Tri-n-octylamine Research Articles

Reactive extraction of succinic acid using supercritical carbon dioxide

ABSTRACTReactive extraction using supercritical carbon dioxide (scCO2) and tri-n-octylamine (TOA) was evaluated as a separation method of succinic acid from an aqueous solution. The reactive extraction of succinic acid was performed at varying initial acid concentrations in aqueous solution (0.07–0.45 mol∙dm−3), temperature (35–65°C) and pressure (8–16 MPa). The succinic acid separation was conducted in both batch mode and semi-continuous mode. The highest reactive extraction efficiency of approx. 62% was obtained for the process conducted in semi-continuous mode at 35°C and 16 MPa for the initial acid concentrations in aqueous phase of 0.39 mol∙dm−3.

Effect of Plate Wettability on Dispersed-Phase Holdup in a Pulsed Disc-and-Doughnut Solvent Extraction Column

ABSTRACTThe effect of plate wettability on the dispersed-phase holdup in a pulsed disc-and-doughnut solvent extraction column is presented. Teflon, nylon, and stainless steel plates have been used to simulate a change in the wetting characteristics of the plate material that can occur in an operating column due to ageing or deposits accumulating on the plate. Experimental holdup data have been measured over a range of operating conditions using a 1.0 m long glass column with an internal diameter of 72.5 mm containing alternating discs and doughnuts. The liquid-liquid system studied was tri-n-octylamine (TOA)-kerosene-water with sulphuric acid as the solute. Results show that there are noticeable changes in the characteristic velocity (determined from measured holdup) and operational regimes for the different plate materials, particularly at low pulsation intensities, when operating under dispersed aqueous conditions. Experimental holdup data from this study have also been compared to correlations from literature for predicting holdup. As none of these correlations for holdup incorporate plate wettability, a new correlation for predicting holdup has been proposed that incorporates the contact angle of the plate material to allow for changes in the wettability of the plate surface. This correlation is able to predict the holdup data from this study to within 10.5% for aqueous dispersed conditions.

Mechanism studies on thermal dissociation of tri-n-octylamine hydrochloride with FTIR, TG, DSC and quantum chemical methods

The thermal dissociation of tri-n-octylamine hydrochloride (TOAHCl) was investigated using both the quantum chemical simulation and experimental methods. The pathway through which a mixture of tri-n-octylamine (TOA) and hydrogen chloride (HCl), rather than di-n-octylamine (DOA) and 1-chlorooctane, are produced has been determined through transition state (TS) search with Intrinsic Reaction Coordinate (IRC) calculations. Particularly, strong agreement between the experimental FTIR spectra and that of TOA demonstrates the same result for the first time. Moreover, the thermal dissociation of TOAHCl proceeds in two continuous steps, which is different from the low molecular mass amine hydrochlorides. The experimental enthalpy of the dissociation was 70.793 $$\hbox {kJ mol}^{-1}$$ with DSC measurement which is very close to the density functional theory (DFT) calculation result 69.395 $$\hbox {kJ mol}^{-1}$$ . Furthermore, with the aid of DFT calculations, some other important thermochemical characteristics such as crystal lattice energy with the value of 510.597 $$\hbox {kJ mol}^{-1}$$ were evaluated by means of Born–Fajans–Haber cycle. The thermal dissociation of tri-n-octylamine hydrochloride was investigated with both the quantum chemical simulation and experimental methods. Intrinsic reaction coordinate (IRC) calculations suggest that the products are tri-n-octylamine and HCl rather than di-n-octylamine and 1-chlorooctane. Furthermore, the dissociation is a two-stage process as determined by experimental analysis.

Effects of Tri-n-octylamine with or without Diluents on Microporous Ethylene Chlorotrifluoroethylene Membranes

Microporous ethylene chlorotrifluoroethylene (ECTFE) membranes are expected to become industrially useful. Its solvent resistance is important in applications involving solvent microfiltration, organic synthesis, and membrane solvent extraction (MSX). Recent characterizations of microporous ECTFE membrane after exposure to different liquid media and radiation, indicated that pure tri-n-octylamine (TOA) does have some effect. However, it is used in MSX with diluents, e.g., xylene. Therefore, many material and porous-structure characterization techniques and dead-end microfiltration were employed to study solvent-treatment effects on ECTFE membranes exposed to ethanol, xylene, xylene80/TOA20, and pure TOA. Membrane-surface roughness of virgin, ethanol-soaked, and TOA-soaked membranes indicated TOA-soaked membranes were the roughest, followed by ethanol-soaked and virgin ones. Bubble-point-pressure based maximum pore diameters (dmax) of solvent-treated membranes were: dmax,TOA > dmax,Xylene/TOA > dmax,Xylene...

