US3108943A - Wax deoiling process - Google Patents

Description

CPS

VISCOSITY Oct. 29, 1963 V. E. M DANIEL WAX DEOILING PROCESS Filed April 26, 1960 4 Sheets-Sheet 2 I600 I l -2|oo AT 45 F.

SINGLE DILUTION 5o% MEK IN TOLUENE 5.5 SOL. ICRUDE WAX /WATER FREE SLURRY f/SLURRY WITH 2.3 WATER 20o X I20 I00 80 so 40- 2o 0 TEMPERATURE DEGREES FAHRENHEIT."

FIG. 2

THE EFFECT OF 7.3 EXCESS WATER ON SLURRY VISCOSITY BY [0M 94 M HIS AGENT VISCOSITY CPS Oct. 29, 1963 V. E. M DANIEL WAX DEOILING PROCESS Filed April 26, 1960 4 Sheets-Sheet 3 OIL N0. VOL.DIL AT TEMP.

bUlN- NOO- l/WATER FREE SLURRY SLURRY WITH 2.5 /o WATER (BASIS SOLV.)

TEMPERATURE DEGREES FAI'IRENHEIT FIG.

THE EFFECT OF 7.5% EXCESS WATER 0N SLURRY VISCOSITY INVENTOR VICTOR E.Mc DANIEL BY HIS AGENT Oct. 29,1963

Filed April 26, 1960 4 Sheets-Sheet 4 WATER FREE A SOLVENT 4 A L K r x 4' {I c W v I 3.3 WATER BASIS SOLVENT 4/ x I40 I20 I00 80 e0 40 TEMPERATURE, DEGREES FAHRENHEIT FIG. 4

INVENTOR VICTOR E. Mc DANIEL BY MAM T M HIS AGENT Unite Filed Apr. 2s, No. seats 5 laims. crass-4,1

This invention relates to a process for separating petroleum wax from associated petroleum oils. More particularly, it relates to a process for the solvent dewaxing and/or deoiling of oil-wax mixtures.

The separation of Wax from oil is normally carried out by cooling the wax-oil mixture to such a temperature that the wax crystallizes and then separating, preferably by filtration, the wax from liquid oil components. Prior art processes include the steps of dewaxing without any solvent, the use of numerous types of solvents and nonsolvents as diluents, so-zcalled emulsion dewaxing, and variations of these processes. -t is the usual experience that the wax initially separated from a petroleum oil is contaminated with substantial amounts of the oil and requires further processing for purification to a low oil content. This latter purification step is normally referred to as deoiling as difierentiated from dewaxing, wherein a relatively greater proportion of oil is present. However, the basic steps involved in both dewaxing and deoiling are essentially the same, the difierences involved being ratio of solvents and temperatures of filtration or the equivalent.

Not only are solvents, such as aromatic hydrocarbons, utilized in dewaxing processes but non-solvents, and limited solvents such as ketones, are employed either alone or together with aromatic hydrocarbon solvents. The purpose of the non-solvents is principally to reduce the viscosity of the wax-oil mixture, while the particular utility of the solvent hydrocarbons is to promote solution of the oil component therein. Mixtures of these types of onganic liquids are utilized, the ratio of them and the temperatures at which they are empolyed being adjusted to obtain the desired separation of wax and oil.

Several disadvantages are inherent in the prior art wax-oil separation pr cesses. One of these comprises the unduly high viscosity of the wax oil slurry, which reduces the throughput of a given wax processing plant or requires increased amounts or diluents or solvents. Fur thermore, due to the high viscosity of the mixtures, the pressure drop across the chillers is undesirably great.

Another disadvantage of many dewaxing and deoiling processes comprises the undesirable adherence of wax to the wax processing equipment surfaces. This necessitates periodic warm-up periods so as to melt adhering wax from the equipment surfaces.

Still another major disadvantage of many wax processes comprises the lack of permeability of the wax cake deposited on a filter. Due to low permeability, it is difficult to wash the wax on the filter and it is also the reason for slow filtration rates through the deposited wax cake.

