US2742401A - Methyl-ethyl ketone dewaxing process - Google Patents

Description

April. 17, 1956 J. D. KINCHEN METHYL-ETHYL KETONE DEWAXING PROCESS Filed July 23, 1952 J. D. Kin. c rz arm/enter Qttoraeg U ie W PM 0 1 2,742,40l Patented Apr. 17, 1956 search and Engineering Com any, a corporation of Delaware Application July 23-, 1952, Serial No. 300,550

3 Claims. Cl. 196-18) This invention concerns a process for dewaxin'g petroleum fractions and particularly lubricating oil blending stocks in which methyl-ethyl ketone in combination with toluene is employed as a dewaxing solvent. The invention concerns a processing technique whereby the dewaxing solvent is adjusted to have optimum methylethyl ketone content in the sequential dewaxing of a variety of feed stocks. The invention involves the segregation of a toluene-rich stream from the solvent processing and recovery portion of the system which is withheld from the circulatory system or is added to the circulatory system to vary and control the solvent composition.

At the present time in the dewaxing of petroleum fractions the so-called MEK, or methyl-ethyl ketone process is commonly employed. In this process methyl-ethyl ketone or another low molecular weight aliphatic ketone is mixed with waxy hydrocarbons and is chilled to cause the precipitation of wax which is then filtered from the hydrocarbons. In this process it is essential that the solvent be capable of forming a miscible oil-solvent mixture at dewaxing temperatures. To meet this criterion it is common practice to employ an aromatic hydrocarbon such as benzene or toluene in combination with the methylethyl ketone so as to lower oil-solvent miscibility temperatures. For those feed stocks which are commonly dewaxed, it is essential thatat least some portion of aromatic hydrocarbon be included with the. methyl-ethyl ketone solvent to avoid conditions of oil-solvent immiscibility.

Thus, as much as 50% of. toluene or benzene or both may be employed in combination with the methyl-ethyl ketone.

It is now known thatinclus'ion of aromatic hydrocarbons with the methyl-ethyl ketone has several adverse efie'cts. Thus, as thepercentage of aromatic hydrocarbon in a MEK solvent is increased, filtering rates are decreased and/or overall yields suffer. Again, it is necessary to employ lower chilling and filtering temperatures asthe concentration of aromatic hydrocarbon is increased. Consequently, it is highly desirable to employ a dewaxing solvent having the minimum amount of aromatic hydrocarbon included. This minimum amount of aromatic hydrocarbon as indicated is set by the oil-solvent miscibility temperature of the particular feedstock.

Attempts to maintain minimum concentrations of mo matic hydrocarbons in methyl-ethyl ketone dewaxing solvents in plant scale operations is a difiicult problem. In plant operations feed stocks having widely difierent oilsolvent miscibility characteristics are commonly processed over a period of time. Thus, plant operation may necessitate dewaxing of a feed stock requiring 60% of methylethyl ketone and 40% of an aromatic hydrocarbon for several weeks. Thereafter, it may be necessary to dewax a feed stock preferably requiring about 80% of methylethyl ketone and only 20% of toluene. The present invention is directed to a means for varying solvent composition to meet the extreme requirements indicated, readily and effectively Without undue operation costs.

In accordance with this invention, toluene or a higher boiling point solvent of high solvency power for oil such as kerosene must be employed in combination with a methyl-ethyl ketone type solvent. The present invention is not of application when benzene is employed as the aromatic hydrocarbon in the dewaxing solvent. Ketones other than methyl-ethyl ketone may be employed providing the boiling point of the ketone chosen is substantially lower than the component added tomai'ntain the oil insolution at the filtering temperature. Thus, acetone, methyl normal propyl and methyl isobrutyl ketones may be employed if desired. Only acetone may be used with toluene. These requirementsare determined by the operational procedure used in this invention for adjusting solvent composition depending upon a substantial difference between the boiling point of the ketone and the aromatic hydrocarbons, as exemplified by the boiling points of methyl-ethyl ketone and toluene. The process of this invention depends upon the segregation of a solvent fraction which is rich in toluene, as obtained by the prior selective removal of a ketone-rich fraction. By segregating the toluene-rich fraction as disclosed hereinafter, it is possible to rapidly and conveniently change the solvent composition in a dewaxing process so as to increase or decrease the methyl-ethyl ketone content of the solvent.

In the operation of this process it is necessary that suitable solvent processing and storage provisions be maintained. Sufficient solvent must be available in the circulating, system or blended solvent storage at all times to provide a sufficient solvent inventory to supply the maximum methyl-ethylketone concentration requirements. In addition to this amount of solvent, additional solvent comprising principally toluene, must be available at all times to permit dilution to minimum concentrations of methyl-ethyl ketone. By this means it is possible to vary and adjust solvent concentrations by segregating and recycling or by segregating and withholding a toluene-rich stream.

