Removal of paracetamol on biomass-derived activated carbon: Modeling the fixed bed breakthrough curves using batch adsorption experiments

The remediation of paracetamol (PA), an emerging contaminant frequently found in wastewater treatment plants, has been studied in the low concentration range (0.3–10 mg L−1) using as adsorbent a biomass-derived activated carbon. PA uptake of up to 100 mg g−1 over the activated carbon has been obtained, with the adsorption isotherms being fairly explained by the Langmuir model. The application of Reichemberg and the Vermeulen equations to the batch kinetics experiments allowed estimating homogeneous and heterogeneous diffusion coefficients, reflecting the dependence of diffusion with the surface coverage of PA. A series of rapid small-scale column tests were carried out to determine the breakthrough curves under different operational conditions (temperature, PA concentration, flow rate, bed length). The suitability of the proposed adsorbent for the remediation of PA in fixed-bed adsorption was proven by the high PA adsorption capacity along with the fast adsorption and the reduced height of the mass transfer zone of the columns. We have demonstrated that, thanks to the use of the heterogeneous diffusion coefficient, the proposed mathematical approach for the numerical solution to the mass balance of the column provides a reliable description of the breakthrough profiles and the design parameters, being much more accurate than models based in the classical linear driving force.

Drying of rye (Lolium miltiflorum l.) in fixed bed with parallel air flow.

This work aimed to study the drying of ryegrass seeds (Lolium multiflorum L.) in fixed bed dryer with parallel air flow.

Pentachlorophenol (PCP) dechlorination in horizontal-flow anaerobic immobilized biomass (HAIB) reactors

This study verifies the potential applicability of horizontal-flow anaerobic immobilized biomass (HAIB) reactors to pentachlorophenol (PCP) dechlorination. Two bench-scale HAIB reactors (R1 and R2) were filled with cubic polyurethane foam matrices containing immobilized anaerobic sludge. The reactors were then continuously fed with synthetic wastewater consisting of PCP, glucose, acetic acid, and formic acid as co-substrates for PCP anaerobic degradation. Before being immobilized in polyurethane foam matrices, the biomass was exposed to wastewater containing PCP in reactors fed at a semi-continuous rate of 2.0 mu g PCP g(-1) VS. The applied PCP loading rate was increased from 0.05 to 2.59 mg PCP l(-1) day(-1) for RI, and from 0.06 to 4.15 mg PCP l(-1) day(-1) for R2. The organic loading rates (OLR) were 1.1 and 1.7 kg COD m(-3) day(-1) at hydraulic retention times (HRT) of 24 h for R1 and 18 In for R2. Under such conditions, chemical oxygen demand (COD) removal efficiencies of up to 98% were achieved in the HAIB reactors. Both reactors exhibited the ability to remove 97% of the loaded PCP. Dichlorophenol (DCP) was the primary chlorophenol detected in the effluent. The adsorption of PCP and metabolites formed during PCP degradation in the packed bed was negligible for PCP removal efficiency. (C) 2009 Elsevier Ltd. All rights reserved.

On the applicability of the Aris' equivalent sphere in multicomponent reacting systems

The validity of the concept of equivalent sphere introduced by Aris in 1957 to multicomponent reacting systems is investigated in this paper. A network of C6 hydrocarbon reforming reaction and a fixed bed reactor are taken as the model reaction network and the reactor configuration, respectively.

Effects of promoters on catalytic activity and carbon deposition of Ni/gamma-Al2O3 catalysts in CO2 reforming of CH4

Catalytic reforming of methane with carbon dioxide was studied in a fixed-bed reactor using unpromoted and promoted Ni/gamma-Al2O3 catalysts. The effects of promoters, such as alkali metal oxide (Na2O), alkaline-earth metal oxides (MgO, CaO) and rare-earth metal oxides (La2O3, CeO2), on the catalytic activity and stability in terms of coking resistance and coke reactivity were systematically examined. CaO-, La2O3- and CeO2-promoted Ni/gamma-Al2O3 catalysts exhibited higher stability whereas MgO- and Na2O-promoted catalysts demonstrated lower activity and significant deactivation. Metal-oxide promoters (Na2O, MgO, La2O3, and CeO2) suppressed the carbon deposition, primarily due to the enhanced basicities of the supports and highly reactive carbon species formed during the reaction. In contrast, CaO increased the carbon deposition; however, it promoted the carbon reactivity. (C) 2000 Society of Chemical Industry.