The use of emulsion dewaxing or of flotation dewaxing (in which gas is injected in a Water-oil wax slurry) alleviates some features of these disadvantages but does not entirely cure them. Furthermore, according to prior art emulsion and flotation dewaxing processes, it was necessary to utilize surface active agents for the promotion of suitable emulsions and also to promote transfer of the Wax crystals from the oil phase into the water phase. The presence of the surface active agents, while beneficial in these respects, also have certain inherent defects. For example, it was often difiicult to separate the waterhydrocarbon phases due to a relatively stable emulsion being formed. Consequently, in order to overcome this rates atent ice disadvantage it was often necessary to utilize deemulsifying agents in addition to the sunface active agents. Thus, correspondingly increasing the complexity of the Wax processing operations. In attempting to overcome these diificulties, other means were attempted, such as the injection of sufiicient water to saturate the solvent being employed. This resulted in a certain increase in Wax yields but did not beneficially affect the crystal structure of the wax cake nor its filtration characteristics. Moreover, the use was confined to the use of about 2 percent Water in ketones having 5 to 6 carbon atoms per molecule, the benefit not being extended to lower molecular weight ketones or their mixtures with aromatic hydrocarbons. Aqueous emulsions have been added in small amounts to Waxy oils [for the purpose of providing nuclei on which the wax crystals would grow. In this case, however, it appears necessary to reduce the temperature of the composition to below the freezing point of water in order to provide such nuclei. Moreover, relatively complex mixtures of solvents were present, one being utilized in formation of the water emulsion, another being employed in the dispersion of the waxy oil.

It is an object of the present invention to provide an improved process for the separation of wax from oil. It is another object of the invention to provide a wax separation process showing improved filtration rates and lower viscosity of the wax-oil solvent slurry. Other objects will become apparent during the following description of the invention.

Now in accordance with the present invention, a process for the separation of Wax from oil is provided wherein the wax-oil mixture is diluted with a wax separation medium such as methyl ethyl ketonc-toluene, raised to a temperature suflicient to dissolve all of the components into a single phase, adding 2-25 percent by weight of liquid Water based on the solvent in an amount sufhcient to form a separate aqueous phase, cooling to a wax separation temperature and separating wax from the oil solution. The use of the process is limited to one in which the water or equivalent aqueous phase is in liquid form at all times. Moreover, the process is conducted in the absence of any surface active agents and in the substantial absence of any efiective amounts of foam-producing gases. The latter will be interpreted to mean that incidental amounts of air or other atmosphere may be present but that it is not employed in such a way as to produce a foam, such as is necessary in the so-called foam dewaxing processes. FIGURE 1 accompanying this specification illustrates preferred embodiments of the process utilizing controlled Water injection.

The process in its preferred form is particularly applicable to the use of a so-called multiple injection of ketonetoluene diluent. In contrast to other wax separation diluents, it has been found that when the amount of water is restricted within the proportions claimed, certain material advantages are derived, including particularly a substantial reduction (in the order of 10-fold) of the viscosity of the wax-oil solvent slurry while, at the same time the rates of filtration are correspondingly raised.

In a preferred version of this invention, the water-containing mixture which is filtered to separate wax from oil is sent to suitable settling areas so that the aqueous phase may be conveniently removed and recycled for treatment of further portions of the oily wax mixture. Of course,

. in place of settling, centrifuging or equivalent means such as extraction may be employed.

The process of this invention can be applied to the deoiling of crude waxes, the dewaxing of waxy oils, or the splitting of wax mixtures. The waxes may be derived from distillate cuts or residual fractions and comprise Q either parafiin waxes, microcrystalline waxes or mixtures of the same. Any of the well-known aliphatic ketone dewaxing (deoiling) media may be utilized including their mixtures with aromatic hydrocarbons. Methyl ethyl ketone, methyl isobutyl ketone and their mixtures with toluene or xylenes may be used.

