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AZERBAIJAN CHEMICAL JOURNAL № 2 2022
ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)
UDC 536.7
THERMODYNAMICS OF THE FORMATION OF DIISOPROPYL ETHER
E.A.Guseinova, S.S.Zlotskiy*, N.N.Mikhaylova*, S.E.Yusubova
Azerbaijan State Oil and Industry University *Ufa State Petroleum Technological University
elvira_huseynova@mail.ru
Received 25.12.2021 Accepted 10.01.2022
The results of thermodynamic calculations have showed that the condensation reaction of isopropyl alcohol with propylene, even at room temperature, is accompanied by complete transformation into the target product, di-isopropyl ether. At temperatures above 400 K, an almost equal degree of conversion of isopropyl alcohol to acetone and propylene, as well as the same temperature dependence of the equilibrium yield of reaction products, has been noted. Under conditions of parallel reactions of the conversion of isopropyl alcohol (with the exception of condensation with propylene), at 300 K theoretically, the most probable is the formation of di-isopropyl ether (38.28%) > propylene (16.75%) > acetone (12.32%), while at 400K and higher propylene (48.49%) > acetone (48.1%) > di-isopropyl ether (30.69%).
Keywords: thermodynamic calculations, isopropyl alcohol, di-isopropyl ether, acetone, propylene, Tem-kin-Shvartsman method, Gibbs energy, entropy, enthalpy.
doi.org/10.32737/0005-2531-2022-2-54-62 Introduction
Since the beginning of the 2000s, the ecological problem of pollution of large cities and roadsides by exhaust gases has been one of the most acute in the Republic of Azerbaijan. Until recently, the quality of ambient air was directly related to the number of cars. According to the State Statistics Committee of the Republic [1, 2], in 2019 their number reached 1 million 418 thousand 404, and the volume of harmful emissions from the vehicle fleet reached a peak value of 976 thousand tons, which is 84% of the total amount of emissions into the atmosphere on the territory of the AR.
Azerbaijan in 2011 approved new national standards for fuel of the EURO class. However, the gasoline introduced in most countries that meets the Euro-5 environmental standards is currently not produced in Azerbaijan. SOCAR Company plans to start production of diesel fuel according to Euro-5 standards at the Baku Oil Refinery Plant named after Heydar Aliyev in mid-2022, and Euro-5 gasoline in 2023 (statement dated 02/01/2021 [3]). This will improve both the fuel performance and the vehicle exhaust formula.
A fundamental solution to these issues is achieved by creating the production of so-called
"reformulated" gasolines, which, in addition to hydrocarbons, include such oxygen-containing compounds (oxygenates) as methyl tert-butyl ether (MTBE), methyl tert-amyl ether (MTAE), ethyl tert-butyl ether, di-isopropyl ether, lower alcohols (methanol, ethanol) and other compounds [4-8]. In our Republic, to solve this problem, the Heydar Aliyev Oil Refinery Plant is working on construction of a technological unit for the production of methyl tert-butyl ether (MTBE) (Ezermaks). World factories for the production of MTBE are based on the combination of technologies for n-butane isomerization, isobutane dehydrogenation and esterification. However, new sources of oxygenate additives will also play a significant role in the future, since the refineries cannot produce enough tertiary olefins in catalytic fluid cracking units for their esterification to meet the growing demand for ester production.
Di-isopropyl ether (DIPE) is a very promising additive to motor gasolines. DIPE is a high-octane (road octane number 105) oxygen-containing additive with low Reid vapor pressure (0.35 atm.) and reduced volatility [6] has no toxicity compared to MTBE, DIPE also compares favorably with other ethers by a much greater availability of raw materials: propylene
and isopropyl alcohol resources. In addition, DIPE is used to dissolve animal fats, vegetable and mineral oils, natural and synthetic resins, as a solvent in the dewaxing process of lubricating oils, during extraction to separate uranium from its fission products, to isolate acetic acid from aqueous solutions, etc. [10].
DIPE is obtained by two methods: catalytic hydration of propylene and dehydration of isopropyl alcohol. Both reactions are reversible, and the yield of the target product entirely depends on the reaction conditions [11].
