Chemical Equilibrium and LiquidâLiquid Equilibrium in Aqueous

1508

Ind. Eng. Chem. Res. 2003, 42, 1508-1516

Chemical Equilibrium and Liquid-Liquid Equilibrium in Aqueous Solutions of Formaldehyde and 1-Butanol Roger Peschla,† Baudilio Coto Garc´ ıá,‡ Michael Albert,§ Cornelius Kreiter,| and Gerd Maurer* Lehrstuhl fu¨ r Technische Thermodynamik, Fachbereich Maschinenbau und Verfahrenstechnik, Universita¨ t Kaiserslautern, D-67653 Kaiserslautern, Germany

A thermodynamic model for liquid-liquid phase equilibrium and chemical equilibrium in the formaldehyde + water + 1-butanol system is presented. The model is an extension of the vaporliquid phase equilibrium model for the formaldehyde + water + methanol system. Formaldehyde reacts with water and alcohols to form oligomers. New experimental results (from NMR spectroscopic investigations) are reported for the chemical equilibrium in liquid formaldehyde + 1-butanol and formaldehyde + water + 1-butanol systems at temperatures from 278 to 348 K. New liquid-liquid phase equilibrium data are reported for temperatures of 298, 313, and 333 K. The model is able to reliably describe the liquid-liquid phase equilibrium, as well as the specification in the liquid phases. Introduction Formaldehyde is one of the most versatile intermediates in the chemical industry. The largest amount of formaldehyde is used for the production of formaldehyde polymers, i.e., polyacetal plastics and resins. The quality of the polymers strongly depends on the water concentration before polymerization. Anhydrous formaldehyde is of fundamental importance when high-quality products are required. The common method of “drying” formaldehyde is to convert it to trioxane, a stable cyclic intermediate of formaldehyde that is usually purified by distillation and crystallization. Because trioxane depolymerizes to produce formaldehyde, it can be used for almost all formaldehyde reactions, particularly when anhydrous formaldehyde is required. Another possibility for reducing the amount of water in formaldehyde solutions is to use reactive extraction with monohydric alcohols. A liquid-liquid phase split takes place when the alcohol chain is sufficiently hydrophobic. 1-Butanol is the first (in terms of increasing size) aliphatic monohydric alcohol that is not completely miscible with water. Because of its extraordinary reactivity, which differs substantially from that of higher homologues and aliphatic ketones, formaldehyde is predominantly present as methylene glycol [MG, HO(CH2O)H] and poly(oxymethylene) glycols [MGn, HO(CH2O)nH), n > 1] in aqueous solutions.

CH2O + H2O a HO(CH2O)H

(I)

HO(CH2O)n-1H + HO(CH2O)H a HO(CH2O)nH + H2O (II) * To whom correspondence should be addressed. E-mail: [email protected]. Phone: +49-631-2052410. Fax: +49631-2053835. † Present address: MiRO Mineralo¨lraffinerie Oberrhein, D-76187 Karlsruhe, Germany. ‡ Present address: ESCET, Universidad Rey Juan Carlos, E-28934 Mostoles, Madrid, Spain. § Present address: Degussa AG, VT-T, D-63403 Hanau, Germany. | Present address: Fachbereich Chemie, Universita¨t Kaiserslautern, D-67653 Kaiserslautern, Germany.

Formaldehyde undergoes similar chemical reactions with alcohol as it does with water, resulting in the formation of hemiformal [HF, HO(CH2O)R] and poly(oxymethylene) hemiformals [HFn, HO(CH2O)nR), n > 1], where, for example, R- represents CH3- in the case of methanol and CH3(CH2)3- in the case of 1-butanol.

CH2O + ROH a HO(CH2O)R

(III)

HO(CH2O)n-1R + HO(CH2O)R a HO(CH2O)nR + ROH (IV) In an equilibrated ternary liquid mixture of formaldehyde, water, and an alcohol, all chemical reaction equilibria are observed simultaneously. The interchange between formaldehyde in poly(oxymethylene) glycols and formaldehyde in poly(oxymethylene) hemiformals can be described (at least in principle) by taking into account the usually very small concentration of formaldehyde monomers through chemical reactions I and III. The above chemical reactions have an essential influence on the properties of formaldehyde-containing aqueous solutions, and they need to be taken into account in any thermodynamic model intended for formaldehydecontaining systems. Because of the small amount of monomeric formaldehyde in the liquid phase, the effects of reactions I and III on the binary formaldehyde + water and formaldehyde + alcohol systems can be neglected, whereas the properties of the ternary system formaldehyde + water + alcohol are strongly influenced by these reactions (because of the formaldehydeinterchange effect). A physicochemical model1 that considers both chemical reactions as well as physical interactions in the liquid phase has been shown to be very successful in describing the vapor-liquid equilibria and enthalpies of formaldehyde-containing mixtures. This model has been continuously updated and extended by, for example, Hasse et al.,2,3 Hahnenstein et al.,4-6 Albert et al.,7-10 and Maiwald et al.11 This model was adopted for describing the phase equilibrium in the formaldehyde + water + 1-butanol system.

10.1021/ie020743o CCC: $25.00 © 2003 American Chemical Society Published on Web 02/08/2003

