T. García

Multifunctional Hybrid Organic−Inorganic Catalytic Materials with a Hierarchical System of Well-Defined Micro- and Mesopores

Novel layered zeolitic organic-inorganic materials (MWW-BTEB) have been synthesized by intercalation and stabilization of arylic silsesquioxane molecules between inorganic zeolitic MWW layers. The organic linkers are conformed by two condensed silyl-arylic groups from disilane molecules, such as 1,4-bis(triethoxysilyl)benzene (BTEB), which react with the external silanol groups of the zeolitic layers. The hybrids contain micropores within the inorganic layers and a well-defined mesoporous system in between the organic linkers. An amination post-treatment introduces basic groups in the organic linkers close to the acid sites present in the structural inorganic counterpart. Through this methodology it has been possible to prepare bifunctional acid-base catalysts where the acid sites are of zeolitic nature located in the inorganic building blocks and the basic sites are part of the organic structure. The resultant materials can act as bifunctional catalysts for performing a two-step cascade reaction that involves the catalytic conversion of benzaldehyde dimethylacetal into benzylidene malononitrile.

Valorisation of waste tyre by pyrolysis in a moving bed reactor

The aim of this work is to assess the behaviour of a moving bed reactor, based on a screw transporter design, in waste tyre pyrolysis under several experimental conditions. Waste tyre represents a significant problem in developed countries and it is necessary to develop new technology that could easily process big amounts of this potentially raw material. In this work, the influence of the main pyrolysis process variables (temperature, solid residence time, mass flow rate and inert gas flow) has been studied by a thorough analysis of product yields and properties. It has been found that regardless the process operational parameters, a total waste tyre devolatilisation is achieved, producing a pyrolytic carbon black with a volatile matter content under 5 wt.%. In addition, it has been proven that, in the range studied, the most influencing process variables are temperature and solid mass flow rate, mainly because both variables modify the gas residence time inside the reactor. In addition, it has been found that the modification of these variables affects to the chemical properties of the products. This fact is mainly associated to the different cracking reaction of the primary pyrolysis products.

Critical review on atmospheric PAH. Assessment of reported data in the Mediterranean basin

Polycyclic aromatic hydrocarbons (PAH) are a special group of atmospheric contaminants included in the persistent toxic substances (PTS) and also in the volatile organic compounds (VOC) groups. PAH are present in the atmosphere and its origin can be due to anthropogenic and/or biogenic activities. Their specific characteristics, high volatility, mutagenic and/or carcinogenic power, easily transportable for long distances with the wind undergoing photodecomposition processes, which imply reactions with solar light, NOx and O3, make them important contaminants despite of the fact that they are present at very low concentrations. These characteristics make some of the PAH to be listed by the Environmental Protection Agency (EPA) as priority pollutants with negative environmental impact due to their toxicity and they can affect very negatively the living being due to their carcinogenic/mutagenic character. Because of atmospheric PAH properties, it is not worth to study them in small areas because they do not know about natural or political borders and they can affect to a huge population. The growing use of transport and energy consumption, PAH have mainly anthropogenic origin, joined the growing cancer incident, must be the alarm to take these toxic organic contaminants into account and under control. This paper is a revision on the reported data on atmospheric PAH in the Mediterranean basin and was shown at the Workshop of the United Nations Environmental Protection (UNEP), meeting held in Athens, February 2002.

Study of the viability of the process for hydrogen recovery from old tyre oils

In this paper, an approach to the production of hydrogen from waste rubber is proposed. The process consists in performing the pyrolysis of waste rubber to produce the raw material (oils) that will be used in a gasification process with oxygen to obtain hydrogen. Tyre pyrolysis runs were experimentally performed to study the influence of temperature and reaction time on oils production, concluding that tyre pyrolysis requires low-severity process variables because at severe conditions, no improvements in conversion are obtained and a slight decrease in oils production is observed. In addition, thermodynamic calculations were performed to know the energy requirements for the oils gasification process. The equilibrium constants in terms of process pressure and temperature were calculated observing that all the processes are spontaneous and clearly lead to conversion products. The hydrogen recovery is calculated and from overall data, it is concluded that the production of hydrogen from old tyre seems to be a feasible process and a way of obtaining a clean energy for the future from a non-biodegradable waste material.

Sorbent characteristics influence on the adsorption of PAC: I. PAH adsorption with the same number of rings

Abstract The aim of this paper is to study the abatement of three-ring polycyclic aromatic hydrocarbons (PAHs) from hot gas emissions during energy generation in coal combustion. The three-ring PAHs are one of the most abundant PAH groups emitted during coal combustion. Four of them—Acenaphthene (Ac), Phenanthrene (Phe), Fluorene (Fu) and Anthracene (An)—have been listed by US EPA as priority pollutants. The three-ring PAH adsorption capacities are related to the textural properties of the 16 sorbents used in this work. Single and multiple linear regressions —principal component regression (PCR)—were applied in this study. The main conclusions reached are two: (1) the micropore volume is the most determinant parameter for these PAH removal; (2) the adsorption of three-ring PAH by sorbents from waste hot gas emissions is inversely proportional to their volatility: the lower the PAH volatility, the higher the adsorbent adsorption capacity. The adsorption isotherms show that Phe and An, both examples of PAHs with three aromatic rings, behave similarly. However, their behaviour differs from that of Ac and Fu, compounds where only two of their three rings exhibit an aromatic nature.

