Temperature and Pressure Effects on the Separation Efficiency and

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Temperature and Pressure Effects on the Separation Efficiency and Desorption Kinetics in the TMA-CO2-H2O System Georgios Kolliopoulos, and Vladimiros G. Papangelakis Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b03926 • Publication Date (Web): 08 Oct 2018 Downloaded from http://pubs.acs.org on October 13, 2018

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Industrial & Engineering Chemistry Research

Temperature and Pressure Effects on the Separation Efficiency and Desorption Kinetics in the TMA-CO2-H2O System

Georgios Kolliopoulos and Vladimiros G. Papangelakis*

Department of Chemical Engineering and Applied Chemistry, University of Toronto 200 College Street, Toronto, Ontario, Canada M5S 3E5 (*Corresponding author: [email protected]) ABSTRACT Draw solute separation from a draw solution is the main source of energy consumption in Forward Osmosis. The draw solute separation efficiency from a TMA-CO2-H2O draw solution and the decomposition kinetics of the latter were investigated in this study from 30 to 50 °C and 0.75 to 0.35 bar. The former proved stoichiometric and efficient with ~100% draw solute removal after 60 min at 50 °C, 0.35 bar. The rate determining step proved to be the physicochemical phenomenon of the desorption of the less volatile gas, TMA. It was found to be first order with respect to TMA(aq) concentration. The combined effects of temperature and pressure on the k values proved that only the temperature has a significant effect. Finally, an Eyring-Arrhenius model was designed to estimate k values for the TMA desorption rate in the temperature and pressure range studied in this work.

Keywords: Forward osmosis, carbonated trimethylamine draw solution, draw solute separation, desorption kinetics, industrial process water recovery

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1. Introduction The regulatory restrictions on fresh water use in industry alongside the need for sustainable processes have motivated engineers to seek new economic solutions to recover and recycle process water while minimizing fresh water intakes. Conventional methods used to purify and recover process water (reverse osmosis and evaporation) are energy demanding and expensive 1. Forward Osmosis (FO), a spontaneous process where an engineered concentrated draw solution (CDS) osmotically draws water from a more dilute solution (the feed solution), is a promising alternative for process water recovery and recycle. Due to the osmotic pressure gradient across the membrane solutions, water moves spontaneously through the pores to equalize its chemical potential 2-4. The main advantages of FO are its high water recovery (more than 90% of the total water processed) 2 and its potential for low cost 5, 6. The latter depends on the selection of the draw solution, which determines the economics of the overall FO process. An ideal CDS must generate high osmotic pressure values to recover water into it and be easily separable and recoverable from the resulting diluted draw solution (DDS). The main source of energy consumption in FO thus arises from the separation and the regeneration of the draw solution 7. Thermolytic salts are promising draw solute candidates

3, 8.

They exhibit a sudden phase

change from aqueous to gaseous at low temperatures, thus facilitating their separation. The most studied thermolytic draw solutions in FO are aqueous carbonated ammonia (NH3-CO2-H2O) 3-5, 9 and aqueous carbonated trimethylamine (TMA) (TMA-CO2-H2O)

6, 8, 10-12.

Apart from their

application in FO to recover water, these solutions can also be used in the Osmotic Heat Engine (OHE) process to generate energy from waste heat

13-15.

Both solutions decompose into gaseous

CO2 and NH3 or TMA upon mild heating. The gaseous decomposition products are recoverable and recyclable, thus enabling the regeneration of the CDS. Despite the low odor threshold of TMA


2

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(0.11-0.58 ppb) 8, 16-19, which may limit its application in FO, TMA-CO2-H2O is considered more effective 8. Its performance has been evaluated and compared to NH3-CO2-H2O in FO using a 1M draw solution concentration baseline. It resulted in comparable water flux (14.5 L m-2 h-1 vs. 15.2 L m-2 h-1 produced by NH3-CO2-H2O 8), reduced reverse flux (0.1-0.2 mol m-2 h-1 vs. 0.3-0.4 mol m-2 h-1 for NH3-CO2-H2O 8), lower draw solution regeneration requirements (254 MJ/m3 of feed water vs. 397 MJ/m3 of feed water for NH3-CO2-H2O 8), and its effects were proven nontoxic in people who were chronically exposed to < 8 ppm of TMA 8, 20. Though the fresh water product from a TMA-CO2-H2O based FO process requires additional treatment to produce drinking water, its purity is often sufficient for usage in industrial process circuits. The treatment of contaminated industrial effluents for water recovery, however, potentially requires CDS of higher than 1 M. The performance of higher concentrations (1, 3, and 5 M) of TMA-CO2-H2O draw solutions has only been evaluated and compared to NH3-CO2-H2O in a pressure retarded osmosis (PRO) setup 21. In such setup, the water flux values produced by the two systems were similar (35-80 L m-2 h-1 for TMA-CO2-H2O vs. 25-85 L m-2 h-1 for NH3CO2-H2O

