Application of the Aldolization Reaction in Separating the Mixture of

Article pubs.acs.org/IECR

Application of the Aldolization Reaction in Separating the Mixture of Ethylene Glycol and 1,2-Butanediol: Thermodynamics and New Separation Process Hong Li,†,‡,§,⊥ Weijin Huang,†,§,⊥ Xingang Li,†,‡,§ and Xin Gao*,†,‡,§ †

School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China National Engineering Research Center of Distillation Technology, Tianjin 300072, China § Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, China ‡

ABSTRACT: The separation of ethylene glycol (EG) and 1,2butanediol (1,2-BDO) azeotrope is a key technical problem in the synthesis process of EG via dimethyl oxalate (DMO) from syngas. On the basis of systematic investigation, aldolization is expected to be the solution to this industrial problem. Thus, the essential thermodynamics data were determined and correlated well by the corresponding thermodynamic equation, including the vapor pressure of 2-methyl-1,3-dioxolane (2MD) and 4-ethyl-2-methyl-1,3-dioxolane (4EMD), vapor−liquid equilibrium (VLE) data of binary mixture 2MD−4EMD at 101.3 kPa, and liquid−liquid equilibrium (LLE) data of binary system 4EMD−water at atmospheric conditions. The vapor−liquid−liquid equilibrium (VLLE) of binary system 4EMD−water has been successful predicted by LLE experimental data. Finally, the thermodynamics parameters were provided as a reference to design a separation process of the EG and 1,2-BDO mixture. The simulation and optimization results indicate that EG and 1,2BDO could been separated effectively, which presents the potential of applying aldolization in synthesis of EG basic coal.

1. INTRODUCTION Ethylene glycol (1,2-ethanediol, EG), as a significant organic chemical raw material, is mainly used in polyester manufacturing, antifreeze, and plasticizers. A way to produce and separate to acquire EG has attracted intense research interests, especially for fiber-grade EG. At present, a traditional industrial approach to producing EG is via ethylene oxide (EO) hydration.1 However, a lot of ethylene is consumed in this process, which is uneconomical. With the development of C1 chemistry, synthesis of EG via dimethyl oxalate (DMO) from syngas has attracted widespread attention2−5 as a new synthetic technique. It is considered as an alternative economical and energyefficient process.1 Unfortunately, some propanediols and butanediols are formed in the process owing to some undesirable Guerbet reactions.2 Among those glycols, it is difficult to separate the mixture of 1,2-butanediol (1,2-BDO) and EG, even using vacuum operation,6 because of their approximate boiling points and existing a minimum azeotrope.7 Therefore, in the synthesis process of EG via oxalate (DMO) form syngas, the column that removes the 1,2-BDO is very high (with 80 theoretical stages or more). Moreover, the high pressure drop caused by a mass of tower internals increases the temperature in the bottom, which is uninviting considering the heat sensitivity of EG. Besides, the energy consumption is very high due to a high reflux ratio, and about 10 wt % or more of the material has to be wasted accounting for 1−4 wt % 1,2BDO contained in industrial feeding. To solve this problem, © XXXX American Chemical Society

some available publications show the upsurge of interest in azeotropic distillation8−10 and extractive distillation.11−13 However, further research of low-cost and highly efficient separation processes of this mixture is still needed. A novel idea has been developed here. A mixture of 2-methyl-1,3-dioxolane (2MD) and 4-ethyl-2-methyl-1,3-dioxolane (4EMD) was obtained by the aldolization of a mixture of glycols and acetaldehyde and then separated by a distillation process. EG or 1,2-BDO was obtained naturally by hydrolysis of 2MD or 4EMD, respectively. If this idea could be adopted in the process of synthesis of EG basic coal, the 1,2-BDO removal column could distillate more product from the top, which could effectively reduce the reflux ratio and theoretical stages. In other words, it could reduce the energy consumption and the bottom temperature and increase the recovery of EG by recovered EG from the discharge distillation with aldolization. The phase equilibria, such as vapor + liquid or liquid + liquid equilibrium (VLE or LLE) data, are fundamental physicochemical properties for designing, modeling, simulating, and performing economic assessment of separating EG and 1,2BDO using the process presented above. Chopade et al.14 have measured the vapor pressure of 2MD ranging from 298 to 353 Received: June 28, 2016 Revised: August 17, 2016 Accepted: August 23, 2016

A

DOI: 10.1021/acs.iecr.6b02469 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research K, as well as the vapor + liquid + liquid equilibrium (VLLE) data for the binary systems 2MD + water at atmospheric pressure. However, VLE or VLLE data for the binary systems of 2MD + 4EMD and 4EMD + water are not available currently, and the vapor pressure of 4EMD over temperature has also not been reported. This study aims to develop an efficient method for separating an EG and 1,2-BDO mixture using an aldolization reaction with acetaldehyde. First, the isobaric VLE data of the mixture 2MD + 4EMD at 101.3 kPa, LLE data of the binary system 4EMD + water at atmospheric conditions, and the vapor pressures of these dioxolanes were systematically measured. The experimental VLE data were confirmed for thermodynamic consistency and correlated with the modeling equations NRTL15 and UNIQUAC.16 The experimental LLE data of the binary system 4EMD + water were correlated with the NRTL equation, and the VLLE data were predicted by using the NRTL parameters. Moreover, on the basis of these thermodynamics parameters, a novel separation process of the EG and 1,2-BDO mixture was proposed and optimized.

arrangement was described in detail by previous works.18−21 Thus, only a brief characterization is given in the following.

