Removal of diamondoid compounds from hydrocarbonaceous fractions

According to this invention, substantially hydrocarbonaceous fractions comprising diamondoid compounds are peculiarly suitable for separation by a thermal gradient diffusion process. Applicability of this process to this service is dependent upon the fact that the diamondoid compounds exhibit a large change in viscosity relative to temperature, that is, their viscosity goes down significantly per degree of increase in temperature.

CROSS REFERENCE TO RELATED APPLICATIONS 
The present application is related by the disclosure of similar subject 
matter to commonly-assigned application Ser. Nos. 358,758, 358,760, and 
358,761, filed concurrently herewith. 
BACKGROUND OF THE INVENTION 
This invention relates to the removal of certain components from 
hydrocarbon streams. It more particularly refers to separating diamondoid 
organic compounds from hydrocarbon streams containing such. 
Many hydrocarbonaceous mineral streams contain some small proportion of 
diamondoid compounds. These high boiling, saturated, three-dimensional 
polycyclic organics are illustrated by adamantane, diamantane, triamantane 
and various side chain substituted homologues, particularly the methyl 
derivatives. These compounds have high melting points and high vapor 
pressures for their molecular weights and have recently been found to 
cause problems during production and refining of hydrocarbonaceous 
minerals, particularly natural gas, by condensing out and solidifying, 
thereby clogging pipes and other pieces of equipment. For a survey of the 
chemistry of diamondoid compounds, see Fort, Jr., Raymond C., The 
Chemistry of Diamond Molecules, Marcel Dekker, 1976. 
In recent times, new sources of hydrocarbon minerals have been brought into 
production which, for some unknown reason, have substantially larger 
concentrations of diamondoid compounds. Whereas in the past, the amount of 
diamondoid compounds has been too small to cause operational problems such 
as production cooler plugging, now these compounds represent both a larger 
problem and a larger opportunity. The presense of diamondoid compounds in 
natural gas has been found to cause plugging in the process equipment 
requiring costly maintenance downtime to remove. On the other hand, these 
very compounds which can deleteriously affect the profitability of natural 
gas production are themselves valuable products. 
BROAD STATEMENT OF THE INVENTION 
In order to recover the diamondoid values in the hydrocarbonaceaous 
mineral, or in a fraction thereof, this source may be treated directly 
with a suitable solvent, such as an aromatic distillate fuel oil, in order 
to partition the diamondoids from their source into the distillate 
extractant which can be further resolved. Alternatively, if the source 
fraction has an appropriate composition, it can itself be subjected to 
resolution to remove the diamondoid compounds directly therefrom. Further, 
in some instances, the diamondoid compounds will precipitate out in the 
processing equipment and such equipment needs to be periodically flushed 
to remove the diamondoid precipitants, or to remove deposited diamondoids 
before their concentration reaches precipitation levels, thus forming a 
liquid fraction comprising the flushing medium and the diamondoid 
compounds dissolved therein. Suitable flushing liquids are exemplified by 
aromatic distillate fuel oils. These compositions can then be resolved. 
According to this invention, substantially hydrocarbonaceous fractions 
comprising diamondoid compounds are peculiarly suitable for separation by 
a thermal gradient diffusion process. Applicability of this process to 
this service is dependent upon the fact that the diamondoid compounds 
exhibit a large change in viscosity relative to temperature, that is, 
their viscosity goes down significantly per degree of increase in 
temperature. In fact, their viscosity rate of change with temperature is 
substantially greater than that of other hydrocarbons of similar boiling 
point range. 
The invention further includes a method for collecting diamondoid comounds 
from hydrocarbonaceous gas streams by contacting the gas stream with a 
liquid solvent in which diamondoid compounds are at least partially 
soluble. It has been found that the diamondoid compounds are 
preferentially dissolved from the gas stream into the selected liquid 
solvent thereby providing a method not only for preventing or reducing 
plugging of downstream process equipment but also for recovering valuable 
diamondoid compounds. Solvents useful in the solvation process of the 
invention include normally liquid hydrocarbons containing aromatics 
including petroleum-based solvents such as kerosene, diesel fuel, and 
heavy gasoline, with diesel fuel being the most preferred solvent. 
