Valorisation of glycerol by new mechanochemical processes

The search for new applications of glycerol, as a chemical platform from which a broad spectrum of new valuable derivatives can be obtained, is ongoing. In the present communication, a new mechano-chemical reactor is used for the valorisation of glycerol, and some examples of potential chemical processes by using mechano-chemical energy will be provided in order to reduce the residence time, to minimize the use of solvents or to decrease the temperature. In this sense, the mechano-chemical synthesis of calcium diglyceroxide from glycerol and CaO has been optimised. Finally, a new and more efficient mechano-chemical synthesis of CaDG has been achieved, requiring short synthesis time without heating and no need of solvents. The stability of this catalyst is studied under presence of free fatty acids and water, compounds presents in waste oils that decrease the yield to fatty acid methyl ester (FAME) during the reaction. Moreover, the transesterification reaction of used and refined vegetable oils with methanol has also been studied and optimised in the presence of CaDG as basic solid catalyst, using the same mechano-chemical reactor that promotes the oil-methanol mixing, minimizing the mass transfer problems associated to the immiscibility of reactants. Low methanol:oil ratios and low temperature can be used with promising results using a mechanical reactor even with used oils and in plant pilot scale under flow conditions. Glycerol carbonate is a green chemical glycerol derivative with several industrial applications (solvents, pharmaceutics, detergent, adhesives, lubricants, beauty, among others). Preliminary tests using a mechano-chemical reactor under continuous flow conditions shows the possibility to reduce the time of reaction to 1h and lowering the temperature. Finally, the production of Zn glycerolate (good candidate for the tire industry) is also studied.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

An efficient and sustainable biodiesel production in a mechanochemical pilot reactor under heterogeneous catalysis

Fatty acid methyl esters (FAME) produced from vegetable oils or animal fats by transesterification, or from the esterification of fatty acids, with methanol, is labeled as ‘‘Biodiesel”. Current industrial processes for biodiesel production are mainly based on homogeneous catalysis, in presence of an alkali hydroxide or methoxide dissolved in methanol, a large excess of methanol (methanol:oil molar ratio > 6), a temperature around 60 ºC and 1-2 h of reaction. However, this process suffers from different drawbacks, mainly related with the generation of large amount of wastewater associated to the washing and neutralization steps, the non-recovery of the homogeneous catalyst, or the formation of stable emulsions difficult to separate. These problems cause an increase of the overall biodiesel production cost. To overcome them, different approaches have been proposed, such as the use of heterogeneous catalysis, CO2 under supercritical conditions or enzymes, coupled to microwave and ultrasonic systems as alternative to conventional heating. In the present communication, a new mechanochemical reactor is used for the transesterification reaction that promotes the oil-methanol mixing, minimizing the mass transfer problems associated to the immiscibility of reactant mixtures. Moreover, in order to achieve a more sustainable biodiesel production process, a new heterogeneous basic catalyst is prepared from calcium oxide and glycerol, the by-product of biodiesel industry.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Mechanochemistry for a smart and sustainable biodiesel production under heterogeneous catalysis

Fatty acid methyl esters (FAME) produced from vegetable oil by transesterification, labeled as ‘‘Biodiesel”, is industrially accomplished in the presence of a homogeneous basic catalyst, such as alkali hydroxide or methoxide dissolved in methanol. This process requires a large excess of methanol (methanol:oil molar ratio> 6), temperature around 60 ºC and 1-2 h of reaction. However, this process suffers from important drawbacks: low FFA and water tolerance, generation of process wastewater, etc. To overcome them, different approaches have been proposed: such as the use of heterogeneous catalysis, CO2 under supercritical conditions or enzymes; coupled to microwave and ultrasonics systems as an alternative to conventional heating. Among all the researches, heterogeneous catalysts show potential in the transesterification reaction. Unlike homogeneous catalysts, heterogeneous ones are environmentally benign and can be reused and regenerated. Nevertheless, higher catalyst loading and alcohol:oil molar ratio are required for biodiesel production in the presence of solid catalysts. A new mechanochemical reactor is used for the transesterification reaction to promotes the reactants mixing, minimizing mass transfer limitations associated to the inmiscibility of reactants. This solution allows to reduce the methanol need to an amount close to the stoichiometry (methanol:oil molar ratio= 4:1), and at room temperature after less than one minute, more than 90 wt% FAME is reached. Glycerol, obtained as by-product in the transesterification reaction is used to prepare calcium diglyceroxide by mechanosynthesis, and is used as heterogeneous catalyst. A new and more efficient mechanochemical synthesis of FAME is proposed, with shorter reaction and lower temperature, compared to other synthesis proposed in literature.Universidad de Málaga.Campus de Excelencia Internacional Andalucía Tec

