EHigh-pressure liquid-liquid equilibrium boundaries for systems containing polybutadiene and/or...

Elsevier Editorial System(tm) for The Journal of Supercritical fluids Manuscript Draft Manuscript Number: SUPFLU-D-12-00163R2 Title: High-pressure liquid-liquid equilibrium boundaries for systems containing polybutadiene and/or polyethylene and a light solvent or solvent mixture Article Type: Regular Paper Keywords: Polybutadiene; Polyethylene; Dimethyl ether; n-Pentane; Cloud point; Liquid-liquid equilibrium Corresponding Author: Dr. Marcelo Santiago Zabaloy, PhD Corresponding Author's Institution: Universidad Nacional del Sur - Planta Piloto de Ingeniería Química -CONICET First Author: Juan M Milanesio, Ph D Order of Authors: Juan M Milanesio, Ph D; Guillermo D Mabe, Bachelor in Chemical Engineering; Andrés E Ciolino, Ph D; Lidia M Quinzani, Ph D; Marcelo Santiago Zabaloy, PhD Abstract: In this work, we have obtained experimental cloud points, i.e., liquid-liquid equilibrium boundaries at constant composition, for the systems 'polybutadiene (PB) + n-pentane (C5)', 'PB + dimethyl ether (DME) + C5', 'polyethylene (PE) + DME + C5', and 'PB + PE + DME + C5'. The temperature range of the experiments was from 50 to 184 °C. The maximum pressure was 303 bar. In all cases the overall polymer concentration was less than or equal to 4.1 wt%. At the ranges of conditions of the experiments we have found the following: (a) For PB + C5, the minimum pressure required to guarantee homogeneity is 140 bar. (b) For 'PB + C5 + DME', the cloud point pressure (CPP) curves lie in between the CPP curves of 'PB + DME' and 'PB + C5', and the maximum CPP was 226 bar. The CPP increases with the increase of the DME/C5 ratio in the solvent mixture. (c) For 'PE + DME + C5', there is a substantial decrease in the CPPs with the addition of C5 to the DME + C5 solvent mixture, and the maximum CPP was 303 bar. (d) The CPPs for 'PB + PE + DME + C5' are higher than the CPPs of 'PB + DME + C5' but lower than the CPPs of 'PE + DME + C5'.

October 23rd 2012

Ms. Ref. No.: SUPFLU-D-12-00163R1

Dear Richard,

In response to your e-mail, which I reproduce below, I inform you that we have

made all the required editorial corrections, and have uploaded the corresponding

files.

Among the files uploaded yesterday, we have not replaced the one

corresponding to the Supplementary Material, which did not require changes.

The problems in the “References” section seems to arise during the production

of the PDF file by the EES web site. Please Check the source file, i.e., the file

“MiMaCiQuiZa REV paper corr UNLINKED.doc”, which should show all the

references with their complete bibliographic information.

Best Regards.

Dr Marcelo S. Zabaloy Profesor Adjunto – Investigador Independiente Universidad Nacional del Sur - Planta Piloto de Ingenieria Quimica PLAPIQUI (UNS-CONICET) Camino La Carrindanga Km 7 Casilla de Correo 717 (8000) Bahia Blanca ARGENTINA Phone: 54-291-486-1700 Ext. 232 FAX : 54-291-486-1600 e-mail: [email protected]

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Title: High-pressure liquid-liquid equilibrium boundaries

for systems containing polybutadiene and/or polyethylene and

a light solvent or solvent mixture

The Journal of Supercritical Fluids

Dear Marcelo,

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Note: a “Response to Reviewers” file is not required, according to the e-mail

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will need to be resubmitted, responses to the reviewers

are not needed or a reply to this letter can be used instead if the EES system requires the file.”

Your Submission martes, 23 de octubre de 2012, 7:55

De:

"Richard Smith" <[email protected]> Agregar remitente a Contactos

Para: [email protected]

Cc:

[email protected]


Title: High-pressure liquid-liquid equilibrium boundaries

for systems containing polybutadiene and/or polyethylene and

a light solvent or solvent mixture


Dear Marcelo,

I have studied the revisions made to the text and am very

satisfied with the changes made by the authors. However,

there are a number of editorial corrections (attached pdf

file) that I hope that you can make at your earliest

convenience. Please note that many of these changes are

small. However, some may require some checking due to some

missing numbers in the reference section that may be due to

only formatting.

After I receive the next revision, I will be able to issue a


will need to be resubmitted, responses to the reviewers are

not needed or a reply to this letter can be used instead if

the EES system requires the file.

To submit a revision, please go

to http://ees.elsevier.com/supflu/ and login as an Author.

*Response to Reviewers

http://ees.elsevier.com/supflu/

Your username is: mszabaloy

If you need to retrieve password details, please go to:


On your Main Menu page is a folder entitled "Submissions

Needing Revision". You will find your submission record

there.

Yours sincerely,

Richard L. Smith

Receiving Editor



1

High-pressure liquid-liquid equilibrium boundaries for systems containing

polybutadiene and/or polyethylene and a light solvent or solvent mixture

Juan M. Milanesio, Guillermo D. B. Mabe, Andrés E. Ciolino, Lidia M. Quinzani and Marcelo S. Zabaloy

PLAPIQUI – Planta Piloto de Ingeniería Química, Universidad Nacional del Sur - CONICET, Cno. La Carrindanga km. 7, CC 717 – 8000 – Bahía Blanca, Argentina

Corresponding author. Tel 0054 (0291-4861700 ext 232). E-mail: [email protected]

*Graphical Abstract (for review)

1

High-pressure liquid-liquid equilibrium boundaries

for systems containing polybutadiene and/or polyethylene and a

light solvent or solvent mixture

Juan M. Milanesio, Guillermo D. B. Mabe, Andrés E. Ciolino, Lidia M. Quinzani and

Marcelo S. Zabaloy

PLAPIQUI – Planta Piloto de Ingeniería Química, Universidad Nacional del Sur - CONICET, Cno. La

Carrindanga km. 7, CC 717 – 8000 – Bahía Blanca, Argentina

Cloud point pressure (CPP) of the system ‘polybutadiene (PB) + n-pentane (C5)

+ dimethyl ether (DME)’ increases with an increase in DME/C5 ratio.

