Equilibrium Sorption of Propane and 1-Hexene in Polyethylene

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Equilibrium sorption of propane and 1-hexene in polyethylene: experiments and PC-SAFT simulations Josef Chmelar, Kate#ina Haškovcová, Martina Podivinská, and Juraj Kosek Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 23 May 2017 Downloaded from http://pubs.acs.org on May 30, 2017

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Industrial & Engineering Chemistry Research

Equilibrium sorption of propane and 1-hexene in polyethylene: experiments and PC-SAFT simulations Josef Chmelař, Kateřina Haškovcová, Martina Podivinská, Juraj Kosek* Department of Chemical Engineering, University of Chemistry and Technology, Prague, Technická 5, 166 28 Prague 6, Czech Republic * Corresponding author: Tel.: +420 220 44 3296; fax: +420 220 44 4320; e-mail: [email protected]

Abstract The availability of sorption equilibrium data is important for the design and optimization of polymerization processes. In this work, we used a gravimetric apparatus based on a magnetic suspension balance and the PC-SAFT equation of state to study the equilibrium sorption of propane and 1-hexene in polyethylene (PE). Propane is used as a diluent in the gas-phase catalytic polymerization of ethylene, while 1-hexene is a commonly used co-monomer. Experiments were carried out at industrially relevant conditions using a large set of PE samples with densities from 902 to 967 kg m-3. The solubilities were rigorously evaluated using temperature dependent crystallinities and swelling corrections were considered. The solubilities of both penetrants increased with decreasing temperature and decreasing PE crystallinity. Additionally, the PC-SAFT binary interaction parameters did not depend on the temperature. Such dependencies are predicted by theory, but only rarely obtained for complex samples such as semi-crystalline polymers. The fact that the penetrant solubilities depend on the crystallinity despite being evaluated per gram of amorphous PE supports the concept of elastic constraints. Keywords: polyethylene; gravimetry; PC-SAFT.

1. Introduction Polyethylene (PE) is amongst the most widely used synthetic polymers. The sorption of low molecular weight species in PE plays an important role in PE production, where it influences the polymerization rate in the reactor, the composition of ethylene copolymers with α-olefins (and thus the product properties), the duration of the subsequent degassing step and the agglomeration of PE particles due to softening1. This paper is concerned with equilibrium sorption in PE at conditions relevant to the catalytic gas-phase ethylene polymerization, which is carried out in fluidized bed reactors. Various low molecular weight species are present in the

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industrial reactors, namely the monomer ethylene, co-monomer(s) and other compounds such as diluents or condensing agents. Sorption processes in PE were studied in a large number of papers, however, only a few of these were carried out at conditions relevant to industrial catalytic gas-phase polymerization. Furthermore, the published studies are often limited to a narrow range of temperatures and/or PE properties. The only exception is ethylene, the sorption of which is well described both in semicrystalline PE2-6 and in PE melts4, 6-10. In the case of typical co-monomers, a reasonable set of data is available for 1-hexene2, 4, 11, 12, while only limited results were published for 1-butene2, 11 and 1-octene11. However, there is no work that would study and theoretically interpret the sorption of a co-monomer in PE over a broad range of temperature, pressure and PE crystallinity. The situation is even worse for the inert species. The solubility of n-hexane, which is commonly used as a condensing agent13, was only measured at industrially relevant conditions by Yao et al.5. To the best of our knowledge, no solubility data at reactor conditions are available for propane, which is the most commonly used organic diluent. The sorption of propane in PE was only measured at low temperatures from 5 to 35 °C 14 or in molten PE15. Currently, gravimetry based on a magnetic suspension balance (MSB) can be regarded as the state-of-the-art technique for solubility measurements due to its high precision and also because the weighing mechanism is separated from the measuring cell, which eliminates the pressure and temperature limitations present in quartz spring devices. This technique was used to measure the sorption of ethylene3 and ethylene and 1-hexene4 in HDPE and of ethylene in a broad range of PE samples at temperatures from 60 to 150°C6. In this work, we used the MSB to measure the sorption of 1-hexene and propane in a broad range of PE samples at temperatures and pressures relevant to the industrial catalytic gasphase polymerization. The measured data were rigorously evaluated using temperature dependent crystallinities and swelling corrections were considered. The obtained solubilities were then correlated using the PC-SAFT equation of state16 and the observed trends were theoretically interpreted and compared with our previous results6 obtained for the sorption of ethylene in PE.

