Volume 3, Issue 5 - Special issue: 4th International Congress on Green Process Engineering (GPE 2014), Part 1 / Issue editor: Martine Poux

Possible drawbacks of microreactors are inefficient reactant mixing and the clogging of microchannels when solid-forming reactions are carried out or solid (catalysts) suspensions are used. Ultrasonic irradiation has been successfully implemented for solving these problems in microreactor configurations ranging from capillaries immersed in ultrasonic baths to devices with miniaturized piezoelectric transducers. Moving forward in process intensification and sustainable development, the acoustic energy implementation requires a strategy to optimize the microreactor from an ultrasound viewpoint during its design. In this work, we present a simple analytical model that can be used as a guide to achieving a proper acoustic design of stacked microreactors. An example of this methodology was demonstrated through finite element analysis and it was compared with an experimental study found in the literature.

A case study of the green metrics analysis of several processes is described. The considered system is the simultaneous etherification of isobutene and isoamylenes with ethanol over Amberlyst™ 35. Experimental results are compared under the green metrics methodology with those for the isolated ethyl tert -butyl ether and tert -amyl ethyl ether syntheses previously reported over acid ion-exchange resins using different reaction batch devices and different synthesis pathways, such as the production of both ethers from tertiary alcohols and from ethanol. The best results, from an environmental point of view, were obtained for ether syntheses from olefins and ethanol in terms of the parameters measured in the green metrics analysis. A process allowing the separation of ethers from the product stream and the reactants recirculation has been proposed and simulated. The suggested process depicts a suitable alternative for the simultaneous production of tertiary ethers from pure olefin feed and their downstream implementation as greener fuel additives with environmental benefits.

We show the potential of miniemulsion photopolymerization for the continuous production of aqueous poly(acrylate) dispersions in a microreactor at room temperature. While the starting acrylate nanoemulsions are amenable to limit scattering, their polymerization within a microreactor provides additionally small microchannels and short diffusion path enabling an efficient mixing in order to alleviate the constraints associated with non-uniform through-cure in turbid medium. Two key features prove that this process design is highly eco-efficient: i) two types of energy-saving and compact UV sources (fluorescent or light-emitting diode) were employed; ii) high conversions were achieved using the fluorescent lamp with short residence times (10 min), low irradiance (3 mW cm -2 ) and without the need of solvent. The present study describes briefly the influence of various parameters – flow rate, photo-initiator type/concentration, droplet size, solid content, UV source – on the photopolymerization course (kinetics) and the properties of the nanolatex obtained (particle size and molecular weight).

A reactor setup consisting of two stainless steel microreactors [gas-phase microreactor (GPMR)-mix from the Institut für Mikrotechnik Mainz (IMM)] coupled in series was used for production of methyl chloride by hydrochlorination of methanol. The catalyst was γ-alumina on microreactor platelets. The influence of temperature on the methanol conversion and methyl chloride selectivity was investigated. A maximum conversion of 97.6% and a selectivity of 98.8% were reached at 340°C, which is close to the calculated thermodynamic equilibrium. Comparison with results obtained from a single microreactor and the modified setup of two microreactors revealed that the serial coupling resulted in a dead volume with a blind activity, which cannot be neglected when describing the setup. Furthermore, the separation of methyl chloride using condensers was investigated. The proposed microreactor-condenser concept enables the production of methyl chloride with a high purity.

A two-step sustainable process for the enzymatic saccharification of lignocellulosic materials (e.g., crystalline cellulose, paper and corn cob) was evaluated. In the first step, pretreatment of crystalline cellulose, paper and lignocellulose by the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride, [Bmim][Cl], was carried out to obtain an amorphous substrate. This step included the recovery of the IL for further reuse. Then, the amorphous cellulosic materials were hydrolyzed by different industrial enzyme preparations. The pretreatment of cellulose, paper and lignocellulose (corn cob) with [Bmim][Cl] led to an up to 2.5-fold increase in the yield of the enzymatic hydrolysis, compared to the same substrate without pretreatment; this produced nearly 100% hydrolysis. The combined action of Celluclast 1.5L (cellulase from Trichoderma reesei ) and Novozyme 188 (cellobiase from Aspergillus niger ) was essential in the process of enzymatic saccharification of corn cob. By combining the enzyme complex Ultraflo L (β-endoglucanase from Humicola insolens mixed with arabanase and xylanase enzymes) with Celluclast 1.5L and Novozyme 188, the soluble sugar concentration was increased 1.5-fold, resulting in the best choice for enzymatic saccharification of lignocellulosic materials. The effectiveness of lignocellulose pretreatment with [Bmim][Cl] for improving enzymatic saccharification yield was also confirmed.

The objectives were to study the potential of Azolla pinnata whole plant in green synthesis of nanoparticles (NPs), and the effect of the extract ethanol concentration on the produced NPs. A. pinnata whole plants were freshly collected, air dried at room temperature, powdered and sieved. Hydroalcoholic extracts (70% and 96%) were prepared by percolation of the plant powder. The reaction mixtures contained (final concentrations): AgNO 3 (1 m m ) as the substrate, plant extract as the biocatalyst and phosphate buffer (pH=7, 100 m m ) as the reaction medium. The aforementioned ingredients were added in appropriate volumes into Duran bottles and were incubated at room temperature. Silver ions were determined using atomic absorption analysis. Samples for transmission electron microscopy (TEM) were prepared by drop-coating the silver NP suspensions onto carbon-coated copper grids. Particle size distribution of NPs was analyzed using Nano-Zeta Sizer. Hydroalcoholic extract (96%) of A. pinnata successfully produced quite small (as small as 0.93 nm and a mean size of 6.5 nm), spherical, and polydispersed silver NPs with low aggregates in the early hours of the biotransformation. The conversion was fast and complete in 5 h. Therefore, this plant and extraction method seems to be attractive for industrial scale production of NPs.