On the hydrothermal stability of MCM-41. Evidence of capillary tension-induced effects

MCM-41's limited hydrothermal stability has been often related to the hydrolysis of Si-O-Si bonds due to the low degree of condensation, its thin walls or a combination of them. In this work, evidence for an additional factor is provided; a physical effect that occurs during the drying of the hydrothermally treated calcined material due to the intense capillary stress exerted in water. Depending on both physical (i.e. mechanical) and chemical (i.e. hydrolysis) resistances, the structure undergoes differently. Three MCM-41 samples with different degree of condensation were investigated. The most remarkable results are found with un-aged TEOS based material, which gets fully disordered and shrunk for all applied hydrothermal temperatures in water. Comparison between water and a low-surface-tension-solvent drying revealed that capillarity is responsible for the loss of ordering (and shrinkage) at moderate hydrothermal temperatures. The material's structure is hexagonal and shrinkage-free under the low-surface-tension-solvent route. At a high hydrothermal temperature, hydrolysis is extensive and responsible for the loss of ordering. The other remarkable finding regards the aged MCM-41 mesostructure that maintains the hexagonal features at all applied temperatures in water, and it is more stable against capillarity at high temperature. The Na-metasilicate based material is mechanically very stable and gets disordered at high temperature due to hydrolysis.

Hot-spots during the calcination of MCM-41:a SAXS comparative analysis of a soft mesophase

The phenomenon of microscopic hot-spots, during the calcination of MCM-41, was investigated by quantifying the magnitude of the temperature increase during the calcination of a soft MCM-41 mesophase using a SAXS comparative study. This was performed by thermally treating a soft material that was detemplated via Fenton chemistry followed by equilibrating and drying in a low-surface-tension solvent (n-butanol or N,N-dimethylformamide); these samples have limited structural shrinkage. The resulting samples were thermally treated at increasing temperatures, and the structural shrinkage was compared with that of the directly calcined material. By comparing the structural shrinkage, it was found that the microscopic temperature increase would fall between 190 and 250 C, as deduced from N,N-dimethyl-formamide and n-butanol. The order of magnitude of the temperature increase appears to be consistent with the well-known glow effect. It is, however, substantially higher than the experimentally determined macroscopic temperature increase. Several aspects are discussed to interpret this difference. © 2013 Elsevier B.V.

Fast pyrolysis of cassava rhizome in the presence of catalysts

Cassava rhizome was catalytically pyrolysed at 500 °C using analytical pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) in order to investigate the effect of catalysts on bio-oil properties. The catalysts studied were zeolite ZSM-5, two aluminosilicate mesoporous materials Al-MCM-41 and Al-MSU-F, and a proprietary commercial catalyst alumina-stabilised ceria MI-575. The influence of catalysts on pyrolysis products was observed through the yields of aromatic hydrocarbons, phenols, lignin-derived compounds, carbonyls, methanol and acetic acid. Results showed that all the catalysts produced aromatic hydrocarbons and reduced oxygenated lignin derivatives, thus indicating an improvement of bio-oil heating value and viscosity. Among the catalysts, ZSM-5 was the most active to all the changes in pyrolysis products. In addition, all the catalysts with the exception of MI-575 enhanced the formation of acetic acid. This is clearly a disadvantage with respect to the level of pH in the liquid bio-fuel.

Evaluation of catalytic pyrolysis of cassava rhizome by principal component analysis

Rhizome of cassava plants (Manihot esculenta Crantz) was catalytically pyrolysed at 500 °C using analytical pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) method in order to investigate the relative effect of various catalysts on pyrolysis products. Selected catalysts expected to affect bio-oil properties were used in this study. These include zeolites and related materials (ZSM-5, Al-MCM-41 and Al-MSU-F type), metal oxides (zinc oxide, zirconium (IV) oxide, cerium (IV) oxide and copper chromite) catalysts, proprietary commercial catalysts (Criterion-534 and alumina-stabilised ceria-MI-575) and natural catalysts (slate, char and ashes derived from char and biomass). The pyrolysis product distributions were monitored using models in principal components analysis (PCA) technique. The results showed that the zeolites, proprietary commercial catalysts, copper chromite and biomass-derived ash were selective to the reduction of most oxygenated lignin derivatives. The use of ZSM-5, Criterion-534 and Al-MSU-F catalysts enhanced the formation of aromatic hydrocarbons and phenols. No single catalyst was found to selectively reduce all carbonyl products. Instead, most of the carbonyl compounds containing hydroxyl group were reduced by zeolite and related materials, proprietary catalysts and copper chromite. The PCA model for carboxylic acids showed that zeolite ZSM-5 and Al-MSU-F tend to produce significant amounts of acetic and formic acids.