2. EXPERIMENTAL SECTION 2.1. Materials. The suppliers and specifications of the chemicals used in this research are listed in Table 1. Pure Table 1. Suppliers and Purity of the Used Chemicals chemical name ethanol acetic ether EG 1,2-BDO acetaldehyde distilled water 2MD 4EMD(cis/trans-) a

supplier Tianjin Guangfu Tianjin Guangfu Tianjin Guangfu J & K Scientific Ltd. Tianjin Guangfu Tianjin Longshunda prepared in lab prepared in lab

mass fraction purity

analysis method

0.998 0.998 0.995 0.980

GCa GCa GCa GCa

0.400b

GCa

0.997 0.998

GCa GCa

Figure 1. Double circulating equilibrium still and other device: (1) a precision mercury thermometer, (2) equilibrium still, (3) riser tube, (4) liquid sample connection, (5) liquid sample sump, (6) heating rod, (7) boiling chamber, (8) equilibrium chamber, (9) vapor (cooled to liquid) sample sump, (10) vapor (cooled to liquid) sample connection, (11) condenser, (12) Panasonic gas pressure sensor DP-101, (13) connected with a vacuum pump (with a buffer tank itself) or highpressure nitrogen, (14) a buffer tank, and (15) absorbent silicone.

The still was operated only with a small quantity of sample (about 40 mL). Both the condensed vapor and liquid phases were continuously circulated to provide intimate contact, which ensured that the thermodynamic equilibrium could be acquired rapidly. The still pressure was regulated by a pressure control system consisting of a vacuum pump, a buffer tank, and two valves and measured by a Panasonic gas pressure sensor (DP101) with a standard uncertainty of 0.1 kPa. The temperature was measured with a precise mercury-in-glass thermometer whose standard uncertainty is no more than 0.05 K. For the measurement of vapor pressures, 30 mL of pure 2MD or 4EMD was placed into the still, and then, the device was sealed. Subsequently, the still was evacuated to a proper degree of pressure and heated. The heating was controlled to ensure that the boiling was constant. When the thermodynamic equilibrium was built, the temperature and pressure were recorded at the same time. Through setting different still pressures as planned, all of the thermodynamic equilibrium temperatures could be measured following the steps above. When the pressure was under atmosphere, a vacuum pump was used; otherwise, a nitrogen cylinder was applied to guarantee that there would be a positive pressure in the still. To ensure the accuracy, all of the measurements were repeated. In the measurements of the isobaric VLE, about 40 mL of a liquid mixture of 2MD and 4EMD with a desired proportion was put into the still each time. In each experiment, equilibrium was reached when the temperature and pressure were maintained constant for 30 min or longer. Then, the condensed

GC: gas chromatography. bAqueous solution.

acetals 2MD and 4EMD are not available in commercial industry. Therefore, they were prepared in the laboratory using the method of Dhale et al.:17 Acetaldehyde was purified by a distillation device at first. Then, EG and 1,2-BDO were reacted with excess acetaldehyde in two round-bottom flasks. After that, excess acetaldehyde was removed from the reaction product by treatment with sodium bisulfite. Some potassium chloride was added before separating the organic and aqueous solution. The organic was dried by adding anhydrous sodium sulfate. Finally, 2MD or 4EMD was obtained by distillation. MS (mass spectrometry) and IR (infrared spectroscopy) spectra were used to confirm the acetals. The result showed that both the cis and trans isomers were formed in 4EMD, as shown below. Determined by gas chromatography, the mass purities of 2MD and 4EMD were greater than 0.997 and 0.998, respectively. The contained water was less than 0.0005 (in mass fraction) by Karl Fischer moisture titration. 2.2. Apparatus and Procedures. Vapor pressure and VLE data measurement. A double circulating equilibrium still (a modified Rose−Williams still) was used for the vapor pressure and the VLE data measurements; a graphical representation is shown in Figure 1. The experimental B


Article

Industrial & Engineering Chemistry Research

for water and 4EMD. To our knowledge, LLE data of only binary systems of 2MD + water have been presented in previous literature.14 Therefore, LLE data of 4EMD (1) + water (2) binary systems are presented in this work. LLE data were measured over a range of temperatures in a jacketed glass vessel containing a magnetic stirrer. The temperature was controlled by a circulating water bath whose temperature fluctuation could be maintained within ±0.3 K and measured using a mercury thermometer with an accuracy of 0.1 K. Because the influence of pressure in LLE is slight, the vessel was connected to the atmosphere directly without a pressure control system. The atmospheric pressure was measured by a precision aneroid barometer (DYM3 model) with an uncertainty of ±0.4 kPa. The liquid mixture consisting of about 20 mL of 4EMD and 20 mL of water was put into the vessel. Then, the temperature was adjusted to a certain value. The mixture was stirred vigorously for 4 h and then left standing for 7 h. The aqueous and organic phase samples were taken by syringe simultaneously. The samples became heterogeneous with temperature reduction; therefore, some ethanol was added to homogenize them for convenience in analysis. The water contained in these samples did not performed well in our GC analysis with a thermal conductivity detector (TCD). Therefore, the 4EMD and water contained in these samples were measured by GC and Karl Fischer moisture titration, respectively. The gas chromatography used was as above but equipped with a Wax column (30 m × 0.25 mm × 0.25 μm, Agilent). The injector and column temperatures were changed to 473.15 and 348.15 K. The injected sample was 0.3 μL. The mole fraction uncertainty of GC analyses was also ensured within ±0.001. The precision of the Karl Fischer moisture titration was 0.00025 g, which could ensure that the mole fraction uncertainty of water remained under ±0.001 easily.