At all stages of planning, conducting and analyzing the research results, chemical processes of processing hydrocarbons and their derivatives, it is necessary to conduct thermodynamic analysis. Contributions to the field of thermody-namic analysis of chemical and petrochemical processes were made by such outstanding scientists as A.V.Frost, M.F.Naghiyev, Y.M.Zhorov, A.V.Kireev, Y.I.Gerasimov, A.A.Vvedensky, I.B.Rabinovich, G.A.Krestov, I.M.Kolesnikov and many others.
The use of the thermodynamic analysis method makes it possible to select the most appropriate area for a specific reaction of obtaining, and therefore, the works that make it possible to clarify the existing ones or to obtain new data are of high importance [12-15]. This work is devoted to the analysis of the thermodynamic functions of the reactions of the conversion of isopropyl alcohol to DIPE using the Temkin-Shvartsman method.
Experimens and thermodynamic modeling
Thermodynamic functions were determined for the following reactions of gas-phase transformation of isopropyl alcohol:
Reactions c and d are considered comparative in determining the equilibrium composition of the reaction mixture. The calculation of thermodynamic parameters was carried out by the Temkin-Shvartsman method (1947) [16, 17] and for each of the 4 chemical reactions it was carried out in the following sequence: 1. Using thermodynamic tables [16-18], we se-
cp =
1,
lect the numerical values A , H a + bT + cTuArG^ (Table 1).
298
2. Using the G.I. Hess formula we calculate the thermal effect ArU the change in the absolute entropies and the change in the coefficients Ara, Arb, Arc for a chemical reaction.
3. Using the Kirchhoff formula, we calculate, the change in the enthalpy of reaction with an increase in temperature within the range of 298-625 K in 250 increments (Table 2, Figure 1).
4. We calculate the change in the entropy of the reaction within the range of 298-625 K with a step of 250 (Table 3, Figure 2). Calculations are carried out in 250 increments.
5. We calculate the change in heat capacity within the range of 298-625 K (Table 4, Figure 3). Calculations are carried out in 250 increments.
6. We calculate the change in the Gibbs energy within the range of 298-625 K with a step of 250 using the Temkin-Schwartsman formula (Table 5, Figure 4). Calculations are carried out in 250 increments.
7. We calculate the equilibrium constants of chemical reactions Keq.
8. We calculate the equilibrium composition of the reaction mixture according to the law of effective masses.
Results and discussions
The absolute value of the enthalpy of DIPE formation has the greatest value, which indicates the greatest complexity of the compound (Table 1). Negative values of the enthalpies of DIPE and acetone formation in the case of the formation of these compounds from simple substances, indicates the exothermicity of these reactions which, the greatest again for DIPE.
According to Hess's law, the change in thermodynamic functions is determined by the difference between the thermodynamic functions of the reaction products, multiplied by their stoichiometric coefficients, and the ther-modynamic functions of the starting compounds, also multiplied by their stoichiometric coefficients v,.
For a general reaction: ViAi + V2A2 = vjAj[ + V2Ai
V1A1 + V2A2
the changes in enthalpies, entropies and heat capacities are determined by the formulas (the
second consequence of Hess's law): ArH °93 =Ev[ AfH°93, prod^vi A/if , im ,.„/,,,, (2) where/- formation, r - reaction. Ar = ¿Vj Sjgg^j-od — ¿Vj in.subs., (3) A rCp = Aa+ AbT + AcT2 , (4)
where A a = Ev[ aprod - AV, a in.sUbs,
Ab = Zv\ ¿prod - 2V; b in. subs,
Ac = Xv[ Cprod - c in. subs.
As a model reaction, consider the intermolecular dehydration of isopropyl alcohol to DIPE (reaction b, see experimental procedure). For this, the change in enthalpy was calculated:
ArH^s = A/Hij3(c3H7oc3H7) + A/fii)93(h20) -2 AfH293(c3h7OH) = (-319.03) + (-241.81) -- 2 (-272.71) =-15.42 J/mol
As you can see, the change in the enthalpy of the reaction of the formation of diisopropyl ether has a low absolute but still negative value, therefore, this process is exothermic. The same conclusion becomes obvious for the reaction of DIPE formation during the addition of olefin to alcohol. In contrast to these two reactions, the change in enthalpies obtained for the reactions of isopropyl alcohol conversion to acetone and pro-pylene are higher in absolute value and positive,
which indicates their endothermicity.
