Synthesis of titanate nanostructures using amorphous precursor material and their adsorption/photocatalytic properties

This article reports on a new and swift hydrothermal chemical route to prepare titanate nanostructures (TNS) avoiding the use of crystalline TiO2 as starting material. The synthesis approach uses a commercial solution of TiCl3 as titanium source to prepare an amorphous precursor, circumventing the use of hazardous chemical compounds. The influence of the reaction temperature and dwell autoclave time on the structure and morphology of the synthesised materials was studied. Homogeneous titanate nanotubes with a high length/diameter aspect ratio were synthesised at 160 degrees C and 24 h. A band gap of 3.06 +/- 0.03 eV was determined for the TNS samples prepared in these experimental conditions. This value is red shifted by 0.14 eV compared to the band gap value usually reported for the TiO2 anatase. Moreover, such samples show better adsorption capacity and photocatalytic performance on the dye rhodamine 6G (R6G) photodegradation process than TiO2 nanoparticles. A 98% reduction of the R6G concentration was achieved after 45 min of irradiation of a 10 ppm dye aqueous solution and 1 g L-1 of TNS catalyst.

Produção de biodiesel etílico por via enzimática a partir de óleo de milho transgénico

Mestrado em Engenharia Química

Desidratação/oxidação seletiva de metanol recorrendo a catalisadores heterogéneos para a obtenção de biocombustíveis (DME e DMM)

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

Synthesis of biodiesel from wastes of food industry via direct transesterification with methanol/carbon dioxide mixtures

Dissertation presented at Faculdade de Ciências e Tecnologia from Universidade Nova de Lisboa to obtain the degree of Master in Chemical and Biochemical Engineering

The ruthenium-tin system

The Ru-Sn liquid-solid and some solid-solid equilibria have been completely revised by means of differential thermal analysis, X-ray powder diffraction and microprobe investigations. The existence of two intermetallic phases has been clearly established: Ru(0.4)Sn(0.6)decomposed by a peritectic reaction at 1266(+/-4)degrees C and Ru0.3Sn0.7 congruently melting at 1257(+/-2)degrees C.

Synthesis, structural order and magnetic behavior of self-assembled epsilon-Co nanocrystal arrays

The synthesis of magnetic nanoparticles with monodispere size distributions, their self assembly into ordered arrays and their magnetic behavior as a function of structural order (ferrofluids and 2D assemblies) are presented. Magnetic colloids of monodispersed, passivated, cobalt nanocrystals were produced by the rapid pyrolysis of cobalt carbonyl in solution. The size, size distribution (std. dev.< 5%) and the shape of the nanocrystals were controlled by varying the surfactant, its concentration, the reaction rate and the reaction temperature. The Co particles are defect-free single crystals with a complex cubic structure related to the beta phase of manganese (epsilon-Co). In the 2D assembly, a collective behavior was observed in the low-field susceptibility measurements where the magnetization of the zero field cooled process increases steadily and the magnetization of the field cooling process is independent the temperature. This was different from the observed behavior in a sample comprised of disordered interacting particles. A strong paramagnetic contribution appears at very low temperatures where the magnetization increases drastically after field cooling the sample. This has been attributed to the Co surfactant-particle interface since no magnetic atomic impurities are present in these samples.

Kinetics of selective oxidation of lactose to lactobionic acid over Pd-active carbon catalyst

