What is raw material for pvc resin?

PVC (polyvinyl chloride) resin is mainly composed of two raw materials, one is ethylene or acetylene, and the other is chlorine.

Let's start with the part concerning carbon - based parts. Ethylene is an extremely ubiquitous building block. It is detkived from hydrocarbons by steam cracking(generally from naphtha, which is a fraction of crude oil). Naphtha is subjected to high - temperature steam cracking in the presence of steam in a cracking furnace. In this process, long-chain hydrocarbons in naphtha are cracked into shorter-chain hydrocarbons, and ethylene is one of the key products. For instance, a common reaction could be the break down of a hydrocarbon and one of it is C₆H₁₄ in naphtha to this then its called ethylene C₂H₄ with other by-products as propylene and methane.

Acetylene is another carbon - based feedstock. Calcium carbide (CaC₂), when reacted with water, can produce acetylene. The production of calcium carbide is done in an electric arc furnace, whereby lime (CaO) and coke (a form of carbon) are heated up to high temperatures (in the range of 2000 – 2200 °C). When calcium carbide reacts with water, it produces acetylene gas in a highly exothermic reaction: CaC₂ + 2H₂O → C₂H₂ + Ca(OH)₂.

PVC resin contains chlorine mainly derived from the electrolysis of brine (sodium chloride solution; NaCl). In (...)  In the chlor - alkali industry, brine is electrolyzed in a diaphragm cell, a mercury cell, or a membrane cell. At the anode, chlorine gas (Cl₂) and at the cathode hydrogen gas (H₂) and sodium hydroxide (NaOH) are formed when an electric current passes through a brine. The overall reaction for brine electrolysis is 2NaCl + 2H₂O → Cl₂ + H₂ + 2NaOH.

Ethylene or acetylene and chlorine are produced and then polymerized into PVC resin. If ethylene is employed, the first stage is typically the synthesis of ethylene dichloride (EDC). The EDC is formed from ethylene and chlorine through the catalyzed process by using the metal chlorides, like ferric chloride (FeCl₃). The reaction: C₂H₄+ Cl₂ → C₂H₄Cl₂. In addition, EDC can be synthesized from the oxychlorination of ethylene, in which ethylene reacts with hydrogen chloride and oxygen using a catalyst such as cupric chloride (CuCl₂), resulting in the formation of EDC and water: 2C₂H₄ + 4HCl+ O₂ → 2C₂H₄Cl₂ + 2H₂O.

Once EDC has been produced, it undergoes thermal cracking at elevated temperatures (typically between 480 - 550 °C) to generate vinyl chloride monomer (VCM) and hydrogen chloride. The reaction is: C₂H₄Cl₂ → C₂H₃Cl + HCl. If EDC was produced by oxychlorination then the hydrogen chloride generated has potential to be recycled to oxychlorination. If acetylene is used as the feedstock, the reaction proceeds between acetylene and hydrogen chloride in the presence of a mercury - based catalyst (mercury - free catalysts have been developed in more recent years due to environmental concerns) to give VCM directly. The reaction is: C₂H₂ + HCl → C₂H₃Cl.

Finally, the vinyl chloride monomers are polymerized to create PVC resin. And this polymerisation is then performed by different methods like suspension polymerisation, emulsion polymerisation or bulk polymerisation. In suspension polymerization, VCM is dispersed in the water as droplets and a polymerization initiator is added. Initiators decompose to give rise to free radicals, which trigger the polymerization reaction by linking the VCM monomers into long-chain PVC polymers.

In summary, the supplies of PVC resin which include either ethylene or acetylene as the carbon framework, and chlorine produced from brine electrolysis are the building blocks for this common polymer. These raw materials are processed into PVC resin through established and complex processes in industry. Comprehending these raw materials and their processing is necessary to optimize PVC production, enhance product quality, and consider environmental and economic factors in the manufacturing process.