The change in entropy in the reaction of intermolecular dehydration of isopropyl alcohol to DIPE (reaction b, see the experimental procedure) is:
A/'5Íij3 =A5 л93(с3 н7ос3 н7)+A5Í93(h2 о,
-2 • AS i93( c3 н7 о H) = 391.25+188.72-2-310.49 =
= -41.04 J/mol K.
The entropy of this particular reaction is negative due to the fact that the system becomes more ordered. The results obtained for all considered reactions are summarized in Table 2. The change in the molar heat capacity of the resulting reaction is calculated by the formula:
A rCp = A,a + ArbT +Arcf, где А,а=а(Сэн7осэн7)+а (Н^О)—2 а (С3н7он) = 30.02 + 21.01 - 17.34 = 33.69 Arb = b (С3н7ос3н7)+b (H20) — 2-¿(C3h7oh) = 10.71 • 103 + 488.8-103 - 606.2-103 = 106.69-103
А,с = C(C3H70C3H7) + C(H3c>) — 2-е (С3Н70Н) =
0.33-106- 162.5-106 + 231.6-106 = 69.43-106
Consequently, the change in heat capacity for the intermolecular dehydration of isopro-pyl alcohol to DIPE (reaction b, see the experimental procedure):
A rCp = 33,67 - 106,69 • 103 Т + 69,43 • 106 Т2.
Table 1. Numerical values of thermodynamic functions of substances under standard conditions
Compound АН : : , kJ/mol А/ ■ : : , kJ/mol K с; a bio3 ciO6
изо-С3Н1ОН -272.71 310.49 89.16 8.61 303.10 -115.80
С3Н6 20.33 261.36 64.18 12.44 188.38 -41.60
С3Н1ОС3Н1 -319.03 391.25 158.95 21.01 488.80 -162.50
С3Н6О -211.65 295.43 15.19 22.41 201.80 -63.50
Н2О (г) -241.81 188.12 33.60 30.00 10.11 -
Н2 0 130.52 28.85 21.28 3.26 -
Table 2. Change of thermodynamic functions for reactions (a-d)
Reaction АН ■ : : , kJ/mol А_- - ; ; , kJ/mol К Equation coefficients А rCv = f(T)
Aa Ab103 Ac106
a) -25.99 348.12 25.08 0.0314 -94.3
b) -15.42 -41.04 33.61 -106.69 69.43
c) 50.9 145.59 33.11 -104 68.2
d) 55.06 115.46 41.08 -98 52.3
Notes: The letter designations of the reactions are given in accordance with that shown in the experimental procedure.
Fig. 1. Dependence A rCp = f(T) for the reactions of isopropyl alcohol conversion to DIPE (a and b), propylene (c), and acetone (d). The designations of the reaction products are given in accordance with that shown in the experimental procedure.
Notes: The designations of the reaction products are given in accordance with that shown in the experimental procedure.
Fig. 2. Dependence ArH 'i = f(T) for the reactions of isopropyl alcohol conversion to DIPE (a and b), propylene (c), and acetone (d).
Notes: The letter designations of the reactions are given in accordance with that shown in the experimental procedure.
The calculation results for both a specific and other 3 reactions are presented graphically in Figure 1. The results shown in the figure indicate that the heat capacity of all the considered reactions in the conversion of isopropyl alcohol depends on temperature. The nature of the changes indicates that the heat effect of the formation reaction of DIPE remains negative up to 450 K, propylene - up to 470 K, DIPE (during the addition reaction) - up to 515 K, and acetone over the entire temperature range under consideration.
The correctness of the results obtained is confirmed by the data obtained in the course of the calculations of the isobaric heat effect of the reactions of isopropyl alcohol conversion according to the Kirchhoff formula (Figure 2).
Only for a reaction accompanied by the formation of acetone, the thermal effect increase, with increasing temperature, i.e., it is exothermic. For the other 3 reactions, the dependence of the isobaric thermal effect on temperature passes through an extremum at the maximum point for DIPE at 450 and 515 K, propylene - up to 470 K, with further decreasing, which indicates that these reactions in the high-temperature region proceed with heat absorption.
