How Graphene-Based Materials Can Be Used to Remove Contaminants from Water

Table of Contents

Introduction to Grafysorber
Advantages of Grafysorber
Applications of Grafysorber
How does Grafysorber Work on Visible Oil Slicks Floating on Water?
Dispersed and Dissolved Hydrocarbons

Introduction to Grafysorber

Grafysorber is an advanced technological solution for the removal of oils and hydrocarbons from contaminated water. This solution is based on an innovative adsorbent material family known as graphene plus (G+), which comprises pristine graphene nanoplatelets connected by the edges to form a porous and highly hydrophobic structure which is responsible for its unique adsorption capacity.

Grafysorber is made from natural graphite using a rapid thermal process based on a patented technology developed in its entirity by Directa Plus. This method can be scaled-up based on market demands.

Figure 1. Grafysorber macrostructure as loose adsorbent material

Grafysorber has been promoted by a Directa Plus project (GEnIuS – Graphene Eco Innovative Sorbent – ECO/12/332920), which is co-founded by the European Union within the program Eco-Innovation. The project began in June 2013 and will be completed in June 2015.

It has been chosen by the European Commission as one of the most successful Eco-innovative projects and was presented during the 18th Forum on Eco-Innovation (held in Barcelona, 20-21 May 2015).

Advantages of Grafysorber

The key advantages of Grafysorber compared with competitive materials and equipment in the market are listed below:

  • Higher and faster elimination of hydrocarbons down to 0.5 ppm
  • Higher and faster adsorption capacity of up to 80-90 g/g
  • Causes no toxicity for humans or the environment
  • Possibility of at least 80% adsorbed oil recovery
  • Reusability (in asphalts)
  • No flammability
  • Potential on-site and on demand production
  • Waste production reduced

Applications of Grafysorber

Grafysorber can be applied in the removal of the following:

  • Visible oil slicks floating on water – such as spills from oil tankers, tanks and bilge waters. Grafysorber has been approved by the Italian Environmental Ministry for marine oil spills decontamination activities.
     
  • Dispersed and dissolved hydrocarbons – oil droplets not visible to the human eye such as produced water or industrial contaminated water e.g., ground-water resulting from leakage of oil and refined petroleum products during extraction and processing operations.

How does Grafysorber Work on Visible Oil Slicks Floating on Water?

Grafysorber can be used as loose adsorbent material or placed inside specific containment means in cases where there is a high concentration of oil slicks on the water surface. Here the maximum adsorption capacity of Grafysorber strictly depends upon the type of oil – whether it is low viscous oils or high viscous oils, low viscous oils are faster to remove.

Grafysorber’s maximum adsorption capacity of (80-90 g/g in one minute as loose material) has been achieved with medium viscosity oils at room temperature. When Grafysorber is packed inside booms, the maximum adsorption capacity reduces to 50-60 g/g, however it is comparatively at least 2-3 times higher than other adsorbent materials (Bi et al., 2012).

Test conducted in marine and deionised water reveal that the high absorption capacity of Grafysorber is not impacted by pH conditions and salinity, therefore it can be used in many situations and environments.

Figure 2. Prototype of adsorbent boom filled up with Grafysorber tested during the inauguration of Graphene Factory (Directa Plus’ production plant) on 23rd June 2014. The test was performed with the supervision of Didier Gambier (The Head of Department Executive Agency EASME of European Commission). The boom is able to adsorb immediately 5 liters of diesel spilled on water.

Moreover, it has been shown that Grafysorber does not absorb water like other adsorbents, and hence it is able to float on the water surface, simplifying the recovery of spilled oil.

When Grafysorber is saturated, the oil can be recovered using various methods such as squeezing, filtration under suction, steam stripping, and centrifugation.

Another feature of Grafysorber is that it does not establish stable chemical bonds with other molecules, thereby supporting pollutants recovery during simple physical/mechanical processes. for the same reason, Grafysorber does not modify the quality of adsorbed oil, thus ensuring not only the recovery of a product without water but also with high quality.

Steam stripping is very effective method for oil recovery as well as sorbent recycling as it is capable of preventing the material morphology from being destroyed and allows for better rates of oil recovery. Grafysorber is highly sensitive to mechanical stress, thus easily becoming graphite after the application of pressure.

