A process for dewaxing including the steps of mixing a waxy feedstock near its pour point with an ambient or below ambient temperature solvent essentially free of a selected cosolvent, to form a solvent/feedstock mixture, essentially free of a selected cosolvent, and subsequently adding the cosolvent to the solvent/feedstock mixture to cause instantaneous precipitation of wax on addition of cosolvent with the amount of wax precipitation being controlled by the quantity and temperature of cosolvent added. The cosolvent is essentially completely miscible with the solvent, but immiscible with the oil and wax. For example, alcohols (methanol, ethanol, propanol), ketones (ketene, acetone), amines, etc. The process of the present invention provides the advantages of lower solvent ratios (higher solvent recovery), higher filtration temperatures, "environmentally compatible" solvents, rapid filtration rates, and debottlenecking of existing dewaxing plants.

BACKGROUND OF THE INVENTION 
The present invention relates to dewaxing of petroleum products and other 
heavy hydrocarbon mixtures. It also relates to similar processes for 
deoiling the waxes that are found in combination with heavy hydrocarbon 
mixtures. The present invention also relates to wax fractionation and the 
production of low pour point oils. It will be understood that when the 
term dewaxing is used herein it will also include other similar processes 
such as deoiling. Wax as used in the present description will include all 
compounds or mixtures to which the term wax is applied, both natural and 
synthetic, and also will include in general saturated hydrocarbon chain 
link compounds. 
Crude petroleum and partially refined petroleum commonly contain waxes 
(usually paraffin waxes). Such waxes crystallize at low temperatures, and 
this is particularly notable with high molecular weight n-paraffins, 
certain iso-paraffins, and cycloparaffins. 
When the petroleum is being refined for use as lubricating oil, the 
presence of these materials which crystallize within a range of 
temperatures for which the lubricating oil is intended is very 
deleterious. Such materials are therefore commonly removed in the refining 
process and this subprocess is referred to as dewaxing. 
There is great variety in the processes used for dewaxing as it cannot be 
carried out as a normal consequence of the conventional fractional 
distillation process. The oldest and simplest form of dewaxing is chilling 
of the crude lubricating oil to about the desired pour point temperature 
causing crystallization of most of the wax components, after which they 
are physically removed by filtration or the like. This process is largely 
of historical interest because of its high cost and unsuitability for 
processing heavy oils. 
The straight chilling process for dewaxing was improved by inclusion of an 
initial step of adding a relatively large proportion of solvent or diluent 
to the oil prior to the chilling process. Early types of diluents used in 
this solvent dewaxing process were heavy naphtha or gas oil. In recent 
years a great variety of solvents have been employed in conjunction with 
the chilling step to endeavor to increase efficiency and otherwise improve 
results. 
it was found that somewhat better solvent-chilling dewaxing results were 
achieved with a mixture of two solvents and thus various mixtures of two 
different solvents have been employed as dewaxing solvents. Perhaps the 
most frequently used dewaxing solvent mixture has been a mixture of methyl 
ethyl ketone (MEK), toluene, and benzene. A common dewaxing solvent 
mixture may contain 25% to 50% of MEK, 40% to 60% of benzene, and 12% to 
25% of toluene. Sometimes ketones of higher molecular weight have been 
used in place of MEK. This permits one to obtain a higher solvent power 
for heavy oil. In some solvent-chilling dewax operations the high 
crystallization temperature (about 5.degree. C.) of benzene has caused 
toluene to be substituted for the benzene so that the diluent is 
essentially a mixture of MEK and toluene. 
A common solvent-chilling dewax process may proceed as follows. The solvent 
may be an MEK/benzene or an MEK/toluene combination. After the solvent is 
added to the oil charge to form a mixture, the mixture is normally heated 
slightly to Insure complete solution of wax components. The mixture is 
then chilled to the required filtration temperature, usually on the order 
of -20.degree. C. utilizing a conventional refrigeration process. 
Refrigeration is typically carried out by pipe-in-pipe type heat 
exchangers (scrape-surface heat exchangers) with the solvent and waxy oil 
in the inside pipe and a refrigerant such as propane or sulfur dioxide in 
the annular space between the two pipes. The surface of the inner pipe 
must be kept free of wax by scraper blades to maintain adequate heat 
transfer. The wax is removed by filtration under vacuum in conventional 
rotary filters in a well known manner. 
There are other processes for solvent-chilling dewaxing, such as propane 
dewaxing in which a single effective constituent is present in the 
solvent. Propane dewaxing has certain advantages in that it may be a 
follow-on to propane deasphalting, thereby eliminating a propane-oil 
separation step between the stages of the process. A disadvantage of 
propane dewaxing is that the required dewaxing temperatures are generally 
lower. 
In light of the foregoing, there is a need for an improved, simplified and 
economical petroleum-wax separation process which provides for the 
effective dewaxing or deoiling of waxy feedstocks. 
SUMMARY OF THE INVENTION 
In accordance with the present invention a sequential solvent and cosolvent 
petroleum-wax separation process provides for dewaxing of waxy feedstocks, 
for example, lube oil, raffinates, resids, or slack wax, deoiling, wax 
fractionation, and the production of low pour point oils. In accordance 
with one embodiment of the present invention, the dewaxing process does 
not require chilling of the solvent, cosolvent, feedstock, or mixtures 
thereof below normal ambient temperature for crystallization of and 
precipitation of the wax. However, in accordance with other embodiments of 
the present invention the dewaxing process is carried out in a dewaxing 
system including refrigeration apparatus and includes a chilling step. 
The dewaxing process of the present invention involves two separate 
dilution steps or solvent addition steps with two distinctly different 
solvents. Hereinafter the first solvent will be referred to as the primary 
solvent, or simply the solvent, and the second solvent will be referred to 
as the cosolvent (or selected cosolvent). The term "cosolvent" as used 
herein will have a specially defined meaning, not to be confused with 
various meanings for cosolvent which may be found in other contexts. 
The second solvent, or the "selected cosolvent" as it will be termed, is 
selected from a group of chemical compounds, for example, alcohols, 
ketones, and amines, which are essentially completely miscible with the 
solvent, but immiscible with the wax, and in the liquid state at or above 
room temperature (at a pressure of less than ten atmospheres). In this 
discussion, room temperature will be understood to be a rather wide range 
of temperatures about 20.degree. C. (68.degree. F.) plus or minus 
10.degree. C. (18.degree. F.). Also, it is preferred that the cosolvent be 
essentially immiscible with the oil and significantly miscible with water. 
The group from which the selected cosolvent is taken is preferably the 
group of alcohols having a molecular composition with a low carbon number, 
preferably of three or less, and having one oxygen atom plus an even 
number (2-8) of hydrogen atoms. Specifically these compounds are: 
methanol, ethanol, propanol, and isopropanol. The above four compounds 
have the physical characteristic of total miscibility with 
light-to-intermediate (herein defined as C number of less than fourteen) 
hydrocarbons, tertiary ethers, dimethyl carbonate, and water. At the same 
time, they have low solubility for waxes. 
In the process according to the present invention, the requirements for the 
primary solvent are not very strict and most light-to-intermediate 
hydrocarbons known and commonly used as solvents may be employed alone, or 
in admixture, for the primary solvent. In accordance with a preferred 
embodiment of the present invention, the primary solvent is selected from 
a group of tertiary ethers including MTBE, TAME, ETBE, and esters of 
carbonic acid such as dimethyl carbonate. The primary solvent should not 
contain more than twenty-five percent of the selected cosolvents described 
above. Admixture of the cosolvent with the solvent before addition to the 
petroleum feedstock substantially destroys the effectiveness of the 
selected cosolvent in crystallizing and precipitating the wax components 
from the feedstock/solvent mixture. 
Where the process according to the invention is directed to dewaxing a 
petroleum feedstock to obtain an end product with sufficiently low 
residual wax content for high quality lubricating oil, this can be 
accomplished, if desired, in a single stage of steps of primary solvent 
dilution, selected cosolvent dilution, precipitation and filtering. Of 
course, a practical industrial process normally involves a closed loop 
system for recovery and reuse of solvents and cosolvents, as will be more 
fully explained hereinafter. 
There are two desirable objectives in the separation of wax from petroleum 
or other hydrocarbons, one of which is obtaining a high quality 
lubricating oil with minimal residual wax content as previously described. 
The other advantage to be obtained is to maximize the potential value of 
the recovered waxes themselves. Waxes are used in a great many industrial 
processes for wax coating paper or paperboard products and other uses too 
numerous to mention. High quality waxes are also a component of numerous 
consumer products. In general, the desirability and hence the value of 
waxes is directly related to their high melting or softening temperature 
which is in turn related to their high molecular weight. The process 
according to the present invention can be carried out in a manner to 
provide fractionation so as to separately recover waxes of highest value, 
thereby inexpensively producing a by-product capable of substantially 
contributing to the profitability of the overall operation. The process 
when carried out in this form is still capable of further removal of the 
waxes of lower molecular weight (and generally lower value) substantially 
in their entirety to produce a nearly wax-free lubricating oil of high 
quality. 
In accordance with an embodiment of the present process used to maximize 
the value of recovered waxes, the selected cosolvent diluent is added in 
at least two different stages rather than in one stage. It has been found 
that reducing the amount or proportion of the selected cosolvent diluent 
has two effects. One is that the quantity of wax precipitated is reduced. 
The other effect is that the wax produced is of a higher average molecular 
weight and higher melting point, and thus has substantially higher 
potential value. These higher value waxes are removed in a conventional 
filtering process and may be further deoiled by additional washing with 
the same or similar solvents. The value of the wax recovered in this form 
of the process is quite high and may be on the order of $1.00 a pound. 