Laktoosi eli maitosokeri on tärkein ainesosa useimpien nisäkkäiden tuottamassa maidossa. Sitä erotetaan herasta, juustosta ja maidosta. Laktoosia käytetään elintarvike- ja lääketeollisuuden raaka-aineena monissaeri tuotteissa. Lääketeollisuudessa laktoosia käytetään esimerkiksi tablettien täyteaineena. Hapettamalla laktoosia voidaan valmistaa laktobionihappoa, 2-keto-laktobionihappoa ja laktuloosia. Laktobionihappoa käytetään biohajoavien pintojen ja kosmetiikkatuotteiden valmistuksessa, sekä sisäelinten säilöntäliuoksissa, joissa laktobionihappo estää happiradikaalien aiheuttamien kudosvaurioiden syntymistä. Tässä työssä laktoosia hapetettiin laktobionihapoksi sekoittimella varustetussa laboratoriomittakaavaisessa panosreaktorissa käyttäenkatalyyttinä palladiumia aktiivihiilellä. Muutamissa kokeissa katalyytin promoottorina käytettiin vismuttia, joka hidastaa katalyytin deaktivoitumista. Työn tarkoituksena oli saada lisää tietoa laktoosin hapettamisen kinetiikasta. Laktoosin hapettumisessa laktobionihapoksi havaittiin selektiivisyyteen vaikuttavan muunmuassa reaktiolämpötila, paine, pH ja käytetyn katalyytin määrä. Katalyyttiä kierrättämällä eri kokeiden välillä saatiin paremmat konversiot, selektiivisyydet ja saannot. Parhaat koetulokset saatiin hapetettaessa synteettisellä ilmalla 60 oC lämpötilassa ja 1 bar paineessa. Tehdyissä kokeissa pH:n säätö tehtiin manuaalisesti, joten pH ei pysynyt koko ajan haluttuna. Laktoosin konversio oli parhaimmillaan 95 %. Laktobionihapon suhteellinen selektiivisyys oli 100% ja suhteellinen saanto 100 %. Kinetiikan matemaattinen mallinnus tehtiin Modest-ohjelmalla käyttäen kokeista saatuja mittaustuloksia.Ohjelman avulla estimoitiin parametreja ja saatiin matemaattinen malli reaktorille. Tässä työssä tehtiin kineettinen mallinnus myös ravistelureaktorissa tehdyille laktoosin hapetuskokeille, missä pH pysyi koko ajan haluttuna 'in-situ' titrauksen avulla. Työn yhteydessä selvitettiin myös mahdollisuutta käyttää monoliittikatalyyttejä laktoosin hapetusreaktiossa.

Acylation of chiral alcohols: a simple procedure for chiral GC analysis

The use of iodine as a catalyst and either acetic or trifluoroacetic acid as a derivatizing reagent for determining the enantiomeric composition of acyclic and cyclic aliphatic chiral alcohols was investigated. Optimal conditions were selected according to the molar ratio of alcohol to acid, the reaction time, and the reaction temperature. Afterwards, chiral stability of chiral carbons was studied. Although no isomerization was observed when acetic acid was used, partial isomerization was detected with the trifluoroacetic acid. A series of chiral alcohols of a widely varying structural type were then derivatized with acetic acid using the optimal conditions. The resolution of the enantiomeric esters and the free chiral alcohols was measured using a capillary gas chromatograph equipped with a CP Chirasil-DEX CB column. The best resolutions were obtained with 2-pentyl acetates (α = 3.00) and 2-hexyl acetates (α = 1.95). This method provides a very simple and efficient experimental workup procedure for analyzing chiral alcohols by chiral-phase GC.

Kineettinen tarkastelu keskisakeusalueella toimivalle happivaiheelle

Työn tavoitteena oli tarkastella keskisakeudessa toimivan happidelignifioinnin kinetiikkaa ja vertailla sitä olemassa olevien kineettisten tutkimuksien kanssa. Lisäksi tutkittiin kuinka happivaiheen suodos vaikuttaa delignifiointiasteeseen sekä selektiivisyyteen. Työn kirjallisuusosassa perehdyttiin happidelignifioinnin kineettisiin malleihin, jotka on kehitetty ennustamaan alkalin, paineen, lämpötilan ja ajan vaikutusta ligniinin poistumiselle sekä hiilihydraattiketjujen katkeilulle. Delignifioituminen on nopeaa ensimmäisen kymmenen minuutin aikana ja hidastuu jäännösdelignifiointivaiheessa. Laboratoriotutkimuksissa selvitettiin kuinka prosessimuuttujat vaikuttavat kappaluvun ja viskositeetin muutokseen. Tuloksia tarkasteltiin lineaarisella regressioanalyysillä, jonka avulla muuttujien vaikutukset saadaan selkeästi esille. Happivaiheen ensimmäisessä vaiheessa suurin vaikutus delignifiointiasteeseen sekä viskositeetin alenemiseen on alkaliannoksella. Pienillä hapen annostuksella saavutettiin hyvä selektiivisyys, suurillakin alkaliannoksilla. Lämpötilan vaikutus on lähes olematon, kun paine on pieni. Kun paine kasvaa, kasvaa myös lämpötilan vaikutus delignifiointiasteeseen. Hiilihydraattien depolymerisoituminen lisääntyy lämpötilan kasvaessa lähes lineaarisesti, riippumatta paineesta. Hyvä loppuselektiivisyys saavutetaan kun ensimmäisen vaiheen selektiivisyys on hyvä. Ensimmäisessä vaiheessa saavutettiin hyvä selektiivisyys, kun alkali ei pääse kulumaan loppuun eikä delignifioituminen jatku liian pitkälle. Toisessa vaiheessa selektiivisyys säilyy parhaiten, kun lisättävä alkaliannos on pieni. Lämpötila ja paine vaikuttavat alkaliannokseen verrattuna hyvin vähän loppuselektiivisyyteen.