21),

while the reported reverse flux was one order of magnitude lower in the case of

TMA-CO2-H2O (< 5 mol m-2 h-1 vs. 5-50 mol m-2 h-1 for NH3-CO2-H2O). The reaction chemistry of CO2 with tertiary amines (such as TMA) (Reaction 1) is described as a base-catalysed hydration of CO2, which forms an ion-pair in solution, comprised of the protonated amine and bicarbonate ion, i.e., R1R2R3NH+:HCO3- 22, 23: R1R2R3N + CO2 + H2O ⇌ R1R2R3NH+ + HCO3-

(R1)

The following reactions also occur 22: CO2 + OH- ⇌ HCO3-

(R2)

CO2 + H2O ⇌ H2CO3

(R3)


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R1R2R3N + H2O ⇌ R1R2R3NH+ + OH-

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(R4)

Reaction 4 is assumed to be at equilibrium since it involves a proton transfer, and the contribution of Reaction 3 to the overall rate is usually negligible 22. Also, the formation of carbamate ions is precluded since there is no direct reaction between tertiary amines and CO2. Specifically, for the TMA-CO2-H2O system, Kolliopoulos et al. 11, 24 studied its chemical properties (speciation, vapor liquid equilibria, density, and conductivity) and proposed an experimentally verified chemical model that predicts these properties. Their model is based on the mixed solvent electrolyte (MSE) model 25-30 and was developed using the OLI software (www.olisystems.com). The draw solute separation accounts for the majority of energy requirements in an FO process 7. Especially the separation mechanism and the desorption kinetics of TMA and CO2 from a TMA-CO2-H2O DDS are critical for the FO process. Especially in the case of TMA-CO2-H2O there is not enough information on the draw solution decomposition mechanism and the draw solute separation efficiency. The reactor equipment design depends on the successful identification of the rate determining step of the separation process and the accurate estimation of the k values. In this work, we study the combined effects of temperature (30, 40 and 50 °C) and pressure (0.75, 0.55 and 0.35 bar) on the separation efficiency of the draw solutes from a TMA-CO2-H2O DDS. Further, we investigate the draw solute desorption kinetics, and decomposition reaction mechanism.

2. Materials and Methods 2.1 Materials TMA-CO2-H2O CDS was prepared by injecting CO2(g) (grade 4.0, Linde, Canada) under pressure in a 2 L autoclave filled with aqueous TMA solution (~45 wt.%, Sigma-Aldrich, CAS


4

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No. 75-50-3, Canada). The CDS was diluted 2 times using DI water in the laboratory, assuming a two-fold dilution in an FO cell. The resulting solution was used as the DDS in this study. It contained 17.4±0.8 wt.% total dissolved TMA, i.e., the sum of TMAH+ and TMA(aq), and 11.5±0.3 wt.% total dissolved CO2, i.e., the sum of HCO3-, CO32-, and CO2(aq). The above DDS concentration is equivalent to 2.46±0.09 M TMAH:HCO3 with a TMA:CO2 molar ratio of 1.13±0.07. A 2 M HCl standard solution (Fisher Sci., CAS No. 7647-01-0, Canada) and a 2 M CH3COONa were used to determine total dissolved TMA. The 2 M CH3COONa was prepared using sodium acetate trihydrate certified ACS crystalline powder (Fisher Sci., CAS No. 6131-904, Canada), and was standardized by titration against the 2 M HCl standard. A 4 M CaCl2 solution was prepared using calcium chloride dihydrate (99+%, ACROS ORGANICS, CAS No. 10035-04-8, Canada) and was used to determine total dissolved CO2 by precipitation as CaCO3. The precipitation was carried out in a pH-controlled environment (pH range: 9-10.5) by addition of a 2 M NaOH standard solution (Fisher Sci., CAS No. 1310-73-2, Canada) and the 2 M HCl standard.