Following the recovery of the high molecular weight wax, the filtrate is 
transported to a second stage of selected cosolvent dilution, generally 
with little or no further treatment of the filtrate. At this point the 
filtrate contains the original petroleum feedstock with the residual wax 
that has not been removed, the added primary solvent, and a limited 
proportion of the selected cosolvent. 
With the addition of a greater quantity of selected cosolvent, it has been 
found that additional quantities of wax in the solution will crystallize 
and precipitate allowing them to be removed by a physical process such as 
filtration. The addition of water at this point will aid in completing the 
wax crystallization process. Still further crystallization may be induced 
by the use of brine with or in place of the water, but certain 
disadvantages accruing from brine introduction make this generally a less 
preferable variation of the process. If desired, substantially complete 
removal of waxes can be accomplished in the second stage or the wax 
removal can be divided into still more stages of selected cosolvent 
(possibly with water) dilution, precipitation, and filtration, each stage 
having a wax product produced with lower molecular weight and lower 
melting point than the previous stage. 
In accordance with one embodiment of the present process, refrigeration or 
cooling by artificial means is not required, thereby greatly simplifying 
the process and greatly reducing the expense of this essential aspect of 
petroleum refining. In accordance with another embodiment of the present 
petroleum-wax separation process, selected solvents and cosolvents can be 
used in separation apparatus including conventional refrigeration and 
cooling means. In accordance with yet another embodiment of the present 
process, wax precipitation is facilitated by evaporative cooling involving 
evaporation or absorption of at least some of the solvent, cosolvent, or 
both. Such evaporation is accomplished, for example, by a change in 
pressure across a filter unit, a vacuum drawn on the 
feedstock/solvent/cosolvent mixture or a filtrate (adiabatic flash), or an 
absorption of solvent or cosolvent by an inert gas (adiabatic stripper). 
Evaporative cooling enhances the wax-oil separation by reducing the 
filtration temperature without requiring the use of conventional 
scrape-surface heat exchangers. 
In accordance with one aspect of the present invention, a process for 
separating oil and wax from a waxy feedstock includes an evaporative 
cooling step involving a vaporization of cosolvent into an inert gas, such 
as, nitrogen. More particularly, the evaporative cooling step involves the 
passing of an inert gas through the feedstock/solvent/cosolvent slurry. As 
a result of the presence of the inert gas, some of the cosolvent (and 
small quantities of solvent) will be vaporized. When this process is 
carried out adiabatically (no heat added or removed), the temperature of 
the slurry will drop resulting in additional wax precipitation 
(crystallization). The final slurry temperature can be controlled by 
controlling the amount of cosolvent evaporated. This can be adjusted by 
varying the nitrogen flow rate, column height, etc. 
This evaporative cooling step can be carried out prior to the first 
filtration, resulting in a fully dewaxed oil in the first step. 
Alternatively, the evaporative cooling can be carried out after a first 
filtration in which the high melt waxes are removed so that the resulting 
filtrate is cooled and refiltered to remove the low melt waxes and produce 
a lube oil of low pour point. After some of the cosolvent has been 
evaporated into the inert gas stream it must be recovered from the gas. 
This can be accomplished by either using a cooler (condenser) or 
reabsorbing the cosolvent into fresh feed. 
Some of the advantages of the present process include lower solvent ratios, 
higher filtration temperatures, environmentally compatible solvents 
(tertiary ethers, dimethyl carbonate, and alcohols), rapid filtration 
rates, less overall refrigeration, and potential for debottlenecking lube 
operations. 
In accordance with one aspect of the present invention, environmentally 
compatible solvents and cosolvents such as MTBE, ETBE, TAME, dimethyl 
carbonate, and alcohols are used in place of MEK, toluene and acetone. 
These environmentally compatible oxygenated solvents and cosolvents allow 
existing lube plants and dewaxing operations or facilities to continue to 
be operated without modification or with minor modifications for splitting 
the solvent and cosolvent for reuse. 
In addition to providing the features and advantages described above, it is 
an object of the present invention to provide a solvent dewaxing process 
for substantially complete dewaxing of crude or partially refined 
petroleum. 
It is another object of the present invention to provide a dewaxing process 
for liquid or amorphous heavy hydrocarbons in which two distinctly 
different diluents are used sequentially with the second of such diluents 
being a selected cosolvent consisting essentially of one or more ketones, 
alcohols or organic acids with a carbon number of three or less, and the 
first of the diluents being any one or more of a general class of commonly 
used solvents or octane enhancers except that such primary solvent contain 
no more than twenty-five percent of such selected cosolvents. 
It is yet another object of the present invention to provide a petroleum 
wax separation process for waxy feedstocks in which two distinctly 
different diluents are used sequentially in the process, the first of such 
diluents being either a tertiary ether or a dimethyl carbonate and the 
second diluent being an alcohol. 
It is still another object of the present invention to provide a process 
for separating wax from a liquid or amorphous hydrocarbon mixture 
including two steps of adding controlled amounts of selected cosolvents 
consisting essentially of one or more alcohols, ketones, or organic acids 
with a carbon number of three or less, the first quantity of such 
cosolvent being limited to cause crystallization and precipitation of only 
high molecular weight, high melting point waxes, while the second quantity 
of selected cosolvent is sufficient to crystallize and precipitate 
substantial quantities of lower molecular weight waxes. 
It is yet another object of the present invention to provide a process for 
separating wax from a waxy feedstock or waxy feedstock/solvent mixture 
including the step of evaporatively cooling the solvent, cosolvent, 
feedstock/solvent mixture, feedstock/solvent/cosolvent slurry, filtrate, 
or solvent/cosolvent mixture by evaporating or absorbing some of the 
solvent or cosolvent. 
It is still another object of the present invention to provide a deoiling 
process for waxes recovered from liquid or amorphous hydrocarbon mixtures 
producing high quality wax of high molecular weight wherein a quantity of 
selected cosolvent is added to a liquid hydrocarbon mixture at room 
temperature or above and crystallized wax is thereby precipitated, after 
which it is recovered by filtering and washed with a liquid including the 
same selected cosolvent to further remove residual oil from the wax after 
which the washing cosolvent is separated from the high quality, high 
molecular weight wax by filtration or evaporation. 
It is yet another object of the present invention to provide a petroleum 
wax separation process producing low pour point oils. 
It is still yet another object of the present invention to produce high 
normal paraffin content waxes with narrow carbon distributions. 
Other objects and advantages of the present invention will be apparent from 
consideration of the following description in conjunction with the 
accompanying drawings wherein like parts are designated by like reference 
numerals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In accordance with one embodiment of the present invention, the petroleum 
wax separation process provides for dewaxing with or without integral 
deoiling, stand alone deoiling, and wax fractionation, all of which can be 
carried out at or near ambient temperatures, depending on the product or 
products desired, without requiring the use of scraped-surface heat 
exchangers or scraped-surface chillers. The present process involves 
bringing a waxy feedstock (distillate, raffinate, slackwax, resid, gas 
oil, lube oil, etc.) at or slightly above its pour point into contact with 
ambient, near ambient, or below ambient temperature solvent and achieving 
a homogeneous solution or feedstock/solvent mixture having a pour point 
below that of the feedstock. Mixing may be achieved by any of several 
methods, however, simple static mixers are usually more than sufficient. 
After mixing, the solvent/feedstock feedstock mixture is well below the 
pour point of the original waxy feedstock. The solvent selection is not 
too critical. There are a large number of solvents that will work. The 
solvent should be chosen such that the oil and all or most of the wax are 
soluble at ambient temperature. The amount of solvent used should be kept 
low for economic reasons and this can gave an impact on the solvent 
selection. The solvent/feedstock ratio in general is around 0.5/1.0 by 
weight, however, it can be higher or lower depending on the feedstock and 
the product or products desired. Solvent selection can come from several 
classes of compounds, for example; paraffins, aromatics, chlorinated 
compounds, and oxygenated compounds (MEK, MIBK, ethers, MTBE, TAME, ETBE, 
esters of carbonic acid, dimethyl carbonate, higher alcohols, etc.) The 
solvent can also be selected from any of the dewaxing solvents known in 
the prior art such as the aliphatic ketones having from three to six 
carbon atoms, e.g., acetone, methylethyl ketone (MEK), methylisobutyl 
ketone (MIBK) especially when warm and the like, the lower molecular 
weight hydrocarbons such as propylene, and aromatics such as benzene and 
toluene. In addition, halogenated low molecular weight hydrocarbons such 
as the C.sub.2 -C.sub.4 chlorinated hydrocarbons, e.g., dichloromethane, 
dichloroethane and mixtures thereof, may be used. Specific examples of 
solvents include toluene, MIBK, MEK/Toluene, MEK/MIBK, and the like. 
However, virtually anything that allows for a homogeneous solution at the 
mixing temperature will work. 
After the solvent and feedstock have been mixed, the solvent/feedstock 
mixture is mixed with a cosolvent to form a feedstock/solvent/cosolvent 
slurry. The term "slurry" as used herein will refer to the 
feedstock/solvent/cosolvent mixture which is usually a predominantly 
liquid mixture containing some solids in the form of crystallized and/or 
precipitated wax. The key to the present process is the successive 
addition of a cosolvent, in one or more steps. Cosolvent selection is 
critical and of greater importance than the solvent. The cosolvents are 
any compounds that are essentially immiscible with the wax at and below 
the mixing temperature. The cosolvents are preferably essentially 
immiscible with the oil, but miscible with the oil/solvent mixture. In 
addition, most of the cosolvents that work well have significant (almost 
total) miscibility with water. The following cosolvents are specifically 
mentioned: alcohols (methanol, ethanol, propanol, isopropanol), ketones 
(ketene, acetone, MEK and MIBK if cold), amines, ethers and aldehydes, 
However, this list is not complete and exhaustive, but simply 
illustrative. The importance in cosolvent selection is to meet the 
criteria set forth above. 
