Ramadan, Hasanat Hohammed.... spent caustic soda, thesis.pdf

QATAR UNIVERSITY Graduate Studies College of Engineering

CHARACHTERIZATION CHARACHTERIZA TION AND TREATMENT OF SPENT CAUSTIC FROM AN ETHYLENE PLANT

A Thesis in Environmental Engineering By Hasanat Mohammed Ramadan

© 2013 Hasanat Mohammed Ramadan Submitted in Partial Fulfillment Of the Requirements For the Degree of Master of Science in Environmental Engineering December 2013

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The thesis of Hasanat Mohammed Ramadan  was reviewed and approved by the following: We, the committee members listed below accept and approve the Thesis of the student named above. To the best of this committee’s knowledge, the Thesis conforms the requirements of Qatar University, and we endorse this Thesis for examination.  Name _____________________ ________________________________ _____________________ __________ Signature _______________________ __________________________________ ________________ _____ Date__________  Name _____________________ ________________________________ _____________________ __________ Signature _______________________ __________________________________ ________________ _____ Date__________  Name _____________________ ________________________________ _____________________ __________ Signature _______________________ __________________________________ ________________ _____ Date__________ 

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ABSTRACT

Spent caustic solution is generated in oil refineries and petrochemical  plants as a result of scrubbing processes where hydrogen sulfide and carbon dioxide compounds are removed. Spent caustic is considered as one of the most difficult streams to handle by wastewater treatment plants. Selecting the best treatment technique is considered to be a critical task, in order to meet the discharge limit. The present work aims to find an effective treatment process to treat spent caustic

solution

produced

from

an

ethylene

plant.

Neutralization

and

neutralization coupled with oxidation are the two processes studied. Two methods of oxidation are tested, classical oxidation by using H2O2  alone and advanced oxidation by using Fenton’s reagent.

Applying neutralization alone or

neutralization with oxidation was verified for the achievement of the required degree of treatment. For the neutralization alone, it was found that the highest chemical oxygen demand removal achieved was 88 % (1699 mg/l) at pH=1 while the sulfide removal was 99.8 % ( 9.9 mg/l). For classical oxidation using H 2O2, the best removal was achieved at pH=2.5. The COD % removal was 89 % with a COD value of 1630 mg/l. Furthermore, the sulfide removal reached a value of almost 100%. While for the advanced chemical oxidation using Fenton’s process, the best result was obtained at pH=2.5. The COD % removal was 96 % with a COD value of 542 mg/l. This was achieved with hydrogen peroxide to ferrous sulfate ratio of 1: 7.5. The sulfide removal also als o reached a value of almost 100%.

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TABLE OF CONTENTS  Abstract ……………………………………..……………………...……… III  List of Figures ………….….………………..……………………...……… VII  List of Tables ……………………………….……………………...………

VIII

 Abbreviation ………………………………..……………………...………

IX

 Acknowledgment …………………………………………..………………

X

CHAPTER 1:

1.

Introduction ………………...…………………………………………

1

1.1.

Spent Caustic ………………………………………………...…

1

1.2.

Sources of Spent Caustic Solution from the Ethylene Plant…….

4

1.2.1. Hot section ………………...…………………………………

8

1.2.1.1.

Steam Cracker..…… ………….………………………

8

1.2.1.2.

Quenched Tower ..…………………………………….

9

1.2.2. Compression Section ………………………………………... 1.2.2.1.

10

Gas Compressors …….……………………………….

10

1.2.3. Cold Section.……………………..….…………………….....

10

1.2.4. Treating (Caustic Tower) …………………………………

10

1.2.5. Fractionation Section ……………………………………..

11

Spent Caustic Management Background………………………..

14

1.3.1. Reduction ……………………………………………………

14

1.3.2. Reuse within the Process …………………………………….

15

1.3.3. Recycle Outside the Facility ………………………………...

15

1.3.4. Treatment and Disposal ……………………………………...

15

1.3.

1.4.

Spent Caustic Treatment ……………………………………….

16

1.4.1. Biological Treatment of Spent Caustic ……………………...

17

1.4.2. Thermal Treatment …………………………………………..

18

1.4.3. Chemical Treatment………………………………………….

20

1.5.