In order to understand the principles of this invention it is important to appreciate the significance of solvent composition in dewaxing results. This is well shown by typical data in which a particular waxyfeed stock was dewaxed in two comparative tests employing MEK- toluene dewaxing solvent of 'diiferent MEK concentrations. The waxy feed stock employed had the inspections shown in the following table:

Table I Oil feed:

Gravity, API 33.7 Flash, COC, F 360 Viscosity, SSU 210 F 42 /2 Pour, F 105 Color, TR ll Distillation (ASTM, 10 mm), F.:

IBP 287 5% .379 10% 405 20% 440 30% 470 40% 490 50% 513 60% a 535 559 581 620 FBP 620 Recovery, percent 90.0

In a test this feed stock was dewaxed witha sol ventcomposit'ionconsisting of 65% of methyl-ethyl ketone, 34.7% of toluene, and 0.3% of benzene; the henzene being present as an impurity of the toluene. In a second test this same feed stock was dewaxed with a solvent composition consisting of 60% of methyl-ethyl ketone, 39.7% of toluene, and 0.3% of benzene. The tests were conducted on a full scale plant basis employing a feed rate of about 4,700 barrels per day. In adjusting conditions of the operation to a strictly comparable basis in order to provide a dewaxed oil having a pour point of 10 F., it was found that a 15% improvement in filter rate could be appreciated by using the solvent composition richer in methyl-ethyl ketone. Furthermore, a F. higher filtering temperature could be employed when employing the higher MEK concentration; that is, the solvent composition containing 65% of methyl-ethyl ketone. Due to the improved filtering rate, the substantial feed rate increase possible is equivalent to a 3.0% increase for each percent increase in methyl-ethyl ketone, although this advantage in filter rate varies with dilution method employed and with feed stock. From this data therefore, it is apparent that in dewaxing operations, it is extremely valuable to employ an MEK type solvent having the maximum possible MEK content. As empha sized, by employing a solvent of maximum MEK content, higher feed rates, higher filtering rates and higher filtering temperatures may be employed. While each of these advantages are clearly important, the change in filtering temperature possible is of particular interest in many plant operations where sufficient chilling capacity is not available.

The maximum MEK concentration of a dewaxing solvent composition varies substantially among feed stocks commonly dewaxed, for example, in the case of a particular 43 V/ 21.0 lubricating oil fraction derived from a paraffinic base crude oil, an MEK content of 70 volume percent is preferably employed. However, in the case of a 56 V/ 210 lubricating oil fraction, only a 60% concentration of MEK should be used.

Other feed stocks require even greater differences in MEK content for optimum dewaxing operation. It is clearly a difiicult problem in plant operation to provide a suitable method of changing solvent composition to adapt the process to handle differing feed stocks with the optimum concentration of methyl-ethyl ketone. The manner in which this invention satisfies this need is illustrated in the accompanying drawing which diagrammatically illustrates a dewaxing flow plan embodying the invention.

Referring to the drawing, a waxy feed stock is introduced to the system through line 1. This feed stock may he admixed with a portion of solvent introduced through line 2 and is then passed to a first series of heat exchangers 3. As will be seen, cold filtrate passed through line may be passed in heat exchange relation with the waxy feed in a series of chillers 3 to lower the temperature of the waxy feed. The chilled feed may then be admixed with additional solvent or filtrate introduced through line 4. The chilled feed is then passed through line 5 to a second series of chillers 6. Chillers 3 and 6 are employed to lower the feed solvent mixture to dewaxing temperatures. The temperature will depend upon the particular feed stock, the solvent composition employed and the desired pour point of the oil product. In general, however, chillers 3 and 6 together serve to lower the temperature of the feed solvent mixture to about 0 F. This chilled mixture is passed through line 7, is admixed with additional solvent or filtrate through line 8, and is introduced to filter 9. As illustrated, filter 9 may constitute a rotary filter equipped with means to remove the filtered wax through withdrawal line 11. Filtrate removed from the filter is passed through line 12 to a receiver 13 and is subsequently pumped through line 10 and thence to a storage tank 14. This filtrate constitutes the solvent employed, together with dewaxedoil.

The remaining processing steps illustrated in the drawing concern the processing of the filtered wax and the 4 processing of the dewaxed oil stream for solvent removal. The processing of the wax will first be considered.

