Our company, Yixing Wencheng Chemical Co., Ltd., is a manufacturer of polyol series fine chemicals, and has been engaged in the production and sales of polyols and their derivatives for 40 years. Propylene glycol, as an important member of the polyol series, is one of our core products. Our ability to supply USP grade propylene glycol in bulk is a core competitive advantage. USP grade propylene glycol can be safely used in direct human contact, oral administration, and even injection, while also meeting the high purity requirements of high-end industrial synthesis, applications that industrial grade propylene glycol cannot fully replace.
USP propylene glycol is a relatively niche fine chemical with a small global annual demand. Based on our past experience, pharmaceutical companies typically use it as a drug solvent; cosmetic companies use it as a moisturizer and penetration enhancer in skincare products; and e-cigarette liquid companies use it in combination with vegetable glycerin (VG) as a primary solvent in e-liquids. These are the main buyers of USP propylene glycol, but their consumption is not large. Furthermore, USP propylene glycol must be produced under CGMP (Good Manufacturing Practice) principles and undergo rigorous release testing. Each batch of product has complete traceability documentation to ensure product quality. Without the incentive of substantial profits and given the cumbersome and stringent requirements for production, testing, and storage, there are very few companies globally capable and willing to produce USP propylene glycol. Based on our understanding of the Chinese market, there are no more than three companies capable of compliantly and in large-scale production of USP propylene glycol. This is the biggest pain point for most companies that need to purchase USP propylene glycol: the inability to find a manufacturer. Yixing Wencheng Chemical Co., Ltd., with a certain customer base and order volume, is one of the few manufacturers capable of and currently producing USP propylene glycol in large quantities.
There are two main global production processes for USP propylene glycol:
1. The propylene oxide hydration method, represented by Dow Chemical Company: Propylene oxide reacts with water in an acidic or alkaline catalyst (such as ion exchange resin, a small amount of sulfuric acid or alkali) to produce industrial-grade 1,2-propanediol, which is then purified through multiple stages to synthesize USP propylene glycol.
2. The USP propylene glycol produced by Yixing Wencheng Chemical Co., Ltd. is synthesized via ester exchange: Using propylene oxide, methanol, and carbon dioxide as raw materials, propylene carbonate is first synthesized, then reacted with methanol via ester exchange to co-produce dimethyl carbonate and 1,2-propanediol. This method uses mild reaction conditions (66-90°C, atmospheric pressure), and the conversion rate can reach over 99.5% by breaking the equilibrium through reactive distillation. However, this only produces industrial-grade propylene glycol, which requires further purification through multiple stages to synthesize USP propylene glycol.
To help you make a better choice, we provide the most straightforward and detailed comparison between industrial-grade and USP-grade (pharmaceutical-grade) propylene glycol, making it easier for you to quickly determine which to use.
| Propylene Glycol USP VS Industrial Grade Propylene Glycol | |||
| Category | Item | USP/Pharma Grade (USP/Pharma Grade) | Industrial Grade |
| Core Chemical Indicators | Purity (Assay) | ≥ 99.8%(Some manufacturers require ≥99.85%~99.9%) | ≥ 99.5%(Divided into premium grade ≥99.5% and standard grade ≥99.0%) |
| Water Content | ≤ 0.1% or ≤ 0.2% | ≤ 0.2%(Premium grade ≤0.1%, standard grade ≤0.2%) | |
| Color (APHA/Pt-Co) | ≤ 10 | ≤ 10 or ≤ 5 (premium grade) | |
| Distillation Range | ~184-189 °C (>95% volume distills over) | ~184-190 °C (>95% volume distills over) | |
| Key Impurities | Heavy Metals (as Pb) | ≤ 5 ppm | Usually not explicitly defined in industrial standards |
| Chlorides | ≤ 0.007% (≤ 70 ppm) | Usually uncontrolled, or limited to ≤ 75 ppm as free chlorine | |
| Sulfates | ≤ 0.006% (≤ 60 ppm) | Usually uncontrolled | |
| Residue on Ignition / Ash | ≤ 0.007% | ≤ 80 ppm (or 0.008%) | |
| Ethylene Glycol (EG) | ≤ 0.10% | ≤ 0.1% | |
| Diethylene Glycol (DEG) | ≤ 0.10% | Usually not explicitly defined in industrial standards | |
| Aldehydes | Strictly controlled (via specific tests) | Usually uncontrolled | |
| Key Difference Interpretation | |||
| Purity (Assay) | USP grade has higher purity requirements, leaving less room for impurities. | ||
| Water Content | Water control is a baseline for pharma-grade products, with lower moisture being a key feature. | ||
| Color (APHA/Pt-Co) | Top-tier products perform equally well in color; visual differences are minimal. | ||
| Distillation Range | Both ranges overlap significantly, a characteristic of high-purity liquids. | ||
| Heavy Metals (as Pb) | USP grade’s strict limits ensure safety in human-related applications. | ||
| Chlorides | USP grade controls harmful ions that may affect human health or equipment from the source. | ||
| Sulfates | Like chlorides, this is a higher-level purity control item for pharma-grade use. | ||
| Residue on Ignition / Ash | USP grade has stricter limits, indicating fewer residual non-volatile inorganic impurities. | ||
| Ethylene Glycol (EG) | The upper limit is the same; the core difference lies in USP-grade testing accuracy. | ||
| Diethylene Glycol (DEG) | This is one of the most critical differences; without hard limits, industrial grade carries higher risks. | ||
| Aldehydes | USP grade controls aldehydes to reduce potential irritation to patients. | ||
Our company's high-quality USP propylene glycol series products are stable in performance and excellent in quality. They are exported to many countries around the world and are widely used in the pharmaceutical, food, cosmetic, and e-cigarette liquid industries. With over forty years of experience in the industry, we remain committed to quality and stable production capacity. We sincerely welcome inquiries and cooperation from customers from all sectors!
