Adsorption

Fact Sheet - Adsorption

   
 
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This fact sheet describes technologies that remove oil and organics by adsorption onto different types of media. Adsorption technologies can quite effectively remove most organic materials from produced water. Adsorption is generally utilized as a polishing, rather than a primary or secondary treatment step. This avoids rapid loading of the adsorption media, which fill up at a rate proportional to the concentration of organic compounds in the influent. Once the media become fully loaded, they must be regenerated or disposed of. Four types of adsorbent materials are covered here — organoclay, activated carbon, MyCelx, and zeolite.

Photo of organoclay cartridges.
Organoclay cartridges for offshore use; Source: CETCO Oilfield Service Co.
 
Organoclay cartridges on Texas A&M produced water treatment trailer.
Organoclay cartridges on Texas A&M produced water treatment trailer; Source: J. Veil, Argonne Nat'l Lab.
 
Photo of organoclay columns.
Organoclay columns in lab demo; Source: J. Veil, Argonne National Laboratory.
 
Flow chart.
Flow chart showing how organoclay can help achieve compliance on variable quality effluent; Source: CETCO Oilfield Service Co.
 

Organoclay

Organoclays are manufactured by modifying bentonite clay with quaternary amines. Organoclay mixtures are effective at attracting and adsorbing a wide range of hydrocarbons. They can be designed to attract and adsorb more than their own weight in organic compounds (Ali et al. 1999, Occhipinti et al. 2007). Several companies supply cartridge filters containing different types of granular organoclays.

Some of the advantages of organoclay cartridge technology include:

  • Uses an adsorption process that does not require chemicals;
  • Has a performance record that is unaffected by droplet size;
  • Does not require a power supply;
  • Increases oil recovery rates and ensures maximum platform productivity;
  • Removes total petroleum hydrocarbons (TPH) and other soluble components;
  • Is unaffected by surges.

Depending on the discharge standard, different levels of organoclay treatment are used. The cost of treating is somewhat proportional to the amount of oil removed. As an example, the U.S. produced water discharge standard for oil and grease in the Gulf of Mexico is 29 mg/L. If an operator can achieve 35 mg/L using other treatment devices, it may employ organoclay to remove incremental levels of oil and grease. It is not necessary to achieve 15 mg/L or 10 mg/L; the cost to reach those levels may be prohibitive. The operator may treat using enough organoclay to reach 20 mg/L or 25 mg/l. This allows compliance plus some cushion to account for variation.

Once organoclay cartridges become fully loaded, they must be brought back to shore for disposal. At present, cost-effective methods for recycling or reusing the cartridges are not available.

Activated Carbon 

Activated carbon has been used for decades in wastewater treatment operations. It effectively removes many organic chemicals, in part due to its very large surface area. Activated carbon is typically employed in large pressurized vessels. Compared to organoclay, it does not adsorb as much organic material per unit volume. This means that larger volumes (and weights) of activated carbon are needed to remove the same amounts of organic materials. Because space and weight are at a premium on offshore platforms, activated carbon is not used extensively in offshore installations. Unlike organoclay, however, activated carbon can be regenerated and used again, although the regenerated material may not have the same adsorptive capacity as fresh activated carbon.

Organoclay and activated carbon are sometimes used in sequence. For example, Doyle et al. (1997) describe onshore tests at the Rocky Mountain Oilfield Testing Center. Project operators used three adsorption canisters in serial arrangement to treat produced water. The first two contained organoclay, and the third contained activated carbon. The results showed that total petroleum hydrocarbons (TPH) and oil and grease were removed to nondetectable levels. BTEX (benzene, toluene, ethylbenzene, and xylene) was reduced to very low levels.

MyCelx
MyCelx is a patented molecule that has a strong affinity for hydrocarbons (Harikrishnan 2010). It can be coated on the outside of different types of filter media (e.g., cartridges, sheets, etc.). The reaction between MyCelx and hydrocarbons is nearly instantaneous. There is no desorption or leaching as the process permanently captures oil on the filter media. In a lab demonstration at a Texas A&M University workshop in August 2010, the author of this fact sheet observed the removal of crude oil from a beaker of water. The demonstrator inserted a rod coated with MyCelx into the beaker. Immediately, the liquid crude formed a highly viscous mass on the rod. The rod was lifted up, taking the oil with it (see photo).

photo showing Liquid crude oil collected into viscous mass using MyCelx
Liquid crude oil collected into viscous mass using MyCelx.

