Abstract

Kolbasa Viktoria

Faculty of Ecology and Chemical Technology

Speciality: Chemical technology of fuel and carbon materials

Theme of master's work:

Research the process of carbon bisulphide extraction from the head fractions of crude benzene

Scientific adviser: c.t.s., assistant professor Krut’ko Irina

Introduction

      Volatile form with coke in the high-temperature coking of coal blend at coke oven chamber chemicals, which are the complex of heterogeneous system, that consists of gaseous and vaporous substances, which are the product of the thermal decomposition of coal.

       Crude benzene is a product that is extracted from the coke gas Carboniferous by the coal absorbing oil. There is sulfuric acid method and the method of catalytic purification of crude benzene from sulphureous compounds and the result of it is the isolation of carbon bisulfide (head) fractions.

      One of the common methods of processing the head fraction is the method of thermopolymerization, which has significant drawbacks. Therefore, at this time the working out new methods of purification and processing of carbon bisulfide fraction is very, as well as are educing from it organic products (eg, thiourea or ammonium thiocyanate, etc.).

      Objective: The aim of the work is studing the physicochemical principles of extraction of carbon bisulfide from the head fraction of crude benzene by binding it with chemical reagents for obtaining valuable, safe for storage, using and transportation chemical products.

       Relevance of work:

• irrational use of the parent fraction of crude benzene, and difficulties in implementation due to high toxicity;
• lack of environmentally safe method of processing the head fraction of crude benzene;
• high demand for sulfur-organic compounds (thiourea, ammonium thiocyanate) for industrial synthesis.

1 Analytical review of the literature

      The crude benzene obtained in the process of coking coals, in itself does not find practical application and is subjected to further processing of pure products. The scheme of the processing of crude benzene preliminary includes the stage of rectification, which provides separation of low-boiling and high boiling sulfur and unsaturated compounds. The resultant mixture of low-boiling components, called the leading, or carbon disulfide fraction contains 25 - 45 % of carbon disulfide, 15 - 25 % cyclopentadiene, and 15 - 35 % of benzene. The yield of the parent fraction is 2,0 - 3,5 %.

      Carbon bisulfide and cyclopentadiene possess similar boiling points (42,5 and 46,5 °C, correspondingly) so it is almost impossible to separate them but only by rectification.

      At that time, the recycling industry head faction is done by the thermal polymerization, based on the property of cyclopentadiene to form under the influence of heating dicyclopentadiene with much higher temperature than all the other components of fractions have boiling 166,6 °C.

      This method of processing the head fraction of crude benzene requires the bulky equipment, the high expenditure of time and energy. The process is accompanied by a large (up to 30 %) losses of carbon disulfide, benzene, cyclopentadiene, raw materials for which is in this case coal - non-renewable source of energy. These substances are highly toxic, falling into the atmosphere, they are damaging the environment. Thus, the irretrievable losses of energy and resources are accompanied by environmental degradation. Isolation of carbon bisulfide from the head faction in the free state associated with fire and explosion danger.

2 Experimental

      For reactions we used crude head fraction of benzene and ammonia 25 % water.

Table 2.2 shows the characteristics of the head fraction.

      The laboratory facility is an autoclave, which consists of the body and the lid. A glass is inserted into the body, which is closed by the lid. There is a nut In the autoclave, which provides the opening of the autoclave.

      A certain amount of head fraction of crude benzene and 25 % aqueous ammonia solution are placed in the glass. Then the glass was placed in the autoclave body and tightly closed. We placed the autoclave in an thermostat heated to a certain temperature. The autoclave was heated to the desired temperature and kept for some time. After this, the autoclave was placed on the air, then we cooled it under water for about 30 min. After this mixture, which was in a glass autoclave, was moved into a separatory funnel and we separated it into two phases: ammonium salt solution and the head fraction.

      Analysis of the initial reagents and the reaction products was carried out by using the chromatographic method.

3 Experimental results

      It was investigated the effect of temperature, ratio of reagents and the contact time of reagents on the degree of CS₂ extraction from the head fractions of crude benzene.

      With increasing contact time (Fig. 3.1) the degree of extraction increases CS₂. When the contact time is 1:00 the degree of extraction is 85.22 %, with 5 hours - 97.1 %. The optimal time for further experiments was taken time of 3 hours.

      The degree of purification increases when increasing the ratio of carbon disulfide and ammonia (Figure 3.2) at a constant temperature (t = 120 ⁰C). At 2:1 the degree of extraction is 77.34 %, at 7:1 - 99.84 %.

Figure 3.1 - Dependence of the degree of extraction CS₂ on contact time head fractions and ammonia
The molar ratio of NH₃: CS₂ = 5:1, temperature t = 115 ⁰C

Figure 3.2 - Dependence of the degree of extraction of CS₂ GFSB of changing ratio of NH₃: CS₂
Temperature t = 120 ⁰C, holding time τ = 3 hours.

      When the temperatures becomes higher (Fig. 3.3) the degree of purification increases. According to the results of experiments we can see that with increasing temperature in the range 80 - 160 ⁰C the degree of extraction varies for sample 1 from 75.51 to 99.11 %, and for sample 2 from 91.76 % to 99.99 %. With increasing temperature for samples 2, we observe slight changes in the degree of extraction from CS₂ GFSB. The optimum temperature was taken to be 115 - 120 ⁰C.

Figure 3.3 - Dependence of the extraction CS₂ on temperature
Sample 1: molar ratio of NH₃: CS₂ = 5:1, holding time τ = 3 years;
Sample 2: molar ratio of NH₃: CS₂ = 7:1, holding time τ = 3 hours.

Findings

• For the first time we investigated the reaction between carbon disulfide and ammonia in a mixture of aromatic compounds;
• We found that with increasing contact time the extraction CS₂ increases. The optimal time for follow-up experiments was taken as 3 hours;
• We found that the degree of purification increases when increasing the ratio of carbon disulfide and ammonia at a constant temperature (t = 120 ⁰C). Almost complete removal of carbon disulfide from the organic phase into the water in the form of thiocyanate compounds is achieved when molar ratio of NH₃: CS₂ = 7:1.
• When temperature increases the degree of purification increases too. The optimum temperature was taken to be 115 - 120 ⁰C;
• We demonstrated the principal possibility of virtually complete extraction of carbon disulfide from the head fractions by treatment with aqueous ammonia in obtaining products that can be used for organic synthesis.

      At writing of this abstract of thesis master's degree work is not yet completed. Final completion is December, 2010.

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