Unraveling the mechanism of catalytic reactions through combined kinetic and thermodynamic analyses: Application to the condensation of ethanol

The combination of kinetic and thermodynamic analyses can provide an in-depth knowledge of the crucial steps of catalyzed reactions. Earlier examples are recalled to stress how a reaction mechanism can be supported or rejected based on trivial reactant and product concentration analyses. The method is then applied to the important reaction of alcohol condensation, the so-called Guerbet reaction, which enables converting ethanol, a renewable feedstock, into higher alcohols. Important conclusions regarding the design of ethanol condensation processes can be drawn, as the main reaction mechanism occurring at high temperatures (ca. 350–420 °C) appears to be different from that proposed at low temperatures (< 250 °C). In the former case, the pathway involving acetaldehyde is negligible, and therefore a multi-step process based on ethanol dehydrogenation followed by acetaldehyde self-aldolization would be irrelevant.     

Application of two-stage biofilter system for the removal of odorous compounds

Biofiltration is a biological process which is considered to be one of the more successful examples of biotechnological applications to environmental engineering, and is most commonly used in the removal of odoriferous compounds. In this study, we have attempted to assess the efficiency with which both single and complex odoriferous compounds could be removed, using one- or two-stage biofiltration systems. The tested single odor gases, limonene, α-pinene, and iso-butyl alcohol, were separately evaluated in the biofilters. Both limonene and α-pinene were removed by 90% or more EC (elimination capacity), 364 g/m³/h and 321 g/m³/h, respectively, at an input concentration of 50 ppm and a retention time of 30 s. The iso-butyl alcohol was maintained with an effective removal yield of more than 90% (EC 375 g/m³/h) at an input concentration of 100 ppm. The complex gas removal scheme was applied with a 200 ppm inlet concentration of ethanol, 70 ppm of acetaldehyde, and 70 ppm of toluene with residence time of 45 s in a one- or two-stage biofiltration system. The removal yield of toluene was determined to be lower than that of the other gases in the one-stage biofilter. Otherwise, the complex gases were sufficiently eliminated by the two-stage biofiltration system.     

A method for direct,semi-quantitative analysis of gas phase samples using gas chromatography–inductively coupled plasma-mass spectrometry

A new and complete GC–ICP-MS method is described for direct analysis of trace metals in a gas phase process stream. The proposed method is derived from standard analytical procedures developed for ICP-MS, which are regularly exercised in standard ICP-MS laboratories. In order to implement the method, a series of empirical factors were generated to calibrate detector response with respect to a known concentration of an internal standard analyte. Calibrated responses are ultimately used to determine the concentration of metal analytes in a gas stream using a semi-quantitative algorithm. The method was verified using a traditional gas injection from a GC sampling valve and a standard gas mixture containing either a 1 ppm Xe + Kr mix with helium balance or 100 ppm Xe with helium balance. Data collected for Xe and Kr gas analytes revealed that agreement of 6–20% with the actual concentration can be expected for various experimental conditions.To demonstrate the method using a relevant “unknown” gas mixture, experiments were performed for continuous 4 and 7 hour periods using a Hg-containing sample gas that was co-introduced into the GC sample loop with the xenon gas standard. System performance and detector response to the dilute concentration of the internal standard were pre-determined, which allowed semi-quantitative evaluation of the analyte. The calculated analyte concentrations varied during the course of the 4 hour experiment, particularly during the first hour of the analysis where the actual Hg concentration was under predicted by up to 72%. Calculated concentration improved to within 30–60% for data collected after the first hour of the experiment. Similar results were seen during the 7 hour test with the deviation from the actual concentration being 11–81% during the first hour and then decreasing for the remaining period. The method detection limit (MDL) was determined for the mercury by injecting the sample gas into the system following a period of equilibration. The MDL for Hg was calculated as 6.8 μg · m^− 3. This work describes the first complete GC–ICP-MS method to directly analyze gas phase samples, and detailed sample calculations and comparisons to conventional ICP-MS methods are provided.     