Further, it has been found that a second separation step, silica gel 
sorption, is effective to sorb diamondoid compounds from a hydrocarbon gas 
stream. Depending upon the composition of the hydrocarbon gas stream, 
solvent addition may optionally be employed to reduce diamondoid 
deposition in the silica gel sorption equipment, with solvent injection to 
the silica gel regeneration circuit as described below being particularly 
beneficial. 
In the most preferred embodiment of the invention for extracting diamondoid 
compounds from hydrocarbon gas streams, both the solvation and sorption 
steps are employed. The resulting diamondoid-enriched hydrocarbon liquid 
streams are then further resolved via thermal gradient diffusion. The 
diamondoid compound-containing hydrocarbon gas stream is first contacted 
with a suitable solvent as described above. The gas/liquid mixture is then 
separated, e.g. flashed, to form an at least partially purified gas stream 
and a liquid solvent stream enriched in diamondoid compounds. If the 
diamondoid compound-containing gas stream to be purified is rich in 
substituted higher boiling point adamantane homologues, the solvation and 
gas/liquid separation steps may produce a gas stream having acceptable 
purity. If, however, if the diamondoid compound-containing gas feedstream 
contains a substantial fraction of less substituted lower boiling point 
adamantane homologues, the silica gel sorption step may be necessary to 
achieve the desired gas product stream purity or extent of diamondoid 
recovery. 
The present invention, then, provides a solvation process for extracting 
diamondoid compounds from a gas stream comprising the steps of providing a 
gas stream containing a recoverable concentration of diamondoid compounds, 
mixing the gas stream containing diamondoid compounds with a solvent in 
which diamondoid compounds are at least partially soluble, controlling the 
conditions including temperature and pressure of the mixture to maintain 
at least a portion of the mixture in the liquid phase, separating the 
mixture under these controlled conditions into a vapor stream and a 
diamondoid-enriched solvent stream, and recovering diamondoid compounds 
from the diamondoid-enriched solvent stream by passing said 
diamondoid-enriched solvent stream between two surfaces spaced apart up to 
about 0.01 inch at a temperature higher than the melting point of the 
lowest melting diamondoid in said diamondoid-enriched solvent stream up to 
about 500.degree. F., and at a temperature differential between said 
surfaces of at least about 10.degree. F. for a time sufficient to recover 
therefrom a first stream enriched in said diamondoid compounds, and a 
second stream depleated in said diamondoid compounds. The process may 
further comprise recycling the diamondoid-depleated solvent stream and 
mixing said diamondoid-depleated solvent stream with said 
diamondoid-containing hydrocarbon gas stream to at least partially 
saturate the diamondoid-depleated solvent. 
The invention further provides a sorption process for extracting diamondoid 
compounds from a diamondoid-containing gas stream comprising the steps of 
providing a gas stream containing a recoverable concentration of 
diamondoid compounds, contacting the diamondoid-containing gas stream with 
silica gel in a sorption zone under conditions of temperature and pressure 
to prevent substantial formation of solid diamondoid desposits in the 
sorption zone for a period of time sufficient for the silica gel to sorb 
at least a poriton of the diamondoid compounds from the hydrocarbon gas, 
and regenerating the silica gel by contacting the silica gel with a 
regeneration fluid in which diamondoid compounds are at least partially 
soluble to desorb diamondoid compounds from the silica gel, and recovering 
diamondoid compounds from at least a portion of the regeneration fluid by 
passing at least a portion of the regeneration fluid between two surfaces 
spaced apart up to about 0.01 inch at a temperature higher than the 
melting point of the lowest melting diamondoid in the regeneration fluid 
up to about 500.degree. F., and at a temperature differential between said 
surfaces of at least about 10.degree. F. for a time sufficient to recover 
therefrom a first stream enriched in said diamondoid compounds, and a 
second stream depleated in said diamondoid compounds. 
