Effects of Natural and Artificial Surfactants on Diffusive Boundary Dynamics and Oxygen Exchanges across the Air–Water Interface

Comparing measurements of the natural sea surface microlayer (SML) and artificial surface films made of Triton-X-100 and oleyl alcohol can provide a fundamental understanding of diffusive gas fluxes across the air–water boundary layers less than 1 mm thick. We investigated the impacts of artificial films on the concentration gradients and diffusion of oxygen (O2) across the SML, the thickness of the diffusive boundary layer (DBL), and the surface tension levels of natural seawater and deionized water. Natural and artificial films led to approximately 78 and 81% reductions in O2 concentration across the surfaces of natural seawater and deionized water, respectively. The thicknesses of the DBL were 500 and 350 µm when natural SML was added on filtered and unfiltered natural seawater, respectively, although the DBL on filtered seawater was unstable, as indicated by decreasing thickness over time. Triton-X-100 and oleyl alcohol at a concentration of 2000 µg L−1 in deionized water persistently increased the DBL thickness values by 30 and 26% over a period of 120 min. At the same concentration, Triton-X-100 and oleyl alcohol decreased the surface tension of deionized water from ~72 mN m−1 to 48 and 38 mN m−1, respectively; 47% recovery was recorded after 30 min with Triton-X-100, although low surface tension persisted for 120 min with oleyl alcohol. The critical micelle concentration values of Triton-X-100 ranged between 400 and 459 µg L−1. We, therefore, suggest that Triton-X-100 resembles natural SML because the reduction and partial recovery of the surface tension of deionized water with the surfactant resembles the behavior observed for natural slicks. Temperature and salinity were observed to linearly decrease the surface tension levels of natural seawater, artificial seawater, and deionized water. Although several factors leading to O2 production and consumption in situ are excluded, experiments carried out under laboratory-controlled conditions are useful for visualizing fine-scale processes of O2 transfer from water bodies through the surface microlayer.

Synthesis, Characterization and Optimization of Oleyl Oleate Wax Ester Using Ionic Liquid Catalysts

In this work, the synthesis of oleyl oleate wax ester using Brønsted acidic ionic liquid catalysts was carried out. Confirmation of oleyl oleate molecular structure has been performed using FTIR, NMR, and ESI-MS spectroscopies. The ability of ionic liquid catalysts for catalyzing the esterification reaction of oleic acid and oleyl alcohol to produce oleyl oleate was optimized. The ionic liquid catalyst ([NMP][CH3SO3]) was found to be the best catalyst for the esterification reaction of oleic acid and oleyl alcohol compared with the other acidic ionic liquids studied. The optimal reaction conditions were determined at a reaction time of 8 h; oleic acid to oleyl alcohol mole ratio of 1:1; ([NMP][CH3SO3]) with 9.9 wt.%; and reaction temperature of 90 °C. Under these conditions, the percentage yield of oleyl oleate wax ester was 86%.

Group 13 Lewis Acid Catalyzed Synthesis of Cu2O Nanocrystals via Hydroxide Transmetallation

The colloidal synthesis of metal oxide nanocrystals (NCs) in oleyl alcohol requires the metal to catalyze an esterification reaction with oleic acid to produce oleyl oleate ester and M-OH monomers, which then condense to form MxOy solids. Here we show that the synthesis of Cu2O NCs by this method is limited by the catalytic ability of copper to drive esterification and thus produce Cu+ -OH monomers. However, inclusion of 1-15 mol% of a group 13 cation (Al3+, Ga3+ , or In3+) results in increased yields for the consumption of copper ions toward Cu2O formation and exhibits size/morphology control based on the nature of M3+ . Using a continuous-injection procedure where the copper precursor (Cu2+ -oleate) and catalyst (M3+ -oleate) are injected into oleyl alcohol at a controlled rate, we are able to monitor the reactivity of the precursor and M3+ catalyst using UV-visible and FTIR absorbance spectroscopies. These time-dependent measurements clearly show that M3+ catalysts drive esterification to produce M3+ -OH species, which then undergo transmetallation of hydroxide ligands to generate Cu+ -OH monomers required for Cu2O condensation. Ga3+ is found to be the “goldilocks” catalyst, producing NCs with the smallest size and a distinct cubic morphology not observed for any other group 13 metal. This is believed to be due to rapid transmetallation kinetics between Ga3+ -OH and Cu + -oleate. These studies introduce a new mechanism for the synthesis of metal oxides where inherent catalysis by the parent metal (i.e. copper) can be circumvented with the use of a secondary catalyst to generate -OH ligands.

