Combustion chemistry aspects of alternative fuels reforming for high-temperature fuel cell applications

Solid-oxide fuel cells (SOFC) constitute a particularly attractive technology for sustainable, combined heat and power generation, both at domestic and district levels. The elevated operating temperature of SOFC systems, allows the utilization of a wide spectrum of conventional and alternative fuels, through suitable reforming processes. The high temperatures and fuel rich conditions prevailing in SOFC reformers, enhance syngas yield and reforming efficiency but may give rise to unwanted effects, such as ignition, soot and coke formation and deposition. The above phenomena cannot be described via thermodynamic considerations and can only be effectively tackled through a detailed chemical kinetic approach. The present study provides a comparative assessment of SOFC reformer operation on conventional and alternative hydrocarbon fuels in terms of syngas yield, thermal efficiency and pollutants formation. In particular, the reforming of methane, a typical biogas (comprising of 60% CH₄ and 40% CO₂), methanol and ethanol is numerically assessed by utilizing a recently developed and validated comprehensive detailed kinetic mechanism for C₁–C₆ hydrocarbons, augmented with a PAH model. Chemical aspects of the fuel reforming process are investigated through rate-of-production path and sensitivity analyses. The study supports design guidelines aiming towards identification of optimum operating conditions, for specific applications and fuels. The analysis reveals that the extent of coupling between syngas formation and molecular growth processes is strongly dependent on fuel and operating conditions choice and identifies windows of efficient operation, for each case.     

Electrodeposited Cu–ZnO and Mn–Cu–ZnO nanowire/tube catalysts for higher alcohols from syngas

Cu–ZnO and Mn–Cu–ZnO catalysts have been prepared by electrodeposition and tested for the synthesis of higher alcohols via CO hydrogenation. The catalysts were prepared in the form of nanowires and nanotubes using a nanoporous polycarbonate membrane, which served as a template for the electrodeposition of the precursor metals from an aqueous electrolyte solution. Electrodeposition was carried out using variable amounts of Zn(NO₃)₂, Cu(NO₃)₂, Mn(NO₃)₂ and NH₄NO₃ at different galvanostatic conditions. A fixed bed reactor was used to study the reaction of CO and H₂ to produce alcohols at 270 °C, 10–20 bar, H₂/CO = 2/1, and 10,000–33,000 scc/h g_cat. In addition to methane and CO₂, methanol was the main alcohol product. The addition of manganese to the Cu–ZnO catalyst increased the selectivity toward higher alcohols by reducing methane formation; however, CO₂ selectivity remained high. Maximum ethanol selectivity was 5.5%, measured as carbon efficiency.     

The tribological behavior of alkyl ethers and alcohols in low sulfur automotive diesel

This paper presents the impact of alkyl ethers and alcohols on the lubricity of automotive diesel. Seven ethers and five alcohols were used as lubricating additives on two low sulfur diesel fuels, at the concentration range of 50-2000 ppm. Tribological experiments carried out on the high frequency reciprocating rig showed that six of seven ethers used provide satisfactory mean wear scar diameter (WS 1.4) of less than 0.46 mm, at the concentration levels of 750-1500 ppm. Among the ethers of the same molecular type, those having the oxygen in the middle of the molecule appeared to have marginally better lubrication performance for some concentration ranges. In the case of alcohols, the effective concentration was 750 ppm or higher. Overall, alcohols appear to be better lubricants than ethers at high concentrations, maybe due to their more pronounced polar nature.     

Monitoring the oxidation of edible oils by Fourier transform infrared spectroscopy

Edible fats and oils in their neat form are ideal candidates for Fourier transform infrared (FTIR) analysis, in either the attenuated total reflectance or the transmission mode. FTIR spectroscopy provides a simple and rapid means of following complex changes that take place as lipids oxidize. Safflower and cottonseed oils were oxidized under various conditions, and their spectral changes were recorded and interpreted. The critical absorption bands associated with common oxidation end products were identified by relating them to those of spectroscopically representative reference compounds. The power and utilty of FTIR spectroscopy to follow oxidative changes was demonstrated through the use of “real-time oxidation plots.” A quantitative approach is proposed in which standards are used that are spectroscopically representative of oxidative end products and by which the oxidative state of an oil can be defined in terms of percent hydroperoxides, percent alcohols and total carbonyl content. By using either relative absorption as a basis or calibrating on representative standards, FTIR analysis provides a rapid means of evaluating the oxidative state of an oil or of monitoring changes in oils undergoing thermal stress.     

