Cellulose-based materials in wastewater treatment of petroleum industry

Journal Pre-proof Cellulose-based Materials in Wastewater Treatment of Petroleum Industry Baoliang Peng, Zhaoling Yao, Xiaocong Wang, Mitchel Crombeen, Dalton Gsweene, Kam Chiu Tam PII:

S2468-0257(19)30107-4

DOI:

https://doi.org/10.1016/j.gee.2019.09.003

Reference:

GEE 179

To appear in:

Green Energy and Environment

Received Date: 9 July 2019 Revised Date:

6 September 2019

Accepted Date: 19 September 2019

Please cite this article as: B. Peng, Z. Yao, X. Wang, M. Crombeen, D. Gsweene, K.C. Tam, Cellulosebased Materials in Wastewater Treatment of Petroleum Industry, Green Energy & Environment, https:// doi.org/10.1016/j.gee.2019.09.003. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019, Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd.

GRAPHICAL ABSTRACT

Cellulose-based materials have been used in wastewater treatment due to their low cost, renewability, biodegradability, and non-toxicity. This review summarized the uses of cellulose-based materials for crude oil spill cleaning and other applications in the oil & gas industry.

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Cellulose-based Materials in Wastewater Treatment of Petroleum Industry Baoliang Peng,1,2,* Zhaoling Yao,3 Xiaocong Wang,1,2,4 Mitchel Crombeen,3 Dalton Gsweene,3 Kam Chiu Tam,3,* (1. Research Institute of Petroleum Exploration & Development (RIPED), PetroChina, Beijing 100083, China; 2. Key Laboratory of Nano Chemistry, Key Laboratory of Oilfield Chemistry, CNPC, Beijing 100083, China; 3. Department of Chemical Engineering, Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada; 4. Institute of Porous Flow & Fluid Mechanics, Chinese Academy of Sciences, Langfang, Hebei065007, China;)

Abstract The most abundant natural biopolymer on earth, cellulose fiber may offer a highly efficient, low-cost, and chemical-free option for wastewater treatment. Cellulose is widely distributed in plants and several marine animals. It is a carbohydrate polymer consisting of β-1,4-linked anhydro-D-glucose units with three hydroxyl groups per anhydroglucose unit (AGU). Cellulose-based materials have been used in food, industrial, pharmaceutical, paper, textile production, and in wastewater treatment applications due to their low cost, renewability, biodegradability, and non-toxicity. For water treatment in the oil and gas industry, cellulose-based materials can be used as adsorbents, flocculants, and oil/water separation membranes. In this review, the uses of cellulose-based materials for wastewater treatment in the oil & gas industry are summarized, and recent research progress in the following aspects are highlighted: crude oil spill cleaning, flocculation of solid suspended matter in drilling or oil recovery in the upstream oil industry, adsorption of heavy metal or chemicals, and separation of oil/water by cellulosic membrane in the downstream water treatment. Keywords Cellulose; Wastewater treatment; Petroleum industry *Authors to whom correspondence may be addressed. E-mail addresses: [email protected] (Baoliang Peng); [email protected] (Kam Chiu Tam) 1

1. Introduction Oil and gas producers are responding to increasing demand for energy[1,2,3]. There are more than 65,000 on- and offshore oil and gas fields in the world[4]. Billions of gallons of produced water and process water are generated annually as waste products in the oil and gas industry[5]. Water can be polluted at every stage of oil production, such as oil spills occurring in offshore oil exploration and during oil transportation; contamination of produced water, which is a mixture of formation water, re-injected water, and treatment chemicals used for drilling or oil recovery; and contamination of process water generated during oil refining[6]. Produced water contains various organic and inorganic components, and its discharge can pollute soil and surface/underground water. The challenge to oil industry is the adoption of technologies for the treatment of contaminated water that are economically feasible. The use of renewable materials from agriculture and biomass feedstock in wastewater treatment not only decrease the carbon emissions, but it may also reduce the cost of wastewater treatment. Cellulose is a long linear polysaccharide polymer consisting of β-1,4-linked glucose units (C5H8O4)m. Natural and modified types of cellulosic materials are used to remove organic and inorganic pollutants from wastewater, such as removal of heavy metals using cellulose material as adsorbents, and cellulose membranes for water purification. [7,8]. Pollutants in oil industry wastewater can be removed through physical, chemical, and biological methods, such as adsorption, flocculation, evaporation, chemical precipitation, chemical oxidation, membrane microfiltration, or ultrafiltration. This review will focus on the use of cellulose materials, including clean up of oil spills, removal of solid particulates, and removal of organic or inorganic matters. 2. Cellulose and its derivatives Cellulose was first isolated from plant matter by the French chemist Anselme Payen in 1839[9]. The worldwide production of cellulose is estimated to be ca. 1000 tons per year[10], and it can be extracted from wood, plant, algae, tunicates, and bacteria[11]. It is composed of a linear chain of several hundreds to manythousands of linked glucose units, and the degree of polymerization (DP) is approximately 10,000 for cellulose chains found in nature and 15,000 for native cellulose cotton[10], and Figure 1 shows the chemical structure of cellulose. Cellulose possesses many attractive physical properties, such as high Young’s modulus (as high as 114 GPa) [12] for a single fibril, high degree of crystallinity (89%) [13], high degree of polymerization (14,400) [14], and high specific surface area (37 m2/g) [15]. Natural materials containing cellulose include plants, algae, and bacteria. Cellulose extracted from bacteria is free from wax, lignin, pectin, and hemicelluloses, which are commonly found in cellulose prepared from plants. The separation of cellulose from cellulose raw 2

materials requires two stages: 1) pretreatment of raw materials to make subsequent treatment reactions more uniform; 2) separate the pretreated raw materials into microfibers or crystals using mechanical treatment, acid hydrolysis and enzyme hydrolysis. The cost of cellulose prepared from bacteria, however is relatively high [16,17]. Plant cellulose is therefore preferred for mass production due to lower costs. Cellulose materials can be found in plant fibres, woods, stalks, stems, shells, straw, and grasses, and the composition of cellulose is summarized by Malik et al.[7].

