Marco Aurélio Cremasco

Parameters estimation for amino acids adsorption in a fixed bed by moment analysis

Equilibrium constant and mass transfer parameters are needed for the study of amino acid separation in any process involving adsorption in fixed beds. The adsorption constants, effective diffusion coefficients, and axial dispersion coefficients for two amino acids, L-phenylalanine (Phe) and L-tyrosine (Tyr), are determined from a series of pulse tests in a fixed bed packed with PVP (poly-4-vinylpyridine) resin. Total bed voidage at different flow rates is estimated from NaCl pulse test data. The effective pore diffusivities of Phe, Tyr, and NaCl are estimated from moment analysis of pulse data. A detailed rate model is then solved numerically and adsorption constants, effective diffusion coefficients, axial dispersion coefficients are determined by moment analysis and compared with the pulse data. The advantage of this method is that the effective intraparticle diffusivities can be determined without the influence of extracolumn dispersion or intracolumn axial dispersion effects.

Experimental purification of paclitaxel from a complex mixture of taxanes using a simulated moving bed

A laboratory-scale simulated moving bed (SMB) was designed and tested for the separation of paclitaxel, a powerful anti-cancer agent known as Taxol@, from impurities of a plant tissue culture (PTC) broth. The innovative strategy of a pseudo-binary model, where mixtures A and B were treated as single solutes A and B, was used in the linear standing wave analysis to fix the SMB operating parameters for a multicomponent and complex system. Linear standing wave design was used to specify the zone flow rates and the switching time for the laboratory-scale SMB unit, with two steps of separation. The SMB consists of four packed columns, where each column is 12.5 cm in length and 1.5 cm in diameter. Two sequential separation steps were used to recover paclitaxel from a small feed batch (less than one liter). Placlitaxel was recovered from the complex plant tissue culture broth in 82% yield and 72% purity.

Experimental Study in a Short Circulating Fluidized Bed Riser

Experiments were performed with gas and solids flow in a 2.42 m high circulating fluidized bed (CFB). This equipment has both solids and gas fed into the downer section. Local solids holdup was measured using an optical fiber probe. By the axial solids concentration distribution, it was verified that (1) the curve that precedes the entrance into the riser provides further acceleration to the flow and (2) the abrupt exit causes an increase in solids concentration in the top zone. Results of radial distributions in the bottom zone show that the flow is more concentrated near the wall. For the exit zone, the distributions show high values of solids holdup both near the wall and on the axis.

Adsorption of aromatic amino acids in a fixed bed column

Phenylalanine (Phe) and tyrosine (Tyr) are two of the twenty amino acids in proteins; they are classified as aromatic amino acids, because both have a benzene ring in their structures. These amino acids are important in the synthesis of several biologically active amines, such as b-endorphin, a neurotransmitter. Amino acids can be separated by ion-exchange chromatography. In this case, it is important that fixed-bed adsorber design adequately predict the breakthrough curve. This work presents a mathematical model for both fluid and porous phases. In the solution proposed for this model the liquid-phase concentration inside the particles is solved analytically and is related to the liquid-phase concentration in the bed using Duhamels theorem. The solution for liquid-phase concentration in the bed is then solved numerically instead of analytically. The basic mass transfer parameters are from the literature. The results from the model are compared with those obtained experimentally using Phe and Tyr diluted in aqueous solutions in a fixed bed of PVP (poly-4-vinylpyridine) resin.

Experimental Fluid Dynamics Study in a Fluidized Bed by Deterministic Chaos Analysis

Differential pressure fluctuations in gas-solid fluidized beds were analyzed by chaos analysis (construction of attractors, correlation dimension, Kolmogorov entropy) and mutual information. Experimental fluidization tests of three different particles were conducted. Two of them are from Geldart group B and one from Geldart group D. The fluidization experiments were performed in a cylindrical bed with 0.07 m i.d. and 1.0 m high. Pressure fluctuations were measured by three pressure transducers, and their signal time series were analyzed in the time domain (mean and standard deviation) and in the frequency domain (power spectra) for comparison and complementation of chaos analysis. Analyses in the time domain allowed a good estimation for determining whether or not the system is fluidized. The Fourier spectra provided more detailed information that could identify other phenomena such as the presence of bubbles. The chaos tools produced sensitive results, offering a qualitative and quantitative analysis for identification of the phenomena that occur in fluidization. Three different fluidization regimes could be indentified: multiple bubble bed, slugging bed, and exploding bubble bed.

