US 3650942 A
Description (OCR text may contain errors)
United States Patent US. Cl. 208-31 8 Claims ABSTRACT OF THE DISCLOSURE A process for de-oiling a wax containing both oil and solvent obtained from the dewaxing of a hydrocarbon oil by adding additional solvent, heating and refiltering at least a portion of the additional solvent being supplied in the form of vapor from the solvent recovery system.
This invention relates to the de-oiling of the oil-containing paraffin wax obtained in the dewaxing of wax-containing hydrocarbon oils and more particularly to the heating required for the de-oiling.
Wax-containing hydrocarbon oils obtained, for example, in the processing of petroleum or in the hydrogenation of coals, tars, mineral oils, and similar materials are generally dewaxed by diluting them with solvents while applying heat, if required. The solvents used include, for example, chlorinated hydrocarbons, such as dichloromethane and dichloroethane, ketones such as methyl isobutyl ketone, methyl ethyl ketone, acetone and 'butanone, and aromatics such as toluene and benzene or mixtures of these materials. Upon cooling of the solution obtained, the wax will crystallize out. It is then separated by filtering or centrifuging and, in addition, maybe washed with additional. solvent. The wax thus obtained may have an oil content of to 10% by weight of oil, for example. Since a commercial wax should not contain more than 0.5% by weight of oil, the product wax must be subjected to a de-oiling treatment.
For the de-oiling, the oil-containing wax is mixed with the solvent, which preferentially absorbs the oil. By subsequent filtration or centrifugation the mix is separated into oil containing solvent and de-oiled wax. If necessary, the latter is subjected to one or more additional solvent treatments of the type described, until the oil content of the wax is reduced to the desired level. Solvent is then recovered from the oil by distillation and ordinarily is condensed and sent to solvent storage.
Effective separation of the wax and oil during the mixin g step essentially depends on the temperature. The higher the mixing temperature, the more wax will be absorbed by the solvent together with oil. The mixing temperature will also govern the melting range of the waxes absorbed by the solvent. At low mixing temperatures only low-melting waxes will pass into the solvent together with the oil. Waxes of medium melting range will remain in the deoiled wax giving it a relatively low melting point. Thus, the oil recovered from the solvent phase by evaporation of the solvent will contain only the low-melting waxes and will therefore have a relatively low pour point. If, however, higher mixing temperatures are used, mediummelting waxes will also be absorbed by the solvent in addition to the low-melting waxes together with the oil. The de-oiled wax will then contain only high-melting or very high-melting components and will thus have a relatively high melting point, while the oil recovered from the solvent phase will have a relatively high pour point due to its content of medium-melting wax components. The mixing temperature may also be increased to a point where all of the wax is absorbed by the solvent. Then, by subsequent cooling of the mix, practically oil free wax can 'be crystallized out.
By a suitable adjustment of the mixing temperature, it is thus possible to obtain a de-oiled wax having a desired freezing point, and/or an oil having a desired pour point. However, accurate adjustment of the mixing temperature can only be achieved if the mixing is rapid and the temperature throughout the mix is substantially uniform.
In conventional processes, the mix is heated indirectly. This requires heat exchange arrangements, such as heating coils in the mixing zone, or mixing vessels with double walls or jackets permitting the passage of the heating medium. However heat exchange of this type does not meet the requirements of rapid mixing and uniform temperature control.
. In conventional processes, the solvents used for de-oiling are always recovered. This is effected by evaporation from the oil-containing solvent phase or from the separated solvent-containing wax. The solvent vapors formed during the evaporation are condensed in the conventional processes, and the condensates, possibly after further purification, are recycled to the process.
It is one object of the invention to heat the mix in such a way as to permit a particularly accurate adjustment of its temperature. Another object of the invention is to effect the heating of the mix without using a heat exchanger. A further object of the invention is to reduce the load on, or permit a reduction in the size of, the cooling systems used for condensing the solvent vapors formed during the solvent recovery step. A still further object is to reduce the energy required for heating the mix.
