How Diethylene Glycol Is Used in Antifreeze and Coolant | DEG Diethylene Glycol Supplier
发布于 2026-10-16
Introduction
Since Q4 2024, the domestic diethylene glycol (DEG, CAS 111-46-6) market has shown pronounced seasonal fluctuations driven by antifreeze and coolant demand. According to mainstream East China market data, industrial diethylene glycol spot quotes rose from RMB 4,980/ton in early October to RMB 5,420/ton by mid-December, a cumulative increase of approximately 8.8%. Over the same period, port inventory dropped from 32,000 tons to 21,000 tons, a decline of 34%. For antifreeze formulators and coolant buyers, understanding DEG's functional role in formulations, substitution boundaries, and cost transmission logic has become critical to controlling B2B procurement costs. This article analyzes formulation essentials, market supply-demand dynamics, and procurement strategies to support purchasing decisions.
I. Functional Role of Diethylene Glycol in Antifreeze and Coolant
Diethylene glycol serves three primary functions in antifreeze formulations: lowering the freezing point, raising the boiling point, and inhibiting metal corrosion. Compared with monoethylene glycol (MEG), DEG has a lower freezing point (pure DEG approximately -10.45°C) but higher viscosity, so it is typically not used alone as the primary antifreeze agent. Instead, it is blended with MEG and propylene glycol in specific ratios to adjust the freezing point curve and improve anti-vapor-lock performance under high-temperature conditions. In heavy-duty diesel engine coolants, industrial circulating cooling water systems, and certain aviation de-icing fluids, DEG commonly appears as a secondary antifreeze component, typically at 5%–20% addition rates.
From a formulation design perspective, incorporating DEG also reduces overall raw material costs. Taking current market conditions as an example, the latest diethylene glycol price is approximately RMB 5,300/ton, while industrial-grade propylene glycol quotes generally range from RMB 7,800–8,500/ton — a price gap exceeding RMB 2,500/ton. When freezing point requirements are met, partially substituting propylene glycol with DEG can save approximately RMB 300–500 per ton of finished coolant in raw material costs. This is the direct reason why DEG usage has increased in some mid-to-low-end antifreeze formulations over the past two years.
It should be noted that DEG has higher swelling effects on certain rubber seals (such as nitrile rubber) compared with MEG, so formulations require appropriate corrosion inhibitors and seal compatibility agents. Additionally, the application of diethylene glycol polyurethane raw materials in cooling system pipe coatings is worth attention, as their hydrolysis resistance outperforms certain polyester systems, extending pipe service life.
II. Formulation Essentials and Quality Control
Adding DEG to antifreeze formulations is not a simple proportional substitution. Four key points require attention:
**First, balancing freezing point and boiling point.** In typical formulations, when DEG mass fraction exceeds 15%, the freezing point decline flattens while the boiling point rises significantly (from 108°C to above 112°C). For heavy-duty coolants requiring a boiling point ≥110°C, DEG addition can be controlled at 10%–15% in combination with MEG.
**Second, corrosion inhibitor system compatibility.** DEG affects the stability of traditional silicate corrosion inhibitors to some degree. Organic acid technology (OAT) or hybrid organic acid technology (HOAT) inhibitor systems are recommended. Phosphate, benzotriazole, and sebacate dosages need adjustment based on DEG ratio, with total inhibitor addition generally at 1.5%–3.0%.
**Third, moisture and impurity control.** Industrial diethylene glycol purity is typically ≥99.5% with moisture ≤0.2%. If recycled or low-purity feedstock is used, moisture and aldehyde impurities accelerate inhibitor depletion, shortening coolant service life from 5 years to 2–3 years. Buyers should request batch COAs from suppliers, focusing on moisture, acidity, and color metrics.
**Fourth, storage and feeding.** DEG is highly hygroscopic and must be sealed after opening. The 220kg iron drum packaging for DEG shipments is common among small and medium-sized formulators, but drum opening seals and warehouse humidity control (recommended relative humidity ≤60%) require attention. For large-volume procurement, ISO tanks or tank cars can reduce packaging costs by approximately RMB 200–300/ton.
