Organochlorine Compounds with Low Boiling Point in Desalted Crude

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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


480459

5.651

5.210

2

13.246

tetrachloroethylene

482244

8.369

7.159

3

18.673


46980

1.712

1.336

4

30.089


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


266247

3.131

2.887

2

13.237

tetrachloroethylene

217337

3.772

3.227

3

18.662


19489

0.710

0.554

4

30.095


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


91582

1.077

0.993

2

13.245

tetrachloroethylene

148938

2.585

2.211

3

18.660


29651

1.081

0.843

4

30.093


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


2 × 10−6

formic acid

4 × 10−7

tetrachloroethylene

2 × 10−6

hydrogen

4 × 10−7


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


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.


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

Energy & Fuels

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.


Organochlorine Compounds with Low Boiling Point in Desalted Crude

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