2. Materials and methods 2.1. Polyethylene samples For the experiments, we used a large set of PE samples (Table 1) provided by the courtesy of LyondellBasell. Except for those with the highest densities, the samples were copolymers of ethylene and 1-hexene with varying content of the co-monomer. All samples were nascent reactor powders from the gas-phase process and no further processing (e.g., annealing or pelletization) was performed. The densities of PE samples ranged from 902 to 967 kg m-3, the samples thus included linear very low density PE (VLLDPE), linear low-density PE (LLDPE), medium-density PE (MDPE) and high-density PE (HDPE). The weight fraction crystallinity wcr was calculated from 2 ACS Paragon Plus Environment

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the sample density using the values of 855 and 1000 kg m-3 for the amorphous and crystalline phase densities, respectively17, 18. Full molecular weight distribution data were not provided by the sample supplier, but all samples had weight average molecular weights (Mw) well above 50 kg mol-1 and none of them contained fractions with ultra-high or very low molecular weight. In this range of Mw, the equilibrium solubilities of penetrants per unit mass of a polymer are independent on Mw19-21 and, therefore, the knowledge of precise Mw values is not necessary for the discussion of our results. Table 1: Overview of PE samples used for the experiments. The density ρ and weight fraction crystallinity wcr are values obtained at room temperature. Sample ρ / kg m-3 wcr VLLDPE A 902 0.359 VLLDPE B 902 0.359 LLDPE A 910 0.417 LLDPE B 918 0.473 LLDPE C 918 0.473 LLDPE D 923 0.508 LLDPE E 927 0.534 MDPE A 936 0.600 MDPE B 938 0.608 MDPE C 939 0.617 HDPE A 941 0.630 HDPE B 941 0.631 HDPE C 947 0.668 HDPE D 950 0.690 HDPE E 951 0.696 HDPE F 967 0.799

2.2. Gravimetric apparatus The gravimetric apparatus (Fig. 1) used to measure the sorption equilibrium data is based on a magnetic suspension balance (Rubotherm GmbH) connected to a pressure cell that contains the polymer sample. The temperature in the pressure cell can be precisely regulated, which together with the sensitivity of the balance (10 µg) results in a very high precision of the measurement. A more detailed description of the apparatus can be found elsewhere6. During the experiment, the pressure, temperature, and sample mass are recorded. The sorption isotherms are then evaluated from the pressure dependence of the sample mass at sorption equilibrium. In order to obtain correct solubilities, several phenomena must be considered: the time drift of the balance, buoyant forces and polymer swelling. If all necessary corrections are applied, the uncertainty of the obtained solubilities is well below 3%22.



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80.0

Industrial computer

Balance Balance 0.00001g 0.00001g

He N2

Thermostat

C N32 Hot oil circulation Control unit

Vacuum pump Waste

T

Gas outlet P 40.0

T

P 1-hexene in thermostated bath

Liquid outlet

Polymer sample

Fig. 1: Simplified scheme of the gravimetric apparatus. The correction to the time drift of the balance is calculated from the polymer sample mass in vacuum measured at the beginning and end of the experiment. Assuming a linear drift of the balance, we get: m exp (0, T ,0 ) − m exp (0, T , t end ) (1) m tcor ( p, T , t ) = m exp ( p , T , t ) + t t end where mtcor(p,T,t) and mexp(p,T,t) are the mass corrected to the time drift and experimentally measured mass at pressure p, temperature T and time t, and tend is the overall time of the experiment. Subsequently, the following correction is applied to account for the buoyant forces and polymer volume changes due to swelling: (2) mcor ( p, T ) = m tcor ( p, T ) + ρ gas ( p, T )[Vtotal (0, T ) + ∆Vswell ( p, T )] where mcor(p,T) is the mass with all corrections, ρgas(p,T) is the gas phase density, Vtotal(0,T) is the volume of the weighed object (sample, basket and hook) measured in vacuum23 and ∆Vswell is the polymer volume change due to swelling. The dependence of ∆Vswell on the temperature and penetrant pressure is obtained experimentally using video-microscopy23, 24. This is an important point, since the use of equations of state for predicting polymer swelling can result in large errors4, 25. The solubility S is then calculated as: m ( p, T ) − mcor (0, T ) S ( p, T ) = cor (3) mpolymer where mpolymer is the mass of the polymer sample. 4 ACS Paragon Plus Environment