A design and study of the effects of selectivity on binary separation in a four-zone simulated moving bed for systems with linear isotherms

The simulated moving bed (SMB) is potentially an economical method for the separation and purification of natural products because it is a continuous processes and can achieve higher productivity, higher product recovery, and higher purity than batch chromatographic processes. Despite the advantages of SMB, one of the challenges is to specify its zone flow rates and switching time. In this case it is possible to use the standing wave analysis. In this method, in a binary system, when certain concentration waves are confined to specific zones, high product purity and yield can be assured. Appropriate zone flow rates, zone lengths and step time are chosen to achieve standing waves. In this study the effects of selectivity on yield, throughput, solvent consumption, port switching time, and product purity for a binary system are analyzed. The results show that for a given selectivity the maximum throughput decreases with increasing yield, while solvent consumption and port switching time increase with increasing yield. To achieve the same purity and yield, a system with higher selectivity has a higher throughput and lower solvent consumption.

Experimental determination of benzene uptake rate in Tenax TA diffusive samplers

This paper proposes a methodology to predict benzene uptake rate in ambient air, using passive samplers with Tenax TA. Variations in the uptake rate were found to occur as a function of the sampling time; and were greater at the beginning of sampling. An empirical model was obtained and values for uptake rate agree with literature. Concentration prediction errors can be minimized by using sampling times of 4 to 14 days, thus avoiding the influence of excessive uptake rates in the initial days and the influence of back diffusion at the end of the sampling period.

Isomerização do óleo essencial de pimenta-longa (Piper hispidinervium C. DC) para a obtenção de isosafrol

The Brazilian peppers present proprieties that can be used in fragrance and pharmaceutical industries, for example. One these pepper is long pepper (Piper hispidinervium C. DC.), who its essential oil is rich in safrole. Safrole is an important compound with application in several industries, such as pharmaceutics, cosmetics. After its chemical conversion, for example, it is possible to obtain heliotropin, a fixative agent for fragrances. The sequence to obtain the heliotropin is by safrole isomerization, that, initially, produce isosafrole. In this work, however, presents the synthesis of isosafrole directly from essential oil of Piper hispidinervium C. DC. In this case, the isomerization of essential oil was done getting 79,4 % of cis, trans-isosafrole mixture. The essential oil presented 86,4 % of safrole, resulting in 97,1 % yield to cis, trans-isosafrole.

Separation of l-tryptophan present in an aromatic amino acids mixture in a four-column simulated moving bed: experimental and simulation studies

An experimental and theoretical study is presented for the fractionation of L-Tryptophan (Trp) from L-phenylalanine (Phe) and L-tyrosine (Tyr). A Simulated-Moving Bed (SMB) with four-column system was tested, and the results are presented as effluent histories of the raffinate and extract ports. L-phenylalanine and L-tyrosine were recovered as major products in the raffinate, while L-Tryptophan was recovered at the extract. To simulate the L-Tryptophan separation, a general rate model was used to represent the mass transfer phenomena that occur in each individual column of the SMB, for each solute present in the multicomponent system. A hybrid method was used to solve the model. An analytic solution was used for the intra-particle concentration, and was correlated to the liquid bed concentration by Duhamels theorem. The results from simulation are compared with the experimental data presented in this work.

Síntese do piperonal a partir do óleo essencial de pimenta longa (Piper hispidinervium C. DC.)

The essential oil of long-pepper (Piper hispidinervum C. DC) is rich in safrole, then susceptible to isomerization reaction to obtain cis, trans-isosafrole. In this paper it is presented the eletroxidation of cis, trans-isosafrole from direct isomerization of essential oil of long-pepper, with 99,7% of convertion to isosafrole glicol, that it is react by oxidation to convert 99% into piperonal with 84,9% purity.