vapor and liquid samples were taken out almost at the same time for GC analysis by a microsyringe. The temperature was recorded simultaneously. The compositions of the condensed vapor and liquid samples were analyzed on a gas chromatograph (PE, American) equipped with a HP-5 capillary column (30 m × 0.32 mm × 0.25 μm, Agilent) and a flame ionization detector (FID). Highpurity nitrogen (mass fraction 0.99999) was used as carrier gas with a rate of 1.0 mL/min. The hydrogen and air flow rates were 35 and 350 mL/min, respectively. The injector temperature was 433.15 K with a split ratio of 100:1. The column temperature was constant at 358.15 K. The detector temperature was 503.15 K. The injected volume of the samples was 0.2 μL. The analysis was performed at least three times for each sample to ensure that the mole fraction uncertainty was within ±0.001. The averaged data are recorded in tables herein. The performance of the experimental instruments was tested in our previous work by the binary system of benzene (1) + toluene (2) at 101.33 kPa.18 Here, we present the tested results of the binary system ethyl acetate (1) + ethanol (2) in Table 2 and Figure 2. These tests verified the reliability of the equilibrium instrument. Table 2. Experimental VLE Data for the Binary System Ethyl Acetate (1) + Ethanol (2) at 101.3 kPaa T/K

x1

y1

351.30 349.05 347.80 346.70 345.90 345.35 345.05 345.15 345.65 346.60 348.75 350.20

0.000 0.099 0.161 0.226 0.300 0.398 0.518 0.630 0.743 0.840 0.946 1.000

0.000 0.178 0.262 0.323 0.389 0.463 0.536 0.603 0.669 0.761 0.901 1.000

3. EXPERIMENTAL RESULTS AND DISCUSSION 3.1. Vapor Pressure. The experimental vapor pressure data of 2MD and 4EMD and pertinent results are given in Tables 3

a

Standard uncertainties u are u(T) = 0.05 K, u(p) = 0.1 kPa, and u(x1) = u(y1) = 0.001.

Table 3. Experimental Vapor Pressure Data of 2MDa

Figure 2. Plot of the x−y phase equilibrium for the ethyl acetate (1) + ethanol (2) system at 101.3 kPa: ■, experimental data in this work; Δ, work by Topphoff et al;22 , calculated data by the Wilson equation using Aspen Plus.

T/K

psexp/kPa

ΔTb/kPa

Δpb/kPa

311.65 319.25 325.80 329.85 336.25 340.85 344.15 347.35 350.15 352.70 355.25 355.95 357.15 359.50 362.30 364.90

18.2 25.6 34.0 40.1 51.5 61.1 69.0 77.2 85.3 93.1 101.4 103.6 107.9 116.3 127.3 138.2

0.02 0.07 −0.04 −0.04 −0.02 0.03 0.00 0.04 −0.02 −0.03 −0.03 0.03 −0.01 0.04 0.01 −0.02 0.03 0.04

−0.02 −0.07 0.06 0.06 0.04 −0.07 0.01 −0.12 0.06 0.10 0.09 −0.09 0.03 −0.13 −0.02 0.06 0.06 0.08

ax = sx =

Standard uncertainties u are u(T) = 0.05 K and u(ps) = 0.1 kPa. bΔT = Texp − Tcal and Δ = psexp − pscal.

a

Collection of LLE Data. Binary systems containing water and 2MD are not homogeneous in all proportions; the same is true C


Article


where R is the universal gas constant. The coefficients of Antoine’s equation, predicted normal boiling points, and calculated enthalpies of vaporization of 2MD and 4EMD are summarized in Table 5. The percent deviation distributions and arc representation are shown in Figure 3. As can be seen from Tables 3−5 and Figure 3, the calculated values fit the experimental data well, and the experimental data of 2MD are also in good agreement with the values calculated by Extended Antoine from Aspen Plus v7.3, as shown in eq 3. Almost all of the relative deviations in pressure are within 1%, which means that the measurement of the vapor pressure by this method is enough for industrial application. The arc representations in Figure 3 are nearly smooth convex curves, indicating data with good quality.23 The vapor pressure of 2MD in Chopade’s work14 is apparently higher than that in this work, as well as the values calculated by Aspen Plus. The reason, except for the systematic error, may be that there is some water contained in the material that they have declared.

and 4, respectively. The vapor pressure of the pure component is described by Antoine’s equation, as shown in eq 1. Table 4. Experimental Vapor Pressure Data for 4EMDa T/K

psexp/kPa

ΔTb/kPa

Δpb/kPa

327.35 335.75 345.15 351.55 357.70 363.15 367.95 372.75 375.80 380.45 383.45 386.20 390.35 392.90

10.9 15.5 22.5 28.6 35.7 43.1 50.6 59.1 65.2 75.3 82.6 89.6 101.0 108.7

−0.01 0.02 −0.01 −0.01 −0.02 −0.01 0.01 0.04 0.00 0.02 −0.03 −0.01 −0.02 0.03 0.02 0.03

0.01 −0.02 0.03 0.01 0.03 0.01 −0.02 −0.08 −0.01 −0.04 0.09 0.03 0.07 −0.09 0.04 0.06

ax = sx =

ln(pis /kPa) = 66.44 −

+ (1.2503 × 10−17) × (T /K)6

Standard uncertainties u are u(T) = 0.05 K and u(ps) = 0.1 kPa. bΔT = Texp − Tcal and Δ = psexp − pscal.

a

ln(pis /kPa) = A −

B T /K − C

(3)

n

αX =

where psi and T are the saturated vapor pressure and absolute temperature of the pure i component, respectively. Presented in Table 5, Antoine’s coefficients A, B, and C were obtained by a nonlinear optimization method to minimize the average absolute deviation in pressure.