Exhausted Grafysorber can be utilized as filler in asphaltic bitumen, burnt in incineration plants (T > 850°C) or disposed in dumping grounds. Using Grafysorber as an additive in asphaltic bitumen is the most environmentally sustainable and added value method. According to different studies (Liantong et. al, 2005; Shao-peng et al., 2002-2005-2008), graphite is one of the most suitable additives for asphalts.

Adding Grafysorber can significantly enhance the electrical conductivity as well as impact other properties, such as mechanical ones (Liu et al., 2008; Liu et al., 2009).

Over the past decade, a number of research projects have been conducted to reduce or eliminate the formation of ice, snow or frost on roadways and bridge decks. One of the promising solutions is electrically conductive asphalt mixtures.

Electrically conductive asphalt is known to produce an automatic snow-melting surface due to the outstanding thermoelectric properties the material has. Because asphalt is an insulating material with high electrical resistivity, conductive additives must be chosen to lower the resistivity of the asphalt mixtures.

Another feature of Grafysorber is that it can improve the softening point of asphalts, thus providing mechanical reinforcement.

Several economic and environmental benefits can be obtained by the production and use of Grafysorber in oil spill clean-ups. Grafysorber also greatly reduces the impact of clean-up action on oil spilled areas. These factors are further discussed below:

  • Absence of flammability - Grafysorber is derived wholly from natural graphite, thereby making it completely non-flammable. This feature is very crucial as it can even be used in burning oil spills, thus preventing the discharge of toxic air pollutants.
     
  • Prevention in using toxic chemicals - The product used as a bulk loose material can prevent or restrict the use of several sinking agents, dispersants or other chemicals known to cause severe and chronic toxicity on ecosystems and negatively affect the health of humans.
     
  • Reduction of waste - due to Grafysorber’s high and swift adsorption capacity, reusability and recovery. Also the usage of large quantities of raw materials and energy resources are considerably reduced. Adsorbed oil can be easily recovered or burnt without any hazards such as the release of toxic substances (as Grafysorber particles do not contain any solvents), heavy metals or other harmful compounds. Therefore synthetic non-biodegradable adsorbents and natural adsorbents can be replaced by Grafysorber.

    Grafysorber is fully hydrophobic and insoluble in water, thus water cannot be absorbed. Hence oil and material flakes do not swell up and become heavier than water as other absorbents or chemicals like sinking agents do. In this manner, environmental pollution in oil spillage areas can be minimized. Another point is that oil is not easily released after adsorption, therefore restricting environmental impacts on storage areas.
     
  • On-site production - The scalability and flexibility of the Grafysorber production unit enables on-site production. Transportation costs could be limited.

Dispersed and Dissolved Hydrocarbons

Grafysorber can eliminate dispersed hydrocarbons (Total Petroleum Hydrocarbons - TPH) down to 0.5 ppm, and further, as loose adsorbent material arranged as filtering cartridge or placed within mixing tanks.

Two examples where G+ Basic can be applied as effective decontamination are described below:

  • Ground-water and site remediation – This contamination is likely to result from oil or refined petroleum leakage during their extraction, processing operations or transport to storage areas. A basic method frequently used for treating this type of contaminated water involves the adsorption process.

    The most frequently used adsorbent is activated carbons (AC). ACs have an adsorption capacity of a few grams of hydrocarbons per grams of adsorbent material (Ayotamuno et. Al, 2006). Grafysorber on the other hand can be used as an effective solution with an adsorption capacity approximately 2-3 times higher than ACs.
     
  • Produced water – During oil and gas extraction operations water is produced, which represents the industry’s most significant waste stream due to the sheer volume. This water however differs in quality and quantity but usually contains about 2000-100 ppm of dispersed hydrocarbons in the form of oil droplets.

    Conventional treatment equipment used to remove dispersed oil from water depends up on mechanical and physical principles such as gravity separation, gas flotation, centrifuge separation, and cyclonic separation (Henni et al., 2013).

    However, these methods are unsuccessful in removing very-small oil droplets which can be removed only via a filtration phase with AC, granular activated carbons (GAC), powdered activated carbons (PAC) or with chemicals and membranes. Grafysorber can be a resourceful substitute to all of these mechanical treatment methods.

This information has been sourced, reviewed and adapted from materials provided by DIRECTA PLUS S.p.A.

For more information on this source, please visit DIRECTA PLUS S.p.A.

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