2.2 Chemical Analysis Total dissolved TMA (wt.%) and total dissolved CO2 (wt.%) were determined following the titration and precipitation analytical procedures developed by Kolliopoulos et al.

11,

respectively. The reported error is 4% for TMA and 5% for CO2. Nuclear Magnetic Resonance (NMR) spectroscopy, as proposed by F. Mani et al. 31, was used to obtain the CO2 speciation at 25 °C in all samples collected in this study. The 13C NMR spectra were obtained with an Agilent DD2 500 MHz spectrometer, equipped with 5mm XSens


5


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cryoprobe, and were externally referenced to 0 ppm line of tetramethylsilane. D2O (20%) and 20 mM Chromium (III) acetyl-acetonate (relaxation agent) were added to each sample to provide enough signal for the deuterium lock and to shorten relaxation times, respectively. Spectra were acquired with 128 scans and 10 s relaxation delay. Reference solutions for calibrating the 13C NMR were prepared by dissolving accurate proportions of KHCO3 and K2CO3 in D2O. Our resulting calibration curve is presented in Figure 1; it follows the same trend as the one presented by F. Mani et al. 31. Finally, TMA speciation was calculated based on solution electroneutrality and by using the total dissolved TMA and CO2 measurements, CO2 speciation data obtained from 13C NMR.

Figure 1 – 13C NMR calibration curve for identifying CO2 speciation

2.3 Experimental Design The experiments were conducted in an agitated (1200 rpm) 1 L jacketed glass separation reactor obtained from Ace Glass Inc., for t=0, 15, 30, 45, and 60 min at each temperature and pressure combination (Figure 2). The temperature in solution was controlled using a J-KEM Scientific Temperature Controller (Model 210) purchased from VWR. The pressure was


6

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monitored using an Ashcroft Digital Pressure Gauge (0-15 psi) purchased from Cole Palmer Canada. The vacuum pump used was the Welch Dry Fast Ultra, Model 2032B-01 and was purchased from Fisher Sci. An acid trap, containing a predetermined amount of H2SO4 able to capture all TMA(g), and a base trap, containing a predetermined amount of KOH capable of capturing all CO2(g), were connected sequentially to the reactor for mass balance determination. A certain DDS mass (470.4±1.1 g) was introduced in the separation reactor; t=0 was designated as the moment when both temperature and pressure reached the values of interest. The reactor was stopped at t=0, and the mass of (i) the remaining solution in the separation reactor, (ii) the solution in the acid trap, and (iii) the solution in the base trap was measured. Liquid samples were collected from all three solutions in 50 mL falcon tubes (Fisher Sci., Canada) having minimum free headspace and were stored at 3.5 °C to avoid further desorption. The same procedure was then carried out for each time t. No intermediate samples were taken. All experiments and chemical analyses were performed on a mass basis. Our approach accounted for evaporative water losses and reagent concentration changes. The samples were analyzed after 24 h for total dissolved TMA, total dissolved CO2, speciation, and pH at 25 °C (1.01 bar) for all experimental conditions. The experimental methodology is summarized in Figure 2.


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Figure 2 – Experimental conditions, setup, and analytical procedure

The amount of TMA collected in the acid trap was determined by Kjeldahl-type steam distillation

32.

The amount of CO2 captured in the base trap was measured by titration of the

unreacted KOH in the trap with HCl. The mass balance for TMA and CO2 closed within 3% and 6% error, respectively. Selected triplicates were performed to evaluate experimental reproducibility. Thereafter, it was assumed that similar errors apply in all experimental runs.

3. Results and Discussion 3.1 Draw Solute Separation Efficiency The % removal of TMA and CO2 from the DDS as a function of time with respect to temperature and pressure is shown in Figures 3 to 5. The lines connecting our experimental data points in Figures 3 to 5 were calculated using the kinetic model developed in this work, i.e., Equation 2 with the rate constant computed from the Eyring-Arrhenius model (Sections 3.3 to 3.5).


