Fact Sheet - Adsorption

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. Three types of adsorbent materials are covered here — organoclay, activated carbon, and zeolite.

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, Smith et al. 2002). Several companies supply cartridge filters containing different types of granular organoclays.

	Organoclay cartridges on Texas A&M produced water treatment trailer; Source: J. Veil, Argonne National Laboratory.

	Organoclay columns in lab demo; Source: J. Veil, Argonne National Laboratory.

	Organoclay cartridges for offshore use; Source: CETCO Oilfield Service Company.

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.

	Flow chart showing how organoclay can help achieve compliance on variable quality effluent; Source: CETCO Oilfield Service Company.

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.

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.

Smith, J.J., J. Occhipinti, J.W. Darlington, T.F. Marcotte, W.J. Zenon, and M. Berger, 2002, "Produced Water Polishing," CETCO Offshore Technology Brochure, December. Available at http://www.touchbriefings.co.uk/pdf/25/cetco.pdf.

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.

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.

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.