If the solvent, feedstock, and cosolvent are simultaneously mixed in the 
ratios used by this process (solvent/feedstock/co-solvent ratios are about 
1.0/0.5/2.0 by weight when using Texaco 325N raffinate as feedstock) at 
the elevated mixing temperature of a conventional MEK/toluene process, two 
liquid phases may result. The wax will be removed from solution, but it 
will be liquid at the high mixing temperatures. As a liquid, it will have 
a high oil solubility and the process does not work. In order to prevent 
problems of a liquid wax/oil phase forming, the solvent used should be 
relatively low in cosolvent contamination because of the higher mixing 
temperature of the solvent/feedstock mixture. Solvents containing up to 
ten percent cosolvent by weight are not usually a problem, but 
contamination much higher than twenty-five percent may cause problems with 
some feedstocks, particularly slack waxes. 
The cosolvent can be added at ambient or near ambient temperature or 
chilled well below ambient temperature depending on the feedstock and the 
desired product or products. As the cosolvent is added to the 
solvent/feedstock mixture, wax immediately precipitates from the solution. 
The amount of wax removed is controlled by the cosolvent chosen (and to a 
limited extent, the solvent chosen), the amount of cosolvent used 
(solvent/cosolvent ratio, solvent/feedstock ratio), and by the temperature 
of the resulting mixture. The process carried out in this fashion is an 
equilibrium process, not a rate based process. In general, when attempting 
to achieve a low pour oil, if the ratios of solvent and cosolvent are 
chosen carefully, a pour point can be obtained which is well below the 
filtration temperature. Pour points 30.degree. F. below filtration 
temperature are typical and with some optimization, 40.degree. to 
45.degree. F. below filtration temperature can be obtained. In order to 
achieve lower pour oils, the slurry that has formed after the cosolvent 
addition may be chilled further by use of some means of solid-surface heat 
exchange, by evaporative cooling (absorptive cooling or auto 
refrigeration), or by addition of cold cosolvents or solvents. 
When wax precipitation is carried out by this process, the first waxes to 
precipitate are very high in normal paraffins. By sequentially adding 
limited amounts of cosolvent, very high normal paraffin content 
(ninety-five percent or greater) waxes with narrow carbon distributions 
(five carbons or less) and narrow melting point ranges (plus or minus five 
.degree.F. or less) can be produced by this process. Thus, the process can 
be used as a wax fractionation process. Also, the oils produced by this 
process may have some enhanced properties. 
Water may have a significant effect on the process by acting as a second 
cosolvent. The water is miscible with the cosolvents and, if added to the 
solvent/feedstock/cosolvent slurry, it will act to enhance the cosolvent 
action and remove more wax from solution. The amount of water must be 
controlled to prevent the formation of separate water/cosolvent and 
oil/wax/solvent liquid phases. 
Some of the advantages of this process are: use with or without 
scraped-surface exchangers and scraped-surface chillers; lower solvent 
ratios; higher filtration temperatures; "environmentally compatible" 
solvents; rapid filtration rates and less overall refrigeration. As a 
result of elimination of scraped-surface exchangers and higher filter 
rates from higher filter temperatures, the process provides for 
debottlenecking lube operations. 
Because the crystal formation in this process is an equilibrium process, 
not a rate based process such as the heat transfer based refrigeration 
process used by conventional dewaxing technology, the crystal structure is 
likely different. Crystals formed by the present process appear to have 
structural advantages which allow for more rapid filtration. In addition 
to the structural differences, the higher filtration temperatures of the 
present process allow for more rapid filtration rates. Filtration rates of 
10 gal/hr ft.sup.2 (based on oil feed) have been obtained using only 5 
inHg vacuum on a conventional rotary vacuum filter. 
Some means of refrigeration can be used to chill the solvent or cosolvent 
streams which can be used as cold dilution solvent at the mixers or for 
other temperature control. Refrigeration can also be used to cool or 
condense various vapors (such as solvent or cosolvent vapors from the 
vacuum system). In addition, cold solvents or cosolvents can be obtained 
by cross exchanging the solvents or cosolvents with cold filtrate. 
As shown in FIG. 1 of the drawings, a waxy feedstock enters the process at 
1 where it is mixed in a conventional mixing tank M with a primary 
solvent. By way of example only, the feedstock may consist of waxy heavy 
vacuum gas oil and the primary solvent, for example methyl tertiary butyl 
ether (MTBE), may be in ratio of 2:1 by weight to the feedstock. Unless 
otherwise stated all proportions herein are proportions by weight. 
The primary solvent provided through line 10 and the feedstock provided 
through line 1 are mixed in mixing tank M to obtain a homogeneous 
solution. This step may be facilitated by heating the feedstock or 
solution to a temperature above ambient temperature, up to about 
120.degree. F. (or 48.9.degree. C.). The output from mixing tank M is 
supplied through line 2 to mixing tank M1 where it is mixed with a 
selected cosolvent, for example methanol, the ratio of methanol to 
feedstock being 3:8 in this example, it should be noted that the primary 
solvent may include commonly used solvents other than MTBE, but it should 
not contain significantly more than twenty-five percent of the selected 
cosolvent, methanol. 
The temperature of the mixing tank M1 and contents is not critical but will 
normally be slightly above ambient temperature, in this example 78.degree. 
F. (or 25.6.degree. C.). The addition of the selected cosolvent in the 
mixture of mixing tank M1 spontaneously produces crystallization of a high 
melt fraction of the wax content of the feedstock. The relatively low 
ratio of cosolvent to feedstock causes only high molecular weight, high 
melt temperature wax crystals to form. The wax crystals precipitate from 
the solution, and this slurry is fed through line 3 to a conventional 
vacuum filter apparatus V1. Exiting the vacuum filter apparatus V1 through 
line 4 is a wax product, at this point comprising a waxy slurry which is 
conveyed through line 4 to a solvent evaporation step at F1 which may be 
performed by a conventional flash evaporation or distillation apparatus. 
From F1, the removed wax product P1 is conveyed through line 5 to product 
P1 storage tank T1. Although product P1 may be further washed or refined, 
such steps are conventional and not shown in FIG. 1 for simplicity and 
clarity. Product P1 in storage tank T1 may be heated and mildly agitated 
to prevent solidification pending further processing thereof. 
The evaporated feedstock, primary solvent, and cosolvent from flash 
evaporator F1 is supplied to distillation column C through line 13. As 
will be more fully explained hereinafter, the process flow diagram of FIG. 
1 includes solvent and cosolvent recovery steps which are necessary for a 
practical system, although they are not a critical feature of the present 
invention. In this regard, it may be desired to select the chemical 
compounds utilized for the primary solvent (or solvents) and the selected 
cosolvent (or cosolvents) with a view to ease of separating them in the 
recovery process. As previously explained, this separation is necessary 
particularly from the point of view of eliminating an amount of selected 
cosolvent significantly greater than twenty-five percent of the primary 
solvent make up. In the example being described, the selected cosolvent 
methanol has a higher boiling point than the primary solvent MTBE, thus 
making virtually complete separation of the cosolvent and primary solvent 
easy to accomplish in a conventional distillation column. 
Considering now the filtrate from rotary vacuum filter V1 which is now at a 
lower temperature due to the effects of the first vacuum filtration, it is 
supplied through line 18 to a mixing tank M2. Thus, the filtrate from the 
first stage may be used essentially without further treatment in a second 
stage of wax separation. An additional quantity of selected cosolvent is 
supplied through line 6 to mixing tank M2. The quantity of additional 
cosolvent for the second stage will normally be equal to or greater than 
the amount of cosolvent for the first stage. In the present example, the 
additional selected cosolvent in the second stage is double that of the 
first stage. That is, the ratio of second stage cosolvent to original 
feedstock is 3:4. The process flow for the second stage proceeds 
substantially the same as for the first stage with the slurry output of 
mixing tank M2 passing along a line 7 to a rotary vacuum filter V2 having 
a wax product output along a line 8 to a solvent flash unit F2, which 
evaporates the residual oil, solvent and cosolvent from the wax product 
into line 12 arid on to distillation column C via line 13. The wax product 
P2 of flash unit F2 proceeds through line 9 to product P2 storage tank T2 
in the same fashion as with product P1 and tank T1. The filtrate output of 
vacuum filter V2 passes along line 11 to distillation column C. 
Dewaxed feedstock (oil) is transferred through line 14 from the recovery 
distillation column C to a flash evaporator F3 in which the cosolvent is 
flashed and transported through line 15 to be recycled while the dewaxed 
lube oil product is fed through line 16 to a lube oil storage tank T3. 
Solvent is transferred along line 10 from the distillation column C to 
mixing tank M. The recycled solvent should contain twenty-five percent or 
less cosolvent contamination. 
The solvent in line 10 can be cooled or chilled, by for example, 
cross-exchange with the filtrate in line 11, evaporative cooling, or 
refrigeration, to provide cold solvent injection in mixing tank M. 
Likewise, the cosolvent in line 15 can be cooled or chilled to provide 
cold cosolvent injection in mixing tanks M1 and M2. 
The number of stages of wax separation is not limited to two and additional 
stages may be employed. For example, a third stage may add an additional 
quantity of selected cosolvent (methanol) equal to that added in the 
second stage. In the third stage the vacuum filtered wax cake may be 
washed with a 1:1 MTBE/methanol wash in a quantity of two and two-thirds 
of the amount of methanol added in the third stage. The filtrate from the 
third stage and the oil/solvent and cosolvent from the flash evaporator 
would be returned to the recovery distillation column C in the same manner 
as for the second stage. Still further stages of wax separation could be 
employed and the number of stages will generally be determined with a view 
to economic factors which are subject to wide variation. Based on 
experiments and calculations, excellent yield of different qualities of 
wax can be obtained. 
