high cation exchange capacity and expansion), is suitable for various applications including as catalysts and catalyst supports. In this work, the acid leaching of clay vermiculite was performed, coming from Santa Luzia-PB, with nitric acid (2, 3 and 4 mol / L) and subsequent calcination of the materials obtained. The materials were named as Vx/400, where x is the acid concentration employed and 400 used in calcination temperature. The effectiveness of changes made was determined by XRD techniques, FT-IR, EDS, TG/DTG, nitrogen physisorption and DTP of n-butylamine. Acid leaching has improved some properties of the clay - specific area and acidity - but the control of the acid concentration used is of vital importance, since the highest concentration caused the partial destruction of vermiculite entailing a decline in their properties. For analysis of the catalytic activity of the modified clay was made a comparative study with the SBA -15 mesoporous materials, synthesized via hydrothermal method, using the pyrolysis of low density polyethylene (LDPE). The results showed that the acid plays a fundamental role in the conversion of the polymer into smaller molecules, the material V3/400 was more selective for the source monomer (ethylene) due to their increased acidity, which promotes more breaks bonds in the polymeric chain, while materials and V0/400 V2/400, lower acidity, showed higher selectivity to light hydrocarbons, the range of fuel (41.96 and 41.23%, respectively), due to less breakage and secondary condensation reactions chains; already V4/400 SBA-15/550 and resulted in lower percentages of light hydrocarbons and the partial destruction of the structure and low acidity, respectively, responsible for the inefficiency of materials / Os processos catal?ticos est?o largamente presentes no cotidiano. Isso resulta no grande n?mero de pesquisas buscando materiais que possam aliar baixo custo ? efici?ncia catal?tica. Partindo desse pressuposto, as argilas t?m sido muito utilizadas como catalisadores, sendo sua grande disponibilidade, diversidade e possibilidade de melhoria de suas propriedades, a partir de modifica??es estruturais, os principais respons?veis por esse grande uso. Entre as argilas naturais, a vermiculita devido ?s suas propriedades caracter?sticas (alta capacidade de troca cati?nica e de expans?o), ? apta para diversas aplica??es, entre elas, como suportes catal?ticos e catalisadores. Neste trabalho, foi realizada a lixivia??o ?cida da argila vermiculita, oriunda de Santa Luzia-PB, com ?cido n?trico (2, 3 e 4 mol/L) e posterior calcina??o dos materiais obtidos. Os materiais foram nomeados como Vx/400, onde x corresponde ? concentra??o ?cida empregada e 400 ? temperatura usada na calcina??o. A efici?ncia das modifica??es realizadas foi determinada pelas t?cnicas de DRX, FT-IR, EDS, TG/DTG, fisissor??o de nitrog?nio e DTP de n-butilamina. A lixivia??o ?cida melhorou algumas propriedades da argila ?rea espec?fica e acidez , por?m o controle da concentra??o ?cida empregada ? de vital import?ncia, visto que a maior concentra??o provocou a destrui??o parcial da vermiculita, acarretando em um decr?scimo das suas propriedades. Para an?lise da atividade catal?tica das argilas modificadas fez-se um estudo comparativo com o material mesoporoso SBA-15, sintetizado via m?todo hidrot?rmico, empregando-os na pir?lise de polietileno de baixa densidade (PEBD). Os resultados mostraram que a acidez exerce papel fundamental na convers?o do pol?mero em mol?culas menores; o material V3/400 foi o mais seletivo para o mon?mero de origem (eteno), devido ? sua maior acidez, que promove mais cis?es nas liga??es da cadeia polim?rica; enquanto os materiais V0/400 e V2/400, de menor acidez, apresentaram maior seletividade para hidrocarbonetos leves, da faixa dos combust?veis (41,96 e 41,23%, respectivamente), em virtude de menos cis?es e rea??es secund?rias de condensa??o nas cadeias; j? V4/400 e SBA-15/550 resultaram nos menores percentuais de hidrocarbonetos leves, sendo a destrui??o parcial da estrutura e baixa acidez, respectivamente, respons?veis pela inefici?ncia dos materiais