Isooctane is widely used in chromatographic analysis and organic synthesis, which has resulted in a large increase in the demand for high purity isooctane. There are two production processes for isooctane, one is the dimerization of isobutene, the other is the reaction of isobutene and butene. How much does the impurity composition of the raw material in the production and preparation of isoctane affect the quality of the product?

Effects of ethylene

Ethylene is a simple alkene, and although it has unsaturated double bonds similar to butene, their effects on alkylation are quite different. When ethylene enters the alkylation container, butene, unlike butene, is alkylated with alkanes; Ethylene reacts with sulfuric acid, the catalyst in the alkylation reaction, and the product is ethyl bisulfate. The ethyl bisulfate produced by the reaction will continue to react with sulfuric acid in the alkylation reaction vessel, further reducing the concentration of sulfuric acid and producing a great dilution effect on sulfuric acid. The ethylene in the raw material also has a cumulative effect on alkylation, so even if the content of ethylene in the raw material is small, it will gradually accumulate during the synthesis process, resulting in a large amount of waste acid.

The effect of butadiene

Alkylation refers to the process of alkanes and alkenes addition reaction, the unsaturated double bond in the alkenes is broken, which is also a carbon chain lengthening process. The raw materials are isobutane, butene and isobutene in the four components of carbon in petroleum catalytic cracking. In the preparation process of isoctane, the actual chain growth process. The butadiene in the feedstock is not alkylated with isobutane, although it has a similar structure of the predetermined system. Butadiene reacts with sulfuric acid to form acid-soluble ester compounds. Another direction of reaction is to form heavy acid-soluble composites. The heavy acid soluble compound is a heavy oil with high viscosity. Its presence will cause the dry point of the product to increase, and the octane number and yield of the product will be seriously decreased. If the heavy acid-soluble composites are separated, a part of the acid will be lost, resulting in a great waste of raw materials.

Effects of sulfide

In order to remove some sulfur-containing impurities and ensure raw material purity and product quality, LPG desulphurization and mercaptan removal stages are generally carried out before the raw material enters the human alkylation reaction vessel. By desulphurization, the sulfur content in the raw material is reduced to less than 10ug/g. The effect of sulfide on the alkylation reaction is mainly through the effect of acid, sulfide has a very large dilution effect on sulfuric acid. For every ton of sulfide in the raw material, 15-60 tons of sulfuric acid will be lost.

If the sulfide in the raw material is in the form of methyl mercaptan, the mercaptan can reduce the concentration of sulfuric acid, five times its weight, by 10 percent per ton. The presence of sulfide in raw materials not only increases the consumption of sulfuric acid, but also makes the catalytic action of sulfuric acid tend to polymerization and some other side reactions, which will directly lead to the decrease of product purity and the increase of impurity.

The effect of Water

The raw material contains water, the most immediate effect is to reduce the acid concentration. When sulfuric acid is diluted, it not only has a great influence on the catalysis of alkylation reaction, but also produces corrosion to the alkylation reaction vessel. When the water in the liquefied gas is saturated, it is about 500ug/g. What's more serious is that the free water carried by the C4 fraction is over the saturated state, and the content of the water in this part is generally several times that of the saturated water in the gas, which will further aggravate the dilution of sulfuric acid.

The influence of oxygen containing compounds such as dimethyl ether and methanol

Most of the alkylation feedstock comes from C4, and most of the world's C4 hydrocarbons come from the catalytic cracking process in the petroleum industry. Most butadiene was used as industrial or civil fuel before the 1980s, when C4 resources were abundant in by-product in Chinese refineries. In recent years, due to the rapid development of separation technology, the chemical industry has made great progress in the use of C4 hydrocarbons. Alkylation reaction is the addition reaction of alkanes and alkenes with the participation of acid catalyst. In the reaction process, the active hydrogen atoms of alkanes are replaced by alkenes. From the perspective of the activity of hydrogen atoms, the hydrogen atoms on the tertiary carbon atoms of isomeric alkanes are more active than the hydrogen atoms on the primary carbon atoms of normal alkanes, and are more easily replaced in the alkylation reaction. Therefore, the hydrocarbons involved in alkylation are mostly iso-alkanes. Usually, the alkylated isomeric alkanes are isobutane, and alkenes are usually alkenes with carbon number of 3--6. At present, the main alkylation catalysts used are sulfuric acid and hydrofluoric acid. During the alkylation process, impurities such as dimethyl ether and methanol in the reaction vessel will also consume a large amount of acid and reduce the octane number of the alkylated oil.

The impurities that may normally be present in the preparation of isoctane are grouped into ethylene, butadiene, sulphides, moisture, and oxygen-containing compounds such as dimethyl ether and formaldehyde. In addition to the influence on the alkylation reaction itself, the impurity components mainly affect the alkylation reaction indirectly through the influence of the catalyst sulfuric acid. The presence of impurities will lead to the reduction of the utilization rate of raw materials, the reduction of product quality, and the occurrence of side reactions resulting in the production of industrial waste, which will directly lead to the destruction of ecological environment.

Isooctane is stored in a storage tank. The ignition and heat source should also be stored separately from the oxidizer. All mechanical equipment and tools that are easy to produce sparks are prohibited. In addition, the storage area should be equipped with spill emergency treatment equipment and suitable holding materials. In the operation to avoid contact with the body, do all the protection, avoid inhalation or ingestion. Contraindications of isooctane include strong oxidants, strong acids, strong bases, and halogens.