Method for determining effectiveness of catalytic dewaxing reactor

The pour point of a catalytically dewaxed hydrocarbon oil is determined manually by the ASTM D-97-66 method and also by automatic apparatus such as the Herzog Electronic Pour Point Automatic MC 850 apparatus. A substantial divergence of the two indicates contamination by a waxy hydrocarbon oil such as the feedstock to the dewaxing process.

NATURE OF INVENTION 
This invention is concerned with the manufacture of high-quality 
lubricating oils and in particular is concerned with the catalytic 
dewaxing and hydrotreating of waxy lubricating oils. More specifically, 
this invention is concerned with a method for determining if channeling of 
waxy feedstock through the dewaxing catalyst bed is occurring. The method 
is also useful in detecting fluid leakage in heat exchange between the 
incoming waxy feedstock (waxy raffinate) and outgoing dewaxed product. 
BACKGROUND OF THE INVENTION 
The refining of petroleum crude oils to obtain lubricant-stocks is based 
primarily on a series of steps including distillation, solvent refining 
and dewaxing. 
For the preparation of a high grade distillate lubricating oil stock, the 
current practice is to vacuum distill an atmospheric tower residuum from 
an appropriate crude oil as the first step. This step provides one or more 
raw stocks within the boiling range of about 450.degree. to 1050.degree. 
F. After preparation of a raw stock of suitable boiling range, it is 
extracted with a solvent, e.g., furfural, phenol, n-methyl pyrrolidone, 
sulfolane, or chlorex, which is selective for aromatic hydrocarbons, and 
which removes undesirable components. The raffinate from solvent refining 
is then dewaxed, for example, by admixing with a solvent such as a blend 
of methyl ethyl ketone and toluene. The mixture is chilled to induce 
crystallization of the paraffin waxes which are then separated from the 
raffinate. Sufficient quantities of wax are removed to provide the desired 
pour point for the raffinate. 
Other processes such as hydrofinishing or clay percolation may be used if 
needed to reduce the nitrogen and sulfur content or improve the color of 
the lubricating oil stock. 
In recent years catalytic techniques have become available for dewaxing 
petroleum stocks. Although some attention has been directed to treating 
gas oils and manufacturing specialty oils, primary interest has been and 
is the catalytic dewaxing and subsequent treatment of lube oil stocks. 
Processes relating to the dewaxing of gas oils and specialty oils are 
described in U.S. Pat. Nos. 3,894,938 and 4,137,148. 
U.S. Pat. No. 3,894,938 discloses a catalytic dewaxing process in which 
high-pour-point, high-sulfur gas oils having a boiling range of about 
400.degree. F. to 900.degree. F. are first contacted, in the presence or 
absence of added hydrogen, with a ZSM-5 type zeolite hydrodewaxing 
catalyst which may contain a hydrogenation/dehydrogenation component. The 
effluent therefrom is subsequently desulfurized and denitrogenated by 
contacting it with a cobalt-molybdenum-alumina catalyst. 
U.S. Pat. No. 4,137,148 discloses a process wherein specialty oils of low 
pour point and excellent stability are produced from waxy crude 
distillates having a boiling range of 450.degree. F. to 1050.degree. F. by 
solvent refining, catalytic dewaxing over a zeolite catalyst such as 
ZSM-5, and hydrotreating. The catalytic dewaxing reaction produces olefins 
which would impair properties of the dewaxed oil product if retained. 
These are saturated by hydrogenation in the hydrotreater, as confirmed by 
chemical analysis of the hydrotreated product for bromine number. Low 
bromine numbers are an indication of a satisfactory level of saturation. 
The hydrotreating step constitutes cascading effluent from the catalytic 
dewaxing step into a hydrotreating reactor of the type now generally 
employed for the finishing of lubricating oil stocks. Any of the known 
hydrotreating catalysts consisting of a hydrogenation component on a 
non-acidic support can be employed, for example, cobalt-molybdate or 
nickel-molybdate or molybdenum oxide, on an alumina support. Subsequent to 
this treatment, the effluent of the hydrotreater is topped by distillation 
to meet flash and firepoint specifications. 
Techniques for dewaxing and subsequent treating of lubricating oil stocks 
are exemplified in U.S. Pat. Nos. 3,755,138 and 4,222,855. 