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The solubility S is obtained in g penetrant per g of PE. Since PE is semi-crystalline and the solubility of penetrants in the crystals is zero, it is reasonable to evaluate solubilities in g penetrant per g of amorphous PE (Sam PE), which are calculated as: S ( p, T ) (4) S am PE ( p, T ) = 1 − wcr (T ) where wcr(T) is the weight fraction crystallinity at temperature T. The temperature dependence of the crystallinity was estimated according to Paricaud et al.21. As we demonstrated in our previous paper6, the use of wcr(T) instead of a constant crystallinity (the room temperature value is often used) is an essential step of the data evaluation process, which is, however, not usually employed. 2.3. PC-SAFT Equation of State At the moment, molecular based equations of state can be regarded as state of the art tools for calculating the phase equilibria of polymer systems. In this manuscript, the solubility data are correlated using the Perturbed-Chain Statistical Associating Fluid Theory equation of state (PCSAFT), which was developed by Sadowski and co-workers16, 26-28. PC-SAFT accounts for the size and shape of molecules, dispersion forces, and association. Advantageously, PC-SAFT can explicitly consider the chain-like structure of polymers. In the PC-SAFT model, each compound is described by a set of pure component parameters, which are constants that do not depend on the temperature, pressure and composition of the system. They can thus be tabulated and are available in the literature for a large number of compounds. These parameters are: (i) the number of segments per molecule m, (ii) the temperature independent segment diameter σ and (iii) the segment energy parameter ε/k, where k is the Boltzmann constant. In general, the pure component parameters of polymers are functions of the molecular weight. However, σ and ε/k converge to constant values for sufficiently high molecular weights26. Furthermore, the solubility of penetrants per unit mass of a polymer reaches a limit value for long polymer chains19-21. Since the PE samples studied in this work all had high weight average molecular weights above 50 kg mol-1, we could consider the molecular weight of PE to be 50 kg mol-1 without affecting the calculated solubilities 29, 30. We also considered PE as monodisperse, which is a reasonable approximation when calculating solubilities in polymers with high molecular weights26, 28, 31. To calculate the sorption equilibria, only the pure component parameters and the binary interaction parameter ki,j are required. The pure component parameters used in this work (Table 2) were carefully selected from the literature according to a procedure presented previously23. In the literature, the binary interaction parameters ki,j are often considered temperature dependent for pairs containing a polymer and the type of the dependence can vary among individual authors. We therefore did not take any values from the literature and rather obtained the ki,j by the fitting of experimental solubility data.



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Table 2. List of pure component parameters used in this study. For PE, a weight average molecular weight of 50 kg mol-1 was considered. Compound m/σ/Å (ε/k) / K Reference propane 2.0020 3.6184 208.11 Gross and Sadowski, 2001 16 1-hexene 2.9853 3.7753 236.81 Gross and Sadowski, 2001 16 polyethylene 1316.9 3.9876 246.00 Novak et al., 2006 4 It should be noted that PC-SAFT is based on a high-temperature perturbation theory of fluids and therefore does not consider the solid state. However, PC-SAFT provides satisfactory results also for amorphous solids, including the amorphous phase of PE. sA more detailed discussion on the use of PC-SAFT for semi-crystalline PE can be found elsewhere6. To evaluate the accuracy of the PC-SAFT calculations, we have to quantify the deviations between experimental and calculated solubility data. For this purpose, the average relative deviation (ARD) was chosen: ARD =

100 n

n

∑ i =1

exp model S am PE, i − S am PE, i

(5)

exp S am PE, i

exp model where n is the number of experimental points in an isotherm and S am PE, i and S am PE, i are the

experimental and calculated solubilities at the i-th point of the isotherm, respectively.

3. Results and discussion In this section, we present the measured propane and 1-hexene sorption isotherms (full data set in tabular form can be found in the Supporting information), correlate these isotherms using the PC-SAFT equation of state and discuss the obtained results with emphasis on the theory of elastic constrains. 3.1. Effect of swelling on the evaluation of propane and 1-hexene solubilities As described in Section 2.2., polymer swelling must be considered in the evaluation of gravimetric sorption data (see Equation 2). On the basis of sorption and swelling experiments, Podivinska et al. evaluated the errors in solubility data resulting from neglecting the polymer swelling in the case of propane and 1-hexene sorption in PE24. A detailed description of the error calculation can be found in the literature23. In the case of propane, the maximum error is about 12 % (at 100°C and 30 bar), meaning that the swelling of PE by propane must be accounted for. However, in the case of 1-hexene, the error is always below 1 %. Consequently, the swelling of PE by 1-hexene can be neglected in the evaluation of gravimetric data, since the introduced error is well below the accuracy of the gravimetric measurement itself.