8

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Figure 3 – Removal (%) of TMA and CO2 vs. time at 0.75 bar



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The draw solute separation process of TMA-CO2-H2O is fast and efficient; according to Figure 5, almost 100% of the draw solutes in the DDS can be separated at 50 °C and 0.35 bar within 60 min. Further, the average molar ratio of TMA:CO2 in solution was found to be constant at 1.140.04 in all separation experiments (Figure 6), indicating that the separation process is stoichiometric. There is a systematic, though insignificant, temperature trend with the TMA:CO2 ratio being smaller at 50 °C, which may be attributed to the uncertainty of the measurements. The stoichiometric separation is an important finding for the design of the overall FO process, as it will facilitate the subsequent CDS regeneration. As seen in Reaction 1, the reaction of CO2 with TMA is a base-catalyzed hydration of CO2. Therefore, for a successful CDS regeneration the TMA concentration must be present at similar or higher concentration than CO2. A stoichiometric separation of TMA and CO2 suggests that the gaseous draw solutes from the separation process can be reused directly to regenerate the CDS. The amount of the draw solutes escaping from the DDS and captured in the traps could be reused to regenerate the CDS in a


10

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different setup configuration; however, this was out of the scope of the current work. A packed absorption column could be used to enable a high efficiency TMA-CO2 absorption in a recovery medium and hence, a successful CDS regeneration. The packed absorption column can be designed to operate at atmospheric pressure to minimize both the capital and operating costs. The DDS is known to be an effective recovery medium for the reabsorption of the draw solutes in the case of NH3-CO2-H2O system 33, and is expected to work in the TMA-CO2-H2O system as well.

Figure 6 – Molar ratio of TMA:CO2 in solution during separation experiments

3.2 Procedure to Obtain Speciation at High Temperature As mentioned, total dissolved TMA, total dissolved CO2, pH, and speciation corresponding to each temperature and pressure tested were experimentally measured at 25 °C in all samples collected. Once sampled at the test temperature, total dissolved TMA and total dissolved CO2 remain constant when cooled to 3.5 °C. However, speciation and pH are temperature dependent. Nevertheless, to analyze the draw solute desorption kinetics, speciation data at the test temperature


11


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are required. Figure 7 summarizes the procedure developed to reconstruct the solution speciation at test temperature, by using measurements at room temperature and the OLI chemical model.

Figure 7 – Procedure to reconstruct speciation at test temperature and pressure

In this procedure, the room temperature measurements of total TMA and CO2 were used as inputs to the OLI-MSE model developed by Kolliopoulos et al.

11.

The model then calculated the

speciation and the pH at 25 °C, 1.01 bar (Step 1). The experimentally measured solution speciation was directly compared with the calculated speciation (Step 1 in Figure 7). The speciation measurements at room temperature showed that the dominant species in solution throughout the draw solute separation experiments are TMAH+ and HCO3-, while the pH changes were insignificant. Excellent agreement was found between the experimentally measured and calculated (at 25 °C) speciation (within 4.212.61% for the dominant species in solution) and pH (within 1.511.04%) under all 9 conditions tested. Consequently, the model was used to extrapolate the speciation at the temperature at which the experiment was conducted (Step 2 in Figure 7). The model takes into account density changes with temperature and the whole procedure assumes that


12

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solution equilibria are instantaneous. The latter assumption was also made by KierzkowskaPawlak and Chacuk

34

in their study of CO2 desorption kinetics from aqueous N-

methyldiethanolamine solutions. Table 1 presents the chemical reactions that occur during draw solute separation. Based on the above assumptions, the concentration of the chemical species involved in Reactions 5, 7, 8, 10 in Table 1 should correspond to the equilibrium concentrations. The OLI-MSE model was used to obtain their equilibrium constant values (Keq) at each temperature in Table 1.

Table 1 – Equilibrium reactions occurring during separation of TMA and CO2 Keq

Equilibrium Reaction 30 °C

40 °C

50 °C

(R5)

TMAH+ + OH- ⇌ TMA(aq) + H2O

1.42 ∙ 104

1.16 ∙ 104

9.87 ∙ 103

(R6)

TMA(aq) ⇌ TMA(g)

0.19

0.29

0.41

(R7)

CO32- + H3O+ ⇌ HCO3- + H2O

1.94 ∙ 1010

1.66 ∙ 1010

1.47 ∙ 1010

(R8)

HCO3- + H3O+ ⇌ CO2(aq) + 2H2O

2.09 ∙ 106

1.92 ∙ 106

1.85 ∙ 106

(R9)

CO2(aq) ⇌ CO2(g)

33.59

42.37

51.57

(R10)

2H2O ⇌ H3O+ + OH-

1.46 ∙ 10-14

2.89 ∙ 10-14

5.37 ∙ 10-14

(R11)

H2O ⇌ H2O(g)