Figure 1. Structure of cellulose

The functionalization of cellulose through the hydroxyl groups can greatly extend its applications[18-23]. Owing to its promising physical and chemical properties, significant effort has been devoted to translate this material from the academic research laboratories to industrial applications. Generally speaking, the surface functionalization methods of cellulose can be divided into two major categories: 1) chemical modification, such as TEMPO oxidation, polymer grafting and so on; 2) physical adsorption, i.e. electrostatic surface adsorption of surfactants and so on. Apart from the original cellulose fibers, microfibrillated cellulose (MFC), which is 10-100 nm in diameter and 0.5-10 mm in length or nanofibrillated cellulose (NFC), which is 4-20 nm in diameter and 500-2000 nm in length, can be prepared using mechanical treatments, such as homogenization and grinding. In the homogenizing or grinding process, high pressure is applied to cellulose fibers, breaking them down into smaller fibers. The resulting MFC or NFC contains amorphous and crystalline regions. The mechanical treatment is very energy intensive[24]; therefore, pre-treatments such as enzymatic [25,26], TEMPO-mediated oxidation [27,28], carboxymethylation, and acetylation [29-32] are used to facilitate the disintegration of cellulose fibers. Cellulose nanocrystals (CNC) [33,34] are prepared by acid hydrolysis of native cellulose. Depending on the origin and hydrolysis conditions, CNCs with different morphologies can be obtained. Strong acid, such as hydrochloric acid or sulfuric acid, is used to break down the amorphous regions, resulting in highly crystalline cellulose particles. The dimensions of the resultant nanocrystals are highly dependent on the source. The length can range from less than 100 nm to over 1000 nm, and the width can range from a few nanometers to 50 nm [35]. 3. Water pollution in petroleum industry 3

Water can be polluted or generated at every stage of the oil processing, including extraction, transportation, and refining. In this review, we will discuss the treatment of water contaminated by oil spills, produced water during oil extraction, and process water in oil refinery operations. 3.1 Water pollution caused by Oil Spills In 2014, 40.7% of global energy consumption is attributed to energy generated by oil and its refined products, and hence it is the world’s most common energy resource (Key World Energy Statistics, 2014). Offshore production, where spill accidents are likely to occur, accounts for 30% of the world’s oil [36]. As oil resources become scarcer and reserves become less accessible, accidental spillage poses a greater risk now than previously. Empirical analysis has shown that as oil platforms move to increasingly deeper waters, water depth correlates with the likelihood of oil spills [37]. Each 30 meters of added depth increases this likelihood by 8.5% [38]. Strikingly, this only accounts for 10% of hydrocarbon discharge. The remaining 90% comes from small routine discharges from offshore platforms, pipelines, and oil transportation. Spilled oilcauses short- and long-term negative impacts on surrounding ecosystems[39,40]; therefore, development of efficient techniques to remove spilled oil has drawn attention from the academic and industrial sectors[41,42]. 3.2 Produced water/process water in oil production Produced water is generated as a consequence of oil extraction operations[5]. Process water is an inherent component in oil refining of the downstream oil industry, and Figure 2 illustrates the formation of produced and process water in the oil/gas industry [6].

Figure 2 (a). General schematic representation of oil & gas well with the formation (produced) water in the reservoir and (b). The refinery process which produces process waste water. Reprinted with permission from (ref. [6]). Copyright (2016) Elsevier. 4

Produced water contains dispersed oils, minerals, production chemicals, solids, and dissolved gases. Global produced water is estimated at around 250 million barrels per day for around 80 million barrels per day of produced oil [43]; therefore, finding efficient ways to treat drilling wastewater is an important task in the oil and gas industry. Produced water contains more dissolved mineral ions than process water. On the other hand, process water contains more chemical compounds, such as phenols, ammonia, H2S, and BTEX (benzene, toluene, ethylbenzene and xylenes) than produced water[6]. In general, the produced water has high salt content, whereas the refinery process water contains large amounts of organic compounds. 3.3 Pollutants in produced/process water The pollutants in produced/process water can be divided into three categories: organic matter, inorganic matter, and suspended solid particulates. ORGANIC MATTER Organic matter, called TOC (total organic carbon), is a mixture of hydrocarbons, including BTEX, naphthalene, phenantherene, dibenzothiophene (NPD), polyaromatic hydrocarbons (PAHs), phenols, carboxylic acid, and low-molecular-weight aromatic compounds. The solubility of some hydrocarbons in water is very low, so they form small oil droplets in water [44,45]. INORGANIC MATTER Dissolved inorganic compounds in produced water includecations, such as Na+, K+, Ca2+, Mg2+, Ba2+, Sr2+, Fe2+; anions, such as Cl−, SO42−, CO32−, HCO3−; and heavy metals, such as cadmium, chromium, copper, lead, mercury, nickel, silver, and zinc [46]. The concentrations of heavy metals in produced water depend on the age of the wells and formation geology [47]. Sometimes, radioactive materials, such as 226radium and 228radium, can be found in produced water as well [47]. SUSPENDED SOLID MATTERS Production solids, denoted TSS (total suspended solids), comprise a wide range of materials, including formation solids, clay, sand, corrosion and scale products, bacteria, waxes, and asphaltenes. The pollutants in produced and process water are summarized by Munirasua et al.[6]. 4. Technologies used for wastewater treatment in oil industry