Wax removed from filter 9 through line 11, constituting a mixture of wax and solvent, is pumped through a heater 15 and thence to a settling tank 16. A lower water phase separates in the settler 16 and an upper phase consisting of a solution of wax in the dewaxing solvent is formed. The water phase may be withdrawn from the lower portion of the settler through line 17 and is passed to stripper 18 which is operated to drive the dewaxing solvent, plus azeotropic water, overhead through line 19. Solvent-free water is removed as a bottoms product through line 20. The solvent of line 19 may be passed through condenser 21 for reintroduction to settler 16. This solvent-water azeotrope is contacted with additional excess water in settler 16 and is recycled again to stripper 18 for water removal. The solution of wax in the dewaxing solvent is then passed from zone 16 by way of line 22 through a series of heaters represented by 23, and thence to an evaporator 24 wherein solvent is removed overhead through line 25. The wax solution is then passed to a second heating zone 26 and thence to a flash zone 27 where additional solvent is removed overhead through line 28. The solvent of lines 25 and 28 may be passed in heat exchange relation with the wax solution in heating zone 23, and is then passed to a solvent storage tank 29. This solvent is subsequently used by recycling to lines 2, 4 or 8. The wax bottoms from flash zone 27 are removed through line 30 and are passed through a steam stripping zone 31. In zone 31 steam is introduced in the lower portion of the tower through line 32 permitting removal of wax product as a bottoms withdrawal through line 33 which has been stripped of all solvent. Stripping steam, together with residual solvent, removed from the stripper overhead through line .34, is condensed in condenser 35 and is passed to storage tank 36.

Returning now to the processing of the dewaxed oilsolvent mixture of tank 14, this mixture is passed through line 37 to a series of heating zones 38 and is then intro duced to a flash tower 39 to secure the overhead flashing of a portion of the solvent. This solvent is removed through line 40 and is condensed and passed to storage tank 29 for recycle in the system as described. The bottoms of flash tower 39 are passed through furnace 41 and thence to a second flash tower 42 where additional solvent is removed overhead through line 43, which is condensed and passed to storage zone 29. The bottoms of flash tower 42 comprising principally dewaxed oil together with residual solvent are passed through line 45 to stripper 46. Stripping steam is introduced to the bottom of tower 46 through line 47 serving to drive solvent overhead through line 48. Dewaxed oil stripped of solvent is removed as the bottoms product through line 50. The overhead stream of line 48 constituting solvent togetherwith some water is passed through condenser 35 to storage vessel 36.

As described, both the wax solution in solvent and the dewaxed oil-solvent mixture are separately subjected to two flashing operations followed by steam stripping. in the two flashing operations dry solvent is removed overhead and is passed to storage zone 29. This solvent constitutes a methyl-ethyl ketone-rich stream, since substantially greater portions of methyl-ethyl ketone will vaporize in the flashing operations than toluene. Consequently the solvent composition obtained from the two steam stripping zones is rich in toluene. Thus, the solvent streams of lines 34 and 48 contain substantially greater proportions of toluene than the initial solvent composition. Consequently, the solvent fraction of storage zone 36 is a segregated portion of toluene-rich solvent composition. The present invention particularly concerns the manner of segregating and utilizing this toluene-rich fraction. 1

The toluene-rich solvent of storage zone 36 is admixed with water which separates as a lower phase in storage zone 36. The water dissolves a portion of any methylethyl ketone present in zone 36. This served to further enrich the toluene layer in the vessel. The lowermost phase consisting of water together with methyl-ethyl ketone may be continuously withdrawn from zone 36 through line 61 and may be passed through line 17 to stripper 18. The distillation operation in stripper 18 serves to recover the methyl-ethyl ketone from the water for recycle through line 19, while permitting elimination of water through line 20.

Solvent rich in toluene may be removed from the upper portion of liquid in zone 36 through line 62 when desired. In processing a particular feed stock when optimumsolvent composition has been attained, to maintain the fixed solvent composition, toluene rich solvent will in effect be continuously withdrawn from zone 36 through line 62 for re-entry to the system. This may be accomplished by passing solvent from zone 36 to zone 16 through line 65. Again, the toluene rich stream may be introduced to solvent storage 29 or to solvent storage tank 14 for continued use in the system. By this means the composition of the solvent may be maintained at a fixed level. However, if, for example, it is desired to enrich the solvent composition in methyl-ethyl ketone, the following operation will be conducted. This operation may be initiated whenever plant feeds are changed to a stock which permits the use of higher concentrations of methyl-ethyl ketone in the dewaxing solvent. In this case, during a change-over period, toluene-rich solvent accumulating in vessel 36 will be permitted to remain there, so as to cause the continuous MEK enrichment of the remaining solvent in the system, by virtue of the removal of toluene from this solvent. This elimination of toluene from the solvent circulatory system is continued until the remaining solvent is sufliciently enriched in methyl-ethyl ketone. Thereafter, to maintain balance and to maintain the fixed solvent composition, toluene-rich solvent may again be recycled. This can be conveniently conducted, for ex ample, by closing valve 63 and opening valve 64 so that the solvent rich streams from the two strippers will by-pass settler 36, and will be passed to the wax settling zone 16 through line 65.