0.04

0.07

0.12

3.3 Draw Solute Desorption Kinetics The consumption rates of TMA(aq) and CO2(aq) in the DDS were estimated, hypothesizing that they follow pseudo-first-order kinetics 35. The rate equation for the desorption of a gas from a liquid is given by Equation 1:


13


d(C ― C ∗ ) r=― = kL ∙ a ∙ (C ― C ∗ ) dt

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(E1)

where r is the desorption rate (mol min-1 L-1), C is the concentration of the gas on the liquid phase (mol L-1), C* is the concentration at equilibrium (mol L-1), kL is the liquid mass transfer coefficient (m min-1), and a is the volume-specific gas-liquid interfacial area (m-1). In our experimental setup, C* was assumed to be zero since the vapor phase is continuously removed from the overhead. Also, the product kL ∙ a is reported as k (min-1) in this work. The integrated form of Equation 1 was used to determine the k values for Reactions 6 and 9 by linear regression of C vs. t using the calculated C values for TMA(aq) and CO2(aq) at temperature, and Equation 2: ln C = ―k ∙ t + ln C0

(E2)

The rate constants k for the desorption of TMA and CO2 are presented in Table S1 in the Supporting Information. Given the R2 values obtained, the hypothesis of first-order kinetics was validated. The data presented in Table S1 were assessed by analysis of variance (ANOVA), using STATISTICA 7 (Statsoft Inc., Tulsa, USA), while significant differences of mean values were estimated at the probability level P < 0.05. Duncan's multiple range test was used to separate means of data when significant differences were observed. According to ANOVA results, the temperature showed significant effect on the rate constant k values for the desorption of TMA (Reaction 6), while the pressure did not affect the k values. Moreover, Duncan’s test showed that k values did not differ significantly at 30 and 40 °C, whereas they increased significantly at 50 °C. Similarly, the k values for the desorption of CO2 (Reaction 9) were found to be significantly influenced only by the temperature. However, according to Duncan’s test the k values showed significant differences at all 30, 40, and 50 °C.


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3.4 Decomposition Mechanism The TMA(g) desorption appears to be the rate determining step in the separation process from the TMA-CO2-H2O DDS. This conclusion is supported by the fact that there is no direct reaction between TMA and CO2

22, 23

and the rate constant values for Reaction 6 are lower than

those of Reaction 9. Upon desorption, TMAH+ and HCO3- generate more TMA(aq) and CO2(aq) respectively and CO2 desorbs from the aqueous solution at slightly higher rates than TMA (Table S1). This is also consistent with the average molar ratio of TMA:CO2 in solution, which is 1.140.04 as shown in Figure 6. The k values obtained for Reaction 6 were found to be similar to the ones obtained for the overall drop in the concentration of total dissolved TMA in solution (Table S2); this serves as a validation of the assumptions made.

3.5 Eyring-Arrhenius Model: Combined Effects of Pressure and Temperature on the Rate Constant (k) The temperature dependence on the desorption rate can be expressed through the Arrhenius equation (Equation 3):

[ (

k(T) = kref,Texp ―

Ea 1 1 ― R T Tref

)]

(E3)

where kref is the rate constant at a reference temperature Tref, Ea is the activation energy, and R is the Universal Gas Constant. The activation energies calculated for each individual pressure are presented in Table 2. A Tref = 50 °C (323 K) was selected.


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Table 2 – Activation energy values calculated for the desorption of TMA TMA(aq) ⇌ TMA(g) P (bar)

Activation Energy, Ea (kJ/mol)

R2

0.35

61.5±1.8

0.9965

0.55

59.0±3.1

0.9832

0.75

51.4±1.1

0.9881

The pressure dependence on the desorption rate can be expressed with the Eyring equation (Equation 4) 36:

[

k(P) = kref,Pexp ―

ΔV ≠ (P ― Pref) RT

]

(E4)

where kref is the rate constant at a reference pressure Pref, ΔV ≠ is the volume of activation, and R is the Universal Gas Constant. The values of the activation volume calculated for each individual temperature are presented in Table 3. A Pref = 0.35 bar was selected.

Table 3 – Activation volume values calculated for the desorption of TMA TMA(aq) ⇌ TMA(g) Activation Volume, ΔV R2

T (°C) (L/mol) 30

27.9±3.0

0.9999

40

45.0±3.0

0.9007

50

51.8±4.3

0.9739


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The volume of activation (ΔV ≠ ) for a reaction represents the difference in the partial molar volumes between the transition state and the reactants (Vt ― ∑Vr) and is directly related to the equilibrium constant (Keq) of the reaction

36,

37.

