Preparation of Extended Abstract for NS2008

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© Science and Research Pioneers Institute (www.srpioneers.org) 2nd International Conference on Chemistry, Chemical Engineering and, Chemical Process, (ICCC2014) 9 -11 July 2014, Istanbul, Turkey

Treatment of petroleum refinery wastewater containing phenolic compounds by electron beam irradiation

Naser Dalali, Masoud Kazeraninejad* Phase separation & FIA-Lab., Department of Chemistry Faculty of Science, University of Zanjan Zanjan, Iran * m_ [email protected]

Abstract— The degradation of phenolic compounds from aqueous solutions and petroleum refinery wastewater by electron beam irradiation have been studied. The removal of phenol was investigated in terms of various parameters in batch mode namely: pH, initial phenol concentration, absorbed dose, effect of salt, effect of functional groups. The measurement percentage removal of phenolic compounds was done by UV-Vis spectrophotometry with 4-aminoantipyrine method. Experiments were conducted at phenol concentration 10-100 mg/L over the pH range 3-11 and addition of 0.5-20% (w/v) NaCl. Absorbed dose ranged 1-10 kGy. The chemical oxygen demand (COD) and determination of phenol concentration was also measured in petroleum refinery waste water. The optimum conditions for phenolic compound removal were achieved at pH=4, dose=6 kGy, initial phenol concentration=20 mg/L and concentration of NaCl=10% (w/v). Keywords- Electron beam irradiation; Phenolic compounds; petroleum refinery wastewater

I.

INTRODUCTION

Treatment of industrial wastewaters is a problem of major concern nowadays. Phenol and substituted phenols are important industrial chemicals of environmental concern since they are involved in many industries such as coking, synthetic rubber, oil refineries, petrochemical, pharmaceuticals, pesticides, dyes, plastics, paper and manufacture of resin, and can also occur in their wastewaters[1]. Phenol compounds are some of the major hazardous compounds in industrial wastewater due to their

Azam Akhavan Radiation Applications Research School Research Institute of Nuclear Science and Technology Tehran, Iran

poor biodegradability, high toxicity and ecological aspects [2]. Wastewaters containing phenols and other toxic compounds need careful treatment before discharge into the receiving bodies of water. There are different methods for the separation of phenols such as steam distillation [3], separation by extraction [4], separation by adsorption [5], separation by membrane [6], destruction of Phenol by wet-air oxidation [7], electrochemical oxidation [8], biochemical abatement [9], polymerization [10]. Such problems as low efficiency and generation of toxic byproducts are associated with the above methods [11]. Advanced oxidation processes (AOP), such as electron beam (EB) irradiation, is a promising technology for the removal of toxic organic compounds from the industrial effluents [12]. The electron beam technology is used to destroy organic compounds in liquid wastes. This technology irradiates water (H2O) with a beam of highenergy electrons, causing the formation of three primary transient reactive species: aqueous electrons (e-aq), hydrogen radicals (H·), and hydroxyl radicals (OH·). Because both strong reducing species (e-aq and H·) and strong oxidizing species (OH·) are formed in approximately equal concentrations, multiple mechanisms or chemical pathways for organic compound destruction are provided by the technology. This paper presents the destruction of phenol compounds in aqueous solution and petroleum refinery wastewater using electron beam irradiation process and measurement percentage removal of these compounds by 4-aminoantipyrine method [13].

II.

EXPERIMENTAL

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A. Materials A stock solution of each phenolic compound was prepared by using an analytical grade of chemicals and dissolving them in distilled water. Experimental solutions of the desired concentrations were obtained by successive dilution with distilled water. A 1% solution of potassium ferricyanide was prepared by dissolving 1g of potassium ferricyanide in 100 mL of distilled water. A 1% solution of 4-aminoantipyrine was prepared by dissolving 1g of 4-aminoantipyrine in 100 mL of distilled water. Petroleum refinery wastewater was obtained from refineries in centre and south of Iran. B.

Equipments Electron beam irradiation was done with a Rhodotron TT200 accelerator (Belgium). The pH of the solution was adjusted by means of HCl and /or NaOH solution. A digitally calibrated pH - meter Metrohm, model 827 (Switzerland) and a conductivity - meter WTW, model LF 90 (Germany) were used to measure the pH and the conductivity of waste solutions. The analytical determination of phenol and other phenolic compounds was carried out with using UV-Vis spectrophotometer Perkin lamber Lambda, model 25 (USA). Chemical Oxygen Demand (COD) of the wastewater solution before and after EB was determined by UV-Vis spectrophotometer HACH, model DR5000 (Germany). C.

