Biodiesel is produced on a large scale as an eco-friendly substitute and additive to fossil fuels. Catalytic homogeneous processes using strong acids, alkalis, and natural oils have been realized in industry. However, these traditional methods have several disadvantages, such as the generation of large volumes of waste, high water and reagent needs, use of hazardous reagents, high operation costs, and utilization of valuable feedstocks and catalysis, respectively. Different solutions have subsequently been investigated, such as cheap alternative feedstocks, co-solvents and catalysts, sustainable operational conditions, advanced reactor designs and scales, and advantageous pre- and post-reaction treatments. This review explores and analyzes the main aspects of current biodiesel technologies and opportunities. It also describes some advanced improvement strategies.

Fatty acid esters were produced by phototransesterification of canola oil using TiO 2 as a photocatalyst and UVA or sunlight as radiation sources. Conversions of approximately 73% (±1.41) and 19% to fatty acid methyl ester (FAME) were achieved with methanol (1 TGL (triglyceride) mol:55 MeOH mol, 20% TiO 2 w/w TGL, 65°C, 4 hours). Using ethanol resulted in a decreased conversion of 38% instead. Conventional acid- and alkali-catalysed methods were used to compare their reaction products, FAME, with that obtained by photocatalysis. The kinetic curves were established for temperatures between 25 and 65°C. Six different kinetic mathematical models were applied, and a second forward/fourth backward model showed the highest accuracy (R 2 of 0.996). This suggests that a homogeneous model is suitable for a heterogeneous process, with mass transfer to the active sites of the catalyst not being the rate-limiting step. The thermodynamic results (ΔG 328.15K =29.98 kJ/mol, ΔG 338.15K =-6.88 kJ/mol, ΔH=83.00 kJ/mol, and ΔS=0.26 kJ/mol.K) indicate that this endothermic reaction requires temperatures higher than 65°C to reach high conversions.

Thin film science plays a crucial role in high-technology industries with many applications in electronics, energy generation and conservation strategies. Crystallization from the vapor phase is an important method for the preparation of semiconductors, insulators and metals. Therefore, it is crucial that the mechanism of thin film growth be understood. Unfortunately, this is not the case and developments in thin films have been made mostly by trial and error, and explained using an outdated mechanism. Generally, the mechanism of thin film deposition by CVD/PVD is considered a surface reaction with atoms and/or reactive species produced in the gas phase of the reaction chamber. Gas phase nucleation is generally considered a detriment to thin film quality, and engineers tend to assume that this process does not occur to a significant extent under ordinary thin film deposition conditions. An alternative mechanism, the charged cluster model, suggests instead that a thin film is a three dimensional assembly of charged nanoparticles that nucleated in the gas phase. This book shows that the charged cluster model applies to metal thin film deposition by thermal evaporation.

This study presents a novel cleaning application which investigates the ability of high power ultrasound (HPU) to remove crystalline potassium hydrogen tartrate sediment from the porous structure of American oak wine barrels. Tartrate deposits within stave samples were imaged by X-ray tomography. Volumetric reconstruction software enabled tartrate volumes to be quantified after successive treatments at varied solvent temperatures by re-imaging samples and modelling obtained tomographic projections. The removal of microscopic tartrate crystals from stave surfaces by HPU was also investigated. It was demonstrated that HPU can significantly remove tartrate deposits from the first two millimetres of oak surfaces however such ability at depth 2-8 mm was not reproducible. An average of 89% total tartrate volume was removed from the surface layer in the first treatment but was further increased to 98% by increasing solvent temperature and irradiation time. A highly significant removal of stave surface tartrate crystals with this cleaning technique was also demonstrated at temperatures studied.Industrial Relevance: Fouling of the interior surface and porous membranes of wine barrels is a significant problem encountered by every wine maker. This problem occurs in white and red wine production by precipitated tartrate crystallisation which forms a robust scale inhibiting oak compound extraction by wine, additionally harbouring spoilage microorganisms and contaminants. Tartrate scale is typically removed by spray techniques, but often with less than optimal results. Ultrasonic cleaning is a well established practice in many industries; this industrial scaled study demonstrates a high power ultrasonic (4 kW/20 kHz) application in the effective and efficient removal of tartrate sediment from the surface of staves, and to a depth of two millimetres, with a relatively short treatment time (12 min) at mild temperatures (40-60 degrees C). Such outcomes are expected to benefit the wine industry, consumers and environment by increased barrel functionality and less frequent replacement, an improvement in oak compound extraction rate and concentration in wine, increased product quality, as well as the minimisation of cleaning water consumption and excessive use of preservatives. (C) 2011 Elsevier Ltd. All rights reserved.