As previously explained in part, solvent and cosolvent recovery is provided 
for in the process flow diagram of FIG. 1. In the example given, the 
cosolvent methanol has a higher boiling point than the solvent MTBE and 
this will be the case when using MTBE as the solvent and an alcohol such 
as methanol, ethanol, propanol or isopropanol as the cosolvent. When using 
a solvent having a higher boiling point than the cosolvent, the 
distillation column C would have separate cosolvent and solvent/oil 
outputs. Distillation column C obtains virtually complete separation of 
the selected solvent and cosolvent so that solvent line 10 has no 
significant amount of selected cosolvent. 
The following yields can be expected in a system corresponding to the 
process flow diagram of FIG. 1. With a feedstock of from 25% to 30% wax 
content one may expect a yield of approximately 5% (by weight) of high 
melting point wax (congealing point 172.degree. F.) from stage 1 (P1), and 
a yield of approximately 8% of feedstock weight of an intermediate melting 
point wax (congealing point of about 160.degree. F.) from stage 2 (P2). In 
a third stage as described, low melting point waxes will be recovered with 
an expected quantity of about 12% of original feedstock weight, and a low 
melting point (congealing point of about 135.degree. F.). 
It should be particularly noted that contrary to most prior dewaxing 
systems, the present system allows the waxes to be recovered in separate 
stages characterized by different melting points, and thus different 
values. In most prior systems, it was necessary to conduct further 
processing of removed wax to separate desirable waxes of high value from 
those of little or no value. As seen from the above description, the 
separation of waxes is accomplished within the dewaxing process itself 
according to the present invention. 
The process according to the present invention is subject to wide variation 
not limited to the following examples. For clarity and definiteness 
certain terms will be considered to have special meaning for the purpose 
of this description and claims. Light-to-intermediate hydrocarbon will 
mean a hydrocarbon with a C-number of thirteen or less. Dewaxing will mean 
any process for separation of wax from oil or vice-versa. Oil will mean 
any liquid or amorphous hydrocarbon, natural or synthetic. Wax will mean 
any compound or mixture to which the term wax is applied, natural or 
synthetic. Cosolvent will mean a solvent in which the feedstock/solvent 
mixture is soluble but which promotes separation of wax from the 
feedstock. Room temperature means a range of temperatures of 20.degree. C. 
(68.degree. F.) plus or minus 10.degree. C. (18.degree. F.). Liquid will 
mean any material which enters a liquid state at ambient temperature and 
at a pressure of ten atmospheres or less. 
The following examples of processes according to the above-described 
embodiment of the present invention with specific materials, quantities, 
times, temperatures and other parameters should be considered to be 
illustrative and not restrictive of the scope of the present invention. 
EXAMPLE 1 
Example of multi-stage dewaxing or deoiling to sequentially and selectively 
remove wax fractions. Two hundred parts of a waxy heavy vacuum gas oil 
(feedstock) is mixed with four hundred parts of toluene (solvent) and 
gently heated until a homogeneous solution is obtained. The mixture is 
allowed to cool to 78.degree. F. (25.6.degree. C.). In a first stage, 
seventy-five parts of acetone (cosolvent) is added to precipitate a high 
melt fraction of wax crystals. The mixture is filtered by vacuum 
filtration and the wax cake product is washed with forty parts of a 
toluene/acetone mixture having a ratio of toluene/acetone of 5:1. After 
the cake is heated to remove any solvents or cosolvents and weighed, a 
yield of eleven parts of wax with a congealing point of 172.degree. F. 
(77.8.degree. C.) is measured. 
The filtrate from the first stage, its temperature having dropped to around 
-3.degree. C. because of the vacuum filtration, is used in a second stage 
which removes additional wax. In the second stage an additional one 
hundred fifty parts of acetone is added to the filtrate from the first 
stage and additional wax precipitates. The mixture is vacuum filtered and 
washed with one hundred fifty parts of a toluene/acetone mixture having a 
ratio of toluene/acetone of 2:1. After the wax cake is heated and weighed, 
a yield of fifteen parts of wax is measured with a congealing point of 
about 160.degree. F. (71.1.degree. C.). 
The filtrate from the second stage is used in a third stage, its 
temperature having dropped an additional 10.degree. C., to remove 
additional wax. In the third stage an additional one hundred fifty parts 
of acetone is added to the filtrate from the second stage and additional 
wax precipitates. The mixture is vacuum filtered and the wax cake is 
washed with one hundred parts toluene/acetone having a ratio of 1:1. After 
the wax cake is heated and weighed, a yield of twenty-four parts of wax 
with a congealing point of about 135.degree. F. (57.2.degree. C.) is 
measured. 
EXAMPLE 2 
This is an example of a dewaxing of heavy vacuum gas oil to produce a wax 
and low pour point oil suitable for lube oil stock. Twenty parts of 
toluene (solvent) are mixed with ten parts of heavy vacuum gas oil 
feedstock and gently heated. The mixture is then allowed to cool to about 
78.degree. F. (25.6.degree. C.). Thirty-six parts of acetone (cosolvent) 
are added and within minutes a wax precipitate forms. After adding the 
acetone, approximately one part of water (secondary cosolvent) is added to 
the mixture and additional wax precipitates. The wax is recovered by 
vacuum filtration and wax amounting to about seven parts by weight is 
obtained. The solvents are removed from the filtrate by flashing at about 
232.degree. C. (450.degree. F.) maximum and an oil product is obtained 
having a pour point of approximately 45.degree. F. (7.2.degree. C.). 
EXAMPLE 3 
Two hundred parts of a waxy heavy vacuum gas oil (feedstock) is heated to 
about 120.degree. F. (48.9.degree. C.) and mixed with four hundred parts 
of cold toluene (solvent) at about 30.degree. F. (-1.11.degree. C.) to 
form a homogeneous solution at about 78.degree. F. (25.6.degree. C.). In a 
first stage, seventy-five parts of acetone (cosolvent) at about 78.degree. 
F. (25.6.degree. C.) is added to precipitate a high melt fraction of wax 
crystals. The mixture is filtered by vacuum filtration and the wax cake 
product is washed with forty parts of a toluene/acetone mixture having a 
ratio of toluene/acetone of 5:1. After the cake is heated to remove any 
solvents or cosolvents and weighed, a yield of eleven parts of wax with a 
congealing point of 172.degree. F. (77.8.degree. C.) is measured. 
In accordance with another aspect of the present invention, the petroleum 
wax separation process is enhanced using evaporative cooling, that is 
cooling by evaporation of some of the cosolvent or solvent depending on 
the particular solvent/cosolvent combination. The term evaporative cooling 
as used in the present application refers to cooling by evaporating 
solvent or cosolvent by, for example, a change it pressure across a vacuum 
filter, auto refrigeration by pulling a vacuum on the filtrate from a 
first vacuum filter before it passes to a second vacuum filter using an 
adiabatic flash and recirculating cold solvent or cosolvent, or 
absorbative cooling by using an adiabatic inert gas (nitrogen) stripper to 
cool the filtrate as it passes from one vacuum filter to another vacuum 
filter. Usually, in the context of the present invention, evaporative 
cooling is effected by evaporating one of the solvent or cosolvent. For 
example, when using MTBE as a solvent and methanol as a cosolvent, 
evaporative cooling is effected by evaporating the solvent MTBE. This also 
applies when using MTBE as a solvent and ethanol, propanol, or isopropanol 
as the cosolvent, and when using ethyl tert-butyl ether (ETBE) as a 
solvent and, either ethanol, propanol, or isopropanol as cosolvent. 
When, however, using a heavier solvent, such as tetra loral amil ether 
(TAME) with a lighter cosolvent such as methanol, ethanol, propanol, or 
isopropanol, evaporative cooling is effected by evaporating some of the 
cosolvent. Although most of the examples described below accomplish 
evaporative cooling by evaporating cosolvent, it is to be understood that 
when using a lighter solvent than cosolvent, for example, MTBE or ETBE, 
with ethanol, propanol, or isopropanol, it is the solvent that is 
evaporated and recycled through the process to effect the desired cooling. 
Also, evaporative cooling could be effected by evaporating at least some 
of both the solvent and cosolvent. 
As shown in FIG. 2 of the drawings and in accordance with another 
embodiment of the present invention, evaporative cooling involves the 
recirculation or return of a relatively cold filtrate which is added to 
the feedstock/solvent/cosolvent slurry input to a vacuum filter so as to 
reduce the temperature of the slurry and thereby enhance wax precipitation 
and removal. The evaporative cooling dewaxing system and process is 
generally designated by the reference numeral 20 and shown to include a 
supply of waxy feedstock FS, a supply of solvent SS, and a supply of 
cosolvent CS, each having a respective outlet leading to feedstock, 
solvent and cosolvent pumps, FP, SP and CP. The waxy feedstock and solvent 
are fed along lines 22 and 24 to a first static mixer 26 having a 
feedstock/solvent mixture output which passes along line 28 and is 
combined with cosolvent from line 30 in a second static mixer 32. 
The feedstock/solvent/cosolvent slurry output of static mixer 32 passes 
along a line 34 and is combined with additional cosolvent via a line 36 
before being input into a third static mixer 38. The 
feedstock/solvent/cosolvent slurry output of the third static mixer 38 
passes along a line 40 and is input to a rotary vacuum filter VF. The wax 
output of the vacuum filter VF is fed to a holding tank WT and then fed 
via line 42 to solvent recovery such as flash evaporation or a 
distillation column to remove the solvent and cosolvent from the waxy 
cake. Typically, the wax cake can contain up to fifty percent moisture, 
and as such, needs to be processed to remove the solvents and cosolvents 
therein. 