Ind. Eng. Chem. Res., Vol. 42, No. 7, 2003 1509

Experimental Procedures Chemical Equilibrium. Information on transformation of formaldehyde into its reaction products with water or alcohol is accessible from nuclear magnetic resonance (NMR) spectroscopic investigations. Using a high-resonance-frequency NMR spectrometer, it is possible to separate signals from -CH2 groups bound in different poly(oxymethylene) glycols and poly(oxymethylene) hemiformals. Experimental studies to determine chemical reaction equilibrium properties for reactions II and IV in formaldehyde-containing solutions with water and/or methanol have been performed by Hahnenstein et al.,5 Balashov et al.,12 Albert et al.,8 and Maiwald et al.11 To our knowledge, no investigations of chemical equilibria in mixtures involving formaldehyde and 1-butanol have been reported to date. NMR spectra of formaldehyde-containing solutions yield different peaks from -CH2 groups (in both 13C and 1H NMR spectroscopy) depending on the chain length of the poly(oxymethylene) glycols or/and poly(oxymethylene) hemiformals present. The peak areas are obtained by integration of the spectra. It is assumed that the area of a peak is proportional to the total amount of the species responsible for the peak. This results in a direct relation between the peak area fraction and the mole fraction of true species in the solution. Binary formaldehyde + 1-butanol stock solutions were prepared by dissolving paraformaldehyde in 1-butanol at high temperature. These solutions were stored over molecular sieves for several days to remove the water liberated from the paraformaldehyde. All solid residues and the molecular sieves were then removed by filtration. The remaining amount of water in the formaldehyde + 1-butanol solutions was estimated by gas chromatography and/or a modified Karl Fischer titration to below 0.003 g‚g-1 . The stoichiometric formaldehyde concentration was determined using the sodium sulfite method with a relative uncertainty of less than 1%. The formaldehyde stock solutions were diluted with 1-butanol and/or bidistilled water. The NMR tubes used were half-filled to reduce the vapor phase and, consequently, an essential change in the liquid composition. To ensure equilibrium, all samples were kept in a thermostated bath for several days (weeks for the lowest temperatures) at the temperature of the NMR spectroscopic investigations. 13C NMR spectroscopy was performed with a Bruker AMX 400 NMR spectrometer (400.13 MHz), fully decoupled from the 1H nucleus. The temperature of a probe was determined from the set point of the temperaturecontrol system. The temperature-determination procedure was checked by comparison with data for the influence of temperature on the chemical shift of pure liquid ethylene glycol (cf. Gu¨nther13). The uncertainty of the temperature measurement found by this method is (1 K. Benzene-d6 (in sealed capillaries in the NMR sample tubes) was used both as a lock and as a reference substance. NMR spectroscopic investigations of the chemical reaction equilibrium in the binary formaldehyde + 1butanol system were carried out at stoichiometric formaldehyde concentrations from ∼0.2 to ∼0.5 mol‚mol-1. The range of compositions covered in the ternary formaldehyde + water + 1-butanol system was limited by the phase splitting occurring in that system. Measurements were carried out for formaldehyde and 1-butanol compositions ranging from about 0.3 to 0.4

mol‚mol-1 and from 0.28 to 0.36 mol‚mol-1, respectively. The temperature range of the experimental work was from 278 to 348 K. The 13C NMR spectrum of the binary formaldehyde + 1-butanol solution is very similar to the spectrum of the formaldehyde + methanol system. Peak assignments were adopted from a previous work.4,5 Some difficulties arose in the investigations of the ternary formaldehyde + water + 1-butanol system because the peaks given by one of the -CH2 endgroups in poly(oxymethylene) hemiformals give a chemical shift (between 85 and 87 ppm) very similar to that of the peaks caused by the -CH2 endgroups in poly(oxymethylene) glycols. In some cases, the resulting overlapping of peaks did not allow for a reasonably accurate separation and integration. At high formaldehyde concentrations, the peak areas could be reproduced to within about 1%. For dilute formaldehyde solutions, however, peaks corresponding to higher poly(oxymethylene) hemiformals were very small, and the reproducibility decreased. Liquid-Liquid Equilibrium. Experimental work on the liquid-liquid equilibrium of the formaldehyde + water + 1-butanol system was performed at 298 K. For temperatures of 313 and 333 K, some liquid-liquid phase equilibrium data are available from Lavrova and Lesteva.14 Liquid two-phase systems were prepared in thermostated glass vessels by diluting formaldehyde stock solutions with water and 1-butanol. The total mass of the two-phase systems was typically between 90 and 120 g, and the organic-phase formaldehyde concentration was up to 0.235 mol‚mol-1. The two-phase systems were intensively stirred at constant temperature for up to 5 days. Afterward, the systems were allowed to separate for another 5 days before samples were taken from the coexisting liquid phases. The formaldehyde content of a sample was analyzed by applying the sodium sulfite method. The concentration of water in a liquid sample was determined either by a modified Karl Fischer titration15 or by gas chromatography.15 Modeling The model applied to correlate the experimentally determined data for the chemical equilibrium, as well as for the liquid-liquid phase equilibrium of the formaldehyde + water + 1-butanol system, was adopted from previous work on the system formaldehyde + water + methanol.1,7-10 The outline of the extension of the model to describe the equilibrium in partially miscible aqueous-alcoholic formaldehyde-containing mixtures is shown in Figure 1. The model takes into account chemical reactions as well as differences in interactions between all species in both liquid phases, i.e., a liquid phase is treated as a real, chemically reactive mixture of water (W), 1-butanol (1B), formaldehyde momoners (FA), methylene glycol (MG1), poly(oxymethylene) glycols (MGn), hemiformal (HF1), and poly(oxymethylene) hemiformal (HFn). The chemical potential of a component in a liquid phase is normalized according to Raoult’s law i.e., the reference state for the chemical potential of species i is the same for both phases. The influence of pressure on the properties of a species i in a liquid phase is neglected. The condition for liquid-liquid phase equilibrium is therefore

xi′γi′ ) xi′′γi′′ i ) FA, W, 1B, MG1, MGn, HF1, HFn (1)

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Ind. Eng. Chem. Res., Vol. 42, No. 7, 2003

pSFA pSW vap KMG1 S pMG p0 1

(6)

pSFA pS1B vap KHF1 ) S 0 KHF1 pHF1p

(7)

KMG1 )

The stoichiometric composition of a liquid phase follows from mass balances in that phase ∞ ∞ ntotal (xFA + ixMGi + ixHFi) n˜ total i)1 i)1

(8)

x˜ W )

∞ ntotal (xW + xMGi) n˜ total i)1

(9)

x˜ 1B )

∞ ntotal (x1B + xHFi) n˜ total i)1

(10)

∑

x˜ FA )

Figure 1. Scheme for modeling the liquid-liquid equilibrium of the formaldehyde + water + 1-butanol system

The nonideality of the liquid phase is taken into account through the UNIFAC group contribution method.16 The following chemical reaction equilibria are considered: the formation of methylene glycol and hemiformal from the reactions of formaldehyde with water and 1-butanol, respectively, and the polymerizations of methylene glycol and hemiformal to poly(oxymethylene) glycols and poly(oxymethylene) hemiformals, respectively. Although the amount of formaldehyde present as monomers is very small, the chemical reaction equilibria for the formation of methylene glycol and hemiformal are very important, as they provide the transfer from formaldehyde in poly(oxymethylene) glycols to formaldehyde in poly(oxymethylene) hemiformals (and vice versa). As in the model for the formaldehyde + water + methanol system, further chemical reactions (resulting, for example, in methylal and dimethoxy ether) are neglected as they are of minor importance under the conditions of interest in the present work. Chemical reaction equilibrium is taken into account through “true” chemical reaction equilibrium constants, i.e., using activities

xMG1 γMG1

KMG1 )

