What is the production process for PVC, which is manufactured in factories using the calcium carbide method these days?

The main component of PVC chemical raw materials is polyvinyl chloride resin, namely PVC; its molecular formula is –(CH2-CHCl)n– (where n represents the average degree of polymerization). Acetylene produced from calcium carbide, together with hydrogen chloride, is used to synthesize vinyl chloride monomer (VCM), which is then polymerized to form PVC resin. Simply put, it involves two steps: ① Acetylene reacts with hydrogen chloride to form vinyl chloride, CH≡CH + HCl → CH2=CHCl. ② Vinyl chloride undergoes polymerization to form polyvinyl chloride, nCH2=CHCl → --n. For more detailed information, see this post: http://bbs.hcbbs.com/thread-128662-1-1.html. This post was last edited by zhouchu2001 on 2009-3-23 at 14:07

1. Production methods, principles, and reaction equations of PVC. PVC is a thermoplastic polymer compound. The main production method is the acetylene process: vinyl chloride monomer is polymerized in a polymerization reactor, with the help of various ingredients and additives, to produce polyvinyl chloride resin. Qualified PVC is produced through stripping, centrifugation, and drying. Principle: Calcium carbide reacts with water to produce acetylene; HCl gas and acetylene combine in a mixer to form vinyl chloride. Vinyl chloride is purified and separated using distillation equipment to yield high-quality vinyl chloride monomer. The initiator is dissolved in this monomer and decomposed into free radicals through heating in a jacket; these free radicals initiate the polymerization of the vinyl chloride monomer. Under the action of a dispersant, polyvinyl chloride is formed as powdered particles, and the heat generated is removed via the jacket. Production method: Suspension polymerization process (1) Calcium carbide and water react in a generator to produce acetylene. (2) HCl gas and acetylene undergo oxidation in a converter under the action of a catalyst and at elevated temperatures, resulting in the formation of crude polyvinyl chloride. (3) The crude polyvinyl chloride is purified and separated using distillation equipment to produce high-quality vinyl chloride monomer. (4) The vinyl chloride monomer is polymerized in a polymerization reactor (under the action of ingredients and additives) to produce polyvinyl chloride resin, which is then stripped and centrifuged to yield qualified PVC. Reaction equations: (1) CaC2 + H2O → C2H2 + Ca(OH)2 (2) C2H2 + HCl → CH2=CHCl (3) nCH2CHCI → -n- 2. Brief description of the process flow: (1) Acetylene production section: Task – to produce high-quality acetylene gas. Production principle: CaC2 + 2H2O → C2H2 + Ca(OH)2. Calcium carbide is crushed and, in the absence of air, acetylene is generated in a generator; it then passes through a cooling tower before reaching the acetylene pump. From there, it is sent to neutralization towers and synthesis towers via 1.2 stages of purification. 2. Synthesis section: Task: Oxidize HCl and C2H2 using a catalyst under heated conditions; an addition reaction takes place in the converter, and the resulting crude vinyl chloride is sent to the compression unit. Production principle: CH≡CH + HCl → CH2CHCL. Both HCl and C2H2 are passed through coolers before being fed into a mixer; thereafter, they go through a graphite cooler, an acid mist separator, a graphite preheater, and a regenerative preheater, after which they enter the converter for conversion, and finally reach the compression stage. 3. Refining section: Task: To produce high-quality vinyl chloride monomer through purification and separation using refining equipment. Production principle: By taking advantage of the different boiling points of the various components in the mixture, heating and cooling are used to remove unwanted substances (C2H2, C2H2Cl). The compressed crude vinyl chloride passes through a total condenser, a water separator, a low-boiling-point tower, and a high-boiling-point tower; after that, C2H2 and C2H2Cl are separated, and the resulting product then enters a final condenser. The non-condensable gases include C2H2 and VC. 4. Polymerization section: Task: To polymerize vinyl chloride monomer in a polymerization reactor (with the action of ingredients and additives) into polyvinyl chloride resin; subsequent steaming (to remove residual vinyl chloride monomer), centrifugation, and drying are used to produce qualified resin products. Production principle: 1. Suspension polymerization method, in which the monomer is divided into droplets under stirring in the polymerization reactor, and polymerization occurs in a water medium. 2. Initiator ； The initiator dissolved in the monomer is decomposed into free radicals by jacket heating. Under the action of additives, VC enters the discharge tank through the polymerization tank; from there it goes to the stripping mixing tank and then to the stripping tower. After stripping, it enters the drying mixing tower for drying, and subsequently proceeds to the separator. It then moves via a screw conveyor to the drying tower, cyclone dryer, and cyclone separator for further drying. It is then packaged after being vibrated. 5. Process control parameters for key positions: 1. Acetylene unit: The temperature of the generator should be maintained between 80–90°C; the effective chlorine content of NaClO should be 0.08–0.12%; the purity of C2H2 should be at least 98%, with no sulfur present. P 2. Synthesis section: Temperature of the converter is 90–180°C; temperature of the mixer is 45°C. The concentration of C2H2 is less than 0.5%, and that of HCl is less than 4%. The purity of crude VC is at least 85%. The ratio of HCl to C2H2 is 1.05–1.1:1. 3. Polymerization section: Initiator, dispersant, buffer; washing tank, water removal; polymerization tank, heating, normal reaction process, then completion. Volume: 48 m3, 24 m3; weight: 16.3 t, 30 m3, 16 m3; weight: 10.3 t. SG3: 52.6°C for C2H2; SG4: 57.5°C for C2H2CL. Last edited by QXZ-1966 on 2009-3-23 at 19:21.]