The role of mesoporosity and Si/Al ratio in the catalytic etherification of glycerol with benzyl alcohol using ZSM-5 zeolites

A comparative study of the influence of three different acid solids as catalysts (conventional zeolites Z15c with Si/Al = 19.5 and Z40c with Si/Al = 48.2, and a hierarchical zeolite Z40c-H with Si/Al = 50.0) for the etherification of glycerol with benzyl alcohol was performed. The catalytic activity and selectivity of these zeolites was elucidated at different catalyst contents. Three different ethers (3-benzyloxy-1,2-propanediol, which is a mono-benzyl-glycerol ether (MBG) and 1,3-dibenzyloxy-2-propanol, which is a di-benzyl-glycerol ether (DBG) and dibenzyl ether (DBz) were identified as the main products. MBG was the major product of the reaction catalyzed by the microporous Z15c zeolite with low Si/Al molar ratio, whereas DBG was formed in higher yield with the use of microporous Z40c and hierarchical Z40c-H zeolites, both of them having a similar high Si/Al molar ratio (≈50). MBG is a value-added product and it is obtained with good yield and selectivity when using the conventional zeolite Z15c as a catalyst. Under the best conditions tested, i.e., 25 mg of catalyst for 8 h at 120 °C, a 62% of conversion was obtained without the need of solvent, with an excellent 84% selectivity toward the MBG and no formation of DBz.

Bimetallic PtSn/C catalysts obtained via SOMC/M for glycerol steam reforming

A detailed study on the preparation of bimetallic PtSn/C catalysts using surface-controlled synthesis methods, and on their catalytic performance in the glycerol steam reforming reaction has been carried out. In order to obtain these well-defined bimetallic phases, techniques derived from Surface Organometallic Chemistry on Metals (SOMC/M) were used. The preparation process involved the reaction between an organometallic compound ((C4H9)4Sn) and a supported transition metal (Pt) in a H2 atmosphere. Catalysts with Sn/Pt atomic ratios of 0.2, 0.3, 0.5, and 0.7 were obtained, and characterized using several techniques: ICP, H2 chemisorption, TEM and XPS. These systems were tested in the glycerol steam reforming varying the reaction conditions (glycerol concentration and reaction temperature). The best performance was observed for the catalysts with the lowest tin contents (PtSn0.2/C and PtSn0.3/C). It was observed that the presence of tin increased the catalysts’ stability when working under more severe reaction conditions.

Sn@Pt and Rh@Pt core–shell nanoparticles synthesis for glycerol oxidation

The development and optimization of electrocatalysts for application in fuel cell systems have been the focus of a variety of studies where core–shell structures have been considered as a promising alternative among the materials studied. We synthesized core–shell nanoparticles of Sn x @Pt y and Rh x @Pt y (Sn@Pt, Sn@Pt2, Sn@Pt3, Rh@Pt, Rh@Pt2, and Rh@Pt3) through a reduction methodology using sodium borohydride. These nanoparticles were electrochemically characterized by cyclic voltammetry and further analyzed by cyclic voltammetry studying their catalytic activity toward glycerol electro-oxidation; chronoamperometry and potentiostatic polarization experiments were also carried out. The physical characterization was carried out by X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The onset potential for glycerol oxidation was shifted in 130 and 120 mV on the Sn@Pt3/C and Rh@Pt3/C catalysts, respectively, compared to commercial Pt/C, while the stationary pseudo-current density, taken at 600 mV, increased 2-fold and 5-fold for these catalysts related to Pt/C, respectively. Thus, the catalysts synthesized by the developed methodology have enhanced catalytic activity toward the electro-oxidation of glycerol, representing an interesting alternative for fuel cell systems.

Thermogravimetric analysis of the pyrolysis of several materials used in the preparation of commercial cigarettes

Comunicación presentada en forma de póster en el "12th Mediterranean Congress of Chemical Engineering", Barcelona (Spain), November 15-18, 2011

Catalytic effect of MCM-41 in the pyrolysis of tobacco and several substances used as additives in the preparation of commercial cigarettes

Comunicación presentada en forma de póster en el "12th Mediterranean Congress of Chemical Engineering", Barcelona (Spain), November 15-18, 2011.