KHF1 )

KMGn )

KHFn )

(2)

xFAxW γFAγW xHF1

γHF1

(3)

xFAx1B γFAγ1B

xMGnxW

γMGnγW

xMGn-1xMG1 γMGn-1γMG1 xHFnx1B

γHFnγ1B

xHFn-1xHF1 γHFn-1γHF1

ng2

ng2

(4)

(5)

Literature data were obtained for the formation of vap vap methylene glycol, KMG , and hemiformal, KHF , in the 1 1 vapor phase. Those data were converted into values of KMG1 and KHF1 via

∑

∑

∑

where

ntotal n˜ total

∞

) (1 +

∞

ixMG + ∑ixHF )-1 ∑ i)1 i)1 i

i

(11)

Model Parameters. The chemical reaction equilibrium constant for the formation of methylene glycol from vap ) was water and formaldehyde in the vapor phase (KMG 1 17 taken from Hall and Piret. The chemical reaction constant for the formation of hemiformal from 1-butanol vap ) was apand formaldehyde in the vapor phase (KHF 1 proximated by the constant for the formation of hemiformal from methanol and formaldehyde, which was taken from Kogan.18 The chemical reaction equilibrium constants (KMGn, n g 2) for the formation of poly(oxymethylene) glycols (reaction II; cf. eq 4) were taken from an earlier publication by Albert et al.9 on the vapor-liquid phase behavior of the binary formaldehyde + water system. These chemical reaction equilibrium constants are listed in Table 1. The vapor pressures of formaldehyde (pSFA), S ) were also water (pSW), and methylene glycol (pMG 1 9 taken from Albert et al. The vapor pressure of 1-butanol (pS1B) was taken from a technical data sheet from BASF.19 The vapor pressure data (as parameters of the Antoine equation) are listed in Table 2. The activity coefficients were calculated according to the UNIFAC model. Formaldehyde, water, methylene glycol, 1-butanol, and hemiformal were treated as single UNIFAC groups. Poly(oxymethylene) glycols [HO(CH2O)nH] were assumed to consist of (n - 1) formaldehyde groups, one -CH2 group, and two HO- groups. Poly(oxymethylene) hemiformals [CH3(CH2)3O(CH2O)nH] were spilt into (n - 1) formaldehyde groups and one hemiformal group [CH3(CH2)3O(CH2O)H]. The group arrangement is also given in Table 3. The sizes and surface parameters of all groups are given in Table 4. Albert et al.9 used the same group assignment for the binary formaldehyde + water system. Therefore, UNIFAC parameters ai,j for interactions between groups (i, j) ) CH2O, H2O, HO(CH2O)H, OH, and CH2 were adopted from Albert et al.9 Many more group interactions parameters are required. Those between 1-butanol and water were assumed to

Ind. Eng. Chem. Res., Vol. 42, No. 7, 2003 1511 Table 1. Chemical Reaction Equilibrium Constants

Table 5. UNIFAC Interaction Parameters ai,j/K

ln K ) A + B/(T/K)

j i

reaction

A

B

source

vap KMG 1 vap KHF 1 KMG2 KMGn, n g 3 KHFn, n g 2

-16.984 -20.263 0.00498 0.01908 0.34739

5233.2 7368.3 869.5 544.5 -605.7

Kogan18 Hall and Piret17 Albert et al.9 Albert et al.9 this work

Table 2. Antoine Coefficients for Pure-Component Vapor Pressures ln(pSi /kPa) ) A + B/[(T/K) + C] component

A

B

C

source

formaldehyde water methylene glycol 1-butanol hemiformal

14.4625 16.2886 19.5527 15.2021 18.7262

-2204.13 -3816.44 -6189.19 -3138.95 -6505.73

-30.00 -46.13 -9.15 -94.255 0.00

Albert et al.9 Albert et al.9 Albert et al.9 BASF19 this work

Table 3. Division of Components into UNIFAC Groups component

UNIFAC group(s)

formaldehyde water methylene glycol poly(oxymethylene) glycol 1-butanol hemiformal poly(oxymethylene) hemiformal

1 CH2O 1 H2O 1 HO(CH2O)H (n - 1) CH2O, 1 CH2, 2 HO CH3(CH2)3OH CH3(CH2)3O(CH2O)H CH3(CH2)3O(CH2O)H, (n - 1) CH2O

ng2 ng2

Table 4. UNIFAC Size and Surface Parameters group

no.

r

q

CH2O H2O HO(CH2O)H HO-CH2 CH3(CH2)3OH CH3(CH2)3O(CH2O)H

1 2 3 4 5 6 7

0.9183 0.9200 2.6744 1.0000 0.6744 3.4543 4.3726

0.780 1.400 2.940 1.200 0.540 3.052 3.832

depend on temperature and were fitted to literature data for the liquid-liquid equilibrium of the binary water + 1-butanol system.14,20,21 To reduce the number of adjustable parameters, some interaction parameters were neglected (i.e., both UNIFAC group interaction parameters were set to zero), including all parameters between formaldehyde on one side and 1-butanol and hemiformal on the other side; all parameters between 1-butanol on one side and methylene glycol, the HOgroup, and the -CH2 group on the other side; and the interaction parameters between hemiformal and the -CH2 group. With these simplifications, the remaining, unknown model parameters are as follows: the chemical reaction equilibrium constants for the formation of poly(oxymethylene) hemiformals (KHFn, n g 2); the vapor presS ); and eight UNIFAC paramsure of hemiformal (pHF 1 eters for binary interactions between hemiformal on side and H2O, methylene glycol, the HO- group, and 1-butanol on the other side. These parameters were fitted simultaneously to the new NMR data for the chemical reaction equilibrium (specification in a single liquid phase) and the liquidliquid equilibrium data of the ternary formaldehyde + water + 1-butanol system. This parameter adjustment process started with the determination of first estimates for the chemical equilibrium constants for poly(oxymethylene) hemiformal formation from the NMR data, followed by first estimates for the vapor pressure of

1

2

3

4

5

6

7

1 774.81 189.21 237.70 83.36 0.00 0.00 2 -142.35 189.52 -229.10 300.00 a2,6 312.34 3 59.20 -191.82 -229.10 300.00 0.00 4.59 4 28.06 353.50 353.50 156.40 0.00 615.46 5 251.50 1318.00 1318.00 986.50 0.00 0.00 6 0.00 a6,2 0.00 0.00 0.00 17.40 7 0.00 -66.02 4.08 3.90 0.00 -36.08 ai,j/K ) A + B(T/K) function