The proportion of methyl ethyl ketone to toluene utilized in this invention is preferably between about 0.5-5.0 parts of ketone per part of toluene by volume. In the operation of a dewaxing or deoiling process wherein the diluent is injected in a single stage there is little flexibility in selecting an optimum ratio since this must be determined to coordinate properly with the specific waxy oil stock being treated and the particular temperature conditions which will be utilized in the wax separation. However, in the preferred version of the invention, wherein at least two stages of diluent injection are employed, it is possible to vary the proportion of ketone to toluene so as to obtain optimum working conditions and products. Normally, this would comprise varying the time at which the several injections of diluent are employed relative to the temperature of the specific oilwax mixture being treated.

The other variable includes the relative amount of the portions of diluents to be injected in the muliple injection steps and, lastly, the proportion of ketone to toluene which may be varied from one injection to another. Preferably, the injection in the later stages (colder stages) of the cooling cycle just prior to filtration employs a diluent in which the toluene content is relatively higher than in the initial stages. 7

Water injection may be made simultaneously with or separately from diluent injection, the specific steps utilized being coordinated with the particular oil-wax mixture being treated. It is preferred that a multiple injection system be employed, particularly if the diluent is injected into two or more steps. The water may be at the same or different temperature from the wax-oil mixture being treated but preferably is substantially cooler, since it then can act as a direct heat exchanger of high efiiciency, which is more effective than the indirect heat exchangers normally employed. It could, in fact, act \as the sole or as supplementary cooling means for the wax separation process.

Preferably, the water is added, at least in its initial step, subsequent to warming the oily wax mixture to such a temperature that a single phase is present, that is, where the wax is melted in the oil or at least forms of homogeneous liquid phase therewith. As the mixture cools it tends to become more viscous, particularly after the Wax has been precipitated. Hence, it is advantageous, if it is desirable to maintain a relatively small change in viscosity, to add the water incrementally in such proportions as to minimize viscosity change. By this means not only is the viscosity of the system maintained at a relatively constant viscosity but it is also possible to inject Water of progressively lower temperature so as to *aid in or cause the oily wax mixture to reach its proper filtration temperature. According to one aspect of the invention, the proportion of water in the diluent is increased during the cooling step prior to filtration, since the maximum effect of water is attained at temperature such that wax crystals have commenced forming.

The proportion of water utilized in this process will depend in part upon the characteristics of the oily-waxy mixture and the proportion will be related to the volume of the ketone-toluene diluent employed. The proportion should be no less than about 2 percent by volume based on the diluent and no more than about 25 percent by volume based on diluent. If smaller amounts are employed, the benefits of the Water injection are insignificant, and if larger proportions are utilized then cooling problems are encountered due to the relatively large volume of liquids being handled. Preferably, the proportion of water utilized is between about 7.5 and 18.5 percent by volume based on the diluent phase.

One mode of operation of the invention comprises injection of all of the water 'at or near the initial relatively high temperature of the oily wax mixture wherein the latter is in a homogeneous condition. This may be effected either when the diluent is injected or prior or subsequent thereto and may be utilized when the diluent is injected in a single or multiple steps. The preferred operation comprises mixing the diluent with heated oily wax resulting in a homogeneous phase, injecting water which is relatively cooler than this homogeneous phase and continuing cooling with additional sol-vent injection at periodic points down to the temperature of filtration.

Cooling may be effected by utilizing relatively cold diluent or by indirect heat exchange in well known types of heat exchangers. In its preferred form, the proportion of water is initially higher relative to diluent when the oily was mixture is at a relatively elevated temperature than it is just prior to filtration when the temperature is substantially lower. The use of water permits the use of a solvent of increased MEK content. The high water content, on the other hand, which is present at relatively high temperatures and throughout the process of cooling, results in relatively low slurry viscosity, the slurry comprising oil, crystallized wax, diluent and Water.

The proportion of diluent utilized again will depend upon the specific character of the operation, namely, whether it is a dewaxing operation of a deoiling step. In the latter case the proportion of wax is relatively high compared with that of oil, consequently, the proportion of diluent employed is substantially larger than is normally utilized in a dewaxing operation. During the ordinary dewaxing of typical waxy lubricating oils, the proportion of methyl ethyl ketone-toluene diluent employed is preferably between about 2 and 4 volumes per volume of waxy oil, which may be utilized as noted above in a single injection or, more preferably, in a multiple injection. During a deoiling operation on the other hand where wax may be present in excess of about 50 percent by volume the proportion of diluent is normally between about 5 and about 10 volumes per volume of oily wax.