Kinetic spectrophotometric determination of acetaldehyde in medical ethanol

A novel method has been introduced for the determination of trace amounts of acetaldehyde in medical ethanol based on its inhibition effect on the reaction between piperidine and sodium nitroprussiate. The reaction is monitored by a spectrophotometric technique, measuring a decreasing rate of absorbance at 560 nm during a fixed time of 60 s. The method allows for the determination of acetaldehyde in the range of 2.5–55 ppm. The limit of detection is 0.5 ppm and the relative standard deviation for 16 determinations of 30.0 ppm acetaldehyde is 0.038, while it is 0.173 in the common simple spectrophotometric method. The reliable results make the proposed method applicable to the determination of acetaldehyde in medical ethanol. The text was submitted by the authors in English.     

Analysis of thermolabile residual solvents in a spray dried dispersion using static headspace gas chromatography

In this study, we discuss the development of a static headspace gas chromatography method for the analysis of residual acetone as well as its enriched impurities including mesityl oxide and diacetone alcohol, in a spray dried dispersion. The major challenges include the instability of mesityl oxide and diacetone alcohol at high temperature and peak tailing of diacetone alcohol. It was found that the headspace oven temperature has to be controlled to 150°C or below to prevent degradation beyond an acceptable level (< 1%). The peak tailing of diacetone alcohol was attributed to the “Phase Soaking” effect due to excessive diluent, which may condense and temporarily modify the stationary phase. The peak shape of diacetone alcohol is dependent on the column loading capacity and the peak area of N‐methyl pyrrolidone, the solvent that elutes after diacetone alcohol. The headspace oven temperature was set at 140°C, where the highest response ratio of diacetone alcohol/N‐methyl pyrrolidone at 1.46 and thus the best sensitivity was obtained. The calculated quantitation limits were 1 ppm for acetone, 3 ppm for mesityl oxide and 31 ppm for diacetone alcohol. The method successfully passed validation criteria for specificity, linearity, accuracy, and precision.     

2D spatiotemporal visualization system of expired gaseous ethanol after oral administration for real-time illustrated analysis of alcohol metabolism

A novel 2-dimensional spatiotemporal visualization system of expired gaseous ethanol after oral administration for real-time illustrated analysis of alcohol metabolism has been developed, which employed a low level light CCD camera to detect chemiluminescence (CL) generated by catalytic reactions of standard gaseous ethanol and expired gaseous ethanol after oral administration. First, the optimization of the substrates for visualization and the concentration of luminol solution for CL were investigated. The cotton mesh and 5.0 mmol L⁻¹ luminol solution were selected for further investigations and this system is useful for 0.1-20.0 mmol L⁻¹ of H₂O₂ solution. Then, the effect of pH condition of Tris-HCl buffer solution was also evaluated with CL intensity and under the Tris-HCl buffer solution pH 10.1, a wide calibration range of standard gaseous ethanol (30-400 ppm) was obtained. Finally, expired air of 5 healthy volunteers after oral administration was measured at 15, 30, 45, 60, 75, 90, 105 and 120 min after oral administration, and this system showed a good sensitivity on expired gaseous ethanol for alcohol metabolism. The peaks of expired gaseous ethanol concentration appeared within 30 min after oral administration. During the 30 min after oral administration, the time variation profile based on mean values showed the absorption and distribution function, and the values onward showed the elimination function. The absorption and distribution of expired gaseous ethanol in 5 healthy volunteers following first-order absorption process were faster than the elimination process, which proves efficacious of this system for described alcohol metabolism in healthy volunteers. This system is expected to be used as a non-invasive method to detect VOCs as well as several other drugs [1] in expired air for clinical purpose.     