Classification of the Chemical Oxidation Processes …………...

22

1.5.1. Classical Chemical Oxidation ……………………………….

22

IV

1.5.2. Advanced Oxidation Processes (AOPs) …………………….. 1.6.

Objectives of Present Study …………………………………...

25 35

CHAPTER 2 :

2.

Research Methodology………………………………………………. 2.1.

37

Spent Caustic Characteristics …………………………………... 37

2.1.1. Total Suspended Solids and Total Dissolved Diss olved Solids…………

37

2.1.2. Measurements of Chemical Oxygen Demand (COD)………..

38

2.2.3. Biological Oxygen Demand (BOD) ……...………………….

39

2.2.4. Total Sulfide S −2 , H2S, HS −   by Titration (sulfide above 1

39

mg/l) ………………………………………...……………… 2.2.5. Determination of Total Sulfide S −2, H2S, HS − (sulfide 0 to

40

800 μg/l)…………………………………………………….. 2.2.6. Free Soda and Complete Alkalinity……….…………………

40

2.2.7. Total Petroleum Hydrocarbons (TPH)……………………….

41

2.2.8. Inorganic anions ……………………………………………..

42

2.2.9. Heavy Metals ……………………………..…………………

43

2.2.10. Phenol ………………………………………………….…….

43

2.3. Experimental Setup and Procedure ……………………………….

46

2.3.1.  Neutralization ………………………………………………..

46

2.3.2.  Neutralization Coupled with Oxidation ……………………..

48

CHAPTER 3 :

3.

Results and Discussion..………………………………….…………..

49

3.1. Neutralization  Neutralization ………...………………………………...…………... 49 3.1.1. Effect of pH on Sulfide Removal…………………………….

49

3.1.2. Effect of Temperature on Sulfide Removal ……….………...

52

3.1.3. Effect of pH on COD Removal……..…………………….…

53

3.1.4. Effect of pH on TDS Removal …………………….…….…

55

3.2. Neutralization  Neutralization Coupled with Oxidation: Classical Oxidation ...……

55

3.2.1. Effect of Hydrogen Peroxide Concentrations on COD Removal ……………………………………………………..

56

3.2.2. Effect of Hydrogen Peroxide Concentrations at Different pH

V

on COD Removal ……………………………………………

59

3.3. Neutralization  Neutralization coupled with Oxidation: Advance oxidation …...….. …...…..

63

3.3.1. Effect of pH in Fenton’s Reagent on the Removal of COD.…

63

3.3.2. Effect of Ferrous Sulfate Concentrations on COD Removal...

68

3.3.3. Effect of Hydrogen Peroxide to Ferrous Sulfate Ratio on COD Removal………………………………………………..

70

3.3.4. Effect of Hydrogen peroxide to COD ratio on COD Removal……………………………………………………...

73

CHAPTER 4:

4. Conclusions and Recommendations …..…………………….…...…

76

CHAPTER 5:

