Table 841 Disposal Or Recovery Of Phenolic Spent Caustics



Operating Information or Conditions

Beneficial Characteristics

Possible Adverse Characteristics

Sale of Phenolic Causticsb

Flue Gas Neutral-

d ization

Mineral Acid Neutralizatione


Deep Well Disposal

Biological Oxidation

Ocean Dumping

Phenolic caustics are sold to a commercial plant specializing in the recovery of valuable cresylic acidsc, thio-phenols, aromatic disulfides, and sodium salts.

After contacting with flue gas in a batch or continuous system, cresylic acids and thio-phenols phase separate from the Na2CO3 which is formed. Sulfides and mercaptans are carried overhead with the flue gas.

After neutralization, cresylic acids and thiophenols phase separate from the sodium salt solution. Considerable H2S and mercaptans stay in solution, unless stripping steam is used. Process can be batch or continuous.

Phenolic caustics can be burned simultaneously with other oily wastes in a fluid bed incinerator.

Spent caustics are pumped into a deep underground formation with impervious rock above and below.

Small quantities of dilute caustics can be mixed with contaminated wastewaters and be biologically degraded.

Spent caustics are dumped about 100 miles offshore in federally approved areas.

Concentrated caustic (25-30°Be') should be used for gasoline treatment to minimize spent caustic shipping charges. Phenolic caustics should be segregated from sulfidic caustics.

Neutralization tower operates at about 180°F and 2-5 psig. Flue gas and steam strip most of the H2S and mercaptans from solution. Final pH is above 8.5.

The pH is usually reduced to 3-4. Stripping steam is used to ensure maximum liberation of H2S and mercaptans. Operating pressure is essentially atmospheric.

Incinerator operates at 1200°-1500°F. Na2CO3, Na2SO4, and ash are withdrawn from the incinerator and hauled to a landfill.

Caustics must initially be tested to determine if they are compatible with the formation.

Aerated lagoons, activated sludge, and trickling filter units can be utilized.

Wastes are diluted with sea water or discharged so they sink.

Phenolic caustics can be sold at a profit for the refiner. A commercial recovery plant is more capable of preventing pollution problems from developing during processing of spent caustics.

Flue gas is more economical than mineral acids. Cresylic acids and thiophenols are recovered for sale. The final pH is above 8.5 and corrosion problems are not as severe as when using mineral acids.

Valuable cresylic acids and thiophenols are recovered for sale. Resulting sodium salt solution may be less contaminated than with flue gas neutralization.

Sulfur, in the thiophenols, H2S and mercaptans, reacts to form Na2SO4. Odors are not a problem since complete combustion occurs.

Daily operating attention is minimized. There are no byproducts to be sold.

This method is limited to small quantities of dilute caustics.

Low cost

Shipping charges may be excessive for some locations. Gasoline treatment facilities may need to be revised in some refineries before switching to concentrated virgin caustic.

The Na2CO3 solution is usually contaminated with phenols, thiophenols and H2S. If this solution cannot be sold, a serious disposal problem still exists. The process is subject to foul odors. Burning of H2S and mercaptan off gases produces SO2 emissions.

Low pH requires corrosion resistant construction material. Reagent costs are higher. If the contaminated salt solution cannot be sold, a serious disposal problem still exists. This process has the same odor and SO2 problems as flue gas neutralization.

Installation of a fluid bed incinerator is very expensive. Flue gas must be cleaned to prevent particulate emissions. Na2CO3 and Na2SO4 may leach into the soil during rainfall.

Groundwater contamination is possible if formation is not tightly sealed. Plugging may occur in the formation if chemical reactions occur.

Spent caustics are toxic to biological organisms at low concentrations. This method increases dissolved solids in the plant effluent and creates severe odor problems.

Spent caustic is toxic to some sea creatures if concentrated sufficiently.

aMethods are listed in descending order of overall ability to recover or dispose of phenolic caustics.

bThe Merichem Company purchases phenolic caustics.

cCresylic acids = phenols, cresol isomers, and xylenol isomers.

dSome NaHCO3 is formed simultaneously with Na2CO3.

eH2SO4 or HCl can be utilized.

FIG. 8.4.1 Typical flue gas neutralization system for phenolic caustic.

to 10,000 (Beychok 1967) ppm phenolics and 3,000 ppm H2S. Therefore, it must be purified and concentrated into a salable product. H2S and mercaptan off gases may create air pollution in the form of sulfur dioxide if burned. These gases, plus thiophenols, create severe odor problems if leaks or spills occur.

These problems can be solved by large commercial plants specializing in the recovery and marketing of phenolic caustic products. Such firms purchase concentrated spent caustics from numerous refineries. In most cases the refiner can actually profit from the sale of the waste materials (Price 1967).

In caustic treatment, a fluidized bed incinerator converts caustic to sodium carbonate and sodium sulfate without creating air pollution (EPA).

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