Two-stage sorption in rubbery semicrystalline polymers: transport of primary alcohols in polyesteramide

This paper deals with the two-stage sorption of methanol, 1-propanol and 1-hexanol in a rubbery semicrystalline polyesteramide. This is the first time two-stage sorption is reported for a semicrystalline rubbery polymer. Mass uptake, specimen geometry and surface concentration were measured independently. The two-stage sorption curve describes two overlapping processes; a very rapid diffusion (mode 1) superimposed onto a normal s-shaped sorption curve (mode 2). Mode 1 swelling was uni-dimensional and mode 2 swelling was initially uni-dimensional and later three-dimensional. It was possible to model the sorption curves by assuming time-dependent solute-surface-concentration conditions, similar to those used to describe simple s-shaped sorption. The obtained time dependence, characterised by a single relaxation time, agreed with experimental values of the surface concentration obtained by infrared spectroscopy. The relaxation time increased exponentially with increasing size of the diffusing alcohol molecule. The solubility of the alcohols in the polymer increased with increasing hydroxyl-group density. The diffusivity of alcohol decreased nonlinearly with increasing length of the molecule, size effects being less important for larger solutes.     

Optimal conditions for fractionation of rapeseed lecithin with alcohols

Deoiled rapeseed lecithin was fractionated with ethanol, and optimum conditions have been determined to improve purified lecithin yield and phosphatidylcholine (PC) enrichment. The effect of extraction time, solvent volume, ethanol concentration and temperature on the yield and the PC enrichment have been described in the form of regression equations. A full factorial experiment method and a second-order orthogonal design were used in the study. The regression equations were calculated for the maximum value of the response functions optimized by an electronic data processing method, and the results (yield and PC enrichment calculated from regression equations) were compared with those obtained in control experiments. The use of calculated optimal parameters in the fractionation process led to 81–96% and 58% increments in yield and PC enrichment, respectively.     

Effect of SO2 on the formation and evolution of volatile compounds in wines

The aim of this work was to study the influence of SO₂ on the formation and later evolution of volatile compounds in wine bottles made from fermentations of sterilized and inoculated must. For this purpose, Parellada must, sterilized and inoculated with Saccharomyces cerevisiae, was fermented with and without SO₂. Subsequently, the obtained wines were aged in bottle during 6 months at room temperature with and without SO₂. The results show that SO₂ hardly had any effect on the formation of volatile compounds during fermentation. However, the wine stored in bottle with SO₂ showed a higher concentration of volatile compounds, mainly esters and alcohols, than the wine aged in bottle without SO₂.     

Oxidation of alcohols using RuMnCe catalysts

The combination of ruthenium, manganese as well as cerium oxides formed an active catalytic system for the oxidation of 2-octanol and other alcohols. The addition of manganese species as promotors resulted in more active catalysts than comparable cobalt-doped oxidic materials. The application of RuMnCe oxides on redox-active supports, such as TiO₂ or CeO₂, by deposition–precipitation caused a further improvement of catalytic activity. A tolerance to nitrogen-containing substrates was observed.     

Liquid–liquid equilibrium correlations using lattice fluid equation of state with hydrogen bonding

The nonrandom lattice equation of state with hydrogen bonding (NLF-HB EOS) was examined for the correlation of liquid–liquid equilibria (LLE) for binary alcohol and hydrocarbon mixture in a wide pressure range. For hydrocarbon + alcohol mixtures the consideration of a hydrogen-bonding term in the lattice equation of state clearly improves the prediction for vapor–liquid equilibrium (VLE) as shown in previous works, but the prediction of LLE is still in question. In this paper, LLE data for alcohols (methanol and ethanol) + hydrocarbons (n-hexane to n-hexadecane) were correlated by NLF-HB EOS and results were compared with a cubic equation of state (Peng–Robinson EOS with the T–K Wilson based G^E model). Both equations of state showed similar degree of accuracies but with different number of adjustable parameters. The Peng–Robinson EOS based approach requires six temperature dependent coefficients for accurate calculation whereas NLF-HB EOS requires only two temperature dependent coefficients. The effects of varying hydrogen-bonding energies for NLF-HB EOS are discussed.