Group 13 Lewis Acid Catalyzed Synthesis of Cu2O Nanocrystals via Hydroxide Transmetallation

The colloidal synthesis of metal oxide nanocrystals (NCs) in oleyl alcohol requires the metal to catalyze an esterification reaction with oleic acid to produce oleyl oleate ester and M-OH monomers, which then condense to form MxOy solids. Here we show that the synthesis of Cu2O NCs by this method is limited by the catalytic ability of copper to drive esterification and thus produce Cu+ -OH monomers. However, inclusion of 1-15 mol% of a group 13 cation (Al3+, Ga3+ , or In3+) results in increased yields for the consumption of copper ions toward Cu2O formation and exhibits size/morphology control based on the nature of M3+ . Using a continuous-injection procedure where the copper precursor (Cu2+ -oleate) and catalyst (M3+ -oleate) are injected into oleyl alcohol at a controlled rate, we are able to monitor the reactivity of the precursor and M3+ catalyst using UV-visible and FTIR absorbance spectroscopies. These time-dependent measurements clearly show that M3+ catalysts drive esterification to produce M3+ -OH species, which then undergo transmetallation of hydroxide ligands to generate Cu+ -OH monomers required for Cu2O condensation. Ga3+ is found to be the “goldilocks” catalyst, producing NCs with the smallest size and a distinct cubic morphology not observed for any other group 13 metal. This is believed to be due to rapid transmetallation kinetics between Ga3+ -OH and Cu + -oleate. These studies introduce a new mechanism for the synthesis of metal oxides where inherent catalysis by the parent metal (i.e. copper) can be circumvented with the use of a secondary catalyst to generate -OH ligands.

Group 13 Lewis Acid Catalyzed Synthesis of Metal Oxide Nanocrystals via Hydroxide Transmetallation

A new transmetallation approach is described for the synthesis of metal oxide nanocrystals (NCs). Typically, the synthesis of metal oxide NCs in oleyl alcohol is driven by metal-based esterification catalysis...

Selective hydrogenation of oleic acid to fatty alcohols over a Rh–Sn–B/Al2O3 catalyst: kinetics and optimal reaction conditions

The selective hydrogenation of oleic acid to oleyl alcohol over a Rh(1 wt%)–Sn(4 wt%)–B/Al2O3 catalyst was studied. A comprehensive set of experimental data was used for elucidating the reaction mechanism.

Hexanol Biosynthesis From Syngas by Clostridium Carboxidivorans P7 - Investigation of Product Toxicity, Temperature Dependence and in Situ Extraction

BackgroundClostridium carboxidivorans P7 converts synthesis gas (also called syngas, a mixture of CO, CO2 and H2) directly into industrially relevant alcohols (hexanol, butanol and ethanol) and their corresponding acids (caproate, butyrate and acetate). The product titers and ratios are highly dependent on fermentation parameters and the compositions of syngas as well as the growth medium. Hexanol titers produced by C. carboxidivorans P7 have recently been improved by optimizing these conditions, but little is known about the toxicity of hexanol towards Clostridium species. We hypothesized that the hexanol titers currently produced by C. carboxidivorans P7 are limited by product toxicity. ResultsWe tested our hypothesis by analyzing IC50 values for hexanol at 30 °C and 37 °C, which we determined as 17.5 ± 1.6 mM and 11.8 mM ± 0.6 mM, respectively, indicating a major influence of growth temperature on hexanol sensitivity. We found that 20 mM hexanol was acutely toxic to C. carboxidivorans P7 at 30 °C and growth was already completely inhibited in the presence of 15 mM hexanol at 37 °C. Membrane fatty acid analysis showed that the cell membrane composition of C. carboxidivorans adapted strongly to the higher growth temperature but surprisingly did not change significantly when grown in the presence of 10 mM hexanol. To avoid product toxicity during hexanol production we added oleyl alcohol as an extraction solvent. At 30 °C, addition of the solvent increased total hexanol titers nearly 2.5-fold from 10.5 to 23.9 mM. However hexanol titers decreased from 7.0 to 5.6 mM in the presence of oleyl alcohol at 37 °C. At 30 °C, the extraction phase contained large amounts of hexanol (448 ± 130 mM) and butanol (102 ± 20 mM). Values were lower at 37 °C with 101 ± 27 mM hexanol and 50 ± 6 mM butanol. Growth was not inhibited by oleyl alcohol. Biomass remained high in the presence of oleyl alcohol at 30 °C, but rapidly decreased in the absence of the solvent. At 37 °C biomass decreased even in the presence of oleyl alcohol. We tested corn oil and sunflower seed oil as potentially cheaper and more sustainable extraction solvents. While oleyl alcohol displayed the highest extraction efficiency for hexanol, total hexanol titers were similar with all solvents tested. ConclusionsBoth, product toxicity and growth temperature were identified as limiting factors during the conversion of syngas to hexanol by C. carboxidivorans P7. At 30 °C the addition of a biocompatible solvent led to detoxification and a significant increase in hexanol titers, 80% higher than highest previously reported titers. These findings help to mediate the limitation of product toxicity in hexanol production from syngas for the development of more efficient process designs and production strains.