A new generation of aprotic yet Brønsted acidic imidazolium salts: effect of ester/amide groups in the C-2, C-4 and C-5 on antimicrobial toxicity and biodegradation

Imidazolium Bronsted acidic catalysts substituted with ester/amides have been assessed for both antimicrobial toxicity and biodegradation. Low toxicity to a screen of 20 microbial strains (12 fungi and 8 bacteria) was demonstrated. Imidazolium salts incorporating either ester or amide groups at N-1, C-2, C-4 and C-5 did not pass the readily biodegradable test (ISO 14593). Catalyst selection based on Traffic Signal Light classification of performance, (eco)toxicity, and efficient synthesis is described.

Synthesis and Catalytic Properties of Hybrid Mesoporous Materials Assembled from Polyhedral and Bridged Silsesquioxane Monomers

A family of hybrid mesoporous materials with high temperature stability was obtained by the suitable covalent combination of two types of siloxane precursors. Specifically, cubic T(8) polyhedral oligomeric (POSS) and aryl bridged silsesquioxane monomers (1,4-bis(triethoxysilyl)benzene, BTEB) play the role of nanobuilders. An optimal molar ratio of the two precursors (5-25 mol% of total silicon content from the BTEB disilane) generated a homogenous, highly accessible, and well-defined mesoporous material with hexagonal symmetry and narrow pore-size distribution. Physicochemical, textural, and spectroscopic analysis corroborated the effective integration and preservation of the two different nanoprecursors, thereby confirming the framework of the mesoporous hybrid materials. A post-synthesis amination treatment allowed the effective incorporation of amino groups onto the aryl linkers, thereby obtaining a stable and recyclable basic catalyst for use in C-C bond-formation processes.

THE IMPACT OF OCCUPATIONAL SEX-COMPOSITION ON WOMEN'S FERTILITY IN SPAIN

ABSTRACT This paper investigates to what extent variation in the distribution across occupational categories in the labour market affects womens demographic behaviour. It specifically explores which occupational categories are more beneficial for women in the transition to first, second and third birth in Spain. Event-history analyses are applied to retrospective data from the Spanish Fertility and Family Survey (1995). The results show that there are differences in womens fertility according to their occupational choice and demonstrate that health and teaching professionals show an advantage in harmonizing work and motherhood in Spain. This finding is consistent with the idea that not only the impact of occupational sex-segregation on womens fertility is explicable by each womans specific attitudes towards motherhood and career but also by her employment conditions at the workplace. This effect is particularly strong in Spain due to the specific national context of combining family responsibilities and labour force participation.ABSTRACT This paper investigates to what extent variation in the distribution across occupational categories in the labour market affects womens demographic behaviour. It specifically explores which occupational categories are more beneficial for women in the transition to first, second and third birth in Spain. Event-history analyses are applied to retrospective data from the Spanish Fertility and Family Survey (1995). The results show that there are differences in womens fertility according to their occupational choice and demonstrate that health and teaching professionals show an advantage in harmonizing work and motherhood in Spain. This finding is consistent with the idea that not only the impact of occupational sex-segregation on womens fertility is explicable by each womans specific attitudes towards motherhood and career but also by her employment conditions at the workplace. This effect is particularly strong in Spain due to the specific national context of combining family responsibilities a...

Polyaromatic Hydrocarbons in Flue Gases from Waste Tire Combustion

With the aim of studying the polycyclic aromatic hydrocarbon (PAH) emissions when high calorific waste materials are used as nonfossil fuels, waste tire combustion has been performed in a laboratory plant. The goal was to compare the PAH emissions with the ones obtained when a fossil fuel is burned at the same combustion conditions. PAH emissions have been analyzed in solids collected in two cyclones at the exit of the combustor and in the trap system composed of a condenser, a filter (20 w m), and an adsorbent. After PAH extraction with dimethylformamide (DMF) by sonication and fluorescence spectroscopy in the synchronous mode (FS) analyses, it can be concluded that the nonfossil fuel generates higher PAH atmospheric pollution.

Layered hybrid materials with nanotechnological applications: use of disilane precursors as pillaring agents

Abstract A new family of layered organic-inorganic hybrid materials was synthesized using bridged silsesquioxane compounds (disilanes) as pillars which are intercalated between magadiite layers. The organic-inorganic precursors react with the surface silanol groups of the inorganic layers of silicate, bonding covalently with them. The preparation process was followed by DRX and the presence of organic linkers was confirmed by chemical and thermogravimetrical analyses, 13 C and 29 Si NMR spectroscopy. Micro and mesoporosity were also generated due to the existence of interlayer galleries. The layered hybrid materials exhibited thermally stable networks. The resultant materials can be of interest as acid or basic catalysts, sensors and for non linear optics.