CPP of the system ‘polyethylene (PE) + DME + C5’ substantially decreases with

addition of C5 to the DME + C5 solvent mixture.

CPPs for ‘PB + PE + DME + C5’ are higher than the CPPs of ‘PB + DME + C5’ but

lower than the CPPs of ‘PE + DME + C5’.


*Highlights (for review)

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1

High-pressure liquid-liquid equilibrium boundaries

for systems containing polybutadiene and/or polyethylene

and a light solvent or solvent mixture

Juan M. Milanesio, Guillermo D. B. Mabe, Andrés E. Ciolino, Lidia M. Quinzani

and Marcelo S. Zabaloy

PLAPIQUI – Planta Piloto de Ingeniería Química, Universidad Nacional del Sur - CONICET,

Cno. La Carrindanga km. 7, CC 717 – 8000 – Bahía Blanca, Argentina

Abstract

In this work, we have obtained experimental cloud points, i.e., liquid-liquid equilibrium

boundaries at constant composition, for the systems 'polybutadiene (PB) + n-pentane

(C5)', „PB + dimethyl ether (DME) + C5', 'polyethylene (PE) + DME + C5', and 'PB +

PE + DME + C5'. The temperature range of the experiments was from 50 to 184 °C.

The maximum pressure was 303 bar. In all cases the overall polymer concentration

was less than or equal to 4.1 wt%. At the ranges of conditions of the experiments we

have found the following: (a) For PB + C5, the minimum pressure required to

guarantee homogeneity is 140 bar. (b) For „PB + C5 + DME‟, the cloud point pressure

(CPP) curves lie in between the CPP curves of „PB + DME‟ and „PB + C5‟, and the

maximum CPP was 226 bar. The CPP increases with the increase of the DME/C5

ratio in the solvent mixture. (c) For „PE + DME + C5‟, there is a substantial decrease


*ManuscriptClick here to view linked References

http://ees.elsevier.com/supflu/viewRCResults.aspx?pdf=1&docID=3139&rev=2&fileID=111331&msid=AE9DFA9A-C20B-4EDD-B7D0-76978FC3E1E5

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2

in the CPPs with the addition of C5 to the DME + C5 solvent mixture, and the

maximum CPP was 303 bar. (d) The CPPs for „PB + PE + DME + C5‟ are higher than

the CPPs of „PB + DME + C5‟ but lower than the CPPs of „PE + DME + C5‟.

Keywords: Polybutadiene, Polyethylene, Dimethyl ether, n-Pentane, Cloud point, Liquid-

liquid equilibrium

1. Introduction

Supercritical fluids can be used in chemical reactions as solvents and also as reactive

components [1]. Examples of such reactions are oxidative reactions in supercritical water,

the high pressure polymerization of ethylene to produce polyethylene, and the production of

methyl-ethyl-ketone using supercritical butene [1]. In particular, hydrogenation reactions

performed using supercritical or near-critical solvents display higher reaction rates than the

conventional hydrogenation reaction. For example, the hydrogenation of sunflower oil using a

platinum catalyst, and supercritical propane as solvent, can be up to twelve times faster than

the conventional process [2]. Bertucco et al. [3] have reported an increase in the reaction

rate for the hydrogenation of unsaturated ketones, in the presence of supercritical CO2. Van

den Hark et al. [4] also reached extremely high reaction rates in the hydrogenation of fatty

acid methyl esters to obtain fatty alcohols, using supercritical propane as the solvent. The

important advantage of using a solvent at supercritical conditions is that the hydrogenation

process occurs in a homogeneous (fluid) medium, whereas, in the conventional

hydrogenation process, the system has always, at least, two fluid phases during the reaction

progress. The mass transfer resistance in the first case is much smaller than in the

conventional hydrogenation.

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In the particular case of polybutadiene (PB), the complete hydrogenation yields a copolymer

of ethylene and 1-butene (hPB) which highly resembles the structure of linear low-density

(LLD) polyethylene (PE) (LLDPE). Furthermore, PB may be synthesized using the anionic

polymerization technique, that makes possible to obtain polymers of very narrow molecular

weight distribution (Mw/Mn < ~1.2). Consequently, the hydrogenation of PBs obtained by

anionic polymerization can produce LLDPEs of narrow molecular weight distribution [5-16].

Information on conventional methods for hydrogenating PB is provided as supplementary

material.

To hydrogenate the PB under supercritical conditions, the solvent (or solvent mixture) should

be able to simultaneously dissolve the PB and the hydrogen. Moreover, the solvent mixture

should also dissolve the reaction product, i.e., the hydrogenated PB (hPB), if the reaction

rate were not high enough to achieve complete PB saturation before the partially

hydrogenated polymer precipitates. The high asymmetry of the reactive mixture, which is due

to the large difference in size between the H2 and PB molecules, implies a high immiscibility

level in the absence of the supercritical solvent or solvent mixture. On the other hand, the

subsystem 'solvent mixture + H2', should be miscible at the reaction conditions. The

subsystems 'PB + solvent mixture' and „PE + solvent mixture‟ (or hPB + solvent mixture) also

present a significant level of asymmetry. The 'PB + solvent mixture' subsystem should also

be homogeneous at the conditions of temperature, pressure and PB concentration range, at

which the hydrogenation is carried out.

