ISSN 1068-364X, Coke and Chemistry, 2008, Vol. 51, No. 3, pp. 101–104. © Allerton Press, Inc., 2008.Original Russian Text © M.I. Zaretskii, V.V. Rusak, E.M. Chartov 2008, published in Koks i Khimiya, 2008, No. 3, pp. 30–34.

101

It is produced by the reaction of propylene oxidewith CO

2

in the presence of alkali metals or tetraalkylammonium as catalysts [1].

Propylene carbonate is widely used as an extractantof aromatic hydrocarbons, as a solvent in various poly-mer composites, and as an adsorbent for the removal ofCO

2

, H

2

S, and COS from gases.The table presents the basic physicochemical

parameters of propylene carbonate.In the present review, we consider recent applica-

tions of propylene carbonate as an extractant and adsor-bent in the coke and petrochemical industries.

Chemische Werke Hüls (Germany) has developedand introduced the production of ethylene and propy-lene carbonates from oxides of ethylene and propylenewith CO

2

in the liquid phase at 200

°

C and 79 atm, in thepresence of a catalytic solution. Degasification removesthe oxides from the reaction mixture; the catalyst isremoved, and then the mixture is rectified. The yield is93–98%, with 95–98% conversion [2].

Ethylene and propylene carbonates may be obtainedfrom alkylene oxides and CO

2

in the presence of cata-lysts based on metals of groups II and III, tertiaryamines, and compounds obtained in the reaction AlCl

3

+

(C

2

H

5

)

3

N [3]. A method of producing propylene car-bonate by the reaction of propylene oxide with CO

2

in

the presence of catalyst containing Zn[(C

2

H

5

)

2

Zn] andphenol was proposed in [4]. The production of propy-lene carbonate, with 98% yield, by the reaction of pro-pylene with CO

2

at 470–480

°

C, in the presence of(C

2

H

5

)

2

N and CaCl

2

, was described in [5]. The produc-tion of propylene carbonate by the reaction of propy-lene oxide with CO

2

in the presence of quaternaryammonium groups containing strong bases (

≤

0.5%H

2

O), with 96% yield, was patented in [6].

Two other processes have since been patented: theproduction of propylene carbonate and ethylene car-bonate by the reaction of alkylene oxides and CO

2

, withcatalysts such as dimethylalkylamides or chloroparaf-fins [7]; and the production of high-purity alkyl carbon-ates (including propylene carbonate) by the reaction ofCO

2

with epoxides, in the presence of tetraethylammo-nium bromide [8]. This process includes three-step rec-tification and a column with activated coal.

The production of alkylene carbonates by cyclocon-densation of propanediol with urea at 170

°

C, character-ized by a propane-carbonate yield (selectivity) of 96%and by 95% conversion, was proposed in [9].

Propylene carbonate may be used as a solvent in thereaction of diols with diisocyanates, in order to obtainoligomers as a source of oil-based fuel [10].

CHEMISTRY

Using Propylene Carbonate in Extraction and Absorption: A Review

M. I. Zaretskii, V. V. Rusak, and E. M. Chartov

Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences

Abstract

—

Propylene carbonate is a cyclic alkyl carbonate (1,3-dioxolan-2-one, 4-methyl), soluble inalcohol, ether, acetone, aromatic hydrocarbons, and acetic acid and insoluble in aliphatic hydrocar-bons and CS

2

.

DOI:

10.3103/S1068364X08030095

Table

Structural formula

Boiling point (

°

C) at 101.33 kPa

Melting point,

°

CDensity

d

20

, g/cm

3

Dipole moment

µ

1

(D)Dielectric

permittivity

ε

1

Heat of vapor-ization

∆

H

b

at

t

b

, kJ/mole

240.0 –48.0 1.210 5.00 65.10 50.24O O

H3C

O

102

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Propylene carbonate may be used as an extractant inthe liquid–solid system for the purification of rawanthracene containing fluorene, carbazole, and phenan-threne, with the addition of 0.5–10 wt % H

2

O [11]. Thepurified anthracene is used in anthraquinone produc-tion.

Extractive rectification may be used to separate

meta-

and

para-dichlorobenzenes

in the presence ofpropylene carbonate as a splitting agent [12]. Propylenecarbonate is used (with or without H

2

O) as a splittingagent in removing propylene from propane [13].

Extractive rectification, with propylene carbonate orethylene carbonate as the splitting agent, is used toremove H

2

O and methanol from propylene oxide [14].An azeotropic mixture of methanol and dimethyl

carbonate is separated by extractive rectification in thepresence of C

3

–C

5

cyclic carbonates (including propy-lene carbonate) as the splitting agent [15].

The extraction of styrene from pyrolytic benzene ispossible by extractive rectification using dehydratedpropylene carbonate as the splitting agent; alternativesplitting agents are sulfolane,

N

-methylpyrrolidone,and 2-pyrrolidone [16]. The production of styrene frommixtures with ethylbenzene and xylene isomers may bebased on extractive rectification using propylene car-bonate as the splitting agent [17].

The dehydration of ethyl benzene in styrene, whichis removed by extractive rectification using propylenecarbonate as the splitting agent (or by another selectivemethod), was patented in [18].