Samplining Effluent samples of produced wastewater from petroleum refineries of centre and south of Iran were collected from the unite pound (B) during two consecutive visits in June and December 2013 and transported to the laboratory and processed on the same day. Most of the samples were collected again in a second visit to check the consistency of parameters measured and to verify the stability of the treatment process. Procedure The samples were irradiated with 10 MeV electron beam accelerator. The Irradiation was performed in a batch system using plexi-glass vessels (5 cm diameter and 1 cm height) and dose range varied from 1-10 kGy. After irradiation, to a 50 ml portion of sample sufficient concentrated ammonia was added to produce a final pH in the range 10±0.2. The solution was mixed well, 1 ml of 1% aminoantipyrine solution were added, and mixed again. Then 5 mL of the potassium ferricyanide solution were added and the solution was mixed again. The extractions with chloroform were started after 3 minutes. The extraction was carried out as a set of three succedent extractions, 5 mL. The three extracts were combined, made up about 15 mL with chloroform, and compared with a corresponding reagent blank spectrophotometrically at 460 nm. The efficiency of phenol removal, % Removal, was calculated as:

(1) Where A0 is absorbance of phenol solution before treatment and Ai is absorbance of phenol solution after treatment. III.

RESULTS AND DISCUSSION

A. Effect of pH An important parameter in the electron beam irradiation is the pH reaction. To examine the effect of pH, the sample was adjusted to the desired pH using sodium hydroxide or hydrochloric acid solutions. Fig.1 shows the effect of pH on percentage removal of phenol in various doses. The percentage removal decreased with increasing pH from 3 and 5 to 11. The data show that the percentage removal of phenol at pH values 3 and 5 in doses 6 and 10 kGy is >99% and it was observed that the degradation efficiency decreases with increasing pH. So the highest removal efficiency with lower dose occurs in acidic pH. Two possibilities could account for the increased phenol removal with decreasing pH. First, the relative scavenging of the OH· at alkaline pH was greater than at either of lower pH values. Second, it is possible that differences in the reaction rate of the phenol/phenoxide ion (pKa=10) [14] with the relative species (OH·, e-aq and H·) could lead to differences in removal efficiency at different pHs. Therefore, pH of 4 was chosen as the optimum pH for removal of phenol. B. Effect of Initial Phenol Concentration The percentage removal of phenol at each dose and concentration combination is shown in Fig. 2. The greatest percentage removal was observed at the lowest initial solute concentration (10 mg/L) in the same dose. The EB technology generates strong reducing species (e-aq and H·) and strong oxidizing species (OH·) simultaneously and in

D.

Fig. 1. Effect of pH on the percentage removal of phenol (Co=20 mg/L).

approximately equal concentrations. However number of this species was insufficient for degradation at higher phenol concentrations. The results indicate that until 20 mg/L concentration of phenol, we had a high efficiency of 99% at doses of 6 and 10 kGy. Hence 20 mg/L

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Fig. 2. Effect of analyte initial concentration on the percentage removal of phenol (pH=4).

concentration of phenol was chosen for the following experiments. C. Effect of Sodium chloride Concentration As regards some petroleum wastewater have high salinity, so salt effect was investigated on performance electron beam irradiation. We added 0.5% to 20% (w/v) of sodium chloride to phenol solutions. Knipping et al [15] offered that halide ions might act as scavengers that attract reactive species such as hydroxyl radicals in aqueous phase. This mechanism is based on the formation of a OH…Clˉ complex. The structure of the bound complex between OH˙ and Clˉ is likely to involve interaction between the hydrogen of the OH˙ and the chloride ion. This theory corresponded with our results that shown in Fig.3. In low dose the percentage removal of phenol was down but in high dose probably, due to hydroxyl radical production increases, salt concentration was ineffective. In following was used 10% (w/v) of sodium chloride as the optimum value. D. Effect of Functional groups of Different Phenolic compounds Physico-chemical properties of the different phenolic compounds influence its interaction within the EB irradiation and eventual removal mechanism.

Fig. 3. Effect of NaCl concentration on the percentage removal of phenol (Co=20 mg/L, pH=4)

Fig. 4. Effect of variation of side groups on the percentage removal of phenolic compounds (Co=20 mg/L, pH=4, NaCl=10% (w/v)).

