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

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

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

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

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

The green catalytic processes special issue on the 6th International Congress on Green Process Engineering

This special issue of Catalysis Today entitledGreen CatalyticProcessescontains selected contributions in thefield of Catalysis andBiocatalysis that were presented at the6thInternational Congress onGreen Process Engineering(GPE 2018)

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

Stoichio-kinetic modeling and optimization of chemical synthesis: Application to the aldolic condensation of furfural on acetone

The condensation reaction of furfural (F) on acetone (Ac) gives a high added value product, the 4-(2-furyl)-3-buten-2-one (FAc), used as aroma in alcohol free drinks, ice, candies, gelatines and other products of current life. This synthesis valorises the residues of sugar cane treatment since furfural is obtained by hydrolysis of sugar cane bagasse followed by vapor training extraction. In the face of numerous and complex reactions involved in this synthesis, it is very complicated to define the kinetic laws from exact stoichiometry. A solution allowing to cope the problem consists in identifying an appropriate stoichiometric model. It does not attempt to represent exactly all the reaction mechanisms, but proposes a mathematical support to integrate available knowledge on the transformation. The aim of this work is the determination of stoichiometric and kinetic models of the condensation reaction of furfural on acetone. Concentrations of reagents and products are determined by gas and liquid chromatography. Concentration profiles obtained at different temperatures are used to identify kinetic parameters. The model is then used for the optimization of the production of FAc. The interest of such tool is also shown for the scale up of laboratory reactor to a large scale. The anticipation of the reaction behaviour in large scale is crucial especially when the reactor presents important limitations of thermal exchange capacity

Influence of solvent choice on the optimisation of a reaction–separation operation : application to a Beckmann rearrangement reaction

In pharmaceutical syntheses, the solvent choice generally represents a complex design step. Traditionally, this choice is operated according to criteria connected with the reaction step and without any consideration on the following separation steps. The purpose of this study is to highlight the benefits of a global approach of optimisation for the solvent determination. In this way, an optimisation framework dedicated to global synthesis is applied to a simple reaction–separation operation integrating a Beckmann rearrangement reaction, leading to interesting solvent choices