The filtrate output of vacuum filter VF is fed to two holding tanks, FT1 
and FT2, having their outputs combined and transferred along a line 44 to 
either be recycled and thereby added to the incoming slurry upstream of 
vacuum filter VF through a line 46 or passed directly along line 48 to 
solvent recovery such as a distillation column wherein the solvent and 
cosolvent are separated and recycled by, for example, being added to the 
solvent supply SS and cosolvent supply CS. 
The cold filtrate in line 46 which is added to the slurry in line 40 just 
upstream of the vacuum filter VF serves to dilute the solids in the slurry 
and, as such, adjusts the fluid content of the slurry for maximum 
effective filtration in vacuum filter VF and, also, to utilize evaporative 
cooling, that is the reduction in temperature created by the drop in 
pressure in the vacuum filter VF to enhance wax precipitation and 
filtration. The filtrate in return line 46 is colder than the slurry in 
line 40 and, as such, serves to cool the slurry and enhance wax removal. 
Although only a single filtration step and vacuum filter is shown in FIG. 
2, it is to be understood that sequential filtrations can be performed 
with sequential additions of cold filtrate, solvent, cosolvent, and/or 
water to enhance wax precipitation and removal. 
EXAMPLE 4 
Heavy vacuum gas oil is mixed with one part MTBE and then 0.5 parts 
ethanol. As a result of the ethanol addition a wax slurry is formed 
(75.degree. F.). Then, an equal amount of cold filtrate, 45.degree. F., is 
added to the slurry and the resulting slurry is fed to the filter at 
60.degree. F. The wax is stripped of all solvents by evaporation and the 
congeal is 132.degree. F. 
In accordance with yet another embodiment of the present invention, and as 
shown in FIG. 3 of the drawings, a petroleum wax separation process and 
system includes an evaporative cooling (auto refrigeration) step to 
develop a cold cosolvent which is added to the feedstock/solvent/cosolvent 
slurry to reduce the temperature of the slurry prior to filtration. The 
petroleum wax separation process is generally designated by the reference 
numeral 50 and shown to include a waxy feedstock input line 52, a solvent 
input line 54, and a cosolvent input line 56. The feedstock is added at 
about its pour point (120.degree.-150.degree. F.) and mixed with solvent 
at about ambient temperature to produce a feedstock/solvent mixture which 
passes along line 58 at a temperature of about 90.degree. F. Cosolvent at 
about 40.degree.-45.degree. F. is added to the feedstock/solvent mixture 
to form a feedstock/solvent/cosolvent slurry which passes along a line 60. 
Evaporative cooling is accomplished using an auto refrigeration system 
including control valve 62, an adiabatic flash tank 64, a vacuum pump 66, 
a condenser 68, and a return line 70 which recycles vacuum gas and cold 
cosolvent upstream of control valve 62. 
Although as shown in FIG. 3, cosolvent is evaporated to perform the desired 
evaporative cooling (auto refrigeration), it is to be understood that when 
using a solvent and cosolvent combination in which the solvent is lighter 
than the cosolvent, it would be solvent which is evaporated and recycled. 
For example, using MEK as a solvent and toluene as a cosolvent, it is the 
toluene which is evaporated and recycled during evaporative cooling. 
However, when using MTBE as a solvent and methanol as the cosolvent, it is 
MTBE which is evaporated (cooled) and recycled during evaporative cooling. 
Using an inert gas such as nitrogen as the vacuum gas, vacuum pump 66 draws 
a vacuum on adiabatic flash tank 64 causing evaporation of a selected 
quantity of cosolvent with the evaporation causing a desired reduction in 
temperature of the slurry within the flash tank 64. Although condenser 68 
is shown downstream of vacuum pump 66 it is to be understood that the 
condenser 68 may be located upstream, that is ahead of the vacuum pump 66 
in order to liquefy the cosolvent, and, as such, reduce the size of the 
vacuum pump necessary to accomplish the evaporative cooling. In the 
condenser 68, the evaporated cosolvent may be reduced to liquid and 
chilled to, for example, 10.degree. F. This cold cosolvent passes along 
line 70 and is added to the feedstock/solvent/cosolvent slurry to further 
reduce the temperature of the slurry prior to entering flash tank 64. A 
pump 72 pumps cold slurry from the flash tank 64 to a vacuum filter unit 
74. 
The evaporative cooling (auto refrigeration) of the 
feedstock/solvent/cosolvent slurry enhances wax precipitation and 
filtration. The wax output of vacuum filter unit 74 passes along line 76 
to a holding tank or wash receiver 78. The wax output 76 of vacuum filter 
74 contains a high percentage of liquid, for example, fifty percent 
solvent/cosolvent. Some of the wash from tank 78 is pumped by pump 80, 
transferred along line 82, and added to the feedstock/solvent/cosolvent 
slurry upstream of control valve 62. The wash is added to the slurry 
stream to cool the slurry stream and, also, to adjust the solids content 
or dilute the slurry. The wash in line 82 is at about 
30.degree.-40.degree. F. and is a low oil content filtrate, made up mainly 
of solvent and cosolvent. 
Wax is output from holding tank 78 alone a line 84. This wax may be further 
processed for solvent recovery such as in flash evaporation or 
distillation apparatus. A portion of the wash in holding tank 78 is 
transferred via line B6 and combined with the filtrate from vacuum filter 
74 in line 88. The wash and filtrate in line 88 passes to a holding tank 
90 having a liquid (filtrate) output 91 and a gas output 92. The liquid 
output 91 is pumped by fluid pump 93 and combined with a liquid output 94 
of a separator 95. The combined liquid (filtrate) outputs 91 and 94 are 
sent to solvent recovery for recovering and recycling the solvent and 
cosolvent and for removing the oil therefrom. The gas output 92 of holding 
tank 90 passes through a vacuum pump 96 and a condenser 97 upstream of the 
separator 95. A vacuum gas output 98 of separator 95 is returned to 
filtrate line 88. Although only a single stage adiabatic flash and single 
filtration stage are shown in the embodiment of FIG. 3, it is to be 
understood that sequential flashes and filtrations may be used. In the 
solvent recovery stage the solvent splitter can be either direct 
distillation or heat pump distillation. 
EXAMPLE 5 
Medium neutral raffinate was mixed with 0.75 parts toluene and 2.5 parts 
acetone. The temperature of the mixture was reduced by applying 
twenty-five inHg vacuum and N.sub.2 stripping. As a result of the acetone 
evaporation, the temperature was reduced to 15.degree. F. The slurry was 
filtered to produce a wax cake and a filtrate. The filtrate was stripped 
of solvents. and the pour point of the oil was 0.degree. F. 
As shown in FIG. 4 of the drawings and in accordance with a cold solvent 
injection dewaxing (dilution chilling) embodiment of the present 
invention, a dewaxing process and system is generally designated by the 
reference numeral 100 and shown to include waxy feedstock, solvent, and 
cosolvent supplies FS, SS, and CS, and fluid pumps FP, SP, and CP. The 
solvent is passed through a solvent refrigeration unit SR to reduce the 
temperature of the solvent to about 30.degree.-40.degree. F. Likewise, the 
cosolvent is passed through a cosolvent refrigeration unit CR to reduce 
the temperature of the cosolvent to between -10.degree. to -20.degree. F. 
Waxy feedstock in a line 102 is added to the relatively cold solvent in a 
line 104 and mixed in a first static mixer 106. 
The feedstock/solvent mixture output of static mixer 106 passes along a 
line 108 to be mixed with cold cosolvent in a line 110 in a second static 
mixer 112. The feedstock/solvent/cosolvent slurry output of static mixer 
112 passes along a line 114 and is mixed with additional cold cosolvent 
from a line 116 in a third static mixer 118. The slurry output of static 
mixer 118 passes along a line 120 to vacuum filter unit VF. The wax cake 
output of filter unit VF passes to a wax holding tank WT and is output 
along a line 122 to solvent recovery such as a distillation system. The 
filtrate output of the vacuum filter VF passes to a filtrate holding tank 
FT, along a line 124 to a cross flow heat exchanger EX, and then along a 
line 126 to oil, solvent and cosolvent separation and recovery. 
The heat exchanger EX utilizes the cold filtrate (about 0.degree. F.) to 
precool the solvent or cosolvent ahead of the solvent and cosolvent 
refrigeration units SR and CR, respectively. In the embodiment shown in 
FIG. 4, cosolvent from cosolvent supply CS passes along a line 128 to the 
heat exchanger EX so as to be cooled by the cold filtrate passing through 
the exchanger. Cold cosolvent travels along line 130 to be added to the 
cosolvent supply upstream of the cosolvent refrigeration unit CR and 
thereby reduces the energy requirement of the cosolvent refrigeration unit 
and facilitates cooling of the cosolvent. 
EXAMPLE 6 
Two hundred parts of a waxy heavy vacuum gas oil (feedstock) at about 
120.degree. F. is mixed with four hundred parts of cold toluene (solvent) 
at about 30.degree. F. to form a homogeneous solution at about 78.degree. 
F. (25.6.degree. C.). In a first stage, seventy-five parts of acetone 
(cosolvent) at about -20.degree. F. is added to precipitate a high melt 
fraction of wax crystals. The mixture is filtered by vacuum filtration and 
the wax cake product is washed with forty parts of a toluene/acetone 
mixture having a ratio of toluene/acetone of 5:1. 