5. Future Work ……………………………………...………………....

79

References ……………………………………………………………… 80

VI

LISTS OF FIGURES

Figure 1 : Ethylene Eth ylene process flow diagram (PFD) .............................................. .................................................... ...... 7 Figure 2 : Steam cracker diagram ................................. ....................................................... ........................................... ..................... 9 Figure 3 : Quenched tower ............................................ .................................................................. ........................................... ..................... 9 Figure 4 : Gas compressors ........................................... ................................................................. ......................................... ................... 10 Figure 5 : Treating unit ................................................. ....................................................................... ......................................... ................... 11 Figure 6 : Fractionation unit ......................................... ............................................................... ......................................... ................... 13 Figure 7: Waste management hierarchy .......................................... ................................................................ ...................... 14 Figure 8 : Treatment Treat ment technologies according to COD contents. ............................ ............................ 17 Figure 9 : Oxidation potential .................................... .......................................................... ............................................ ...................... 21 Figure 10: Summarized of the treatment processes of ethylene spent caustic ....... 36 Figure 11 : Experimental schematic diagram ................................................ ........................................................ ........ 46 Figure 12 : Hydrogen sulfide sulfi de and pH dependent .................................... ................................................... ............... 50 Figure 13: Neutralization of spent caustic ............................................. ............................................................ ............... 51 Figure 14 : Sulfide Sulfi de % removal re moval at different differ ent pH after neutralization ....................... ....................... 52 Figure 15 : Sulfide % removal at different temperature ........................................ ........................................ 53 Figure 16: COD removal % for pH=1,3,5 before neutralization ........................... ........................... 54 Figure 17: COD removal % at different pH after neutralization ........................... ........................... 54 Figure 18: Effect of pH on TDS removal .......................................................... .............................................................. .... 55 Figure 19: Blank sample with a) 0.1 H 2O2 and b) 1 ml of H 2O2 ........................... ........................... 58 Figure 20 : COD removal % at different H 2O2 concentration ............................... 61 Figure 21 : Sulfide % removal at different H 2O2 concentration ............................ ............................ 62 Figure 22 : Effect of pH on the COD removal......................... removal............................................... .............................. ........ 67 Figure 23 : Effect Ef fect of ferrous sulfate concentration on COD % removal ............... 69 Figure 24 : Effect of hydrogen peroxide to ferrous sulfate ratio on % COD removal ............................................ .................................................................. ............................................ ............................................ .......................... .... 72 Figure 25 : Effect Ef fect of hydrogen h ydrogen peroxide to COD ratio r atio on % COD removal ......... 75

VII

LISTS OF TABLES

Table 1: Spent caustic types and characteristics ......................................................4 Table 2 : Physical properties of ethylene .................................................................5 Table 3: WAO operational conditions ..................................................................19 Table 4: Classical chemical oxidation ................................................................... 22 Table 4: Classical chemical oxidation ................................................................... 23 Table 4: Cont Classical chemical oxidation........................................................... 24 Table 4: Cont Classical chemical oxidation........................................................... 25 Table 5: Advanced chemical oxidation..................................................................28 Table 5: Cont Advanced chemical oxidation ......................................................... 29 Table 5: Cont Advanced chemical oxidation ......................................................... 30 Table 5: Cont Advanced chemical oxidation ......................................................... 31 Table 6 : Spent caustic characteristics used in this experiment ............................. 45 Table 7 : Effect of hydrogen peroxide concentrations on COD removal ..............56 Table 8 : Analyses interfere with H 2O2..................................................................58 Table 9: Effect of H 2O2 at different pH on COD removal ..................................... 59 Table 12: Effect of hydrogen peroxide to ferrous sulfate ratio on COD % removal .................................................................................................................. 71 Table 11: Effect of hydrogen peroxide to COD ratio on % COD removal ........... 74

VIII

ABBREVIATIONS

NaOH

Sodium hydroxide

H2S

hydrogen sulfide

C2H4

Ethylene

C2H6

Ethane

-

-

HS  & S

Sulfide

SO4

Sulfate

-

Sulfide

S

H2O2

Hydrogen peroxide

O3

Ozone

OH•

Hydroxyle redical

HO2•

Hydroperoxyl

+2

Ferrous

Fe

+

Ferric

FeSO4 /H2O2

Fenton’s reagent

UV

Ultra violet

TiO2

Titanium peroxide

DMDS

Dimethyl disulfide

COD

Chemical oxygen demand

TOC

Total organic carbon

BOD

Biological Oxygen Demand

TDS

Total Dissolved Solids

TSS

Total Suspended Solids

TPH

Total Petroleum Hydrocarbons

WAO

Wet Air Oxidation

CWAO

catalytic wet air oxidation

AOPs

Advanced Oxidation Processes

Fe

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ACKNOWLEDGMENTS

My sincere thanks to my supervisors, Dr. Alaa Al Hawari and Professor Ibrahim abureesh, who have supported me throughout my thesis work and  provided me with advice, guidance, and continuous encouragement throughout the work on this thesis. Special thanks to Dr. Ahmed Al Khatat , senior lab technician of chemical engineering department, who provided us with his time and knowledge in the lab measurements. For his sincere help I’m deeply grateful. Also I wish to express my special thanks to Qatar Pertrochemical Company (QAPCO) namely Dr. Mabrouk and Mr. Mejali Al Kuwari, who helped me throughout the period of this research and for the s upply of waste samples. My gratitude is for my loving parents, my husband, and my family for keeping me motivated during this period of research work. At the end, my regards to all people who supported me directly or indirectly during my graduates studies at Qatar University.