Catalytic pyrolysis of agricultural residues for bio-oil production

Agricultural residues from Thailand, namely stalk and rhizome of cassava plants, were employed as raw materials for bio-oil production via fast pyrolysis technology. There were two main objectives of this project. The first one was to determine the optimum pyrolysis temperature for maximising the organics yield and to investigate the properties of the bio-oils produced. To achieve this objective, pyrolysis experiments were conducted using a bench-scale (150 g/h) reactor system, followed by bio-oil analysis. It was found that the reactor bed temperature that could give the highest organics yield for both materials was 490±15ºC. At all temperatures studied, the rhizome gave about 2-4% higher organics yields than the stalk. The bio-oil derived from the rhizome had lower oxygen content, higher calorific value and better stability, thus indicating better quality than that produced from the stalk. The second objective was to improve the bio-oil properties in terms of heating value, viscosity and storage stability by the incorporation of catalyst into the pyrolysis process. Catalytic pyrolysis was initially performed in a micro-scale reactor to screen a large number of catalysts. Subsequently, seven catalysts were selected for experiments with larger-scale (150 g/h) pyrolysis unit. The catalysts were zeolite and related materials (ZSM-5, Al-MCM-41 and Al-MSU-F), commercial catalysts (Criterion-534 and MI-575), copper chromite and ash. Additionally, the combination of two catalysts in series was investigated. These were Criterion-534/ZSM-5 and Al-MSU-F/ZSM-5. The results showed that all catalysts could improve the bio-oils properties as they enhanced cracking and deoxygenation reactions and in some cases such as ZSM-5, Criterion-534 and Criterion-534/ZSM-5, valuable chemicals like hydrocarbons and light phenols were produced. The highest concentration of these compounds was obtained with Criterion-534/ZSM-5.

Catalytic pyrolysis of rice husk for bio-oil production

Catalytic pyrolysis experiments have been carried out on Brunei rice husk (BRH) to obtain bio-oil using a fixed-bed pyrolysis rig. ZSM-5, Al-MCM-41, Al-MSU-F and Brunei rice husk ash (BRHA) were used as the catalysts for the catalytic pyrolysis experiments and comparison was done to analyse the changes in the bio-oil properties and yield. Properties of the liquid catalytic and non-catalytic bio-oil were analysed in terms of water content, pH, acid number, viscosity, density and calorific value. The bio-oil chemical composition shows that ZSM-5 increases the production of aromatic hydrocarbons and light phenols, whilst Al-MCM-41 reduces the acetic acid production. The catalytic runs increased the calorific value and water content in the bio-oil, whilst viscosity, density and acid number is decreased. © 2012 Elsevier B.V. All rights reserved.

Catalytic intermediate pyrolysis of Brunei rice husk for bio-oil production

Rice husks from Brunei were subjected via intermediate pyrolysis for bio-oil production. Two main objectives were set out for this study. The application of intermediate pyrolysis on Brunei rice husk for the production of bio-oil is the main objective of this experiment. Characterisation of the rice husks was inclusive as a pre-requisite step to assess the suitability as feedstock for production of liquid fuels. Following on from the characterisation results, a temperature of 450°C was established as the optimum temperature for the production of bio-oil. A homogenous bio-oil was obtained from the pyrolysis of dry rice husk, and the physicochemical properties and chemical compositions were analysed. The second objective is the introduction of catalysts into the pyrolysis process which aims to improve the bio-oil quality, and maximise the desired liquid bio-oil properties. The incorporation of the catalysts was done via a fixed tube reactor into the pyrolysis system. Ceramic monoliths were used as the catalyst support, with montmorillonite clay as a binder to attach the catalysts onto the catalyst support. ZSM-5, Al-MCM-41, Al-MSU-F and Brunei rice husk ash (BRHA) together with its combination were adopted as catalysts. Proposed criterions dictated the selection of the best catalysts, subsequently leading to the optimisation process for bio-oil production. ZSM-5/Al-MCM-41 proved the most desirable catalyst, which increases the production of aromatics and phenols, decreased the organic acids and improved the physicochemical properties such as the pH, viscosity, density and H:C molar ratios. Variation in the ratio and positioning of both catalysts were the significant key factor for the catalyst optimisation study.

