Diana C.S. Azevedo

Design methodology and operation of a simulated moving bed reactor for the inversion of sucrose and glucose–fructose separation

Abstract This work presents a detailed mathematical model and design methodology for a simulated moving bed reactor (SMBR) intended to invert sucrose by enzymatic action and simultaneously separate the products glucose and fructose. Experimental results for the operation of a SMBR are shown and very good agreement with simulated results was obtained. The design/optimisation package is based on an algorithm, previously developed for non-reactive SMB, used to define both the geometric parameters (column length and diameter), enzyme concentration and operating conditions of a simulated moving bed reactor. In this strategy, a detailed model is used instead of a simple equilibrium stage model. The objective of the strategy is to calculate minimum column lengths and enzyme concentrations for given feed flowrates, constrained by a reaction conversion not Sections 1 and 4 . This way, the effects of the safety margin applied to γ 1 and γ 4 have been investigated on the reaction conversion and separation performance. The results have been compared with predictions from the equilibrium theory for a non-reactive system and the observed deviations have been evidenced and discussed.

Adsorption of Carbon Dioxide onto Activated Carbon and Nitrogen-Enriched Activated Carbon: Surface Changes, Equilibrium, and Modeling of Fixed-Bed Adsorption

It has been reported that the CO2 adsorption capacity of the N-enriched activated carbon can increase or decrease. In this study a commercial activated carbon was functionalized with 3-chloropropylamine hydrochloride and its adsorption characteristics in a fixed-bed column were investigated. The N-enriched activated carbon presented lower BET surface area than the original activated carbon suggesting that the nitrogen incorporation partially blocks the access of N2 to the small pores. Although the surface basicity has increased it is not accomplished by an increase of the capacity of the adsorption of the N-enriched activated carbon. The breakthrough curves in a fixed bed column were obtained at different temperatures (301 K, 323 K, 373 K, and 423 K) and a total pressure of 1.01 bar using CO2 diluted in helium at two feed concentrations—10% and 20% (v/v). A model based on the Linear Driving Force (LDF) model for mass transfer was used to estimate the overall mass transfer coefficient and reproduced the breakthrough curves satisfactorily.

Obtainment of High-Fructose Solutions from Cashew (Anacardium occidentale) Apple Juice by Simulated Moving-Bed Chromatography

The simulated moving-bed (SMB) technology has been successfully used in separations in the petrochemical, food, and fine chemicals industries. This work is intended to demonstrate the possibility of using this technology to obtain high-fructose solutions from the cashew apple juice, which may represent an attractive economic alternative for its industrial exploitation. The cashew tree is a native tropical plant abundant in Northeastern Brazil, the commercial value of which relies mainly on the processing of its nut. Despite the high nutritional value of the penduncle of the fruit, the cashew apple, approximately 90% of the crop spoils on the soil. Simulation and experimental results are presented for SMB separation of fructose from glucose, both present (˜40 kg/m3) in the aqueous phase of concentrated cashew apple juice. Kinetic and equilibrium data for fructose and glucose on packed columns using cation-exchange resins are reported. Experimental results for SMB operation at 30°C indicate purities close to 90% in each product (fructose-rich extract and glucose-rich raffinate). Simulated predictions of the unit performance and internal profiles agree well with experimental data. To increase the added value and versatility of the products, either an isomerization step for the raffinate or diverse SMB fluid–solid flow rate ratios may be applied. In this way, a wide range of products may be obtained, from nearly pure fructose to 42, 55, and 90% solutions, which are the standard high-fructose syrup concentrations. If solids content is conveniently raised to the standards of commercial high-fructose syrups, these products may be used as food additives, thus confirming a potentially attractive use of the cashew apple juice.

Studies on the adsorption behavior of CO2-CH4 mixtures using activated carbon

Separation of CO2 from CO2-CH4 mixtures is an important issue in natural gas and biogas purification. The design of such separation processes depends on the knowledge of the behavior of multicomponent adsorption, particularly that of CO2-CH4 mixtures. In this study, we present a series of experimental binary equilibrium isotherms for CO2-CH4 mixtures on an activated carbon at 293 K and compare them with predicted values using the Ideal Adsorption Solution Theory (IAST) and the Extended Langmuir (EL) model. Even at concentrations of ca. 20% for all binary isotherms, CO2 already presents higher adsorbed amounts with respect to CH4. A maximum selectivity of around 8.7 was observed for a nearly equimolar mixture at 0.1 MPa. The IAST in conjunction with the Toth equation showed slightly better results than IAST using the Langmuir equation and both showed better results than the EL model.

Separation of Fructose and Glucose from Cashew Apple Juice by SMB Chromatography

Abstract The simulated moving bed (SMB) technology has been applied to a number of carbohydrate separations. The cashew apple is the pseudo‐fruit of the cashew tree; it contains approximately equal amounts of fructose and glucose and is presently an agricultural waste largely found in Northeastern Brazil. This work shows experimental results for the separation of fructose from glucose, found in cashew apple juice, using a conventional four‐section SMB. The two sugars were successfully separated with product purities around 90%. The operating conditions were chosen from the equilibrium theory applied to a multicomponent system with linear uncoupled isotherms. The performance at cyclic steady state was well predicted with both TMB‐ (true moving bed) and SMB‐based models. However, during startup, there was a buildup of sugar concentration in the unit, which was not observed for synthetic mixtures. Fixed‐bed adsorption and desorption runs were performed with dilute cashew apple juice. They provided experimental evidence that high molecular weight molecules might have been adsorbed onto the resin, which could be a probable explanation for the anomalous behavior previously observed. Clarified cashew apple juice (free of tannins) was also used as the SMB feed and no anomalous transient behavior was observed. On the contrary, process performance perfectly matched that obtained from simulation assuming a synthetic glucose‐fructose mixture. The results presented herein are the first record of sugar separation in SMB from cashew apple juice and should provide scientific support for economic alternatives to the industrial processing of the cashew crop.