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3.2. Equilibrium sorption of propane and 1-hexene in PE In general, the solubility of penetrants in the amorphous phase of PE (Sam PE) depends on the type of penetrant, its pressure in the gas-phase, temperature and PE properties. The more condensable is the penetrant, the higher will be its solubility in a polymer at a given pressure32. For chemically similar compounds such as the linear aliphatic hydrocarbons studied in this work, the condensability of a gaseous penetrant at a given temperature and pressure increases with the molecular weight of the penetrant. Therefore, also the solubility will increase with the penetrant molecular weight, as shown in Fig. 2.

Solubility / (g/gam PE)

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0.12

1-hexene

1-butene

0.10

Propene

Ethylene

Propane

0.08 0.06 0.04 0.02 0.00 0

5

10

15

20

p / bar Fig. 2: Comparison of various sorption isotherms in LLDPE D at 80°C. Solid lines are to guide the eye. The dependence of Sam PE on the penetrant pressure is relatively simple. The solubility of both propane and 1-hexene increases with the penetrant pressure for all studied PE samples and in the whole temperature and pressure range explored. One can see in Fig. 3 to 6 that Sam PE depends on the pressure non-linearly, especially in the case of 1-hexene. The sorption isotherms are shaped upward (convex), because the interaction force among the penetrant molecules is more favorable than the penetrant-polymer interaction21. Also the clustering of penetrant molecules may be important in this case33. Upward-shaped isotherms are typical for highly soluble hydrocarbons. The solubility of propane (Fig. 3) and 1-hexene (Fig. 4) in the amorphous phase of PE decreases with increasing temperature, in agreement with theory. In short, the enthalpy of sorption ∆HS is the sum of the enthalpy of condensation ∆Hcond and the enthalpy of mixing ∆Hmix. For condensable species such as propane or 1-hexene, ∆Hcond is negative and significantly larger than ∆Hmix, resulting in a negative ∆HS. Therefore, the sorption of these penetrants is exothermic and their solubilities decrease with increasing temperature32. The main reason why the observed trends agree with theory is the rigorous use of the temperature dependent crystallinity. If the room temperature crystallinity would be used for the data evaluation at all experimental temperatures, the results could be much more ambiguous due to the neglecting of the partial melting of PE that takes place at elevated temperatures6.



Solubility / (gprop/gam PE)

0.4

60°C (0.381) 80°C (0.336)

0.3

100°C (0.240) 0.2

0.1

0.0 0

5

10

15

20

25

30

35

p / bar Fig. 3: Sorption isotherms of propane in LLDPE A. Solid lines are fitted PC-SAFT isotherms. Crystallinities wcr at the experimental temperature are listed in the legend.

0.6

Solubility / (ghex/gam PE)

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80°C (0.336) 90°C (0.298) 100°C (0.240)

0.5 0.4 0.3 0.2 0.1 0.0 0.0

0.5

1.0

1.5

p / bar

2.0

2.5

Fig. 4: Sorption isotherms of 1-hexene in LLDPE A. Solid lines are fitted PC-SAFT isotherms. Crystallinities wcr at the experimental temperature are listed in the legend. The effect of PE crystallinity on the solubilities of propane and 1-hexene is demonstrated in Fig. 5 and Fig. 6, respectively. Although the solubilities were calculated in g penetrant per g of amorphous PE, one can clearly see that they decrease with increasing crystallinity. The same trend was obtained at all other experimental temperatures for both penetrants. Similar observations were reported also in other papers concerned with penetrant sorption in semicrystalline PE2, 6, 11, 12. The decrease of penetrant solubility in the amorphous phase of PE at higher crystallinities can be attributed to elastic constraints. This topic will be further discussed in the next section.


