Martine Poux

Powder mixing: some practical rules applied to agitated systems

Investigations into powder mixing in mixing vessels are surveyed, concentrating on practices used in different industries to distinguish this review from that given recently by Fan et al. [1]. The essential points to be examined for the treatment of solids mixing are reviewed and the definitions of the quality of a mixture, the mixing mechanisms, the possibilities for the choice of solid mixer, the experimental assessment of homogeneity and mixing indexes and the numerical simulation of mixing processes are reported.

Key role of temperature monitoring in interpretation of microwave effect on transesterification and esterification reactions for biodiesel production

Microwave effects have been quantified, comparing activation energies and pre-exponential factors to those obtained in a conventionally-heated reactor for biodiesel production from waste cooking oils via transesterification and esterification reactions. Several publications report an enhancement of biodiesel production using microwaves, however recent reviews highlight poor temperature measurements in microwave reactors give misleading reaction performances. Operating conditions have therefore been carefully chosen to investigate non-thermal microwave effects alone. Temperature is monitored by an optical fiber sensor, which is more accurate than infrared sensors. For the transesterification reaction, the activation energy is 37.1kJ/mol (20.1-54.2kJ/mol) in the microwave-heated reactor compared with 31.6kJ/mol (14.6-48.7kJ/mol) in the conventionally-heated reactor. For the esterification reaction, the activation energy is 45.4kJ/mol (31.8-58.9kJ/mol) for the microwave-heated reactor compared with 56.1kJ/mol (55.7-56.4kJ/mol) for conventionally-heated reactor. The results confirm the absence of non-thermal microwave effects for homogenous-catalyzed reactions.

Optical sensors for the characterization of powder mixtures

A double optical-fibre sensor useful for homogeneity measurements of powder mixtures is presented. An application of this methodology to powder mixing achieved in a fluidized bed is given as an example.

Intensification of waste cooking oil transformation by transesterification and esterification reactions in oscillatory baffled and microstructured reactors for biodiesel production

Abstract The transformation of waste cooking oils for fatty acid methyl ester production is investigated in two intensified technologies: microstructured Corning® and oscillatory baffled NiTech® reactors, compared to a reference batch reactor to quantify the process intensification provided by each technology. Both reactors achieve high conversions in shorter times. For transesterification, 96 wt.% of esters are obtained in 1.4 min at 97°C in the Corning® reactor and 92.1 wt.% of esters in 6 min at 44°C in the NiTech® reactor, compared with 94.8 wt.% of esters in 10 min at 60°C in the batch reactor. For esterification, 92% conversion is obtained in 2.5 min in the Corning® reactor at 75°C compared with 20–30 min in the batch reactor at 60°C, and at 40°C, 96.8% conversion is achieved in 13.3 min in the NiTech® reactor, compared with 30 min in the batch reactor. The advantage of the Corning® reactor is that it can operate at higher pressures (1–20 bar) and temperatures (100°C), thereby providing faster kinetics than the NiTech® reactor. However, oils with a high free fatty acid level (73%) cause the Corning® reactor channels to be blocked. A wider range of operating conditions could be obtained in NiTech® with a pressure-resistant material.

Measurement of the voidage in a ploughshare mixer by a capacitive sensor

In powder mixers with internal moving parts, as ploughshare mixer, the rapid rotation of the blades involves the movement of the powder, which is aerated as in a fluidised bed. A capacitance sensor is used to measure the local concentration of a catalyst powder, in a laboratory pilot plant of Lodige type mixer. The variation of local solid hold-up is measured by two couples of electrodes glued at the external surface of the trough, at two levels: in the upper third and lower third. This local solid hold-up is a function of the angular position of the blade. The hold-up in the upper part of the trough increases significantly with the loading of the mixer and with the rotation speed. The electrodes are also introduced into the trough and located here and there of a blade, in order to follow the mass of powder that is lifted by the blade.

Analyse du mélange de poudres en fluidisation gazeuse à l'aide de la méthode de défluidisation et par capteur à fibre optique

Abstract Two methods for the characterization of powder mixing (Geldarts group A type powder) carried out in a fluidized column are compared and used for the determination of the mixing mechanism. The first one, well known, consists in taking samples from the fluidized bed after defluidization, and then analyzing the composition of the mixture. The second one is based on the follow-up of colored particles by means of optical fiber sensors. With this methodology the local concentration and the mixing time can be calculated. The radial and axial concentration profiles have also been determined and the gross circulation patterns identified. It appears that, for the chosen configuration, the mixing is conditioned by the movement of bubbles which provoke a circulation current involving a rising solids flow in the central zone of the column and a solids downflow near the walls.