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Organochlorine Compounds with Low Boiling Point in Desalted Crude Oil: Identification and Conversion Bencheng Wu, Yongfeng Li, Xiaohui Li, Jianhua Zhu, Rui Ma, and Shaojian Hu Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 02 May 2018 Downloaded from http://pubs.acs.org on May 5, 2018
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Organochlorine Compounds with Low Boiling Point in Desalted Crude Oil: Identification and Conversion Bencheng Wu,*,† Yongfeng Li,† Xiaohui Li,‡ Jianhua Zhu,† Rui Ma,† and Shaojian Hu† †
State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering, China University of Petroleum, Beijing 102249, China
‡
College of Chemistry and Chemical Engineering, Xi’an shiyou University, Xi’an 710065, China
Abstract: Organochlorine compounds (OOCs) with low boiling point in desalted crude oil were identified via gas chromatography (GC) with electron capture detection (ECD) and the possibility of their hydrolysis was evaluated thermodynamically under the conditions of industrial distillation of desalted crude oil. Six fractions, namely, gasoline, aviation kerosene, light diesel, heavy diesel, lubricating oil, and residual oil, were obtained via true boiling point distillation. Chlorine concentration results indicated that OOCs with low and high boiling points were concentrated in the gasoline fraction and residual oil, respectively. Qualitative and quantitative analyses of low boiling point OOCs, such as carbon tetrachloride, tetrachloroethylene, 1,1,1,3-tetrachloropropane, and 1,2,4-trichlorobenzene were performed via GC–ECD. The four types of OOCs coexisted in the gasoline, aviation kerosene, and light diesel fractions. Thermodynamic analysis results indicated that the four types of OOCs could hydrolyze to form corrosive HCl during industrial distillation of desalted crude oil. High temperature and low pressure conditions will enhance the OOCs hydrolysis. Key words: crude oil; organochlorine compound; hydrolysis; thermodynamic analysis
1. Introduction Aside from inorganic chlorides (NaCl, MgCl2, and CaCl2), organochlorine compounds (OOCs) are usually presented in trace amounts in crude oil. Previous studies have shown that inorganic chlorides may be hydrolyzed to form HCl gas during industrial distillation of desalted crude oil. Water can dissolve the HCl gas to form a dilute hydrochloric acid that can cause fouling and corrosion of equipment.1–3 Therefore, electric desalting device is usually adopted to remove the majority of inorganic chlorides and avoid their hydrolysis during crude oil distillation. However, although such device can obtain a desalted crude oil with low salt content, obvious corrosion still occurred in overhead condenser and/or tower of atmospheric and vacuum distillation unit. 4,5 Thus, an assumption that OOCs can be hydrolyzed to generate the corrosive HCl was proposed in our previous paper.6 The identification of OOCs in crude oil can not only help us analyze their origin, transfer, and conversion, but also is beneficial for us to take measures to mitigate or eliminate the hazards caused. However, the identification of OOCs has been rarely investigated due to the complexity of crude oil. Up to now, the identification of OOCs in crude oil has mainly depended on analysis to light distillates.6–12 Fan et al.6 detected chloroform, carbon tetrachloride, 1,2-dichlorobenzene, and 1,1,2,2-tetrachloroethane from the naphtha of Liaohe crude oil. Shi et al.7 identified chloroform, carbon
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tetrachloride, methylene chloride, 2-chloropropene, and 1,2-dichloropropane from four kinds of Chinese naphtha. In addition to these chlorinated hydrocarbons, the presence of chlorofluorocarbons, hydroxyl chloroalkanes, and chloroanilines has also been reported.13,14 These OOCs are accidentally induced by using the chlorine-containing chemicals in crude oil exploitation, transportation, storage, and processing, whereas other types also occur naturally in crude oil. OOCs are a hidden danger for some processing units, such as atmospheric and vacuum distillation, reforming prehydrogenation, diesel hydrofining, and catalytic cracking, but the conversion behavior was rarely described in detail.3,15–18 Numerous references and patents have been dedicated for removing OOCs in the hydrocarbon phase.19–26 To date, however, the methods for directly removing OOCs from crude oil remain insufficient. In the present study, in order to solve the corrosion problem occurring in oil refineries, this work aims to study on the origin of corrosive HCl by thermodynamic analysis. The identification of OOCs was first conducted and the thermodynamic analysis of OOC hydrolysis was performed under the conditions of industrial distillation of desalted crude oil. The results will be helpful for analyzing the conversion behavior of OOCs and the formation mechanism of HCl in atmospheric and vacuum distillation of crude oil.