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Based on the pollutants of wastewater produced in the oil industry, the general objectives for the water treatment are: 1) removal of organic matter, including spilled or dispersed oil and small quantities of dissolved organic chemicals; 2) removal of suspended particulates, including suspended particles, clay, and sand; and 3) removal of dissolved inorganic matter, including heavy metals. A variety of techniques [6] have been developed to achieve the above-goals. In this review, we will focus on the following methods: adsorption processes to clean water polluted by spilled oil, heavy metals, and organic matter; flocculation methods to remove solid suspended matter in produced water; and membrane technology to remove dispersed oil from produced/process water. 4.1 Adsorption to treat oil spills Some current strategies for the collection and removal of spilled oil include mechanical collection (skimming), incineration, enzymatic or dispersant treatment, membrane filtration, and the use of absorbent materials [48,49,50]. One of the most economical and efficient methods for combating oil spills is to use a sorption material [51]. Sorbents are a broader class of materials that exhibit absorption, adsorption, and sometimes ion-exchange capabilities. The three major classes of oil sorbents are inorganic, organic synthetic and organic natural [51]. Organic synthetic and organic natural cellulose-based oil sorbents will be discussed in this paper. The benefits of using cellulose-based materials include their abundance, low cost, and biodegradability. These materials have shown promising results in many studies, with potential applications in oil and wastewater treatment for the removal of oil, and in some cases, heavy metal ions. Other materials reported in the literature other than cellulose-based sorbents include activated carbon and natural minerals such as bentonite clay, vermiculite, sepiolite, and organoclays (natural minerals modified with surfactants) [52]. Li et al. [51] tested modified cellulose fibers from corn straw as oil sorbent. The fibers, extracted from the corn straw, were acetylated to increase hydrophobicity. Results showed that these materials had oil sorption capacities of 42.53, 52.65, and 57.64 g/g for pump oil, diesel oil, and crude oil, respectively (by immersion at 25 for 1 h). The sorption process is shown in Figure 3. The abundance of corn straw as a byproduct of corn farming makes it a cheap and easily acquired material. The efficacy, low cost, and biodegradability of this alternative sorbent show potential application for large-scale use in the petroleum industry. This method, the oil absorption ability of cellulose fibers is enhanced by using the liphophilic surface of cellulose fibers modified by acetylation.

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Figure 3. Sorption processes of acetylated cellulose fibers. Reprinted with permission from (ref. [51]). Copyright (2013) American Chemical Society. Raw cotton, another cheap and abundant cellulose-based material, has been studied and reported by Singh et al. [53] as an oil sorption material. Raw cotton was placed in a circular steel mesh and immersed in a glass dish filled with raw crude oil such that the circular mesh floated freely in the oil. Results showed that a lower micronaire cotton had better sorption capacities, and they reported the crude oil sorption capacity of 3.1 micronaire (immature) cotton as 30.5 g/g. Micronaire is used as an indicator for fiber fineness and maturity. Compared with synthetic adsorbent, raw cotton has a higher crude oil adsorption capacity and a good environmental footprint, which is an ecological friendly adsorbent for oil spill cleaning. Cellulose-based aerogels as superabsorbents have been reported by Nguyen et al. [54]. They treated recycled cellulose fibers with sodium hydroxide/urea solution, and then placed the fibers in a refrigerator until gelation occurred. The mixture was then thawed and immersed in ethanol for coagulation. A solvent exchange was performed using DI water, andthe specimen was freeze-dried for 2 days. The aerogel underwent a silanation reaction at 70 °C for 2 h using methyltrimethoxysilane (MTMS). The resultant highly porous and low-density aerogel doped with MTMS exhibited nearly double the absorbent capacity of polyproplylene, a commonly used but less biodegradable sorbent. Variation on temperature was also studied, and the highest sorption capacity for RB crude oil was 24.4 g/g at 40 °C. Regenerated cellulose aerogel coated with MTMS has a strong affinity for crude oil and is a good adsorbent for oil spill purification. Feng et al. [55] developed a more economical method for synthesizing the silanated cellulose aerogel. A quantityof 0.075-0.3 g of Kymene was dispersed and sonicated in 30 mL of DI water for 10 min. This mixture was placed in the refrigerator at -18 °C for at least 24 h for gelation. The cellulose aerogel was then prepared by freeze drying. The aerogel was further 7

cured at 120 °C for 3 h to completely crosslink the Kymene molecules. After this, the aerogel was silanated with MTMS by placing the two components in a capped container and heating at 70 °C for 3 h. The research group tested the sorption capacity of the aerogel for temperatures between 25 °C and 70 °C and cellulose compositions between 0.25wt% and 1.0wt%. The highest motor oil sorption capacity in artificial sea water reported was 95 g/g for the 0.25wt% cellulose. The cellulose aerogels with silane modification can enhance the oil absorption capacity of cellulose, which have a good development prospect for crude oil pollution treatment. Wang et al. [56] prepared silanized cellulose for oil-water separation by sol-gel reaction of microcrystalline cellulose (MCC) with hexadecyl trimethoxy silane (HDTMS). They prepared the parent cellulose mixture in an aqueous alkaline solution using a one-cycle freeze-thaw process. HDTMS was then added dropwise to the solution, and HCl was used to catalyze the formation of the hydrosol. Oil/water separation was tested, which revealed only the HDTMS:MCC at 5:10 mass ratio cellulose was effective; however, this experiment was performed only on vegetable oil. No separation capability was tested for diesel or gasoline oil. However, it displayed exceptional recyclability. The silanized cellulose decreased in separation efficiency from 99.93% on the first use to 99.77% on the tenth use. Adsorption results using cellulose materials are summarized in Table 1. Cellulose-based materials can be used as adsorbent materials in oil spill treatment in the petroleum industry. The hydroxyl groups on the surface of cellulose were modified into oil-absorbing groups by means of acetylation and silanization. However, there is a major issue associated with the use of oil sorbents to treat oil spills, namely, the disposal of used sorbents. Many methods have been suggested, each with its own set of benefits and drawbacks. Practices include land filling, regeneration (i.e., reuse), incineration, and composting [57]. More research to develop a disposal method that is both economically viable and environmentally friendly ought to be done. Table 1. Summary of adsorption results of cited paper. Reprinted with permission from (ref. [57]). Sorbents

Key Finding(s)

Test Methods Modified ASTM Standard

Raw Cotton 35.85 g/g sorption of crude oil

F726-06

(Micronaire 3.1) 24.4 g/g sorption of crude oil.