Mechanistic modeling and equilibrium prediction of the reactive extraction of organic acids with amines: A comparative study of two complexation-solvation models using 3-hydroxypropionic acid

Abstract A comprehensive study of equilibrium states involved in the reactive extraction of 3-hydroxypropionic acid (3-HP) by tri- n -octylamine (TOA) in n -decanol is described. Complexation phenomena between 3-HP and TOA were revealed by infrared spectroscopy (FT-IR). This study demonstrated that the main extraction mechanism is the formation of an ion pair involving the dissociated form of 3-HP. Chemical models were then formulated, taking the formation of the ion pair between 3-HP and TOA and the influence of the amount of solvent in the organic phase into account. Two models are proposed: (1) a stoichiometric model where the solvent is seen as a reagent that is involved in the complexation as a synergistic extractant, but with competition for solvation via H-bond interactions with TOA; (2) a model where the solvent is seen as a phase modifier that improves the physicochemical properties of the extractant and that changes the complexation equilibrium. Both models describe the extraction yields in the investigated ranges, with Model (2) being particularly predictive since it provides a mean absolute prediction error of less than 2% in yield units. According to this latter model, the complexation equilibrium coefficient increases with the increase of the n -decanol proportion in the organic phase. Model (2) shows that solvation effects are better described as non-stoichiometric interactions. Therefore, the two mechanistic models accurately represent extraction yields over a wide range of initial conditions and are potentially transposable to other reactive extraction systems. Such knowledge is essential for further implementation of downstream processes.

Zn2+ Ion Adsorption from Aqueous Solution Using Montmorillonite Clay Impregnated with Tri-n-octylamine

Montmorillonite (Mt) clay was used to remove zinc (Zn2+) ion from the aqueous solution. This clay material was modified (Mt-TOA) by impregnating trin-octylamine (TOA), a tertiary amine. The experiments on equilibrium and kinetics were done to analyze the effect of adsorbent amount (w, 0.05 to 0.3 g for Mt, 0.01 to 0.06 g for Mt-TOA), initial Zn2+ ion concentration (C0, 15 mg·L–1 to 35 mg·L–1), pH (1 to 9), and contact time (t, 0 to 100 min) on the efficacy of both adsorbents. With a greater amount of adsorbent, the intake capacity of Mt and Mt-TOA for Zn2+ ion removal was found to lower but there was an increase in the separation efficiency. The optimum amount of Mt and Mt-TOA was found to be 0.1 and 0.01 g, respectively. The pH of the aqueous solution could be maintained at 7 to achieve a better adsorption of Zn2+ ion. In the kinetic experiments, after 90 min, the separation efficiency of Zn2+ ion from aqueous solution reached to a value of 86.68% with Mt (0.1 g) and 84.56% with Mt-TOA (0.01 g). Modeling...

Characterization of microporous ECTFE membrane after exposure to different liquid media and radiation

Changes in the properties of microfiltration (MF) membranes exposed to acids, bases and organic solvents used in semiconductor processing are of interest. Microfiltration membranes used for sterilization in beverage, biotechnology and pharmaceutical industries are sterilized by gamma radiation among others. Irradiation-induced degradation in membrane properties should be known. Microporous membranes of ethylene chlorotrifluoroethylene (ECTFE) membranes subjected to caustic soaking, organic solvent soaking and γ-irradiation were characterized extensively and compared with widely-used polyvinylidene fluoride (PVDF) membranes for selected properties. ECTFE membrane swellings by seven solvents including tri-n-octylamine (TOA) were much larger than those of nonporous ECTFE films. Scanning electron microscopy, atomic force microscopy, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) indicated significant defects in TOA-soaked membranes. Thermogravimetric analysis (TGA) and DSC confirmed TOA presence in membrane pores. Solvents THF (tetrahydrofuran), toluene, acetonitrile and TOA decreased Young's modulus by 6–30%. ECTFE membranes resisted plasticization by these solvents: glass transition temperature variations were limited. In TOA-treated membranes, XRD indicated more significant defects in PVDF membranes. Treatment with NaOH solutions showed no effect on contact angle and bubble point pressure (BPP). Only 3M caustic solution reduced liquid entry pressure by 13.8 kPag. ECTFE membranes showed greater hydrophobicity, stronger wetting resistance and better ability to maintain hydrophobicity vis-à-vis PVDF membranes. ECTFE membranes subjected to γ-radiation (up to 45 kGy) showed almost no effect on morphology, porosity and Young's modulus. Slight variations were observed in BPP, melting enthalpy obtained via DSC and energy loss measured in dielectric relaxation spectroscopy.