Oxidation of toluene in waste gas streams using mesoporous Ti-hexagonal mesoporous silica

Various mesoporous catalysts with titanium loadings between 0.5 and 4 Ti wt. % and surface areas between 600 and 1,600 m(2)/g were synthesized using the molecular designed dispersion technique. These catalysts were tested using toluene oxidation in a fixed bed reactor at temperatures between 300 and 550degreesC. The reaction products were found to be CO2 and CO with selectivity towards CO2 above 80% for all catalysts. The catalytic activity of the catalysts increases with titanium loading. The total conversion at 550degreesC was not affected by the textural porosity, but increased textural porosity did significantly reduce the ignition temperature by up to 50degreesC. The Thiele modulus was calculated to be much less than one for all these materials indicating that the reaction rate is not diffusion, limited.

Enrichment of autotrophic anaerobic ammonium-oxidizing consortia from various wastewaters

The option for biological nitrogen removal has recently been broadened with the description of simultaneous nitrification/denitrification, anaerobic ammonium oxidation (ANAMMOX) and the concept of CANON (completely autotrophic nitrogen removal over nitrite). An autotrophic anaerobic ammonium oxidation (AAAO) consortium was successfully selected and enriched from municipal treatment plant sludges in Sydney, Australia, but not from industrial coke-oven wastewater sludges. Chemolithoautotrophic basic salt (CLABS) medium was used in the selection of AAAO organisms and chloramphenicol was added to the initial stage of selection to eliminate denitrifiers. Two different temperatures, 37degreesC and 55degreesC, were used in the selection of mesophilic and thermophilic consortia, respectively. Thermophilic AAAO organisms were not selected at 55degreesC. Mesophilic AAAO activities, however, were evident in both batch and continuous cultures, whereby ammonium was consumed concurrently with a decrease of nitrite, giving a ratio of 1:1-1:1.3 in ammonium removal rate over nitrite consumption rate. A continuous-mode mesophilic fixed-bed reactor was established to enrich the AAAO consortium. After 1 year, biofilms, pinkish in color, had developed on the support media and side wall of the feed-line tubing. Ammonium and nitrite consumption increased from similar to15 mg to 60 mg d(-1) L-1 over a period of 243 days. Later, transmission electron microscopy (TEM) and fluorescence in situ hybridization (FISH) techniques revealed that the dominant cell type in the AAAO consortium had a similar morphology and 16S rDNA sequence homology to that of the recently described ANAMMOX organism, Brocadia anammoxidans.

Catálise de hydrocraking baseado em zeólitos

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia Química

The thermal effects on the methanol-to-olefins reaction: A modelling and experimental approach