The preferred embodiment of the invention includes both the solvation and 
sorption stages, providing a process for extracting diamondoid compounds 
from a diamondoid-containing gas stream comprising the steps of providing 
a gas stream containing a recoverable concentration of diamondoid 
compounds, mixing the gas stream containing diamondoid compounds with a 
solvent in which diamondoid compounds are at least partially soluble, 
controlling the conditions including temperature and pressure of the 
mixture to maintain at least a portion of the mixture in the liquid phase, 
separating the mixture under the controlled conditions into a partially 
purified gas stream and a diamondoid-enriched solvent stream, recovering 
diamondoid compounds from the diamondoid-enriched solvent stream by 
passing said diamondoid-enriched solvent stream between two surfaces 
spaced apart up to about 0.01 inch at a temperature higher than the 
melting point of the lowest melting diamondoid in said diamondoid-enriched 
solvent stream up to about 500.degree. F., and at a temperature 
differential between said surfaces of at least about 10.degree. F. for a 
time sufficient to recover therefrom a first stream enriched in said 
diamondoid compounds, and a second stream depleated in said diamondoid 
compounds, contacting the partially purified gas stream with silica gel in 
a first sorption zone under conditions of temperature and pressure to 
prevent substantial formation of solid diamondoid desposits in the 
sorption zone for a period of time sufficient for the silica gel to sorb 
at least a poriton of the diamondoid compounds from the hydrocarbon gas, 
and recovering diamondoid compounds from silica gel by desorption in a 
second sorption zone by contacting the silica gel with a regeneration 
fluid in which diamondoid compounds are at least partially soluble to 
desorb diamondoid compounds from the silica gel, and recovering diamondoid 
compounds from at least a portion of the regeneration fluid by passing at 
least a portion of the regeneration fluid between two surfaces spaced 
apart up to about 0.01 inch at a temperature higher than the melting point 
of the lowest melting diamondoid in the regeneration fluid up to about 
500.degree. F., and at a temperature differential between said surfaces of 
at least about 10.degree. F. for a time sufficient to recover therefrom a 
first stream enriched in said diamondoid compounds, and a second stream 
depleated in said diamondoid compounds.

DETAILED DESCRIPTION OF THE INVENTION 
A thermal gradient diffusion process can operate in either a batch or 
continuous mode. The material to be resolved is placed between two (2) 
surfaces which differ in temperature. One factor effecting efficiency of 
resolution is the temperature of the two surfaces. Efficiency of 
separation is increased as a function of temperature, both the absolute 
temperature of both the surfaces, and the temperature of each surface 
relative to the other. It is preferred that the temperature of both 
surfaces be as high as practical, suitably about 50.degree. to 500.degree. 
F. It is most preferred that the temperatures of the surfaces be about 
100.degree. to 300.degree. F. 
With respect to the temperature differential between the two surfaces, this 
should be as great as practical, within the requirement that the 
temperature of both surfaces should be as high as practical. Suitably, the 
two surfaces should differ in temperature by at least about 10.degree. F., 
preferably at least about 50.degree. F. In accord with this invention 
then, the higher temperature surface is suitably maintained at a 
temperature of about 100.degree. to 500.degree. F., and the lower 
temperature surface is suitably maintained at a temperature of about 
50.degree. to 490.degree. F., while maintaining the temperature 
differential as set forth above. 
In accord with this invention, the two surfaces hereinbefore referred to, 
should preferably be spaced close together. It has been found that 
spacings of less than about 0.01 inch are appropriate. For better 
separation results, preferred spacing between the surfaces are up to about 
0.003 inch. It is of course within the scope of this invention to provide 
multiple series or parallel surfaces and to utilize all the surface pairs, 
as well as the gaps therebetween, simultaneously or sequentially. Further, 
the surfaces of this invention may vary in length, both in the direction 
of flow of the hydrocarbon feed containing the diamondoid compounds, 
andnormal to the flow direction. 
Differences in density of molecules closer to the hotter surface and 
molecules closer to the cooler surface cause convection currents to be set 
up within the apparatus between the surfaces. The most efficient 
separations are accomplished where the distance between the two surfaces 
is less than the radius of curvature of these convection currents. If this 
parameter is maintained, the molecules will strike a proximate surface 
before they have an opportunity to circulate around past that surface 
toward the other one. It is desired that the diamondoid molecules strike 
the cooler surface, and run down it to a collection point, without eddying 
back around. It is possible to assist in destroying eddy convection 
currents by installing baffles or insulation between the surfaces such 
that these eddy currents are disrupted, but not sufficient to severely 
retard the flow of molecules between the surfaces. 