4EMD

d(1/T )

Δv H R

1/2

X = T, p

(4)

where xi and yi are the mole fraction of component i in the liquid and vapor phases. p is the total pressure, and psi is the saturated vapor pressure of the pure component i at temperature T. The psi values of 2MD and 4EMD were calculated from extended Antoine as eq 3 and the Antoine equation as eq 1 with the constants A, B, and C reported in Table 5, respectively. Data Regression. The activity coefficients of the binary systems 2MD (1) + 4EMD (2) were correlated by the local composition models NRTL15 and UNIQUAC16 for their perfect performance in nonlinear modeling and predicting. The NRTL equations for the n components are presented as follows

Then the enthalpy of vaporization (ΔvH) was acquired from the differential Clausius−Clapeyron equation, as shown in eq 2. The uncertainty in ΔvH by this method was estimated to be 2% =−

⎢⎣

− Xcal, i)2 ⎤ ⎥ ⎥⎦ n−m

pyi = γipis xi

Reference 14. bReference 24. cReference 25. dReference 26.

d

n ⎡ ∑n (X ⎢ i exp, i

where n is the number of experimental observations and m is the number of parameters in the correlating equation (m = 3 for eq 1). 3.2. Vapor−Liquid Equilibrium. Correlation of Binary VLE Data. Isobaric VLE data of the binary system 2MD (1) + 4EMD (2) have been obtained at 101.3 kPa, which are listed in Table 6. The experimental liquid phase activity coefficients γi of component i were obtained by assuming that the vapor phase behaves as an ideal gas and neglecting the pressure dependence of the liquid phase fugacity; therefore, the calculative equation was simplified as eq 427

Coefficients in Antoine’s Equation 1 A 13.9439 14.5295 B 2616.60 3403.13 C 74.67 47.06 temperature range/K 311−365 327−393 Normal Boiling Point/K predicted by Antoine’s eq 1 355.25 390.42 literature value 353.8a 355b 355.7c Enthalpy of Vaporization at Normal Boiling Temperature/kJ·mol−1 from experimental data eq 2 34.9 ± 0.7 36.6 ± 0.8 literature value 35.6a 34.9b 35.1d

ln(pis )

∑i |Xexp, i − Xcal, i|

sX =

Table 5. Coefficients of Antoine’s Equation, Enthalpies of Vaporization, and the Normal Boiling Point of 2MD and 4EMD

a

T at 212.1−549.2 K

In Tables 3 and 4, the mean absolute deviations αT and αp and the deviations sT and sp are

(1)

2MD

6783 − 7.2793 × ln(T /K) T /K

n

ln γi = (2)

∑ j = 1 τjiGjixj n

∑k = 1 Gkixk

n

+

∑ j=1

⎡ ⎛ ∑n x τ G ⎞⎤ ⎢τ − ⎜ r = 1 r rj rj ⎟⎥ n ij ⎜ ∑ G x ⎟⎥ ∑k = 1 Gkjxk ⎢⎣ ⎝ k = 1 kj k ⎠⎦ xjGij

(5) D


Article


Figure 3. (a) Deviation distributions of the vapor pressure measurements. (b) The arc vapor pressure representation. ⎛ p ⎞ ⎛p ⎞ T / Tmax 1−T/T x = 1 − 1 −min · T / T max , y = ln⎜ p ⎟ − (1 − x) ln⎜ pmin ⎟: ● and * represent 2MD and 4EMD in this work, respectively; Δ, 2MD from Tmin / Tmax ⎝ max ⎠ ⎝ max ⎠ max ref 11; □, calculated values of 2MD by eq 3.

where T is the absolute temperature in K and aij and bij are the UNIQUAC binary interaction parameters. The energy parameters were estimated by minimizing the square errors between the calculated and experimental y with the objective function as

Table 6. Experimental VLE Data for the Binary System of 2MD (1) + 4EMD (2) at 101.3 kPaa T/K

x1

y1

γ1

390.42 387.15 383.60 379.00 377.25 375.15 371.30 368.75 366.50 363.30 361.25 359.45 357.90 356.45 355.25

0.000 0.049 0.106 0.193 0.228 0.278 0.372 0.447 0.521 0.636 0.717 0.796 0.864 0.934 1.000

0.000 0.138 0.269 0.425 0.478 0.542 0.646 0.713 0.769 0.840 0.881 0.918 0.947 0.975 1.000

1.070 1.063 1.050 1.051 1.039 1.038 1.030 1.022 1.012 1.005 1.000 1.000 1.000 0.997

γ2

GE/RT

1.000 0.997 1.000 1.002 1.004 1.006 1.011 1.012 1.013 1.028 1.055 1.074 1.099 1.125

0.001 0.006 0.011 0.015 0.015 0.021 0.020 0.018 0.018 0.019 0.015 0.013 0.007

OF =

k

(gij − gjj)

τii = τjj = 0

RT

αij = αji

where T is the absolute temperature in K and aij and bij are the NRTL binary interaction parameters. The UNIQUAC equation for the n components is expressed by φi

φ θ z + qi ln i + li − i ln γi = ln xi xi 2 φi n ⎡ + qi⎢1 − ln(∑ θτ j ji) − ⎢⎣ j=1

φi =

rx i i n ∑k = 1 rkxk

li =

θi =

n

∑ j=1

∑ xjlj j=1

z = 10

group

Rk

Qk

a ν(1) k

a ν(2) k

CH3 CH2 CH CH2O CHO

0.9011 0.6744 0.4469 0.9183 0.6908

0.848 0.540 0.228 0.780 0.468

1 0 1 2 0

2 1 1 1 1

The regression binary interaction parameters of the binary system 2MD and 4EMD at 101.3 kPa are listed in Table 8, as well as the average deviations of temperature and the vapor phase composition between the experimental data and the calculated values. The experimental and calculated data in the form of T−x−y diagrams at 101.3 kPa are presented in Figure 4. It is suggested from Table 8 and Figure 4 that the NRTL and UNIQUAC equations are well correlated with experimental results. That is to say, the regression parameters are reasonable and satisfactory. In Figure 4, we can see that azeotropic phenomenon does not exist between 2MD and 4EMD, which is good news for separating the dioxolanes. Consistency Tests of Experimental Data. Thermodynamic consistency tests were done for the VLE experimental data. By

θτ j ij

(6)

qixi n ∑k = 1 qk xk

z (ri − qi) − (ri − 1) 2

(7)

i

a (i) νk represents the number of groups in component i for 2MD (1) and 4EMD (2).