2. Experimental Section 2.1. Brief Introduction of Desalted Crude Oil The sample of desalted crude oil was obtained from Sinopec Beijing Yanshan Co. The crude oil was mainly processed into fuel and lubricating oils. The properties, including water content, density, metal content, and chlorine concentration, of the desalted crude oil were determined according to related standards (Table 1). Table 1 2.2. True Boiling Point (TBP) Distillation for Desalted Crude Oil The flow chart of the TBP distillation is presented in Figure S-1 (Supporting Information). A gasoline fraction of 42.4°C to 180 °C and an aviation kerosene fraction of 180 °C to 230 °C were extracted by atmospheric distillation. Other distillates were extracted by vacuum distillation. Among, a light diesel fraction of 230 °C to 300 °C and a heavy diesel fraction of 300 °C to 350 °C were extracted under 1330 Pa pressure, a lubricating oil fraction of 350 °C to 500 °C was extracted under 133 Pa pressure. Meanwhile, The residual oil (>500 °C) was also obtained. 2.3. Chlorine Concentration Determination The inorganic chlorine concentration in the desalted crude oil and its distillates was determined employing a RPP-200C salt content determinator according to SY/T 0536-94. Meanwhile, the total chlorine concentration in the desalted crude oil and its distillates were measured employing a KY-200 microcoulomb titrameter in accordance with GB/T 18612-2001. The difference between the total chlorine concentration value and the inorganic chlorine concentration value was deemed the organochlorine concentration. 2.4. Qualitative and Quantitative OOCs Identification The OOCs in three kinds of light fractions were identified via an agilent 7890A gas chromatography
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(GC) with electron capture detection (ECD) according to the analytical conditions in reference 12. If the GC–ECD spectra of the authentic standard with specified concentration and the distillate sample were obtained under the same GC conditions, then the concentration of OOC can be calculated using Equation (1) as follows:
ci = cs ×
Ai As
(1)
where ci is the OOC concentration in authentic standard, mg/L; cs is the concentration of the specified OOC in light fraction, mg/L; As is the peak area of the OOC in the authentic standard spectrum, Hz·s; and Ai is the peak area of the specified OOC in the light fraction spectrum, Hz·s. We adopted authentic standards with information on purity grade, boiling point, and supplier (Table 2) to identify the OOCs in the distillates. Table 2 2.5. Thermodynamic Analysis of OOC Hydrolysis during Industrial Distillation of Desalted Crude Oil
Low boiling point OOCs in desalted crude oil are in gaseous states under industrial distillation. In such conditions, OOCs, such as carbon tetrachloride, tetrachloroethylene, 1,1,1,3-tetrachloropropane, and 1,2,4-trichlorobenzene, may hydrolyze in the following way. CCl4(g)+2H2O CCl2CCl(g)+4H2O(g)
CO2(g)+4HCl(g)
(R-1)
HCOOH(g)+CO2(g)+4HCl(g)+H2(g)
CCl3CH2CH2Cl(g)+3H2O(g) Cl
(R-2)
CH2OHCH2COOH(g)+ 4HCl(g)
(R-3)
Cl
Cl （ g） + H2O（ g）
Cl
OH （ g） +HCl（ g）
(R-4)
Cl
If the nonvolume work for a process is zero, under any given constant pressure and temperature in a system, determining whether a chemical reaction can occur spontaneously in the system is based on the Gibbs function criterion ∆G < 0. ∆G = ∆Gro + RT ∑ν i ln
pi po
(2)
where ∆Gro is standard change in Gibbs free energy of reaction, kJ/mol; T is the temperature, K; R is the o ideal gas constant, 8.314 J/mol·K; vi is the stoichiometric coefficient of hydrolysis reaction; p is the
standard pressure,100kPa; pi is the partial pressure of species i, kPa. When estimating ∆G using Equation (2) for R-1 to R-4, ∆Gro may be found from a thermodynamics handbook, otherwise, the group contribution method can be employed to estimate it. RT ∑ν i ln
27–31
This term,
pi , can be calculated based on industrial conditions of crude oil distillation and the results of po
quantitative OOCs analysis in the light fractions via GC–ECD.
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3. Results and Discussions 3.1. Properties of the Desalted Crude Oil Table 1 indicates that the desalted crude oil was cataloged as medium crude oil with density of 875.4 kg/m3. The water content was limited and corresponded with processing condition of less than 0.3%. The salt content was 2.406 mg/L, which meet to oil refinery industry standard (500
37.96
98.97
919.8
residual oil
loss
—
1.03
—
—
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Table 4. Distribution of Element Chlorine in the Distillates
sample no.
total chlorine
concentration of
concentration,
inorganic chlorine,
mg/L
mg/L
yield of fraction, v%
concentration of
percentage of
organochlorine, mg/L
organochlorine, wt%
1#
10.19
18.959
0.000
18.959
100.00
2#
5.87
7.633
0.130
7.503
98.30
3#
10.15
6.592
0.120
6.472
98.18
4#
9.05
3.158
0.150
3.008
95.25
5#
27.76
2.365
0.180
2.185
92.39
6#
35.64
14.029
3.490
10.039
71.56
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Table 5. Concentrations, Retention Times, and Peak Areas of the OOC Authentic Standards authentic standards
concentration, mg/L
retention time, min
peak area, Hz·s
carbon tetrachloride
7.311
6.091
621618
tetrachloroethylene
3.387
13.240
195160
1,1,1,3-tetrachloropropane
0.980
18.666
26887
1,2,4-trichlorobenzene
1.190
30.092
24218
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Table 6. Information on the OOCs in Gasoline Fraction of Desalted Crude Oil peak
retention time,
peak area,
OOC concentration,
organochlorine
Hz·s
mg/L
content, mg/L
component no.