The knowledge of the phase behavior of the subsystems of the reaction mixture should be

useful for estimating the operating conditions of the supercritical hydrogenation reactor.

Since the composition of the reaction mixture changes with the extent of reaction, so does its

phase condition. Some of the mentioned subsystems are the following: 'unsaturated polymer

+ solvent mixture', 'saturated polymer + solvent mixture' and 'unsaturated polymer +

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saturated polymer + solvent mixture'. These subsystems are related to the initial, final and

intermediate stages of the hydrogenation reaction, respectively.

The presence of a co-solvent, which together with the solvent makes up a solvent mixture,

could be useful to decrease the pressure needed to have an homogeneous reactive mixture,

throughout the reaction course. If this last condition were met, then, the solvent mixture

would be able to keep the unsaturated and the partially hydrogenated polymers

simultaneously dissolved within a single phase. The effect of the co-solvent concentration, on

the phase behavior of the subsystems of the reaction mixture, should be accounted for to

estimate the operating conditions of the hydrogenation reactor. The study of the phase

behavior of subsystems related to the PB hydrogenation has to pay attention to the nature of

the saturated and partially saturated polymers, to the reaction extent, and to the nature, and

relative concentrations within the solvent mixture, of the solvent and co-solvent.

Few authors have studied the high-pressure fluid phase behavior of „polymer + light solvent‟

systems for PB, hPB or PE. Winoto et al. [17] determined cloud-point pressures (CPPs) for

„PB + supercritical propane‟ and for „hPB + supercritical propane‟ at 0.5 wt% polymer

concentration. Using n-pentane (C5) as the solvent, Yeo et al. [18] determined isothermal

phase boundaries and the critical polymer concentrations for the pseudobinary system 'PE +

C5' at two different polymer molecular weights. Zhang et al. [19] measured isoplethic liquid-

liquid phase transitions for the same pseudobinary system and also studied the effect of the

addition of carbon dioxide as a co-solvent on the CPPs. Lee et al. [20] determined

experimental cloud points for the system 'PE + dimethyl ether (DME)' at high pressure. We

use the word “pseudobinary” instead of the word “binary” to mean that at least one of the

components of the system is not monodisperse.

In a previous work, Milanesio et al. [21] experimentally found, using a variable-volume

windowed equilibrium cell, homogeneity conditions, i.e., cloud points, for the pseudobinary

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mixtures propane + PB, diethyl ether (DEE) + PB, DME + PB, and DEE + high-density PE. In

PB-containing pseudobinary systems, at the ranges of conditions of the experiments [21], the

minimum pressure required to guarantee homogeneity, at any temperature, was below 200

bar for DEE, below 300 bar for DME and in the order of 500 bar when using propane as

solvent. The data for „PE + DEE‟ [21] indicated the need for a minimum pressure of about

240 bar to keep the system within a single phase. Milanesio et al. [21] suggested the use of

binary solvent mixtures, i.e., a combination of two solvents, since this would make it possible

to carry out the supercritical hydrogenation of PB under fluid homogeneity conditions while

operating the supercritical reactor at relatively moderate temperature and pressure. To

dissolve the hydrogen and carry out the hydrogenation reaction, a light solvent with relatively

low critical temperature and pressure is the better choice [21]. In contrast, the dissolution of

the polymers is boosted by a minimum degree of asymmetry between the polymer and the

solvent, i.e., by heavier solvents [21]. This led to suggesting the use of solvent mixtures

made of a light solvent and a relatively heavier one [21].

In this work, we experimentally determined liquid-liquid phase boundaries (CPPs), and hence

homogeneity conditions, not covered in reference [21], for a number of subsystems related to

the potential supercritical hydrogenation of PB. Such subsystems are the following: (a) 'PB +

C5', (b) 'PB + DME + C5' , (c) 'PE + DME + C5', and (d) 'PB + PE + DME + C5'. The choice

of DME as one of the solvents is because it presents a good trade off between the required

pressure for dissolving PB (below 300 bar, [21]) and the value of is critical temperature

(127.0 °C,Table 2). Propane has a more convenient critical temperature value (96.7 °C,

[22]) but requires higher pressures for dissolving PB (in the order of 500 bar, [21]). With

regard to the heavier solvent, which together with DME makes up the solvent mixture

suggested in ref [21], we chose in this work n-pentane (C5). It is non polar, and hence has

affinity with the product of hydrogenation. Besides, it could be more miscible with PB than

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propane, since C5 has a higher molecular weight than propane. This last conjecture was

confirmed by the results obtained in this work.

In system (a) the solvent is a pure compound (C5), and in systems (b), (c) and (d) the solvent

is a mixture (DME + C5). System (b) is a subsystem of the initial reactive mixture, where the

polymer (PB) is unsaturated. System (c) would be representative of a subsystem of the final

reactive mixture, since the polymer (PE) is fully saturated. System (d) corresponds to an

intermediate extent of reaction where the polymer is not fully hydrogenated, and a subsystem

of the reactive mixture is made of the solvent mixture (DME + C5) and a partially

hydrogenated polymer [emulated as a mixture of fully unsaturated (PB) and fully saturated

(PE) polymers].

Notice that in the systems 'PE + DME + C5' and 'PB + PE + DME + C5', the PE is considered

as representative of the hPB. CPP values are determined in this work as a function of

temperature and overall polymer concentration by using a variable-volume windowed

equilibrium cell. This cell can be used at pressures up to 1000 bar and at temperatures up to

200 °C.