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CHAPTER 1: 1. INTRODUCTION : 1.1.

Spent Caustic : Qatar developed and built a strong industrial sector by employing the

latest technological innovations in their production processes [1]. This eventually will create a positive and highly beneficial impact on the national economy. Qatar depends on two main sources of water to meet its need which are conventional water sources that come from groundwater and non-conventional water sources that come from desalination of seawater and recycling of treated wastewater [1]. Qatar is working to achieve a “zero liquid discharge” by 2016. The aim of this  project is not to allow any discharge of treated wast ewater into water bodies but to reuse and recycle the produced water. The project is directed by the Ministry of Energy and Industry with the Ministry of Environment involving various industries in Qatar [2]. The zero discharge can be mainly achieved by enhancing the quality of treated waste water where it could be recycled and reused in irrigation or in operations and production processes. In Qatar several industrial companies such as Qatar Chemical Company (Q-Chem), Qatar Petrochemical Company (QAPCO) and Qatar Petroleum (QP) generate liquid waste that is known as spent caustic solution. Spent caustic is an industrial waste solution that consists of sodium hydroxide, water, and other  pollutants.

1

Sodium hydroxide (NaOH) solutions are used in many industries to wash out acid gases such as hydrogen sulfide (H 2S) and carbon dioxide (CO 2) from different hydrocarbon streams [3]. Once these gases react with the majority of  NaOH, a waste solution known as spent caustic will be produced [4]. Spent caustics are the most difficult class of liquid industrial waste to handle and to dispose due to the high concentration of pollutants in it [5]. According to the Environmental Protection Agency EPA under the Resource Conservation and Recovery Act RCRA used to classify the wastes as hazardous that create potential harmful impact to the human health and to the environment [6]. The classification of waste depends on the specific characteristics of the waste itself. The waste is considered to be hazardous if it exhibits one or more of the four characteristics [6, 7]: 1) Ignitability (D001) 2) Corrosivity (D002) 3) Reactivity (D003) 4) Toxicity (D004 - D043) Spent caustic could be classified as D003 hazardous waste due to the reactive sulfide it contains [8]. Also, spent caustic is the highly corrosive due to the high  pH value. Recent environmental regulations have a great impact on the spent caustic treatment method design since previous usual disposal methods are  becoming legally prohibited [8]. Without treatment, spent caustic stream may cause environmental  problems because of their alkalinity (pH>12), salinity (sodium of 5-12% wt) and high sulfide S-2 levels exceeding 2-3 wt% [9-11]. However, sulfide can be

2

converted to elemental sulfur and/or sulfate that are preferred finishing product as it does not represent COD and maybe allowed to be discharged into the environment [14]. Moreover, spent caustics may contain toxic organo-sulfur compounds such as methanethiol and aromatic hydrocarbons like benzene [12, 13]. Spent caustics can be classified into many types depend upon the industry  producing it and the source of fuel that fresh caustic wash. Table 1 summarizes the type of spent caustic and there characteristics. Usually refineries don’t separate each type of spent caustic and they mix the three types and this is called the mixed refinery spent caustic [9].

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Table 1: Spent caustic types and characteristics

Type of

Sulfidic

Cresylic

Naphthenic

Ref

Source

Ethylene & LPG

Gasoline

Kerosene & Diesel

[5]

Content

High Conc. of Sulfides & Mercaptans

High Conc. of Phenols & Cresols

High Conc. Of Polycyclic aliphatic organic compounds

[5]

Effect after neutralization

Release gases

Foaming and settling issue in the biological

Oil layer & foaming

[5]

Chemical oxygen demand (COD) (ppm)

5,000-90,000

50,000-100,000

150,000-240,000 [15]

Total organic carbon (TOC) (ppm)

20-3,000

10,000-24,000

24,000-60,000

[15]

Sulfides (ppm)

2,000-52,000