With the projection of an increasing world population, hand-in-hand with a journey towards a bigger number of developed countries, further demand on basic chemical building blocks, as ethylene and propylene, has to be properly addressed in the next decades. The methanol-to-olefins (MTO) is an interesting reaction to produce those alkenes using coal, gas or alternative sources, like biomass, through syngas as a source for the production of methanol. This technology has been widely applied since 1985 and most of the processes are making use of zeolites as catalysts, particularly ZSM-5. Although its selectivity is not especially biased over light olefins, it resists to a quick deactivation by coke deposition, making it quite attractive when it comes to industrial environments; nevertheless, this is a highly exothermic reaction, which is hard to control and to anticipate problems, such as temperature runaways or hot-spots, inside the catalytic bed. The main focus of this project is to study those temperature effects, by addressing both experimental, where the catalytic performance and the temperature profiles are studied, and modelling fronts, which consists in a five step strategy to predict the weight fractions and activity. The mind-set of catalytic testing is present in all the developed assays. It was verified that the selectivity towards light olefins increases with temperature, although this also leads to a much faster catalyst deactivation. To oppose this effect, experiments were carried using a diluted bed, having been able to increase the catalyst lifetime between 32% and 47%. Additionally, experiments with three thermocouples placed inside the catalytic bed were performed, analysing the deactivation wave and the peaks of temperature throughout the bed. Regeneration was done between consecutive runs and it was concluded that this action can be a powerful means to increase the catalyst lifetime, maintaining a constant selectivity towards light olefins, by losing acid strength in a steam stabilised zeolitic structure. On the other hand, developments on the other approach lead to the construction of a raw basic model, able to predict weight fractions, that should be tuned to be a tool for deactivation and temperature profiles prediction.

Sakkaroosin hydrolyysi immobilisoidulla entsyymillä

Työssä tutkittiin sakkaroosin hydrolyysiä anioninvaihtohartseihin immobilisoidun entsyymin avulla tavoitteena löytää sellainen kantaja-entsyymi -yhdistelmä, jolla konversio halutuiksi lopputuotteiksi olisi mahdollisimman korkea. Työhön valittiin aikaisemmissa laboratoriokokeissa parhaita tuloksia saavuttaneet kantaja-entsyymi -parit. Entsyymeinä oli kaksi nestemäistä Saccharomyces cerevisiae -hiivasta eristettyjä entsyymivalmistetta. Kokeissa käytetyt kantajamateriaalit olivat erilaisia heikkoja anioninvaihtohartseja. Entsyymit immobilisoitiin kantajaan sekoitusreaktorissa ja niiden aktiivisuudet määritettiin sitomisen jälkeen. Hydrolyysikokeet tehtiin jatkuvatoimisessa kiintopetireaktorissa ja lisäksi panos-kokeina tutkittiin ominaisuuksiltaan erilaisten kantajien eroja hydrolyysissä. Reaktio-olosuhteet pidettiin kaikissa kokeissa samoina. Sakkaroosiliuoksen pitoisuus oli 50 p-%, reaktiolämpötila 50 oC ja pH 5. Kiintopetikolonnissa tutkittiin myös sakkaroosi-liuoksen viipymäajan vaikutusta sivutuotteiden syntyyn. Näytteet analysoitiin neste-kromatografilla. Kiintopetikolonnissa lyhimmän viipymäajan (15 min) kokeissa ainoastaan hitaimmilla kantaja-entsyymi -pareilla muodostui sivutuotteita, jotka hydrolyysireaktion edetessä kuitenkin hävisivät. Kun viipymäaikaa kasvatettiin sivutuotteiden synty väheni ja lopulta niitä ei havaittu syntyvän lainkaan. Hydrolyysin edetessä viipymäajan ollessa tarpeeksi pitkä pienet sivutuotekomponentit hävisivät sakkaroosin hajotessa kokonaan glukoosiksi ja fruktoosiksi. Verrattaessa partikkelikoon ja hartsimatriisin vaikutusta samaan entsyymiin sidottuna havaittiin, että niillä kummallakin on vaikutusta sekä sakkaroosin hydrolyysi-nopeuteen että sivutuotteiden muodostumiseen.