Altough this work has been motivated by the problem of hydrogenating polybutadiene in a

supercritical media, we have not yet measured cloud points for hydrogen-containing

systems, neither have we conducted supercritical hydrogenation experiments. This was also

the case in ref [21].

2. Experimental

2.1 Materials

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One PB and one PE are the polymers used in this work. The PB was synthesized by anionic

polymerization under a high vacuum inert atmosphere [11, 21]. The PE is a high density

commercial polyethylene from Du Pont de Nemours & Co. (USA). The number-average

molecular weight (Mn), the weight-average molecular weight (Mw), polydispersity index

(Mw/Mn) and 1,2-vinyl content of the synthesized PB is given in Table 1, as well as the

molecular properties of the PE. The equipment and conditions used to obtain the information

listed in Table 1 are described elsewhere [21].

Dimethyl ether (DME), with a purity level greater than 99% (GC), was purchased from

Sigma-Aldrich (St. Louis, Missouri, USA). Laboratorios Cicarelli (San Lorenzo, Santa Fe,

Argentina) provided the n-pentane (C5) with a purity level greater than 99% (GC). Table 2

provides the values of some relevant physical properties for the solvents used in our

experiments. Table 3 reports the properties of polymers used in the literature, in papers that

are cited, for comparison purposes, in this work.

2.2 Apparatus and Procedure

We performed the experimental determination of cloud-point pressures in polymer + solvent

systems with the aid of a variable volume equilibrium cell, built on the basis of equipment

described in the literature [23-27]. The details of the apparatus have been given elsewhere

[21]. We describe here only the main features of the apparatus and of the experimental

procedure.

The experimental setup is represented in Fig. 1. The variable-volume windowed equilibrium

cell can operate at pressures up to 1000 bar and temperatures up to 200 °C. The variable-

volume nature of the cell makes it possible to control pressure and temperature

independently. The cell has a movable (free) piston. A manual pressure generator is used to

move the piston, with the help of a hydraulic fluid, so that the system pressure can be

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8

adjusted to the desired value. By using the words “variable volume cell” we mean that the

volume occupied by the sample, i.e., by the mixture of interest, is variable. A stirring magnet

is placed inside the cell. A glass window and an associated system of light-emitting-diodes

(LEDs) makes possible to visually observe the cell contents, i.e., to detect phase transitions.

A PID controller keeps the cell temperature at the desired value. The controller acts on a

couple of heating elements that surround a solid aluminum shell that tightly houses the cell.

The “cell + shell + heating elements” system is placed within an air thermostatized chamber.

The temperature of the fluid system inside the cell is measured using a J-type thermocouple.

The uncertainty in the reported temperature values is estimated to be in the order of ±1 °C.

The pressure of the fluid mixture under study is measured using a certified absolute pressure

transducer (Paroscientific Inc., Model 430K-101, range: 0 to 30.000 psi, accuracy ±0.02% of

reading). The estimated uncertainty in the cloud-point pressure values reported in this work

is about 3 bar.

The experimental procedure is the following. To load the cell, a known amount of polymer, or

mixture of polymers of known polymer/polymer ratio, (weighed to ±0.01 g on a precision

scale BP 410 Sartorius balance) is placed on a small slightly concave piece of glass. Such

glass tray is introduced into the cell, and the cell is closed and placed inside the air

thermostat chamber. The glass tray is used as a polymer loading device and as a dissolution

surface. The solvent (either DME, or C5, or a DME+C5 mixture of known DME/C5 mass

ratio) is loaded into the cell by using an auxiliary cell. The mass of solvent introduced into the

main cell is determined by weighing the auxiliary cell before and after loading the solvent. At

the end of the loading process the cell contains a „polymer/s + solvent/s‟ mixture of known

composition. Next, the system is set under conditions of temperature and pressure such that

a homogenous fluid is seen through the cell window. Then, the pressure is slowly reduced, at

constant temperature, by using the manual pressure generator, until the fluid system

becomes opalescent. The opalescence appearance conditions correspond to the cloud point,

at which a new incipient dense phase arises. When the system was taken back to higher

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9

pressures, to repeat the cloud point determination, a reproducibility of ±3 bar was obtained in

most cases.

3. Results

This section reports the experimental cloud point pressures obtained in this work for a

number of systems. The uncertainties in reported weight fraction values were estimated

through a very conservative propagation of error analysis, for all systems studied in this

work.

3.1. Pseudobinary system PB16 + C5

Raw experimental data (cloud points) for the system 'PB16 + C5' at three different overall

polymer weight fractions: 1.1 0.1, 3.3 0.3 and 3.6 0.4 wt% are reported in Table 4. The

temperature range of the data is from 111 to 184 °C and the pressure range is from 19 to 134

bar. All data correspond to temperatures which are subcritical with respect to that of the

pure solvent (196.7 °C, Table 2). Fig. 2 shows the CPP data (Table 4) obtained in this work as

a function of temperature for this system. At a set overall composition, the homogeneous

region lies above the cloud point experimental data. The dashed lines in Fig. 2 and following

figures correspond to smoothed data and they have been added to facilitate the visualization

of the trends set by the experimental data. Fig. 2 shows the following: (a) a pressure of about

140 bar should be enough to completely dissolve the PB16 in C5, (b) the PB16 overall

concentration influences the behavior of the cloud-point pressure, and (c) the CPP of the

'PB16 + C5' system does not have a monotonical behavior with composition, i.e., the 3.3 PB16

wt% mixture presents the largest values of CPPs within the temperature range of Fig. 2. Item

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(a) confirms the expectation that C5 could be more miscible with PB than propane, which

requires pressures in the order of 500 bar for full miscibility with PB [21]. We ascribe the

higher miscibility of PB in C5 to the higher molecular weight of C5.