Modified ASTM Standard MTMS cellulose aerogel

Optimal sorption temperature of 40 °C

8

F726-06

Oil sorption: immersed in 1:1 63.5 g/g sorption of crude oil. PVA CNF aerogel

2+

(v/v) oil water mixture

2+

Scavenging of Hg , Pb , Cu2+, Ag2+

Metal ion scavenging: stirred in solution for three days

67.54 g/g, 52.65 g/g, 42.43 g/g 0.005 g of sorbent was

Aetylated cellulose sorption of crude oil, pump oil,

immersed in oil for 1 h

fibers from corn straw and vacuum oil respectively

4.2 Suspended particles removal by flocculation method using cellulose materials Physical methods are commonly used to remove suspended particles from produced water, with the preferred techniques being adsorption, separators, centrifuging, and filtration[43,58]. These methods, however, require long periods of time, and they work well only on larger particles[58]. One way to address this challenge is to use coagulation-flocculation to form larger agglomerates, or flocs, in water, which may then be readily removed. Currently, the most common flocculation agents are polymers and metallic salts[59]. As a renewable material, functionalized cellulose could provide a more environmentally friendly alternative to current flocculation agents. Suopajärvi et al. [59] investigated the flocculating ability of five different dicarboxyl cellulose (DCC) samples with increasing levels of carboxylation. To synthesize the DCCs, bleached birch chemical wood pulp was reacted with sodium periodate and then with sodium chlorite. Cellulose nanocrystals (CNCs) with carboxyl contents of 0.38, 0.69, 0.75, 120, and 1.75 mmol/g were synthesized. It was found that CNCs with a carboxyl of 1.75 mmol/g were able to remove up to 80% of turbidity and 60% of chemical oxygen demand (COD) in water. Increasing the dosage of flocculant increases the amount of flocculation for doses up to 5 mg/L, at which point increasing the dosage does not affect the flocculation ability. It was reported that pH has very little impact on the flocculating capability of cellulose. The reduction of turbidity was minimized at a pH of 6.5, with better efficiency at both higher and lower pH values, shown in Figure 4[59].

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Figure 4. Effect of pH and Time on the Removal tubidity. Reprinted with permission from (ref. [59]). Copyright (2013) Elsevier

Zhu et al. [60] also investigated the turbidity reduction using DCC. Bamboo pulp was reacted with NaOH and urea and then kept at -12 oC for 1.5 h to obtain cellulose. The cellulose was reacted with NaIO4 for 5 or 48 h, and the excess NaIO4 was decomposed with ethylene glycol, and the solution was cooled to room temperature. The reaction continued to produce DCC with a carboxyl content of 2.57 mmol/g, which was then raised to pH 7 and washed. The produced DCC was found to remove 99.5% of the turbidity from a 500 mg/L kaolin solution when a dose of 25 mg/L of DCC was used with 300 mg/L of CaCl2. Suopajärvi et al. [61] tested sulfonated CNCs, as opposed to DCC, as a potential flocculant. Cellulose was functionalized with sulfonic groups [21], and the turbidity removal was tested using 25 mg/L of ferric sulfate to aid the flocculation. The sulfonated CNCs were found to remove the turbidity from water at a dosage of 2.5 mg/L. Cellulose with different functionalizations were studied by Yu et al.[62]. The authors synthesized carboxylated CNCs with a one-step method instead of the conventional methods. The cellulose was reacted with a mixture of 3 M citric acid and 6 M hydrochloric acid at 80 o C while stirring for 2, 3, 4, 5, or 6 h. The carboxylic acid content of samples CNCs-2H, CNCs-3H, CNCs-4H, CNCs-5H, and CNCs-6H were 1.15, 1.32, 1.39, 1.21, and 1.10 mmol/g, respectively. Therefore, the carboxylic content reaches a maximum with a reaction time of 4 h. The drop-off in carboxylic content is due to acid hydrolysis and esterification side reactions that occur beyond 5 h. Flocculation tests were performed on a 1 g/L suspension of kaolin with the pH adjusted to 7.30 mg of CaCl2. The CNCs being tested were added to 100 mL of the kaolin; the turbidity was then measured with a Turb550 turbidimeter. The CNCs-4H was found to remove more turbidity than all other samples, reaching up to 95.4% removal with a dosage of 40 mg/L. CNCs with sulfate groups (CNCs-S) and formate groups (CNCs-F) were also tested by Yu et al. [62]. CNCs-S was synthesized by reacting cellulose with sulfuric acid. CNCs-F was synthesized by reacting cellulose with a mixture of formic acid and hydrochloric acid. Using the same test Yu et al. [62] used for carboxylated CNCs, the CNCs-S removed 82.9% of turbidity, while the CNCs-F removed 34.3% of turbidity. Nourani et al. [63] synthesized sulfonated cellulose as a flocculant using cotton instead of wood pulp. Cotton was reacted with chlorosulfonic acid to obtain anionic sulfonated cellulose. To test the flocculation capability of the cellulose, the turbidity reduction from a 5 g/L sample of kaolin suspension was measured after adding 20 mg/L of aluminum sulfate and the sulfonated cellulose. Unlike the DCC investigated by Suopajärvi et al. [61], the sulfonated 10