Ethanol/water solutions as certified reference materials for breath alcohol analyzer calibration

The Federal Institute for Materials Research and Testing (BAM), Germany, has issued a series of large volume ethanol in water certified reference materials (CRMs), primarily developed for the calibration of evidential breath alcohol analyzers in Germany. The certified parameter is the ethanol mass concentration at 20 °C. When used in a wet bath simulator, the solutions deliver gas samples that meet the requirements set by the Organization of Legal Metrology for calibration of breathalyzers. The materials were prepared gravimetrically by spiking of ethanol into water in single 5 L units. A complete uncertainty budget for the preparation process has been established. The purity of the commercial ethanol stock solution was identified to be the main source of uncertainty. For stability and homogeneity measurements and for the verification of the gravimetric mass concentration of the CRMs, a robust high-precision gas chromatography, with flame-ionization detection method for ethanol determination in aqueous samples was developed and validated. The good performance of this method has been demonstrated in several international comparisons organized by the Consultative Committee for Amount of Substance—Metrology in Chemistry at the International Bureau of Weights and Measures.     

Application of LC–TOF MS to analysis of hemoglobin acetaldehyde adducts in alcohol detoxification patients

Acetaldehyde adducts of hemoglobin have been regarded as potential biochemical markers of alcohol exposure. In this study a novel sensitive method using liquid chromatography coupled to time-of-flight mass spectrometry (LC–TOF MS) has been used to investigate changes in adduct levels in alcohol detoxification patients. Hemoglobin and authentic blood samples from 66 adults with an alcohol-dependence syndrome and from 12 children were analyzed for acetaldehyde modifications with and without trypsin digestion using LC–TOF MS. After in-vitro incubation of hemoglobin with increasing concentrations of acetaldehyde, followed by tryptic digestion, 21 modified peptide fragments could be identified from their accurate mass and retention time shift. Eight of these could also be detected in authentic human blood samples. Trace amounts in children’s blood were indicative of an endogenous source. Modified peptide levels in patients’ samples with and without ethanol were significantly different, as also were levels in samples from admission and from five days later. Samples obtained 5, 10, or 15 days after admission did not differ in adduct levels. The LC–TOF MS method was sensitive enough to detect acetaldehyde-modified hemoglobin peptides in blood samples from patients with an alcohol-dependence syndrome. However, elevated levels were only observed after recent ethanol consumption and decreased during five days of abstinence, suggesting that acetaldehyde-modified tryptic peptides of hemoglobin are potential biomarkers only for short-term ethanol ingestion.     

Continuous Flow Determination of Blood Alcohol Using Biamperometric Monitoring of Enzymatic Reaction

Abstract

Ethanol was determined by reaction with NAD in the presence of alcohol dehydrogenase in a continuous flow system. NADH produced was allowed to react with hexacyanoferrate (III) in the presence of diapharase. The concentration of the produced hexacyanoferrate (II) was monitored biamperometrically using open tubular carbon electrodes. A level of 1.5 × 10² mg/100 ml ethanol was detected, with an average precision of 4% relative standard deviation. The ethanol level in blood samples was determined, obtaining a 0.08 correlation coefficient with gas chromatography results.     

GC-MS analysis of ethanol and other volatile compounds in micro-volume blood samples—quantifying neonatal exposure

A static headspace gas chromatography coupled mass spectrometry (GC-MS) method was developed and fully validated for the quantitative measurement of acetaldehyde, acetone, methanol, ethanol and acetic acid in the headspace of micro-volumes of blood using n-propanol as an internal standard. The linearity of the method was established over the range 0.2–100 mg/L (R ²?>?0.99) and the limits of detection were 0.1–0.2 mg/L and lower limits quantification 0.5–1 mg/L. Precision and accuracies fell within acceptable limits (20 % for LLOQ and 15 %) for both intra- and inter-day analyses for all compounds except acetaldehyde which had inter-day variability of ≤25 %. The method was applied to analyse blood samples from neonatal patients receiving courses of ethanol excipient containing medications. Baseline levels of acetaldehyde, acetone, methanol and ethanol could be measured in patients before dosing commenced and an increase in levels of some volatiles were observed in several neonates after receiving ethanol-containing medications.     

