Removal of oil from water using polyurethane foam modified with nanoclay
Introduction
Oil discharge into the natural environment and aquatic ecosystems can cause serious global, ecological, and environmental problems [1]. Industrial development has increased oily wastewater discharge to the environment [2]. Petroleum transportation with a yearly average of about 5 million tons across seas poses a great risk of pollution to the marine ecosystem [3]. Oil industry, especially oil refining processes and transport, has a major role in this problem. However, increasing oil consumption and establishing more refineries near the cities and populated regions have caused severe pollution in the underground and surface waters [4]. Oily contaminants in polluted water may be detected in different forms like fats, lubricants, cutting liquids, heavy hydrocarbons (tars, grease, crude oils and diesel oil), and light hydrocarbons (kerosene, jet fuel and gasoline) [2]. So, the removal of in situ oil and other types of organic pollutants is crucial to prevent them from migrating and to reduce their disastrous effects on the ecosystem [1].
Different techniques have been developed for the removal of oil contaminants from water. They are classified into chemical, biological and physical methods [5]. These include different types of filters [6], chemical dosing, reverse osmosis [7], gravity separation [8], ultra-filtration [9], micro-filtration [10], biological processes [10], air flotation [11], membrane bioreactor [12], chemical coagulation, electrocoagulation and electroflotation [13]. Adsorption is among the most profitable methods for the removal of oil contaminants as it can effectively remove or recover oil from the water [14].
Oil sorbents are divided into three basic types: natural organic, natural inorganic and synthetic adsorbents [15]. Some examples of natural sorbents used for the adsorption of oil are sugar cane bagasse [16], vegetable fibers [17], sawdust bed [18], bentonite, chitosan, activated carbon [19], vermiculite [20], chrome shavings [21] and peat [22]. Synthetic sorbents used for oil contaminants adsorption include rubber powder [23], expanded perlite [24], polymeric material based on butyl rubber [25], high-silica zeolites [26], carbonized pith bagasse [27], wool-based nonwoven [28], hydrophobic aerogels [29], acetylated rice straw [30], exfoliated graphite [31], inorgano clays [32], polypropylene [33] and oleophilic polyurethane foams [34].
Polyurethane (PU) in the form of foam provides a large specific area and enough space for adsorption. Polyurethane foams (PUFs) have shown the noticeable capability of oil adsorption due to their special features such as low density, open-cell, high porosity, and industrial production. Nanoclay is one of the possible materials that can modify the polyurethane foam structure. The presence of cloisite 20A nanoclay in the structure of PUF has been found to enhance the foam strength [35] and open its cells [36]. Furthermore, nanoclay itself is an oil adsorbent, but it needs structural modification.
The main objective of this study is to investigate the effect of cloisite 20A nanoclay presence within the PU foam structure on the removal efficiency of oil. The effect of chemical regeneration of the foam and its performance are also investigated. The isotherm of the oil adsorption is also studied using this sorbent.
Section snippets
Materials
NIXOL AM-313 polyether polyol was provided from KPX chemical CO. (South Korea) and methylene diphenyl diisocyanate (MDI) was obtained from Daeyang International CO. (South Korea). 1,1-Dichoro-1-fluoroethane (HCFC 141b) was purchased from Lińan E-COOL Refrigeration Equipment CO. (China). Cloisite 20A nanoclay was purchased from Sigma Aldrich (USA). Light crude oil was obtained from Isfahan refinery feed stream (Iran). Toluene and Xylene were supplied by Isfahan petrochemical complex (Iran) and
Fourier transform infrared spectroscopy (FTIR)
FTIR spectra of the synthesized PU foam are depicted in Fig. 1. The characteristic peaks of PU are evident close to 3340 cm−1. These peaks belong to the corresponding vibration of hydroxyl functional group (O–H), probably due to their existence in unreacted polyol (reaction of polyol with isocyanate). The peaks near the wave number of 2950 cm−1 are associated with the vibration of –CH2 and –CH functional group in the carbonic chains. The sharp peak with the wave number of 1730 cm−1 was related to
Conclusions
It is concluded from the results of this research that the oil sorption capacity has increased in low initial oil concentrations, while it has decreased in high initial oil concentrations in the case of nanocomposites with 2 wt% and 4 wt% of cloisite 20A. The nanocomposite with 3 wt% clay has shown increase in adsorption at all initial oil concentrations. The adsorption efficiencies of nanocomposites have increased in comparison with the pure PU foam. The chemical regeneration of the pure foam has
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