U.S. Pat. No. 3,755,138 discloses a process wherein a lube oil stock 
boiling between 650.degree. F. and 1100.degree. F. is subjected to mild 
solvent dewaxing and subsequently to hydrodewaxing. The hydrodewaxing step 
constitutes contacting the lube oil stock with a crystalline 
aluminosilicate of the ZSM-5 type which contains a metal hydrogenating 
component in the presence of added hydrogen. In U.S. Pat. No. 4,222,855 
lube oil stocks boiling between 600.degree. F. and 1050.degree. F. are 
catalytically dewaxed by contacting them with a crystalline 
aluminosilicate having particularly characterized pore openings such as 
ZSM-23 and ZSM-35. 
U.S. Pat. No. 3,668,113 discloses a process in which petroleum fractions 
such as gas oil and wax distillate fractions are first passed over a 
catalyst comprising a crystalline mordenite of reduced alkali metal 
content and a metal hydrogenating component to remove wax. The reaction 
product is then passed over a catalyst comprising a refractory inorganic 
oxide support and a hydrogenating component selected from metals and 
compounds thereof of Groups VI and VIII of the Periodic Table to remove 
sulfur. 
A currently preferred process is one wherein the actual dewaxing is 
accomplished in a first reactor using a zeolite catalyst such as the ZSM-5 
zeolite and then hydrofinishing the dewaxed effluent in a second reactor 
in order to reduce olefinic compounds produced in the first reactor. The 
hydrofinishing step produces a base stock having an acceptable oxidative 
stability. 
A problem associated with the dewaxing step in the first reactor is that 
channeling or bypassing might occur in which a small portion of the waxy 
raffinate from the solvent refining step flows almost directly through the 
reactor bed with minimal contact with the catalyst. Consequently, little 
if any, dewaxing occurs in this portion of the raffinate. The resulting 
product may not meet critical performance tests even though pour point or 
cloud point specifications are met. Another possible problem can occur in 
the heat exchange system. Ordinarily the system is designed to transfer 
heat from the heated dewaxed product stream downstream to the cooler 
incoming waxy raffinate upstream where the pressure is higher. If any 
leaks across the physical barriers separating the two systems occur, the 
product effluent (the dewaxed product) will be contaminated and be of 
unacceptable specifications. 
OBJECTS OF THE INVENTION 
A primary object of this invention is to provide a method of determining 
when channeling or bypassing is occurring in a reactor bed, such as that 
used in catalytic dewaxing, or when heat exchanger leaks are occurring. 
Other objects of the invention will become apparent from the disclosure 
which follows. 
SUMMARY OF THE INVENTION 
We have discovered that the presence of wax in supposedly catalytically 
dewaxed raffinate can be detected by determining the pour point of a 
sample by each of two separate methods and then comparing the pour points. 
A substantial difference in the determined pour points is indicative of 
the presence of wax impurities. The methods are of the type which, if used 
on a uncontaminated sample, would yield nearly identical pour point 
readings. The tests are: 
1. The ASTM Standard Test Method for determining the pour point of 
petroleum oils designed as ASTM test D-97-66 (reapproved 1978) and 
2. The pour point determined using a shear pour point device such as that 
described in U.S. Pat. No. 4,164,136 to Wiggins et al.

DESCRIPTION OF THE INVENTION 
As noted previously, the method of this invention is based on two 
independent determinations of pour point. The first of these tests is a 
manual test and is best described as that test corresponding to the ASTM 
test designated D-97-66 (reapproved 1978) I.P. designation: 15/67 (75). 
This test is described in Volume 5.01 of the 1985 Annual Book of ASTM 
Standards published by the American Society of Testing Materials, 
Philadelphia, PA, Publication Code No. (PCN:01-050185-12). That test is 
described on pages 85 through 88 of this publication. Those pages are 
incorporated herein by reference. This test can be summarized as one 
wherein the sample to be tested for pour point is placed in a tube and is 
successively cooled and after routine thermoequilibrium is tilted to 
determine if the sample will still flow. The temperature at which no flow 
of oil is discernible is adjusted and called the pour point for that 
particular sample. Those skilled in the art are well acquainted with the 
techniques for conducting this test. 