Modeling and Optimization of Reactive Extraction of Gallic Acid Using RSM

Reactive extraction was experimentally investigated for recovery of gallic acid (GA) from the aqueous solution using tri-n-octylamine (TOA) as extractant in hexanol. All experiments were carried out according to statistical design in order to develop a regression model used to optimize the extraction of GA. Two independent variables were selected as: initial concentration of GA (CGA0) in aqueous phase and concentration of TOA (CTOA) in organic phase. The statistical analysis showed that both the independent variables had significant effect on response value, followed by the quadratic and interactive effect on response. A five-level central composite rotatable design (CCRD) was employed. Analysis of variance (ANOVA) showed a high coefficient of determination (R2 = 99.0%). The optimal extraction conditions of GA were determined as: CGA0 = 2.01 g/L, CTOA = 6.8% v/v. At the optimum conditions, the experimental yield of GA was 91.9%, which was in close agreement with the predicted value of 93.2%.

Mass transfer studies in a horizontal pulsed sieve-plate column for uranium extraction by tri-n-octylamine using axial dispersion model

In this work, uranium extraction from an aqueous sulfate solution with 0.25M concentration acid, by using 5% v/v tri-n-octylamine (TOA) solvent, 90% v/v kerosene diluent and 5% v/v decanol modifier is studied. The effect of operation parameters (i.e., phase flow rates and pulsation intensity) on the volumetric overall mass transfer coefficients and axial dispersion in a horizontal pulsed sieve-plate column is evaluated using axial dispersion model (ADM). According to the results, increasing pulsation intensity and phase flow rates leads to the enhancement of the mass transfer performance. The continuous phase axial dispersion is found to be significantly higher than that in the dispersed phase. Axial dispersion of a phase is found to be mostly influenced by pulsation intensity and the flow rate of the phase itself and is minor influenced by the second phase flow rate. The overall height of mass transfer unit (HTUoc) is obtained to be less than 0.2 m, indicating high performance of a horizontal pulsed sieve-plate column for solvent extraction of uranium. Furthermore, new correlations are proposed for prediction of Koca, Ec and Ed, which are in satisfactory agreement with the experimental data with AARE values of 1.03%, 3.35% and 1.89% respectively.

New insights in reactive extraction mechanisms of organic acids: An experimental approach for 3-hydroxypropionic acid extraction with tri-n-octylamine

A detailed study of 3-hydroxypropionic acid (3-HP) reactive extraction with tri-n-octylamine (TOA) is proposed for the first time. It aims at uncovering some solvent-solutes interactions and providing global mechanisms to better understand and design the reactive liquid-liquid extraction of 3-HP in a biotechnological process. Eleven solvents of similar molecular sizes and several chemical types (alcohols, esters and alkanes) were investigated to understand their role on the extraction ability. Alcohols were found to be the best solvents thanks to their H-bond donor characteristic and water loading that allowed good solvation of the acid-amine complexes. Further investigations were then undertaken, for n-decanol and oleyl alcohol as solvents, varying acid (0.0028-0.56 mol/L corresponding to 0.25-50 g/L) and amine (02,3 corresponding to 0-100% v/v) concentrations. At 0.011 mol/L (1 g/L) of 3-HP, maximum extraction yields of 77% for n-decanol and 51% for oleyl alcohol were found for 0.46 mol/L TOA (20% v/v). The initial TOA purity proved to have a major impact on the extraction yield at low initial acid concentration (<0.1 mol/L = 10 g/L). Impurities from the TOA manufacturing process were identified as n-octylamine and di-n-octylamine and quantified in the aqueous phase after extraction. Their major effect on the extraction yield has been assessed (up to 86% decrease).