A

B

a2,6 a6,2

-674.46 531.75

3.1628 -1.8132

hemiformal and the UNIFAC interaction parameters from the liquid-liquid equilibrium data. Finally, these first estimates were used as initial values for a simultaneous adjustment of all parameters to NMR and phase equilibrium data. The final results are given in S ), and Table 5 Table 1 (KHFn, n g 2), Table 2 (pHF 1 (UNIFAC interaction parameters). As hemiformal does not exist as a pure compound, its vapor pressure is not directly accessible by experiments. The vapor pressure of hemiformal is required vap to KHF1 (cf. only to convert the (first estimate) for KHF 1 eq 7). Therefore, fitting the hemiformal vapor pressure to NMR data as well as liquid-liquid equilibrium data is essentially an adjustment to the experimental information. The quality of predictions for the vapor-liquid equilibrium data of, for example, the binary formaldehyde + 1-butanol system is still open, as experimental data are not available. From NMR spectroscopic investigations of chemical reaction equilibrium, true species composition data for the binary formaldehyde-1-butanol system were used for the simultaneous parameter determination described above. The peak areas determined by NMR spectroscopy were converted into concentrations, assuming that the peak areas are proportional to the numbers of the corresponding groups and that the constant of proportionality is the same for all NMR-active -CH2 groups. However, because no peak due to formaldehyde monomers is present and because it is not possible to distinguish between the peaks caused by poly(oxymethylene) glycols and poly(oxymethylene) hemiformals containing more than four formaldehyde groups, some additional assumptions were required to qualitatively ascribe the peak areas to the concentrations of formaldehyde oligomers. As described previously by Hahnenstein et al.5 and applied by Albert et al.,8 the experimental results for the peak areas obtained in investigations of the formaldehyde + 1-butanol system were used to estimate (for a given temperature and average formaldehyde concentration) a pseudo-chemical equilibrium constant, Kx,HFi, for chemical reaction IV. It was assumed that this constant does not depend on the number of formaldehyde groups in the poly(oxymethylene) hemiformal. These results were then used (instead of the direct NMR data), along with the experimental results for the liquid-liquid equilibrium, to determine the true chemical reaction equilibrium constants. In the modeling of the liquid-liquid equilibrium data, poly(oxymethylene) glycols with more than 16 formaldehyde segments and poly(oxymethylene) hemiformals with more than 10 formaldehyde segments were neglected. However, the quality of the experimental

1512


Table 6. Chemical Equilibrium (Specification) for the Formaldehyde + 1-Butanol System: Comparison of Model Calculations with Experimental Dataa T (K)

x˜ FA (mol‚mol-1)

278.15

0.5446 0.3416 0.1959 0.5446 0.3416 0.1959 0.5351 0.5282 0.5282 0.2495 0.3939 0.5282 0.2495 0.3939 0.4538 0.5282 0.5446 0.3416 0.1959 0.2495 0.3939 0.5282 0.2495 0.3939 0.4538 0.5282 0.2495 0.3939 0.2495 0.3939 0.4538 0.5282

298.15

323.15

348.15

a

xHF1 (mol‚mol-1) exp cal 0.4897 0.4053 0.2171 0.4581 0.3954 0.2184 0.4627 0.4698 0.4825 0.2843 0.4331 0.4789 0.2825 0.4218 0.4504 0.4773 0.4528 0.3810 0.2162 0.2747 0.4181 0.4478 0.2768 0.4272 0.4434 0.4524 0.2687 0.4002 0.2680 0.4068 0.4388 0.4293

0.4783 0.4004 0.2233 0.4595 0.3885 0.2203 0.4630 0.4651 0.4651 0.2854 0.4337 0.4651 0.2854 0.4337 0.4647 0.4651 0.4387 0.3749 0.2166 0.2787 0.4159 0.4438 0.2787 0.4159 0.4436 0.4438 0.2721 0.3996 0.2721 0.3996 0.4247 0.4247

∆xHF1 (%) -2.3 -1.2 2.8 0.3 -1.7 0.9 0.1 -1.0 -3.6 0.4 0.1 -2.9 1.0 2.8 3.2 -2.6 -3.1 -1.6 0.2 1.5 -0.5 -0.9 0.7 -2.7 0.1 -1.9 1.3 -0.1 1.5 -1.8 -3.2 -1.1


0.1757 0.0486 0.0095 0.1745 0.0522 0.0108 0.1692 0.1652 0.1652 0.0209 0.0793 0.1652 0.0209 0.0793 0.1170 0.1652 0.1726 0.0560 0.0123 0.0234 0.0829 0.1640 0.0234 0.0829 0.1191 0.1640 0.0255 0.0854 0.0255 0.0854 0.1200 0.1620

∆xHF2 (%) -0.3 3.3 -21. 0.01 4.0 -7.0 -0.1 -0.1 -0.3 -2.2 -0.3 -0.3 -5.3 -3.3 -1.4 -0.3 -0.9 2.7 -1.8 -6.2 0.2 -0.3 -3.4 2.6 -0.3 -0.5 -5.7 -0.8 -6.7 0.7 0.3 -0.7


0.0646 0.0059 0.0004 0.0663 0.0070 0.0005 0.0618 0.0587 0.0587 0.0015 0.0145 0.0587 0.0015 0.0145 0.0295 0.0587 0.0679 0.0084 0.0007 0.0020 0.0165 0.0606 0.0020 0.0165 0.0320 0.0606 0.0024 0.0182 0.0024 0.0182 0.0339 0.0618

∆xHF3 (%) 1.7 7.4 -42. -0.3 9.7 -12. -0.3 0.8 3.1 -4.0 -0.7 2.4 -9.7 -8.8 -5.9 2.2 1.5 7.1 -0.5 -14. 0.7 0.3 -6.7 7.9 -0.4 1.1 -11. -1.5 -14. 3.0 3.7 -0.5

From NMR spectroscopy.

data does not allow any distinction to be made between nine different chemical reaction constants (KHF2, ..., KHF10). Therefore, sensitivity studies were performed to determine the optimum number of different chemical reaction equilibrium constants. It was found that a single constant was sufficient, i.e.

