Which chemical absorbs oil?

3.1

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Zeolites

Previous works (Carmody et al. 2007; Alayande et al. 2016) focused on the synthesis of hydrophobic zeolites as an alternative for activated carbon absorbents. Natural zeolites are aluminosilicate minerals with a 3-D structure. Their wide pores and large surface area make possible the removal of impurities from water and air (Al-Haddad et al. 2007). The absorption of petroleum hydrocarbons, heavy metals, and sulfur or ammonia compounds has been studied using zeolites (natural and synthetic) as absorbents. Natural and manufactured zeolites have been tested in wastewater where zeolites performed a better absorption process of several ammonia compounds (84.4% of removal) than activated carbons (15.6% of removal). The selective absorption of metals and ammonia makes zeolite a potential absorbent for wastewater treatment, but not for refinery wastewater due to high content of oil derivatives.

In a related report (Carmody et al. 2007), Wyoming Na-montmorillonite, octadecyltrimethylammonium bromide (ODTMA), dodecyldimethylammonium bromide (DDDMA), and di(hydrogenated tallow) dimethylammonium chloride (commercial name Arquad 2HT-75) were used to synthesize organo-clays which might present hydrophobic or organophilic surface depending on the exchanging ions. The absorption capacity of the synthetized organo-clays was tested using three types of oil (diesel, hydraulic oil, and engine oil). It was observed that with increasing content of long chain hydrocarbon, the absorption capacity of the organo-clay was found to be higher. Organo-clay with certain hydrophobicity, absorption and retention capacities might be synthesized through the control of variables and their combinations. However, organo-clays exhibit some disadvantages including high cost, low biodegradability and low recyclability.

On the other hand, the synthesis of functionalized nanosorbents with residues from the distillation of oil (vacuum residue) and alumina nanoparticles have a great potential due to their low cost and high hydrophobicity (Franco et al. 2014). The materials were tested under different conditions where high absorption capacity and retention of oil can be achieved at neutral pH and a 4% load of vacuum residue. The synthesis of this material has the economic advantage of the use of an industrial residue as precursor; however, its use requires specific conditions to obtain the maximum absorption capacity restricting the adaptability. In a similar report (Alayande et al. 2016), an expanded polystyrene (EPS) and zeolite were used to synthetize beaded fibers with a zeolite matrix by electrospinning, as shown in Figs. 1 and 2. The material presents superhydrophobic properties (Fig. 3) and high absorption capacity of oil due to the zeolite porous matrix.

Fig. 1

Surface morphology of 20% EPS electrospun at A1 11.5 kV, 20% PS; A2 15 kV, 20% PS; B1 20% PS/zeolite at ×500; B2 ×50,000. Reproduced with permission of Elsevier from (Alayande et al. 2016)

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Fig. 2

Surface morphology of C1 EPS/zeolite film; C2 EPS film. Reproduced with permission of Elsevier from (Alayande et al. 2016)

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Fig. 3

Water contact angle of a 20% PS/zeolite and b 20% PS. Reproduced with permission of Elsevier from (Alayande et al. 2016)

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Concluding this section, such properties of zeolites as high porosity and large surface area are key features in the processes of oil removal from water. However, other properties as hydrophobicity, absorption capacity, and retention of oil are also important in order to achieve a complete cleaning of impurities in wastewater, seawater or other aquatic systems.

3.2

Aerogels

The term “aerogel” is a gel material, in which its liquid component has been replaced with gas to leave an intact solid micro- or nanostructure without pore collapse; aerogels contain ~99% air by volume (Zuo et al. 2015). Different types of aerogels are known, for instance silica-based aerogel (Rao et al. 2007; Wang et al. 2010, 2012; Olalekan et al. 2014), cellulose-based aerogels (Korhonen et al. 2011), clay-based aerogels (Rotaru et al. 2014), carbon-based aerogels (Kabiri et al. 2014; Yang et al. 2015a; Zeng et al. 2009; Zuo et al. 2015), etc. The methods of synthesis for each type of aerogel vary depending on the final application; however, supercritical drying or freeze-drying is fundamental in order to obtain final aerogels.