Two-stage extraction has been proposed to reducethe aromatic-hydrocarbon content in lubricating oils. Inthe first stage, phenol,

N

-methylpyrrolidone, or furfurolis used to isolate the oils from the hydrocarbons; in thesecond stage (reextraction), extraction is based on pro-pylene carbonate, sulfolane, or dimethyl sulfoxide(DMSO) [19].

The separation of maleic and phthalic anhydrides byextractive rectification, with propylene carbonate as thesplitting agent, was proposed in [20].

The removal of

n

-propanol from allyl alcohol byextractive rectification has also been proposed, with pro-pylene carbonate,

N

-methylpyrrolidone, or

γ

-butyrolac-tone as the splitting agent [21].

Two-stage production of high-purity pyromelliticanhydride was described in [22]. The raw pyromelliticanhydride obtained in the vapor phase by the oxidationof tetraalkyl benzene is washed with 1,4-dioxane andrecrystallized in solvents such as propylene carbonate,

γ

-butyrolactone, or cyclohexanone. Then the 90.4%anhydride is oxidized in air with V

2

O

5

catalyst andrecrystallized, to obtain 99.99% anhydride (90.5%yield).

The extraction of organic sulfur compounds frommixtures with hydrocarbons (in particular, oil-industrycracking products), was proposed in [23]; extractiverectification using propylene carbonate as the splitting

agent yields hydrocarbons with a reduced olefin con-tent.

At the Institute of Petroleum Chemistry, SiberianBranch, Academy of Sciences of the USSR, a methodwas developed for isolating and concentrating organicsulfur compounds from oil fractions: extraction of sul-fur-compound complexes by a coordinating solvent:DMSO,

N

,

N

-dimethylformamide (DMFA), or propy-lene carbonate. All these solvents are highly soluble inwater. Therefore, after decomposition of the complexesusing water, the solvent enters the aqueous phase, whilethe sulfur compounds enter the organic phase [24].

The extraction of sulfur compounds (dihexylsulfide,dibenzothiophene) from distillate fractions of petro-leum with

t

b

= 200–350

°

C was studied in [25]; theextractive agents are solutions of metal (Cd, Cu, Co,etc.) chlorides in electron-donor organic solvents(DMFA, DMSO, propylene carbonate). The extractionof condensed aromatic compounds—such as naphtha-lene, anthracene, phenanthrene, pyrene, and chry-sene—was studied in [26]. Two immiscible solvents areemployed here: a nonpolar solvent (

n

-octane) and apolar solvent (DMFA, DMSO, propylene carbonate,acetonitrile, or cellulose). These condensed compoundsare present as complex mixtures in oil, coal tar, andproducts of the pyrolysis of organic compounds. Manyhave valuable properties and may be used in industrialorganic synthesis.

Experimental data on the extractive dearomatizationof kerosene oil fractions using various selective sol-vents were compared in [27]. It was found that theextractive properties are best for propylene carbonateor

N

-methylpyrrolidone with added water.The removal of 1,1,1,4,4,4-hexafluorobutene from

1,1-dichloro-2,2,2-trifluoroethane by extractive rectifi-cation was proposed in [28]. The splitting agentsemployed are solvents such as propylene carbonate,sulfoxides, sulfones, or amides. When using propylenecarbonate, the relative volatility of the pair of compo-nents obtained is

α

r

= 2.8.The separation of 2-methyl-1-propanol from

1-butanol by extractive rectification was proposed in[29]. The splitting agents employed are solvents such aspropylene carbonate, 2-hexanone, amyl acetate, butylpropionate, or DMFA.

The liquid–liquid phase equilibrium at 25

°

C inthree-component heptane–

o

-xylene (toluene)–extract-ant systems was studied in [30]. The goal was to selecta solvent for the separation of aromatic hydrocarbonsfrom aliphatic hydrocarbons. The extractants employedwere propylene carbonate and triethylene glycol. It wasfound that the capacity of propylene carbonate is 2–3times that of triethylene glycol, and its selectivity istwice that of triethylene glycol. In subsequent studiesof the liquid–liquid phase equilibrium in multicompo-nent

n

-hexane–heptane–toluene–

o

-xylene–propylene-carbonate systems at 25

°

C, the experimental data wereapproximated using UNJQUAC and NRTL equations

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USING PROPYLENE CARBONATE 103

adopted as the mathematical models for calculating theextraction parameters [31, 32].

The interaction of various solvents (the immobilephase) at infinite dilution in aromatic–aliphatic sol-vents was studied in [33]. The goal was to select aneffective extractant. The solvents considered includedpropylene carbonate, ketones, esters, alkenes, DMSO,and

N

-ethylformamide. The activity coefficients

γ

ij

of

the components and the selectivity were calculated.