KHF2 ) KHF3 ) ‚‚‚ ) KHF9 ) KHF10

(12)

Thus, the thermodynamic model for describing the liquid-phase properties of the formaldehyde + 1-butanol system is somewhat simpler than that for the formaldehyde + water system. In the latter system, two different values for the chemical reaction equilibrium constants of poly(oxymethylene) glycol formation were used (KMG2 and KMG3 ) KMG4 ) KMG5 ) ‚‚‚ ) KMG15 ) KMG16). Comparison with Experimental Results Chemical Equilibrium (Specification). The new experimental data from NMR spectroscopic investigations are compared to the correlation results in Table 6, as well as in Figures 2-5 (formaldehyde + 1-butanol) and Table 7(formaldehyde + water + 1-butanol). Table 6 gives the experimental results for the mole fractions of hemiformal (HF1) and the two oligomers HF2 (containing two formaldehyde segments) and HF3 (containing three formaldehyde segments) in liquid mixtures of formaldehyde and 1-butanol at 278, 298, 323, and 348 K as measured by NMR spectroscopy in comparison to the correlation. The experimental data cover stoichiometric formaldehyde concentrations be-

tween 20 and 55 mol %. In these solutions, formaldehyde is predominantly present as hemiformal. The relative deviations between the calculated and experimental mole fractions exceed 4% only when the mole fraction is below 3%. Relative deviations of more than 10% are observed only when the mole fraction is below 1%. Table 7 gives, in an analogous manner, the experimental data for the concentrations of eight oligomers: four oligomers containing formaldehyde and water, as well as the analogous four oligomers containing formaldehyde and 1-butanol. Fifteen NMR spectroscopic investigations were performed at temperatures between 278 and 348 K with aqueous solutions containing formaldehyde and butanol (stoichiometric mole fractions between 30 and 40 mol % and between 25 and 37 mol %, respectively). In such solutions, formaldehyde is predominantly present as hemiformal (HF1). The relative deviations between the calculated and experimental mole fractions of hemiformal are below 5%. About as much formaldehyde is converted to HF2 as to methylene glycol (MG1), but the concentrations of these species are only about 5 mol %. The relative deviations between the NMR data and the calculations for these concentration is generally better than 10%, particularly at higher formaldehyde concentrations. However, the deviations might increase to more then 20% at low formaldehyde concentrations. The mole fractions of the higher oligomers decrease by approximately a factor of 3 (for MGi) and 4 (for HFi) as the number of formaldehyde groups in the oligomers increases from i to (itl). There is no systematic deviation between experiment and calcula-

Ind. Eng. Chem. Res., Vol. 42, No. 7, 2003 1513 Table 7. Chemical Reaction Equilibrium (Specification) in Liquid Phases of the Formaldehyde + Water + 1-Butanol System: Comparison of Model Calculations with Experimental NMR Data Poly(oxyl methylene) Glycols T (K) 278.15 298.15 323.15

348.15

x˜ FA x˜ 1B (mol‚mol-1) (mol‚mol-1) 0.4063 0.3168 0.2923 0.4063 0.3168 0.2923 0.4063 0.3168 0.2923 0.4141 0.3212 0.2949 0.4141 0.3212 0.2949

0.3567 0.2781 0.2566 0.3567 0.2781 0.2566 0.3567 0.2781 0.2566 0.3699 0.2870 0.2635 0.3699 0.2870 0.2635

xMG1 (mol‚mol-1) exp cal 0.0181 0.0336 0.0314 0.0253 0.0381 0.0388 0.0269 0.0448 0.0411 0.0244 0.0388 0.0482 0.0227 0.0404 0.0413

∆xMG1 (%)

0.0249 0.0398 0.0430 0.0253 0.0404 0.0436 0.0269 0.0425 0.0458 0.0243 0.0409 0.0445 0.0266 0.0440 0.0477

37 18 37 -0.1 5.9 12 0.1 -5.1 11 -0.5 5.4 -7.7 17 8.9 15


∆xMG2 (%)

0.0145 120 0.0199 26 0.0203 62 0.0126 5 0.0177 -3.2 0.0182 4.1 0.0124 4.6 0.0177 -23 0.0183 5.7 0.0112 5.6 0.0170 -1.1 0.0177 -30 0.0123 52 0.0187 12 0.0195 23


0.0052 0.0060 0.0058 0.0041 0.0049 0.0048 0.0039 0.0048 0.0047 0.0035 0.0046 0.0045 0.0039 0.0052 0.0051

∆xMG3 (%) 248 28 80 7.8 -15 -7.5 4.9 -42 -7.9 8.8 -13 -51 86 3.6 16


0.0019 0.0018 0.0016 0.0013 0.0014 0.0013 0.0012 0.0013 0.0012 0.0011 0.0012 0.0012 0.0012 0.0014 0.0013

∆xMG4 (%) 370 29 105 11 -28 -21 10. -55 -19 8.3 -22 -65 148 -4.6 12

Poly(oxymethylene) Hemiformals T (K) 278.15 298.15 323.15

348.15

x˜ FA x˜ 1B (mol‚mol-1) (mol‚mol-1) 0.4063 0.3168 0.2923 0.4063 0.3168 0.2923 0.4063 0.3168 0.2923 0.4141 0.3212 0.2949 0.4141 0.3212 0.2949

0.3567 0.2781 0.2566 0.3567 0.2781 0.2566 0.3567 0.2781 0.2566 0.3699 0.2870 0.2635 0.3699 0.2870 0.2635

xHF1 (mol‚mol-1) exp cal 0.2980 0.2018 0.1801 0.2876 0.1933 0.1717 0.2754 0.1822 0.1644 0.2894 0.1923 0.1619 0.2782 0.1851 0.1632

0.2960 0.1995 0.1764 0.2837 0.1922 0.1705 0.2688 0.1816 0.1611 0.2826 0.1887 0.1660 0.2678 0.1771 0.1554

∆xHF1 (%) -0.7 -1.2 -2.0 -1.3 -0.6 -0.7 -2.4 -0.3 -2.0 -2.4 -1.9 2.5 -3.8 -4.3 -4.8


∆xHF2 (%)

0.0883 -7.7 0.0499 -7.5 0.0416 -16 0.0906 -0.6 0.0526 2.2 0.0442 -1.1 0.0906 -0.6 0.0531 15 0.0447 -1.1 0.0949 -0.6 0.0550 1.3 0.0459 27 0.0933 -4.1 0.0537 -2.2 0.0446 -5.9


∆xHF3 (%)

0.0263 -14 0.0125 -13 0.0098 -28 0.0289 0.4 0.0144 5.1 0.0115 -1.1 0.0305 1.4 0.0155 31 0.0124 0.1 0.0319 1.3 0.0161 4.9 0.0127 59 0.0325 -4.4 0.0163 -0.2 0.0128 -7.2