Enantiomers separation by simulated moving bed chromatography. Non-instantaneous equilibrium at the solid-fluid interface

The simulated moving bed (SMB) technology, first conceived for large bulk-scale separations in the petrochemical industry, has found increasingly new applications in the pharmaceutical industry. Among these, the separation of fine chemicals has been the subject of considerable study and research. This work presents the modeling, simulation and design of the operation of a SMB plant in order to separate a binary chiral mixture. The usual assumption of instantaneous equilibrium at the solid-fluid interface is questioned and a first-order kinetics of adsorption is taken into account. The cases of linear, Langmuir and modified Langmuir equilibria are studied. The equivalent true moving bed (TMB) model was used assuming axial dispersion for the fluid flow and plug flow for the solid-phase flow. Intraparticle diffusion was described by a linear driving force (LDF) approximation. Simulation results indicate that, under certain conditions, equilibrium is not actually reached at the adsorbent surface. This leads to different unit performances, in terms of product purities and recoveries, as compared to those predicted assuming instantaneous equilibrium. Moreover, SMB units may be improperly designed by the usual methods (flow-rate ratio separation regions) if non-equilibrium effects are overlooked.

Adsorption Equilibria of Natural Gas Components on Activated Carbon: Pure and Mixed Gas Isotherms

A typical Natural Gas (NG) composition in South America contains ca. 86% methane, 10% ethane, 1.5% carbon dioxide, 1% nitrogen and other heavier hydrocarbons. The composition plays an important role in studies of NG storage systems since heavier alkanes may accumulate in the adsorbent bed, saturate it in long-term use and affect the storage capacity. In this study, measurements of experimental data for the adsorption equilibria of binary mixtures of CH4 with C2H6, CO2, C3H8 and N2 — as obtained in a volumetric/chromatographic set-up — are presented and compared with mathematical models for multi-component adsorption based on pure component adsorption data. Experimental results were compared with predictions from the Extended Langmuir (EL) model and the Ideal Adsorbed Solution Theory (IAST) model. The IAST model was capable of providing a more accurate fit to most of the obtained data, other than those measured for the least adsorbed gases (CH4/N2).

Dextran and fructose separation on an SMB continuous chromatographic unit

A dextran/fructose mixture was obtained by fermentation of a sucrose rich media using Leuconostoc mesenteroides NRRL B512(f). The dextran and fructose mixture obtained by fermentation as well as a synthetic mixture of pure components were separated using simulated moving bed (SMB) chromatography. In the case of the synthetic feed, the purity in the raffinate (dextran) and extract (fructose) was 96 and 81%, respectively. For the fermented mixture the purity values were 87.2% for the extract and 100% for the raffinate.

Sorption and Diffusion of p-Xylene and o-Xylene in Aluminophosphate Molecular Sieve AlPO4-11

This paper presents experimental results for equilibrium and diffusion of C8 aromatics in laboratory synthesised crystals of AlPO4-11. The samples were prepared by the hydrothermal method, starting from pseudobohemite (CONDEA), 85% phosphoric acid, water and di-isopropilamine as organic template. Adsorption and diffusion data were obtained mainly by gravimetry at temperatures between 60–100°C. Saturation capacities were found in the range of 4 wt%. Equilibrium constants were estimated using virial plots yielding heats of adsorption between 10–12 Kcal/mol at low coverage. Intracrystalline diffusivities at higher temperatures (150–180°C) were also measured, using the Zero-Length-Column (ZLC) method. Diffusivities from both methods (gravimetric and ZLC) agreed reasonably well and followed a typical Arrhenius behaviour, with low activation energy (ca. 7 Kcal/mol).

“Low Cost” Pore Expanded SBA-15 Functionalized with Amine Groups Applied to CO2 Adsorption

The CO2 adsorption capacity of different functionalized mesoporous silicas of the SBA-15 type was investigated and the influence of textural properties and the effect of the silicon source on the CO2 uptake studied. Several adsorbents based on SBA-15 were synthesized using sodium silicate as silicon source, replacing the commonly used tetraethyl orthosilicate (TEOS). Thus, we synthesized three couples of supports, two at room temperature (RT, RT-F), two hydrothermal (HT, HT-F) and two hydrothermal with addition of swelling agent (1,3,5-triisopropylbenzene) (TiPB, TiPB-F). Within each couple, one of the materials was synthesized with ammonium fluoride (NH4F). The supports were functionalized via grafting 3-aminopropyltriethoxysilane (APTES) and via impregnation with polyethylenimine ethylenediamine branched (PEI). The adsorption behavior of the pure materials was described well by the Langmuir model, whereas for the amine-silicas, a Dualsite Langmuir model was applied, which allowed us to qualify and quantify two different adsorption sites. Among the materials synthesized, only the SBA-15 synthesized at room temperatures (RT) improved its properties as an adsorbent with the addition of fluoride when the silicas were functionalized with APTES. The most promising result was the TiPB-F/50PEI silica which at 75 °C and 1 bar CO2 captured 2.21 mmol/g.