Catalytic gasification of glycerol in supercritical water

The conversion of glycerol in supercritical water (SCW) was studied at 510-550 °C and a pressure of 350 bars using both a bed of inert and non-porous ZrO2 particles (hydrothermal experiments), and a bed of a 1% Ru/ZrO2 catalyst. Experiments were conducted with a glycerol concentration of 5 wt% in a continuous isothermal fixed-bed reactor at a residence time between 2 and 10 s. Hydrothermolysis of glycerol formed water-soluble products such as acetaldehyde, acetic acid, hydroxyacetone and acrolein, and gases like H2, CO and CO2. The catalyst enhanced the formation of acetic acid, inhibited the formation of acrolein, and promoted gasification of the glycerol decomposition products. Hydrogen and carbon oxides were the main gases produced in the catalytic experiments, with minor amounts of methane and ethylene. Complete glycerol conversion was achieved at a residence time of 8.5 s at 510 °C, and at around 5 s at 550 °C with the 1 wt% Ru/ZrO2 catalyst. The catalyst was not active enough to achieve complete gasification since high yields of primary products like acetic acid and acetaldehyde were still present. Carbon balances were between 80 and 60% in the catalytic experiments, decreasing continuously as the residence time was increased. This was attributed partially to the formation of methanol and acetaldehyde, which were not recovered and analyzed efficiently in our set-up, but also to the formation of carbon deposits. Carbon deposition was not observed on the catalyst particles but on the surface of the inert zirconia particles, especially at high residence time. This was related to the higher concentration of acetic acid and other acidic species in the catalytic experiments, which may polymerize to form tar-like carbon precursors. Because of carbon deposition, hydrogen yields were significantly lower than expected; for instance at 550 °C the hydrogen yield potential was only 50% of the stoichiometric value.

Start-up of anaerobic reactors for slaughterhouse wastewater treatment

This study aimed to evaluate the start-up of a horizontal anaerobic fixed bed reactor (HAFBR) followed by an upflow anaerobic sludge blanket (UASB) for the slaughterhouse wastewater treatment. HAFBR was filled with bamboo rings and had 1.2 m in length, 0.10 m in diameter and volume of 7.5 L. The UASB had the volume of 15 L. The HAFBR and UASB operated at organic loading rate and hydraulic retention time average of 8.46 and 3.77 kg m-3 d-1 of COD and 0.53 and 0.98 days, respectively. During 150 days of monitoring system it was found pH 6.8, relatively high values of bicarbonate alkalinity (> 1000 mg L-1) and reduced values of volatile acids (70 to 150 mg L-1), which afforded average removal efficiencies of COD total and total suspended solids of the order of 31 and 23% in HAFBR and 79% and 63% in UASB. It can be concluded that the generation and consumption of bicarbonate alkalinity and total volatile acids, thereby maintaining the pH during the study indicated stable operation of the reactors. The COD removal in the reactors was satisfactory especially when it considers that the assessment was conducted in a period of adaptation of organisms to the effluent and also the high organic load applied during this period.

Aqueous-phase reforming of renewables for selective hydrogen production in the presence of supported platinum catalysts

The evolution of our society is impossible without a constant progress in life-important areas such as chemical engineering and technology. Innovation, creativity and technology are three main components driving the progress of chemistry further towards a sustainable society. Biomass, being an attractive renewable feedstock for production of fine chemicals, energy-rich materials and even transportation fuels, captures progressively new positions in the area of chemical technology. Knowledge of heterogeneous catalysis and chemical technology applied to transformation of biomass-derived substances will open doors for a sustainable economy and facilitates the discovery of novel environmentally-benign processes which probably will replace existing technologies in the era of biorefinary. Aqueous-phase reforming (APR) is regarded as a promising technology for production of hydrogen and liquids fuels from biomass-derived substances such as C3-C6 polyols. In the present work, aqueous-phase reforming of glycerol, xylitol and sorbitol was investigated in the presence of supported Pt catalysts. The catalysts were deposited on different support materials, including Al2O3, TiO2 and carbons. Catalytic measurements were performed in a laboratory-scale continuous fixedbed reactor. An advanced analytical approach was developed in order to identify reaction products and reaction intermediates in the APR of polyols. The influence of the substrate structure on the product formation and selectivity in the APR reaction was also investigated, showing that the yields of the desired products varied depending on the substrate chain length. Additionally, the influence of bioethanol additive in the APR of glycerol and sorbitol was studied. A reaction network was advanced explaining the formation of products and key intermediates. The structure sensitivity in the aqueous-phase reforming reaction was demonstrated using a series of platinum catalysts supported on carbon with different Pt cluster sizes in the continuous fixed-bed reactor. Furthermore, a correlation between texture physico-chemical properties of the catalysts and catalytic data was established. The effect of the second metal (Re, Cu) addition to Pt catalysts was investigated in the APR of xylitol showing a superior hydrocarbon formation on PtRe bimetallic catalysts compared to monometallic Pt. On the basis of the experimental data obtained, mathematical modeling of the reaction kinetics was performed. The developed model was proven to successfully describe experimental data on APR of sorbitol with good accuracy.