EXAMPLE 7 
One part medium neutral raffinate feedstock having a pour point of 
112.degree. F. is mixed with one part cold MTBE (30.degree. F.). As a 
result of the addition of cold MTBE wax crystals are formed and the slurry 
is fed to a second mixer where cold methanol (-10.degree. F.) is added in 
a quantity of 0.5 parts. The slurry is filtered at 15.degree. F. and the 
filtrate is stripped of solvents by vaporization producing an oil with a 
pour point of 10.degree. F. The wax is stripped of all solvents by 
vaporization and a wax with a congeal of 121.degree. F. is obtained. 
In accordance with an incremental dilution dewaxing embodiment of the 
present invention as shown in FIG. 5 of the drawings and generally 
designated by the reference numeral 150, a waxy feedstock travels along a 
line 152 and is mixed with a primary solvent in line 154 at or below 
ambient temperature. The primary solvent, for example MTBE, ETBE, TAME, or 
dimethyl carbonate, may contain some cosolvent contamination, up to 
twenty-five percent with some cosolvents. The solvent/feedstock mixture is 
cooled by cross-exchanging with cold filtrate in scraped-surface heat 
exchangers EX1 and EX2. Ambient or below ambient temperature cosolvent 
passes alone a line 156 to a heat exchanger EX3 wherein it is cooled by 
cross-exchange with cold filtrate. Prior to the solvent/feedstock mixture 
being chilled in heat exchanger EX2 to 35.degree. F. or below, a quantity 
of cool cosolvent (40.degree.-50.degree. F.) in line 158 is added to act 
as an antifreeze and prevent the formation of ice crystals. The resultant 
solvent/feedstock/cosolvent slurry is chilled in exchanger EX2 to about 
30.degree. F. by cross-exchanging with cold filtrate. 
At about 30.degree. F. the efficiency of cross-exchanging is reduced to the 
point where it is more economical to reduce the temperature further by 
other means. A cosolvent refrigeration unit CR is used to further reduce 
the temperature of the cool cosolvent to about -10.degree. to -20.degree. 
F., this cold cosolvent is incrementally added to the 
solvent/feedstock/cosolvent slurry along lines 160, 162, and 164. 
Scraped-surface chillers CH1 and CH2 further reduce the temperature of the 
solvent/feedstock/cosolvent slurry to about 0.degree. F. When the desired 
filter temperature is reached, the slurry is filtered in vacuum filter VF. 
The filter temperature is generally about 20.degree. F. above the desired 
pour point of the oil product. The wax output of vacuum filter VF contains 
a relatively large quantity of moisture and as such is sent to solvent 
recovery. The cold filtrate output of vacuum filter VF travels along lines 
166 and 168 to exchangers EX1, EX2, and EX3 to serve as a source of cold 
fluid so as to reduce the energy requirements of the dewaxing process and 
facilitate cooling of the cosolvent, solvent/feedstock mixture and 
solvent/feedstock/cosolvent slurry. The filtrate output of exchangers EX1 
and EX3 is sent to oil, cosolvent and solvent recovery. 
EXAMPLE 8 
One part medium neutral raffinate was mixed with one part cold (20.degree. 
F.) MTBE. The mixture temperature was further reduced to 25.degree. F. by 
solid surface chilling. The chilled mixture was filtered at 25.degree. F. 
and a resulting oil had a pour point of 30.degree. F. 
EXAMPLE 9 
One part medium neutral raffinate was mixed with 1.25 parts cold 
(40.degree. F.) MTBE. The mixture temperature was reduced to 40.degree. F. 
by solid surface exchange (freezer). Cold ethanol (0.degree. F.) was added 
equal to 1.5 parts. The resulting mixture was chilled further to 0.degree. 
F. and filtered. The oil had a pour point of 7.degree. F. 
EXAMPLE 10 
One part medium neutral raffinate was mixed with one part MTBE. The mixture 
was cooled to 40.degree. F. by solid surface chilling and then two parts 
cold ethanol (0.degree. F.) were added. The resulting 20.degree. F. 
mixture was filtered and the oil had a pour point of 8.degree. F. 
EXAMPLE 11 
One part medium neutral raffinate wax mixed with 1.25 parts cold 
(40.degree. F.) MTBE. The mixture temperature was further reduced to 
40.degree. F. by solid surface exchange. The 40.degree. F. 
solvent/feedstock mixture was mixed with 0.5 parts cold (0.degree. F.) 
methanol. The resulting solvent/feedstock/cosolvent slurry was at a 
temperature of 32.degree. F. The slurry was filtered and an oil with a 
pour point of 20.degree. F. was produced. 
EXAMPLE 12 
One part medium neutral raffinate was mixed with 1.25 parts cold 
(40.degree. F.) MTBE. The raffinate/MTBE mixture was cooled to 40.degree. 
F. and mixed with 0.5 parts cold (0.degree. F.) methanol. The resulting 
slurry was chilled further to 0.degree. F. by solid surface exchange and 
filtered. An oil with a pour point of -8.degree. F. was produced. 
As shown in FIG. 6 of the drawings, and in accordance with an exemplary wax 
fractionation embodiment involving evaporative cooling (auto 
refrigeration), the apparatus and process is generally designated by the 
reference numeral 200 and shown to include a solvent/feedstock mixture 
input 202 and a cosolvent input 204. The solvent/feedstock mixture and 
cosolvent are mixed to form a solvent/feedstock/cosolvent slurry which 
travels along a line 206 to a first vacuum filter VF1. 
The vacuum filter VF1 produces a filtrate output along a line 208 and a 
hard wax output at 210. The hard wax product is sent to solvent recovery. 
The filtrate output of vacuum filter VF1 travels to an adiabatic flash 
tank AF where a sufficient quantity of cosolvent is evaporated to cause a 
reduction in temperature of the filtrate to about 30.degree. F. Cosolvent 
vapors from the adiabatic flash tank AF travel along a line 212 and pass 
through a condenser 214 and a vacuum pump 214 before being added to the 
solvent/feedstock/cosolvent slurry in line 206. The cold cosolvent (less 
than 20.degree. F.) being added to the slurry in line 206 reduces the 
temperature of the slurry and facilitates the precipitation and removal of 
hard waxes. 
The cold liquid (filtrate) output of adiabatic flash tank AF passes along a 
line 218 to a second vacuum filter VF2. The second vacuum filter VF2 
produces a soft wax product at 220 and a filtrate at 222. The soft wax in 
line 220 is sent to, for example, a holding tank and thereafter to solvent 
recovery. The filtrate in line 222 is separated in a separator 230 into 
solvent, cosolvent, and oil product streams 224, 226, and 228. 
Although the embodiment shown in FIG. 6 is directed to the evaporation of 
cosolvent, it is to be understood that when using a solvent which is 
lighter than the cosolvent, it would be the solvent which is evaporated 
and accomplishes the desired reduction in temperature of filtrate. Also, 
even though the embodiment shown in FIG. 6 is a dual stage or two stage 
filtration process, it is to be understood that additional sequential 
filtrations and adiabatic flashes may be added so as to provide for three 
or more wax fractionation and evaporative cooling stages. 
EXAMPLE 13 
One part medium neutral raffinate was mixed with 0.75 parts toluene and 3.0 
parts acetone. The mixture temperature was reduced to 20.degree. F. by 
twenty-five inHg vacuum. The filtrate oil was stripped with the oil 
produced having a pour point of 5.degree. F. 
EXAMPLE 14 
One part medium neutral raffinate was mixed with one part MTBE and 0.5 
parts ethanol. The mixture temperature was reduced to 30.degree. F. by 
applying a twenty-five inHg vacuum. 0.5 parts of 30.degree. F. MTBE were 
added back to the mixture to account for the lost MTBE (evaporated) and 
the slurry was filtered at 30.degree. F. The resulting oil had a pour 
point of 22.degree. F. 
As shown in FIG. 7 of the drawings and in accordance with another wax 
fractionation embodiment of the present invention involving adiabatic 
inert gas stripping, the apparatus and process is generally designated by 
the reference numeral 250 and shown to include a waxy feedstock input line 
252, a solvent input line 254 and a cosolvent input 256. The waxy 
feedstock In line 252 passes through a feedstock supply tank 258 where it 
picks up solvent from a nitrogen/solvent stream as will be described 
later. 
The feedstock/solvent mixture travels alone a line 260 where it is combined 
with additional solvent from line 254 and cosolvent from line 256. The 
resultant feedstock/solvent/cosolvent slurry travels along a line 262 to a 
first vacuum filter VF1. The vacuum filter VF1 has a wax product output 
264 and a filtrate output 266. The wax (hard wax) product is sent to 
solvent recovery. The filtrate in line 266 travels to an inert gas 
stripper or absorption tower 268 which in this case is an adiabatic 
nitrogen stripper which strips a small quantity of solvent from the 
filtrate and thereby reduces the temperature of the filtrate down to 
30.degree. F. Thus, evaporative cooling is accomplished by inert gas 
stripping or absorptive cooling of the filtrate using nitrogen. 
Nitrogen in a line 270 enters the base of the absorption tower 268 and 
exits from the top of the tower carrying with it some of the solvent. The 
nitrogen and stripped or absorbed solvent travel alone a line 272 to a 
heat exchanger EX and exit the exchanger through line 274 which leads to 
the feedstock tank 258. The inert gas (nitrogen) exits the tank 258 via a 
line 276 which leads to the exchanger EX. 
Cold filtrate exits the stripper tower 268 via a line 278 which extends to 
a second vacuum filter VF2. The second vacuum filter VF2 has a filtrate 
product output line 280 and a soft wax product output line 282. The soft 
wax product is sent to solvent recovery. The filtrate in line 280 is 
separated into solvent, cosolvent and oil product streams 284, 286 and 
288, by a separator 290, for example by a distillation column. Although 
the embodiment in FIG. 7 is shown to include only two filtration stages, 
it is to be understood that the present invention is adaptable to numerous 
filtrations, and as such, provides a wax fractionation process which may 
produce multiple grades of wax. Also, it is contemplated that stripper 
gases other than nitrogen may be used. 