Industrial scale food and beverage processes that utilize microorganisms are typically faced with issues related to the exclusion, suppression or elimination of spoilage organisms. Yet the use of traditional anti-microbial treatments such as heat, chemical biocides or sterile filtration may themselves be restricted by regulations or else be undesirable due to their adverse sensory impacts on the product. High power ultrasound (HPU) is a technology whose application has been evaluated if not exploited in several food and beverage processes but has yet to be introduced into the wine industry. This review examines the research findings from related industries and highlights possible applications and likely benefits of the use of HPU in winemaking.

This paper reports the effect of niobium on the structure of titanium dioxide (TiO2) thin films deposited on glass. The results obtained indicated that the direct current (DC) co-sputtering of Ti and Nb onto glass substrates in the presence of oxygen results in the formation of Nb-doped anatase thin films with strong preferential orientation. In the concentration range between 0 and 40 at.% Nb, niobium is incorporated into the TiO2 lattice according to a substitution mechanism, entering Ti sites in the cation sub-lattice. No evidence exists for a solubility limit <40 at.% of Nb under the applied deposition conditions, however, it is not believed that an equilibrium situation prevails. Lattice charge compensation was concluded to occur by the formation of cation vacancies for samples with up to 10 at.% Nb, and by Ti3+ or Nb4+ ions for the samples with ≥15 at.% Nb, the latter in conjunction with cation vacancy compensation.

It has been reported that TiO2 film deposition by direct current (DC) magnetron reactive sputtering can occur according to the mechanism proposed by the theory of charged clusters (TCC). In the current study, the TCC was used to explain the mechanism of low temperature TiO2 crystalline thin film growth. Highly oriented anatase thin films were deposited on unheated substrates. The degree of crystallinity of the thin film was found to depend on the cluster size and its crystallinity as well as the charging efficiency in the reactor. Larger clusters tend to be crystalline. These produce amorphous (nanocrystalline) films. Smaller clusters tend to be amorphous and adopt the structure of clusters already deposited to produce an ordered crystalline film. Increasing the substrate-to-target distance increased the cluster size. In addition, the charge density decreased as the target to substrate distance was increased. Clusters of <2 and 3 nm in diameter were observed at a substrate-to-target distance of 50 and 250 mm, respectively, which correspondingly produced crystalline and amorphous films. The DC power level did not appear to have a large effect on the cluster size nor did it affect the degree of crystallinity of the resulting thin film. The main factors affecting whether or not a crystalline film is deposited are the cluster size and the charge density in the reactor.

Thin films are generally thought of as being the product of a reaction between the surface and atoms and/or molecules in the gas phase. However, a relatively new theory, the theory of charged clusters (TCC), suggests that charged clusters nucleate in the gas phase and become the growth unit for a thin film. The aim of this study was to determine whether or not TiO2 thin film deposition by DC reactive sputtering occurs via this mechanism. TiO2 was deposited on unheated transmission electron microscopy grids to observe TiO2 clusters, as well as glass and silicon substrates to observe the resulting thin films. The results showed that TiO2 clusters were indeed produced in the chamber of a direct current reactive sputtering system. Furthermore, these clusters were observed as close as 50 mm away from the target. Clusters 3 nm and <2 nm in diameter were found 250 mm and 50 mm away from the target, respectively The cluster size was found to have a direct effect on the film deposited. Smaller clusters produced a facetted crystalline anatase film whereas larger clusters produced an amorphous film.

In the thin-film formation process, it is generally accepted that thin film growth occurs via a reaction between the surface and atoms and/or molecules in the gas phase. The theory of charged clusters proposes instead that a thin film is a self-assembly of charged clusters that nucleate in the gas phase. It was demonstrated that similar-sized anatase clusters have quite different deposition behaviors depending on the RF power in the reaction chamber. At 180 W a highly crystalline nanostructured film was produced. However, at 90 W, a nanopowder was deposited instead. This can be explained by the theory of charged clusters, in that the clusters become charged at higher RF power, i.e. the charging efficiency of clusters increases with increasing RF power. Lower power (90 W) did not efficiently charge the anatase clusters. Cluster charging at 180 W resulted in Coulombic repulsion, which prevented the agglomeration observed at 90 W. The self-assembly characteristics of charged clusters is highlighted by the formation of a nanostructured film.