cellulose was found to remove turbidity most effectively in solutions with a pH of 4.5 to 6.5. It was predicted by mathematical modeling that turbidity removal of 98.9% could be obtained using 23.1 mg/L of aluminum sulfate and 7.2 mg/L of sulfonated cellulose at a pH of 6.2. DCC was produced by Suopajärvi et al. [61] with a yield of 66%, while the sulfonated CNCs were produced with a yield of 88.3%, which could make sulfonated cellulose a more practical flocculant than DCC. Liu et al. [64] investigated the flocculating capability of cellulose grafted with polyacrylamide. To synthesize bamboo pulp cellulose-grafted polyacrylamide flocculant (BPC-g-PAM), bamboo pulp cellulose was reacted first with ammonium persulfate, and then with polyacrylamide. The flocculating capability was determined by flocculating a 200 mg/L solution of kaolin and measuring the residual turbidity with a Turb550 turbidimeter. At the optimal pH value of 7, a 500 mL kaolin solution was pretreated with 0.05 g of CaCl2 and a dose of 0.04 g of BPC-g-PAM, resulting in 98% turbidity abatement. At pH values greater than 7, even with the addition of BPC-g-PAM, turbidity abatement slowed significantly. Kan et al. [65] modified CNC with pH-sensitive poly(4-vinylpyridine) (P4VP) using cerium(IV) ammonium nitrate as the initiator. Their results indicated that CNCs grafted with P4VP flocculated in solutions of pH greater than 5 formed stable suspensions at pH values below 5. Further research on the flocculating effect of P4VP-grafted CNCs on solutions containing other particles, such as kaolin, should be conducted to determine if this is a practical solution for treating wastewater. In addition to anionic cellulose, cationic functionalized cellulose has also been investigated as a flocculation agent. Liimatainen et al. [21] modified cellulose with(2-hydrazinyl-2-oxoethyl)-trimethylazanium chloride to obtain cationized dialdehyde cellulose (CDAC). Samples with varying sizes and charge densities were synthesized. To prepare the CDAC, bleached birch chemical wood pulp was first reacted with NaIO4 and LiCl to obtain dialdehyde cellulose (DAC). The DAC samples were then reacted with(2-hydrazinyl-2-oxoethyl)-trimethylazanium chloride to produce the CDACs. To test the flocculation capability of the samples, the CDACs were mixed into the kaolin solution and centrifuged. The residual transmission was then measured. All samples were found to effectively flocculate a 1wt% kaolin suspension. Unlike DCC, the flocculation ability of CDAC relies heavily on the pH of water. CDACs were found to be effective flocculation agents at a pH lower than 8.5; however, at a pH greater than 9, the flocculation capability decreased dramatically, due to the reduction in charge density and particle size at higher pH value. The flocculating capability of cellulose-based materials reviewed in this section is summarized in Table 2. Table 2. Turbidity removal efficiency of cellulose based flocculants 11

Flocculants

Coagulants

Turbidity Removal

5 mg/L DCC

25 mg/L ferric sulphate

80%

300 mg/L CaCl2

95.4%

300 mg/L CaCl2

99.5%

25 mg/L ferric sulphate

40%

CNCs-S

300 mg/L CaCl2

82.9%

CNCs-F

300 mg/L CaCl2

34.3%

80 mg/L BPC-g-PAM

100 mg/L CaCl2

98%

40 mg/L Carboxylated CNCs 25 mg/L DCC 2.5 mg/L sulfonated Cellulose

This section mainly introduces that cellulose, as a renewable material, is a more environmentally friendly alternative to flocculant at present. By means of carboxylation, sulfonation, graft copolymerization and other approaches, cellulosic materials can be functionalized to achieve the best flocculation effect. The turbidity removal efficiency of some functional cellulose was compared, among which DCC, CNCs, BPC-g-PAM and other samples showed significant turbidity removal efficiency. 4.3 Heavy metal removal using cellulose materials Heavy metals in wastewater can be removed by techniques, such as chemical precipitation [66], ion exchange [67], membrane filtration [68,69], reverse osmosis [70-72], electrodialysis[73,74], and adsorption [76-78]. Comparatively, the adsorption process seems to be the preferred technique due to its ease of operation, economic feasibility, wide availability, and simplicity of design. In this section, we will discuss research progress using adsorption to remove heavy metals with cellulose materials [78-82]. Zhou et al. [78] modified cellulose with maleic anhydride (CM) and used it as an adsorbent to remove Hg(II). The degree of carboxyl group of the modified cellulose was found to be 2.7 mmol/g by the titration method. The adsorption results indicated that the CM has a good adsorption capacity for Hg(II) with a maximum adsorption capacity of 172.5 mg/g. The influence of different experimental parameters such as pH, contact time, and temperature on removal process was also evaluated. Thirumavalavan et al. [79] explored the removal of heavy metal ions such as Cu2+, Ni2+, Zn2+, Cd2+, and Pb2+ from aqueous solution using three types of fruit peels (orange peel (OP), lemon peel (LP), and banana peel (BP)). The surface of the LP and lemon peel cellulose (LPC) 12

was chemically modified. The adsorption capacity of metal ions such as Cu2+ and Ni2+ was found to be greater than that of other metal ions. From the comparison of the adsorbents, surface-modified LPC (LPCACS) was found to display enhanced adsorption activity. They also compared the results with activated carbon (AC) and found that the order of the adsorption capacity was: LPCACS > LPC > AC > LP. The adsorption capacities of the studied materials are summarized in Table 3[79]. Table 3. Comparison of Adsorption activities of LP, LPC, surface modified LP and LPC and AC. Reprinted with permission from (ref. [79]). Copyright (2010) American Chemical Society. Adsorption of metal ions (mg/g) Adsorbents