The change in entropy, taking into account the change in the heat capacities of the components of the reaction mixture, is determined:
where A rCp - change in the heat capacity of a chemical reaction; A rCp = A,a + ArbT +ArcT2. After substituting and integrating the resulting equation, we obtain:
ArS° = ArS%3 Ara In ^ + Arb (T-298) +
Substituting numerical values and A ra,
A rb and Arc, we obtain:
A/'5° =-41,04+3 3,691n^+106,69 1 03(T-
298) + +6%43;i°V:-29S:)
The results obtained in the course of calculating the entropy values for the considered
4 reactions of isopropyl alcohol conversion are shown in Table 3.
Table 3. Entropy change results for isopropyl
alcohol conversion reactions
T, K Isopropyl alcohol conversion reactions
а) b) c) d)
300 115.57 348.23 -40.96 145.65
325 116.82 349.51 -40.39 146.29
350 117.85 350.58 -39.97 146.78
375 118.71 351.47 -39.69 147.14
400 119.41 352.18 -39.51 147.39
425 119.99 352.74 -39.42 147.56
450 120.46 353.15 -39.40 147.65
475 120.84 353.43 -39.45 147.67
500 121.13 353.57 -39.54 147.65
525 121.35 353.60 -39.68 147.59
550 121.52 353.51 -39.84 147.49
575 121.63 353.31 -40.04 147.37
600 121.69 352.99 -40.25 147.23
625 121.72 352.59 -40.48 147.07
Notes: The letter designations of the reactions are given in accordance with that shown in the experimental procedure.
Among all the reactions of isopropyl alcohol conversion, the entropy increased with increasing temperature only in the case of the formation of acetone, increasing from 145.65 to 147.07 J/mol. For other reactions, the enthalpy passes through a maximum, decreasing at higher temperatures, which indicates an increase in the ordering of the systems under these conditions.
The graphical representation of the Gibbs energy versus temperature (Figure 3) clearly indicates that the DIPE formation during intermolecular dehydration is thermodynamically more probable at low temperatures (up to 3500C) (reaction b), and during the condensation of alcohol with propylene it occures in the entire temperature range, i.e. proceeds without thermodynamic restrictions. In the process of converting isopropyl alcohol to acetone and propylene, the direction of the reaction shifts to the right at temperatures above 350 and 475 K, respectively.
As a result of the above mentioned, it is expected that the highest values of the equilibrium constants are characteristic of the reaction of DIPE formation by condensation of isopropyl alcohol with propylene. Despite the fact that with an increase in temperature, a slight decrease in the equilibrium constant of this reaction is ob-
served, nevertheless, it remains very significant, which indicates that, under these conditions, the equilibrium of the reaction is strongly shifted to the right. The transformation of individual iso-propyl alcohol in the direction of the acetone and propylene formation is characterized by an equilibrium constant increasing with temperature. The data in Table 4 also indicate that with an increase in the temperature of the process, the equilibrium constant for the DIPE formation in the course of intermolecular dehydration shifts to the left, towards the initial substances.
The calculation of the composition of the equilibrium mixture for the specifically considered reaction of intermolecular dehydration to DIPE versus temperature was carried out according to the law of effective masses:
2 iso-CsHyOH^ C3H7OC3H7+ H2O 2(1-a) a a
Table for iso 4. Results of calculating the equilibrium constants propyl alcohol conversion reactions
T, Isopropyl alcohol conversion reactions
K a) b) c) d)
300 4.45 1022 2.671 0.042 0.020
325 2.111022 1.712 0.210 0.116
350 1.121022 1.171 0.830 0,525
375 6,471021 0,842 2,736 1.942
400 4.021021 0.631 7.768 6.117
425 2.641021 0.488 19.489 16.850
450 1.821021 0.388 44.089 41.497
475 1.311021 0.316 91.360 92.932
500 9.681020 0.261 175.621 191.867
525 7.37T020 0.220 316.392 369.252
550 5.75T020 0.187 538.697 668.449
575 4.57T020 0.161 872.842 1146.799
600 3.7 • 1020 0.140 1353.638 1876.234
625 3.04 • 1020 0.122 2019.055 2942.675
Notes: The letter designations of the reactions are given in accordance with that shown in the experimental procedure.