Squeezed Nanocrystals: Equilibrium Configuration of Metal Clusters Embedded Beneath the Surface of a Layered Material

Shapes of functional metallic nanocrystals, typically synthesized either free in solution or supported on surfaces, are key for controlling properties. Here, we consider a novel new class of metallic nanocrystals, copper islands embedded near the surface of graphite, which can be considered a model system for metals embedded beneath surfaces of layered materials, or beneath supported membranes. We develop a continuum elasticity (CE) model for the equilibrium shape of these islands, and compare its predictions with experimental data. The CE model incorporates appropriate surface energy, adhesion energies, and strain energy. The agreement between the CE model and the data is—with one exception—excellent, both qualitatively and quantitatively, and is achieved with a single adjustable parameter. The model predicts that the embedded island shape is invariant with size, manifest both by constant side slope and by constant aspect ratio. This prediction is rationalized by dimensional analysis of the relevant energetic contributions. The aspect ratio of an embedded Cu cluster is much larger than that of a supported but non-embedded Cu cluster, due to resistance of the graphene membrane to deformation. Experimental data diverge from the model predictions only in the case of the aspect ratio of small islands, below a critical height of ~10 nm. The divergence may be due to bending strain, which is treated only approximately in the model. Strong support for the CE model and its interpretation is provided by additional data for embedded Fe clusters. Most of these observations and insights should be generally applicable to systems where a metal cluster is embedded beneath a layered material or supported membrane, provided that shape equilibration is possible

Shapes of Fe nanocrystals encapsulated at the graphite surface

We describe and analyze in detail the shapes of Fe islands encapsulated under the top graphene layers in graphite. Shapes are interrogated using scanning tunneling microscopy. The main outputs of the shape analysis are the slope of the graphene membrane around the perimeter of the island, and the aspect ratio of the central metal cluster. Modeling primarily uses a continuum elasticity (CE) model. As input to the CE model, we use density functional theory to calculate the surface energy of Fe, and the adhesion energies between Fe and graphene or graphite. We use the shaft-loaded blister test (SLBT) model to provide independent stretching and bending strain energies in the graphene membrane. We also introduce a model for the elastic strain in which stretching and bending are treated simultaneously. Measured side slopes agree very well with the CE model, both qualitatively and quantitatively. The fit is optimal for a graphene membrane consisting of 2-3 graphene monolayers, in agreement with experiment. Analysis of contributions to total energy shows that the side slope depends only on the properties of graphene/graphite. This reflects delamination of the graphene membrane from the underlying graphite, caused by upward pressure from the growing metal cluster. This insight leads us to evaluate the delamination geometry in the context of two related, classic models that give analytic results for the slope of a delaminated membrane. One of these, the point-loaded circular blister test model, reasonably predicts the delamination geometry at the edge of an Fe island. The aspect ratio also agrees well with the CE model in the limit of large island size, but not for small islands. Previously, we had speculated that this discrepancy was due to lack of coupling between bending and stretching in the SLBT model, but the new modeling shows that this explanation is not viable

Semi-continuous mechanochemical process for biodiesel production under heterogeneous catalysis using calcium diglyceroxide

