Ethylene Carbonate CAS 96-49-1: Key Properties and Industrial Uses

Anhydrous 1,3-dioxolan-2-one (CAS 96-49-1), commonly designated ethylene carbonate, is a five-membered cyclic carbonate that remains a waxy solid at standard ambient conditions; its melting onset determined by differential scanning calorimetry under ASTM E794-06 falls between 36.4 °C and 38.5 °C for high-purity material, while water and ethylene glycol impurities depress the freezing point into the 35 °C to 37 °C band reported on typical certificates of analysis. Transfer therefore requires either melting and maintaining the material at 45 °C to 55 °C in jacketed stainless steel lines or dissolving it in a linear carbonate co-solvent. The normal boiling point is 248 °C at 101.3 kPa, but prolonged exposure above 180 °C promotes reversible ring-opening and trace formation of polycarbonate oligomers, so commercial evaporation is usually performed under vacuum in short-residence-time thin-film equipment. Density at 40 °C measured by an oscillating U-tube density meter according to ISO 12185:1996 is 1.3214 g/cm³. Dynamic viscosity at the same temperature, measured by capillary viscometry according to ASTM D445-21, is 1.93 mPa·s; the viscosity increases steeply as the melt cools from 40 °C to the melting range, which is the origin of many transfer-line blockages on batch plants. The relative dielectric constant at 40 °C and 1 kHz is 89.78 as determined by the two-electrode method of ASTM D924-15, and the dipole moment is 4.9 D. The closed-cup flash point is 160 °C under ASTM D7094-20, placing the material outside most flammable-liquid classifications but still requiring trace heating below that limit. The compound is fully miscible with water, lower alcohols, acetone, and methyl ethyl ketone; it is only sparingly soluble in aliphatic hydrocarbons. Because the anhydrous product is hygroscopic, dry nitrogen blanketing at a dew point below −35 °C is required during storage, and the water content of lithium-ion electrolyte-grade material is specified below 20 mg/kg by coulometric Karl Fischer titration under ASTM E1064-24. Refractive index at 40 °C is 1.4148 by ASTM D1218-21, but this value is rarely measured in downstream quality control because density and water content are stronger predictors of batch performance.

Table 1. Physical property benchmarks for anhydrous ethylene carbonate

Property	Typical value	Test method or basis
CAS registry number	96-49-1	—
Molecular formula	C₃H₄O₃	—
Molecular weight	88.06 g/mol	—
Melting range, onset by DSC	36.4 °C to 38.5 °C	ASTM E794-06
Boiling point at 101.3 kPa	248 °C	ASTM D1160-18, vacuum distillation
Density at 40 °C	1.3214 g/cm³	ISO 12185:1996
Dynamic viscosity at 40 °C	1.93 mPa·s	ASTM D445-21
Dielectric constant at 40 °C, 1 kHz	89.78	ASTM D924-15
Flash point, closed cup	160 °C	ASTM D7094-20
Water content, electrolyte-grade	<20 mg/kg	ASTM E1064-24
Refractive index at 40 °C	1.4148	ASTM D1218-21

What Limits Electrolyte Solvent Utility Below −20 °C?

Ethylene carbonate is the primary high-dielectric component in non-aqueous lithium-ion battery electrolytes because its dielectric constant of 89.78 at 40 °C supports dissociation of lithium hexafluorophosphate to reported conductivities of 10 mS/cm to 12 mS/cm at 20 °C in optimized ternary blends. The pure solvent cannot be used alone in most cell designs because it solidifies at 36.4 °C; production electrolytes are therefore formulated as 1 mol/L LiPF₆ in mass ratios of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate such as 1:1:1 or 3:3:4. Dimethyl carbonate and ethyl methyl carbonate reduce the liquidus temperature to below −30 °C and lower the mixed-solvent viscosity to 1.5 mPa·s to 2.5 mPa·s at 25 °C, but they also reduce the bulk dielectric constant. The resulting compromise appears in low-temperature performance: impedance at −20 °C is governed by the viscosity increase and by ion-pair formation, and cells discharged at 1C may exhibit a voltage sag of several hundred millivolts compared with 25 °C. Electrochemical impedance spectroscopy data from graphite half-cells show that the charge-transfer resistance at −20 °C can be 3 to 5 times the room-temperature value for ethylene carbonate-rich blends above 40 wt% ethylene carbonate. The lower mass fraction boundary is also process-relevant: below 20 wt% ethylene carbonate, the bulk dielectric constant is generally insufficient to suppress ion-pairing of LiPF₆, and conductivity drops below 7 mS/cm at 20 °C in several published formulations.

