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Cotton: a renewable resource for oil spill cleanups.

cotton has great potential for use in sorbent products for oil spills; nonwovens can be used, but some education and technological innovations must pave the way for future acceptance

The first question that must be addressed when considering sorbent systems concerns the advisability of adding an additional component to an oil spill. Practical experience has shown that such as addition is desirable. The purpose of the sorbent is to facilitate a change of phase. It is not difficult to pick up oil once it is within a sorbent structure. Since the sorbent oil mixture has decidedly different physical properties than those of a fluid, this will aid in retrieval operations.

Another benefit of using a sorbent is its ability to capture and retain oil for retrieval at a later time. This may be a major advantage due to the rapid initial rate of spreading of oil slicks on water. It is desirable for the oil sorbent mass to be highly oleophilic and hydrophilic, which facilitates later retrieval.

Additional advantages of a properly chosen sorbent are selectivity, effectiveness and general applicability. A sorbent should pick up at least 90% of the oil confronted and, of the fluid removed from the water surface, at least 90% should be oil.

This latter capability can have a very significant impact on the design of on-board storage and processing facilities. Finally sorbents can function with oil slicks of varying thicknesses and viscosities. Such a property is essential to allow the design of general systems that can handle a majority of spill situations. Sorbents have physical properties that make their use in oil spill clean up attractive. Data has shown that cotton has an unusually high potential for use in sorbent systems.

In order to be able to effectively compare different sorbents, it is desirable to specify the characteristics that would be associated with an ideal sorbent.

The function of the sorbent is to induce a separation between the oil and water such that the oil can be easily recovered; because of this, it should be highly oleophilic, which, since like frequently attracts like, suggests that the surface of the sorbent should be a carbon derivative.

It is also desirable that the sorbent be selective with respect to the fluid it absorbs. A sorbent that simply acts as a sponge will be effective with respect to oil removal, but it will also recover significant amounts of water. Since this water must then be processed by the retrieval device, this would impact directly upon its design. Ideally a sorbent would selectively remove the oil from the surface and reject almost all of the water.

The oil removal capability of a sorbent should be large, both on a unit mass and a unit volume basis. The latter should particularly be considered if the spill is located in a remote region that involves difficult transport problems. It is important to recognize that an ideal sorbent should be able to capture a large amount of oil as well as retain a significant percentage of this material during sorbent recovery. Since an oil spill spreads very rapidly, circumstances may well arise in which the purpose for sorbent distribution is spill containment. In order to effectively capture adjacent oil, the sorbent must have the capability of drawing the oil into the material matrix. This is most conveniently accomplished by exploiting capillary phenomena. This in turn suggests that an ideal sorbent have a porous structure with a large surface area to weight.

After the oil has been captured it is desirable to be able to easily remove the oil sorbent mass from the surface of the water. Therefore ease of recovery is an important property of an ideal sorbent. This may not be a serious restriction since the recovery system may be quite primitive. In general, an ideal sorbent will sorb such a large quantity of oil has that material being picked up from the surface will have physical properties between those of a solid and a fluid. As noted earlier, this change in physical properties can markedly improve the ease of sorbent oil retrieval.

Finally, it is essential that the sorbent and its degradation products be non-toxic to the environment. This will ensure that there is no permanent damage to the ecosystem as a result of the utilization of the sorbent even if a fraction is not recovered. In summary, an ideal sorbent should have the following characteristics:

--high oleophilic and hydrophilic properties

--large oil removal capability on a unit mass and unit volume basis.

--high oil sorption rate

--large surface to volume ratio

--good buoyant properties, both as a dry and an oil-loaded sorbent

--ease of retrieval

--non-toxic and biodegradable.

Actual Sorbent Performance Criteria

A review of the manpower and capital resources of several oil spill clean up companies suggests that the primary requirements for an actual sorbent are that it must be usable in a relatively simple, practical system that is low in cost. In addition, the sorbent must be readily available with respect to supply, storable without decomposition over long periods of time and reasonable in cost.

In order to minimize the mass that must be picked up, the sorbency of the material should have a very high ratio--around 20 pounds of fluid per pound of sorbent. In this event, 95% of the mass being removed from the water is fluid with the remainder being sorbent. Higher levels of sorbency are possible but the practical advantages are minimal.

Selectivity with respect to the fluid being removed is also a key variable. Preferably not more than 10% of the fluid picked up should be water. If the fraction that is water rises to a higher level, a secondary fluid separation system may be needed.

The physical parameters associated with the slick can also impact to some extent on the type of sorbent needed. If the slick is located in a very remote region that is not readily accessible to common transport, it may be essential that the sorbent be reusable. In these cases, a system that squeezes and redistributes the sorbent would be needed. However, when the problems associated with slick spreading and system sophistication are considered, reuse appears to have limited merits.

A sorbent must also be effective in handling a spectrum of crude types and slick thickness. Slick thickness in the range of 0.1 to 2.0 millimeters should be sorbable by the material. In addition, the sorbency should not be a strong function of the viscosity. With respect to floatability, the sorbent should be able to float indefinitely in order to facilitate recovery. If the sorbent "beaches," it should have the capability of retaining the oil it has absorbed.

The ecological impact of the sorbent should be such that the material is non-toxic to the environment if not recovered, as well as leading to non-toxic degradation products when disposed of in an incinerator, sanitary landfill or by bio-remediation. In addition, it is desirable that the sorbent be biodegradable. The sorbent should also lend itself to an economical retrieval process of the oil so that the sorbent can be recycled if desired.

Nonwovens Technology In Oil Spill Applications

Nonwovens have made a tremendous contribution through new and innovative products in recent times; Cotton Unlimited has used nonwovens technology to develop an oil sorbent material that meets the desirable characteristics.

The patented process takes advantage of cotton's natural absorbency and its water repellant characteristics as well. Raw cotton in its natural form has a waxy coating on the fibers that assist in repelling water; this in turn helps protect the cotton from mold and mildew. The cotton product then repels water and can float on either or salt water for an indefinite period of time.

The "InstaSorb" product is a highloft cotton web that offers structurally important characteristics. The small fibers create many small internal pores that increase wicking and retention. The saturating effect of oil into the cotton is caused by capillary action within the cotton web structure.

Wave action and salt water do not affect the stability of the encapsulation formed by the cotton. It is bonded and needlepunched to give it tensile strength. The resulting material has a weight of one half to one ounce per square foot. This flat material can be used in rolls, pads, sweeps or as an encasement into which raw cotton is blown. The boom or sock is then placed inside an all cotton knitted tube and cotton rope is run through the middle of the boom. This adds to the strength of the boom. The booms can then be used individually or connected to form a line or circle. The booms lend themselves to quick placement in order to block a directional flow of oil or to encompass a spill.

The material in roll form can be laid out on water or land to absorb spilled hydrocarbons. It can then be placed through a ringer or press to recoup and salvage the spilled product. Tests show that InstaSorb can be placed through a ringer at least five times and still retain its integrity. In this manner approximately 90% of the spilled oil can be picked up and salvaged.
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Title Annotation:excerpt from paper by Joseph Pate, Jr. presented at INDA-TEC'92
Publication:Nonwovens Industry
Date:Jun 1, 1992
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