Inner Mongolia Rongxin Chemical has applied for a patent titled “A Continuous Production Method and Production System for Low-Molecular-Weight Polyglycolic Acid (PGA)”

Thread Content

Inner Mongolia Rongxin Chemical Co., Ltd. applied for a patent titled “A Continuous Production Method and Production System for Low-Molecular-Weight Polyglycolic Acid (PGA)”, with publication number CN120289771A; the application was filed in June 2025. The process for producing PGA from dimethyl oxalate involves the hydrogenation of dimethyl oxalate to yield methyl glycolate ； Then, under the action of a catalyst, methyl glycolate is polycondensed to form PGA ； Polycondensation synthesis includes pre-polymerization (abbreviated as prepolymerization) and final polycondensation; during pre-polymerization, methyl glycolate undergoes multiple stages of prepolymerization reactions to gradually form low-molecular-weight PGA (an intermediate product) ； Then, the low-molecular-weight PGA (intermediate product) undergoes further final polycondensation to yield high-molecular-weight PGA, namely PGA. In actual industrial production, pre-polymerization is a key step in the production of PGA from dimethyl oxalate; whether the pre-polymerization process proceeds smoothly has a direct impact on the subsequent final polycondensation step. In current industrial production, the prepolymerization process involves using five reaction vessels connected in series (in order; these five vessels correspond to the first prepolymerization stage, the second prepolymerization stage, the third prepolymerization stage, the fourth prepolymerization stage, and the fifth prepolymerization stage), after which methyl glycolate with a purity of >97% (the raw material) is fed into the system ； The raw materials undergo five stages of prepolymerization, ultimately yielding PGA with 95% purity, which is the low-molecular-weight PGA (intermediate product). Although the existing prepolymerization method can produce low-molecular-weight PGA through a five-stage prepolymerization reaction, methyl glycolate with a purity of >97% needs to remain in each reactor for a sufficient amount of time in order to obtain low-molecular-weight PGA that meets the required purity standards ； As the reaction proceeds step by step, the purity of low-molecular-weight PGA increases as well; in other words, the content of PGA in the material fed to the next stage becomes higher and higher ； However, as the content of PGA generated through the stepwise prepolymerization reaction increases, its viscosity also increases accordingly ； The high-viscosity PGA produced in the preceding reactor requires a longer time to be gradually transferred to the next reactor downstream. As a result, it is difficult to stably convey the high-viscosity PGA to subsequent reactors in a timely manner, leading to poor production continuity and low production efficiency ； Furthermore, an increase in PGA viscosity can also cause frequent blockages in the transfer pipelines of the reaction vessel; once such blockages occur, it is necessary to shut down the equipment for maintenance, which makes it difficult to maintain continuous and stable prepolymerization reactions. To address the technical issues of poor continuity, low production efficiency in the current production of low-molecular-weight PGA, and frequent blockages in the delivery pipelines, this invention provides a method and system for the continuous production of low-molecular-weight PGA. The patent abstract indicates that this invention falls within the field of polyglycolic acid production technology, and relates to a continuous production method and production system for low-molecular-weight polyglycolic acid. Methyl glycolate with a purity of >97% is fed into the first stage of pre-polymerization; the products resulting from this stage are then sent to the second, third, and fourth stages of pre-polymerization at different flow rates, where they participate in the respective pre-polymerization reactions ； The secondary prepolymerization product generated in the secondary prepolymerization stage directly participates in the tertiary prepolymerization reaction ； The tertiary prepolymerization products generated in the tertiary prepolymerization stage enter the fourth and fifth prepolymerization stages respectively ； The tetrapolymerization prepolymer product formed in the fourth-stage prepolymerization reaction proceeds directly to the fifth-stage prepolymerization stage to participate in the reaction ； The fifth-stage prepolymerization step produces low-molecular-weight polyglycolic acid. The conditions for each stage of the prepolymerization reaction are as follows: First-stage prepolymerization reaction: temperature of 130±2°C, pressure of 2 KPa–3 KPa ； Secondary prepolymerization stage: temperature of 150±2°C, pressure of 2 KPa–3 KPa ； Third-stage prepolymerization stage: temperature of 170±3°C, pressure of 70±1 KPa absolute pressure ； Stage 4 of the prepolymerization reaction: temperature of 180±3°C, pressure of 30±1 KPa absolute. Stage 5 of the prepolymerization reaction: temperature of 220±3°C, pressure of 1.5±0.5 KPa absolute. On January 12, 2022, the 3,000-ton/year dimethyl oxalate-based PGA production project of Inner Mongolia Rongxin Chemical Co., Ltd. was approved for registration, with a total investment of 40 million yuan. The total investment for the project is 40 million yuan, with completion scheduled for March 2023. Building on the existing ethylene glycol facility, the project will utilize dimethyl oxalate as a raw material to construct a plant capable of producing 3,000 tons per year of biodegradable plastic polyglycolic acid.