3.2. Pseudoternary systems

For the pseudoternary system 'PB16 + DME + C5', we obtained the experimental CPPs at

two different overall polymer weight fractions, i.e., at 4.1 ± 0.4 PB16 wt% and at 2.6 ± 0.2

PB16 wt%. The temperature and pressure ranges for the data are from 50 °C to 179 °C and

from 30 bar to 226 bar respectively. Table 5 presents the raw experimental data measured in

this work for this system, and the CPPs values are shown in Fig. 3 (see “x” and “+” markers).

These two isoplethic series differ not only in the overall polymer weight fraction, but also in

the DME/C5 ratio in the solvent mixture. For the isopleth of 4.1 ± 0.4 PB wt% we used a

solvent mixture with 30 wt% of C5 and 70 wt% of DME. For the isopleth of 2.6 ± 0.2 PB wt%

we used a solvent mixture with 67 wt% of C5 and 33 wt% of DME.

Figure 3 also shows two additional data sets. One of them corresponds to PB16 + DME [21]

and the other to PB16 + C5 (Table 4). This last data set has already been shown in Fig. 2.

Due to the varying polymer concentration in Fig. 3, it is not possible to reach definitive

enough conclusions on the effect of the composition of the solvent mixture on the cloud point

pressure. However, the information provided in Fig. 3 supports the following conjectures: (a)

at constant temperature, the CPP increases with the increase in the DME concentration in

the solvent mixture, and (b) at constant pressure the cloud point temperature (CPT)

increases with the increase of the C5 concentration in the solvent mixture. The solubility of

PB16 in a solvent is expected to increase both, with the polarity and with the molecular

weight of the solvent. DME is more polar than C5 (see the dipole moment values in Table 2),

but it has a lower molecular weight than C5 (Table 2). Therefore, when going from DME to

C5, as solvents for PB16, two opposite effects compete: the decrease in the solvent polarity

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and the increase in the solvent molecular weight. Fig. 3 shows that the second effect is

stronger than the first.

For the pseudoternary system 'PE53 + DME + C5', we obtained the CPPs for two different

isopleths with the following overall polymer weight fractions: 2.9 ± 0.3 PE53 wt% and 2.7 ±

0.3 PE53 wt%. The solvent mixture for the first isopleth had 78 wt% of C5 and 22 wt% of

DME, and for the second one it had 53 wt% of C5 and 47 wt% of DME. The raw

experimental data measured in this work for this system are presented on Table 6. The

temperature range for the experimental data is from 115 °C to 176 °C. The pressure range is

from 147 bar to 303 bar. Figure 4 shows the CPPs of Table 6 together with two additional

CPP series from the literature (systems 'PE + DME' and PE + C5', [19-20]). The

pseudobinary data were included to discuss the effect of the solvent mixture on the phase

boundaries. It is important to note that different isopleths have different overall polymer

concentrations in Fig. 4. Besides, we stress that different polyethylenes (PE28, PE53 and

PE65) are considered in Fig. 4. Despite such differences, Fig. 4 suggests the following

conjecture: the addition of DME to the solvent mixture shifts the cloud point curve towards

higher pressures. Notice that DME is a polar co-solvent (Table 2). The solubility of PE is

expected to be higher for non polar solvents, an to increase with the increase in the solvent

molecular weight. When going from DME to C5, as in Fig. 4, the polarity of the solvent

decreases and, simultaneously, the molecular weight of the solvent increases. Both changes

promote the increase in the PE solubility. That is what we observe in Fig. 4.

3.3. Pseudoquaternary system PB16 + PE53 + DME + C5

The system 'PB16 + PE53 + DME + C5' is related to the hydrogenation reaction of PB16 that

would be carried out using a DME + C5 mixture as reaction media. The presence of the two

polymers and of the solvent mixture emulates a subsystem that could be found at

intermediate extents of reaction. The raw CPP experimental data for this system are

presented in Table 7. The composition of the mixture was 1.2 ± 0.1 PE53 wt% and 2.1 ± 0.2

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 61 62 63 64 65

12

PB16 wt% in a solvent mixture made of 42 wt% of DME and 58 wt% of C5. The experimental

data were obtained at temperatures from 134 to 177 °C and pressures from 234 to 292 bar.

Fig. 5 shows the experimental results for the pseudoquaternary system 'PB16 + PE53 +

DME + C5' ( “x” markers). The CPPs for the pseudoquaternary system are located in

between the CPPs measured in this work for the pseudoternary systems 'PB16 + DME + C5'

and 'PE53 + DME + C5'. The three series of experimental data shown in Fig. 5 have a similar

overall polymer concentration. But the composition of the solvent mixture for 'PB16 + DME +

C5' (filled circles) differs significantly from that for the systems 'PB16 + PE53 + DME + C5' (

“x” markers) and 'PE53 + DME + C5' (empty circles). However, from our previous results

shown in Fig. 3, which consider the effect of the solvent mixture composition on the location

of „PB + DME + C5‟ isopleths, there should be no qualitative change in the relative positions

of the different cloud point curves in Fig. 5, if the 'PB16 + DME + C5' system had a solvent

mixture composition comparable to that of the other systems. Because of such expectation,

we have added to Fig. 5 a line of cloud-points predicted for a system made of 2.6 PB16 wt%

in a 50/50 wt% DME/C5 solvent mixture (dotted line). It was obtained by interpolating our

pseudoternary raw experimental data displayed in Fig. 3, which have a variable solvent

mixture composition. The predicted cloud points show more clearly that the behavior of the

pseudoquaternary system is in between those of the corresponding pseudoternary systems,

under the conditions of our experiments.