Fig. 3. Dependence ArGf =f(T) for the reactions of conversion of isopropyl alcohol to DIPE (a and b), propylene (c) and acetone (d).
Notes: The letter designations of the reactions are given in accordance with that shown in the experimental procedure. Table 5. Calculation of the equilibrium constant and the equilibrium composition of the mixture_
Reaction
Equilibrium constant
Equilibrium conversion
a)
/so-C3H7OH + C3H6 ^ C3H7OC3H7
Kp (1 -«r-
a =
(2Jf+l)±^(4A'+l)
2K
b)
2w3o-C3H7OH ^ C3H7OC3H7 + H20
Kv 4i;i-tr)a
a =
c)
iso-C3H7OH ^ C3H6 + H20
K = -
I-tT-
a =
±v'4Jf(14AT) 2(1+A)
d)
iso-C3H7OH ^ C3H60 + H2
K„=-
a =
2(1+JC)
The total number of moles is 2. The material balance of the compounds in the reaction mixture is determined by the expressions: Niso-prop = 1-a; Ndipe = a/2; Nh2o = a/2.
Substituting mole fractions, we obtain an intermediate expression for the equilibrium constant. The expressions obtained for all 4 reactions are summarized in Table 5.
The degree of conversion versus temperature and the composition of the resulting equilibrium reaction mixture are shown in Figure 4 and in Table 6. Depending on the reaction direction the degree of feedstock conversion versus temperature can be illustrated by the following sequences: at 300K a>b>c>d; at 400K a>c>d>b; at 500K and above a,c,d>b.
As can be seen (Table 6), the condensation reaction of isopropyl alcohol with propylene even at room temperature is accompanied by complete conversion into the target product, DIPE. Analysis of the results of the DIPE yield in the course of the intermolecular dehydration reaction in the investigated temperature range indicates that the most preferable region for its production is the region of low temperatures (300-400K). Under these conditions, the maximum theoretical DIPE yield is 30-38%. It should be noted that in the case of the conversion of individual isopropyl alcohol at temperatures above 350 K, the reactions
accompanied by the formation of propylene and acetone begin to make a significant contribution. Under conditions of parallel reactions of the conversion of isopropyl alcohol (with the exception of condensation with propylene), at 300 K theoretically, the most probable is the formation of DIPE (38.28%)>propylene (16.75%) > acetone (12.32%), while propylene (48.49%)>acetone (48.1%)>DIPE (30.69%) is formed at 400 K and higher.
Fig. 4. Effect of temperature on the conversion degree (total equilibrium yield of products) in the reactions of isopropyl alcohol conversion to DIPE (a and b), propylene (c), and acetone (d).
Notes: The letter designations of the reactions are given in accordance with that shown in the experimental procedure.
Table 6. Equilibrium composition of the isopropyl alcohol conversion
T, K Content of components in the equilibrium mixture of products, % mol.
a) iso-C3H70H + C3H6 ^ ^ C3H7OC3H7 b) 2 iso-C3H70H ^ ^ C3H7OC3H7 + + H20 c) iso-C3H7OH ^ ^C3H + H2O d) iso-C3H7OH ^ ^ №0 + H2
Nether Nalcohol Nether Nwater Nalcohol Npropylene N water Nalcohol Nacetone Nhydrosen
300 100 23.426 38.287 38.287 66.497 16.751 16.751 75.356 12.322 12.322
325 100 27.646 36.177 36.177 41.205 29.398 29.398 51.195 24.403 24.403
350 100 31.606 34.197 34.198 19.511 40.244 40.244 26.051 36.975 36.975
375 100 35.269 32.366 32.366 7.772 46.114 46.114 10.345 44.827 44.827
400 100 38.631 30.685 30.685 3.027 48.487 48.487 3.784 48.108 48.108
425 100 41.705 29.148 29.148 1.. 51 49.375 49.375 1.441 49.279 49.279
450 100 44.514 27.743 27.743 0.561 49.720 49.720 0.595 49.702 49.702
475 100 47.085 26.458 26.458 0.272 49.864 49.864 0.267 49.866 49.866
500 100 49.444 25.278 25.278 0.142 49.929 49.929 0.130 49.935 49.935
525 100 51.618 24.191 24.191 0.0789 49.961 49.961 0.068 49.966 49.966
550 100 53.630 23.185 23.185 0.046 49.977 49.977 0.037 49.981 49.981
575 100 55.502 22.249 22.249 0.029 49.986 49.986 0.022 49.989 49.989
600 100 57.252 21.374 21.374 0.018 49.991 49.991 0.013 49.993 49.993
625 100 58.897 20.552 20.552 0.012 49.994 49.994 0.008 49.996 49.996
Conclusion
Thus, the results of calculations of thermodynamic functions showed that
1. taking into account the results of the change in the Gibbs energy with temperature, the reaction of the DIPE formation during the condensation of alcohol with propylene in the entire temperature range proceeds without thermodynamic restrictions.
