The chlorination of paraffin hydrocarbons is a free radical substitution reaction, that is, it proceeds according to the chain reaction process. According to the different initiating methods of the chain, it can be divided into thermal chlorination; light (ultraviolet) chlorination; catalytic chlorination; light, catalytic chlorination, etc. The chlorination of paraffin hydrocarbons is a strongly exothermic reaction, and the reaction temperature is about 1508KJ/kg.
1. Thermal Chlorination
Chlorine molecules are dissociated by thermal energy to form free radical chlorine atoms and undergo a substitution reaction with paraffinic hydrocarbons. The thermal dissociation energy of chlorine molecule is about 350.12KJ/mol.
The paraffin temperature can be initiated at 50 °C, the phase polymerization reaction can occur at 70 °C, and the reaction can be normal at 80 °C. The thermal chlorination method should remove a large amount of heat energy released by the reaction in time and retain enough heat energy for initiation, and increase the chlorination reaction control temperature correspondingly with the increase of the chlorination depth, and the maximum temperature should not exceed 105 °C.
Chlorine atoms are dissociated by ultraviolet radiation to form free radical chlorine atoms and undergo substitution reactions with paraffinic hydrocarbons. The dissociation energy of chlorine molecule is about 238.26KJ/mol, and the wavelength of its ultraviolet light source is 2.5×104, 4.5×102m, and 3.4×107m, the best absorption value of ultraviolet light.
3. Catalytic Chlorination
An "initiator" can activate the chlorine molecule to form free radicals for the substitution reaction. Substances that can activate chlorine molecules to generate free radicals in the reaction are called initiators. such as peroxides or azos.
The paraffin wax manufacturer's production process uses thermal chlorination. The higher the reaction temperature, the faster the chlorination reaction, but the higher the chlorination reaction temperature, the more side reactions, the quality of the chlorinated paraffin decreases, and the appearance color is obviously darker, so the thermal chlorination method should strictly control the chlorination reaction temperature.
1. Medical paraffin is the distillation product of petroleum, its melting point is 30℃-70℃, and its boiling point is 350℃-360℃. When paraffin wax is heated to 100°C or higher, it is easily oxidized by oxygen in the air under the condition of sufficient contact with oxygen.
Medical high-purity paraffin, its melting point is 50℃-54℃, and its oil content is 0.8%-0.9%. China has already produced a large amount of high-purity medical paraffin for the needs of medical work.
2. Industrial paraffin is generally extracted directly from petroleum, and during the industrial extraction process, it will contain polycyclic aromatic hydrocarbons and condensed aromatic hydrocarbons, which are very strong carcinogens. In addition, after the human body ingests paraffin, it will also cause gastrointestinal diseases such as diarrhea.
At present, some hot pot base materials, oil materials, instant noodles and some inferior barrels of instant noodles (barrel walls) contain such substances, and even some instant chopsticks and paper cups can also find the existence of industrial paraffin.
3. The difference between medical paraffin and industrial paraffin is mainly in terms of unit price and heavy metal content. The preparation raw materials of medical paraffin are mainly GR grade, and heavy metals can be precipitated after repeated refining, and the unit price is 3 to 5 times higher than that of industrial grade.
The raw materials for the preparation of industrial paraffin are all LR grade or lower materials, which can be refined once. Their molecular weight, solubility and boiling point, and molecular formula are all the same.
The key point is that the heavy metal content of medical paraffin is very small, because medical paraffin is mainly used as an additive in medicine and food.