The second role of ethylene carbonate is anode passivation. During the first cycle, the solvent undergoes reductive decomposition on graphite at 0.6 V to 0.9 V versus Li/Li⁺ to form lithium ethylene dicarbonate, lithium carbonate, and oligomeric species. This solid-electrolyte interphase prevents co-intercalation of the remaining solvent and permits reversible cycling of graphite. If ethylene carbonate is replaced entirely by propylene carbonate, the interphase does not form in the same manner, and graphite exfoliation is commonly observed by capacity loss between 0.8 V and 3.0 V. In commercial electrolyte production, this passivation chemistry requires strict residual water control: water above 20 mg/kg in the final electrolyte hydrolyzes LiPF₆ to HF and PF₅, which corrodes the cathode and accelerates interphase thickening. Blending vessels are therefore installed in dry rooms with dew points below −40 °C, and the final electrolyte is filtered through 0.2 µm polytetrafluoroethylene membranes to remove LiF particulates before filling. Qualification of such electrolytes is ultimately performed at cell level under IEC 62660-1:2018 or equivalent customer-specific protocols, not through standalone solvent testing.

Table 2. Comparative properties of carbonate solvents used in lithium-ion electrolytes

Solvent	Melting point, °C	Boiling point, °C	Dielectric constant	Viscosity at 25 °C, mPa·s	Typical electrolyte role
Ethylene carbonate	36.4	248	89.78 at 40 °C	1.93 at 40 °C	High-dielectric SEI former
Propylene carbonate	−49	242	64.92	2.53	Low-temperature co-solvent with graphite incompatibility
Dimethyl carbonate	2 to 4	90	3.1	0.59	Viscosity reducer
Ethyl methyl carbonate	−55	109	2.9	0.65	Viscosity reducer and low-temperature diluent
Diethyl carbonate	−43	126	2.8	0.75	Viscosity reducer for high-temperature blends

Low-temperature utility below −20 °C is also limited by precipitation of the ethylene carbonate component. For a 1:1:1 ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate electrolyte, differential scanning calorimetry shows a liquidus near −25 °C, but kinetic supercooling in practical cells often allows discharge testing at −20 °C before crystallization. Published data for specific commercial cell formats with this electrolyte are limited because cell manufacturers treat the exact solvent ratio and additive package as proprietary; however, the observed performance window in published half-cell and full-cell work consistently narrows as the ethylene carbonate mass fraction exceeds 40 wt%.

The conversion of ethylene carbonate to monoethylene glycol by catalytic hydrolysis is practiced in process configurations that recycle the co-produced carbon dioxide to an upstream ethylene oxide carbonation reactor. The stoichiometry consumes one mole of water per mole of ethylene carbonate and releases one mole of carbon dioxide, giving a theoretical mass yield of 70.6 kg of ethylene glycol per 88.1 kg of ethylene carbonate, corresponding to 80.1 wt%. In the Shell OMEGA-type configuration, the carbonation of ethylene oxide with carbon dioxide is carried out first in a fixed-bed or homogeneous catalytic reactor at 2 MPa to 5 MPa and 100 °C to 170 °C; the resulting ethylene carbonate is then hydrolyzed in the liquid phase at 150 °C to 200 °C and 1.5 MPa to 4 MPa with a water-to-ethylene-carbonate ratio between 1.2:1 and 3:1. Reactor internals are usually fixed-bed or bubble-column designs using a hydrolysis catalyst or thermal decomposition promoter, but licensor-specific data for reactor internals and catalyst half-life are not publicly available. The crude product contains water, residual ethylene carbonate, and a small fraction of diethylene glycol; purification by multi-effect evaporation, vacuum distillation, and ion-exchange polishing produces fiber-grade ethylene glycol with UV transmittance above 95 % at 220 nm and residual aldehyde below 10 mg/kg as measured by standard methods such as ASTM E1119-23. The carbon dioxide stream is compressed, dried, and recycled to the carbonation step, which avoids venting and improves overall carbon efficiency. This hydrolysis route is selected over direct ethylene oxide hydration when the ethylene oxide/carbon dioxide carbonation reactor is available and when high selectivity to monoethylene glycol is required, because direct hydration typically produces 8 wt% to 12 wt% diethylene glycol byproduct under comparable operating conditions.