Gas-phase photocatalytic oxidation of volatile organic compounds

Substances emitted into the atmosphere by human activities in urban and industrial areas cause environmental problems such as air quality degradation, respiratory diseases, climate change, global warming, and stratospheric ozone depletion. Volatile organic compounds (VOCs) are major air pollutants, emitted largely by industry, transportation and households. Many VOCs are toxic, and some are considered to be carcinogenic, mutagenic, or teratogenic. A wide spectrum of VOCs is readily oxidized photocatalytically. Photocatalytic oxidation (PCO) over titanium dioxide may present a potential alternative to air treatment strategies currently in use, such as adsorption and thermal treatment, due to its advantageous activity under ambient conditions, although higher but still mild temperatures may also be applied. The objective of the present research was to disclose routes of chemical reactions, estimate the kinetics and the sensitivity of gas-phase PCO to reaction conditions in respect of air pollutants containing heteroatoms in their molecules. Deactivation of the photocatalyst and restoration of its activity was also taken under consideration to assess the practical possibility of the application of PCO to the treatment of air polluted with VOCs. UV-irradiated titanium dioxide was selected as a photocatalyst for its chemical inertness, non-toxic character and low cost. In the present work Degussa P25 TiO2 photocatalyst was mostly used. In transient studies platinized TiO2 was also studied. The experimental research into PCO of following VOCs was undertaken: - methyl tert-butyl ether (MTBE) as the basic oxygenated motor fuel additive and, thus, a major non-biodegradable pollutant of groundwater; - tert-butyl alcohol (TBA) as the primary product of MTBE hydrolysis and PCO; - ethyl mercaptan (ethanethiol) as one of the reduced sulphur pungent air pollutants in the pulp-and-paper industry; - methylamine (MA) and dimethylamine (DMA) as the amino compounds often emitted by various industries. The PCO of VOCs was studied using a continuous-flow mode. The PCO of MTBE and TBA was also studied by transient mode, in which carbon dioxide, water, and acetone were identified as the main gas-phase products. The volatile products of thermal catalytic oxidation (TCO) of MTBE included 2-methyl-1-propene (2-MP), carbon monoxide, carbon dioxide and water; TBA decomposed to 2-MP and water. Continuous PCO of 4 TBA proceeded faster in humid air than dry air. MTBE oxidation, however, was less sensitive to humidity. The TiO2 catalyst was stable during continuous PCO of MTBE and TBA above 373 K, but gradually lost activity below 373 K; the catalyst could be regenerated by UV irradiation in the absence of gas-phase VOCs. Sulphur dioxide, carbon monoxide, carbon dioxide and water were identified as ultimate products of PCO of ethanethiol. Acetic acid was identified as a photocatalytic oxidation by-product. The limits of ethanethiol concentration and temperature, at which the reactor performance was stable for indefinite time, were established. The apparent reaction kinetics appeared to be independent of the reaction temperature within the studied limits, 373 to 453 K. The catalyst was completely and irreversibly deactivated with ethanethiol TCO. Volatile PCO products of MA included ammonia, nitrogen dioxide, nitrous oxide, carbon dioxide and water. Formamide was observed among DMA PCO products together with others similar to the ones of MA. TCO for both substances resulted in the formation of ammonia, hydrogen cyanide, carbon monoxide, carbon dioxide and water. No deactivation of the photocatalyst during the multiple long-run experiments was observed at the concentrations and temperatures used in the study. PCO of MA was also studied in the aqueous phase. Maximum efficiency was achieved in an alkaline media, where MA exhibited high fugitivity. Two mechanisms of aqueous PCO – decomposition to formate and ammonia, and oxidation of organic nitrogen directly to nitrite - lead ultimately to carbon dioxide, water, ammonia and nitrate: formate and nitrite were observed as intermediates. A part of the ammonia formed in the reaction was oxidized to nitrite and nitrate. This finding helped in better understanding of the gasphase PCO pathways. The PCO kinetic data for VOCs fitted well to the monomolecular Langmuir- Hinshelwood (L-H) model, whereas TCO kinetic behaviour matched the first order process for volatile amines and the L-H model for others. It should be noted that both LH and the first order equations were only the data fit, not the real description of the reaction kinetics. The dependence of the kinetic constants on temperature was established in the form of an Arrhenius equation.