The synthesis of silica-based aerogels is carried out by well-known methods for advanced nanoporous materials; however, their applications require deeper studies. Due to their own properties such as high surface area, hydrophobicity and porosity, a study of the sorption of three oils (vegetable oil, motor oil, and crude oil) was carried out (Wang et al. 2012). Using Cabot nanogels (silica-based aerogels) with different particle sizes, a high capacity for adsorption of oils was observed. Their capacity of absorption depends on the stability of the mixture of water and oil. In the cases where the emulsion was stable, the absorption capacity of the aerogel decreased tenfold. In order to avoid this issue, the use of sustainable materials such as plants and some soils as aerogel precursors was offered. These materials exhibit the advantages of being renewable, natural and with low impact on environments due to their high compatibility with nature. For example, the functionalized cellulose aerogel with hydrophobic coating (TiO2) and a process of freeze-drying produce nanocellulose aerogels (Korhonen et al. 2011). Aerogel structure is created by the connected fibers of the nanocellulose, and Fig. 4 illustrates their resulting morphology with and without the coating. The composite exhibited absorption capacity of 20–40 (wt of oil/wt of absorbent) but also, it can be reused (10 times) since the absorption capacity does not change. After the oil absorption, it requires only a wash with solvent in order to be reused as sorbent or can be incinerated in order to use it as a fuel.

Fig. 4

Microscopic structure of the native nanocellulose aerogels. SEM micrographs of a freeze-dried nanocellulose aerogels, and b a magnification of a sheet. c TEM micrograph of a nanocellulose fibril with a uniform 7 nm TiO2 coating. Reproduced with permission of ACS from (Korhonen et al. 2011)

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Also, the use of carbon-based aerogels is more frequent now; in particular, “greener synthesis” has nowadays attracted attention. The development of these nanomaterials which do not only accomplish the final application but also their synthesis using low-toxicity chemicals and reducing the number of steps of the process are important. The synthesis of graphene–carbon nanotube aerogel has been reported by greener techniques, where the interaction of the graphene oxide and carbon nanotubes was performed in a one-step process (Kabiri et al. 2014). A schematic diagram of the synthesis procedure is represented in Fig. 5. Carbon nanotubes provide the hydrophobic and porous property to the product (Fig. 6), promoting the absorption of oil products. The synthesis method used is economically attractive and simple for scalable production. A possible absorption process to implement on a large scale is shown in Fig. 7.

Fig. 5

Schematic diagram for synthesis of the graphene–CNT aerogels: a GO sheets, b CNT bundles, c the mixture of GO and CNT prepared for d the graphene–CNT hydrogel, and e the formation of graphene–CNT aerogel by freeze-drying from hydrogel. Reproduced with permission of Elsevier from (Kabiri et al. 2014)

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Fig. 6

Digital photographs showing the adsorption of vegetable oil on a water surface using prepared graphene–CNT aerogels at different times: a t = 0 s, b t = 10 s, and c t = 20 s. d Adsorption capacity graph of graphene–CNT for oils and several organics using pure oil and solvent and their mixtures with water. e The relationship of adsorption capacity with density of oil and organic solvents without water in the system. The inset shows the contact angle (CA) measurements of graphene (GN), CNT, and graphene–CNT aerogel (GN–CNT), respectively. Reproduced with permission of Elsevier from (Kabiri et al. 2014)

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Fig. 7

Digital photographs showing a the packed plastic tube of graphene–CNT aerogels and b–e the progress of the continuous adsorption and removal of gasoline from a non-turbulent water–oil system. Reproduced with permission of Elsevier from (Kabiri et al. 2014)

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Clay-based aerogels combine the hydrophobicity of organo-clays with the large porosity of the aerogels making them an interesting candidate for oil spill clean-up. Various amounts of montmorillonite (MMT), sodium dodecyl sulfate (SDS), and polyvinyl alcohol (PVA) were tested to synthesize clay-based aerogels (Fig. 8) (Rotaru et al. 2014). The absorption capacity determined under the optimal conditions was 23.6 g g−1 for dodecane and 25.8 g g−1 for motor oil. The process of absorption of dodecane on water with the synthetized aerogel is shown in Fig. 9. The percentage of recovery of the absorbed oil was estimated by free drainage (from 1.06% to 14.9%) followed by centrifugation of the absorbent (from 42.3% to 66.0%). This study reveals the high absorption capacity, hydrophobicity (116°), and the possible recycling of the aerogel under the optimal conditions of synthesis.