Electrocatalytic reduction of NAD+ at glassy carbon electrode modified with single-walled carbon nanotubes and Ru(III) complexes

A simple procedure was developed to prepare a glassy carbon electrode modified with carbon nanotubes and Ruthenium (III) complexes. First, 25 μl of dimethyl sulfoxide–carbon nanotubes solutions (0.4 mg/ml) was cast on the surface of the glassy carbon electrode and dried in air to form a carbon nanotube film at the electrode surface. Then, the glassy carbon/carbon nanotube-modified electrode was immersed into a Ruthenium (III) complex solution (direct deposition) for a short period of time (10–20 s for multiwalled carbon nanotubes and 20–40 s for single-walled carbon nanotubes). The cyclic voltammograms of the modified electrode in aqueous solution shows a pair of well-defined, stable, and nearly reversible redox couple, Ru(III)/Ru(II), with surface-confined characteristics. The attractive mechanical and electrical characteristics of carbon nanostructures and unique properties and reactivity of Ru complexes are combined. The transfer coefficient (α), heterogeneous electron transfer rate constants (k _s), and surface concentrations (Γ) for the glassy carbon/single-walled carbon nanotubes/Ru(III) complex-, glassy carbon/multiwalled carbon nanotubes/Ru(III) complex-, and glassy carbon/Ru(III) complex-modified electrodes were calculated using the cyclic voltammetry technique. The modified electrodes showed excellent catalytic activity, fast response time, and high sensitivity toward the reduction of nicotinamide adenine dinucleotide in phosphate buffer solutions at a pH range of 4–8. The catalytic cathodic current depends on the nicotinamide adenine dinucleotide concentration. In the presence of alcohol dehydrogenase, the modified electrode exhibited a response to addition of acetaldehyde. Therefore, the main product of nicotinamide adenine dinucleotide electroreduction at the Ru(III) complex/carbon nanotube-modified electrode was the enzymatically active NADH. The purposed sensor can be used for acetaldehyde determination.     

Electroanalysis and determination of acetaldehyde in fuel ethanol using the reaction with 2,4-dinitrophenylhydrazine

The voltammetric reduction of acetaldehyde was studied in 0.1 M LiOH: LiCl (60: 40 v/v). Well-defined waves can be seen at −1.77 and −1.60 V with the use of hanging mercury and glassy carbon electrodes. Acetaldehyde was shown to react at room temperature with the 2,4-dinitrophenylhydrazine and the product exhibited a differential pulse voltammetric peak at −0.90 V, which was well separated from the peaks of the derivative. This allowed the indirect determination of acetaldehyde in the presence of 0.1 M ethanol/tetrabutylammonium perchlorate after 10 min of reaction. Calibration graphs were obtained for 1.00 × 10⁻⁶−1.00 × 10⁻⁴ M of acetaldehyde. The detection limit is 8.14 × 10⁻⁷ M. The method has been applied satisfactorily to the determination of total aldehyde in fuel ethanol samples without any pretreatment. The text was submitted by the authors in English.     

Development of Industrial Brewing Yeast with Low Acetaldehyde Production and Improved Flavor Stability

Higher acetaldehyde concentration in beer is one of the main concerns of current beer industry in China. Acetaldehyde is always synthesized during beer brewing by the metabolism of yeast. Here, using ethanol as the sole carbon source and 4-methylpyrazole as the selection marker, we constructed a new mutant strain with lower acetaldehyde production and improved ethanol tolerance via traditional mutagenesis strategy. European Brewery Convention tube fermentation tests comparing the fermentation broths of mutant strain and industrial brewing strain showed that the acetaldehyde concentration of mutant strain was 81.67 % lower, whereas its resistant staling value was 1.0-fold higher. Owing to the mutation, the alcohol dehydrogenase activity of the mutant strain decreased to about 30 % of the wild-type strain. In the meantime, the fermentation performance of the newly screened strain has little difference compared with the wild-type strain, and there are no safety problems regarding the industrial usage of the mutant strain. Therefore, we suggest that the newly screened strain could be directly applied to brewing industry.     