TGA/FTIR study of the MCM-41-catalytic pyrolysis of tobacco and tobacco–glycerol mixtures

In this work, the catalytic effect of MCM-41 on the qualitative composition of the gases evolved in the pyrolysis of glycerol, tobacco and tobacco–glycerol mixtures has been studied by TGA/FTIR. The results obtained reflect that the amount of volatile products obtained from tobacco or from tobacco containing mixtures is noticeably decreased if the catalyst is used as a tobacco additive. The addition of the catalyst also produces noticeable changes in the composition of the gases obtained at each temperature. Such changes are more significant in the case of the pyrolysis of the tobacco–glycerol–mixture than in the pyrolysis of tobacco. The evolution patterns for different types of compounds reveal that the catalyst contributes to a noticeable decrease of the yields of methane, CO, CO2 and carbonylic compounds, which could be interesting from the point of view of the use of MCM-41 as a tobacco additive in order to reduce tobacco smoke toxicity.

Functional properties of sodium and calcium caseinate antimicrobial active films containing carvacrol

Active edible films were prepared by adding carvacrol into sodium caseinate (SC) and calcium caseinate (CC) matrices plasticized with two different glycerol concentrations (25 and 35 wt%) prepared by solvent casting. Functional characterisation of these bio-films was carried out by determination of some of their physico-chemical properties, such as colour, transparency, oxygen barrier, wettability, dye permeation properties and antibacterial effectiveness against Gram negative and Gram positive bacteria. All films exhibited good performance in terms of optical properties in the CIELab space showing high transparency. Carvacrol was able to reduce CC oxygen permeability and slightly increased the surface hydrophobicity. Dye diffusion experiments were performed to evaluate permeation properties. The diffusion of dye through films revealed that SC was more permeable than CC. The agar diffusion method was used for the evaluation of the films antimicrobial effectiveness against Escherichia coli and Staphylococcus aureus. Both SC and CC edible films with carvacrol showed inhibitory effects on both bacteria.

Structure and mechanical properties of sodium and calcium caseinate edible active films with carvacrol

Edible active films based on sodium caseinate (SC) and calcium caseinate (CC) plasticized with glycerol (G) at three different concentrations and carvacrol (CRV) as active agent were prepared by solvent casting. Transparent films were obtained and their surfaces were analysed by optical microscopy and scanning electron microscopy (SEM). The influence of the addition of three different plasticizer concentrations was studied by determining tensile properties, while Fourier transformed infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were used to evaluate the structural and thermal behavior of such films. The addition of glycerol resulted in a reduction in the elastic modulus and tensile strength, while some increase in the elongation at break was observed. In general terms, SC films showed flexibility higher than the corresponding CC counterparts. In addition, the presence of carvacrol caused further improvements in ductile properties suggesting the presence of stronger interactions between the protein matrix and glycerol, as it was also observed in thermal degradation studies. FTIR spectra of all films showed the characteristic bands and peaks corresponding to proteins as well as to primary and secondary alcohols. In summary, the best results regarding mechanical and structural properties for caseinates-based films containing carvacrol were found for the formulations with high glycerol concentrations.

A systematic study on the influence of carbon on the behavior of hard-to-ionize elements in inductively coupled plasma–mass spectrometry

A systematic study on the influence of carbon on the signal of a large number of hard-to-ionize elements (i.e. B, Be, P, S, Zn, As, Se, Pd, Cd, Sb, I, Te, Os, Ir, Pt, Au, and Hg) in inductively coupled plasma–mass spectrometry has been carried out. To this end, carbon matrix effects have been evaluated considering different plasma parameters (i.e. nebulizer gas flow rate, r.f. power and sample uptake rate), sample introduction systems, concentration and type of carbon matrix (i.e. glycerol, citric acid, potassium citrate and ammonium carbonate) and type of mass spectrometer (i.e. quadrupole filter vs. double-focusing sector field mass spectrometer). Experimental results show that P, As, Se, Sb, Te, I, Au and Hg sensitivities are always higher for carbon-containing solutions than those obtained without carbon. The other hard-to-ionize elements (Be, B, S, Zn, Pd, Cd, Os, Ir and Pt) show no matrix effect, signal enhancement or signal suppression depending on the experimental conditions selected. The matrix effects caused by the presence of carbon are explained by changes in the plasma characteristics and the corresponding changes in ion distribution in the plasma (as reflected in the signal behavior plot, i.e. the signal intensity as a function of the nebulizer gas flow rate). However, the matrix effects for P, As, Se, Sb, Te, I, Au and Hg are also related to an increase in analyte ion population caused as a result of charge transfer reactions involving carbon-containing charged species in the plasma. The predominant specie is C+, but other species such as CO+, CO2+, C2+ and ArC+ could also play a role. Theoretical data suggest that B, Be, S, Pd, Cd, Os, Ir and Pt could also be involved in carbon based charge transfer reactions, but no experimental evidence substantiating this view has been found.