n

⎤ ⎥ n ∑k = 1 θkτkj ⎥⎦

2

Table 7. Group Volume Rk and Area Qk24

Standard uncertainties u are u(T) = 0.05 K, u(p) = 0.1 kPa, and u(x1) = u(y1) = 0.001. τij =

− ln yiexp )k

where yi is the mole fraction of component i in the vapor phase, k represents the number of the tie lines, and superscripts “cal” and “exp” represent calculated and experimental values, respectively. For the NRTL model, the nonrandomness parameter αij was set to 0.3. For the UNIQUAC model, the r and q used to generate the UNIQUAC parameters were calculated by using the group volume and area parameters as listed in Table 7.

a

Gij = exp(− αijτij)

∑ ∑ (ln yical

⎛ uij ⎞ ⎟ τij = exp⎜ − ⎝ RT ⎠ E


Article

Industrial & Engineering Chemistry Research Table 8. Correlated Parameters of NRTL and UNIQUAC at 101.3 kPa for the System Studied model g12 − g22 = 1459.57 u12 = −551.61

NRTL UNIQUAC a

Here, ΔM =

Δy1a

max Δy1

ΔTa/K

max ΔT

0.0018 0.0019

0.0044 0.0034

0.05 0.05

0.10 0.12

parameter

1 N

g21 − g11 = −1050.95 u21 = 766.41

αij = 0.3

N

∑k = 1 |Mkcalc − Mkexp|, where N is the number of data points and M represents y1, T.

Figure 4. Plot of the experimental and calculated temperatures against the mole fraction to illustrate the isobaric VLE for the system 2MD (1) + 4EMD (2) at 101.3 kPa: □, experimental data for T−y; ■, experimental data for T−x; , calculated data by NRTL; - - -, calculated data by UNIQUAC.

Figure 6. Plot of the excess Gibbs energy against the mole fraction for the system 2MD (1) + 4EMD (2) at 101.3 kPa: ■, experimental data; , calculated by the Margules equation.

than 0.01, Van Ness test is considered passed. Therefore, the data were thermodynamically consistent, as shown in Table 8. Besides the Fredenslund test, the direct test of consistency suggested by Van Ness30 was also used to verify the quality of the VLE experimental data. In the direct test, a proposed consistency index, which starts at 1 for highly consistent data and goes to 10 for data of very poor quality, was in accordance with the appropriate measurement of the root-mean-square (RMS) value of δ ln(γ1/γ2) from eq 6. The δ ln(γ1/γ2) value for the VLE data of the binary system 2MD (1) + 4EMD (2) was 0.018 using the NRTL equation with two temperature dependence parameters. The corresponding consistency index was 1, suggesting that the VLE data were highly consistent

checking on the experimental values γ1, γ2, and GE/RT plotted vs x1 in Figures 5 and 6, we note that a positive deviation from

N

δ ln(γ1/γ2) =

{∑ [ln(γ1/γ2)ical − ln(γ1/γ2)iexp ]2 }/N i=1

(8)

where γi is the activity coefficient of component i, N represents the number of experimental observations, superscripts “cal” and “exp” represent calculated and experimental values, respectively. 3.3. Liquid−Liquid Equilibrium. Isobaric LLE data for the binary system 4EMD (1) + water (2) have been obtained at atmospheric pressure and are listed in Table 9. The equation that described LLE is shown as follows15

Figure 5. Plot of experimental and calculated activity coefficients against the mole fraction for the system 2MD (1) + 4EMD (2) at 101.3 kPa: ■, experimental activity coefficients; , calculated by the Margules equation.

ideal behavior exists in this system. The smooth curves in Figures 5 and 6 give an immediate impression of the quality of the data and were consistent. Some slightly erratic behaviors were illustrated due to approximately ideal conditions for the system (γi are nearly to 1). The Herington consistency test based on Gibbs−Duhem27 was used to test the VLE data. Similar work can be seen in our previous work.18 The test result was obtained as |D − J| = 2.6 < 10, which indicates that the experimental data were consistent. Additionally, regarded as a modeling capability test, the pointto-point test of Van Ness,28 modified by Fredenslund et al.,29 was also applied to test the VLE data. While the average absolute deviation of vapor phase compositions Δy is lower

γiαxiα = γi βxiβ

(9)

where γi and xi are the activity coefficient and mole fraction of the liquid phase for components i = 1 and 2. α and β represent different liquid phases. The liquid solubility is greatly influenced by temperature. Therefore, the parameters in the activity coefficient models are usually treated as the function of temperature. Thus, an improved five parameter activity coefficient model NRTL was used to calculate the interaction parameters τ τij = aij + F

bij T

(10) DOI: 10.1021/acs.iecr.6b02469 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research Table 9. Experimental LLE Data for the Binary System of 4EMD (1) + water (2) at (101.8 ± 0.4) kPaa

a

T/K

xα1

xα2

xβ1

xβ2

293.2 298.2 303.2 308.2 313.2 323.2 328.2 333.2 338.2

0.004 0.006 0.004 0.005 0.005 0.006 0.006 0.008 0.008

0.996 0.994 0.996 0.995 0.995 0.994 0.994 0.992 0.992

0.918 0.909 0.905 0.895 0.893 0.868 0.853 0.826 0.821

0.082 0.091 0.095 0.105 0.107 0.132 0.147 0.174 0.179

Standard uncertainties u are u(T) = 0.3 K and u(x1) = u(x2) = 0.001. Figure 7. Plot of experimental and predicted isobaric VLLE data for the system 4EMD (1) + water (2) at atmospheric pressure: □ and ■, experimental data for T−x−x; solid lines are predicted VLLE data using the NRTL equation.