Interdependent lateral interactions, hydrophobicity and acid strength and their influence on the catalytic activity of nanoporous sulfonic acid silicas

A series of propylsulfonic (MCM-SOH) and octyl co-functionalised propylsulfonic (MCM-Oc-SOH) catalysts have been prepared by post modification of MCM-41 with mercaptopropyltrimethoxysilane (MPTS) to achieve SOH surface coverages spanning the range 0.12-1 monolayer. Within the MCM-Oc-SOH series, samples with submonolayer MPTS coverages were further grafted with octyltrimethoxysilane to cap bare hydroxyl sites and tune the hydrophobicity of the support. For the MCM-SO H series NH calorimetry revealed acid strength increases as a function of sulfonic acid loading, with -ΔH(NH ) increasing from 87 to 118 kJ mol. In contrast, MCM-Oc-SOH exhibits a dramatic enhancement of acid strength for submonolayer SOH coverages, with -ΔH(NH ) found to increase to 103 kJ mol. In line with these acid strength measurements the per-site activity of the MCM-SOH series in the esterification of butanol with acetic acid was found to increase with SOH content. Incorporation of octyl groups further promotes esterification activity of all the samples within the MCM-Oc-SOH series, such that the turn over frequency of the sample with the lowest loading of SOH more than doubles. Molecular dynamic simulations indicate that the interaction of isolated sulfonic acid groups with the pore walls is the primary cause of the decrease in acid strength and activity of submonolayer samples within the MCM-SOH series. Incorporation of octyl groups results in a combination of increased hydrophobicity and lateral interactions between adjacent sulfonic acid head groups, resulting in a striking enhancement of acid strength and esterification activity. © 2010 The Royal Society of Chemistry.

Green preparation of tuneable carbon-silica composite materials from wastes

Bio-oil has successfully been utilized to prepare carbon-silica composites (CSCs) from mesoporous silicas, such as SBA-15, MCM-41, KIT-6 and MMSBA frameworks. These CSCs comprise a thin film of carbon dispersed over the silica matrix and exhibit porosity similar to the parent silica. The surface properties of the resulting materials can be simply tuned by the variation of preparation temperatures leading to a continuum of functionalities ranging from polar hydroxyl rich surfaces to carbonaceous aromatic surfaces, as reflected in solid state NMR, XPS and DRIFT analysis. N2 porosimetry, TEM and SEM images demonstrate that the composites still possess similar ordered mesostructures to the parent silica sample. The modification mechanism is also proposed: silica samples are impregnated with bio-oils (generated from the pyrolysis of waste paper) until the pores are filled, followed by the carbonization at a series of temperatures. Increasing temperature leads to the formation of a carbonaceous layer over the silica surface. The complex mixture of compounds within the bio-oil (including those molecules containing alcohols, aliphatics, carbonyls and aromatics) gives rise to the functionality of the CSCs.

Advanced UV inscribed fibre grating structures and applications in optical sensing and laser systems

This thesis presents detailed investigation of UV inscribed fibre grating based devices and novel developments in the applications of such devices in optical sensing and fibre laser systems. The major contribution of this PhD programme includes the systematic study on fabrication, spectral characteristics and applications of different types of UV written in-fibre gratings such as Type I and IA Fibre Bragg Gratings (FBGs), Chirped Fibre Bragg Gratings (CFBGs) and Tilted Fibre Gratings (TFGs) with small, large and 45º tilted structures inscribed in normal silica fibre. Three fabrication techniques including holographic, phase-mask and blank beam exposure scanning, which were employed to fabricate a range of gratings in standard single mode fibre, are fully discussed. The thesis reports the creation of smart structures with self-sensing capability by embedding FBG-array sensors in Al matrix composite. In another part of this study, we have demonstrated the particular significant improvements made in sensitising standard FBGs to the chemical surrounding medium by inducing microstructure to the grating by femtosecond (fs) patterning assisted chemical etching technique. Also, a major work is presented for the investigation on the structures, inscription methods and spectral Polarisation Dependent Loss (PDL) and thermal characteristics of different angle TFGs. Finally, a very novel application in realising stable single polarisation and multiwavelength switchable Erbium Doped Fibre Lasers (EDFLs) using intracavity polarisation selective filters based on TFG devices with tilted structures at small, large and exact 45° angles forms another important contribution of this thesis.

High birefringence fibre interrogating interferometer for optical sensing applications

The use of high birefringence fibre forming a differential path interferometer as an interrogation unit for heterodyne fibre optic sensing applications is described.