The rate constant of a reaction

aA+bBXProducts, is given by Equation 5 38: k=

RT ≠ γAγB RT ≠ K = Keq Κγ Nh eq γΧ≠ Nh

(E5)

≠ where Keq is the equilibrium constant at infinite dilution for the conversion of the reactants to the

transition state X, and γ are the corresponding activity coefficients. Kγ is used to symbolize the ratio of γAγB γΧ≠ . The pressure dependence of the rate constant is split into two contributions as per Equation 6 38: ≠ ∂lnKeq

( ) ( ∂lnk ∂P

≠ By substituting lnKeq =-ΔG/RT and

=

∂P

T

) ( ) +

T

∂lnΚγ ∂P

(∂∂ GP)T = V, we obtain Equation 7

( ) ∂lnk ∂P

T

∂lnΚγ ΔV ≠ =― + ∂P RT

(E6)

T 38:

( )

(E7)

T

ΔG corresponds to the change in the standard partial molar free energies (chemical potentials) between the transition state and the reactants 38. The Eyring-Arrhenius model (Equation 8) has been proposed by several researchers, and summarized by Serment-Moreno et al.

36,

to describe the combined effects of pressure and

temperature on the rate constant (k).

[

]

Ea(P) 1 1 ΔV ≠ (T) (P ― Pref) k = kref,T,Pexp ― ― ― RT R T Tref

(

)


(E8)

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Based on the data in Tables 2 and 3, a linear relation of Ea (kJ/mol) and ΔV ≠ (L/mol) with respect to pressure and temperature, respectively, was found (Equations 9-10). Ea(P) = ―25.2 ∙ (P ― Pref) + 62.6

(R2=0.9195)

(E9)

ΔV ≠ (T) = 1.2 ∙ (T ― Tref) + 53.5

(R2=0.9410)

(E10)

Using Equations 8, 9 and 10, the k values were estimated for the temperature (30-50 °C) and pressure (0.35-0.75 bar) range of interest in this study. The very good agreement between the modeled and the experimental k values is presented in Figure 8, where a direct comparison between them is conducted.

Figure 8 – Eyring-Arrhenius model validation for the estimation of k values for TMA desorption

The k values presented for TMA desorption can be used in a process simulation software, such as Aspen Plus or OLI Flowsheet, to develop a rate-based process model to design and scale-up the draw solute separation process. Such a model is more accurate for scale-up and design than an equilibrium-based one, given the mass-transfer limited nature of the reactions.


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4. Conclusions The draw solute separation process accounts for the majority of the energy requirements in Forward Osmosis. A rate-based model is necessary to design and scale-up the unit operations infrastructure in a process simulation software. The development of such model relies on the availability of accurate k values for the rate determining step. This study focused on the TMACO2 draw solute separation efficiency and investigated the combined effects of temperature (30, 40 and 50 °C) and pressure (0.75, 0.55 and 0.35 bar) on the TMA-CO2-H2O draw solution decomposition. The draw solute separation was found to be stoichiometric and efficient. Approximately 100% of the draw solutes was separated at 50 °C, 0.35 bar after 60 min, while the molar ratio of TMA:CO2 in solution was always around 1.1. This suggest that TMA(g) and CO2(g)

escape from solution at similar rates, and thus, can be reused directly in a subsequent CDS

regeneration process. The draw solute separation is controlled by the desorption of the less volatile gas from solution, which is TMA. The k values for TMA desorption were significantly affected only by the temperature (not by the pressure), based on ANOVA results. An Eyring-Arrhenius model was developed to describe the combined effects of pressure and temperature on TMA desorption rate constants (k) and estimate their values from 30 to 50 °C, and 0.75 to 0.35 bar.

5. Acknowledgements The authors would like to acknowledge the Natural Sciences and Engineering Research Council of Canada (NSERC Fund Number: RPGIN 105655-2013) for the financial support in this project,


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and Amy M. Holland and Timothy J. Clark from Forward Water Technologies Inc., ON, Canada for their technical assistance.

6. Supporting Information Tables S1 and S2 present the k values for the desorption of TMA (Reaction 6) and CO2 (Reaction 9), and the k values for the overall drop in the total dissolved TMA concentration, respectively.

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Table of Contents Graphic


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Temperature and Pressure Effects on the Separation Efficiency and

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