∆xHF4 (%)

0.0079 -21 0.0031 -18 0.0023 -38 0.0092 1.4 0.0039 6.6 0.0030 -0.9 0.0103 2.8 0.0045 51 0.0034 1.4 0.0107 3.1 0.0047 8.9 0.0035 95 0.0113 -4.8 0.0049 2.7 0.0037 -8.1

Figure 2. Specification in liquid mixtures of formaldehyde and 1-butanol at 278 K: experimental results (O, NMR spectroscopy) and model calculations (solid lines).


tion for these mole fractions, but because the concentrations are sometimes very small, the relative deviations can rise to more than 50%, but they are never much larger than the experimental uncertainty. Liquid-Liquid Equilibrium. The UNIFAC results for the liquid-liquid equilibrium of the binary, nonreactive system water + 1-butanol are shown in Table 8 and Figure 6. The model represents the experimental results for the mole fraction of butanol in the coexisting phases with relative deviations of about 2% at temper-

atures up to about 350 K, i.e., in the range of temperatures of interest in the present work. However, it is obvious that the influence of temperature on the miscibility gap is not sufficiently well described at higher temperatures, resulting in an upper critical end-point temperature for the liquid-liquid equilibrium that is much too large. A better description at higher temperatures would have required a more complicated expression for the influence of temperature on the interaction parameters.

1514

Ind. Eng. Chem. Res., Vol. 42, No. 7, 2003 Table 8. Liquid-Liquid Equilibrium of the Water + 1-Butanol System: Comparison between Calculated and Experimental Data T (K)



x1B′ (mol‚mol-1) exp cal

273.15 0.0271 0.0242 278.15 0.0250 0.0227 283.15 0.0230 0.0215 0.0232 0.0215 288.15 0.0213 0.0204 293.15 0.0197 0.0195 0.0202 0.0195 0.0210 0.0195 298.15 0.0189 0.0188 0.0185 0.0188 0.0189 0.0188 303.15 0.0179 0.0181 0.0182 0.0181 308.15 0.0175 0.0176 313.15 0.0167 0.0171 0.0169 0.0171 0.0166 0.0171 323.15 0.0163 0.0164 0.0165 0.0164 333.15 0.0162 0.0159 0.0167 0.0159 0.0165 0.0159 343.15 0.0166 0.0156 0.0172 0.0156 353.15 0.0175 0.0155 0.0177 0.0155 363.15 0.0195 0.0155 373.15 0.0232 0.0156 383.15 0.0295 0.0158 393.15 0.0440 0.0162 398.15 0.0710 0.0164

∆x1B′′ (%) -11 -9.2 -6.6 -7.5 -4.0 -0.8 -3.1 -6.8 -0.7 1.3 -0.4 1.3 -0.3 0.5 2.5 1.4 3.0 0.6 -0.7 -1.8 -4.6 -3.5 -6.0 -9.4 -12 -12 -22 -32 -46 -63 -77

x1B (mol‚mol-1) exp cal 0.5112 0.4989 0.5061 0.4981 0.4952 0.4980 0.4919 0.4914 0.4888 0.4942 0.4906 0.4861 0.4834 0.4767 0.4717 0.4715 0.4702 0.4562 0.4568 0.4381 0.4401 0.4391 0.4152 0.4190 0.3890 0.4030 0.3600 0.3290 0.2875 0.2180 0.1490

∆x1B (%)

ref

0.5140 0.6 20 0.5110 2.4 21 0.5071 0.2 20 0.5071 1.8 21 0.5023 1.4 21 0.4969 -0.2 20 0.4969 1.0 21 0.4969 1.1 21 0.4910 0.4 21 0.4910 -0.6 21 0.4910 0.1 this work 0.4846 -0.3 20 0.4846 0.2 21 0.4777 0.2 21 0.4705 -0.3 20 0.4705 -0.2 21 0.4705 0.1 14 0.4551 -0.2 20 0.4551 -0.4 21 0.4388 0.2 20 0.4388 -0.3 21 0.4388 -0.1 14 0.4218 1.6 20 0.4218 0.7 21 0.4042 3.9 20 0.4042 0.3 21 0.3863 7.3 20 0.3680 12 20 0.3496 22 20 0.3310 52 20 0.3217 116 20

maximum formaldehyde concentrations in the coexisting phases was about 14 mol % (in the aqueous phase) and about 25 mol % in the butanol-rich liquid phase. The model nicely describes the ternary liquid-liquid phase equilibrium, but the formaldehyde concentration is underestimated in the aqueous phase and overestimated in the organic phase, i.e., the slopes of a liquidliquid tie lines in Figures 7-9 are somewhat too large. Conclusion

Figure 6. Liquid-liquid phase equilibrium of the binary system water + 1-butanol: experimental results (0, Lavrova and Lesteva;14 ], v. Erichsen;20 3, Sœrensen and Arlt21) and model calculations (solid lines).

The new liquid-liquid phase equilibrium data for the formaldehyde + water + 1-butanol system are given in Table 9 and Figures 7-9. The stoichiometric formaldehyde concentration in the butanol-rich phase is always higher than that in the coexisting aqueous phase. The miscibility gap decreases with increasing formaldehyde concentration, resulting in a closed miscibility gap. The

A thermodynamic model for the liquid-liquid phase equilibrium of the formaldehyde + water + 1-butanol system is presented. The model takes into account the rather complex chemical equilibrium caused by chemical reactions of formaldehyde with water as well as with butanol. Information on the chemical reaction equilibrium is obtained from NMR spectroscopic investigations. Physical interactions also have an essential influence on the partitioning of formaldehyde between the coexisting phases and were therefore also taken into account (through the UNIFAC model). Chemical reaction equilibrium constants for the formation of poly(oxymethylene) glycols were adopted from earlier work on aqueous solutions of formaldehyde. New NMR spectroscopic data were used to determine the chemical reaction equilibrium constants for the formation of oligomers of formaldehyde and butanol [i.e., poly(oxymethylene) hemiformals]. Although the concentration of formaldehyde monomers is very small and can be neglected in the mass balances in most cases, formaldehyde monomers play an important role, as their concentration governs the partitioning of formaldehyde between poly(oxymethylene) glycols and poly(oxymethylene) hemi-

Ind. Eng. Chem. Res., Vol. 42, No. 7, 2003 1515 Table 9. Liquid-Liquid Equilibrium of the Formaldehyde + Water + 1-Butanol System: Comparison between Calculated and Experimental Data T (K) 298.15

