Electrochemical determination of ferrocene diffusion coefficient in liquid media under high CO2 pressure: Application to DMF–CO2 mixtures

Electrochemical method can be useful for the determination of diffusion coefficients in various media. For low polarity media, ultramicroelectrodes are preferably used. In this work, the electro-oxidation of ferrocene has been studied in dimethylformamide (DMF)–CO2 mixtures under various CO2 pressures, using a 100 lm diameter Pt microelectrode. Tetrabutylammonium perchlorate (TBAP) was chosen as the supporting electrolyte. Cyclic voltammetry was used in order to obtain values of diffusion coefficient of ferrocene, which were determined by using the Randles–Sevcik relation. This method proved to be convenient in such low polarity solvent. In addition, fluid phase equilibria of CO2–DMF mixtures were calculated and pressure–composition phases diagrams were established for the concerned binary mixtures, thanks to commercial Prophy PlusTM software (Prosim S.A., France). So, both liquid phase expansion, due to swelling by high-pressure CO2 and effective bulk concentration of ferrocene were estimated. Nevertheless, electrochemical measurements were problematic when high-pressure single phase conditions of CO2–DMF mixtures were reached

Clean synthesis of adipic acid from cyclohexene in microemulsions with stearyl dimethyl benzyl ammonium chloride as surfactant: From the laboratory to bench scale

Adipic acid, HOOC(CH2)4COOH, is a white crystalline solid used primarily in the manufacture of nylon-6,6 polyamide. In industry, adipic acid is mainly produced by oxidation of cyclohexane with air and nitric acidfollowing a homogeneous two-step route. However, this process leads to the formation of nitrous oxide, a greenhouse gas that has to be decomposed. The aim of this study was the development of a clean technology at pilot scale in order to obtain and recover pure adipic acid, and the evaluation of its industrial practicability. Adipic acid was synthesized from cyclohexene and hydrogen peroxide in microemulsions with stearyl dimethyl benzyl ammonium chloride as surfactant. The non-polluting catalyst sodium tungstate, which contains no heavy metal, was used and the reaction conducted under mild conditions (85 C, 8 h). Yields of up to 81% were reached at the 0.14 L scale. However at the end of the reaction the catalyst and the surfactant must be separated and recycled for subsequent cycles. The reuse of the reaction media enabled the conversion to be increased up to 92% but a loss of surfactant and/or catalyst through the cycles progressively reduced the yields. Yields at the bench scale (1.4 L) increased during the two first cycles and then decreased to conversions of between 60% and 70%. Globally the yield is a little lower at bench scale. The results obtained show that the synthesis of adipic acid by a heterogeneous one-step oxidation of cyclohexene in the presence of hydrogen peroxide is an attractive route for developing a future green industrial process

Green process for adipic acid synthesis: oxidation by hydrogen peroxide in water micromelusions using Benzalkonium Chloride C12-14 surfactant

Adipic acid was synthesized by the oxidation of cyclohexene using 30% hydrogen peroxide in a microemulsion in the presence of sodium tungstate as catalyst. The proposed green process is environmentally friendly since catalyst and surfactant are recycled and pure adipic acid is produced in high yield (70% to 79%). Microemulsions are used as a “green solvent” and give a better contact between the phases. Alkyldimethylbenzylammonium chloride (C12-C14) was used as a surfactant for the generation of the microemulsion since it enables the use of harmful organic solvents and phase-transfer catalysts to be avoided. Optimised operating conditions (temperature, reaction time, separation process) have been defined and applied to evaluate the industrial practicability. The main interest of the present work is the easy recovery of pure adipic acid and the reuse of the reaction media (surfactant and catalyst). This shows promise for developing a future green industrial process that will enable greenhouse gas emissions (N2O), among others, to be reduced

Electrocarboxylation in supercritical CO2 and CO2-expanded liquids

In this study, the electrocarboxylation of benzyl chloride in pressurized CO2, or pressurized mixtures of dimethylformamide (DMF) and CO2, was investigated in order to synthesize phenylacetic acid. A stainless steel cathode was used as the working electrode, whereas a sacrificial massive magnesium rod or a platinized platinum grid was used as the anode, tetrabutylammonium perchlorate (TBAP) or tetrakis(decyl)ammonium tetraphenylborate (TDATPhB) being the supporting electrolyte. The electrocarboxylation was carried out at 40 ◦C, at operating pressures of 1, 6, 7, 8, 9 and 12MPa, using current densities ranging from 0.1 to 150mAcm−2. It was found that a small amount of DMF was necessary to ensure the solubility of the supporting electrolyte, to obtain sufficient electrical conductivity of the medium. The best resultswere obtained using the magnesium sacrificial anode, at 6MPa. After consumption of the theoretical amount of electrical current (2F mol−1), 65.7% benzyl chloride conversion was reached, together with an 82.4% phenylacetic acid selectivity and a 54.2% faradaic yield. Detected by-productswere toluene, bibenzyle, benzyl alcohol and benzaldehyde