Since this separation process is dependent upon temperature differences and 
density differences between molecules, the separations can be assisted by 
artificially increasing gravitational forces acting on the molecules. This 
can be accomplished by carrying out the process under artificial gravity, 
such as by the application of centrifugal force. Artificial gravity up to 
about 100 G forces seems to be suitable. 
The process of this invention can be carried out in several different modes 
to accomplish different objectives. If it is desired to remove as much 
diamondoid compound as possible from a hydrocarbon fraction without too 
much concern for the purity of the diamondoid fraction of the product, 
residence time in the instant process should be made relatively short, 
e.g. about 10 minutes. Further, if this is the object, low ratios of 
process direction length of the surfaces to width of the surfaces are 
desired, e.g. about 2 to 1. Still further, the highest achievable 
temperature and the highest achievable temperature differential should be 
used. 
On the other hand, if it is desired to produce a lower rate of diamondoid 
recovery, but produce a purer diamondoid product stream, higher length to 
width ratios can be used. In this aspect of this invention, length to 
width ratios of as much as about 100 to 1 have been found to be suitable, 
with temperature differentials of about 10.degree. to 50.degree. F. being 
acceptable, and higher temperature differentials being desirable. 
It is important in the practice of this invention that the overall 
temperature of the operation be such that the adamantane compounds do not 
precipitate from the feed stream. Thus, the operating temperatures may be 
limited by the melting point of the highest melting diamondoid compound in 
the feed. Adamantane is the highest melting diamondoid, 296.degree. C. at 
atmospheric pressure, and so if the operating temperature is maintained 
above 296.degree. C. with the pressure at atmospheric or higher, this 
condition will be fulfilled. However, because of mutual solubilities of 
diamondoids, crystallization is often inhibited and temperatures lower 
than the melting point of the highest melting point diamondoid present can 
be used. It is of course within this invention to operate at higher or 
lower pressures than atmospheric, depending upon other desirata, 
particularly good process operation. Therefore the absolute temperature 
requirement will vary depending upon the pressure. In any case, the 
functional requirement that the diamondoid be maintained as a liquid will 
govern. 
Referring now to FIG. 1, a preferred embodiment of the present invention is 
schematically illustrated. A diamondoid-laden natural gas stream 12 is 
withdrawn from wellhead 10 at high pressure, generally 3000 to 15,000 
psig, typically around 11,000 psig. Pressure reduction valve 14, commonly 
referred to as a choke, reduces the natural gas pressure downstream of the 
choke to between about 900 and about 1400 psig. Recycled solvent 18 is 
injected into the reduced pressure diamondoid-laden natural gas stream 16 
upstream of process cooler 20 to prevent deposition of diamondoid solids 
within the cooler. Process cooler 20 is typically an air cooled exchanger 
with extended heat exchange tube surface area, commonly known as a fin-fan 
exchanger. 
Solvent injection rates of about 2 to 6 gallons per minute (GPM) at natural 
gas flowrates of 10 to 15 million standard cubic feet per day (MMSCF/D) 
have been found to be effective to reduce diamondoid deposition. Thus to 
achieve the desired diamondoid sorption in the added solvent, solvent 
charge rates of about 100 to 1000 gallons per million standard cubic feet 
of natural gas (G/MMSCF) are acceptable, and rates of between about 200 
and 800 G/MMSCF are preferred. The optimum charge rate within the 
disclosed ranges to minimize solvent costs while preventing diamondoid 
deposition in the downstream process equipment may be determined by one of 
ordinary skill in the art with a reasonable amount of trial and error. 
If the solvent dosage selected for process operation is insufficient to 
maintain the diamondoids in solution through the process cooler, or if 
solvent injection is temporarily discontinued for operational reasons such 
as injection pump failure, diamondoids will likely be deposited on the 
inner surfaces of the process cooler heat exchange tubes, increasing the 
pressure drop across the air cooled exchanger. Thus one recommended method 
for determining optimum solvent dosage would be to monitor the change in 
natural gas pressure (.DELTA.P) across the process cooler with respect to 
time. An decrease in the .DELTA.P across the process cooler would likely 
indicate diamondoid deposition on the inner surfaces of the cooler tubes 
and could be corrected with increased solvent dosage. The technique of the 
monitoring heat exchanger operation by evaluating .DELTA.P over time is 
well known to those skilled in the art of heat exchanger design and 
maintenance. 
