Of TEXOX Process
Are Spent Caustics?
Are Spent Caustics Generated?
Of Spent Caustics
Characteristics Of Spent Caustics
Alternatives For Spent Caustics
Tragedy In The Ivory Coast - What Not To Do
An Introduction to Spent Caustic Chemistry, Treatment and Disposal
Spent Caustics are
the most difficult of all industrial wastes to dispose properly, with
the exception of radionuclide wastes. Since the dawn of petroleum
refining, caustic solutions containing sodium hydroxide (common lye) have been used to wash sulfur and other undesirable
compounds out of petroleum. Its use has been in
washing crude oils, intermediate fractions, and finished fuels
throughout the refining processes. The result of this washing is
the generation of Spent Caustics, also called Waste Caustics and Toxic
Wastes. Another form of sulfur bearing wash solutions from other refining operations is
Sour Water. Sour Water contains less amounts of sulfur
compounds, but is generated in much greater volumes.
In addition to the refining industry,
other industries including chemical manufacturing, LPG (liquefied petroleum gas), Natural Gas
(methane), and geothermal energy plants produce huge volumes of Sour
Water and Spent Caustics. Chemical manufacturing produces spent
caustics containing specific compounds compared to the wide variety from refining
operations. LPG and Natural Gas plants predominately produce
potassium hydroxide spent caustic, whereas, most other sources produce
sodium hydroxide spent caustic.
Common to all spent caustics is a high concentration of the extremely deadly and odorous HYDROGEN SULFIDE,
an acutely toxic gas most recognized as the odor of rotten
eggs when in low ppb (parts per billion)
concentrations. Hydrogen sulfide gas readily dissolves in caustic
solutions due to its solubility at high pH or "caustic pH" conditions,
typically above pH 10 to 12. It can be released from solution as
easily when the solution is disturbed or the pH is lowered. It is
more toxic than hydrogen cyanide to humans and death can occur in
exposures of just 100 to 500 ppmv (parts per million by volume) in the
Hydrogen sulfide gas is responsible for "multiple sewer-worker's
death syndrome". It starts with 1 worker while working in a sewer
suddenly collapses, one by one up to 4 more workers rush in to
help the collapsed worker then collapse on-top of each other like a
dog-pile. By now the 6th worker sees the calamity and decides to
get help instead of entering the sewer. Multiple deaths have
occurred in cities
worldwide since the first wastewater sewers were built. It was
believed that sewer deaths were due to a lack of oxygen before the
toxicity of hydrogen sulfide was understood. Furthermore,
hydrogen sulfide contained in an oxygen environment can be explosive
when ignited, thus adding to the danger.
Gaseous Hydrogen Sulfide Molecule
Contains 94% Sulfur
(Yellow - Sulfur atom | White - Hydrogen atoms)
Petroleum, LPG and Natural Gas manufacturing plants may also generate spent caustics containing high levels MERCAPTANS. Naturally occurring mercaptans,
also known as organic sulfides or thiols, contain a sulfur atom
typically near the end of an organic molecule or chain. Mercaptans are the most
odoriferous compounds known to man and even a minuscule amount in ppb concentration (parts-per-billion), is easily detected by the human nose. For
example, the odor of Skunk is mostly butyl-mercaptan.
Ethyl-mercaptan is intentionally fed into natural gas pipelines in ppb levels to
serve as an "odorizer". When a
person "smells a gas leak" they're not smelling the Natural Gas,
instead, they're smelling the mercaptan odorizer since LPG and Natural Gas are odorless.
(Black - Carbon atoms | Yellow - Sulfur atoms | White - Hydrogen atoms)
The LPG propellants used in aerosol canned
products (after CFC's were banned) must be specially deodorized to
prevent the odor of mercaptans being detected by the user. For
example, men's aerosol shaving cream is particularly sensitive to
discovery if any mercaptans remain in the propellant. Therefore,
LPG aerosol propellants are much more expensive than other LPG
Refinery spent caustics contain several other compounds in high levels including PHENOL together with cresylic and naphthenic acids that also exhibit toxic and odorous
properties. Phenol is a known biocide used in medicines and for
early sanitation in hospitals, etc. For example, the trademark
Champo-Phenique stands for camphor and phenol and is sold over-the-counter to
treat bacteriological infections. It has been established that
when as little as 64 square inches (or an area of 8 inches x 8 inches)
of skin is covered with pure phenol death will occur. Other
hydroxy-phenols include catechol, resorcinol, and hydroquinone (these
compounds, shown with their common names, are also known as hydroxy-benzenes and di-hydroxy-benzenes).