The supplementary material provides additional information on the significance of

experimental data from the literature related to this work.

4. Remarks and conclusions

In this work we experimentally found, using a variable-volume windowed equilibrium cell,

homogeneity conditions, i.e., cloud point pressures (CPPs) at given temperature and overall

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 61 62 63 64 65

13

composition, for the systems C5 + PB, 'PB + DME + C5', „ PE + DME + C5' and 'PB + PE +

DME + C5'. This new information should be helpful in the process of identifying proper

conditions for carrying out the supercritical hydrogenation of PB. In all cases the overall

polymer concentration was less than or equal to 4.1 wt%. The temperature range for the

experiments done in this work goes from 50 to 184 °C. The maximum pressure measured is

303 bar.

The maximum temperature for the „PB + C5‟ experiments is below (but fairly close to) the

critical temperature of C5 (Table 4). For PB + C5, at the ranges of conditions of the

experiments (111 to 184 °C, 1.1 to 3.6 PB wt%), the minimum pressure required to

guarantee homogeneity is about 140 bar (Fig. 2, Table 4). For „PB + C5 + DME‟, the CPP

curves (Table 5) were found to be located in between the CPP curves of the corresponding

pseudobinary systems „PB + DME‟ and „PB + C5‟ (Fig. 3). The maximum CPP obtained for

this system is 226 bar (at 156 °C). The CPP at a given temperature increases with the

increase in the DME/C5 ratio in the solvent mixture (Fig. 3).

For „PE + DME + C5‟ we observe a substantial decrease in the CPPs, mainly at low

temperatures, with the addition of C5 to the DME + C5‟ solvent mixture (Fig. 4). The

maximum CPP, measured in this work, for this pseudoternary system was 303 bar (at 176

°C, Table 6).

To emulate a subsystem of the reactive mixture at an intermediate reaction extent in a

potential PB hydrogenation progress, we measured the phase boundary (CPPs) of the

pseudoquaternary system „PB + PE + DME + C5‟ (Table 7, Fig. 5) . The solvent mixture has

a solvent ratio close to 1:1 (DME/C5, weight basis). The CPP values for this system are

higher than the CPPs obtained for the pseudoternary system „PB + DME + C5‟ but lower

than the CPPs for the saturated polymer (PE) in the same solvent mixture.

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 61 62 63 64 65

14

The experimental data obtained in this work make it possible to partially establish the effect

of the nature of the polymer (saturated, unsaturated), of the composition of the solvent

mixture, and of the reaction extent, on the liquid-liquid phase boundaries of a number of

subsystems of the reaction mixture in the potential hydrogenation of PB in supercritical

media. From considering “PB hydrogenation”-related experimental data, from this work and

from the literature, it seems that the use of a solvent mixture constituted by a lighter, e.g.,

DME, and a heavier, e.g., C5, solvent is a convenient choice to carry out the single-fluid-

phase supercritical hydrogenation of PB at relatively moderate conditions. These

observations should be confirmed in the future through phase equilibrium experiments on

“PB hydrogenation”-related hydrogen-containing mixtures and also by performing actual

hydrogenation experiments.

The experimental data obtained in this work could be useful to develop models of the

equation of state (EOS) type. The accurate reproduction of the complex phase behavior of

the highly asymmetric systems here studied would be a stringent test for such models.

5. Acknowledgements

We gratefully acknowledge the financial support of the Argentinean institutions:

Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad

Nacional del Sur (UNS), and Agencia Nacional de Promoción Científica y

Tecnológica (ANPCyT). We also wish to thank, for their valuable contributions, to Dr.

Angel Satti (PLAPIQUI/UNS), Dr. Horacio Thomas (CINDECA/UNLP) and Dr.

Cristian Vitale (INIQO/UNS). We are also grateful to Prof. Esteban A. Brignole and to

Dr. Pablo E. Hegel (PLAPIQUI/UNS) for helpful discussions.

6. Supplementary Material

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 61 62 63 64 65

15

Additional information related to this work is available as supplementary material.

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 61 62 63 64 65

16

Table 1. Characteristics of polymers used in this work

Polymer Acronym Mw / (g/mol) Mn / (g/mol) PD Index* 1,2-Vinyl content / %

Polybutadiene PB16 16600 15800 1.05 15

Polyethylene

(HDPE)

PE53 53000 22000 2.4 -

* PD = Mw / Mn

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 61 62 63 64 65

17

Table 2: Properties of Pure Solvents [22]

Compound M / (g/mol) Tc / °C Pc / bar C m

n-pentane (C5) 72.2 196.7 33.6 0

dimethyl ether (DME) 46.1 127.0 53.7 4.34 10-30

M = Molecular weight, Tc =critical temperature, Pc =critical pressure, = dipole moment. The

unit C m corresponds to “coulomb times meter”

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 61 62 63 64 65

18

Table 3. Polymers from the literature cited in this work

Polymer Acronym Mw / (g/mol) Mn / (g/mol) PD Index* Reference

polyethylene

polyethylene

PE65

PE28

64800

27700

52100

13900

1.2

2.0

[20]

[19]

* PD = Mw / Mn

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 61 62 63 64 65

19

Table 4. Experimental Cloud Points for the pseudobinary system

polybutadiene (PB) + n-pentane (C5) (This work)