In the event that change in feed stocks necessitate employing increased concentrations of toluene, this may readily be accomplished by withdrawing sufiicient toluene from the toluene-rich reservoir of vessel 36. This toluenerich composition removed through line 62 is introduced to any appropriate portion of the solvent system in sulficient quantities to cause the desired change in solvent composition.

To more clearly indicate the process of this invention, typical operating data may be referred to. In a test run, for example, in a first portion of the run, a solvent composition consisting of 59% MEK, and 41% toluene, was employed in the system. During dewaxing employing this solvent composition, the toluene-rich streams from strippers 31 and 46 were maintained in the system by passage through line 65 to wax settling zone 16 as indicated. In a second portion of the run, however, the toluene-rich streams were passed to settling and storage zone 36 so as to remove a portion of the toluene from the solvent system. In an actual plant operation, by removing 13,800 gallons of toluene-rich material from the stripping stills, the methyl-ethyl ketone content of the remaining solvent was increased from 59% to 66% in twenty hours. In this run the composition of the solvent phase of the stripper overheads was about 75% toluene, and 25% methylethyl ketone; approximately 25% of the total stripper solvent.

overhead was water. It will be seen therefore, that the process of this invention permits ready adjustment of the methyl-ethyl ketone concentration of a dewaxing solvent composition.

In the practice of this invention, solvent storage capacity is provided to permit storing the total circulating solvent inventory in at least two vessels. Thus, the dewaxed oil filtrate storage vessel 14 and storage zone 36 may each have a capacity equal to at least one-half of the normal solvent circulating inventory. Based on these storage capacities, the solvent composition can be adjusted as shown in the table below by withdrawal of toluene rich The table also shows the possible range of toluene concentration in the stripper overheads obtained by variation in temperature and reflux in the solvent recovery system.

Toluene Content of Stripper Overhead (Solvent Phase),

Range of Adjustm 1 Vol. Percent 1 Range is reversible.

2 This concentration can be obtained by adjusting operating conditions prtviged that reflux and bubble cap trays are employed in flash zones 27 an What is claimed is:

l. A process for increasing the methyl-ethyl ketone concentration from about 60% to about of total solvent in a dewaxing operation employing a mixture of methyl-ethyl ketone and toluene as a dewaxing solvent during chilling and wax separation in which at least one flash zone and one steam stripping zone are employed to recover solvent from the dewaxing operation, said solvent from the flashing zone being continuously recycled in the dewaxing operation and said solvent from the steam stripping zone being segregated and withheld from the dewaxing operation.

2. In a methyl-ethyl ketone dewaxing process in which an admixture of methyl-ethyl ketone and. toluene is employed as a dewaxing solvent during chilling and filtration of a wax containing oil the improvement which comprises passing the dewaxing solvent mixture separated from wax by filtration to at least one flash zone, withdrawing a gas stream rich in methyl-ethyl ketone from said flash zone, withdrawing a liquid stream rich in toluene from said flash zone and passing said stream to a steam stripper zone, withdrawing a gas stream rich in toluene from said steam stripping zone, passing said last named stream to a storage zone, and thereafter combining said methyl-ethyl ketone rich stream and said toluene in selected proportions such that the total solvent contains from about 60% to about 80% methyl ethyl ketone and from about 20% to 40% toluene for the dewaxing step of the process.

3. The process defined by claim 2 in which the said toluene from the steam stripping zone is mixed with water and separated to provide a water phase and a toluene phase, said water phase being stripped to provide a second methyl-ethyl ketone rich stream.

References Cited in the file of this patent UNITED STATES PATENTS 2,142,359 Lederer Jan. 3, 1939 2,443,532 Berg June 15, 1948 2,550,058 Gee Apr. 24, 1951 2,625,502 Backlund et a1. Jan. 13, 1953

Claims (1)

1. A PROCESS FOR INCREASING THE METHYL KETONE CONCENTRATION FROM ABOUT 60% TO ABOUT 80% OF TOTAL SOLVENT IN A DEWAXING OPERATION EMPLOYING A MIXTURE OF METHYL-ETHYL KETONE AND TOLUENE AS A DEWAXING SOLVENT DURING CHILLING AND WAX SEPARATION IN WHICH AT LEAST ONE FLASH ZONE AND ONE STEAM STRIPPING ZONE ARE EMPOLYED TO RECOVER SOLVENT FROM THE DEWAXING OPERATION, SAID SOLVENT FROM THE FLASHING ZONE BEING CONTINUOUSLY RECYCLED

Images