313.15

333.15

x˜ FA′ (mol‚mol-1) exp cal 0.0000 0.0073 0.0163 0.0246 0.0393 0.0849 0.0664 0.1036 0.1347 0.1422 0.0000 0.0037 0.0077 0.0160 0.0272 0.0351 0.0484 0.0517 0.0667 0.0889 0.0000 0.0041 0.0082 0.0182 0.0302 0.0539 0.0588 0.0732 0.0928

0.0000 0.0074 0.0154 0.0232 0.0358 0.0794 0.0612 0.0986 0.1311 0.1391 0.0000 0.0028 0.0056 0.0141 0.0234 0.0312 0.0424 0.0455 0.0588 0.0824 0.0000 0.0034 0.0069 0.0157 0.0254 0.0479 0.0519 0.0673 0.0842

∆x˜ FA′ (%) 1.4 -5.5 -5.7 -8.9 -6.5 -7.8 -4.8 -2.7 -2.2 -24 -27 -12 -14 -11 -12 -12 -12 -7.3 -17 -16 -14 -16 -11 -12 -8 -9

x˜ 1B′ (mol‚mol-1) exp cal 0.0189 0.0181 0.0183 0.0181 0.0206 0.0200 0.0193 0.0229 0.0317 0.0338 0.0166 0.0166 0.0166 0.0167 0.0172 0.0174 0.0180 0.0182 0.0188 0.0220 0.0165 0.0163 0.0164 0.0168 0.0171 0.0194 0.0196 0.0226 0.0250

∆x˜ 1B′ (%)

0.0188 0.0195 0.0186 0.0189 0.0189 0.0223 0.0206 0.0256 0.0334 0.0364 0.0171 0.0168 0.0165 0.0171 0.0174 0.0182 0.0188 0.0191 0.0206 0.0247 0.0159 0.0161 0.0164 0.0170 0.0180 0.0210 0.0215 0.0244 0.0276

Figure 7. Liquid-liquid phase equilibrium of the ternary system formaldehyde + water + 1-butanol at 298 K: experimental results (0) and correlations (O).


formals. Therefore, predictions for the specification of formaldehyde in aqueous solutions of butanol from binary data alone (formaldehyde + water, formaldehyde + butanol, or water + butanol) are not reliable. This problem can be solved when the chemical reaction equilibrium constants for the formation of poly(oxy-

-0.5 7.7 1.6 4.4 -8.3 12 6.7 12 5.4 7.7 3.0 1.2 -0.6 2.4 1.2 4.6 4.4 5.0 9.6 12 -3.6 -1.2 0.0 1.2 5.3 8.3 9.7 8.0 10

x˜ FA′′ (mol‚mol-1) exp cal 0.0000 0.0539 0.1071 0.1363 0.1725 0.2319 0.2162 0.2409 0.2388 0.2352 0.0000 0.0292 0.0540 0.0966 0.1330 0.1534 0.1785 0.1836 0.2010 0.2195 0.0000 0.0272 0.0497 0.0914 0.1241 0.1691 0.1745 0.1908 0.1983

0.0000 0.0525 0.1083 0.1404 0.1822 0.2411 0.2264 0.2478 0.2431 0.2334 0.0000 0.0304 0.0568 0.1016 0.1415 0.1640 0.1903 0.1956 0.2137 0.2315 0.0000 0.0282 0.0517 0.0975 0.1327 0.1798 0.1852 0.1997 0.2042

∆x˜ FA′′ (%) -2.6 1.1 3.0 5.6 4.0 4.7 2.9 1.8 -0.8 4.1 5.2 5.2 6.4 6.9 6.6 6.5 6.3 5.5 3.7 4.0 6.7 6.9 6.3 6.1 4.7 3.0

x˜ 1B′′ (mol‚mol-1) exp cal 0.4906 0.4668 0.4044 0.3677 0.3149 0.2221 0.2586 0.1941 0.1457 0.1345 0.4702 0.4421 0.4196 0.3762 0.3372 0.3117 0.2830 0.2756 0.2485 0.2089 0.4391 0.4113 0.3924 0.3453 0.3141 0.2553 0.2469 0.2174 0.1865

0.4910 0.4529 0.4049 0.3755 0.3296 0.2245 0.2648 0.1937 0.1449 0.1272 0.4705 0.4474 0.4261 0.3893 0.3507 0.3270 0.2926 0.2847 0.2539 0.2133 0.4388 0.4181 0.3999 0.3601 0.3245 0.2623 0.2519 0.2201 0.1806

∆x˜ 1B′′ (%) 0.1 -3.0 0.1 2.1 4.7 1.1 2.4 -0.2 -0.6 -5.4 0.1 1.2 1.6 3.5 4.0 4.9 3.4 3.3 2.2 2.1 -0.1 1.7 1.9 4.3 3.3 2.7 2.0 1.2 -3.2


methylene) hemiformals are determined from experimental data for the specification in the binary system formaldehyde + 1-butanol as well as in the ternary system formaldehyde + water + 1-butanol. Furthermore, physical interactions between groups present only in the ternary mixture are important. These parameters can only be determined from experimental data of the ternary system. Experimental results from both NMR spectroscopic and liquid-liquid phase equilibrium investigations were used to determine the model parameters. The model reliably describes the phase equilibrium and the specification of the formaldehyde + water + 1-butanol system at temperatures from 298 to 333 K. Nomenclature A, B ) parameters in equations for the chemical reaction equilibrium constant as well as for the influence of temperature on the UNIFAC interaction parameters A, B, C ) parameters in the Antoine vapor-pressure equation

1516


ai,j ) UNIFAC parameter for interactions between groups i and j cal ) calculated result exp ) experimental result FA ) formaldehyde HF1 ) hemiformal (reaction product of formaldehyde and 1-butanol) HFn ) poly(oxymethylene) hemiformal with n formaldehyde groups KHF1 ) chemical reaction equilibrium constant for the formation of HF1 vap KHF ) chemical reaction equilibrium constant for the 1 formation of HF1 in the vapor phase KHFn ) chemical reaction equilibrium constant for the formation of HFn KMG1 ) chemical reaction equilibrium constant for the formation of MG1 vap KMG ) chemical reaction equilibrium constant for the 1 formation of MG1 in the vapor phase KMGn ) chemical reaction equilibrium constant for the formation of MGn MG1 ) methylene glycol MGn ) poly(oxymethylene) glycol with n formaldehyde groups n ) number of formaldehyde segments in the oligomer ntotal ) total number of moles n˜ total ) total stoichiometric number of moles pSi ) vapor pressure of pure component i r ) UNIFAC size parameter 1B ) 1-butanol p0 ) standard pressure (0.1 MPa) q ) UNIFAC surface parameter T ) absolute temperature W ) water xi ) true mole fraction of species i x˜ i ) stoichiometric mole fraction of component i

(3) Hasse, H.; Maurer, G. Kinetics of the Poly(oxymethylene) Glycol Formation in Aqueous Formaldehyde Solutions. Ind. Eng. Chem. Res. 1991, 30, 2195-2200.