The invention achieves these objects by using solvent from the solvent recovery, introducing part of the solvent required for mixing into the mixing vessel in the form of solvent vapor obtained in the solvent recovery, and adjusting the temperature of the mix by the quantity of vapor introduced. Distribution of the vapor and its condensation in the mix assures a uniform and rapid heat transfer throughout the mix. As soon as the mix has reached the desired temperature, any further increase in temperature can be prevented by reducing the flow of the vapor, which is not possible in conventional processes owing to the thermal inertia of the heat exchangers used. Since this mode of operation will condense part of the vapor from the solvent recovery step, it results in a saving of cooling medium and permits the use of smaller condensers.
The solvent vapors may be introduced near the bottom of the mixing vessel and allowed to bubble upwardly through the mix. However, if the wax is being pumped to another vessel or returned to the original vessel advantageously the solvent vapors are introduced into the transfer line preferably just prior to the introduction of the mix into the pump.
The process of the invention is particularly suited to the de-oiling of wax recovered from an oil which has been produced by hydrocracking. Wax recovered from hydrocracked oils is more difficult to filter than wax obtained from unhydrocracked oils, probably due to the variety of molecular structures found in wax recovered from hydrocracked oils.
The following example is submitted for illustrative purposes only and is not to be construed as limiting the invention in any respect.
In the dewaxing of spindle oil, filtration subsequent to cooling produces a solvent-soaked filter cake mix containing both wax and solvent. The mixing vessel is charged with about 21,740 kg./hr. of filter cake, that is, 2090 kg./hr. of oil-containing wax and about 19,650 kg./hr. of solvent (50% by weight dichloromethane and 50% by weight dichloroethane) at a temperature of 20 C. In
order to obtain the desired de-oiling effect, the 2090 kg. /hr. of oil-containing wax must be mixed with considerably more solvent than that contained in the filter cake, the total amount of solvent required being 43,220 kg./hr. Moreover, the mixing temperature must be maintained at precisely +5 C. To meet these two requirements, additional quantities of 21,355 kg./hr. of liquid solvent at +5 C. and 2215 kg./hr. of solvent vapor at +80 C. are fed to the mixing vessel. Mixing is followed by a filtering step in which the temperature is maintained at +5 C. The wax left on the filter is washed on the filter with fresh solvent at +5 C. to bring it to the desired freezing point of +43 C. The washing filtrate obtained at a temperature of +5 C. is used to supply the aforesaid 21,355 kg./hr. of liquid solvent. By increasing the flow of solvent vapor and simultaneously decreasing the flow of liquid solvent while maintaining the total flow at 23,570 kg./hr., the mixing temperature may be increased to obtain a de-oiled wax having a higher freezing point.
1. In a process for the solvent dewaxing of a lubricating oil in which the lubricating oil is mixed with a solvent, the mixture is chilled to crystallize wax and the wax containing occluded oil is separated from the chilled solvent-oil mixture, the improved method of recovering a substantially Oil-free wax which comprises distilling solvent from the substantially wax-free chilled solvent-oil mixture, adding to said wax containing occluded oil additional solvent in liquid form together with at least a portion of the solvent distillate in vapor form and recovering from the resulting mixture substantially oil-free wax.
2. The process of claim 1 in which the wax is obtained from a hydrocracked oil.
3. The process of claim 1 in which the solvent comprises dichloromethane.
4. The process of claim 1 in which the solvent comprises dichloroethane.
5. The process of claim 1 in which the solvent comprises a mixture of a ketone and an aromatic hydrocarbon.
6. The process of claim 5 in which the ketone is acetone.
7. The process of claim 5 in which the aromatic hydrocarbon is toluene.
8. The process of claim-5 in which the solvent comprises methyl ethyl ketone and toluene.
References Cited UNITED STATES PATENTS 1,857,810 5/1932 Gee 208-31 2,005,984 6/1935 Adams et a1. 20831 2,307,130 1/1943 Henry et a1 208-31 3,006,839 10/1961 Arabian et a1. 208-31 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 20833