Cleaner Routes for Friedel-Crafts Acylation

Friedel-Crafts acylation is among the most fundamental and useful reactions to yield aromatic ketones but it is one of the less acceptable in terms of unwanted polluting by-products or atom economy because of the overconsumption of catalyst which is used in stoichiometric quantities in the conventional process. This route is nevertheless widely used in the fine chemical industry.In recent years, awareness of the impact of industrial activities on the environment has led chemists to work on new chemical routes, less dangerous and more environmentally friendly.We considered here the acylation of a benzofurane derivative by an acyl chloride, as an intermediary step for a pharmaceutical product. In this study, one of the first alternatives was to replace conventional catalysts (FeCl3 or AlCl3), by reusable solid catalysts. Indeed, a wide variety of new solid catalysts, more efficient and less polluting, has now emerged (zeolites, ion-exchange resins…). In this work, these catalysts were first tested in “conventional” conditions, i.e., using an organic solvent (1,2-dichlorobenzene in our case), to determine the best one, in terms of reactivity, lifetime and reusability. The zeolite Y was found the most appropriate.However, the use of an organic solvent still remains questionable and the use of supercritical carbon dioxide as the solvent was also considered. Its inherent properties include non-flammability, mild critical conditions, tuneable solubility near to the critical point and very low environmental impact. The reaction was operated using a continuous high pressure fixed bed. Results concerning yield and selectivity are presented

Direct numerical simulations of mass transfer in square microchannels for liquid-liquid slug flow

Microreactors for the development of liquid-liquid processes are promising technologies since they are supposed to offer an enhancement of mass transfer compared to conventional devices due to the increase of the surface/volume ratio. But impact of the laminar flow should be negative and the effect is still to be evaluated. The present work focuses on the study of mass transfer in microchannels by means of 2D direct numerical simulations. We investigated liquid-liquid slug flow systems in square channel of 50 to 960 μm depth. The droplets velocity ranges from 0.0015 to 0.25 m/s and the ratio between the channel depth and the droplets length varies between 0.4 and 11.2. Droplet side volumetric mass transfer coefficients were identified from concentration field computations and the evolution of these coefficients as a function of the flow parameters and the channel size is discussed. This study reveals that mass transfer is strongly influenced by the flow structure inside the droplet. Moreover, it shows that the confinement of the droplets due to the channel size leads to an enhancement of mass transfer compared to cases where the droplets are not constrained by the walls

Flow rate--pressure drop relation for deformable shallow microfluidic channels

Laminar flow in devices fabricated from soft materials causes deformation of the passage geometry, which affects the flow rate--pressure drop relation. For a given pressure drop, in channels with narrow rectangular cross-section, the flow rate varies as the cube of the channel height, so deformation can produce significant quantitative effects, including nonlinear dependence on the pressure drop [{Gervais, T., El-Ali, J., G\"unther, A. \& Jensen, K.\ F.}\ 2006 Flow-induced deformation of shallow microfluidic channels.\ \textit{Lab Chip} \textbf{6}, 500--507]. Gervais et. al. proposed a successful model of the deformation-induced change in the flow rate by heuristically coupling a Hookean elastic response with the lubrication approximation for Stokes flow. However, their model contains a fitting parameter that must be found for each channel shape by performing an experiment. We present a perturbation approach for the flow rate--pressure drop relation in a shallow deformable microchannel using the theory of isotropic quasi-static plate bending and the Stokes equations under a lubrication approximation (specifically, the ratio of the channel's height to its width and of the channel's height to its length are both assumed small). Our result contains no free parameters and confirms Gervais et. al.'s observation that the flow rate is a quartic polynomial of the pressure drop. The derived flow rate--pressure drop relation compares favorably with experimental measurements.Comment: 20 pages, 6 figures; v2 minor revisions, accepted for publication in the Journal of Fluid Mechanic

Optimisation of operating conditions in batch for more sustainable continuous process transposition

Implementation of exothermic and fast reactions requires a perfect temperature control to avoid thermal runaway and in most cases to limit by-products production. In order to fit with the heat removal capacity of common devices, expensive strategies are currently used to slow down this kind of reactions in order to avoid a strong temperature increase such as reactants dilution. Within the concept of process intensification, industries could move towards more sustainable process by reducing technology constraints to the benefit of chemistry. For that purpose, a two-step methodology is implemented. The first step consists in the optimisation of the operating conditions only based on stoichio-chemical scheme and kinetic laws. This is carried out by adjusting temperature profile and feeding rate strategy in a batch operation. Then a design for a continuous process is proposed, trying to approach the optimal batch operating conditions. This methodology is applied to the linear alkylbenzene sulfonation

Giant Quantum Reflection of Neon Atoms from a Ridged Silicon Surface

The specular reflectivity of slow, metastable neon atoms from a silicon surface was found to increase markedly when the flat surface was replaced by a grating structure with parallel narrow ridges. For a surface with ridges that have a sufficiently narrow top, the reflectivity was found to increase more than two orders of magnitude at the incident angle of 10 mRad from the surface. The slope of the reflectivity vs the incident angle near zero was found to be nearly an order of magnitude smaller than that of a flat surface. A grating with 6.5% efficiency for the first-order diffraction was fabricated by using the ridged surface structure.Comment: 5 pages, 4 figures. To be published in J. Phys. Soc. Jp