2. the nature of the change in heat capacity, as well as enthalpy, indicates that the heat effect of the reaction of formation of acetone, in contrast to the others considered, remains negative in the entire temperature range (exo-);
3. in the course of intermolecular dehydration to DIPE, the process is thermodynamically more likely at low temperatures (up to 350 K),
4. during the conversion of isopropyl alcohol to acetone and propylene, the direction of the reaction shifts to the right at temperatures above 350 and 475K, respectively,
5. with parallel reactions of isopropyl alcohol conversion (with the exception of condensation with propylene), at 300K, theoretically, the most probable is the formation of DIPE (38.28%) > propylene (16.75%) > acetone (12.32%), while propylene (48.49%) > acetone (48.1%) > DIPE (30.69%) is formed at 400K and above.
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DÜZOPROPÍL efírínín omolo golmo reaksíyalarinin termodínamíkasi
E.O.Hüseynova, S.S.Zlotski, N.N.Mixaylova, S.E.Yusubova
Termodinamiki hesabatlann naticalari gôstarmiçdir ki, izopropil spirtinin propilen ils kondenslaçma reaksiyasi hatta otaq temperaturunda maqsadli mahsula - diizopropil efirina tam çevrilma ila mûçayat olunur. 400K-dan yuxan temperaturlarda izopropil spirtinin aseton va propilena praktiki olaraq barabar daracada çevrilmasi , hamçinin reaksiya mahsullannin tarazliq çiximinin eyni temperatur asililigi qeyda alinmiçdir. izopropil spirtinin çevrilma reaksiyalannin paralel baç vermasi çaraitinda (propilenla kondensasiya istisna olmaqla) 300 K temperaturda diizopropil efiri (38.28%) > propilen (16.75%) > aseton (12.32%) amala galmasi nazari olaraq nisbatan daha ehtimalli hesab edilir, halbuki 400 K va daha yüksak temperaturda propilen (48.49%) > aseton (48.1%) > diizopropil efiri (30.69%).
Açar sözlzr: termodinamik hesablama, izopropil spirti, diizopropil efiri, aseton, propilen, Tyemkin-^vartsman metodu, Hibbs enerjisi, entropiya, entalpiya.
ТЕРМОДИНАМИКА РЕАКЦИЙ ОБРАЗОВАНИЯ ДИИЗОПРОПИЛОВОГО ЭФИРА
Э.А.Гусейнова, С.С.Злотский, Н.Н.Михайлова, С.Э.Юсубова
Результаты термодинамических расчетов показали, что реакция конденсации изопропилового спирта с пропиленом даже при комнатной температуре сопровождается полным превращением в целевой продукт -ДИПЭ. При температурах свыше 400 К отмечена практически равная степень превращения изопропилового спирта в ацетон и пропилен, а также одинаковая температурная зависимость равновесного выхода продуктов реакций. В условиях параллельного протекания реакций превращения изопропилового спирта (за исключением конденсации с пропиленом), при 300 К теоретически наиболее вероятным является образование ДИПЭ (38.28%) > пропилена (16.75%) > ацетона (12.32%), тогда как при 400 К и выше пропилена (48.49%) > ацетона (48.1%) > ДИПЭ (30.69%).
Ключевые слова: термодинамический расчет, изопропиловый спирт, диизопропиловый эфир, ацетон, пропилен, метод Темкина-Шварцмана, энергия Гиббса, энтропия, энталпия.