Recently, charged copper clusters of a few nanometers were shown to be generated spontaneously during the thermal evaporation of copper at 1573K, and were shown to be the major flux for the film growth. In order to identify the charging mechanism at low temperatures, the activation energy for positive charging was estimated based on the temperature dependence of the current generated during thermal evaporation. The activation energy was ∼ 2.81eV at 1573K. This low activation energy could be explained by a Saha–Langmuir equation if the copper clusters are formed and undergo surface ionization on the oxidized tungsten. According to this mechanism, the activation energy for charging decreases with increasing cluster size and with increasing work function of the related surface. Based on this charging mechanism, some puzzling phenomena in the thermal evaporation of metals such as the irreproducibility of the process and the degraded film quality with decreasing evaporation rate could be explained.

Investigating the generation of charged clusters during thermal evaporation of gold at 1523K has created a new understanding of film growth. In order to verify the presence of charged clusters in the gas phase and their polarity biases of +200, 0 and −200V were applied to the substrate. The charge on the majority of clusters was shown to be positive by observing their deposition behaviors under the applied electric field. These charged clusters were shown to be the major flux for gold film formation. The charge carried by clusters could be detected on a Faraday cup as an electric current. From the temperature dependence of the current, the activation energy for positive charging was estimated to be 1.56eV. Such a low activation energy suggests that the charging mechanism of clusters is the surface ionization described by the Saha–Langmuir equation.

Charged copper clusters of a few nanometers were spontaneously generated under typical copper thin film processing by evaporation at 1573K. The deposition behavior of these clusters was drastically influenced under an electric field. After deposition for 10s with a bias of +200, 0, and −200V applied to the substrate, the number density of clusters was negligible on a positively biased substrate but ∼1010mm−2 on neutral and negatively biased substrates. After deposition for 5min, the film thickness was 10, 100 and 120nm on positive, neutral and negative substrates, respectively.

The mechanisms and kinetics of precipitation of heat exchanger scale-forming sodium aluminosilicates (sodalite and cancrinite crystals) investigated under a range of conditions reflecting the Bayer alumina-refining process are reported. A systematic, 6-year study shows that, over the temperature range 90 - 240 degreesC, steel substrate fouling by heated, optically-clear, synthetic, spent Bayer liquors occurs by the formation of the more soluble sodalite scale, via substrate-mediated heterogeneous nucleation. Sodalite subsequently undergoes a dimorphic transformation to the less soluble cancrinite phase at a rate which is first order (with respect to the sodalite concentration). The activation energy for heterogeneous nucleation of sodalite is 95 kJ mol(-1). The transformation mechanism is solution-mediated, involving sodalite dissolution and subsequent nucleation and growth of cancrinite, the activation energy of which is 133 kJ mol(-1). Sodalite and cancrinite seeding significantly enhanced liquor desilication, suppressing the scale formation process. The activation energies for sodalite and cancrinite crystal growth are 30 kJ mol(-1) and 80 kJ mol(-1) respectively. The kinetics of growth depended upon SiO2 relative supersaturation to the power of 2 and 3 for sodalite and cancrinite, respectively. Agitation rate, solution flow velocity and the nature of steel substrate surface roughness had no noticeable effect on scale deposition rate. Data and correlations for predicting dimorphic phase-dependent, equilibrium SiO2 solubility in spent Bayer liquor and scale-related desilication/crystal growth rates are presented with a discussion on scale mitigation strategy.

The charged cluster model states that chemical vapor deposition (CVD) begins with gas-phase nucleation of charged clusters followed by cluster deposition on a substrate surface to form a thin film. Gold deposition by thermal evaporation was studied in a two-chambered CVD system in order to determine if this mechanism applies to the present case. The presence of nanometer-sized gold clusters was confirmed by transmission electron microscopy (TEM). The charge on the primary clusters was found to be positive. Smaller clusters were found to be amorphous and combined with clusters already deposited on a substrate surface to form larger amorphous clusters on the surface. Larger clusters were also observed by TEM to form after 120 and 300s. These clusters exhibited a lattice structure and may have grown by attachment of small clusters in the gas phase.