Selective extraction of Pt(IV) over Fe(III) from HCl with an amide-containing tertiary amine compound

The separation properties of Pt(IV) over Fe(III) in HCl solutions using N-2-ethylhexyl-bis(N-di-2-ethylhexyl-ethylamide)amine (EHBAA) were investigated and then compared with those using the conventional extractant tri-n-octylamine (TOA). Also, the structural analyses of Pt(IV) in both of the aqueous (HCl solution) and organic (EHBAA in n-dodecane–2-ethylhexanol solution) phases were performed with EXAFS spectroscopy. The extractability of Pt(IV) was much higher with EHBAA than with TOA in the studied HCl concentration range (0.2–8 M HCl); additionally, EHBAA selectively extracted Pt(IV) over Fe(III) under the condition of [EHBAA] ⩽ 0.1 M and [HCl] ⩽ 1 M. The Pt(IV) loading capacity of 0.1 M EHBAA was about 9.2 g/L (about 0.05 M). Most of the Pt(IV) extracted with 0.1 M EHBAA from 1 M HCl was stripped with 0.1 M NaOH; the co-extracted Fe(III) was selectively scrubbed with distilled water. The structural studies indicated that the Pt(IV) extracted with EHBAA from 1 M HCl formed an ion-pair complex, [PtCl6]·(EHBAA·H)2.

Electrodeposition of Cobalt and Lead in the Hybrid Liquid Membrane - Electrodialysis-Electrolysis Process

A novel method for Co (II) and Pb (II) recovery from acidic solutions is presented. The extraction of Co (II) and Pb (II) ions using the bulk liquid membranes during a galvanostatic electrodialysis process accompanied by cathodic electrodeposition of the metals was studied. Solutions of di (2-ethylhexyl) phosphoric acid (D2EHPA) with admixtures of tri-n-octylamine (TOA) in 1,2-dichloroethane were used as the liquid membranes. Effects of current density, Co (II) and Pb (II) concentrations in the feed solution, sulfuric or nitric acid concentration in the feed solution, D2EHPA and TOA concentration in the liquid membrane, of the type and concentration of acid in the cathodic solution were studied, and optimal conditions were determined. It is demonstrated that a practically complete (98-99%) removal of Co (II) and Pb (II) from the feed solutions containing 0.01 mol∙L-1 CoSO4 or 0.01 mol∙L-1 Pb (NO3)2 is achieved during 1.0 − 4.0 h of electrodialysis. A possibility of effective transfer of Pb (II) into dilute solutions of perchloric and nitric acids was demonstrated. The liquid membranes ensure the recovery of Co (II) ions into dilute solutions of perchloric, sulphuric, hydrochloric and nitric acids. Adherent, compact cobalt and lead electrodeposits with a fine-grained structure were obtained in the studied systems.

SYNERGIC EXTRACTION OF PANTOTHENIC ACID WITH TWO DIFFERENT EXTRACTANTS

The influences of extractants concentrations and solvent polarity on the efficiency of pantothenic acid separation by synergic extraction with tri-n-octylamine (TOA) and di(2-ethylhexyl) phosphoric acid (D2EHPA) mixture have been analyzed. The results indicated the formation of an interfacial compound which includes one molecule of pantothenic acid and one of D2EHPA, its hydrophobicity being increased by solvation with additional TOA molecules. For solvents with lower dielectric constants, n-heptane and n-butyl acetate, the number of amine molecules participating in the interfacial complex formation was controlled by solvent polarity and D2EHPA concentration, decreasing with the increase of these two parameters. For dichloromethane, the chemical structure of the extracted compound remained the same regardless of D2EHPA concentration. The most important synergic effect corresponded to the extractant mixture dissolved in n-heptane, at low D2EHPA concentration in the organic phase (5 g/l).

