Ethylene glycol (EG), also known as mono ethylene glycol (MEG), is widely used in antifreeze, coolants, heat-transfer fluids, polyester fiber, PET production, and chemical manufacturing. For buyers, the difference between 99%, 99.5%, and 99.9% ethylene glycol is not determined by assay alone. Water, diethylene glycol (DEG), aldehydes, iron, acidity, color, and other impurities also affect whether an EG product meets a specific application or standard.
Which Ethylene Glycol Purity Should You Buy?
For most general industrial applications, 99% ethylene glycol may be sufficient, while polyester and PET production generally require higher-purity EG with tighter impurity limits.
99% ethylene glycol: Commonly used for antifreeze, coolants, heat-transfer fluids, and general industrial applications.
99.5% ethylene glycol: Suitable for applications requiring higher assay, but the 99.5% value alone does not define a specific industry grade.
99.9% ethylene glycol: Commonly used where tighter control of impurities is required, including polyester and PET production.
For bulk procurement, buyers should compare the ethylene glycol specification and COA, rather than selecting a product only by its advertised purity.
99% vs 99.5% vs 99.9% Ethylene Glycol
The main difference between 99%, 99.5%, and 99.9% ethylene glycol is the required level of EG assay and, depending on the grade, the tighter control of impurities.
| Parameter | 99% EG | 99.5% EG | 99.9% EG |
|---|---|---|---|
| Typical positioning | Industrial/technical | Higher-purity industrial | High-purity/polyester applications |
| EG assay | ≥99.0% | ≥99.5% | ≥99.9% |
| Water control | Application-dependent | More controlled | Strictly controlled |
| DEG control | Application-dependent | Grade-dependent | Strictly controlled |
| Iron control | Application-dependent | Grade-dependent | More stringent |
| Aldehyde control | Grade-dependent | More stringent | Strictly controlled in relevant specifications |
| Typical applications | Antifreeze, coolants, industrial chemicals | Specialty chemical applications | Polyester, PET and high-specification processes |
These percentages should not be treated as universal international grade classifications.
For example, 99.5% ethylene glycol is not automatically USP or ACS grade, and 99.9% ethylene glycol is not automatically electronic grade. The applicable specification determines the actual grade.
Why Ethylene Glycol Purity Is More Than Assay
Ethylene glycol assay shows the EG concentration, but water, DEG, iron, aldehydes, acidity, and color often determine whether the material is suitable for a specific process.
A buyer comparing two high-purity ethylene glycol products should check the complete impurity profile.
| Quality Parameter | Purchasing Importance |
|---|---|
| EG assay | Confirms the main component concentration |
| Water | Affects concentration and some downstream processes |
| DEG | Particularly important for polyester and PET production |
| Aldehydes | Can affect color and downstream product quality |
| Iron | Important for high-purity and color-sensitive applications |
| Acidity | Indicates acidic impurities and supports process control |
| Color | Helps identify color-forming impurities |
| Chloride | Important where ionic impurities are restricted |
| Ash | Indicates inorganic residue |
This is why a supplier quotation stating only "Ethylene Glycol 99.9%" does not provide enough information for many industrial purchases.
How Impurities Affect Ethylene Glycol Performance
The impact of ethylene glycol impurities depends on the downstream process, with water, DEG, aldehydes, and iron being particularly important for polyester-grade EG.
Water
Excess water changes the effective EG concentration and can affect processes that require tightly controlled raw-material composition.
For polyester and PET production, water content is therefore an important item on the ethylene glycol COA.
Diethylene Glycol (DEG)
DEG should be checked separately because a high EG assay does not necessarily mean low DEG content.
This is particularly important when purchasing ethylene glycol for polyester production, where DEG limits are normally much tighter than those for general industrial material.
Aldehydes
Aldehyde content is an important quality parameter for polyester-grade EG because excessive aldehydes can affect color and downstream product quality.
Iron
Iron is particularly relevant for applications requiring low metal contamination and good color stability.
For example, GB/T 4649-2018 specifies an iron limit of ≤5.0 mg/kg for industrial grade and ≤0.10 mg/kg for polyester grade.
Acidity and Color
Acidity and color provide additional information about EG quality and are commonly included in specifications for higher-grade material.
For buyers, these values should be compared directly with the required standard instead of judged from the EG assay alone.
Ethylene Glycol Grades and Applications
The right ethylene glycol grade depends on the application, so buyers should define the end use before selecting 99%, 99.5%, or 99.9% EG.
| Application | Typical Purchasing Requirement |
|---|---|
| Antifreeze | Industrial/coolant-grade EG |
| Engine coolant | Coolant or industrial specification |
| Heat-transfer fluid | EG meeting the required heat-transfer specification |
| General chemical manufacturing | 99% or application-specific grade |
| Polyester fiber | High-purity/polyester-grade EG |
| PET production | Polyester-grade EG with controlled impurities |
| Laboratory analysis | Laboratory/reagent-grade specification |
| Pharmaceutical applications | Applicable USP/EP specification |
| Electronic applications | Application-specific high-purity specification |
Ethylene Glycol for Antifreeze and Coolants
For standard antifreeze and coolant formulations, industrial-grade ethylene glycol can be suitable when it meets the required coolant specification.