From a cost structure perspective, DEG accounts for approximately 25%–40% of antifreeze raw materials, and its price fluctuations significantly impact finished product costs. At the current diethylene glycol price of RMB 5,300/ton, a 10% price increase would add approximately RMB 130–200 per ton to antifreeze costs. Therefore, buyers must closely monitor the DEG price trend and arrange inventory cycles accordingly.
III. Market Supply-Demand and Price Transmission
China's 2024 diethylene glycol production capacity is approximately 1.2 million tons, of which about 35% is used for unsaturated polyester resins, 20% for antifreeze and coolant, and the remainder for polyurethane, solvents, and pharmaceutical intermediates. Q4 antifreeze production peak season (September–November) generates additional DEG demand of approximately 15,000–20,000 tons per month, accounting for 12%–15% of total monthly consumption.
On the supply side, East China main port inventory dropped from 32,000 tons in October to 21,000 tons in December, at a three-year low for the same period. Regarding imports, January–November 2024 DEG imports totaled approximately 280,000 tons, down 6.3% year-on-year, primarily from Saudi Arabia, Kuwait, and Taiwan region. Domestic coal-to-MEG co-produced DEG output has increased, though quality consistency still needs improvement.
Regarding pricing, the question of diethylene glycol price per ton is what buyers care about most. As of mid-December, East China spot quotes were RMB 5,300–5,450/ton, and South China quotes were RMB 5,400–5,550/ton, up approximately 4.5% from early November. Futures main contracts traded at a discount of approximately RMB 80–120/ton to spot, indicating market expectations of short-term supply tightness. It is expected that in Q1 2025, as antifreeze production winds down, DEG prices may retreat to the RMB 5,000–5,200/ton range, though crude oil prices and MEG plant maintenance schedules warrant monitoring.
For buyers, current inventory levels are low. Moderate restocking is recommended when prices correct below RMB 5,100/ton to lock in Q1 production needs. Meanwhile, attention can be given to substitution opportunities for diethylene glycol polyurethane raw materials in high-end coolant piping to expand formulation optimization space.
Procurement Recommendations
1. **Lock in long-term agreements**: Sign quarterly or annual framework agreements with mainstream suppliers, linking DEG procurement prices to East China spot averages to reduce unilateral price increase risk.
2. **Focus on purity and packaging**: Prioritize industrial diethylene glycol with purity ≥99.5% and moisture ≤0.2%. For large volumes, use tank cars or ISO tanks; for smaller volumes, choose 220kg iron drum packaging.
3. **Optimize formulations for cost reduction**: While meeting freezing point and boiling point requirements, increase DEG addition to 10%–15% to replace some high-priced propylene glycol, reducing costs by RMB 300–500 per ton of finished product.
4. **Inventory management**: Maintain 7–10 days of safety stock to avoid supply disruption risks from low port inventory. Monitor the latest DEG prices and plant dynamics to flexibly adjust procurement pacing.
5. **Quality verification**: Test moisture, acidity, and color for each incoming batch to ensure compliance with GB/T 4649-2018 or internal enterprise standards.
Conclusion
Diethylene glycol delivers clear cost-reduction and efficiency value in antifreeze and coolant formulations, particularly in substituting propylene glycol and adjusting freezing/boiling points. Current market supply-demand is tight, with prices at a阶段性 high. Buyers should combine the DEG price trend analysis with their own inventory positions to formulate reasonable procurement strategies. In the medium-to-long term, as domestic capacity is released and antifreeze demand stabilizes, DEG prices will return to a reasonable range of RMB 5,000–5,300/ton. Enterprises are advised to optimize formulation design, expand downstream applications such as diethylene glycol polyurethane raw materials, and strengthen supply chain resilience to address cost pressures from raw material price volatility.
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