EVALUATION OF DIFFERENT POLYMERIC MEMBRANE SUPPORT FOR ACETIC ACID REMOVAL BY SUPPORTED LIQUID MEMBRANE PROCESS

In this study, the removal of acetic acid from aqueous solution through supported liquid membrane (SLM) process by using tri-n-octylamine (TOA) as a carrier and sodium hydroxide as a stripping agent was conducted. Acetic acid can inhibit the microbial activity during fermentation process of biomass hydrolysate, thus decreasing the bioethanol production. It is crucial to remove acetic acid prior to fermentation process in order to increase the yield of bioethanol from biomass resources. In this study, the removal of acetic acid was conducted using different types of polymeric membrane in supported liquid membrane process. Three types of polymeric membranes support which are polyethersulfone (PES), polysulfone (PSF) and polyvinyflouride (PVDF) prepared by vapour induced phase separation (VIPS) were used as a support material. The types of polymer give a significant effect on membrane morphology and its physical characteristics. PES exhibited a porous membrane support with a symmetric structure and high contact angle. Almost 86% of 10 g/l of acetic acid was successfully removed by using PES as a support membrane, compared to the 6% and 38% removal using PSF and PVDF membrane, respectively.

The Influence of the Hofmeister Bias and the Stability and Speciation of Chloridolanthanates on Their Extraction from Chloride Media

ABSTRACTThe possibility of recovering rare earth elements from solutions containing their chloridometalate anions [LnClx](x−3)− via the process: LnClx(x−3)− + (x − 3)Lorg + (x–3)H+ ⇌ [(LH)x−3LnClx]org has been tested using 2-(1,3-bis(hexylamino)-1,3-dioxopropan-2-yl)-4,6-di-tert-butylpyridine (PMA), tri-n-butylphosphate (TBP), and tri-n-octylamine (TOA), which are known to be strong extractants for transition metal chloridometalates. While DFT calculations indicate that the formation of the neutral assembly [(PMAH)3LaCl6] in the gas phase is favorable, no uptake of La(III) from 6 M HCl by toluene solutions of PMA (or of TBP or TOA) was observed in solvent extraction experiments. Successful uptake of the [PtCl6]2− dianion by PMA and the failure to extract the [IrCl6]3− trianion under the same conditions indicate that the higher hydration energy of the latter makes transfer to the toluene solution less favorable and that this militates against extraction of La(III) chlorido complexes carrying charges of −3 or larger in which all the inner-sphere water molecules have been replaced. Computational results confirm literature observations that, in contrast to transition metal trications, formation of REE metalate anions such as [LnClx](x−3)− is not very favorable, particularly so for chloride, compared with nitrato or sulfato systems. Also, they indicate that the formation of outer-sphere assemblies such as {[La(H2O)9]·xCl} in which water ligands are retained in the inner sphere, H-bonded to anions, is more stable than inner-sphere complexes containing an equivalent number of anions. The high level of hydration of such species disfavors their transfer into nonpolar water-immiscible solvents. It is unlikely that recovery of [LnClx](x−3)− from acidic solutions can be achieved efficiently using currently available anion exchange extractants operating in a “pH-swing” process. Receptors giving very high binding energies to chloridolanthanates will be needed to offset the high dehydration energies required.

The kinetic analysis of optimization and selective transportation of Cu(II) ions with TNOA as carrier by MDLM system

This study covers the transportation of Cu(II) ions by multi-dropped liquid membrane (MDLM) system and tri-n-octylamine (TNOA) as carrier in kerosene. Batch experiments are held to obtain optimum conditions for the transportation of Cu(II) ions such as volume of donor, organic, and acceptor phase 100ml, pH of donor phase 9.00, temperature 298.15K, concentration of H2SO4 in acceptor phase 1.00mol·L−1, concentration of TNOA in organic phase 5.00×10−3mol·L−1 and rate of peristaltic pump 50ml·min−1. Optimum circumstances of this extraction are as follows: pH of donor phase is 9.00, concentration of TNOA is 5.00×10−3mol·L−1, 1.00mol·L−1 H2SO4 as acceptor phase, and flux rate is 50ml·min−1. Cu(II) ion transportation is consecutive first order irreversible reaction. Activation energy is found as 5.22kcal·mol−1 (21.82kJ·mol−1), this process is called as diffusion controlled system. Selective transportation of Cu(II) ions with alkaline, alkaline earth, and different heavy metal ions at optimum conditions of single Cu(II) extraction was conducted. According to the selective transportation Cu(II) ions with alkaline and alkaline earth metal ions, Na+, K+, and Ba2+ ions are not detected in the acceptor phase, but 12.00% of Ca2+ ions is transported from donor phase to acceptor phase. At the end of the simultaneous extraction of Zn(II), Fe(III), and Mo(VI) with Cu(II) ions, 2.20% of Mo(VI), 0.80% of Fe(III) and 3.60% of Zn(II) are detected in the acceptor phase.