The process, as illustrated by FIGURE 1, includes the mixing of an oily wax (or waxy oil) from a source 1 with a diluent (solvent) from a source 2, this mixture being heated by a means not shown to form a homogeneous liquid phase. Water is then injected from circulating line 3 and the mixture is then passed, if desired, through cooler 4. If a single injection of water and diluent are employed the slurry so formed is then passed when at the proper temperature through line 5 to the filter feed tank 6. The mixture is then fed through line 7 to the filter 3, the Wax being sent to a wax settler 9 Where it is warmed until liquified so :as to allow for the settling and separation of Water which is occluded by the wax. The wax is then sent to a stripper not shown where residual amounts of diluent are removed. The filtrate, which will include oil, diluent and water is transported by line 10 to a filtrate settler Ill so as to allow for water withdrawal, after which the oil and diluent are separated in a stripping means not shown in the figure. It will be noted that the filter feed tank, filtrate settler and Wax settler all allow for recycling of water back for further treatment of portions of the liquid oily wax-solvent mixture. Any make-up water which is necessary may be injected any where in this line, such as from source 12 into line 3.

According to FZGURE I, allowance is made for multiple injection of both Water and solvent or of either one when a multi-stage injection system is utilized. Cooling is conducted between these injection stages through the supplementary coolers 2h, 30 and 40, etc., the cooled slurry then being sent by means of line 13 to the filter feed tank 6. It is possible to pass the recycle water through an additional chiller 14 prior to its injection in the treatment of further quantities of liquid oily wax.

While the use of limited water injection applies particularly to deoiling operations, it is also possible to utilize it in connection with dewaxing processes. In deoiling operations the temperatures may vary normally between about 140 F. and about 35 F. while during dewaxing operations the minimum temperature may be substantially lower, in the order of about 0 F. In a multiple dilution operation, wherein the diluent is being injected in two or more stages, it is preferable to lower the temperature from its initial homogeneous phase to a lower temperature after the injection of the first portion of the diluent.

Filtration may be effected by well known means or by equivalent means, such as centrifuging. Rotary filters are preferred, although filter plate presses may be used.

The benefits of this invention are especially noteworthy with respect to reduction in slurry viscosity as will be seen from the working examples which follow. However, other benefits comprise the increase in rate of filtration and in the lack of adherence of Wax to equipment utilized in connection with the Wax separation process. The precise reason for the surprisingly large reduction in slurry viscosity has not been ascertained nor has the reason for increase in filtration rate been deter-mined. Possibly, the presence of a second liquid phase reduces the viscosity and/or a higher ketone content in the solvent phase at the start of cooling is responsible. The lack of adherence of wax to the metallic equipment surfaces appears to be due to preferential wetting thereof by the water present in the system.

While it is preferred to utilize water as the only aqueous phase in the process, modifying materials may be utilized therein if it is necessary to prevent ice formation due to low temperature conditions such as may be encountered in dewaxing processes and the like. The modifications may take the form of presence of effective freeze point depressing amounts of alcohols or glycols or of an inorganic salt, such as sodium chloride. Suitable alcohols include methanol, ethanol and isopropanol, while the suitable glycols include ethylene glycol or propylene glycol.

The use of the limited water injection permits a decrease in the solvent-to-waxy oil charge ratio required to process a crude wax or a waxy oil. Therefore, due to the reduction of the solvent to charge ratio, it also permits an increased throughput for any given size wax separation plant and thereby reduces the size of the solvent recovery and refrigeration requirements for a given throughput in such a plant. The increased permeability of the wax cake permits faster filtration rates which also increases plant throughput. The resulting solvent composition temperature gradient permits the use of a toluenenich final dilution in an incremental dilution scheme which results in reduced oil content of the process wax while maintaining the advantages of a more permeable wax cake. Due to the increase in wax filter cake thickness which may be occasioned by the use of large quantities of water, the wax cake for stocks having a low wax content is increased in the oil content, since oil is not soluble to any extent in the water phase.