When Methanol-to-Ethylene Carbonate Molar Ratio Drops Below 4:1 in Reactive Distillation

Transesterification of ethylene carbonate with methanol to dimethyl carbonate and monoethylene glycol is an equilibrium-limited reaction that is often carried out in a reactive distillation column to remove dimethyl carbonate as it forms. The stoichiometry consumes 2 mol of methanol per mole of ethylene carbonate and forms 1 mol each of dimethyl carbonate and monoethylene glycol; the reaction is catalyzed by alkali metal methoxides, solid bases, or calcined hydrotalcites. The methanol-to-ethylene carbonate feed ratio is normally held between 4:1 and 10:1. At ratios below 4:1, the liquid-phase viscosity in the reaction zone increases from approximately 1.5 mPa·s to more than 3.5 mPa·s at 60 °C to 65 °C, reducing liquid holdup on structured catalytic packing and shifting the apparent reaction rate from kinetic control to mass-transfer control. The single-pass conversion of ethylene carbonate falls below 55 %, and the dimethyl carbonate mass fraction in the distillate drops because the methanol-dimethyl carbonate azeotrope is not generated at sufficient rate. The reboiler temperature must be limited to 140 °C to prevent dimethyl ether formation from methanol dehydration and ring-opening of residual ethylene carbonate. Overhead separation is constrained by the methanol-dimethyl carbonate minimum-boiling azeotrope near 63 °C at atmospheric pressure; this stream is typically separated by pressure-swing distillation or extractive distillation with an entrainer. Published data for specific reactive distillation configurations are limited, but commercial operation is generally acknowledged to prefer packed columns with 0.25 m to 1.0 m of catalyst-loaded structured packing per theoretical stage, operated at reflux ratios between 1.5:1 and 3:1. Sodium methoxide catalyst is deactivated by water above 200 mg/kg, so the methanol feed is dehydrated by molecular sieves to water below 100 mg/kg. The monoethylene glycol product is drawn as a bottom stream and purified by vacuum distillation to meet the same ASTM E1119-23 grade requirements described for the hydrolysis route.

Molten ethylene carbonate at 50 °C to 70 °C is used as a high-boiling polar aprotic solvent for polymer dissolution, membrane casting, and selected substitution reactions in fine chemical synthesis. The five-membered carbonate ring is susceptible to nucleophilic attack at the carbonyl carbon, so the solvent cannot be regarded as inert toward primary or secondary alkylamines, which form carbamate and oligourethane by-products under mild heating; this incompatibility prevents use as a solvent for amine-capped oligomers but is exploited in some resin-curing systems. In polyacrylonitrile solution processing, the molten solvent dissolves 15 wt% to 25 wt% polymer at 65 °C, and the solution can be wet-spun into water coagulation baths; residual solvent is recovered by countercurrent extraction because complete removal requires wash ratios above 5:1 water-to-fiber at 60 °C. Published data for specific fiber-grade lines are limited because manufacturers blend ethylene carbonate with lower-melting co-solvents to avoid the solidification risk at ambient startup and shutdown. The same solidification risk defines the lower operating boundary: transfer lines, pumps, and spin packs must be jacketed above 40 °C, and any unplanned shutdown below that temperature requires hot-water flushing before restart.

Thermal Degradation Pathways Above 180 °C Are a Design Constraint for Vacuum Distillation

Distillation of ethylene carbonate at atmospheric pressure is rarely practiced because the normal boiling point of 248 °C lies above the temperature at which reversible decarboxylation to ethylene oxide and carbon dioxide becomes measurable. Vacuum thin-film evaporators operating at 1 kPa to 5 kPa reduce the boiling temperature to 120 °C to 160 °C, which allows purification of electrolyte-grade material without excessive formation of ethylene oxide. The decomposition equilibrium is influenced by residual alkali and alkaline earth cations; sodium and potassium at concentrations above 5 mg/kg accelerate ring-opening to low-molecular-weight polycarbonate and polyether species that increase the acid number and haze. Stainless steel distillation surfaces are generally acceptable if the material is kept dry, but chloride-containing residues may initiate stress corrosion cracking at welds, so post-distillation piping is specified as 316L stainless steel or fluoropolymer-lined carbon steel. The overhead line from a vacuum evaporator requires a cold trap at −10 °C because ethylene oxide formed during short-term thermal excursions is volatile and flammable; the carbon dioxide partial pressure also increases the total condenser load. These thermal limits explain why production-scale purification avoids conventional packed columns in favor of short-residence-time wiped-film or falling-film equipment with residence times below 2 minutes at 140 °C.