There have been numerous studies of CO

2

, H

2

S, andCOS removal from gases of different origin, using pro-pylene carbonate with certain additives as the adsor-bent. Thus, decarbonization and desulfurization of gasmixtures by physical absorption was proposed in [34].In this method, the additives (0.5–6.0 wt %) used withpropylene carbonate include tertiary amino alcohols or

N

-bearing heterocycles, their mixtures, or dimethylpip-erazines. The removal of CO

2

from natural gas using amixture of propylene carbonate and triethanolamine asthe adsorbent was proposed in [35]. The removal ofchlorinated hydrocarbons from waste gases using anadsorbent such as propylene carbonate, phthalic,maleic, or adipic esters, or

N

-methylpyrrolidone wasproposed in [36]. In this method, antioxidants are usedto stabilize the adsorbent, and N

2

is the desorbingagent.

Propylene carbonate was used as an absorbent inremoving synthetic gases from CO

2

in [37]. Thesegases were then used for NH

3

production. The extrac-tion of ethylene oxide by absorption from the gas mix-ture using precooled propylene carbonate was proposedin [38]. The possibility of desorption of ethylene oxidewas shown; with the addition of water, ethylene glycolwas obtained.

The absorption of H

2

S and concurrent removal of(H

2

S

+

CO

2

) mixture at atmospheric pressure and 10–40

°

C was investigated in [39]. A mixture of propylenecarbonate and triethanolamine (0–10 wt %) wasemployed. The kinetics and mechanism of CO

2

+

H

2

Sabsorption by a mixture of absorbents (propylene car-bonate

+

triethanolamine) were studied in [40]. Tests ofthe process on a pilot unit and in industry are planned.A complex absorbent consisting of propylene carbon-ate

+

a tertiary amine (methyldiethanolamine), withsome quantity of activator, was proposed for the extrac-tion of CO

2

from gases in [41].The specific molecular interaction in systems con-

sisting of propylene carbonate with various alcohols,acetonitrile, esters, and glycols has been studied with aview to using such binary mixtures as extractants. Thus,the viscosity in the binary system consisting of propy-lene carbonate and acetonitrile at 25–45

°

C was consid-ered in [42]. A strong dipole–dipole interaction wasestablished in this system. The excess molar enthalpy inbinary systems consisting of propylene carbonate withlinear ketones (2-propanone, 2-hexanone, 2-octanone,or 2-undecanone) and cyclic ketones (cyclohexanone,

Sij∞

2-methylcyclohexanone, and 2,6-dimethylcyclohex-anone) at 298.15 K was studied using a microcalorime-ter in [43]. The experimental data were approximatedusing the Redlich–Kister equation. The excess molarenthalpy and excess molar volumes of binary mixturesof propylene carbonate with aliphatic alcohols (metha-nol, ethanol, 1- and 2-propanol, and 1- and 2-butanol)and pentanol isomers at 298.15 K were studied in [44,45]. In those studies, a flow-through microcalorimeterand a dilatometer were used, over the whole range ofbinary-mixture concentrations. The experimental datawere again approximated by the Redlich–Kister equa-tion.

The excess mole volumes and the viscosity in binarysystems consisting of propylene carbonate with tet-rahydrofuran and methanol were studied in [46]. Inbinary systems consisting of propylene carbonate withtetraethylene glycol and its dimethyl ester, the variationin excess molar volumes, viscosity, and refractive indexwere investigated at 298.15 K and atmospheric pres-sure in [47].

The excess molar enthalpy at 298.15 K and323.15 K was studied by means of a microcalorimeterin binary systems consisting of propylene carbonatewith methyl, ethyl, and propyl alcohols in [48]. Theexcess enthalpy was greatest in the system consisting ofpropylene carbonate with 1-propanol. The results wereapproximated by means of the Redlich–Kister equa-tion. The excess molar volumes and viscosity in binarysystems consisting of propylene carbonate with thediethyl ester of diethylene glycol and its dibutyl esterwere studied at 298.15, 308.15, and 318.15 K and atatmospheric pressure in [49, 50].

As an example, we may note some research in thisperiod associated with the use of propylene carbonateas a solvent in the pharmaceutical industry, polymeriza-tion, industrial organic synthesis, and electronics. Thus,the production of a homopolymer by the reaction ofacrylonitrile and propylene carbonate was proposed in[51]. The production of low-molecular polymers(molecular mass 400–25 000) on the basis of butadienein a homogeneous solution of propylene carbonate inhydrogen peroxide was proposed in [52]. A mixture ofcomposition H

2

O

2

: propylene carbonate : H

2

O = 1 : 2 :1 yields a polymer of molecular mass 2800.

In the electronics industry, propylene carbonate isused, in combination with triethanolamine and

N

-methylpyrrolidone, to purify the matrices [53]. Theproduction of pharmaceuticals on the basis of propy-lene carbonate was proposed in [54]: in particular,cyclosporine (in oil) + a hydrophilic block copolymerbased on propylene carbonate and polyoxyethylene.

In industrial organic synthesis,

α

-tocopherol andtocopherol acetate may be prepared by the reaction of2,3,5-trimethylhydroquinone in propylene-carbonatesolution with phytol or isophytol at 150

°

C, in the pres-ence of a catalyst; the tocopherol is esterified with ace-tic anhydride [55, 56].

104

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When using propylene carbonate in Li-ionic batter-ies, purification of the propylene carbonate in a combi-nation of absorption and rectification processes hasbeen proposed [57].

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