where a and b are the parameters of this model and i and j represent the components. The five parameter activity coefficient model NRTL described in eq 10 was used to correlate the LLE data by minimizing the objective function as below 2 ⎛ γiαxiα ⎞ OF = ∑ ∑ ⎜⎜1 − β β ⎟⎟ γi xi ⎠ k i ⎝ k

(11)

where k represents the number of the tie lines and superscripts “cal” and “exp” represent calculated and experimental values, respectively. The correlated binary interaction parameters together with the average deviations of temperature and the liquid phase composition for the binary system 4EMD and water between experimental data and calculated values are listed in Table 10. The T−x−x diagram is presented in Figure 7. It shows that the regression parameters are reasonable. Using the parameters listed in Table 10, VLLE data were predicted by the NRTL equation in Aspen Plus v7.3. The equations describing the VLLE relations are shown as eq 12. The predicted data are presented in Figure 7. The result shows that an azeotrope of 4EMD and water is observed at 362.15 K with a 0.34 mol fraction of 4EMD pyi = γiαxiαpis = γi βxiβpis

(12) Figure 8. Boiling scatter of the potential mixture to be separated at atmospheric conditions.

4. APPLICATIONS IN THE SEPARATION PROCESS According to the above study and previous work,14,31,32 Figure 8 presents the boiling scatter of the potential mixtures to be separated. Because the boiling temperature difference between 2MD and 4EMD is much bigger than that for EG and 1,2BDO, the separation of 2MD and 4EMD is easier than that of EG and 1,2-BDO. Actually, we achieve separation of 2MD and 4EMD by separating the azeotrope 2MD−water and the azeotrope 4EMD−water, which also have big boiling temperature differences.

According to Figure 8, a process has been designed to separate the EG and 1,2-BDO mixture (0.567 mol fraction of EG, which approaches the azeotrope concentration) using the Aspen Plus software, shown in Figure 9. The parameters of the NRTL equation used in this process are presented in Table 11. Besides our work and previous research, the absent parameters, such as the glycols with the acetals, were acquired by the group contribution method UNIFAC.33 The REACTOR in the

Table 10. Correlated Parameters of NRTL at Atmospheric Pressure for the System 4EMD (1) + Water (2) model NRTL

a

parameters a12 = −3.7495 b12 = 1652.44 α12 = 0.30

Average absolute ΔM =

1 N

a21 = 1.2328 b21 = 970.36

Δxα1 a

Δxβ1a

max Δxα1

max Δxβ1

ΔTa/K

max ΔT

0.0005

0.0045

0.0017

0.0120

0.21

0.63

N

∑k = 1 |Mkcalc − Mkexp|, where N is the number of data points and M represents x1, T. G


Article


Figure 9. Separation process of the EG and 1, 2-BDO mixture using aldolization.

Table 11. Binary Interaction Parameters of the NRTL Model Used for 2MD (1), 4EMD (2), Water (3), EG (4), 1,2-BDO (5), and Acetaldehyde (6)a

a

i−j

aij

aji

bij

bji

αij

source

1−2 1−3 1−4 1−5 1−6 2−3 2−4 2−5 2−6 3−4 3−5 3−6 4−5 4−6 5−6

0 1.711 0 0 0 −3.750 0 0 0 0.348 0 3.779 0 0 0

0 −0.224 0 0 0 1.233 0 0 0 −0.057 0 10.912 0 0 0

175.56 −454.04 561.31 670.46 −202.64 1652.44 782.61 784.24 −187.47 34.82 989.68 −977.15 476.84 −173.04 −422.33

−135.63 1128.05 173.35 −61.10 439.29 970.36 547.77 113.49 498.62 −147.14 −226.91 −2709.53 −234.77 334.11 966.86

0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3

this work ref 11 predict by UNIFAC predict by UNIFAC predict by UNIFAC this work predict by UNIFAC predict by UNIFAC predict by UNIFAC from Aspen predict by UNIFAC from Aspen ref 34 predict by UNIFAC predict by UNIFAC

Interaction parameters τ calculated as τij = aij + bij/T.

Table 12. Results of the Simulation and Optimization temperature/K tower

pressure/atm

theoretical stages

feeding stages

reflux ratio

S-ACET S-2MD S-4EMD

1.4 1.0 0.1

21 36 11

10 17 8

0.686 2.23 0.2

−1

distillate rate/kg·h 157.0 363.2 401.1

top

bottom

304.0 349.0 305.5

368.7 369.6 401.9

Table 13. Component Split Fractions in Each Distillation Tower S-ACET

S-2MD

S-4EMD

component

top

bottom

top

bottom

top

bottom

acetaldehyde EG 1,2-BDO 2MD 4EMD water

0.9990 0 0 0.0022 0 0.0043

0.0010 1.0000 1.0000 0.9978 1.0000 0.9957

1.0000 0 0 0.9991 0.0009 0.3479

0 1.0000 1.0000 0.0009 0.9991 0.6521

0 0 0 1.0000 1.0000 0.9976

0 1.0000 1.0000 0 0 0.0024

H


Article

Industrial & Engineering Chemistry Research Table 14. Material Results Data of Each Stream

a

streams

F−A

T/°C P/atm MFa/kg·h−1 mass fraction acetaldehyde EG 1,2-BDO 2MD 4EMD water

20.0 1.6 284.7 1 0 0 0 0 0

F−G 20.0 1.6 479.5 0 0.474 0.526 0 0 0

3 46.7 1.6 1174.8 0.375 0.317 0.307 0.001 0 0.001

4 60.0 1.5 1174.8 0.133 0.124 0.092 0.275 0.277 0.100

6 95.6 1.4 1017.8

D−A

7

30.9 1.4 157.0

0 0.143 0.106 0.317 0.320 0.115

30.9 1.6 157.0

0.992 0 0 0.005 0 0.003

0.992 0 0 0.005 0 0.003

9 96.5 1.0 654.6 0 0.222 0.165 0 0.496 0.116

D-2b 75.8 1.0 363.2 0 0 0 0.887 0.001 0.112

11

12

128.7 0.1 253.6

128.9 1.6 253.6

0 0.573 0.427 0 0 0.001

0 0.573 0.427 0 0 0.001

D-4c 32.3 0.1 401.1 0 0 0 0.001 0.810 0.189

MF: mass flow. bD-2: represent the stream D-2MD. cD-4: represent the stream D-4EMD.