TGA/FTIR study of tobacco and glycerol–tobacco mixtures

In this work, the evolution with temperature of the qualitative composition of the gases evolved in the pyrolysis of glycerol, tobacco and tobacco–glycerol mixtures has been studied. The pathways for different types of compounds (i.e., water, CO, CO2, carbonylic compounds, alkenyl or alkyl groups containing compounds, alcohols and phenols and aromatic compounds) have been established, and their relationship with the different reaction steps involved in the pyrolysis process have been suggested. The comparison among the behavior observed in the pyrolysis of tobacco, glycerol and a mixture glycerol–tobacco has permitted us to suggest possible interactions between tobacco and glycerol affecting the composition of the gases evolved.

Biodiesel wastes: An abundant and promising source for the preparation of acidic catalysts for utilization in etherification reaction

Environmentally friendly sulfonated black carbon (BC) catalysts were prepared from biodiesel waste, glycerol. These black carbons (BCs) contain a high amount of acidic groups, mainly sulfonated and oxygenated groups. Furthermore, these catalysts show a high catalytic activity in the glycerol etherification reaction with tert-butyl alcohol, the activity being larger for the sample prepared with a higher glycerol:sulfuric acid ratio (1:3). The yield for mono-tert-butyl glycerol (MTBG), di-tert-butyl glycerol (DTBG) and tri-tert-butyl-glycerol (TTBG) were very similar to those obtained using a commercial resin, Amberlyst-15. Furthermore, experimental results show that the carbon with the lowest acidic surface group content, BC prepared in minor glycerol:sulfuric acid ratio (10:1), can be chemically treated after carbonization to achieve an improved catalytic activity. The activity of all BCs is high and very similar, about 50% and 20% for the MTBG and DTBG + TTBG, respectively.

Carbon-, sulfur-, and phosphorus-based charge transfer reactions in inductively coupled plasma–atomic emission spectrometry

In this work, the influence of carbon-, sulfur-, and phosphorus-based charge transfer reactions on the emission signal of 34 elements (Ag, Al, As, Au, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, Ga, Hg, I, In, Ir, K, Li, Mg, Mn, Na, Ni, P, Pb, Pd, Pt, S, Sb, Se, Sr, Te, and Zn) in axially viewed inductively coupled plasma–atomic emission spectrometry has been investigated. To this end, atomic and ionic emission signals for diluted glycerol, sulfuric acid, and phosphoric acid solutions were registered and results were compared to those obtained for a 1% w w− 1 nitric acid solution. Experimental results show that the emission intensities of As, Se, and Te atomic lines are enhanced by charge transfer from carbon, sulfur, and phosphorus ions. Iodine and P atomic emission is enhanced by carbon- and sulfur-based charge transfer whereas the Hg atomic emission signal is enhanced only by carbon. Though signal enhancement due to charge transfer reactions is also expected for ionic emission lines of the above-mentioned elements, no experimental evidence has been found with the exception of Hg ionic lines operating carbon solutions. The effect of carbon, sulfur, and phosphorus charge transfer reactions on atomic emission depends on (i) wavelength characteristics. In general, signal enhancement is more pronounced for electronic transitions involving the highest upper energy levels; (ii) plasma experimental conditions. The use of robust conditions (i.e. high r.f. power and lower nebulizer gas flow rates) improves carbon, sulfur, and phosphorus ionization in the plasma and, hence, signal enhancement; and (iii) the presence of other concomitants (e.g. K or Ca). Easily ionizable elements reduce ionization in the plasma and consequently reduce signal enhancement due to charge transfer reactions.