MyCelx can serve as a polishing material before discharge or as a pretreatment step before reverse osmosis. It can remove oil and grease to levels below 10 mg/L and is effective at removing dissolved organics.

Filter cartridges hold from 5 to 8 pounds of oil and are not affected by influent loading rates. Used filter cartridges can be incinerated or disposed of in some other manner (Harikrishnan et al. 2009).

Zeolite 
Zeolite is a natural mineral composed primarily of clinoptilolite. It has a cage-like structure with a high affinity for adsorption. The external surface of zeolite can be treated with surfactants to improve its attraction for organic compounds.

Researchers from several institutions have collaborated to study the effectiveness of surfactant-modified zeolite (SMZ) in removing BTEX from produced water (Ranck et al. 2002, Katz et al. 2005, Sullivan et al. 2006). They concluded that SMZ was capable of removing BTEX from produced water. Moreover, SMZ was amenable to numerous cycles of regeneration without loss of BTEX capacity. The researchers developed a vapor-phase bioreactor (VPB) to treat the vapor-phase BTEX released during regeneration of the SMZ. The system was found to be resilient to spikes, although loss of efficiency may require dilution of the influent stream at the initial period of regeneration depending on the off-gas effluent limitations at a site. The recovery time after periodic shutdowns depended on the length and frequency of the shutdown. Laboratory studies are continuing, with field trials expected late in 2007.

References 
Ali, S.A., L.R. Henry, J.W. Darlington, and J. Occhipinti, 1999, "Novel Filtration Process Removes Dissolved Organics from Produced Water and Meets Federal Oil and Grease Guidelines, presented at the 9th Annual Produced Water Seminar," Houston, TX, January 21-22.

Doyle D.H., F. Daniel, and A.B. Brown, 1997, "Field Test of Produced Water Treatment with Polymer Modified Bentonite," paper SPE 38353, presented at the 1997 Rocky Mountain Regional Meeting, Casper, Wyoming, May 18-21.

Harikrishnan, P., 2010, “MyCelx Produced Water Polisher Technology Removal of Oils and Water Soluble Organics,” presented at the 20th Produced Water Seminar, Houston, TX, January 20-22, 2010.

Harikrishnan, P., R. Schlicher, and J. Yu, 2009, “Deoiling for Discharge-Quality Water,” World Oil, December issue.

Katz, L.E., and K.A. Kinney, 2005, "Treatment of Produced Water Using a Surfactant Modified Zeolite/Vapor Phase Bioreactor System," presented at the Fall 2005 PERF Meeting, Annapolis, MD, November 1-4. Available at http://www.perf.org/pdf/katz.pdf.

Occhipinti, J., J. Hugonin, T. Power, and J. Darlington, 2007, "Produced Water Polishing Promotes Compliance During Conventional System Upsets," presented at the 14th International Petroleum Environmental Conference, Houston, TX, November 5-9. Available at http://ipec.utulsa.edu/Conf2007/Papers/Darlington_84.pdf.

Ranck, J.M., J.L. Weeber, G. Tan, E.J. Sullivan, L.E. Katz, and R.S. Bowman, 2002, "Removal of BTEX from Produced Waters Using Surfactant Modified Zeolite," presented at the 9th International Petroleum Environmental Conference, Albuquerque, NM, October 22-25. Available at http://ipec.utulsa.edu/Conf2002/ranck_bowman_32.pdf.

Sullivan, E.J., L. Katz, K. Kinney, S. Kwon, L.-J. Chen, E. Darby, R. Bowman, and C. Altare, 2006, "Pilot Scale Test of A Produced Water Treatment System for Organic Compounds," presented at the 13th International Petroleum Environmental Conference, San Antonio, TX, October 17-20. Abstract available at http://ipec.utulsa.edu/Conf2006/Abstracts/Sullivan_69.pdf.

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