Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G19/00—Refining hydrocarbon oils in the absence of hydrogen, by alkaline treatment
  • C10G19/08—Recovery of used refining agents

Definitions

• the present invention relates to a process for the treatment of spent aqueous solutions of caustic soda used for purification and washing of petroleum products ("spent caustics"), based on the synergical use of ozone and calcium hypochlorite.
• the treatment according to the invention allows reduction of the pollution load of the spent solutions of caustic soda, obtaining two final streams which, as they are or after further routine treatment, are compatible with the ecological specifications of national and international laws regarding emission of substances into the atmosphere, water discharge and final solid waste destined for disposal in authorized waste disposal centers.
• aqueous solutions of NaOH are usually used, in concentrations of between 5 and 15% by weight (fresh caustic).
• the spent caustic soda solution obtained has a different composition dependent on whether it has been used for purification of LPG (propane and butane), of petrols obtained from thermal and/or catalytic "cracking", or of "straight-run” petrols (obtained from distillation of crude oil at atmospheric pressure), bearing in mind the conventional treatments which these products undergo.
• LPG propane and butane
• petrols obtained from thermal and/or catalytic "cracking"
• straight-run petrols obtained from distillation of crude oil at atmospheric pressure
• the spent caustic soda solutions have pH values ranging from 12,5 to 13,5 and the following composition expressed in percentage by weight:
• the process according to the invention is based, generally speaking, on the synergical action of ozone and calcium hypochlorite on the undesired products found in spent caustics.
• the process for the treatment of spent aqueous solutions of caustic soda used for purification and washing of petroleum products is characterized in that the spent solutions of caustic soda are subjected essentially to the following operations:
• the first oxidization is accompanied by a strong oxidating demolition of the phenolic ring and by a partial oxidation of the compounds containing sulphur, until obtaining much less toxic molecules (for example oxalic acid, carbon dioxide, oxygen, water and sulphur).
• the second oxidation stage promotes the breakage of the R-SH bond and the formation of sulphur molecules in the form of a flaky aggregate which is subject to sedimentation.
• the liquid phase produced by this separation is of a reddish colour and has a slight smell of phenols; it is suitable for routine treatments.
• the solid phase obtained after separation of the pulp is dark yellow in colour, flaky in aspect, and a slight smell of compounds containing sulphur; it is suitable for final disposal in waste disposal dumps and/or for controlled recovery as inert re-cycled material.
• the calcium hypochlorite can be added as it is or formed on site, for example by means of a reaction between sodium hypochlorite and lime.
• Phase separation in the process according to the present invention, can be obtained using an operation chosen from the group comprising: centrifugation, optionally under vacuum; filtering, optionally under vacuum; filter pressing; and band-pressing.
• the spent aqueous solution of caustic soda which is to undergo treatment according to the present invention was obtained from the washing of " straight-run" refinery petrol.
• This solution cannot be disposed of as it is, because its pH value is 13 and it contains a high pollution load. In particular, it contains the following:
• this solution is subjected to a first oxidization step with 2 kg of O 3 /kg of total phenols.
• a progressive change in colour of the solution can be seen, turning from dark brown to a lighter shade of brown; at the same time the intense and pungent smell of phenol and organic substance tends to grow less.
• the pH value goes down from 13 to approximately 10.
• the process is accompanied by an increase in temperature up to 38-40°C and by an intense physiological foaming, which grows noticeably less on the controlled addition of an antifoaming agent.
• the second oxidization step is then performed, adding 6% by weight of calcium hypochlorite, with reference to the ozonized spent aqueous solution of caustic soda.
• the formation of dark yellow flakes can be noted, and these tend to sediment, generating a pulp of a colour tending towards dark yellow. There is no emanation of particular smells.
• the flakes are characterized by a high level of sedimentation.
• the pulp is made to undergo centrifugal separation by means of an horizontal mechanical two-way decanter.
• a liquid phase and a solid phase are obtained.
• red in colour with a not particularly intense smell of phenol, a reduction of the content in phenols, sulphides and mercaptans is registered of about 90% with respect to the starting values.
• This stream as it is or after further treatment, is suitable for disposal using current refinery and petrol-chemical waste disposal technology.
• the centrifuged solid phase results easy to shovel and is compatible with the other factory waste, as it can be integrated in the pre-treatment system to be adopted for said waste, before final disposal.
• this residual solid stream can be classified, e.g. according to the Italian Law (DPR 915/82 and the deliberation by the C.I. dated 27/7/84), as special waste. It can therefore be disposed of, after solidification/stabilization by the addition of lime and silicates, as such or together with the pool of special refinery waste, deriving from purification sludge of a chemical-physical and biological nature.

Landscapes

• Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Paper (AREA)
• Treatment Of Water By Oxidation Or Reduction (AREA)
• Physical Water Treatments (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Applications Claiming Priority (2)

Publications (2)

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Cited By (5)

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Citations (1)

• 1991
  • 1991-02-20 IT ITRM910118A patent/IT1244498B/it active IP Right Grant
• 1992
  • 1992-01-27 DE DE69200296T patent/DE69200296T2/de not_active Expired - Fee Related
  • 1992-01-27 EP EP92830030A patent/EP0509964B1/fr not_active Expired - Lifetime
  • 1992-01-27 ES ES92830030T patent/ES2057980T3/es not_active Expired - Lifetime

Patent Citations (1)

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