■

process was operated under 1.5 atm, 333.15 K, and a 1:1 mol ratio of acetaldehyde vs glycols. Besides, the conversion of EG and 1,2-BDO was fixed to 0.61 and 0.70, respectively, based on the experimental results. The S-ACET distillation tower was placed to recover the unreacted acetaldehyde with a mole concentration more than 0.99. The S-2MD distillation tower was designed to achieve the separation of 2MD and 4EMD by distilling the 2MD−water azeotrope from the top, and the S4EMD distillation tower was aimed to recover the unreacted glycols, which would be circulated to the REACTOR. The simulation and optimization results are shown in Tables 12−14. The results show that the S-2MD tower could achieve the separation of 2MD and 4EMD in a inferior way; it demonstrates that the EG and 1,2-BDO azeotrope could be separated effectively through the aldolization reaction. By applying aldolization in the synthesis of EG via DMO from syngas, as well as other separating processes of glycol mixtures, such as product EG or other glycols through biological fermentation, it is possible to reach the advantage of saving energy consumption, ensuring the EG quality and increasing the recovery of the EG.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: +86-022-27404701. Author Contributions ⊥

H.L. and W.H. contributed equally to this work.

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors are grateful for financial support from the National Natural Science Foundation of China (Nos. 21306128, 21336007), the National High Technology Research and Development Program of China (No. 2015AA03A602), and The Key Technology R&D Program of Tianjin (No. 15ZCZDGX00330).

■

REFERENCES

(1) Yue, H.; Zhao, Y.; Ma, X.; Gong, J. Ethylene glycol: properties, synthesis, and applications. Chem. Soc. Rev. 2012, 41 (11), 4218. (2) Yin, A.; Guo, X.; Dai, W.; Li, H.; Fan, K. Highly active and selective copper-containing HMS catalyst in the hydrogenation of dimethyl oxalate to ethylene glycol. Appl. Catal., A 2008, 349, 91. (3) Chen, L.; Guo, P.; Qiao, M.; Yan, S.; Li, H.; Shen, W.; Xu, H.; Fan, K. Cu/SiO2 catalysts prepared by the ammonia-evaporation method: Texture, structure, and catalytic performance in hydrogenation of dimethyl oxalate to ethylene glycol. J. Catal. 2008, 257, 172. (4) Wen, C.; Cui, Y.; Chen, X.; Zong, B.; Dai, W. Reaction temperature controlled selective hydrogenation of dimethyl oxalate to methyl glycolate and ethylene glycol over copper-hydroxyapatite catalysts. Appl. Catal., B 2015, 162, 483. (5) Wen, C.; Cui, Y.; Dai, W.; Xie, S.; Fan, K. Solvent feedstock effect: the insights into the deactivation mechanism of Cu/SiO2 catalysts for hydrogenation of dimethyl oxalate to ethylene glycol. Chem. Commun. 2013, 49 (45), 5195. (6) Yang, Z.; Xia, S.; Shang, Q.; Yan, F.; Ma, P. Isobaric Vapor− Liquid Equilibrium for the Binary System(Ethane-1,2-diol + Butan-1,2diol) at(20, 30, and 40) kPa. J. Chem. Eng. Data 2014, 59, 825. (7) Zhu, L.; Yan, J.; Xiao, W. Measuring and correlating the vapor liquid equilibria of the binary system ethylene glycol and 1,2butanediol. Chem. Eng.(China) 2012, 40, 35. (8) Berg, L.; Bozeman Recovery of Ethylene Glycol from Butanediol Isomers by Azeotropic Distillation. U.S. Patent US4966658, 1990. (9) Guo, Y.; Xiao, J. Process for separating ethylene glycol and 1,2butanediol. U.S. Patent US2013284584-A1, 2013. (10) Qi, W.; Li, Q.; Liu, Y.; Pan, G.; Dai, C.; Yi, C. Separating ethylene glycol and 1,2-butanediol mixture using heterogeneous azeotropic distillation comprises mixing polyol mixture and extracting agent into distillation column, recovering and separating. China Patent CN103396290-A, 2013.

5. CONCLUSION In this work, the vapor pressures of 2MD and 4EMD were measured by ebulliometry and correlated with the Antoine’s equation. Meanwhile, isobaric VLE data of the binary system 2MD + 4MD were measured at 101.3 kPa. The data were tested for thermodynamic consistency by the Herington consistency test, the point-to-point test, and the direct test. The NRTL and UNIQUAC activity coefficient models were correlated well with the experimental data. The interaction parameters were obtained. In addition, isobaric LLE data of the binary systems 4EMD + water were measured at atmospheric pressure. The five parameter NRTL equation was used to correlate the experimental data. The results shows that it could accurately correlate the LLE data. Using the parameters obtained, the isobaric VLLE of the binary systems 4EMD + water was predicted by NRTL. Finally, a simulation of the process for separating the EG and 1,2-BDO mixture was carried out. The results show that EG and 1,2-BDO could been separated effectively through this novel reaction−distillation coupled technology. It indicates that the aldolization reaction could be a potential application in the synthesis of EG via an oxalate (DMO) form syngas, as well as some other separating process of glycol mixtures. I