The buyer should also consider water content and the requirements of the final coolant formulation.
Ethylene Glycol for Polyester and PET
Polyester and PET production require tighter control of EG impurities than many general industrial applications.
Important parameters include:
EG assay
DEG
Water
Iron
Aldehydes
Acidity
Color
For this application, requesting "99.9% ethylene glycol" is less precise than specifying the required polyester-grade standard and impurity limits.
Ethylene Glycol Standards and Specifications
Ethylene glycol grades should be evaluated against the specific standard required by the application rather than matched to a purity percentage alone.
GB/T 4649-2018
For buyers sourcing EG from China, GB/T 4649-2018 is an important reference for industrial and polyester-grade ethylene glycol.
The standard specifies:
Industrial grade: EG ≥99.0%
Polyester grade: EG ≥99.9%
It also covers parameters including:
DEG
Water
Iron
Aldehydes
Acidity
Color
Ash
Chloride ions
UV transmittance
This makes the standard useful when reviewing a Chinese ethylene glycol supplier's COA.
ASTM
ASTM specifications are generally related to specific applications rather than one universal ASTM grade for ethylene glycol.
For example, ASTM specifications can address parameters such as water, acidity, DEG, iron, color, and distillation characteristics depending on the intended use.
Buyers should therefore identify the specific ASTM standard required for their product.
USP and ACS
USP and ACS designations are based on applicable specifications and testing requirements.
A product should not be considered USP-grade ethylene glycol or ACS-grade ethylene glycol simply because its assay is 99.5% or 99.9%.
When these grades are required, buyers should request documentation demonstrating compliance with the relevant specification.
What to Check Before Buying Ethylene Glycol in Bulk
Before placing a bulk ethylene glycol order, buyers should confirm the product specification, COA, impurity limits, grade, packaging, and delivery terms.
Technical Requirements
Specify:
Product: Ethylene Glycol / Mono Ethylene Glycol (MEG)
CAS No.: 107-21-1
EG assay: 99%, 99.5%, 99.9%, or required specification
Application: Antifreeze, coolant, polyester, PET, etc.
Standard: GB/T, ASTM, USP, ACS, or customer specification
Critical impurities: Water, DEG, iron, aldehydes, acidity, color, etc.
Ethylene Glycol COA Checklist
| COA Item | What Buyers Should Check |
|---|---|
| EG assay | Actual EG content |
| DEG | Actual or maximum content |
| Water | Moisture level |
| Iron | mg/kg |
| Aldehydes | mg/kg |
| Acidity | Actual result |
| Color | Pt-Co/Hazen |
| Standard | Applicable specification |
| Batch No. | Product traceability |
| Test date | Testing information |
For high-volume orders, buyers can also arrange third-party testing when the application has strict quality requirements.
Commercial Information
When comparing an ethylene glycol bulk supplier, also confirm:
Packaging: drums, IBC, flexitank, or ISO tank
MOQ
Available quantity
Lead time
Loading port
Shipping terms
Payment terms
COA and SDS availability
Does Higher-Purity Ethylene Glycol Always Cost More?
Higher-purity ethylene glycol generally requires tighter purification and quality control, but the highest assay is not always the most cost-effective choice.
Additional production and quality-control costs may come from:
More precise distillation
Water removal
DEG control
Aldehyde reduction
Trace-metal control
Color control
Additional laboratory testing
For a standard coolant application, purchasing a polyester-grade EG may add unnecessary cost.
For polyester or PET production, choosing a cheaper industrial-grade product may create quality or processing problems.
The better approach is to compare price + specification + COA + application suitability.
FAQ About Ethylene Glycol Purity
Is 99% ethylene glycol the same as 99.9%?
No, 99% and 99.9% ethylene glycol differ in assay and may also differ significantly in impurity limits. For applications such as polyester production, the impurity profile is as important as the EG assay.
What is 99.5% ethylene glycol used for?
99.5% ethylene glycol is used in applications requiring higher assay than standard industrial EG, but its exact suitability depends on the product specification. The 99.5% assay alone does not define USP, ACS, or another specific grade.
What purity of ethylene glycol is required for polyester production?
Polyester-grade EG under GB/T 4649-2018 requires an EG content of at least 99.9%, together with additional limits for impurities such as DEG, water, iron, aldehydes, acidity, and color.
Is 99.9% ethylene glycol high purity?
Yes, 99.9% represents a high EG assay, but it does not automatically define a specific international grade. Buyers should review the complete specification and COA.
What should I check on an ethylene glycol COA?
The key items are EG assay, DEG, water, iron, aldehydes, acidity, color, applicable standard, batch number, and test date.
What is the CAS number of ethylene glycol?
The CAS number of ethylene glycol is 107-21-1.
Conclusion: Choosing the Right Ethylene Glycol Purity
The best ethylene glycol grade is the one that meets the application's specification without paying for unnecessary purity.
For general industrial uses, 99% ethylene glycol may be sufficient. Applications with tighter quality requirements may require 99.5% or 99.9% EG, while polyester and PET production require specific control of impurities in addition to high EG assay.
For bulk procurement, specify:
Application → EG purity → impurity limits → applicable standard → COA → packaging → delivery terms
This gives buyers a more reliable basis for comparing ethylene glycol suppliers and selecting the right product for their process.