Fig. 8

Pillow-type sorbent (P-M17) consisting of clay polymer aerogel (M-17) surrounded by hydrophobic polypropylene (PP) nonwoven fabric as containment barrier. a Top view. b Cross-sectional view. Reproduced with permission of Elsevier from (Rotaru et al. 2014)

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Fig. 9

Pictures showing the application of the pillow-type sorbent (P-M17) for oil spill clean-up. a Sudan IV dyed dodecane spilled onto water surface (oil slick layer of 2.5 mm). b Addition of P-M17 pillow sorbent and dodecane sorption after 10 s contact time. c Dodecane sorption after 15 min contact time. d After separation. Reproduced with permission of Elsevier from (Rotaru et al. 2014)

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3.3

Polymers

The polymeric absorbents such as polyurethane, polypropylene, polyethylene, and cross-linked polymers are the most commonly absorbent for oil spills. Due to their high porosity, absorbent capacity and hydrophobicity, these polymers have been widely used for the absorption of organic compounds. Thus, innovations in this area have become imperative. The creation of novel polymeric systems like polymer-based absorbent (Keshavarz et al. 2015; Li et al. 2012; Liu et al. 2015b; Nikkhah et al. 2015; Zhou et al. 2015; Zhu et al. 2015), polymer absorbents (Kundu and Mishra 2013; Lin et al. 2008; Zhang et al. 2013) and polymeric coatings (Chen et al. 2013; Machado et al. 2006) of different materials are reported. Thus, a common and suitable process was creating an absorbent on the basis of carbon nanotubes and polyurethane (Wang et al. 2015). This absorbent presented superhydrophobicity and a high absorption capacity (34.9 times its own weight). The synthesis method consists of the oxidative self-polymerization of dopamine followed by a reaction with octadecylamine. The mechanical strength of the absorbent was improved by the deposition of carbon nanotubes on the sponge skeleton. The recyclability of the as-prepared absorbent was 150 times without losing its high absorption capacity.

Also, the uses of polymer-coated materials are very common, in particular those having magnetic properties. Thus, the two-step synthesis of magnetic nanoparticles (Fe3O4) coated with polystyrene was carried out and the products were tested as oil absorbents (Chen et al. 2013). The hollow Fe3O4 nanoparticles and the polystyrene-coated Fe3O4 nanoparticles are shown in Figs. 10 and 11, respectively; the use of this polymer on the magnetic nanoparticles generates a hydrophobic property that enhances the oil absorption of the composite. The magnetic properties of the coated nanoparticles were used to remove oil from water using a magnet (Fig. 12). Due to its hydrophobicity, this nanocomposite presented a selective absorption exclusively for the oil. The absorption capacity of its coated nanoparticles was shown to be 3 times its own weight. Furthermore, the oil could be removed from the nanocomposite implementing a simple treatment and does not affect its future performances.

Fig. 10

TEM images (a, b) and SEM images (c, d) of hollow Fe3O4 nanoparticles. Reproduced with permission of Elsevier from (Chen et al. 2013)

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Fig. 11

TEM images (a, b) and SEM images (c, d) of Fe3O4@PS nanocomposites. Reproduced with permission of Elsevier from (Chen et al. 2013)

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Fig. 12

Photographs of the removal of lubricating oil from a water surface by Fe3O4@PS nanocomposites under the magnetic field. The lubricating oil was labeled by Sudan I dye for clarity. Reproduced with permission of Elsevier from (Chen et al. 2013)

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An easy polymerization of poly(dimethylsiloxane) (PDMS) was achieved using sugar to make a porous material that can absorb larger oil quantities at less time (Zhang et al. 2013). This synthesis involves PDMS, p-xylene, and sugar (coarsely granulated sugar, CGS; finely granulated sugar, FGS; soft sugar, SS). A porous skeleton was created (Fig. 13), and the absorption capacity, hydrophobicity, and recyclability of the processes were evaluated. The absorbent presented an absorption capacity in the range of 4–34 g g−1 depending the oil and organic solvent. The recycling process showed a recyclability of 20 times losing only a little of its original absorption capacity. Furthermore, this synthesis method could be used to design novel polymeric absorbents.