Article

Industrial & Engineering Chemistry Research (11) Lei, Z.; Chen, B.; Ding, Z. Special Distillation Processes; Elsevier: Amsterdam, The Netherlands, 2005; p 370. (12) Lei, Z.; Dai, C.; Zhu, J.; Chen, B. Extractive Distillation with Ionic Liquids: A Review. AIChE J. 2014, 60, 3312−3329. (13) Lei, Z.; Li, C.; Chen, B. Extractive distillation: a review. Sep. Purif. Rev. 2003, 32 (2), 121−213. (14) Chopade, S. P.; Dhale, A. D.; Clark, A. M.; Kiesling, C. W.; Myrant, L. K.; Jackson, J. E.; Miller, D. J. Vapor-Liquid-Liquid Equilibrium (VLLE) and Vapor Pressure Data for the Systems 2Methyl-1, 3-dioxolane(2MD)+ Water and 2, 4-Dimethyl-1, 3dioxolane (24DMD)+ Water. J. Chem. Eng. Data 2003, 48, 44. (15) Renon, H.; Prausnitz, J. M. Local compositions in thermodynamic excess functions for liquid mixtures. AIChE J. 1968, 14, 135. (16) Abrams, D. S.; Prausnitz, J. M. Statistical thermodynamics of liquid mixtures: a new expression for the excess Gibbs energy of partly or completely miscible systems. AIChE J. 1975, 21, 116. (17) Dhale, A. D.; Myrant, L. K.; Chopade, S. P.; Jackson, J. E.; Miller, D. J. Propylene glycol and ethylene glycol recovery from aqueous solution via reactive distillation. Chem. Eng. Sci. 2004, 59, 2881. (18) Li, H.; Han, M.; Gao, X.; Li, X. Isobaric vapor−liquid equilibrium for binary system of cinnamaldehyde+benzaldehyde at 10, 20 and 30 kPa. Fluid Phase Equilib. 2014, 364, 62. (19) Liu, T.; Wang, Z.; Xia, S.; Ma, P. Isobaric (vapour+liquid) equilibria for N-formylmorpholine with ethylbenzene, n-butylbenzene, iso-propylbenzene and 1,2,4-trimethylbenzene at 101.33 kPa. J. Chem. Thermodyn. 2012, 53, 9. (20) Yang, C.; Zeng, H.; Yin, X.; Ma, S.; Sun, F.; Li, Y.; Li, J. Measurement of(vapor+liquid) equilibrium for the systems {methanol +dimethyl carbonate} and {methanol+dimethyl carbonate+tetramethylammonium bicarbonate} at p = (34.43, 67.74)kPa. J. Chem. Thermodyn. 2012, 53, 158. (21) Zhang, W.; Wang, X.; Meng, N.; Du, W.; Li, C. Isobaric Vapor− Liquid Equilibrium for the Binary System of Hexamethyl Disiloxane + Isopropyl Acetate at Atmospheric Pressure. J. Chem. Eng. Data 2013, 58, 2425. (22) Topphoff, M.; Kiepe, J.; Gmehling, J. Effects of lithium nitrate on the vapor-liquid equilibria of methyl acetate plus methanol and ethyl acetate plus ethanol. J. Chem. Eng. Data 2001, 46, 1333. (23) Č enský, M.; Rohác,̌ V.; Růzǐ čka, K.; Fulem, M.; Aim, K. Vapor pressure of selected aliphatic alcohols by ebulliometry. Part 1. Fluid Phase Equilib. 2010, 298, 192. (24) Pihlaja, K.; Heikkilä, J.; et al. Enthalpies of formation of cyclic acetals. 1,3-dioxolane, 2-methyl-1,3-dioxolane, and 2,4-dimethyl-1,3dioxolanes. Acta Chem. Scand. 1969, 23, 1053. (25) Rofman, V. M.; Yakubov, R. D.; Trofimov, B. A.; Maksimov, S. M., Liquid-vapor equilibrium in system formed by products of vinylation of triethylene glycol and product of epoxidation of ethylene glycol monovinyl ether witrh epichlorohydrin. Zh. Prikl. Khim. (Leningrad) 1976, 49, 1159; available at: http://webbook.nist.gov/ chemistry/. (26) Pihlaja, K.; Heikkila, J., Heats of formation of cyclic vinyl ethers, a correction. Suom. Kemistilehti 1972, 148; available from http:// webbook.nist.gov/chemistry/. (27) Abbott, M. M.; Smith, J. M.; Van Ness, H. C. Introduction to chemical engineering thermodynamics. McGraw-Hill, 2001. (28) Van Ness, H. C.; Byer, S. M.; Gibbs, R. E. Vapor-Liquid equilibrium: Part I. An appraisal of data reduction methods. AIChE J. 1973, 19, 238. (29) Fredenslund, A.; Gmehling, J.; Rasmussen, P. Vapour-Liquid Equilibria Using UNIFAC: A Group Contribution Method; Elservier: Amsterdam, The Netherlands, 1977. (30) Van Ness, H. C. Thermodynamics in the treatment of vapor/ liquid equilibrium(VLE) data. Pure Appl. Chem. 1995, 67, 859. (31) Schierholtz, O. J.; Staples, M. L. Vapor Pressures of Certain Glycols. J. Am. Chem. Soc. 1935, 57, 2709.

(32) Mamedov, M. K.; Piraliev, A. G.; Rasulova, R. A. Synthesis of bicyclo[2.2.1]heptyl monoethers of aliphatic diols. Russ. J. Appl. Chem. 2009, 82, 518. (33) Fredenslund, A.; Jones, R. L.; Prausnitz, J. M. Groupcontribution estimation of activity coefficients in nonideal liquid mixtures. AIChE J. 1975, 21, 1086. (34) Qin, J. Vapor-Liquid Equilibrium and Separation Process of Ethylene Glycol System. Thesis, Tianjin University, Tianjin, 2015.

J


Application of the Aldolization Reaction in Separating the Mixture of

Recommend Documents