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Solubility / (gprop/gam PE)

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0.3

LLDPE A (0.336) LLDPE D (0.443) MDPE A (0.554)

0.2

HDPE F (0.789) 0.1

0.0 0

5

10

15

20

25

p / bar Fig. 5: Effect of polyethylene crystallinity on the propane solubility in the amorphous phase of PE samples at 80°C. Solid lines are fitted PC-SAFT isotherms. Crystallinities wcr at the experimental temperature are listed in the legend. 0.5

Solubility / (ghex/gam PE)

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VLLDPE B (0.272) 0.4

LLDPE E (0.475) MDPE C (0.575)

0.3

HDPE E (0.671)

0.2 0.1 0.0 0

0.5

p / bar

1

1.5

Fig. 6: Effect of polyethylene crystallinity on the 1-hexene solubility in the amorphous phase of PE samples at 80°C. Solid lines are fitted PC-SAFT isotherms. Crystallinities wcr at the experimental temperature are listed in the legend.

3.3. PC-SAFT fitting and interpretation of the data The measured sorption isotherms were fitted by the PC-SAFT equation of state. One can see in Fig. 3 to 6 that the fitted isotherms are in a good agreement with the experimental data for both penetrants and at all temperatures. The fitting errors (ARD, Equation 5) were: (i) 4.7 % in average with a maximum value of 9.2 % for propane, and (ii) 5.7 % in average with a maximum value of 10.7 % for 1-hexene. The binary interaction parameters kPE,propane and kPE,1-hexene obtained by the fitting are presented in Fig. 7 (data in tabular form can be found in the Supporting information). Both parameters exhibit some scatter, which can be expected, since they were evaluated from experimental data measured for PE samples with a broad range of densities from 902 to 967 kg m-3 (room temperature values) at temperatures from 60 to 90°C.



0.07

Propane, 60°C Propane, 80°C

0.06

Propane, 100°C

0.05

1-hexene, 80°C 1-hexene, 90°C

0.04

ki,j

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1-hexene, 100°C Moore (2001)

0.03 0.02 0.01 0.00 0.0

0.2

0.4

0.6

0.8

Crystallinity at experimental temperature Fig. 7: PC-SAFT binary interaction parameters evaluated from our experimental data and from the 1-hexene sorption isotherms presented by Moore and Wanke2. Several important conclusions can be made based on Fig. 7. Firstly, both kPE,propane and kPE,1-hexene show an approximately linear dependence on PE crystallinity, while not exhibiting any clear dependence on temperature (at least with respect to the scatter of the data). In other words, we can consider that both ki,j depend only on PE properties, but not on the temperature. Although this would be expected based on theory, such results are only rarely obtained for systems comprising polymers with semi-crystalline morphology. For example, even relatively recent studies of ethylene sorption in PE considered strong temperature dependencies of kPE,ethylene despite the use of advanced equations of state, namely PC-SAFT34, 35 and Sanchez-Lacombe35, 36. As already suggested in our previous paper6, the fact that we obtained temperature independent ki,j can be attributed to the rigorous evaluation of gravimetric data using temperature dependent crystallinity and, in the case of propane, swelling corrections based on experimental data. Secondly, kPE,1-hexene is lower than kPE,propane over the entire range of crystallinities explored. Similarly, a comparison with the literature6 shows that kPE,propane is systematically lower than kPE,ethylene (Fig. 8). In PC-SAFT, the purpose of ki,j is to correct the energy interactions of unlike chains segments16, in our case, the chain segments of PE and the penetrant. The more similar the polymer and penetrant are, the lower ki,j is needed. As a result, the ki,j is lower for longer aliphatic hydrocarbons than for the shorter ones, since the former are more similar to PE.