Wear of high aluminium zinc-based alloys in plain bearing applications

Two zinc-based alloys of high aluminium content, Super Cosmal alloy containing 60% Al, 6% Si, 1% Cu, 0.3% Mn and HAZCA alloy containing 60% Al, 8% Si, 2% Cu, 0.06% Mg were produced by sand casting. Foundry characteristics in particular, fluidity, mode of solidification and feeding ability were examined. Metallographic analysis of structures was carried out using optical and scanning electron microscopy and their mechanical properties were determined using standard techniques. Dry wear characteristics were determined using a pin-on-disc test, and boundary-lubricated wear was studied using full bearing tests. Results from casting experiments were evaluated and compared with the behaviour of a standard ZA-27 alloy and those from tribological tests with both ZA-27 alloy and a leaded tin-bronze (SAE660) under the same testing conditions. The presence of silicon was beneficial, reducing the temperature range of solidification, improving feeding efficiency and reducing gravity segregation of phases. Use of chills and melt degassing was found necessary to achieve soundness and enhanced mechanical properties. Dry wear tests were performed against a steel counterface for sliding speeds of 0.25, 0.5, 1.0 and 2 m/s and for a range of loads up to 15 kgf. The high aluminium alloys showed wear rates as low as those of ZA-27 at speeds of 0.25 and 0.5 m/s for the whole range of applied loads. ZA-27 performed better at higher speeds. The build up of a surface film on the wearing surface of the test pins was found to be responsible for the mild type of wear of the zinc based alloys. The constitution of the surface film was determined as a complex mixture of aluminium, zinc and iron oxides and metallic elements derived from both sliding materials. For full bearing tests, bushes were machined from sand cast bars and were tested against a steel shaft in the presence of a light spindle oil as the lubricant. Results showed that all zinc based alloys run-in more rapidly than bronze, and that wear in Super Cosmal and HAZCA alloys after prolonged running were similar to those in ZA-27 bearings and significantly smaller than those of the bronze.

High birefringence fibre interrogating interferometer for optical sensing applications

The use of high birefringence fiber interrogating interferometer for optical sensing applications was discussed. The method is of low cost and permits simple adjustment of the optical path difference and has much lower sensitivity to environmental perturbation. The polarization-maintaining (PM) fiber interferometer adopted a heterodyne approach using interferometric wavelength shift detection. The study showed that the inclusion of power amplifier driving a multi-element piezoelectric stack will enable the bandwidth to be pushed up into the kHz regime.

Adaptive message rate control of infrastructured DSRC vehicle networks for coexisting road safety and non-safety applications

Intelligent transport system (ITS) has large potentials on road safety applications as well as nonsafety applications. One of the big challenges for ITS is on the reliable and cost-effective vehicle communications due to the large quantity of vehicles, high mobility, and bursty traffic from the safety and non-safety applications. In this paper, we investigate the use of dedicated short-range communications (DSRC) for coexisting safety and non-safety applications over infrastructured vehicle networks. The main objective of this work is to improve the scalability of communications for vehicles networks, ensure QoS for safety applications, and leave as much as possible bandwidth for non-safety applications. A two-level adaptive control scheme is proposed to find appropriate message rate and control channel interval for safety applications. Simulation results demonstrated that this adaptive method outperforms the fixed control method under varying number of vehicles. © 2012 Wenyang Guan et al.

Rosemary : a raw material for a new genre of bio-based antioxidants for sustainable applications

The potential replacement, partially or fully, of synthetic additives by bio-based alternatives derived from indigenous renewable non-food crop resources offers a market opportunity for a green supply of raw materials for different industrial and health products, with greater involvement of the farming community in crop production while addressing the ever more stringent environmental and pollution laws that now require the use of less potentially toxic/harmful ingredients, even if they are present in relatively small quantities. The work presented here relates to developing a new genre of environmentally-sustainable bio-based antioxidants (AO) for industrial uses that are obtained from extracts of UK-grown rosemary (Rosmarinus officinalis) plant. The performance of these AOs was tested, and their efficacy compared with some common and benchmark synthetic AOs from the same chemical class, in different products including polymers especially for packaging, as well as lubricants, cosmetics and health products. One of the main active ingredients in rosemary is Rosmarinic acid which is a water-soluble compound. This was chemically transformed into a number of ester derivatives, Rosmarinates, targeted for different applications. The parent and the modified antioxidants (the rosmarinates) were characterised and their antioxidancy were examined and tested in linear low-density polyethylene (LLDPE) and in polypropylene (PP) and compared with compounds of similar structure and with other well known synthetic antioxidants used commercially in polyolefins. The results show that antioxidants sourced from rosemary have the added benefit of being highly efficient and intrinsically more active than many synthetic and bio-based alternatives.