José R. Álvarez

A population balance approach for the description of particle size distribution in suspension polymerization reactors

Abstract There exist modelling and experimental methodologies to meet productivity (conversion and batch time) and product molecular weight distribution (MWD) quality specifications in suspension polymerization reactors. However, no counterpart exists to address the issue of particle size distribution (PSD), which is of fundamental importance in determining suspension stability and product quality attributes. In industrial practice, PSD considerations are guided by mean-size correlations from the Weber number theory. The setting up of an industrial reactor usually demands considerable scaling and testing efforts. In this work, we obtain a model to describe the evolution of the PSD in a suspension polymerization reactor. First, relevant phenomena are identified and modelled individually: suspension MWD, suspension viscoelasticity, interfacial tension, injection—dissipation of mechanical energy and drop breakage—coalescence mechanism. A central point is the derivation of analytic expressions for breakage and coalescence rate distributions. A drop population balance leads to an integrodifferential equation whose numerical solution yields the evolution of the PSD. Breakage—coalescence parameters are estimated from the reported experimental data. Modelling identifies the role of individual phenomena and their interplay.

Simulation of integrated extraction and stripping processes using membrane contactors

A mathematical model has been developed to simulate the performance of an integrated extraction-stripping process based on the use of hollow fiber contactors. The model allows one to predict the time-dependent concentration profiles of the two phases involved in an individual extraction or stripping process, or of the three phases involved in an integrated extraction-stripping process (two aqueous phases — feed and stripping — and one organic phase). The model includes as parameters operating conditions such as the initial concentrations, volumes and flowrates, distribution coefficients and overall mass transfer coefficients.

Industrial Applications of Porous Ceramic Membranes (Pressure‐Driven Processes)

Publisher Summary This chapter discusses the industrial applications of porous ceramics membranes. Pressure-driven membrane processes are among the most mature membrane technologies. They are used for liquid separations and are generally classified into four categories: reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), andmicrofiltration (MF). Pressure-driven membrane processes at present have high industrial impact, with a market constantly growing. They are used in a wide range of separation processes and are considered among the best available technologies (BAT), in the European Union environmental recommendations because they present several advantages with respect to other separation processes. The main applications of RO are found in the desalination of brackish and seawater; the production of ultrapure water (electronic industry); concentration of food juice, sugars, and milk; and in the treatment of wastewater. The performance of the ceramic membrane-based systems depends on the separation and permeation properties of the membrane as well as its mechanical integrity. These properties depend on the selective top layer and on the support system on which the active separation layer is coated. Therefore, pore size, porosity, surface roughness, and mechanical properties—all are important parameters.

MOLECULAR GENETICS OF ICL2, ENCODING A NON-FUNCTIONAL ISOCITRATE LYASE IN SACCHAROMYCES CEREVISIAE

In this work, we identified an open reading frame 5′ to the yeast HALI gene, that shares a 38% identity in the deduced amino acid sequence with gluconeogenic enzyme isocitrate lyase, encoded by ICL1. We therefore termed the new gene ICL2. The latter is not capable of complementing an icl1 deletion for growth on ethanol neither in its original context, nor when expressed under the control of the glycolytic PFK2 promoter. Nevertheless, fusions of the 5′‐non‐coding region of ICL2 to the lacZ reporter gene revealed that the gene is transcribed and that the transcriptional regulation is similar to that of other gluconeogenic genes, i.e. high‐level expression on ethanol that is drastically reduced on glucose media. Therefore, we attribute the lack of complementation to a lack of function of the encoded protein as an isocitrate lyase. The deduced amino acid sequences of Icl1 and Icl2 differ in a conserved motif used to identify isocitrate lyases, the hexapeptide KKCGHM, where the second lysine residue of Icl1 is replaced by an arginine in Icl2. However, we here demonstrated by in vitro mutagenesis of ICL1 that such an exchange, even though it affects Icl activity to some degree, does not lead to a complete lack of function. Thus, the results presented in this work argue for ICL2 encoding a non‐functional isocitrate lyase and provide evidence that lysine 216 of Icl1 is not essential for catalysis. This sequence is deposited as accession number Z48951 entered on4 April 1995 by Barrel et al.

Microfiltration of kraft black liquors for the removal of colloidal suspended matter (pitch)

Abstract The use of microfiltration to eliminate colloidal suspended matter (pitch) from different streams in the pulp production process can lead to the increase of pulp quality as well as the reduction of some problems associated to the accumulation of such matter in the process. Previous studies [1] have aimed at the treatment of white waters and diluted black liquors, the results being successful though a large volume would need to be treated. An alternative could be the direct treatment of more concentrated kraft black liquors (KBL). However, permeation fluxes with this liquor are often too low for a feasible industrial application [2]. In this work the microfiltration of KBL (14–15% solids) has been carried out using a ceramic membrane (0.2 μm). Experiments were carried out on site at around 90°C and at relatively high feed velocities (up to 9 m/s). The introduction of a simple backflushing device (pulses of 15 s every 15 min) allowed to keep a stable flux over 200 L/m 2 h, while without the backflushing a continuous decay in flux was observed. The selectivity of the membrane was above 99.9%.

RECOVERY OF VALERIC ACID FROM AQUEOUS SOLUTIONS BY SOLVENT EXTRACTION

ABSTRACT The recovery of valeric acid from aqueous solutions using several extractants dissolved in different diluents was studied. Commercial extractants Amberlite LA-2 and tributyl phosphate gave the best distribution coefficients. The extraction of valeric acid with Amberlite LA-2 dissolved in toluene was investigated in more detail. The influence of agitation time, agitation rate, extractant concentration and temperature on the equilibrium distribution are reported. Modeling of physical extraction with toluene and reactive extraction with Amberlite LA-2 was carried out using a proposed equilibrium mechanism. The distribution of the valeric acid between water and toluene is regarded as physical extraction taking into account the partial dissociation of the acid in the aqueous phase and its dimerization in the organic phase. The equilibrium behavior with the Amberlite LA-2 is modeled by postulating the formation of various stoichiometric complexes of acid and amine, based on an acid-base-type reaction. ...

Hexavalent chromium removal from chromium plating rinsing water with membrane technology

The objective of this work is to assess the water reuse potential of aqueous streams from a metal finishing industry containing chromium using nanofiltration (NF) and reverse osmosis (RO). Process waters with hexavalent chromium were treated with NF (NF90 and MPS-34) and RO (BW30) membranes. The efficiency in terms of metal removal was very high. The NF90 membrane showed the best performance (highest flux and excellent selectivity, typically above 99%). An ultrafiltration pretreatment was required to remove the solid particles present in the process waters. NF makes possible to recycle the pure water (permeate) into the process whilst the retentate may be subjected to precipitation to recover the metal for reuse or further treatment.