Cu2+

Pb2+

Zn2+

Ni2+

Cd2+

LP

70.92

37.87

27.86

80.00

54.64

LPS

227.27

204.08

196.08

238.10

172.41

LPAC

208.33

99.01

142.86

200.00

117.65

LPACS

314.83

256.41

192.31

277.78

185.19

LPC

263.16

123.46

112.36

232.56

114.94

LPCACS

344.83

277.78

222.22

285.71

192.31

AC

138.80

109.30

112.30

—

—

Mahajan et al. [81] reported the removal of Ni(II) and Cd(II) from model wastewater using lingo-cellulosic agricultural waste material. For this, Arachis hypogea shells (AHS) were used in natural (AHSN) as well as in immobilized forms of beads (AHSB). They found that metal ion removal was highly dependent on pH, initial concentration, and adsorbent dose. Also, the immobilized form demonstrated a better platform for heavy metal removal than the natural form. Maximum removal efficiencies were 72% and 99% for Ni(II) and Cd(II), respectively. Cellulose nanocrystals, prepared by acid hydrolysis of cellulose fibers, were also explored by researchers as adsorbents to remove heavy metals. Recently, Yu et al. [62] modified CNC with succinic anhydride to obtain SCNCs. The SCNCs were further treated with saturated NaHCO3 to obtain NaSCNCs. Pb2+ and Cd2+ adsorption using SCNCs and NaSCNCs as adsorbents was investigated. The maximum adsorption capacities of SCNCs for Pb2+ and Cd2+ were 367.6 and 259.7 mg/g, respectively, and for NaSCNCs for Pb2+ and Cd2+, 465.1 13

and 344.8 mg/g, respectively. Also, they found the adsorption rate of Pb2+ and Cd2+ on NaSCNCs was very fast, with a time to equilibrium of only 5 minutes. At the same time, they studied the selectivity and interference resistance from coexisting ions. It was found that NaSCNCs exhibited a higher adsorption capacity and higher high selectivity for Pb2+ and Cd2+. Further, they proved that the adsorption mechanism of NaSCNCs was dominated mainly by ion exchange, which made NaSCNCs superior to SCNCs; therefore, it was essential to convert the carboxyl groups into carboxylates for this adsorbent, which contains carboxyl groups. They also investigated the regeneration efficiency of the adsorbents, a very important characteristic in terms of practical application. As shown in Figure 5, the adsorption capacities of SCNCs decreased when SCNCs were regenerated using HCl solution because the complexation between the active sites and metal ions was destroyed due to the protonation of the active sites, the COO− groups. When the lead- or cadmium-loaded NaSCNCs were regenerated by saturated NaCl solution through ion exchange process, however, the adsorption capacity of NaSCNCs still remained at a high value after two cycles.

Figure 5. Regeneration efficiency of SCNCs and NaSCNCs. Reprinted with permission from (ref. [62]). Copyright (2013) Elsevier Adsorbents with different shapes, such as beads or fibers made of cellulose and other natural materials also showed very promising results [83,84]. Recently, Ji et al.[84] prepared cellulose acetate/zeolite (CA/Z) composite fibers using the wet spinning method. Cellulose acetate was used as a polymer matrix, and zeolite particles were dispersed and embedded in the cellulose acetate network. The morphology of the CA and CA/Z fiber was investigated by SEM is shown in Figure 6. It was found that CA fiber is a porous structure, with pore size in the range of 300-500 nm. Zeolite particles have a size of about 1 µm; therefore, the zeolite particles could be retained and wrapped within the network of the CA/Z fiber. The average pore size of the CA/Z fiber is 24.6 nm, which is hundreds of times greater than the dimension of any heavy metal ions. Therefore, the fiber allows the rapid passage and diffusion of heavy 14

metal ions into the internal pores for contact with the adsorptive sites of the zeolite particles.

Figure 6. SEM images of CA fiber (a) and CA/Z fiber (b). Reprinted with permission from (ref. [84]). Copyright (2012) Elsevier. The prepared CA/Z fiber was used as an adsorbent to remove Cu(II) and Ni(II) ions from aqueous solution. Various parameters, such as initial solution pH, metal ion concentration, and contact time, were investigated in a batch adsorption model. At the same time, adsorption isotherms, kinetics, thermodynamics, and regeneration of the adsorbent were also evaluated. The results showed that the CA/Z fiber could be used as an efficient absorbent for removal of Cu(II) and Ni(II) ions from aqueous solution. The adsorption isotherms were better fitted by the Langmuir equation under equilibrium condition. The maximum adsorption capacities of the CA/Z fiber for Cu(II) and Ni(II) at 298 K were found to be 28.57 and 16.95 mg/g, respectively. The CA/Z fiber was regenerated, and there was no significant loss in adsorption performance after five adsorption/desorption cycles. In some studies, the heavy metal ion-scavenging capability of the cellulose-based sorbent was investigated in addition to its oil-sorption capability. Zheng et al. [82] developed a green synthesis (freeze-drying) method for a polyvinyl alcohol (PVA) cellulose nanofibril (CNF) hybrid aerogel that displayed exceptional oil absorbency and heavy metal ion-scavenging properties. The TEMPO-oxidized CNFs were prepared following the procedure developed by Isogai and co-workers [85]. This aerogel displayed a 63.5 g/g sorption capacity for crude oil. It could also filter the heavy metal ions Hg2+, Pb2+, Cu2+, and Ag+ much more effectively than pure PVA aerogel. For each metal ion respectively, the results were 157.5, 110.6, 151.3, 114.3 mg/g for PVA/CNF aerogel and 22.0, 24.5, 28.9, and 39.5 mg/g for pure PVA aerogel, indicating that the CNF had a significant impact on scavenging abilities. Wang and coworkers [86] prepared a PVA/carboxymethyl cellulose (CMC) aerogel for heavy metal ion removal. The PVA/CMC hydrogel was prepared by a repeated freeze-thaw process. Solutions of PVA and CMC were mixed at various ratios and frozen and thawed in five cycles. The metal ion adsorption was measured by immersing samples for 24 h at 15 °C in a 100 15