Greek Letters

(14) Lavrova, O. A.; Lesteva, T. M. Liquid-Liquid Phase Equilibria in Formaldehyde-Water-Alcohol Systems. II. Systems with Butanol, Hexanol, and Cyclohexanol. Zh. Fiz. Khim. 1976, 50, 1347.

∆z ) relative deviation between experimental and calculated property z γi ) activity coefficient of species i (on a mole fraction scale) normalized according to Raoult’s law Superscripts ′ ) aqueous phase ′′ ) organic phase Subscripts FA ) formaldehyde 1B ) 1-butanol HF1 ) hemiformal (reaction product of formaldehyde and 1-butanol) HFn ) poly(oxymethylene) hemiformal with n formaldehyde groups i ) species/component i MG1 ) methylene glycol MGn ) poly(oxymethylene) glycol with n formaldehyde groups W ) water

Literature Cited (1) Maurer, G. Vapor-Liquid Equilibrium of Formaldehydeand Water-Containing Multicomponent Mixtures. AIChE J. 1986, 32, 932-948. (2) Hasse, H. Dampf-Flu¨ssigkeits-Gleichgewichte, Enthalpien und Reaktionskinetik in formaldehydhaltigen Mischungen. Ph.D. Dissertation, University of Kaiserslautern, Kaiserslautern, Germany, 1990.

(4) Hahnenstein, I.; Hasse, H.; Liu, Y.-Q.; Maurer, G. Thermodynamic Properties of Formaldehyde Containing Mixtures for Separation Process Design. AIChE Symp. Ser. 1994, 90, 141-157. (5) Hahnenstein, I.; Hasse, H.; Kreiter, C. G.; Maurer, G. 1Hand 13C-NMR-Spectroscopic Study of Chemical Equilibria in Solutions of Formaldehyde in Water, Deuterium Oxide, and Methanol. Ind. Eng. Chem. Res. 1994, 33, 1022-1029. (6) Hahnenstein, I.; Hasse, H.; Albert, M.; Kreiter, C. G.; Maurer, G. NMR Spectroscopic and Densimetric Study of Reaction Kinetics of Formaldehyde Polymer Formation in Water, Deuterium Oxide, and Methanol. Ind. Eng. Chem. Res. 1995, 34, 440-450. (7) Albert. M. Thermodynamische Eigenschaften formaldehydhaltiger Mischungen. Ph.D. Dissertation, University of Kaiserslautern, Kaiserslautern, Germany, 1998. (8) Albert, M.; Coto García, B.; Kreiter, C. G.; Maurer, G. Vapor-Liquid and Chemical Equilibria of Formaldehyde-Water Mixtures. AIChE J. 1999, 45, 2024-2033. (9) Albert, M.; Coto García, B.; Kuhnert, Ch.; Peschla, R.; Maurer, G. Vapor-Liquid Equilibria for Aqueous Solutions of Formaldehyde and Methanol. AIChE J. 2000, 46, 1676-1687. (10) Albert, M.; Hahnenstein, I.; Hasse, H.; Maurer, G. VaporLiquid and Liquid-Liquid Equilibrium in Aqueous and Methanolic Solutions of Methylal. J. Chem. Eng. Data 2001, 46, 897-903. (11) Maiwald, M.; Fischer, H. H.; Ott, M.; Peschla, R.; Kuhnert, Ch.; Kreiter, C. G.; Maurer, G.; Hasse, H. Quantitative NMR Spectroscopy of Complex Liquid Mixtures: Methods and Results for Chemical Equilibria in Formaldehyde-Water-Methanol at Temperatures up to 383 K. Ind. Eng. Chem. Res. 2003, 42 (2), 259266. (12) Balashov, A. L.; Danov, S. M.; Golovkin, A. Yu.; Krasnov, V. L.; Ponomarev, A. N.; Borisova, I. A. Equilibrium mixture of polyoxymethylene glycols in concentrated aqueous formaldehyde solutions. Russ. J. Appl. Chem. 1996, 69 (2), 190-192. (13) Gu¨nther, H. NMR-Spektroskopie; Georg Thieme Verlag: Stuttgart, Germany, 1973.

(15) Peschla, R. Untersuchungen zum Stofftransport u¨ber Flu¨ssig-Flu¨ssig-Phasengrenzfla¨chen formaldehydhaltiger, chemisch reagierender Systeme. Ph.D. Dissertation, University of Kaiserslautern, Kaiserslautern, Germany, 1999. (16) Fredenslund, Aa.; Gmehling, J.; Rasmussen, P. VaporLiquid Equilibria Using UNIFAC, A Group Contribution Method; Elsevier: Amsterdam, 1977. (17) Hall, M. W.; Piret, E. L. Distillation principles of formaldehyde solutions. Ind. Eng. Chem. 1949, 41, 1277-1286. (18) Kogan, L. V. State of the Vapour Phase above Solutions of Formaldehyde in Water and Methanol. Zh. Prikl. Khim. 1979, 52, 2722-2725. (19) Industriechemikalien Marketing Weichmacher und Lo¨semittel; Technisches Merkblattsn-Butanol; BASF AG: Ludwigshafen, Germany, 1991. (20) v. Erichsen, L. Die kritischen Lo¨sungstemperaturen in der homologen Reihe der prima¨ren normalen Alkohole. Brennst. Chem. 1952, 33, 166-172. (21) Sœrensen, J. M.; Arlt, W. Liquid-Liquid Equilibrium Data Collection, Binary Systems; DECHEMA Chemistry Data Series, DECHEMA Deutsche Gesellschaft fu¨r Chemisches Apparatewesen: Frankfurt am Main, Germany, 1979; Vol. V, Part 1, pp 236239.

Received for review September 23, 2002 Revised manuscript received January 2, 2003 Accepted January 7, 2003 IE020743O

Chemical Equilibrium and LiquidâLiquid Equilibrium in Aqueous

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