Determinação das propriedades catalíticas em meio aquoso e orgânico da lipase de Candida rugosa imobilizada em celulignina quimicamente modificada por carbonildiimidazol

Microbial lipase from Candida rugosa was immobilized by covalent binding on wood cellulignin (Eucaliptus grandis) chemically modified with carbonyldiimidazole. The immobilized system was fully evaluated in aqueous (olive oil hydrolysis) and organic (ester synthesis) media. A comparative study between free and immobilized lipase was carried out in terms of pH, temperature and thermal stability. A higher pH value (8.0) was found optimal for the immobilized lipase. The optimal reaction temperature shifted from 37 °C for the free lipase to 45 °C for the immobilized lipase. The pattern of heat stability indicated that the immobilization process tends to stabilize the enzyme. Kinetics tests at 37 °C following the hydrolysis of olive oil obeyed the Michaelis-Menten rate equation. Values for Km = 924.9 mM and Vmax = 198.3 U/mg were lower than for free lipase, suggesting that the affinity towards the substrate changed and the activity of the immobilized lipase decreased during the course of immobilization. The immobilized derivative was also tested in the ester synthesis from several alcohols and carboxylic acids.

Imobilização de lipases em filme de caseinato de sódio/glicerol: aplicação na síntese de ésteres

Lipases from different sources were immobilized in sodium caseinate/glycerol film and used in the esterification reactions of aliphatic acids with alcohols in the presence of organic solvents. Lipases from Pseudomonas sp and Rhizopus oryzae were selected and the influence of several parameters was analyzed, including: lipase loading, organic solvent polarity, reaction temperature, chain length of alcohol and acid and enzyme/support reuse. For comparison, free enzymes were used under similar experimental conditions.

A influência dos ácidos hexenurônicos no rendimento e na branqueabilidade da polpa kraft

This study investigated the impact of pulp hexenuronic acids (HexAs) content on pulping yield by changing cooking reaction temperature. The bleachability of pulps containing variable amounts of HexAs was also investigated. The cooking at 170 ºC produced pulp of kappa number, HexAs and screen yield of 16.2, 49.4 mmol/kg and 50.2%, respectively, whereas the cooking at 156 ºC resulted pulp of kappa 17.0, 61.3 mmol/kg HexAs and 50.8% screened yield. The pulp produced at lower cooking temperature also showed better bleachability as evaluated by the total amount of active chlorine required to achieve 90% ISO. The sequence OA HT D(EP)DD showed the lowest bleaching performance among all.

Fotodegradación heterogénea de bisfenol A en agua con dióxido de titanio

Bisphenol A (BPA) is a monomer used in epoxy resin and polycarbonate manufacture. This molecule is considered as an endocrine disruptor that causes different diseases. The human exposition to this non biodegrable substance is increasing in the time; in particular, water is contaminated by industrial remainder flow. In this article heterogeneous photo degradation of a solution of BPA in water solution using a catalytic photo reactor with UV light and titanium dioxide (TiO2) was evaluated. High performance liquid chromatography (HPLC) was used to analyze the photo degradation of BPA solutions. The influence of titanium dioxide amount, BPA concentration, reaction temperature and the catalyst state like suspension and immobilized were also determinated. The highest elimination of BPA was 83.2%, in 240 min, beginning with 0.05 mM of BPA and 100 mg/L of TiO2 in suspension.

Development and application of spectrophotometric method for the determination of cefaclor in pharmaceutical formulations

A simple, fast and sensitive spectrophotometric method for the determination of cefaclor in pharmaceutical raw and dosage forms based on reaction with ninhydrin is developed, optimized and validated. The purple color (Ruhemenn's purple) that resulted from the reaction was stabilized and measured at 560 nm. Beer's law is obeyed in the concentration range of 4-80 µg mL-1 with molar absorptivity of 1.42 × 10(5) L mole-1 cm-1. All variables including the reagent concentration, heating time, reaction temperature, color stability period, and cefaclor/ninhydrin ratio were studied in order to optimize the reaction conditions. No interference was observed from common pharmaceutical adjuvant. The developed method is easy to use, accurate and highly cost-effective for routine studies relative to HPLC and other techniques.