Effluent Caustic Treating Systems Utilizing
MERICON^SM Technologies

1. Overview

2. Types of Used Caustic

2.1 Sulfidic Caustic

2.2 Cresylic Caustic

2.3 Naphthenic Caustic

3. Effluent Caustic Management

4. Wet Oxidation Chemistry

4.1 Partial Oxidation

4.2 Total Oxidation

5. Neutralization Chemistry

6. MERICON^SM Technologies

6.1 MERICON I^SM—Partial Oxidation

6.1.1 Process Description

6.1.1.1 Oxidizer and Scrubber Systems

6.1.1.2 Neutralization System

6.2 MERICON II^SM—Total Oxidation

6.2.1 Process Description

6.2.1.1 Reactor System

6.2.1.2 Neutralization System

6.3 MERICON III^SM—Deep Neutralization

6.3.1 Process Description

6.3.1.1 Deep Neutralization and 3-Phase Separation

6.3.1.2 Stripping Column and Acidified Brine Neutralization

6.3.1.3 Enhanced Phenol Extraction

7. Commercial MERICON^SM Installations

8. Advantages of MERICON^SM Technologies

1. Overview

Today, refineries and petrochemical plants around the world are facing stricter controls on liquid and gas effluent discharge streams that can cause air or water pollution. Sodium hydroxide (caustic) continues to be one of the primary reagents used in refineries and petrochemical plants to extract hydrogen sulfide, mercaptans and organic acids from hydrocarbon streams because it has been proven safe, economical, effective and, above all, environmentally acceptable. When properly recycled, treated or disposed, used caustic streams do not constitute hazardous waste.

Used caustic solutions coming out of hydrocarbon treating systems are liquid effluents that, if discharged directly to the natural waterways, could contaminate and adversely affect drinking water quality and aquatic populations. Alternatively, if these used caustic solutions are discharged directly into the wastewater treatment plant (WWTP) they can create a burdensome chemical and biological oxygen demand (COD and BOD). Therefore used caustics are normally converted to a form that minimizes the load on the WWTP or sold to chemical companies as a process feedstock.

The first approach to reducing the environmental and remedial challenges of used caustics is to minimize their production by way of more efficient treaters, caustic regeneration and/or reuse. Unfortunately, not all refinery or petrochemical plant caustic discharges can be regenerated and, therefore, they must be disposed of either with the plant effluent waters or through an outside company or sold as a chemical feedstock.

For the past 55 years, Merichem Company has been processing effluent refinery and petrochemical plant caustics in an environmentally sound manner at its two USA plants as chemical feedstocks used in the production of specialty chemicals. These specialty chemicals are used as raw materials in chemical plants to manufacture products such as plastics, pharmaceuticals, pesticides, building products, electrical wire coating, paper and minerals. Unfortunately, the volume and location of some used caustic streams make the economics of sending them to Merichem unattractive. Therefore, most refineries and petrochemical plants must manage the proper handling of their caustic solutions on their own. The following presentation assumes that the producer has chosen onsite treatment of used caustics and, subsequent, discharge of the brine effluent into the WWTP.

Table 1 displays the most common compounds found in used caustic streams produced in refineries.

An important design consideration for all used caustic processing systems is metallurgy since corrosive environments are normally encountered. Merichem has over 55 years of in-house experience selecting proper metallurgy for used caustic processing.

MERICON^SM technologies are treating processes offered by Merichem Chemicals and Refinery Services LLC (MCRS), a wholly owned subsidiary of Merichem Company to treat used caustic solutions onsite. The specific type of MERICON^SM process required depends on the components contained in the used caustic solutions and the specifications that must be met in the brine solutions being discharged to the WWTP. Although not the focus of this paper, MCRS also offers neutralization systems when pH is the only brine effluent requirement.