Postgraduate student Uteyeva R.A., Doctor of Engineering, Professor Shevko
V.M., Candidate of Engineering
Sciences, Associate Professor Tileuova S.T.
M.Auezov South Kazakhstan State
University, Republic of Kazakhstan
EXTRACTION
OF HCL AND Cl2 AT OXIDATION
OF POLYCHLORINATED BIPHENYLS
Polychlorinated
biphenyls (PCBs) are classified as chlorine containing hydrocarbons, widely
used in industry since the 1930s. Many properties of PCBs, making these
compounds ideal for industrial application, create problems ,when as the result
of accident or during utilization of broken down assemblies, PCBs
get into the environment. Harmful
impacts on the human body and
the environment manifest themselves,
primarily, in long-term influence of
PCBs. Like many other chlorine containing hydrocarbons, PCBs bind with organic compounds ,present in soil, sediments, biological
tissues, as well as with dissoluted
organic carbon, present in water bodies and catchments.
PCBs are referred
to xenobiotics, so when they get into
the environment, they are destroyed with difficulty and can be preserved in it
for a very long time. They easily make a cycle between air, water and
soil. In the air, PCBs can be transferred at large distances. There have been cases of detection of them in air, water and organisms far away from the place of emission, such as
the Arctic [1].
This paper presents the results of
studies on the use of polychlorinated biphenyls with the general formula C12H10-nCln (where n=1,5 è 9) for the formation of HCl and Cl2. The studies were carried out , using the
software complex "Astra", developed at the Bauman Moscow State
Technical University [2], on the basis of thermodynamic data base of the Russian Federation and the USA
[3,4].
We were determining the possibility of formation of
HCl and Cl2 at oxidation of biphenysl by oxygen. As a basic reaction
the following one was considered
C12HCl9
+ 12O2 = HCl + 4Cl2 + 12CO2. (1)
Table 1 and
Figure 1 provide information on the
equilibrium distribution of chlorine in the considered reaction, depending on temperature and amount of
oxygen. The table shows that at the lack of oxygen within the temperature range of 500-900K CCl4 is formed
in the system, and in the temperature range of 500- 1200 K. COCl2 is formed. The temperature does not influence on the degree of formation of HCl (11.1% in the temperature range of 500-1800K). The maximum
level of chlorine transition into CCl4 (80.37%) is observed at T =
500 K, and COCl2 (7.53%) at T = 700K. At T> 650 K the basic amount of chlorine passes into Cl2 with a
maximum (87.99%) at T = 1000K. A noticeable degree of
chlorine transition into atomic chlorine is observed at T> 1200 K.,
comprising 25.2% at T = 1800K.
|
À |
 |
||||||||
|
Temperature, Ê Ñ1 Ñ12 ÍÑ1 |
Temperature, Ê temperature temperature,
Ê Ñ1 Ñ12 ÍÑ11 |
||||||||
|
À – Ñ12H9Cl,
B – C12HCl9 Figure 1 -
Effects of temperature on the equilibrium distribution of HCl and Cl (αHCl), (αCl)
in the system C12HCl9-O2, C12H9Cl-O2
at a stoichiometric amount of O2 |
|||||||||
When at
stoichiometric amount of oxygen according to the reaction (1) at 500 K chlorine (to 88.58%) primarily passes into molecular Cl2, at T> 1000K the formation of atomic chlorine becomes
noticeable. Based on the received distribution of elements , the systems
interaction C12HCl9–12Î2 proceeds according to the
scheme:
At T = 500K
C12HCl9
+ 12O2 = HCl + 4Cl2 + 12CO2 (2)
and at Ò=1600Ê
HCl + Cl2 +
12CO2 = HCl + 0,86Cl + 3,57Ñ12 + ÑÎ2 (3)
Increase of the amount of oxygen by 10-20% leads to the fact ,that at T = 500 K
the basic amount of chlorine
(98,39-98,64%) passes into Cl2. At increase of temperature,
the degree of chlorine transition in HCl increases to 10-11% (T =
1000-1800K) in Cl2 - it reduces to 62-63% (T = 1800K), and in Cl it
increases from 0.4% (100K) to 25-26% (T = 1800K).
At the decomposition of C12H9Cl
according to the suggested reaction
C12H9Cl +
12O2 = HCl + 4Í2Î + 12CO2 (4)
in fact, at T = 500 K chlorine for
50% passes into HC1 and for 50% into - Cl2 (Table 2)i.e. the reaction takes place:
C12H9Cl +
14O2 = 0,5HCl + 0,25Cl2 + 24CO2 + 4,25Í2Î (5)
Then, the basic
amount of chlorine passes into HCl (due to the reaction
H2Î + Ñ12 = 2HCl + 0,5O2, which is possible at T> 867K (Table 3).) That is why, at T =
1300K interaction continues according to the scheme:
0,5ÍÑ1+0,25Ñ12+24ÑÎ2+4,25Í2Î=0,996HCl+0,0015Ñ12+0,001Ñl+4,002Í2Î
(6)
Table 3 - Effect of temperature on DG
|
Ò,Ê |
500 |
700 |
800 |
900 |
1000 |
1200 |
1400 |
1600 |
1800 |
|
DG |
+24,7 |
+11,3 |
+4,6 |
-2,2 |
-8,9 |
-22,6 |
-36,3 |
50,0 |
-63,8 |
|
lgKp |
-2,584 |
-0,846 |
-0,300 |
+0,127 |
+0,469 |
+0,985 |
+1,355 |
1,634 |
1,852 |
Based on studies
the following conclusions can be made:
- in the C12HCl9-O2 at the lack of O2 for the oxidation of C to CO2 and T = 500K phosgene is primarily formed,
and at T> 1000K-C12; at stoichiometric amount of O2 ,C12 is formed already in the system at T = 500, and at T> 1000 - 1200 K. formation of atomic CL becomes noticeable; increase of O2 in the system to 110-120% leads to the fact, that the basic part of the
chlorine from chlorohydrocarbon (98,3-98,6%) passes at T = 500 K into C12.
- in the system C12H9Cl-O2 at a stoichiometric amount of O2
and T = 500 K HC1 and C12
are formed; with an increase of temperature ,due to the interaction of H2O with the C12,an
increase of the degree of transition of
C12 into HC1 with a maximum (99.47%) at T = 1200 K takes place.
Literature
1. United Nations Environment Program (UNEP): Inventory of worldwide PCB
destruction capacity, Geneva, 1998.
2. Sinyarev B.G., N.A. Vatolin, et.al. The use of computers for thermodynamic
calculations of metallurgical processes. - Moscow: Nauka. -1982. -263p.
3. JANAF Thermochemical tables: 2-nd edition. NSRDS-NBS 37. Washington: US
Gov. Print. Office. 1971. -1141 P.
4. Gurvich L.V. and et. al.Thermodynamic properties of individual substances
/ / Reference Edition in 4 volumes. -M.: Nauka. - 1972. -605 p.