The following examples illustrate the use of this invention:

EXAMPLE I A sample of East Texas-Louisiana crude wax from a medium viscosity distillate lubricating oil cut was diluted with 5.5 volumes of methyl ethyl ketone-toluene. The diluent had a volume proportion of 1.0 volume ketone to one volume of toluene. The diluted mixture was warmed to form a homogeneous solution of wax and oil in the diluent and then cooled. The viscosity of the mixture was periodically measured during the cooling cycle. The process was repeated using 7.3 percent water basis solvent. The viscosity-temperature curves are presented in FIGURE II.

6 EXAMPLE 11 The process was again repeated using multiple injections of solvent both with and without the addition of water; the diluent being 65 percent methyl ethyl ketone and 35 percent toluene by volume. At about 43 F. the mixture was filtered and the filtration rate noted. The viscosity data are shown in FIGURE III and the filtration data in Table 1.

Table 1 Charge Stock .c Crude Wax From Medium Viscosity Distillate Run Number Solvent Composition, Percent MEKH Percent Water Basis Solvent 0 Dilutions, Solvent/Crude Wax, v.:

Initial 1.9 l

Sooond 0.6 at 120 F. 0 at 120 F. Thir 0.6 at F.... 0. at 90 F. Fourth Fr 2 at, 48 F.

Filtration Temperat Filtration Rate, cc./sec Wash Volume, Solvent/Crude Wax, v. Wash Rate EXAMPLE III EXAMPLE IV East Texas-Louisiana crude wax from a medium viscosity distillate lubricating oil cut was cleoiled as follows. The crude wax had an oil content of about 15%. This crude wax was diluted with 2.5 volumes of 50:50 methyl ethyl ketone-toluene. The diluted mixture was warmed to form a homogeneous solution of the wax and oil in the diluent and then was cooled at about 58 F., the mixture was further diluted with 3 volumes of diluent, cooling was continued to a filtration temperature of about 48 F. The time of filtration for a unit of the slurry so formed was noted. The process was repeated with additional quantities of the same crude wax, in one case modifying the diluent with 7.3% by volume of water and in the second case 18.8% by volume of water based on the solvent. Table 2 shows permeability of the wax filter cake under these varying conditions.

EXAMPLE V The process in Example IV was repeated using 7.3% water based on the solvent, but with less solvent. Table 3 shows filtration rates for varying solvent-to-crude wax ratios. The data illustrates that in the presence of water a good filtration rate can be maintained with less solvent.

Table 3 Chmge Stock Crude Wax From Medium Viscosity Distillate Run Number F G H Solvent Composition, Percent MEK 50 50 50 Water Basis Solvent, Percent 7.3 7.3 Initial Dilution (Solvent/Crude Wax),

v 2.5 2.5 2 5 Dilution at 58 F. (Solvent/Crude Wax), v 3.0 3. 0 2.0 Filtration Temperature, F" 48 48 48 Filtration Rate, cc./sec 100 127 92 "Wash Volume (Solvent/Crude Wax), v. 2. 5 2. 5 2. 5 Wash Rate, coJsec 37 58 45 EXAMPLE VI The process in Example V was repeated using varying amounts of water and varying the composition of the second dilution solvent. Since water dissolves part of the methyl ethyl ketone the composition of the solvent in the non-aqueous phase of the slurry has a decreased ketone content at the second solvent injection point. The composition of the second dilution solvent was adjusted for this change in solvent composition. The data are given in Table 4.

Table 4 Charge Stock Crude Wax From Medium Viscosity Distillate Run Number J K L Water Basis Solvent, Percent 7. 3 24.2 9. 2 Initial Dilution:

Solvent Composition, Percent MEK 50 50 '50 Amount (Solvent/Crude Wax), v... 2. 5 2. 5 2. 5 Dilution at 58 F;