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0.12

Ethylene Propane

0.10

1-hexene 0.08

ki,j

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.06 0.04 0.02 0.00 0.1

0.3

0.5

0.7

0.9

Crystallinity at experimental temperature Fig. 8: Comparison of kPE,1-hexene and kPE,propane (this work) with kPE,ethylene data6 obtained from ethylene sorption isotherms measured at temperatures from 60 to 110 °C. We compared our 1-hexene sorption data with those presented in the work of Moore and Wanke . Data from this particular work were frequently cited and used by other authors and can thus be considered reliable. One can see in Fig. 7 that kPE,1-hexene evaluated from our data and from those of Moore and Wanke2 agree very well. However, when we fitted the data presented by Jin and co-workers12, the obtained kPE,1-hexene were significantly higher than those presented in Fig. 7. We suggest that the possible cause are the crystallinities measured by the authors (DSC data), which are very low when compared to the presented PE densities. Higher crystallinities would lead to higher Sam PE and thus lower kPE,1-hexene. Note that in both cases, the data from the literature were recalculated to include the effect of temperature on PE crystallinity. In the case of propane, no comparison with the literature can be made, since, to the best of our knowledge, no solubility data at similar conditions were published for this penetrant. The last point to address is the dependence of the solubility on PE crystallinity. The solubility Sam PE of both propane and 1-hexene decreases with increasing crystallinity, although the solubilities were calculated per g of amorphous PE. This can be seen in Fig. 7 as an increase of both ki,j with increasing crystallinity. These findings support the theory of elastic constraints29, 37, 38 , which suggests that the chain segments in the amorphous phase of semi-crystalline polymers are constrained by the adjacent crystallites (a detailed discussion on the problem of constrained and un-constrained (free) amorphous phase can be found elsewhere39). The constraining of the amorphous phase will be more significant at higher crystallinities, resulting in lower penetrant solubilities and thus higher ki,j. The same observations were made in our previous study6 of ethylene sorption in PE (see kPE,ethylene in Fig. 8). We can thus generalize and conclude 2



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that the results of systematic studies of penetrant sorption in semi-crystalline PE covering a broad range of temperatures and PE crystallinities clearly support the concept of elastic constraints.

4. Conclusions We measured the equilibrium solubilities of propane and 1-hexene in a large set of PE samples with room temperature densities from 902 to 967 kg m-3 at temperatures and pressures relevant to industrial catalytic gas-phase polymerization of ethylene. The solubilities were evaluated in grams of penetrant per gram of amorphous PE using temperature dependent crystallinities and considering swelling corrections. At a single pressure, the solubility of 1hexene was significantly larger than that of propane. The solubility data follow several trends that are expected from theory, but only rarely observed for systems comprising semi-crystalline polymers. Both propane and 1-hexene solubilities increased with decreasing temperature and decreasing PE crystallinity. Furthermore, the PC-SAFT binary interaction parameters kPE,propane and kPE,1-hexene depended only on the crystallinity of PE, i.e., they could be considered as independent on the temperature. At a given PE crystallinity, kPE,1-hexene is lower than kPE,propane, which in turn is lower than kPE,ethylene6. Since the purpose of ki,j in PC-SAFT is to correct the energy interactions of unlike chains segments (polymer and penetrant), this trend can be explained by the fact that the longer aliphatic hydrocarbons are closer to PE than the shorter ones, at least with respect to their representation in PC-SAFT. Both kPE,propane and kPE,1-hexene are increasing with crystallinity, meaning that the solubility per gram of the amorphous phase decreases with crystallinity. This trend supports the theory of elastic constraints, as the chains segments in the amorphous phase were clearly affected by the adjacent crystallites. The constraining effect is commonly attributed to the so-called elastically effective chains (e.g., tie-chains) that limit the swelling of the amorphous phase. The amount of elastically effective chains should increase with increasing crystallinity. These assumptions are in agreement with our results. The measured experimental data and evaluated PC-SAFT binary interaction parameters should serve as inputs into process models of gas-phase ethylene polymerization or other studies concerned with ethylene polymerization kinetics. The equilibrium solubility of the co-monomer 1-hexene determines the maximum rate of its incorporation into the co-polymer. Furthermore, the sorption of 1-hexene increases the ethylene solubility in PE by the sorption enhancement effect30, thus increasing the rate of ethylene polymerization4 (also known as the co-monomer effect). Propane is used in ethylene polymerization as an inert diluent that helps to improve the heat removal40, 41. However, the sorption of inert species in PE has also an effect on the polymerization rate by influencing the solubilities of other penetrants and the polymer swelling, as was described in detail for the case of n-hexane42. The above mentioned relations between the sorption phenomena and both the ethylene and co-monomer reaction rates are important and must


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be considered, since the reaction rates determine the co-polymer composition and thus the resulting product properties13, 43-45.

Acknowledgements Financial support from the Czech Grant Agency (GA16-07898S) and Specific University Research (MSMT No. 20/2016) is acknowledged. The authors would also like to thank A. Novak and A. Nistor for their contribution to the gravimetric measurements.

Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Full set of experimental solubility data and fitted values of binary interaction parameters kPE,propane and kPE,1-hexene in tabular form (PDF).

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TABLE OF CONTENTS GRAPHIC

Solubility in PE

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Experiments

1-hexene

+

Propane

PC-SAFT simulations

Pressure


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Equilibrium Sorption of Propane and 1-Hexene in Polyethylene

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