Fig. 13

Scanning electron microscopy (SEM) images of sugar particles and PDMS oil absorbents. a–c CGS, FGS, and SS, respectively. d–h PDMS oil absorbents prepared by CGS, FGS, SS, a mixture of CGS and SS, and a mixture of FGS and SS, respectively. Reproduced with permission of ACS from (Zhang et al. 2013)

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3.4

Natural and natural-based products

The study of hydrophobic properties, absorption capacity, and buoyancy in absorbents has been increased over time since these properties are key features in the treatment of oil spills. Most common absorbent materials are based on polymers, which are oil-based. The aim of these innovations is to produce absorbents based on cheap and commercially available natural products. This area can be divided into two large groups, natural absorbents (Abdelwahab 2014; Behnood et al. 2013; Chen et al. 2013; Ifelebuegu et al. 2015; Machado et al. 2006; Muhammad et al. 2012; Rotar et al. 2014; Ribeiro et al. 2003; Sayyad Amin et al. 2015; Wahi et al. 2013; Zadaka-Amir et al. 2013) and natural-based absorbent products (Fu and Chung 2011; Galblaub et al. 2016; Raj and Joy 2015; Kudaybergenov and Ongarbayev 2012; Nwadiogbu et al. 2016; Okiel et al. 2011; Uzunov et al. 2012; Wang et al. 2013; Zang et al. 2015; Zhao et al. 2011). Natural absorbents are those that can be obtained in nature and are used without modifying their hydrophobicity properties, absorption capacity, buoyancy, etc. These materials are commonly used after a drying process to eliminate the water adsorbed on the structure of the material. Some selected works reporting the use of natural absorbents are listed in Table 1.

Table 1 Materials on the basis of natural absorbents

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The natural-based absorbents are natural absorbents with a modified surface using different types of materials or by a change on the chemical composition of their surface to achieve a better hydrophobicity and, oil absorption capacity. The modification of these materials can be carried out by methods such as CVD, dip-coating, pyrolysis, etc. In Table 2 are presented several reports in this field (Figs. 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25).

Table 2 Natural-based reported materials

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Fig. 14

Images showing the morphology of a the EV and b the as-obtained EV/CNT hybrids after a 120-min reaction; SEM images showing the morphology of c the EV and the EV/CNT hybrids with a CNT content of d 11.4% in EV/CNT-5 for a 5-min reaction, e 33.1% in EV/CNT-30 for a 30-min reaction, f 67.6% in EV/CNT-60 for a 60-min reaction, g 91.0% in EV/CNT-90 for a 90-min reaction and h 94.8% in EV/CNT-120 for a 120-min reaction; i TEM and inserted high-resolution TEM images showing the tubular structure of the CNT in the EV/CNT hybrids. The EV layers in d–h are indicated by white arrows, while the aligned CNT arrays in d–h are indicated by black arrows. Reproduced with permission of Elsevier from (Zhao et al. 2011)

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Fig. 15

Cross-sectional FE-SEM images of cotton fibers and CCFs with hollow structures. a, b CCFs-400. c CCFs-600. d CCFs-800. e CCFs-1000. f Cotton fibers. Reproduced with permission of ACS from (Wang et al. 2013)

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Fig. 16

Floating-ability test of CCFs-400 after crude oil sorption. a Crude oil on the water surface. b CCFs-400 sorbents placed on the spill area. c CCFs-400 starting to adsorb oil. d Crude oil adsorbed by CCFs-400. e CCFs-400 floating on the surface after crude oil sorption. f Cleaned water surface. Reproduced with permission of ACS from (Wang et al. 2013)

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Fig. 17

Photographs of a behavior of a water droplet on pristine sawdust, b behavior of a water droplet, and c oil droplet on as-prepared superhydrophobic/superoleophilic sawdust. Reproduced with permission of Elsevier from (Zang et al. 2015)