Novel technology for preparation of optically active chemicals

Asymmetric synthesis using modified heterogeneous catalysts has gained lots of interest in the production of optically pure chemicals, such as pharmaceuticals, nutraceuticals, fragrances and agrochemicals. Heterogeneous modified catalysts capable of inducing high enantioselectivities are preferred in industrial scale due to their superior separation and handling properties. The topic has been intensively investigated both in industry and academia. The enantioselective hydrogenation of ethyl benzoylformate (EBF) to (R)-ethyl mandelate over (-)-cinchonidine (CD)-modified Pt/Al2O3 catalyst in a laboratory-scale semi-batch reactor was studied as a function of modifier concentration, reaction temperature, stirring rate and catalyst particle size. The main product was always (R)-ethyl mandelate while small amounts of (S)-ethyl mandelate were obtained as by product. The kinetic results showed higher enantioselectivity and lower initial rates approaching asymptotically to a constant value as the amount of modifier was increased. Additionally, catalyst deactivation due to presence of impurities in the feed was prominent in some cases; therefore activated carbon was used as a cleaning agent of the raw material to remove impurities prior to catalyst addition. Detailed characterizations methods (SEM, EDX, TPR, BET, chemisorption, particle size distribution) of the catalysts were carried out. Solvent effects were also studied in the semi-batch reactor. Solvents with dielectric constant (e) between 2 and 25 were applied. The enantiomeric excess (ee) increased with an increase of the dielectric coefficient up to a maximum followed by a nonlinear decrease. A kinetic model was proposed for the enantioselectivity dependence on the dielectric constant based on the Kirkwood treatment. The non-linear dependence of ee on (e) successfully described the variation of ee in different solvents. Systematic kinetic experiments were carried out in the semi-batch reactor. Toluene was used as a solvent. Based on these results, a kinetic model based on the assumption of different number of sites was developed. Density functional theory calculations were applied to study the energetics of the EBF adsorption on pure Pt(1 1 1). The hydrogenation rate constants were determined along with the adsorption parameters by non-linear regression analysis. A comparison between the model and the experimental data revealed a very good correspondence. Transient experiments in a fixed-bed reactor were also carried out in this work. The results demonstrated that continuous enantioselective hydrogenation of EBF in hexane/2-propanol 90/10 (v/v) is possible and that continuous feeding of (-)-cinchonidine is needed to maintain a high steady-state enantioselectivity. The catalyst showed a good stability and high enantioselectivity was achieved in the fixed-bed reactor. Chromatographic separation of (R)- and (S)-ethyl mandelate originating from the continuous reactor was investigated. A commercial column filled with a chiral resin was chosen as a perspective preparative-scale adsorbent. Since the adsorption equilibrium isotherms were linear within the entire investigated range of concentrations, they were determined by pulse experiments for the isomers present in a post-reaction mixture. Breakthrough curves were measured and described successfully by the dispersive plug flow model with a linear driving force approximation. The focus of this research project was the development of a new integrated production concept of optically active chemicals by combining heterogeneous catalysis and chromatographic separation technology. The proposed work is fundamental research in advanced process technology aiming to improve efficiency and enable clean and environmentally benign production of enantiomeric pure chemicals.