Mário Eusébio

Chiral separation by two-column, semi-continuous, open-loop simulated moving-bed chromatography.

A two-column version of a multicolumn, semi-continuous, open-loop chromatograph for chiral separation is presented and validated experimentally. The heart of the process is a flexible node design and cyclic flow-rate modulation that succeed at keeping the mass-transfer zone inside the system without resorting to any recycling technique. One advantage of this streamlined design is the simplicity of its physical realization: regardless of the number of columns, it only requires two pumps to supply feed and desorbent into the system, while the flow rates of liquid withdrawn from the system are controlled by material balance using simple two-way valves. A rigorous model-based optimization approach is employed in the optimal cycle design to generate a solution that is physically realizable in the experimental apparatus. The optimized scheme for two-column operation supplies fresh feed into the system where the composition of the circulating fluid is closest to that of the feedstock fluid, and recovers the purified products, extract and raffinate, alternately at the downstream end of the unit while desorbent is supplied into the upstream end of the system. The feasibility and effectiveness of the two-column process are verified experimentally on the separation of reboxetine racemate, a norepinephrine re-uptake inhibitor, under overloaded conditions. Our set-up employs an automated on-line enantiomeric analysis system, comprising an analytical HPLC set-up with two UV detectors to monitor the composition profile at the downstream end of one of the columns; this monitoring system does not use a polarimeter.

On‐line adaptive metabolic flux analysis: Application to PHB production by mixed microbial cultures

In this work, an algorithm for on‐line adaptive metabolic flux analysis (MFA) is proposed and applied to polyhydroxybutyrate (PHB) production by mixed microbial cultures (MMC). In this process, population dynamics constitutes an important source of perturbation to MFA calculations because some stoichiometric and energetic parameters of the underlying metabolic network are continuously changing over time. The proposed algorithm is based on the application of the observer‐based estimator (OBE) to the central MFA equation, whereby the role of the OBE is to force the accumulation of intracellular metabolites to converge to zero by adjusting the values of unknown network parameters. The algorithm was implemented in a reactor equipped with on‐line analyses of dissolved oxygen and carbon dioxide through respirometric and titrimetric measurements. The oxygen and carbon dioxide fluxes were measured directly, whereas acetate, PHB, and sludge production fluxes were estimated indirectly using a projection of latent structures model calibrated a priori with off‐line measurements. The algorithm was implemented in a way that the network parameters associated with biosynthesis were adjusted on‐line. The algorithm proofed to converge exponentially with the steady state error always below 1 mmol/L. The estimated fluxes passed the consistency index test for experimental error variances as low as 1%. The comparison of measured and estimated respiratory coefficient and of the theoretical and estimated yield of sludge on acetate further confirmed the metabolic consistency of the parameters that were estimated on‐line.

A Sensitive Method Approach for Chromatographic Analysis of Gas Streams in Separation Processes Based on Columns Packed with an Adsorbent Material

A sensitive method was developed and experimentally validated for the in-line analysis and quantification of gaseous feed and product streams of separation processes under research and development based on column chromatography. The analysis uses a specific mass spectrometry method coupled to engineering processes, such as Pressure Swing Adsorption (PSA) and Simulated Moving Bed (SMB), which are examples of popular continuous separation technologies that can be used in applications such as natural gas and biogas purifications or carbon dioxide sequestration. These processes employ column adsorption equilibria on adsorbent materials, thus requiring real-time gas stream composition quantification. For this assay, an internal standard is assumed and a single-point calibration is used in a simple mixture-specific algorithm. The accuracy of the method was found to be between 0.01% and 0.25% (-mol) for mixtures of CO2, CH4, and N2, tested as case-studies. This makes the method feasible for streams with quality control levels that can be used as a standard monitoring and analyzing procedure.

On-line monitoring and control of a biological denitrification process for drinking-water treatment

Abstract Online monitoring and control of the biological denitrification process in a cell recyle membrane reactor has been developed and implemented at laboratory scale. The system has been tested with a real groundwater contaminated with nitrate. It is shown that a simple feedforward control strategy that adjusts the feed rate of the carbon source to maintain the optimum inlet carbon/nitrate ratio value is effective at reducing both nitrate and nitrite concentrations in the treated water below the maximum admissible values.

ON-LINE METABOLIC FLUX ANALYSIS IN A PHB PRODUCTION PROCESS

Abstract A model-based algorithm is presented for the on-line monitoring of the oxidative phosphorylation efficiency and intracellular metabolic fluxes in mixed microbial cultures producing Polyhydroxybutyrate (PHB). The method assumes the knowledge of the metabolic reactions and the respective material and energetic balances. The on-line availability of dissolved O 2 , dissolved CO 2 , pH and off-gas concentrations of O 2 and CO2 provides a sufficient set of measurements for the estimation of the remaining fluxes. The estimator was evaluated with simulations.