Depending on the concentration of diamondoid compounds in the natural gas 
stream as well as on the operating temperature and pressure, 
discontinuation of the solvent charge may precipitate partial or complete 
plugging of at least a portion of the process cooler heat exchange tubes. 
Such deposits may be removed via intermittent high dosage or "slug" 
solvent treatment. Slug solvent treatment has been found to be effective 
for removing diamondoid deposits from process cooler heat exchange tubes, 
e.g., charging 50 to 100 gallon slugs of solvent intermittently into the 
10 to 15 MMSCF/D natural gas stream at a point upstream of the process 
cooler. The slugged solvent is then recovered by a method similar to that 
used for the continuously injected solvent, which method is described 
below. 
The cooled mixture of natural gas and solvent 22 flows to production 
separator 30 where it is flashed to form an overhead vapor stream 32 and a 
bottom liquid stream 34. Production separator 30 is illustrated as a flash 
drum, i.e. single stage vapor-liquid separation device, but may also 
comprise any suitable vapor-liquid separation apparatus known to those 
skilled in the art of process equipment design. 
A first portion of the overhead vapor stream 32 flows through control valve 
36 to enter sorption zone 40 while a second portion of the overhead vapor 
stream flow is preferably diverted by control valve 36 to form 
regeneration gas stream 38. The total overhead vapor stream may be charged 
to the sorption zone if an inert gas stream for use as a regeneration gas 
is both inexpensive and easily piped into the sorption process equipment. 
It is generally preferred, however, to use a portion of the overhead vapor 
stream as a regeneration gas due to its inherent economony and 
availability. Regeneration gas flow to the silica gel sorption zone is 
preferably countercurrent, i.e., gas flow for silica gel desorption during 
regeneration should be oriented in the opposite direction from gas flow 
for silica gel sorption during gas purification operation. 
The first portion of the overhead vapor stream 32 then contacts a silica 
gel sorbent contained in sorption zone 40. The overhead vapor stream 
preferably flows downwardly in contact with the silica gel sorbent 
throught the length of the sorption zone 40. Silica gel volume is 
preferably selected such that almost all of the silicia gel sorption 
capacity is utilized before regeneration. 
The purified gas stream 42 is then withdrawn from sorption zone 40 and 
charged to pipeline or storage facilities. The second portion of the 
overhead vapor stream is preferably diverted for use as a regeneration gas 
as described above. Part of the purified gas stream 42 may be compressed 
and heated for use as a regeneration gas (compression equipment not 
shown). Generating silica gel using the purified gas effluent, for example 
from sorption zone 40, may prolong the silica gel useful life by 
decreasing the rate of steam deactivation. Regeneration gas 38 is heated 
in regeneration heat exchanger 50 to a temperature less than 315.degree. 
C. (600.degree. F.), preferably between about 177.degree. and 288.degree. 
C. (350.degree. and 550.degree. F.) and then charged to the bottom of 
sorption zone 60 to countercurrently desorb water and heavy hydrocarbons, 
particularly diamondoids, from the silica gel. The length of the 
regeneration step is a function of regeneration gas temperature and 
flowrate as well as the amount of sorbed material contained in the silica 
gel sorption bed. These operating parameters may be varied to synchronize 
the regeneration cycle (desorption) of a first sorption zone with the gas 
purification cycle (sorption) of a second sorption zone. The sorption 
zones are preferably piped and valved in a parallel configuration such 
that one sorption zone may be operated in the gas purification mode while 
the other sorption zone is countercurrently regenerated. 
Enriched regenerated gas 62 is colled to a temperature of between about 
24.degree. and 60.degree. C. (75.degree. and 140.degree. F.) in 
regeneration cooler 70 and is flashed in regeneration separator 80 to form 
a overhead gas stream 82 and a liquid bottom stream 84. The overhead gas 
stream is preferably recycled and mixed with the production separator 
overhead stream and purified in sorption zone 40. The regeneration 
separator overhead gas stream 82 may optionally be mixed with purified gas 
stream 42. While such optional configuration beneficially reduces the 
total gas flow through the sorption zone operating in the gas purification 
mode, it necessarily reduces both diamondoid compound recovery and natural 
gas product purity. 