Number and position of aromatic hydroxyl groups were found to have strong impact on the activity of phenolic compounds [16]. Electron donating groups, especially alkyl and hydroxyl groups were reported to increase the electron density of the phenoxyl radicals leading to enhancement of the radical scavenging [17]. Second hydroxyl group in the ortho or para positions e.g. catechol and hydroquinone showed higher scavenging activity (98 and 97% respectively). This result can be explained by the strong electron donation ability of the hydroxyl group in ortho and para positions. It is well established that electron donating groups stabilize the resulted phenoxyl radicals through inductive (as in alkyl substituent); thus lower the O-H bond dissociation energy and enhance the radical scavenging activity. The presence of one alkyl group as in o- and p-cresol raised the activity to 12.2 and 15.5% respectively compared to that of phenol (2.3%). The results indicate that alkyl groups in any position (o, m or p) stabilize the phenoxyl radicals through inductive effect and thus enhance the radical scavenging hydroxyl radical [18]. Fig 4 shows that this mechanism is consistent with our results. E.

Treatment of Petroleum Refinery Wastewater Petroleum refineries are the main sources of phenolic wastewaters. A real oil refinery wastewater was collected from the effluent of centre (sample 1) and south (sample 2) refinery, in Iran. The samples were filtered with filter paper and spilled in Pyrex glass vessels then irradiated in dose 1-10 kGy. Tables 1 and 2 show the physical characteristics for samples 1 and 2 applying doses 10 and 6 kGy, respectively. The results indicate that 10 kGy is need for degradation of phenolic compounds with percentage removal of 98% in sample 1 but for sample 2 only 6 kGy is sufficient with >99.5% removal percentage. Higher doses required for sample 1 is more likely due to its complex matrix. COD values are related to the total concentration of organics in the solution. Mineralization of different phenolic compounds solutions were monitored by COD measurements before and after treatment.COD measurement is one of the important parameters usually

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used in wastewater treatment. The parameter of COD has been used to monitor the general status of wastewater effluent and quality of treated water. The measurement of COD is based upon the theoretical amount of oxygen required to oxidize organic compounds to CO2 and H2O. Table 3 shows that electron irradiation is capable to reduce rate of COD in center and south refinery of Iran, 30 and 34% respectively in dose 10 kGy. Because of the low percentage of COD reduction that is phenol was not mineralized and only ring structure rupturing of phenol occurs and converte to other organic compounds [19]. Table 1. Physical Characteristics of Sample (1) Irradiated with 10 kGy Dose Characteristics Parameter

very efficient method. Experimental parameters such as pH, initial phenol concentration, absorbed dose, effect of salt and effect of functional groups were investigated for phenol removal. The optimum pH, initial phenol concentration and absorbed dose for the highest removal were 4, 20 mg/L and 6kGy, respectively. Under the optimum conditions, a degradation efficiency of more than 99% of phenol was achieved when applying dose of 6 kGy. The percentage of COD reduction in petroleum refinery waste water was about 30-34% that shows phenol was not mineralized and only ring structure rupturing of phenol occurs and converts to other organic compounds. The use of 4-aminoantipyrine method for the spectrophotometric determination of phenolic compounds is useful because of its simplicity, sensitivity and selectivity than phenol and substituted phenols.

Before treatment

After treatment

6.3

5.6

1.63

2.34

ACKNOWLEDGMENT

0.4

This work was partly supported by Yazd Radiation Processing Center (YRPC). The authors are grateful to this center especially for irradiation services.

pH Conductivity (mS/cm) Phenol content (ppm)

20

Table 2. Physical Characteristics of Sample (2) Irradiated with 10 kGy Dose Characteristics Parameter Before treatment

After treatment

7.1

6.5

1.73

4.12

15

0

pH Conductivity (mS/cm) Phenol content (ppm)

1

2

Dose(kGy)

COD (ppm)

COD reduction (%)

0

502

0

1

372

26

3

366

27

6

357

29

10

352

30

0

325

0

1

244

25

3

234

28

6

217

33

10

214

34

IV.

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Table 3. Effect of Irradiation Dose on COD Reduction in Petroleum Refinery Wastewater Parameters Sample

REFERENCES

CONCLUSIONS

The degradation of the phenol and phenolic compounds in aqueous solutions and petroleum refinery wastewater by electron beam irradiation seems to be a

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