Reactivation of Spent FCC Catalyst for the Removal of Heavy Metals from Refinery based Stimulated Waste Water

ABSTRACT

The reactivation of spent FCC catalyst for its application in the adsorption of heavy metals from wastewater was investigated in this research. The most effective reactivation route of spent FCC catalyst was the oxidation of the spent FCC catalyst using hydrogen peroxide at an oxidant-to-catalyst ratio of 16 ml/g, contact time of 60 minutes and a temperature of 90oC, followed by treatment with acetic acid solution at an acid-to-catalyst ratio of 20 ml/g, 75 minutes contact time and at a temperature of 50oC. The reactivation process was monitored using the Scanning Electron Microscope Energy Dispersive X-ray (SEM-EDX), X-ray fluorescence (XRF) and X-ray diffraction (XRD). The result showed significant decreases in impurities of coke and metal, and the crystallinity of the treated spent FCC catalyst was much greater than that of the spent FCC catalyst. For the adsorption study, optimum conditions for removal of Pb2+, Zn2+and Cr2+ from refinery-based simulated wastewater by the reactivated spent FCC catalyst were investigated in this study with the help of response surface methodology (RSM). Temperature, adsorbent dose, contact time and pH were the process parameters considered. The results showed that a quadratic model best represented the relationship between the process parameters and the heavy metals removal efficiency. Based on F values, temperature was found to have highest impact on the adsorption efficiency of the reactivated FCC catalyst for each of the heavy metals, while pH had the lowest impact. Maximum removal efficiency of Pb2+, Zn2+and Cr2+was found to be 100%, 100% and 94.75% respectively, and this corresponded to removal efficiencies at temperature of 117oC, adsorbent dose of 1.75 g, contact time of 75 minutes and pH of 7. It was established that this method of spent FCC catalyst reactivation improves the adsorptive capacity of the catalyst and possibly its catalytic activity.

 

 

TABLE OF CONTENTS

DECLARATION.. i

CERTIFICATION.. ii

ACKNOWLEDGMENT. Error! Bookmark not defined.

ABSTRACT. iv

TABLE OF CONTENTS. v

LIST OF FIGURES. x

LIST OF TABLES. xii

ABBREVIATIONS. xiii

1.0 INTRODUCTION.. 1

1.1 PROBLEM STATEMENT. 3

1.2 AIM AND OBJECTIVES. 3

1.3 JUSTIFICATION.. 3

1.4 SCOPE.. 4

2.0 LITERATURE REVIEW... 5

2.1 CATALYTIC CRACKING OPERATION.. 5

2.2 FCC CATALYST. 6

2.2.1 Zeolite. 6

2.2.2 Matrix. 7

2.2.3 Binder. 7

2.2.4 Filler. 7

2.3 MECHANISM OF CATALYSIS DURING CRACKING REACTIONS. 7

2.4 DEACTIVATION OF FCC CATALYST. 8

2.4.1 Deactivation by Coke. 9

2.4.2 Hydrothermal Dealumination. 11

2.5 SPENT FCC.. 11

2.5.1 Properties of Spent FCC.. 12

2.5.1.1 Silica/alumina (Si/Al) ratio. 12

2.5.1.2 Carbon content12

2.5.1.3 Sodium content13

2.5.1.4 Surface area. 13

2.5.1.5 Pore volume. 13

2.5.1.6 Particle size distribution. 13

2.5.2 Adsorption Potential13

2.5.2.1 Metal adsorption. 14

2.5.2.2 Adsorption of organics. 14

2.6 HEAVY METALS SEPARATION TECHNIQUES. 14

2.6.1 Hydroxide Precipitation. 15

2.6.2 Sulfide Precipitation. 15

2.6.3 Chromium Reduction. 15

2.6.4 Oxidation by Hydrogen Peroxide. 16

2.6.5 Treatment of Complexed Metals Wastes. 16

2.7 SPENT FCC CATALYST POTENTIAL AS HEAVY METALS ADSORBENT. 16

2.7.1 Characteristics of Spent FCC Catalyst Responsible for Possible Metal16

2.7.1.1 Matrix. 16

2.7.1.2    Pore-filling. 16

2.7.1.3 Cation exchange in zeolites. 17

2.7.1.4 Chemical reactions. 17

2.7.2 Advantages of Using Spent FCC Catalyst as an Adsorbent for Heavy Metals Removal from Wastewater. 17

2.8 REMOVAL OF WATER CONTAMINANTS. 18

2.9 PREVIOUS WORKS. 18

2.10 FACTORS AFFECTING ADSORPTION.. 22

2.10.1 Initial Concentration. 22

2.10.2 Cation Exchange Capacity (CEC). 23

2.10.3 Hydrated Radii of Cations. 23

2.10.4 Effect of Ionic Strength. 23

2.10.5 Solution pH /Hydroxide Precipitation. 23

2.10.6 Solubility Product. 24

2.10.7      Point of Zero Charge on Adsorbents (PZC). 24

2.10.8 Adsorbent Particle Size. 25

2.10.9 Adsorbent surface area. 25

2.10.10 Silica to alumina (Si/Al) ratio. 25

2.10.11 Zeta potential26

2.10.12 Temperature. 26

3.0 MATERIALS AND METHOD.. 27

3.1 MATERIALS. 27

3.1.2 Equipment27

3.1.2 Reagents. 28

The reagents used in this study are presented in Table 3.2.28

3.2 METHODS. 28

3.2.1 Spent FCC Catalyst Reactivation. 28

3.2.2 Simulation of Wastewater. 30

3.2.3 Batch Study of the Adsorption of Heavy Metals by reactivated spent FCC catalyst. ………………………………………………………………………………………………………………………………..30

CHAPTER FOUR.. 32

4.0 RESULTS AND DISCUSSION.. 32

4.1 CATALYST REACTIVATION.. 32

4.1.1 Oxidation (Coke Removal). 32

4.1.2 Acid Treatment. 37

4.2 ADSORPTION STUDY.. 42

4.2.1. Optimization Analysis. 43

4.3 ADSORPTION ISOTHERMS. 58

CHAPTER FIVE.. 60

5.0      CONCLUSIONS AND RECOMMENDATION.. 60

REFERENCES. 62

APPENDICES. 70