Carbon Nanosheets Synthesis in a Gliding Arc Reactor: On the Reaction Routes and Process Parameters

Non-thermal plasma is a promising technology for high purity nanomaterial synthesis in a fast, flexible and controllable process. Gliding arc discharge, as one of the most efficient non-thermal plasmas, has been widely used in gas treatment but rarely studied for the nanomaterial synthesis. In this study, a comparison study for carbon nanosheets synthesis including toluene dissociation and graphite exfoliation was investigated in a 2D gliding arc reactor at atmospheric pressure. The effects of gas flow rate, precursor concentration and power input on the structures of carbon nanosheets produced through the two synthesis routes were explored and compared. Amorphous carbon nanosheets were produced in both approaches with a few crystalline structures formation in the case of toluene dissociation. The thickness of carbon nanosheets synthesized from graphite exfoliation was less than 3 nm, which was thinner and more uniform than that from toluene dissociation. The flow rate of carrier gas has direct influence on the morphology of carbon nanomaterials in the case of toluene dissociation. Carbon spheres were also produced along with nanosheets when the flow rate decreased from 2 to 0.5 L/min. However, in the case of graphite exfoliation, only carbon nanosheets were observed regardless of the change in flow rate of the carrier gas. The generated chemical species and plasma gas temperatures were measured and estimated for the mechanism study, respectively.

     

Effective synthesis of (S)-3,5-bistrifluoromethylphenyl ethanol by asymmetric enzymatic reduction

The synthesis of (S)-3,5-bistrifluoromethylphenyl ethanol, a pharmaceutically important alcohol intermediate for the synthesis of NK-1 receptor antagonists, was demonstrated from a ketone via asymmetric enzymatic reduction. The isolated enzyme alcohol dehydrogenase from Rhodococcus erythropolis reduced the poorly water soluble substrate with excellent ee (>99.9%) and good conversion (>98%). The optimized process was demonstrated up to pilot scale using high substrate concentration (390 mM) using a straightforward isolation process achieving excellent isolation yields (>90%) and effective space time yield (100–110 g/L d). Process improvements, demonstrated at preparative scale, increased the substrate concentration to 580 mM achieving a space time yield of 260 g/L d.     

Studies on radon concentration in drinking water around Hemavathi river basin,Karnataka State,India

Concentrations of radon in drinking water collected from 32 locations of Hemavathi river basin, Karnataka, India have been measured by emanometry method. The radon concentration in water ranged from 2.7 ± 0.1 to 138.5 ± 1.5 Bq l⁻¹ with a geometrical mean of 25.3 ± 1.1 Bq l⁻¹. The study revealed that about 82.35% of drinking water samples contained radon concentration more than 11.1 Bq l⁻¹, the limit is fixed by Environmental Protection Agency. Among the different parameters measured, concentration of radon showed weak correlation with chloride and no correlation with alkalinity, pH, nitrate, sulphate, fluoride and total dissolved substance.

     

Hydrothermal synthesis of one-dimensional α-MoO3 nanomaterials and its unique sensing mechanism for ethanol

In gas sensor applications, the availability of highly sensitive and rapid response/recovery detector for ethanol gas is sparse. One-dimensional orthogonal crystalline molybdenum trioxide nanomaterials were synthesized by an economical and environmentally friendly hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy spectroscopy (EDS) were used to investigate the structure and morphology of the nanometer materials. The relevant characterization shows that nanobelts are highly crystalline layered structures with a width of about 200 nm and a length of a few micrometers. The synthesized ethanol gas sensors based on α-MoO₃ semiconductor material show the highest response at 350 °C. Gas sensitivity tests indicated that α-MoO₃ nanobelts respond well to 50 ～ 600 ppm ethanol at optimal operating temperatures. The selectivity test among various reducing gases shows that the sensor responds better to ethanol compared to other gases such as xylene, NO₂, CO, and H₂ gases. This excellent sensing performance is attributed to the unique sensing mechanism formed in the layered MoO₃ nanobelts through the catalytic reaction between ethanol and MoO₃ lattice oxygen and adsorbed oxygen. The sensing mechanism of the co-catalytic effect of lattice oxygen and adsorbed oxygen on ethanol is also discussed in depth.     