Refinery spent caustics often contain high levels of CRESYLATES, a form of phenol containing a methyl group (CH3), sometimes called phenolics as a family group. In either of the three forms: ortho-cresol, meta-cresol, and para-cresol,
they are not as toxic as phenol, however, cresylates are generated in
relatively high concentrations, from 1% up to 35%. Cresylates, or cresylic acids, are often referred to
as "Acid Oils" and are solubilized at high pH, but readily separate at
It is not the intent to wash these aromatic compounds from the
petroleum since they increase the octane number in the finished fuel,
however, when present they will partition into the spent
caustic in varying concentrations.
o-Cresol m-Cresol p-Cresol
(Black - Carbon atoms | Red - Oxygen atoms | White - Hydrogen atoms)
Refinery NAPHTHENIC spent caustics are the last of the major chemical classifications that
may contained in relatively high concentrations. Naphthenics
generally do not
impart a toxic or objectionable odor component to spent caustics.
partially soluble in caustic and increase the total organic carbon
considerably. Naphthene is a general term for cyclic alkanes, or
cyclic non-aromatic hydrocarbons called cycloalkanes. Refinery
naphthenes typically include cyclopentane and cyclohexane as the parent
(Black - Carbon atoms | White - Hydrogen atoms)
Many refineries don't discriminate too
closely and often include the family of naphthenic acids, or cyclic
carboxylic acids, when referring to naphthenics in general terms. Naphthenic acids contain a cyclic naphthene parent compound bonded to various hydrocarbon chains containing a carboxylic acid end group. A
"catch-all" analytical procedure includes Total Acid Number (TAN) for a
rough value of the naphthenic acid content. Other analytical methods
necessary for concise identification of each naphthenic species.
GEOTHERMAL spent caustics are in a class by themselves. Produce spent caustic mostly containing lower levels of hydrogen sulfide, and a lessor amount of mercaptans.
In the production of today's "LOW SULFUR" fuel requirements, more spent caustics than ever before are being generated. All of which require proper handling and disposal.
In earlier years, RESOURCE CONSERVATION was a focal point for politicians and environmentalists, some spent
caustics were processed with the intent of recovering the remaining
caustic value (remaining sodium hydroxide). The sulfidic types
were destined for reuse in the Pulp & Paper industry where caustic
sulfides are needed in large quantities. However, today the cost
of reclamation is greater than the value of virgin materials and
therefore, most of the reclamation facilities are now reduced to
disposal facilities. A few exceptions include localized Pulp
& Paper mills where only a pure stream (hydrocarbon free) of sulfidic spent caustic can be reused.
In the United States, "GRANDFATHER CLAUSES" in environmental protection laws permit Deepwell Disposal Sites to remain in operation today. Over 85% of refinery spent caustics are shipped by railcar
and truckload to deepwell disposal facilities (TSD's). Other privately owned Deepwells are also
in operation with captive down-hole waste streams.
DEEPWELL disposal is relatively inexpensive and easy for
industry to utilize. It provides "out of sight and out of mind"
waste handling and disposal options for the generator. But, USEPA (United States Environmental Protection
Agency) legislation defining
"cradle to grave stewardship" will remain a daunting subject for
thousands of years yet to come. The greatest concern of
environmental activists is if potable ground water aquifers are breached by nearby disposal
Deepwell Disposal Site
TEXOXTM PROCESS was developed especially for the effective treatment and
friendly disposal of these troublesome wastewaters. Furthermore,
the TEXOX Process can also transform a wide variety of hazardous wastes
into biodegradable products.
The TEXOX Processes have been proven cost competitive with typical
deepwell disposal facilities pricing, so what's the delay in replacing
your deepwell disposal with a TEXOX Process using environmentally "green" technology?
For Further Information On The TEXOXTM
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