Liquid purification or separation – Processes – Separating
Reexamination Certificate
2002-04-23
2004-02-17
Popovics, Robert J. (Department: 1724)
Liquid purification or separation
Processes
Separating
C210S773000, C210S777000, C210S791000, C210S792000, C203S091000, C494S037000
Reexamination Certificate
active
06692644
ABSTRACT:
The present invention relates to a process for recovering oil and sulfonates from filtration panels.
Oil-soluble sulfonates of earth-alkaline metals are widely used as detergent additives for lubricating oils. They are obtained by sulfonating hydrocarbon mixtures with a high content of aromatic alkyl hydrocarbons, characterized by a long lateral alkyl chain bound to the aromatic ring.
The hydrocarbon mixture can be of synthetic origin (and therefore consisting of aromatic alkyl hydrocarbons produced by the alkylation of benzene with a polymer of propylene) or it can derive from heavy refinery distillates characterized by a high content of aromatic alkyl hydrocarbon. Typical heavy refinery distillates suitable for the purpose have a weight average molecular weight of about 480.
As far as synthetic products are concerned, these can sometimes have a lower molecular weight, but the weight average molecular weight is higher than 400.
The sulfonic acids produced in the sulfonation process are then converted into sulfonates of earth-alkaline metals.
The conversion of sulfonic acids to sulfonates of earth-alkaline metals can be effected by direct neutralization with a base compound of earth-alkaline metal, such as hydroxide, oxide or carbonate. This conversion can also be carried out by the neutralization of sulfonic acids with a hydroxide of an alkaline metal; the alkaline metal sulfonate thus formed is then converted to sulfonate of earth-alkaline metal by metathesis with a compound of earth-alkaline metal such as hydroxide, oxide, carbonate, chloride.
The sulfonates can be neutral salts obtained by the reaction of sulfonic acids with the stoichiometric quantity required for neutralizing acids, or they can be overbased. Overbased sulfonates can be prepared by means of contact of sulfonic acids (or salts of the alkaline metals of the above acids) with an excess, with respect to the stoichiometric value, of a base compound of earth-alkaline metal. The process consists in mixing the sulfonic acid (or its metal alkaline salt) with an excess of base earth-alkaline compound, usually in the presence of a hydrocarbon solvent, and introducing gaseous carbon dioxide into the mixture. An alcohol is commonly used to promote the production of over-based sulfonate.
The process to which the present invention refers is well known to experts in the field, see for example “Procédé de suralcalinisation d'additifs détergents: “RÔle des Promoteurs et determination du régime de la réaction de surbasage” R. Gallo and F Jacquet, Revue de l'Institut Francais du Petrol, Vol. 476, Nr. 2, Mars-Avril 1991.
The final step of the production process of neutral or overbased sulfonates is the separation of the desired products from the by-products, particularly non-reacted compounds of earth-alkaline metals and sediments. It is important for the detergent additive to have a colloidal structure with sufficiently small particle dimensions (usually <0.1 micron) so as to be transparent to visible light (see U.S. Pat. No. 3,155,617) and easily filterable through the usual filtering devices. In fact, if particles of non-reacted alkaline or earth-alkaline material are present in the additive, or if almost insoluble large dimensional colloidal structures have been created in the synthesis phase, without a suitable liquid-solid separation step, abrasions and decantation can occur when using the lubricating oil.
The purification step can be carried out before or after the removal of the reaction solvents.
The end additive proves to consist of a mixture of sulfonate (overbased) formed and of the lubricating base added during the process to lower the viscosity. In the case of overbased additives, the basicity reserve, measured by TBN according to the procedure described in WO 97/46443, depends not only on the ratios between the reagents but also on the dilution with the lubricating base.
The purification step of the additives based on sulfonates usually consists of a filtration with aids. The material to be removed is normally made up of the non-reacted base oxide or hydroxide, impurities of the starting oxide or hydroxide consisting of carbonates of the metal itself or oxides or hydroxides of other metals, sulfonates deriving from the neutralization of the sulfuric acid optionally present in sulfonic acids, crystalline carbonates formed during the reaction, unstable micelles of sulfonate (sediment) formed during the reaction which prove to be non-oil-soluble owing to the considerable dimensions of the carbonate nucleus and/or of an insufficient coating thereof on the part of the surface-active agent based on sulfonate.
The content of “sediment” in the product to be filtered varies according to the synthesis process, the raw materials used and degree of overbasicity required, and it is mainly this impurity which determines the filtration rate and quantity of filter aid to be used U.S. Pat. No. 3,537,996 identifies “considerable quantities of solids prevalently consisting of colloidal particles of calcium carbonate having large dimensions, not dispersible in the oily medium (sediment)”, as main impurities to be eliminated by filtration. U.S. Pat. No. 3,155,616 describes how some processes for producing colloidal dispersions of calcium carbonate which use sulfonates, are made difficult by the presence of materials which tend to deteriorate upon contact with the hot surfaces of the process equipment, forming agglomerates of large dimensional particles which cannot be tolerated in the end lubricating product and which can only be removed with great difficulty due to their substantial non-filterability.
In solid-liquid purification by filtration, U.S. Pat. No. 3,537,996 identifies amorphous diatomaceous siliceous earth as a suitable aid, both for forming the precoat on the filtration surface and to be added to the product to be purified, and indicates a quantity of 1 to 15% in the product to be purified as appropriate. U.S. Pat. No. 3,155,617 also specifies diatomaceous earth as suitable aid and lists known commercial types, such as Filter-Cel, Hy-Flo, Super Cel and Dicalite.
During the filtration process with aids, a filtration panel is produced which contains impurities present in the reaction product, the filter aid and the detergent additive. In particular the content of additive in the panel is very high and is comparable to that of the aid.
The filtration panels obtained in the processes described above should be discharged as undesired by-products of the sulfonation process. This causes a loss in oil and sulfonate. In addition, a more important factor is that these filtration panels are classified as potentially dangerous materials, with obvious disposal problems.
The necessity is therefore felt for improving the purification process of sulfonate, thus avoiding disposal of the above panels.
To solve this problem, U.S. Pat. No. 4,614,597 treats the filtration panel with acid selected from phosphoric acid and sulfuric acid until reaching a pH ranging from 2 to 7, and maintaining the mixture thus obtained at a temperature of over 150° F. The hot mixture is subsequently left to rest until separation of the two phases, the upper phase containing oil and the sulfonate, the lower phase containing the filter aid and the acid.
U.S. Pat. No. 4,501,670 on the other hand, describes a process in which the filtration panels are mixed with hot aqueous solutions of materials selected from hydroxides of alkaline metals, salts of alkaline metals of acids having ionization constants of less than 1.5·10
−4
and relative mixtures. After the separation has been completed at temperatures of over 160° F., two phases are separated which are recovered.
Both processes of the prior art reduce or eliminate the dangerousness of the panel, but have the disadvantage of requiring subsequent washing and neutralization phases. In addition, these phases do not allow the starting additive to be recovered, but rather an intermediate to be recycled, for example sulfonic acid to be recycled to the synthesis process of sulfonates, in the case of
D'elia Luigi
Pianta Orazio
Agip Petroli S.p.A.
Popovics Robert J.
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