The wax fractionation embodiments shown in FIGS. 6 and 7 of the drawings 
are especially adapted for the production of lube oil from a waxy 
feedstock such as slack wax. 
With reference again to FIGS. 6 and 7 of the drawings, in the flash tank 
and absorption tower where the filtrate cooling takes place only a 
relatively small amount of solvent or cosolvent is evaporated to achieve a 
30.degree. F. outlet temperature. 
EXAMPLE 15 
In accordance with one example of the present invention where one pound of 
oily feedstock is mixed with two pounds of methanol and one-half pound of 
toluene at 85.degree. F. and contacted with 1.85 pounds of nitrogen gas in 
an adiabatic absorber, 0.2 pounds of methanol (or 10% of the methanol 
feed) is vaporized resulting in a final liquid temperature of 29.degree. 
F. After filtering the wax crystals and recovering the solvents from the 
filtrate, a lube oil with a 0.degree. F. pour point is produced. 
The dewaxing process of the present invention provides for the production 
of high normal paraffin content waxes having a normal paraffin content of 
90% or greater. 
EXAMPLE 16 
A cut of a heavy vacuum gas oil is added to one part MTBE and 0.5 parts 
ethanol. The slurry is filtered at 75.degree. F. and the wax is stripped 
of all solvents by vaporization. A wax yield of 24% is obtained having a 
content of 98% normal paraffin and 2% isoparaffin and other constituents. 
In accordance with another aspect of the present invention, the deoiled wax 
cake from the dewaxing process is "fractioned" to produce a hard, high 
melting point wax and a soft wax. This method of fractioning involves the 
addition of warm solvent (with little or no cosolvent contamination) at a 
temperature suitable to give a desired resulting slurry temperature. The 
addition of warm solvent causes the soft wax to go back into solution and 
leaves the hard wax as crystals. The resulting slurry is then filtered and 
the filtrate is stripped of solvents to produce soft wax. The hard wax 
cake is then stripped of solvents to produce a hard wax. The amount of 
solvent added to the wax cake will be such that the overall wax/solvent 
ratios will be essentially those described above when using slack wax 
feeds. 
In accordance with yet another embodiment of the present invention, in 
general, the wax cake from the filter in the dewaxing operation contains 
50-75% moisture (solvents and oil). About 25-30% of this moisture may be 
oil. To produce a better wax product and a higher oil yield, the moist wax 
cake is deoiled. Additional cosolvent is added to the moist wax cake in a 
quantity of about 1:1 or 2:1 based on the particular wax cake and the oil 
is rinsed from the wax cake. The resulting slurry is refiltered and the 
low oil wax product is either stripped of solvents or fractioned in a wax 
fractionation step. The filtrate which is cold and contains some oil may 
be used as dilution solvent in the dewaxing step. 
EXAMPLE 17 
A waxy vacuum gas oil having an 80 percent boiling point of 700.degree. F. 
is deoiled using 1 part MTBE (solvent) to feed (waxy vacuum gas oil) 
followed by 1.5 parts anhydrous ethanol (cosolvent). Upon the addition of 
the ethanol wax begins to crystallize. The feed/solvent/cosolvent/wax 
slurry is filtered at 75.degree. F. and the wax cake is washed with a 
volume of wash solution containing 20 percent MTBE and 80 percent ethanol. 
The wax is stripped of solvents. The final wax product has a congealing 
point of 120.degree. F. with 98.7 percent normal paraffin content, 81 
percent of which is between C.sub.22 and C.sub.25, an oil content of less 
than 0.05 percent, and a melting point range of less than plus or minus 
three .degree.F. 
EXAMPLE 18 
A waxy vacuum gas oil (feed) having a 50 percent boiling point of 
720.degree. F. is deoiled with 1.5 parts MTBE (solvent) followed by 4 
parts anhydrous ethanol (cosolvent). The feed/solvent/cosolvent/wax slurry 
is filtered at 75.degree. F. to produce a wax and a filtrate. The wax is 
washed with a volume of wash solution containing 20 percent MTBE and 80 
percent ethanol. The solvents are removed from the wax producing a wax 
with a 120.degree. F. congealing point, containing 97.2 percent normal 
paraffin, 82 percent of which is between C.sub.24 and C.sub.27, an oil 
content of less than 0.05 percent, and a melting point range of less than 
plus or minus two .degree.F. 
EXAMPLE 19 
A waxy vacuum gas oil (feed) having a 50 percent boiling point of 
800.degree. F. is deoiled with 2 parts MTBE (solvent) followed by 2.5 
parts ethanol (cosolvent). The feed/solvent/cosolvent/wax slurry is 
filtered to produce a wax and a filtrate. The wax is washed with a 
solution containing 20 percent MTBE, 80 percent ethanol. The wax is 
stripped of solvents yielding a final wax with a congealing point of 
138.degree. F., containing 96.5 percent normal paraffins, with eighty one 
percent of the paraffins between C.sub.26 and C.sub.29, an oil content of 
less than one percent, and a melting point range of less than plus or 
minus one .degree.F. 
EXAMPLE 20 
Example of deoiling a slack wax: twenty parts of a slack wax (feed) having 
an oil content of approximately 10 percent are mixed with forty parts of 
toluene (solvent) and heated gently to obtain a homogeneous solution. The 
mixture is then allowed to cool to 78.degree. F. (28.6.degree. C.). 
Fifty-five parts of acetone (cosolvent) are added and within minutes a 
precipitate forms. The mixture is filtered to collect a wax cake. The wax 
cake is washed and solvents removed to produce a wax product having an oil 
content of less than one percent, a congealing point of about 182.degree. 
F., a normal paraffin content of at least 95 percent with at least 80 
percent having a carbon distribution of less than 4. 
EXAMPLE 21 
A cut of a heavy vacuum gas oil is added to one part cold MTBE and then 0.5 
parts ethanol. The resultant slurry is filtered at 75.degree. F. and the 
wax is stripped of all solvents by vaporization. A wax yield of 24% is 
obtained having a content of 98% normal paraffin and 2% iso-paraffin and 
other constituents with at least 80 percent of the normal paraffins having 
a carbon distribution of 3 or less. 
In accordance with still yet another aspect of the present invention, the 
primary solvents (tertiary ethers, such as MTBE, ETBE, and TAME and/or 
dimethyl carbonate) and alcohol cosolvents can be used in conjunction with 
a conventional cold solvent injection process for dewaxing waxy 
feedstocks. For example, in a conventional cold solvent injection process 
(dilution chilling) a solvent such as MEK (methyl ethyl ketone) or a 
mixture of solvents such as MEK and toluene is chilled and added to a waxy 
feedstock in a mixture or series of mixtures. As a result of the cold 
solvent addition, wax crystals form. The resulting slurry is filtered 
immediately or may have its temperature further reduced by being chilled 
in a scrape surface chiller prior to filtration. 
EXAMPLE 22 
One part medium neutral raffinate feedstock having a pour point of 
112.degree. F. is mixed with one part cold ETBE (30.degree. F.). The 
mixture is fed to a second mixer where cold propanol (-10.degree. F.) is 
added in a quantity of 0.5 parts. The slurry is filtered at 15.degree. F. 
and the filtrate is stripped of solvents by vaporization producing an oil 
with a pour point of 10.degree. F. The wax is stripped of all solvents by 
vaporization and a wax with a congeal of 121.degree. F. is obtained. 
In accordance with the present invention, a waxy feedstock is first mixed 
with a primary solvent (MTBE, ETBE, TAME, or dimethyl carbonate) at or 
below ambient temperature. The solvent may contain some cosolvent 
contamination, up to 25% depending on the cosolvent chosen. The 
solvent/feedstock mixture is then mixed with cosolvent at or below ambient 
temperature in a single mixer or series of mixers. As a result of the 
cosolvent addition, wax crystals form. The resulting slurry is either 
filtered immediately, or has its temperature reduced further by being 
chilled in scrape surface chillers prior to filtration. 
The solvent/feedstock/cosolvent slurry is filtered at a temperature 
sufficient for producing an oil with the desired pour point. The required 
filter temperature is generally 5.degree.-20.degree. F. above the desired 
pour point of the oil. In order to reduce the refrigeration requirements, 
the cold filtrate may be cross-exchanged with the primary solvent or 
cosolvent prior to the refrigeration unit. 
Typically, the lube plant is the slowest step (bottleneck) in the refinery 
process, therefore, if one can speed up the lube plant process one can 
speed up the whole refinery process, and, as such, reduce cost and 
maximize the profit potential of the refining process. The wax petroleum 
separation process of the present invention provides a means for speeding 
up the lube plant process, and, thereby, provides a means for 
debottlenecking conventional refinery processes. 
An added advantage of using an alcohol as a selected cosolvent is that the 
alcohol serves as an antifreeze to keep ice from forming in the 
solvent/feedstock/cosolvent slurry. The formation of ice reduces the 
filtration efficiency of the vacuum filtration units and, also, causes 
deterioration of conventional scrape surface exchangers. Thus, the use of 
an alcohol cosolvent will serve to increase filtration efficiency and 
increase the effective life of scrape surface exchangers. Also, alcohol 
cosolvents require the use of less primary solvent, and, as such, increase 
overall plant capacity and reduce cost. The less solvent and cosolvent 
that must be added to the waxy feedstock, the greater the amount of 
feedstock that can be dewaxed given a fixed plant capacity. Still further, 
the use of alcohol cosolvents allows for steam stripping to accomplish the 
evaporative cooling of the filtrate. As such, one would not need to use 
nitrogen to strip the cosolvent from the filtrate and cause evaporative 
cooling. As much as conventional dewaxing systems already incorporate the 
use of steam, alcohol cosolvents are especially adapted for use with 
conventional systems. 