This work is aimed at the development of a semi-continuous mechanochemical process for biodiesel production and the subsequent valorization of glycerol, its by-product, via its conversion into calcium diglyceroxide using the same mechanochemical reactor. This basic solid catalyzes the methanolysis of vegetable oils. The implementation of a semi-continuous process allows both the preparation of the solid catalyst and the methanolysis process, overcoming the miscibility problems of methanol and oil. Thus, a biodiesel yield higher than 90% is reached using a methanol:oil molar ratio close to stoichiometric value and 1.5 wt.% catalyst, after passing through the reactor with a flow rate between 4 to 45 L/h. This new process for biodiesel production can easily be scaled up and applied to the conversion of used cooking oils, without any significant yield decrease. A cost study was also performed, demonstrating that this is more economical than the conventional batch stirring-based process.Deasyl: CONTRATO 806/41.5524_08.06.00.35.8

Studying Venom Toxin Variation Using Accurate Masses from Liquid Chromatography–Mass Spectrometry Coupled with Bioinformatic Tools

This study provides a new methodology for the rapid analysis of numerous venom samples in an automated fashion. Here, we use LC-MS (Liquid Chromatography–Mass Spectrometry) for venom separation and toxin analysis at the accurate mass level combined with new in-house written bioinformatic scripts to obtain high-throughput results. This analytical methodology was validated using 31 venoms from all members of a monophyletic clade of Australian elapids: brown snakes (Pseudonaja spp.) and taipans (Oxyuranus spp.). In a previous study, we revealed extensive venom variation within this clade, but the data was manually processed and MS peaks were integrated into a time-consuming and labour-intensive approach. By comparing the manual approach to our new automated approach, we now present a faster and more efficient pipeline for analysing venom variation. Pooled venom separations with post-column toxin fractionations were performed for subsequent high-throughput venomics to obtain toxin IDs correlating to accurate masses for all fractionated toxins. This workflow adds another dimension to the field of venom analysis by providing opportunities to rapidly perform in-depth studies on venom variation. Our pipeline opens new possibilities for studying animal venoms as evolutionary model systems and investigating venom variation to aid in the development of better antivenoms

Highly Evolvable: Investigating Interspecific and Intraspecific Venom Variation in Taipans (Oxyuranus spp.) and Brown Snakes (Pseudonaja spp.)

Snake venoms are complex mixtures of toxins that differ on interspecific (between species) and intraspecific (within species) levels. Whether venom variation within a group of closely related species is explained by the presence, absence and/or relative abundances of venom toxins remains largely unknown. Taipans (Oxyuranus spp.) and brown snakes (Pseudonaja spp.) represent medically relevant species of snakes across the Australasian region and provide an excellent model clade for studying interspecific and intraspecific venom variation. Using liquid chromatography with ultraviolet and mass spectrometry detection, we analyzed a total of 31 venoms covering all species of this monophyletic clade, including widespread localities. Our results reveal major interspecific and intraspecific venom variation in Oxyuranus and Pseudonaja species, partially corresponding with their geographical regions and phylogenetic relationships. This extensive venom variability is generated by a combination of the absence/presence and differential abundance of venom toxins. Our study highlights that venom systems can be highly dynamical on the interspecific and intraspecific levels and underscores that the rapid toxin evolvability potentially causes major impacts on neglected tropical snakebites

Distinct cardiotoxic effects by venoms of a spitting cobra (Naja pallida) and a rattlesnake (Crotalus atrox) revealed using an ex vivo Langendorff heart model

Here we describe the acute myocardial effects of an elapid (red spitting cobra, Naja pallida) and a viper (western diamondback rattlesnake, Crotalus atrox) venom using an ex vivo heart model. Our results reveal two different pathophysiological trajectories that influence heart function and morphology. While cobra venom causes a drop in contractile force, rattlesnake venom causes enhanced contractility and frequency that coincides with differences in myocellular morphology. This highlights the medical complexity of snake venom-induced cardiotoxicity