Solvent Composition, Percent MEK 50 38 45 Amount (Solvent/Crude Wax), 2.0 2.0 2.0 Filtration Temperature, F 48 48 48 Filtration Rate, ce./sec 92 132 91 Wash Volume (Solvent/Crude 'ax), v. 2.5 2. 5 2.1 Wash Composition, Percent MEK- 50 38 45 Wash Rate, cc./seo 45 77 51 EXAMPLE VII East Texas crude wax from a residual stream (generally referred to as bright stock of MX wax) was deoiled as follows: The crude wax contained about 52% by voluume of MX waxes, the balance being a mixture of low melting waxes and lubricating oil. This crude wax mixture was diluted with 3 volumes of methyl ethyl ketonetoluene, the latter diluent having a volume proportion of 1.0 volume ketone to one volume toluene. The diluted mixture was warmed to form a homogeneous solution of the wax and oil in the diluent and then cooled to 65 F. at which time a second dilution of 3 volumes of the same solvent was injected. Filtration temperature was 55 F. The time of filtration for a unit of the slurry so formed was noted. The process was repeated with additional quantities of the same crude wax but with the addition of 19.5% by volume of Water based on the solvent. Table 5 which follows illustrates the relative permeability of the wax cakes prepared under these conditions.

I claim as my invention:

1. A deoiling process which consists essentially of diluting a molten oily petroleum hydrocarbon wax with 2-8 volumes of a diluent per volume of oily wax, the diluent comprising 0.5-5.0 volumes methyl ethyl ketone for each volume of toluene, adding 2-25 percent by volume, based on the diluent, of water and which is present in an amount suilicientto form a separate aqueous liquid phase, cooling the mixture so formed to a wax crystallization temperature, separating wax from the diluted oil, recovering water from at least one of the separated components and recycling at least part of the recovered water for treatment of further portions of oily wax.

2. A process according to claim 1 wherein the diluent is injected in at least two separate stages, the water proportion of the mixture being substantially greater at a relatively higher temperature first stage than it is after further dilution at a relatively lower temperature later stage.

3. A process according to claim 1 wherein the diluent is injected in at least two stages, the toluene proportion in the oil phase being substantially greater after the injection stage immediately preceding wax separation than it is after any prior diluent injection.

4. A process according to claim 1 wherein the diluent is injected in at least two separate stages, the water proportion of the mixture being substantially greater at a relatively higher temperature first stage than it is after further dilution at a relatively lower temperature later stage and wherein the toluene proportion in the oil phase being substantially greater after the injection stage immediately preceding wax separation than it is after any prior diluent injection.

5. A process according to claim 1 wherein proportion of water is increased while cooling to the filtration temperature.

References Cited in the file of this patent UNITED STATES PATENTS 2,000,427 Tears May 7, 1935 2,326,071 Schutte -l Aug. 31, 1943 2,595,468 Kiersted et al May 6, 1952 2,726,988 Macke Dec. 13, 1955 2,734,849 Gross et al. Feb. 14, 1956 2,742,401 Kinchen Apr. 17, 1956 2,743,213 Baeklund- Apr. 24, 1956 2,760,904 Ford Aug. 28, 1956 2,983,664 Camilli May 9, 1961 3,006,339 Arabian et al. Oct. 31, 1961 FOREIGN PATENTS 7 580,040 Canada July 21, 1959

Claims (1)

1. A DEOILING PROCESS WHICH CONSISTS ESSENTIALLY OF DILUTING A MOLTEN OILY PETROLEUM HYDROCARBON WAX WITH 2-8 VOLUMES OF A DILUENT PER VOLUME OF OILY, THE DILUENT COMPRISING 0.5-5.0 VOLUMES METHYL ETHYL KETONE FOR EACH VOLUME OF TOLUENE, ADDING 2-25 PERCENT BY VOLUME, BASED ON THE DILUENT, OF WATER AND WHICH IS PRESENT IN AN AMOUNT SUFFICIENT TO FORM A SEPARATE AQUEOUS LIQUID PHASE, COOLING THE MIXTURE SO FORMED TO A WAX CRYSTALLIZATION TEMPERATURE, SEPARATING WAX FROM THE DILUTED OIL, RECOVERING WATER FROM AT LEAST ONE OF THE SEPARATED COMPONENTS AND RECYLING AT LEAST PART OF THE RECOVERED WATER FOR TREATMENT OF FURTHER PORTIONS OF OILY WAX.

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