RU2344115C2 - Preventive method of thermopolymerisation inhibitors deactivation - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention refers to preventive method of thermopolymerisation inhibitors deactivation accompanying separation of C₄-hydrocarbon fractions containing sulphur compounds. Method is implemented through rectification with aqueous acetonitrile as extactant and implies that secondary amine is used as additive preventing polymerisation inhibitor deactivation. Application of this method provides linking and transformation of sulphurous compounds into persistive salts of dithiocarbamic acid.

EFFECT: prevention of catalyst deactivation.

2 cl, 1 tbl, 3 ex

Description

The invention relates to the petrochemical industry, in particular to the production of monomers, namely the production of divinyl. In industry, the process of separation of divinyl from C ₄ hydrocarbon mixtures is carried out by extractive distillation (ER) using polar solvents, in particular an aqueous solution of acetonitrile (AN).

To eliminate the loss of 1,3-butadiene due to thermopolymerization, an inhibitor sodium nitrite (NaNO ₂ ) is introduced into the aqueous solution of AN.

However, during prolonged residence of polymerization inhibitors in a shared mixture, deactivation occurs due to interaction with the hydrolysis products of the separating agent.

A known method for producing 1,3-butadiene by isolation from C ₄ -hydrocarbon fractions of ER in the presence of a thermopolymerization inhibitor, where furfural is used as a deactivating additive [US Patent No. 3,309,412, 1967, cl. 260-666.5].

The use of this additive in ER processes with AN is limited by the tendency of furfural to gum formation and the low solubility of the resulting resins in aqueous AN.

Closest to the claimed is a method of separation from C ₄ -hydrocarbon fractions of the ER, where an increase in the effectiveness of polymerization inhibitors is achieved by the introduction of a tertiary amine - triethanolamine (TEA) for deactivation [A.s USSR No. 291901 from 01.10.1968].

In the presence of sulfur-containing impurities in the hydrocarbon feedstock (thiols, CS ₂ , etc.), СО ₂ ТЭА does not react with them and, as a result, does not prevent the deactivation of polymerization inhibitors. This leads to unproductive losses of butadiene, solvent, inhibitors, clogging of heat-exchange equipment with polymer deposits, and a reduction in equipment mileage.

The objective of the invention is to develop a method for preventing the deactivation of polymerization inhibitors in the separation of sulfur-containing hydrocarbon mixtures of ER in an aqueous solution of AN.

Using the proposed additives, it is possible to separate C ₄ hydrocarbon fractions containing various amounts of sulfur compounds.

The difference between the proposed technical solution and the closest one is that diethylamine (DEA), a compound of the class of secondary amines, is used as an additive to prevent the deactivation of the polymerization inhibitor.

The proposed method allows you to bind and convert sulfur compounds into stable salts of dithiocarbamic acids and thereby prevent the deactivation of polymerization inhibitors.

The possibility of obtaining a technical result is confirmed by examples of industrial use.

Installation Description

The C ₄ -hydrocarbon fraction is subjected to ER separation using an aqueous AN solution in the presence of a polymerization inhibitor NaNO ₂ and a deactivating agent. The butane-butylene fraction is taken from the top of the ER column. The bottom product of the column is sent to the stripper. From the top of the stripper, a concentrated target fraction (for example, butadiene in the separation of butylene-divinyl fractions, butylene in the separation of butane-butylene fractions) is selected. VAT product - desorbed acetonitrile is returned to the ER column.

The regeneration of the solvent from dimers, the extraction of AN from hydrocarbon streams, the recovery of AN from washing water is carried out by well-known methods.

Examples 1 and 2 show the effectiveness of the protection of the polymerization inhibitor when triggered by a separation unit for sulfur-containing hydrocarbon feeds using aqueous AN as a solvent in the presence of deactivating additives.

The inhibitory activity of NaNO ₂ is determined by the amount of polymer formed when the mixture is heated, consisting of 80 wt.% Of the specified AN, 20 wt.% Divinyl. The mixture is heated in sealed glass ampoules purged with nitrogen for 18 hours at 130-150 ° C. The polymer content in the mixture after heating is determined after distillation of AN and non-polymerized monomer, gravimetrically, by the ratio of the mass of dry residue (taken as polymer) to the mass of the loaded monomer.

The results are presented in table 1.

Table 1 Example The content of sulfur compounds in the C ₄ fraction, wt.% Deactivating additive Dosage, wt.% The amount of polymer formed, wt.% one 0,021 DEA 0,070 0,057 2 0.019 Tea 0,070 0.450 3 - DEA 0.001 0,052

As can be seen from the above examples, DEA effectively prevents the deactivation of the thermopolymerization inhibitor under conditions of separation of sulfur-containing hydrocarbon feedstocks. In the absence of sulfur compounds in the feed, DEA works as a TEA, but its dosage is lower, which indicates better efficiency.

Claims (2)

1. A method for preventing the deactivation of thermopolymerization inhibitors by separation of C ₄ hydrocarbon fractions containing sulfur compounds by distillation using aqueous acetonitrile as an extractant, characterized in that a secondary amine is used as an additive preventing deactivation of the polymerization inhibitor. 2. The method of preventing the deactivation of inhibitors according to claim 1, characterized in that diethylamine is used as an additive.