The second test is based on positioning a probe so that its lower end 
extends within a sample of the oil being tested. The sample is cooled 
slowly while an intermittent torque is placed on the probe inserted in the 
sample. The point at which the probe's ability to rotate in the oil medium 
is lessened or becomes non-existent is known as the pour point of the 
sample. Apparatus for this technique is described in U.S. Pat. No. 
4,164,136 which is incorporated herein by reference. This type of 
apparatus is also embodied in the Herzog Electronic Pour-Point-Automatic 
MC 850 model. This apparatus is manufactured by the Walter Herzog GmbH and 
distributed in the U.S. by UIC, Inc., Joliet, Ill. 
As indicated previously, this latter apparatus operates on the principle 
that if a liquid surrounding the probe is cooled as a rotational force is 
applied to the liquid body, that the probe eventually will rotate when the 
pour point of the liquid has been reached. This occurs because as the 
sample congeals it tends to grab onto the probe as the pour point is 
reached. If pour point determinations are made on a pure sample, i.e., a 
sample uncontaminated by waxy materials, the two pour points by the ASTM 
method and the Herzog method will be essentially the same. We have 
discovered, however, that if the pour points are run on samples containing 
waxy raffinate from the original reactor, there will be a substantial 
difference in pour points which increases as the amount of raffinate or 
other waxy impurity increases. We have made a number of tests showing what 
happens when these samples are tested. 
EXAMPLES 
The following table presents summaries of tests in which portions of 
dewaxed oil was mixed with the undewaxed or waxy-containing raffinate in 
increasing proportions. Tests were then run using each of the previously 
identified tests to determine pour point. From the resulting data it is 
readily apparent that even a minor increase in the concentration of wax in 
the treated oil results in a wide divergence from the pour point of the 
pure uncontaminated sample. The pour point determinations were made using 
the ASTM D-97-66 test and the Herzog Electronic Pour Point Automatic MC850 
model distributed by the UIC Corporation of Joliet, Ill. 
TABLE 
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Comparison of Pour Points of Various Concentrations 
of Waxy Raffinate in Dewaxed Oil as Determined 
By the ASTM D97 Method and by the Herzog Apparatus 
Concentration of 
High Pour Point 
(Waxy Raffinate) 
Pour Point .degree.F. 
Pour Point .degree.F. 
Run No. 
Component, Percent 
by D97 by Herzog 
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73.degree. F. Pour Point Light Neutral Oil 
Added to -10.degree. F. Pour Point Dewaxed Light Neutral Oil 
1 0 -10 -13 
2 1 -10 -13 
3 2 -5 -10 
4 4 15 -9 
5 8 25 -3 
6 12 40 4 
7 16 45 10 
Light Neutral Waxy Raffinate Added to -20.degree. F. Pour 
Point Dewaxed Light Neutral Oil 
8 0 -20 -14 
9 1 -15 -18 
10 2 5 -13 
11 4 20 -6 
12 8 40 2 
13 12 60 18 
14 16 60 21 
Light Neutral Waxy Raffinate Oil Added to 0.degree. F. Pour Point 
Dewaxed Light Neutral Oil 
15 0 0 -2 
16 1 10 0 
17 2 20 2 
18 4 35 4 
19 8 55 19 
20 12 60 26 
73.degree. F. Pour Point Light Neutral Oil Added to 15.degree. F. Pour 
Point Dewaxed Light Neutral Oil 
21 0 15 12 
22 1 15 12 
23 2 15 -8 
24 4 15 12 
25 8 35 18 
26 12 45 20 
27 16 55 28 
Light Neutral Waxy Raffinate Added to 22.degree. F. Pour Point 
Dewaxed Light Neutral Oil 
28 0 20 9 
29 1 25 9 
30 2 35 11 
31 4 35 14 
32 8 55 23 
33 12 55 31 
34 16 65 37 
Heavy Neutral Waxy Raffinate Added to 15.degree. F. Pour Point 
Dewaxed Heavy Neutral Oil 
35 0 15,10 9 
36 1 20,10 9 
37 2 15,10 10 
38 4 25 12 
39 8 50 16 
40 12 80 26 
41 16 80 30 
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