The charged cluster model states that chemical vapor deposition (CVD) begins with gas phase nucleation of charged clusters followed by cluster deposition on a substrate surface to form a thin film. A two-chambered system, separated by a 1-mm orifice, was used to study gold deposition by thermal evaporation in order to determine if the CCM applies in this case. At a filament temperature of 1523 and 1773 K, the presence of nano-meter sized gold clusters was confirmed by transmission electron microscopy (TEM). The charge on the primary clusters was found to be positive and the cluster size and size distribution increased with increasing temperature. Small clusters were found to be amorphous and they combined with clusters already deposited on a substrate surface to form larger amorphous clusters on the surface. This work revealed that gold thin films deposited on a mica surface are the result of the sticking of 4~10 nm clusters. The topography of these films was similar to those reported previously under similar conditions.

The equilibrium SiO2 solubility of sodalite and cancrinite crystals in synthetic spent Sayer liquor has been determined over a range of temperatures (90 - 220 degrees C) and as a function of NaOH and Al(OH)(3) concentration for cancrinite. The equilibrium solubility of both sodalite and cancrinite increased linearly with increasing temperature. The solubility of sodalite was found to be higher than that of cancrinite at all temperatures. For cancrinite, increasing the liquor NaOH and Al(OH)(3) concentration increased the solubility dramatically. The mechanism and kinetics of the transformation of sodalite to cancrinite were investigated under a variety of conditions. The phase transformation involved a solution-mediated mechanism of sodalite dissolution and subsequent nucleation and growth of cancrinite crystals. Furthermore, the transformation reaction was found to be first order with respect to the relative concentration of sodalite. Over the temperature range of 160-240 degrees C, an activation energy 133 kJ mol(-1) was estimated for the overall mechanism of sodalite transformation to cancrinite.

Isothermal, batch desilication kinetics of synthetic, sodium aluminate solution (spent Bayer liquor) via cancrinite and cancrinite/sodalite mixed-phase crystal growth, have been studied under conditions at which sodium aluminosilicate scale forms at the surfaces of steel heat exchangers of alumina plant. Seeding with the pure cancrinite and mixed-phase crystals results in the suppression of scale formation and a faster rate of liquor desilication in comparison with its sodalite dimorph. Cancrinite seed crystals prepared from NO−3-rich solutions exhibited crystal growth mechanism and kinetic behaviour different from dimorphic mixed-phase crystals prepared from CO2−3-rich solutions, when both were used to desilicate CO2−3-rich spent Bayer liquor. The rate of desilication due to crystal growth on CO2−3-cancrinite/sodalite mixed phase crystals followed a second-order dependence on the relative supersaturation of SiO2. An activation energy of 52kJmol−1 was estimated for the crystal growth process. For desilication kinetics involving NO−3-cancrinite seed crystal growth, a third-order dependence on relative supersaturation of SiO2 and an activation energy of 63kJmol−1 were obtained.

The precipitation of zeolite, sodalite and cancrinite and subsequent phase transformations were investigated under a variety of conditions in sodium aluminate liquor. At sufficiently high SiO2 relative supersaturation, amorphous sodium aluminosilicate and zeolite precipitated at temperatures as high as 160°C. They subsequently transformed to sodalite and finally to cancrinite. Thus the sequence of the transformation of phases is:[Aluminosilicate species]→Amorphous phase→Zeolite (Linde A)→Sodalite→Cancrinite.It was found that sodalite did not transform to cancrinite in the absence of a liquid medium. The transformation of sodalite to cancrinite was demonstrated to involve a solution-mediated mechanism with sodalite dissolution and subsequent cancrinite precipitation. Neither the amorphous phase nor the zeolite phase precipitates at typical spent Bayer liquor SiO2 supersaturation.

The kinetics of desilication of synthetic, sodium aluminosilicate solution (spent Bayer liquor) and growth of sodalite crystals have been studied under isothermal, batch crystallization conditions close to those prevailing in Bayer process heat exchangers. The desilication rate of the liquor via the formation and growth of sodalite scale on steel substrates was found to be independent of agitation rate. With sodalite seeding, the desilication rate was observed to increase dramatically due to seed crystal growth with the suppression of scale formation. An activation energy of 30 kJ mol−1 and a second order dependence of the desilication rate on relative supersaturation of SiO2 were obtained for sodalite crystal growth.