ppm metal ion solution. Metals tested include Ag+, Ni2+, Cu2+, and Zn2+ and the results showed that Ag+ displayed the greatest adsorption performance. The authors suggested that the smaller size of Ag+ allowed it to diffuse into the polymer network more easily compared to the larger ions. The results also showed that adsorption capacity decreased for a mixed solution (more than one type of metal ion) compared to solutions with only one type of ion, with Ni2+ being the most affected (a 56% decrease in sorption capacity when mixed with other ions). In addition, the 2:1 PVA:CMC ratio hydrogel had the best sorption capacity. This section mainly introduced the removal of heavy metals from wastewater using cellulose-based materials, which have a strong adsorption ability to heavy metal ions after functionalization, especially the above-metioned SCNCs. Compared with other methods, the adsorption method has the characteristics of simple operation, economic feasibility and strong practicability, and the cellulose material has a wide range of sources and is simple to prepare. 4.4 Removal of organic chemicals using cellulose material Organic matter dissolved in produced water/process water can be removed using an adsorption process with cellulose materials. The effective adsorption of native cellulose for organic pollutants are 100 to 500 times less than that of activated carbon or zeolite [87], due to the low concentration of active sites where organic pollutants could be adsorbed. Modification of cellulose, therefore, is needed for cellulose to be used as an effective adsorbent for the removal of organic matter [87,88]. Alila&Boufi [87] explored the use of modified cellulose fibers as adsorbents for the removal of aromatic organic compounds. The cellulose fibers were modified by grafting long hydrocarbon chains in a heterogeneous environment. In this study, two reagents, 4,4’-methylenebis (phenyl isocyanate) (MDI) and N, N’-carbodimidazole (CDI), were used to graft different hydrocarbons including under mild conditions. The adsorption results of aromatic compounds, including 2-naphthol, nitrobenzene, chlorobenzene, dichlorobenzene, trichlorobenzene, and chlorophenol, showed that the chemical modification of the fibers’ surface greatly enhanced the adsorption capacity, which increased from 20 to 50 mol/g for the virgin fibers to 400 to 1000 mol/g for the modified substrates. They also studied reusability of the modified cellulose by washing the columns with ethanol. The found that the regenerated column can be used in several adsorption/desorption cycles without any loss of capacity. Alolou et al. [89] modified cellulose fibers by heterogeneous esterification with linear octyl anhydride. The adsorption capacities of the modified fibers for various organic molecules, such as benzene, chlorobenzene, dichlorobenzene, trichlorobenzene, nitrobenzene, aniline, quinolone and 2-naphtool, were investigated, and results showed that the modified fibers appeared to be an efficient absorbent for different dissolved organic matter in water. The 16

adsorption capacity increased from 40 to 300 mol/g after modification with octyl chains. Alolou et al.[89] also performed recycling tests and found that the exhausted substrates could be regenerated without losing their capacity. They also found that the adsorption isotherm of different solutes followed the Langmuir model within the studied concentrations. The adsorption equilibrium constant K and the maximum concentration of the solute uptake are summarized in Table 4. Higher values of Langmuir constants were obtained for modified cellulose fibers, which indicated higher affinity of dissolved organic matter. At the same time, the research group also observed higher adsorption capacity for less soluble compounds.

Table 4. Isotherm results of different organic solutes absorbed onto modified/pristine cellulose fibers under equilibrium condition. Reprinted with permission from (ref. [89]). Copyright (2006) Elsevier. Cmax(langma

Cmax(experime

ir)

ntal)

Benzene

220

Chlorobenzene

a

Solubility

Ka(1mol-1)

Kb(1mol-1)

R2c

210

2750

8600

0.995

22.9

185

180

4903

14000

0.996

4.46

Dichlorobenzene

170

170

6185

11100

0.996

0.4

Nitrobenzene

205

207

1771

10400

0.995

16.9

aniline

270

267

779

21200

0.994

389

Trichlorobenzene

295

294

6360

8900

0.993

0.22

Quinoline

288

313

957

15800

0.997

2-Naphthol

286

280

1426

1426

8750

Organic solute

(mmol-1)

5

For surfactant treated fibres. bForoctyl grafted fibres. cR2 relative to the linear form of the Langmuir

equation

This section introduced the removal of organic compounds in the produced water/process water by adsorption of cellulose-based materials. In this section, the most important factors affecting adsorption are the species of organic pollutants, the low concentration and the modification of cellulose. As metioned above, modified fibers appeared to be more efficient, therefore, the high affinity between organic pollutants and modified cellulose can increase adsorption capacity significantly.

17

4.5 Dispersed/emulsified oil removal by membrane separation Wastewater produced during the oil drilling and refining processes also contains large concentrations of oil. In addition to adsorption methods [23], membrane filtration shows promise for removing oil from wastewater. Membrane separation utilizes porous materials to physically remove the trapped particles and contaminants [90]. Researchers have reported on the effectiveness of using microfiltration and ultrafiltration in treating oily wastewaters [91-93]. Oily wastewater is usually treated by membrane filtration in a semi batch process with continuous withdrawal of permeate and recycling of the oil-enriched non-permeate. A schematic is shown in Figure 7 [94].