1.1 PB16 wt% 3.3 PB16 wt% 3.6 PB16 wt%

T / °C P / bar T / °C P / bar T / °C P / bar

123 19 111 26 118 25

127 28 116 35 126 39

133 36 122 44 138 55

136 43 125 50 146 68

141 48 128 55 155 79

145 53 132 63 165 94

149 62 138 72 174 108

154 69 144 82 183 117

158 72 147 87

165 77 152 93

168 83 158 101

173 89 163 109

178 96 170 118

174 122

178 126

184 134

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 61 62 63 64 65

20

Table 5. Experimental Cloud Points for the pseudoternary

system polybutadiene (PB) + n-pentane (C5) + dimethyl ether

(DME) (this work)

4.1 PB16 wt%

Solvent: 70/30 wt% (DME/C5)

2.6 PB16 wt%

Solvent: 33/67 wt% (DME/C5)

T / °C P / bar T / °C P / bar

50 30 96 48

59 47 106 66

69 73 117 87

79 92 127 104

88 100 137 118

98 119 148 136

107 142 158 148

117 160 168 161

127 179 179 174

136 195

147 210

156 226

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 61 62 63 64 65

21

Table 6. Experimental Cloud Points for the pseudoternary

system polyethylene (PE) + n-pentane (C5) + dimethyl ether

(DME) (this work)

2.7 PE53 wt%

Solvent: (47/53) wt% (DME/C5)

2.9 PE53 wt%


T / °C P / bar T / °C P / bar

115 253 116 147

131 265 123 154

137 269 129 160

142 274 134 167

147 279 140 174

152 282 141 177

158 288 147 183

162 292 152 190

167 296 157 195

171 298

176 303

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 61 62 63 64 65

22

Table 7. Experimental Cloud Points for the pseudoquaternary

system polybutadiene (PB) + polyethylene (PE) + n-pentane

(C5) + dimethyl ether (DME) (this work).

1.2 PE53 wt% and 2.1 PB16 wt%


T / °C P / bar

134 234

136 239

139 244

146 251

152 246

155 259

160 272

163 276

168 288

172 287

177 292

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 61 62 63 64 65

23

List f Figure Captions

Figure 1. Experimental setup. 1. Equilibrium cell, 2. Air thermostat, 3. Glass Window, 4. Stirring magnet, 5.

Piston, 6. Polymer loading tray, 7. Aluminum shell. PT: Pressure Transducer, TS: Temperature sensor, PG:

manual Pressure Generator, TC: Temperature controllers, SMD: Stirring magnet driver.

Figure 2. Experimental cloud-point pressure as a function of temperature for the system 'PB16 + C5' at three

different overall polymer weight fractions (This work). Rhombuses: 1.1 PB16 wt%. Triangles: 3.3 PB16 wt%.

Squares: 3.6 PB16 wt%. Rhombuses, triangles and squares: raw experimental data (this work). Dashed lines:

smoothed data. Solid line: liquid-vapor saturation line for pure C5 [22]. Star: C5 critical point [22] (Table 2). For

molecular properties of PB16 see Table 1.

Figure 3. Experimental cloud-point pressure as a function of temperature for the systems 'PB16 + DME', 'PB16 +

C5 + DME' and 'PB16 + C5' at four different overall polymer weight fractions. Markers: Empty squares: 4.6 PB16

wt% in pure DME (raw experimental data from [21]). “X”: 4.1 PB16 wt% in a solvent mixture of (70/30) wt% of

(DME/C5) (This work). “+”: 2.6 PB16 wt% in a solvent mixture of (33/67) wt% of (DME/C5) (This work). Filled

squares: 3.6 PB16 wt% in pure C5 (This work). Dashed lines: smoothed data. For molecular properties of PB16

see Table 1.

Figure 4. Experimental cloud-point pressure as a function of temperature for the systems 'PE65 + DME', 'PE53 +

C5 + DME' and 'PE28 + C5' at four different overall polymer weight fractions. Markers: Empty circles: 5.0 PE65

wt% in pure DME (raw experimental data from [20]). ”+”: 2.7 PE53 wt% in a solvent mixture of (47/53) wt% of

(DME/C5) (This work). “X”: 2.4 PE53 wt% in a solvent mixture of (22/78) wt% of (DME/C5) (This work). Filled

circles: 2.0 PE28 wt% in pure C5 (raw experimental data from [19]). Dashed lines: smoothed data. For molecular

properties of PE53, PE65 and PE28 see Tables 1 and 3

Figure 5. Cloud-point pressure as a function of temperature for the pseudoternary systems „PB16 + C5 + DME‟,

„PE53 + C5 + DME‟ and for the pseudoquaternary system „PB16 + PE53 + C5 + DME‟ at three different overall

polymer weight fractions and with different solvent mixtures. Markers: Experimental data from this work. Empty

circles: 2.7 PE53 wt% in a solvent mixture of (47/53) wt% (DME/C5) (This work). “X”: 1.2 PE53 wt% and 2.1 PB16

wt% in a solvent mixture of (42/58) wt% (DME/C5) (This work). Filled circles: 2.6 PB16 wt% in a solvent mixture of

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 61 62 63 64 65

24

(33/67) wt% of (DME/C5) (This work). Dashed lines: smoothed data. Dotted line: predicted cloud-point pressure

as a function of temperature for 2.6 PB16 wt% in (50/50) wt% (DME/C5). The dotted line was obtained by

interpolating raw experimental data shown in Fig. 3. For molecular properties of PE53 and PB16 see Table 1.

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 61 62 63 64 65

25

Figure 1. Experimental setup. 1. Equilibrium cell, 2. Air thermostat, 3. Glass Window, 4. Stirring magnet, 5.