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Fig. 18

The process of resulting sawdust product as an oil sorbent for the separation of water and gasoil mixture. a As-prepared superhydrophobic/superoleophilic sawdust. b Water and gasoil mixture (gasoil was colored with Sudan III for clear observation). c All given red gasoil was absorbed and red sawdust floated on the water. d After adsorption, the sawdust filled with red liquid was separated. Reproduced with permission of Elsevier from (Zang et al. 2015)

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Fig. 19

a Superhydrophobic recycled cellulose aerogel. b Flexibility of the large-scale cellulose aerogel (38 cm × 38 cm × 1 cm) containing 0.60wt% of the cellulose fibers. SEM images of the cellulose aerogels with different ratios of cellulose fibers (wt%) and Kymene (μl): c 0.25:5, d 1.00:5, e 0.60:5, and f 0.60:20. Reproduced with permission of Elsevier from (Feng et al. 2015)

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Fig. 20

Oil absorption process of the recycled cellulose aerogel having 5.0wt% of the cellulose fibers in the artificial seawater (3.5% NaCl and pH 7) mixed with the 5w40 motor oil and dyed with Sudan Red G before testing. Reproduced with permission of Elsevier from (Feng et al. 2015)

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Fig. 21

Preparation of MCF aerogel (a–d I hydrothermal treatment; II freeze-drying process; III pyrolysis), the morphologies of aerogel before and after thermal treatment (e, f bamboo fiber aerogel; g, h MCF aerogel), and nitrogen adsorption–desorption isotherm of MCF aerogel (i). Reproduced with permission of RSC from (Yang et al. 2015a)

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Fig. 22

Surface wettability of aerogels to different probe liquids. a Adsorption of water stained with methylene blue by fiber aerogel. b Water droplets on a MCF aerogel. c Interaction between MCF aerogel and liquid after immersing into water. d, e Behavior of water and oil droplets on MCF aerogel. Reproduced with permission of RSC from (Yang et al. 2015a)

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Fig. 23

Recyclability of MCF aerogel using different methods and corresponding morphologies after cyclic operation for 6 times. a, b Hexane-adsorbed MCF aerogel recycled by distillation. c, d Hexadecane-adsorbed MCF aerogel recycled by combustion. e, f Gasoline adsorbed MCF aerogel recycled by squeezing). Reproduced with permission of RSC from (Yang et al. 2015a)

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Fig. 24

Photographs showing the regeneration of MCF aerogel via combustion (a) and squeezing (b). Reproduced with permission of RSC from (Yang et al. 2015a)

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Fig. 25

Selective oil sorption from the oil/water mixture by PDMS-coated absorbent cotton. a The set-up of home-built oil-filter. b Oil remained on the SiO2 layer after the sorption process pump oil (dyed red) without filter. c–e The sorption process using the filter fabricated with the dip-coated absorbent cotton. f Filtered clean water in the beaker after the sorption process. Reproduced with permission of Elsevier from (Lee et al. 2016)

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Oil absorbents are materials that are designed to quickly soak up oils and other hydrocarbon liquids. This makes them ideal for use in a variety of settings, from the workshop to the kitchen.

There are many different forms of oil absorbent available, each with its own set of benefits. But what exactly is oil absorbent made of? And what are the different types of absorbents for oil clean up?

Read on to learn more as we explore the common types of absorbent materials—including natural organic and synthetic options—and how they are used for cleaning up oil spills.

What Are Oil Absorbents?

Oil absorbents are commonly used in industrial applications such as spill cleanup or removing oil from water. Which is why they are also a staple component of spill kits.

These spill absorbents can come in many different forms and application methods, but are typically white in color. Some examples are oil absorbent mats, socks, booms, and pillows.

Often, sorbents for oil spills have special oleophilic and hydrophobic properties. Meaning they attract oil and repel water. While less specialized absorbent materials include cloth rags, shop towels, and granular products similar to cat litter.

Regardless of type, oil absorbent products are used to soak up hydrocarbons like gasoline. Hence why they are essential to sites that store and handle oily fluids, like automotive shops and boat yards or marinas.

You can more easily deal with an oil spill by using oil absorbent. Which is important because potential safety hazards are present when leaks, drips, spray, or spills occur. Not to mention, Operational Safety and Health Administration (OSHA) standards require workplaces to be clean and free from hazardous material spills.

