Polyformaldehyde production process

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Background and purpose of the project research: Formaldehyde is an important basic organic chemical raw material. However, due to its low boiling point and reactive properties, it presents various drawbacks such as high requirements for industrial packaging, poor storage stability, difficulties in transportation, and inconvenience in use. Polyformaldehyde is an excellent substitute for industrial formaldehyde. High-quality polyformaldehyde features high purity, good water solubility, complete depolymerization, a loose structure, and uniform particles, making it regarded as an ideal source of pure formaldehyde. Although there are several polyoxymethylene manufacturers in our country, their production scale is small, raw material consumption is high, and the quality of their products is poor, making it difficult for them to compete with foreign products; as a result, large quantities of high-quality polyoxymethylene must be imported from abroad each year. To meet domestic needs, the Petrochemical Technology Development Center of Tianjin University, drawing on the most advanced production technologies available abroad, developed a polyformaldehyde production process with an annual capacity of 20,000 tons. This process utilizes techniques such as two-stage falling-film concentration, spray granulation, and continuous drying, thereby overcoming the shortcomings associated with domestic batch concentration and rake or scraper drying processes – namely limited production scale, high raw material consumption, and poor product quality. As a result, all quality and consumption metrics related to polyformaldehyde production have reached advanced international levels. Technical principle and process: A 37% or 55% aqueous formaldehyde solution is first depolymerized, and then a concentrated formaldehyde solution of around 80% is obtained through two-stage falling-film vacuum concentration. After a polymerization reaction takes place under the action of a copolymerization agent, the final polyformaldehyde product with a concentration of around 96% is produced via spray granulation and continuous drying. Level of performance and key technical parameters: Product quality parameters: Formaldehyde content ≥95%, methanol content ≤0.5%, acidity ≤0.8%, ash content ≤100 ppm, melting point 120–175°C, bulk density 600–800 g/L, pH 3.5–5.0, reaction time 5 minutes, solubility (in water at 100°C for 10 minutes) 95%, degree of polymerization 8–30. Tonnage consumption metrics per product: 37% formaldehyde – 2.8 tons, steam – 3.0 tons, cooling water – 200 tons, electricity – 260 kwh. Production scale and output: 20,000 tons/year. Required floor area for the factory: 10,000 m2. Main equipment: depolymerization kettle, falling film evaporator, polymerization reactor, granulation tower, dryer, absorption tower, and cooler, etc. Main raw material and source: formaldehyde. Market analysis and benefit forecasting: As an ideal substitute for formaldehyde, polyformaldehyde has a broad market potential. However, the total domestic production of polyformaldehyde is less than 6,000 tons per year, which is far from sufficient to meet market demand. In 2001, China imported 37,500 tons of polyformaldehyde, and the import volume continued to grow at an annual rate of over 25%.