Occurrence of 2-methylthiazolidine-4-carboxylic acid, a condensation product of cysteine and acetaldehyde, in human blood as a consequence of ethanol consumption

Acetaldehyde is a strongly electrophilic compound that is endogenously produced as a first intermediate in oxidative ethanol metabolism. Its high reactivity towards biogenic nucleophiles has toxicity as a consequence. Acetaldehyde readily undergoes a non-enzymatic condensation reaction and consecutive ring formation with cysteine to form 2-methylthiazolidine-4-carboxylic acid (MTCA). For analytical purposes, N-acetylation of MTCA was required for stabilization and to enable its quantification by reversed-phase chromatography combined with electrospray ionization–tandem mass spectrometry. Qualitative screening of post mortem blood samples with negative blood alcohol concentration (BAC) mostly showed low basal levels of MTCA. In BAC-positive post mortem samples, but not in corresponding urine specimens, strongly increased levels were present. To estimate the association between ethanol consumption and the occurrence of MTCA in human blood, the time curves of BAC and MTCA concentration were determined after a single oral dose of 0.5?g ethanol per kilogram of body weight. The blood elimination kinetics of MTCA was slower than that of ethanol. The peak concentration of MTCA (12.6?mg?L^-1) was observed 4?h after ethanol intake (BAC 0.07‰) and MTCA was still detectable after 13?h. Although intermediary acetaldehyde scavenging by formation of MTCA is interesting from a toxicological point of view, lack of hydrolytic stability under physiological conditions may hamper the use of MTCA as a quantitative marker of acetaldehyde exposure, such as resulting from alcohol consumption.     

Radiolysis and radiolytic by-product of N,N-diethylhydroxylamine in HNO3 at lower dose

N, N-diethylhydroxylamine (DEHA) is a novel salt-free reducing reagent used in the separation of Pu and Np from U in the treatment of used nuclear fuel. This paper reports on the radiation damage and radiolytic by-product of 0.5 mol L^?1 DEHA in 0.3 mol L^?1?~?1.0 mol L^?1 HNO₃ at dose up to 25 kGy. Results show that the radiolysis rate of DEHA is less than 10%. The main radiolytic products are hydrogen, acetaldehyde, acetic acid and nitrous acid, which increase with the dose. The concentration of acetaldehyde and acetic acid is much higher than that of nitrous acid.

     

Thermodynamic study of alcohol on SnO2 (100)-based gas nano-sensor

Alcohol dehydrogenation and condensation reactions are involved in chain growth pathways of SnO₂. These pathways lead to the formation of acetaldehyde and other products with high selectivity. It is recognised that together with the atmospheric oxygen, the presence of humidity greatly influences gas detection. Accordingly, it is important to understand the role of alcohol vapours in the sensing mechanism. Interaction between alcohol molecules and SnO₂ is investigated using MNDO method by semi-empirical calculations. We study the structural, total energy, thermodynamic properties of absorption of CH₃OH and C₂H₅OH on SnO₂ at 298?K. When exposed to ethanol, the SnO₂-based sensors showed oxidation products consisting of acetaldehyde, ethyl acetate and CH₄?+?CO. All the geometry optimisation structures were carried out using the Gaussian program package. Density functional theory optimised intermediates and transient states. The results show a sensitivity enhancement in resistance and capacitance when ethanol is near the surface, so converted into different products.