min
1
6.090
carbon tetrachloride
480459
5.651
5.210
2
13.246
tetrachloroethylene
482244
8.369
7.159
3
18.673
1,1,1,3-tetrachloropropane
46980
1.712
1.336
4
30.089
1,2,4-trichlorobenzene
93765
4.607
2.703
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Table 7. Information on the OOCs in Aviation Kerosene Fraction of Desalted Crude Oil peak
retention time, component
no.
OOC concentration,
organochlorine
mg/L
content, mg/L
peak area, Hz·s
min
1
6.097
carbon tetrachloride
266247
3.131
2.887
2
13.237
tetrachloroethylene
217337
3.772
3.227
3
18.662
1,1,1,3-tetrachloropropane
19489
0.710
0.554
4
30.095
1,2,4-trichlorobenzene
8651
0.425
0.249
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Table 8. Information on the OOCs in Light Diesel Fraction of Desalted Crude Oil peak
retention time,
peak area,
OOC concentration,
organochlorine
Hz·s
mg/L
content, mg/L
component no.
min
1
6.094
carbon tetrachloride
91582
1.077
0.993
2
13.245
tetrachloroethylene
148938
2.585
2.211
3
18.660
1,1,1,3-tetrachloropropane
29651
1.081
0.843
4
30.093
1,2,4-trichlorobenzene
68490
3.364
1.974
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Table 9. Ratios of the Partial Pressure Values of Each Gaseous Component to the System Pressure in the OOC Hydrolysis during Crude Oil Distillation component
pi/pt
component
pi/pt
carbon tetrachloride
2 × 10−6
formic acid
4 × 10−7
tetrachloroethylene
2 × 10−6
hydrogen
4 × 10−7
1,1,1,3-tetrachloropropane
1 × 10−6
3-hydracrylic acid
2 × 10−7
1,2,4- trichlorobenzene
1 × 10−6
2,5-dichlorophenol
2 × 10−7
water vapor
5 × 10−2
hydrogen chloride
1 × 10−4
carbon dioxide
1 × 10−4
—
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60000
13.240
Hz
Hz 6.091
48000
50000
40000
40000
32000
30000
24000
20000
16000
10000
8000
0
0
0
10
20
30
min
0
10
(a)
20
30
min
(b)
7500
30.092
Hz
Hz
18.666
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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4000
6000
3200
4500
2400
3000
1600
1500
800
0
0 0
10
20
30
min
0
10
(c)
Figure
1.
GC–ECD
20
30
min
(d)
spectra
of
authentic
standards:
(a)
carbon
(c)1,1,1,3-tetrachloropropane, and (d) 1,2,4-trichlorobenzene
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tetrachloride,
(b)
tetrachloroethylene,
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Hz
13.246
6.090
120000
90000
30.089
60000 18.673
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
30000
0 0
10
20
30
min
Figure 2. GC–ECD spectra of gasoline fraction.
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Hz 6.097
75000
13.237
60000 45000 30000 15000
30.095
18.662
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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0 0
10
20
30
min
Figure 3. GC–ECD spectra of aviation kerosene fraction.
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Hz 40000 32000
30.093
6.094
24000 16000
18.660
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
13.245
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8000 0 0
10
20
30
min
Figure 4. GC–ECD spectra of light diesel fraction.
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-350
-400 400K
400K
-450
-400
-500
600K
-550
700K
-600
800K
Δ G, kJ/mol
Δ G, kJ/mol
-500
500K
-450
500K
-550 600K
-600 700K
-650 -700
800K
-750 -800
-650 0
2
4
6
8
10 12
0
100 150 200 250 300 350
2
4
6
8
10 12
100 150 200 250 300 350
Pt , kPa
Pt , kPa
(a)
(b)
-200
-20 400K
-225
-25
400K
-250
-30
500K
500K
Δ G, kJ/mol
Δ G, kJ/mol
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
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-275 600K
-300 -325
700K
-35 600K
-40 700K
-45 -50
-350
800K
800K
-55
-375
-60
-400 0
2
4
6
8
10 12
100 150 200 250 300 350
0
2
4
6
8
Pt , kPa
10 12
100 150 200 250 300 350
Pt , kPa
(c)
(d)
Figure 5. Effects of temperature and pressure on ∆G for (a) R-1, (b) R-2, (c) R-3, and (d) R-4.
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