The preferred primary solvents MTBE, TAME, and ETBE are all tertiary ethers 
which have a conventional use as gasoline additives or octane enhancers, 
and each of which have at least five carbon atoms, at least twelve 
hydrogen atoms, and at least one oxygen atom per molecule, and, as such, 
are oxygenated organic compounds. The other preferred primary solvent is 
dimethyl carbonate, a carbonic acid dimethyl ester, belonging to a class 
of compounds (organic acid esters) having at least three carbons, at least 
one oxygen, and at least three non-hydrocarbon atoms per molecule 
(oxygenated organic compounds). Generally, carbonic acid esters have a 
chemical formula (R).sub.2 CO except for ethyl methyl ester, which has a 
formula R.sub.1 --CO--R.sub.2. Tertiary ethers, dimethyl carbonate, and 
alcohols are all environmentally compatible in that they are oxygenated 
organic compounds as compared with conventional solvents, such as, MEK, 
toluene, and acetone. 
With respect to TABLES I-X, TABLE I provides a comparison of a basic 
solvent/cosolvent/dewaxing (deoiling) process of the present invention 
with a conventional single stage mixed solvent, MEK/toluene process. The 
basic solvent/cosolvent/dewaxing process was a batch-type process wherein 
solvent was added to the waxy feedstock to form a homogeneous mixture, 
then cosolvent was added, wax precipitated and removed, and the wax washed 
with a mixture of solvent and cosolvent. TABLES II-V show the results of 
dewaxing (deoiling) different waxy feedstocks using a batch-type 
solvent/cosolvent/dewaxing process in accordance with the present 
invention. TABLES VI and VII provide equations for the effect of 
temperature on filtration rate and viscosities. TABLE VIII provides 
calculated mixture viscosities. TABLE IX illustrates calculated 
equilibrium temperatures. TABLE X represents information regarding some 
primary solvents. 
Thus, it will be appreciated that as a result of the present invention a 
highly effective petroleum wax separation apparatus and method is provided 
by which the principal objective among others is completely fulfilled. It 
is contemplated and will be apparent to those skilled in the art from the 
preceding description and accompanying drawings that modifications and/or 
changes may be made in the illustrated embodiments without departure from 
the present invention. For example, it is contemplated that in the 
illustrated embodiments the waxy feedstock supply or input to the process 
may contain solvent, and, as such, be a feedstock/solvent mixture with 
little or no cosolvent contamination. Accordingly, it is expressly 
intended that the foregoing description and accompanying drawings are 
illustrative of preferred embodiments only, not limiting, and that the 
true spirit and scope of the present invention be determined by reference 
to the appended claims. 
TABLE I 
______________________________________ 
Comparison of Solvent/Cosolvent Deoiling Process 
with Single Stage MEK/Toluene Process 
using MINAS 650-910.degree. F. Cut 
Process Conditions 
MEK/Toluene: 
Solvent: MEK/Toluene 
Solvent ratio: 3/1 
Wash: MEK/Toluene 
Wash ratio: 5/1 
Filter Temperature: 30-35.degree. F. 
Solvent/Cosolvent: 
Solvent: toluene 
Solvent ratio: 1.5/1 
Cosolvent: acetone 
Cosolvent ratio: 1.0/1 
Wash: acetone/toluene 
Wash ratio: 5.0/1 
Filter Temperature: 75.degree. F. 
Wax Inspections 
MEK/Toluene: 
Yield: 38.5% 
Congealing Point: 140.degree. F. 
Oil Content: 0.83% 
Penetration 100.degree. F.: 
12 
Solvent/Cosolvent: 
Yield: 30.0% 
Congealing Point: 145.degree. F. 
Oil Content: 0.02% 
Penetration 100.degree. F.: 
8 
Filtrate Oil Inspections 
MEK/Toluene: 
Pour Point: +55.degree. F. 
Solvent/Cosolvent: 
Pour Point: +80.degree. F. 
______________________________________ 
TABLE II 
______________________________________ 
Deoiling Results of Waxy Vacuum Distillate (1) 650-910.degree. F. Cut 
Run 1 Run 2 Run 3 
______________________________________ 
Feed Conditions 
Solvent: toluene toluene toluene 
Solvent/Feed: 1.5 0.7 0.7 
Cosolvent: acetone acetone acetone 
Cosolvent/Feed: 
1.0 1.5 1.0 
Temperature: 75.degree. F. 
75.degree. F. 
75.degree. F. 
Wax Inspections 
Yield on Feed: 
8.3 26.8 24.4 
Yield on Wax In Feed: 
52.6 47.9 43.17 
Congealing Point .degree.F.: 
148 137 138 
Oil Content, Wt %: 
0.81 1.03 0.02 
Gravity, API: 41.1 41.8 4.1.4 
Viscosity @ 210.degree. F.: 
4.943 4.10 3.99 
Needle Penetration @ 
17 31 16 
100.degree. F.: 
Oil Inspections 
Gravity, API: 39.8 38.9 39.4 
Pour Point, .degree.F.: 
95 80 85 
Viscosity @ 210.degree. F., cst: 
3.009 2.902 2.884 
______________________________________ 
TABLE III 
______________________________________ 
Deoiling Results of Vacuum Resid 
______________________________________ 
Feed Conditions 
Solvent: toluene 
Solvent/Feed: 1.5 
Cosolvent acetone 
Cosolvent/Feed: 2.0 
Temperature: 75.degree. F. 
Wax Inspections 
Yield on Feed, Wt. %: 
51.4 
Congealing Point, .degree.F.: 
189 
Oil Content, Wt. %: 0.13 
Gravity, API: 34.2 
Viscosity @ 210.degree. F.: 
26.448 
Needle Penetration, 100.degree. F.: 
9 
Oil Inspections 
Gravity, API: 34.2 
Pour Point, .degree.F.: 
105 
Viscosity @ 210.degree. F.: 
16.591 
______________________________________ 
TABLE IV 
______________________________________ 
Dewaxing Results of Light Neutral 
______________________________________ 
Feed: Light Neutral 
API: 33.5 
Pour: 80.degree. F. 
Conditions: 
Feed: 1.0 
Toluene (Solvent): 
0.75 
Acetone (Cosolvent): 
3.2 
Wax Product: 
Yield %: 14.9% 
Congeal: 115.degree. F. 
Oil Content: 13% 
Oil Product: 
Yield: 85.1% 
Pour: 15.degree. F. 
API: 31.2 
V.I.: 110 
______________________________________ 
TABLE V 
______________________________________ 
Slack Wax Deoiling 
______________________________________ 
Stack Wax Feed 
Congealing Point: 131.degree. F. 
Oil Content: 2.0% 
Needle @ 77.degree. F.: 
60 
Conditions 
Feed: 1.0 
Toluene (Solvent): 
1.5 
Acetone (Cosolvent): 
1.0 
Wax Product 
Yield: 60% 
Congeal: 141.degree. F. 
Oil Content: 0.18% 
Penetration (100.degree. F.): 
38 
Secondary Wax 
Yield: 16% 
Congeal: 118.degree. F. 
Oil Content: 0.7% 
______________________________________ 
TABLE VI 
______________________________________ 
Effect of Temperature on Filtration Rates 
______________________________________ 
filtration rate = driving force/resistance 
dv/dt = P * A/(.mu.*[a(W/A) + r]) 
______________________________________ 
P = pressure drop across filter? 
A = filter area? 
.mu. = filtrate viscosity 
a = specific cake resistance? 
W = weight of cake? 
r = resistance of filter media? 
TABLE VII 
______________________________________ 
Effect of Temperature on Viscosities 
.mu. = A * exp(B/T) 
.mu.(cs) 
T (F) oil(100N) acetone toluene 
______________________________________ 
0. 1143. 0.64 1.15 
30. 375. 0.50 0.89 
50. 192. 0.43 0.81 
75. 89. 0.40 0.65 
100. 44. -- -- 
210. 3.8 -- -- 
______________________________________ 
TABLE VIII 
______________________________________ 
Calculated Mixture Viscosities 
.mu. = .SIGMA.x.sub..iota. * .mu..sub.i 
oil x = 0.03 
toluene x = 0.12 
acetone x = 0.85 
T (F) .mu.p(cs) 
______________________________________ 
0. 35. 
30. 12. 
75. 3.1 (5.4 measured) 
______________________________________ 
TABLE IX 
______________________________________ 
Calculated equilibrium temperatures at several different filtration 
pressures for a typical toluene/acetone system. 
Filtration Calculated 
Pressure (mmHg) 
Equilibrium Temperature (.degree.F.) 
______________________________________ 
40 17 
25 3 
15 -12 
10 -23 
______________________________________ 
TABLE X 
______________________________________ 
Structures of primary solvents 
DMC, MTBE, TAME, and ETBE 
______________________________________ 
##STR1## 
DMC; Dimethylcarbonate; carbonic acid dimethyl ester; 
C.sub.3 H.sub.6 O.sub.3 ; (CH.sub.3 O).sub.2 CO 
##STR2## 
MTBE; methyl tertiary butyl ether; 2-methoxy, 2-methyl 
propane; C.sub.5 H.sub.12 O; (CH.sub.3).sub.3 C(OCH.sub.3) 
##STR3## 
TAME; 2-methyl, 2-methoxy butane; tetra loral amil ether; 
C.sub.6 H.sub.14 O 
##STR4## 
ETBE; ethyl tertiary butyl ether; 2-ethyl; 
2-methoxy propane; C.sub.6 H.sub.14 O 
______________________________________