Extraction of levulinic acid using tri-n-butyl phosphate and tri-n-octylamine in 1-octanol: Column design

The reactive extraction of levulinic acid using two different extractants [tri-n-butyl phosphate (TBP) and tri-n-octylamine (TOA)] dissolved in 1-octanol was investigated at 298K. Using the equilibrium data, the distribution coefficient (KD), extraction efficiency (%E) and loading ratios (Z) were calculated. TOA provided highest KD values with 1-octanol. A maximum KD was obtained as 9.571 using 0.689mol/kg TOA while 90.54 % of the initial levulinic acid was extracted. Increasing the initial acid concentration resulted in a decrease in the extraction efficiency. Loading ratios were found to be less than 1 for TBP while both types, i.e. 1:1 and 2:1 acid-amine complexes were expected to form with TOA. The feasibility of the extraction process was assessed by calculating minimum solvent to feed ratio required for 90% recovery of levulinic acid, number of theoretical stages, height and diameter of the extraction column.

Modeling and Optimization of Reactive Extraction of Citric Acid

Reactive extraction of citric acid from dilute aqueous solutions was studied using three different extractants, namely tri-n-butylphosphate (TBP), tri-n-octylamine (TOA), and Aliquat 336 (A336), dissolved in three different diluents: butyl acetate, decanol, and benzene. The isothermal batch equilibrium experiments were carried out at T = 300.15 ± 1 K. The extraction was interpreted in terms of the distribution coefficient (KD). Maximum extraction efficiency (E = 95.5%) was obtained at 20% (v/v) TOA in butyl acetate with complexation constant KE2 = 1039.7 (kg mol–1)2 for the (2:1) complex. In addition to having a higher loading ratio (Z > 0.5), the overloading of amine(TOA) in the case of the citric acid + TOA + decanol system was also confirmed by spectroscopic (FTIR) analysis. The linear solvation energy relationship model was successfully applied to predict the distribution coefficient. The complex stoichiometry was also optimized using differential evolution. A close resemblance was observed between ex...

Reactive extraction of citric acid using supercritical carbon dioxide

This paper presents the results of investigations into reactive extraction of citric acid from an aqueous solution using supercritical carbon dioxide (scCO2) and tri-n-octylamine (TOA). The effect of initial citric acid concentration (0.07–1.04moldm−3), pressure (8–16MPa) and temperature (35–65°C) on reactive extraction efficiency was identified. The reactive extraction process was conducted in both batch mode and semi-continuous mode. The study concluded that the reactive extraction using TOA as a reactant and scCO2 is an efficient method of citric acid separation. Reactive extraction efficiency increases with an increase in pressure, while an increase in temperature decreases the extraction yield. Reactive extraction of citric acid conducted in semi-continuous mode results in high process efficiency (96.9%). Moreover, the formation of (1,1) acid-amine complexes was reported for the considered initial citric acid (0.01–0.04moldm−3) and TOA (0.04–0.07moldm−3) concentrations.

New Reactive Extraction Based Reclaiming Technique for Amines Used in Carbon Dioxide Capture Process from Industrial Flue Gases

A new reclaiming technique based on reactive extraction for removal of heat stable salts (HSS) from monoethanolamine (MEA) used in carbon dioxide (CO2) capture process has been developed. The extraction process was based on the use of tri-n-octylamine (TOA), Aliquat 336, OH– modified Aliquat 336, a two-step extraction (modified Aliquat followed by TOA), and mixed extractant (modified Aliquat and TOA) in 1-octanol diluent. The best parameters were 69% OH– modified Aliquat, two-step extraction, and mixed extractant (modified Aliquat and TOA) and under optimum extraction conditions were able to improve the extraction efficiency of the original Aliquat and TOA to over 90%. The two-step extraction and mixed extractant were also capable of managing Cl– contamination in MEA solution. Extraction was found to be independent of temperature whereas efficiency reduced with increase of CO2 loading. Therefore, it is recommended to apply this extraction technique to the lean MEA stream after the rich/lean heat exchanger...