Piston, 6. Polymer loading tray, 7. Aluminum shell. PT: Pressure Transducer, TS: Temperature sensor, PG:

manual Pressure Generator, TC: Temperature controllers, SMD: Stirring magnet driver.

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 61 62 63 64 65

26

Figure 2. Experimental cloud-point pressure as a function of temperature for the system 'PB16 + C5' at three

different overall polymer weight fractions (This work). Rhombuses: 1.1 PB16 wt%. Triangles: 3.3 PB16 wt%.

Squares: 3.6 PB16 wt%. Rhombuses, triangles and squares: raw experimental data (this work). Dashed lines:

smoothed data. Solid line: liquid-vapor saturation line for pure C5 [22]. Star: C5 critical point [22] (Table 2). For

molecular properties of PB16 see Table 1.

0

20

40

60

80

100

120

140

160

100 120 140 160 180 200

0

20

40

60

80

100

120

140

160

100 120 140 160 180 200

Pre

ss

ure

/ b

ar

Temperature / ºC

1.1 PB16 wt%

3.3 PB16 wt%

3.6 PB16 wt%

VP n-pentane

0

20

40

60

80

100

120

140

160

100 120 140 160 180 200

0

20

40

60

80

100

120

140

160

100 120 140 160 180 200

Pre

ss

ure

/ b

ar

Temperature / ºC

1.1 PB16 wt%

3.3 PB16 wt%

3.6 PB16 wt%

VP n-pentane

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 61 62 63 64 65

27

Figure 3. Experimental cloud-point pressure as a function of temperature for the systems 'PB16 + DME', 'PB16 +

C5 + DME' and 'PB16 + C5' at four different overall polymer weight fractions. Markers: Empty squares: 4.6 PB16

wt% in pure DME (raw experimental data from [21]). “X”: 4.1 PB16 wt% in a solvent mixture of (70/30) wt% of

(DME/C5) (This work). “+”: 2.6 PB16 wt% in a solvent mixture of (33/67) wt% of (DME/C5) (This work). Filled

squares: 3.6 PB16 wt% in pure C5 (This work). Dashed lines: smoothed data. For molecular properties of PB16

see Table 1.

0

50

100

150

200

250

300

20 40 60 80 100 120 140 160 180 200

Temperature / ºC

Pre

ss

ure

/ b

ar

0

50

100

150

200

250

300

20 40 60 80 100 120 140 160 180 200

4.6 PB16 wt% in DME

4.1 PB16 wt% in n-pentane (30%) + DME (70%)


3.6 PB16 wt% in n-pentane

0

50

100

150

200

250

300

20 40 60 80 100 120 140 160 180 200

Temperature / ºC

Pre

ss

ure

/ b

ar

0

50

100

150

200

250

300

20 40 60 80 100 120 140 160 180 200

4.6 PB16 wt% in DME



3.6 PB16 wt% in n-pentane

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 61 62 63 64 65

28

Figure 4. Experimental cloud-point pressure as a function of temperature for the systems 'PE65 + DME', 'PE53 +

C5 + DME' and 'PE28 + C5' at four different overall polymer weight fractions. Markers: Empty circles: 5.0 PE65

wt% in pure DME (raw experimental data from [20]). ”+”: 2.7 PE53 wt% in a solvent mixture of (47/53) wt% of

(DME/C5) (This work). “X”: 2.4 PE53 wt% in a solvent mixture of (22/78) wt% of (DME/C5) (This work). Filled

circles: 2.0 PE28 wt% in pure C5 (raw experimental data from [19]). Dashed lines: smoothed data. For molecular

properties of PE53, PE65 and PE28 see Tables 1 and 3

0

200

400

600

800

1000

1200

1400

110 130 150 170 190

Temperature / ºC

Pre

ss

ure

/ b

ar

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

110 130 150 170 190

5.0 PE65 wt% in DME

2.7 PE53 wt% in n-pentane (53%) + DME (47%)


2.0 PE28 wt% in n-pentane

0

200

400

600

800

1000

1200

1400

110 130 150 170 190

Temperature / ºC

Pre

ss

ure

/ b

ar

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

110 130 150 170 190

5.0 PE65 wt% in DME



2.0 PE28 wt% in n-pentane

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 61 62 63 64 65

29

Figure 5. Cloud-point pressure as a function of temperature for the pseudoternary systems „PB16 + C5 + DME‟,

„PE53 + C5 + DME‟ and for the pseudoquaternary system „PB16 + PE53 + C5 + DME‟ at three different overall

polymer weight fractions and with different solvent mixtures. Markers: Experimental data from this work. Empty

circles: 2.7 PE53 wt% in a solvent mixture of (47/53) wt% (DME/C5) (This work). “X”: 1.2 PE53 wt% and 2.1 PB16

wt% in a solvent mixture of (42/58) wt% (DME/C5) (This work). Filled circles: 2.6 PB16 wt% in a solvent mixture of

(33/67) wt% of (DME/C5) (This work). Dashed lines: smoothed data. Dotted line: predicted cloud-point pressure

as a function of temperature for 2.6 PB16 wt% in (50/50) wt% (DME/C5). The dotted line was obtained by

interpolating raw experimental data shown in Fig. 3. For molecular properties of PE53 and PB16 see Table 1.

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 61 62 63 64 65

30

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Supplementary MaterialClick here to download Supplementary Material: MiMaCiQuiZa REV paper SUPPL MAT UNLINKED.pdf

http://ees.elsevier.com/supflu/download.aspx?id=111327&guid=179f83fd-c044-4c97-9b0f-7821ea46418c&scheme=1

EHigh-pressure liquid-liquid equilibrium boundaries for systems containing polybutadiene and/or...

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