What Are Oil Absorbents Made From?

As already mentioned, oil absorbents come in different shapes and sizes. And they are made from a variety of sorbent materials. For instance, organic compositions—think peat moss and clay—as well as synthetics like polypropylene.

Some common types of absorbent materials include:

• Polypropylene (PP) – This is a synthetic polymer that has good oil absorption properties.
• Natural fibers – These are made with things like wood pulp, cotton, or flax fiber.
• Synthetic fibers – Which includes man-made materials like acrylic, nylon, or polyester.

Each type has its unique absorbency properties and uses. We’ll discuss a few of the different types next.

What Are Oil Absorbent Pads Made Of?

Oil absorbent pads, mats, and rolls are often made of varying thicknesses of polypropylene. These products are technically textiles but repel water. The pads can be woven together from single or multi-layers of polypropylene fibers.

Oil absorbent mats can be made of one or more layers of polypropylene material

Mats can be purchased in rolls or cut into individual pieces depending on the size of the spill you are dealing with. Unlike paper towels, they do not dissolve and have strong tear and abrasion resistance.

Widely used in spill response, absorbent mats and pads are usually placed over the top of oily liquids. Oil absorbing pads are very easy to use and do not leave dust behind, unlike granular absorbents.

Whether you’re dealing with a small spill or a major cleanup, oil absorbent pads can help to keep the mess under control.

What Are Granular Sorbents Made With?

Loose granular absorbent comes in several types but usually look like coarse sand. The granules are often made from recycled or natural, biodegradable compounds.

Unlike common cat litter, granular absorbents do not contain crystalline silica; a substance which is known to cause lung disease.

You can choose different packaging and dispensing methods, from small shaker containers to large sacks.

When you sprinkle the granules on an oil spill, it absorbs the oil and allows it to be swept up. However, this is can sometimes be a less effective and messy way to clean up spills.

Corn Cob

Corncob makes a great eco-friendly option for absorbing oil spills. As you might have guessed, this sorbent is made from ground-up corn cobs. It is also quite inexpensive, and comes packaged in large bags.

The granules are able to hold up to four times its weight in a variety of liquids, including oil. It is biodegradable and also safe to incinerate.

Peat Moss

Another all-natural and environmentally absorbent is peat moss. This plant-based material is biodegradable, incinerable, and comes packaged in bales.

Because it will not absorb water, it is ideal for cleaning up oil spills on water or land.

Gran-Sorb

This cellulose product is 100% biodegradable and is made from paper mill waste. It is versatile and works well on oils, lubricants, gasoline, and more.

Sold in large bags, Gran-Sorb is a popular option to pour over and soak up automobile fluids.

Super Sorbent

With a formula certified free of hazardous materials, Super Sorbent is lightweight and non-toxic. In addition to oil, it is suitable for other types of chemical spills such as coolants, and solvents.

A shaker container quickly dispenses this granulated universal absorbent. Making it ideal for routine maintenance tasks, and small leaks.

What Are Absorbent Pillows, Socks, and Booms For Oil Spills Made From?

Like oil absorbent pads, booms, socks and pillows are largely made with polypropylene fillers. All of these absorbent products have a synthetic fabric or mesh outer casing for additional strength.

Sorbent socks are also available that contain eco-friendly corn cob filler. We described this unique natural material above, in the loose granular absorbents section. Because corn cob socks absorb all kinds of liquid spills, they are not a good choice for using in or around water.

On the other hand, poly-blend oil absorbent socks and booms are perfect for tackling hydrocarbon spills in marine locations. They come in different size diameters and lengths and are flexible. Meaning you can easily shape socks around motors to deal with potential equipment fuel leaks.

Final Thoughts

There are many options for absorbents when it comes to spill response and clean up. Oil absorbents are often made of man-made polymers as well as natural fiber sorbent materials.

Some oil sorbents are better suited for certain situations than others. Be sure to research each option thoroughly before making a purchase. Take into consideration what kind of spill you might encounter, how much time you have to deal with it, and if there will be any residual cleanup required after the spill is removed.

We hope that this article has given you an insight into what oil absorbents for spill cleanup are and what they are made of!

If you want to learn more, please visit our website oil absorbent felt.