Figure 7. Schematic diagram of the laboratory scale cross flow filtration system. Reprinted with permission from (ref. [94]). Copyright (2012) Wiley. The advantages of membrane separation technology include less pollution, low reprocessing cost and lower energy consumption compared to adsorption methods. The existing processes, however, still need to be improved in terms of thermal stability and antifouling properties. Research efforts have been focused on the development of new materials and new methods for film preparation. Materials used to fabricate membranes include cellulose acetate [95]; polysulfone[96]; and inorganic materials such as kaolin/MnO2 [97], ceramic [98], or ceramic/alumina [99]. In this section, we will focus on membrane filtration to treat oily water using cellulose-based materials. Chen et al.[95] fabricated ultrafiltration membranes using cellulose acetate (CA) and polyacrynitrile (PAN). These membranes demonstrate high permeability and excellent antifouling property for oil/water emulsion separation. PAN was grafted to CA via free radical polymerization using cerium ion as the initiator. The CA-g-PAN was used to fabricate membranes by phase inversion method. The research group found that the presence of 18

hydrophobic PAN chains significantly enlarged the pore sizes of the membrane, leading to a substantial increase in the permeation. In addition, the antifouling ability of membranes was evaluated by the oil/water emulsion flux decay ratio (DR) and flux recovery ratio (FRR). Although the CA membrane possessed low DR and high FRR, indicating an excellent antifouling capability, the permeability for the CA membrane was extremely low (only about 3.4 L/(m2 h) under the operation pressure of 0.1 Mpa, which was not feasible for practical oil/water separation application. The experimental results of oil/water emulsion ultrafiltration under different operating conditions, such as pressure, oil concentration, and flux rate, demonstrated that the CA-g-PAN membranes preserved superior antifouling property and 100% removal efficiency. Zhou et al. [100] fabricated ultrathin nanoporous cellulose membranes by freeze-extraction of a very dilute cellulose solution and used this membrane to separate oil-in-water nanoemulsions. The prepared membranes had a cut-off of 10-12 nm and a controllable thickness of 80-220 nm. This membrane demonstrated ultra-fast water permeation of 1620 L/(m2 hbar) and exhibited excellent size-selective separation properties. These membranes have been applied to remove oil from aqueous nanoemulsions with removal efficiency greater than 96.5% for oil droplets with sizes ranging 200-400 nm. Figure 8 [100] shows the sizes of oil droplets, flux, and removal efficiency for different nanoemulsions.

Figure 8. Oil-in-Water nanoemulasion was separated by 112 nm thick membrane. (a) Photographs of cyclohexane-water nanoemualsion before and after filtration. (b) Fluxes of four tested emulsions across the membrane. (c) Rejection of oil for four tested emulsions. Reprinted with permission from (ref. [100]). Copyright (2014) Royal Society of Chemistry. 19

Mansourizadeh et al. [101] fabricated oil removal membrane using cellulose acetate (CA), polyethersulfone (PES), and PEG-400 (used as a phase-inversion promoter to produce highly permeable membranes). The morphology, pore size, surface hydrophilicity, porosity, water flux, hydraulic resistance, and oil rejection were investigated. They found that the PES/CA membrane presented a sponge-like morphology with a thinner outer skin layer and larger pore sizes (mean pore size roughly 0.15 µm.). Higher water flux and lower resistance of the membrane were observed due to the higher hydrophilicity and the produced open structure. However, rejection efficiencies of 88% for PES/CA membrane and 98% for PES membrane were obtained. It was explained that the lower oil rejection of the blended PES/CA membrane was related to the larger pore sizes. From an oil/water separation test, the PES/CA membrane showed stable oil rejection of 88% and water flux of 27 L/(m2 s) after 150 min of the operation. They pointed out that the PES/CA membrane presented a higher permeation flux and a relatively lower separation performance. From an economic point of view, the membranes with higher flux are more favorable to commercialization of the membrane separation system. The flux and removal efficiency for PES/CA/PEG and PES/PEG are shown in Figure 9[101].

Figure 9. The flux and removal efficiency for PES/CA/PEG and PES/PEG. Reprinted with permission from (ref. [101]). Copyright (2014) Springer. Membrane separation is a common method to treat oily wastewater in petroleum industry, due to the advantages of low pollution, low post-treatment cost and low energy consumption. It has a very wide prospect to prepare cellulose membrane by using cellulose film forming characteristics for the treatment of oily wastewater, however the current membrane separation technology still needs to be improved in terms of thermal stability and antifouling performance. 5.Conclusions Due to the increasing amount of wastewater produced in petroleum industry, the discharge effect of produced water have become an important environmental problem. Meanwhile, a single treatment method normally is not enough to remove all pollutants, because of the 20

complexity of pollutants. Cellulose-based materials provide an efficient, low-cost and pollution-free option for the wastewater treatment in petroleum industry. Multiple functions could be achieved on the cellulose-based materials, which can effectively remove pollutants, especially in crude oil spill cleaning, flocculation of solid suspended matter in drilling or oil recovery in the upstream oil industry, adsorption of heavy metal or chemicals, and separation of oil/water by cellulosic membrane in the downstream water treatment and other applications. In addition, cellulose-based materials have many excellent characteristics, such as extensive sources, low energy consumption, economic feasibility, environmental protection, and renewable, and exhibit a very wide application prospect in the petroleum industry. In the future, research efforts will mainly focus on the optimization of existing technologies and the combined physical-chemical and/or biological treatment of produced and process water in order to comply with reuse and discharge limits. 6. Acknowledgements This work was financially supported by PetroChina Scientific Research and Technology Development Project (2018A-0907, YGJ2019-11-01). K. C. Tam also would like to acknowledge the support from CFI and NSERC.

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We have no conflicts of interest to disclose.