Liquid bottom stream 34 from production separator 30 and 84 from 
regeneration separator 80 normally flow to solvent accumulator drum 90. A 
portion of the diamondoid-containing solvent 410 is drawn off the solvent 
accumulator and changed to thermal diffusion unit 200. Partially purified 
solvent 426 is then charged through pump 204 and mixed with 
diamondoid-containing solvent to be recycled. Thermal diffusion unit 200 
is described below with reference to FIG. 2. Fresh solvent 94 is added 
downstream to maintain diamondoid concentration in the solvent below 
saturation. A water stream 93 is drawn off from solvent accumulator drum 
90 and is sent to the process sewer for treatment and hydrocarbon 
recovery. The remaining diamondoid-containing solvent 92 is withdrawn from 
solvent accumulator drum 90, charged through pump 100 and mixed with fresh 
solvent 94 to form recycled solvent stream 18 which is added to the 
natural gas stream 16 upstream from process cooler 20 as described above. 
A slip stream of diamondoid-containing solvent 96 may optionally be 
diverted from recycled solvent stream 18 and mixed with the enriched 
regeneration gas stream 62 upstream of regeration cooler 70. This slip 
steam addition to the enriched regeneration gas stream may be necessary to 
avoid diamondoid deposition in the regeneration gas cooler. 
If the diamondoids contained in the feedstream to the present process 
consist predominately of adamantane and diamantane, it has been found that 
the two compounds may be effectively segregated and recovered separately. 
Given a feedstream in which the diamondoids principally consist of 
adamantane and diamantane, the liquid bottom streams from the production 
separator 30 and regeneration separator 80 have been found to be rich in 
diamantane and adamantane, respectively. Thus to recover the two compounds 
at relatively high purity, streams 35 and 85 are drawn off of streams 34 
and 84, respectively, and are routed to separate diamondoid recovery 
processes (not shown). 
Referring now to FIG. 2, the aforementioned solution of diamondoid 
compounds 410 is fed to an intermediate height inlet 412 on the hotter 
side 414 of a thermal diffusion apparatus 416, as previously described 
herein. The hot surface 414 is maintained at a temperature of up to about 
500.degree. F. and is spaced apart from a parallel cooler surface 418 
maintained at a temperature of less than about 490.degree. F. The space 
between the surfaces is set to between 0.003 and 0.01 inch, which is 
maintained by a gasket 420 of that thickness interposed between the outer 
edges of the hot and cooler surfaces. Proximate to the top 422 of the 
hotter surface 414 is a channel 424 through which a stream of solvent 426, 
depleted in diamondoid compounds, is collected for recycle or other use. 
Proximate to the bottom 428 of the cooler surface 418 is a second channel 
430 through which a concentrated stream of diamondoid compounds 432 is 
collected. 
SPECIFIC EXAMPLES 
In all of the examples, parts and percentages are by volume unless 
expressly stated to be on some other basis. 
In the following examples a mixture of an equilibrium mixture of 10 parts 
of diamondoids dissolved in 90 parts of an aromatic distillate fuel oil 
containing 0.8 wt. % of KW-111 brand carboxylic acid/polyamine antifoam 
and 400 ppm wt. of KP-151 brand thioalkyl substituted phenolic 
heterocyclic corrosion inhibitor was used. The antifoam and corrosion 
inhibitor were purchased from the Petrolite Company of St. Louis, Mo. The 
aromatic distillate fuel oil was a diesel fuel having an approximate 
composition as shown in the following Table. FIG. 3 shows a gas 
chromatographic analysis of the feed material. 
______________________________________ 
Aromatics 46-58 wt. % 
Paraffins 22-29 wt. % 
1-ring Naphthenes 12-18 wt. % 
2-ring Naphthenes 5-6 wt. % 
3-ring Naphthenes 1-3 wt. % 
______________________________________ 
EXAMPLE 
The diamondoid containing feed mixture of diamondoids in aromatic 
distillate fuel described above was resolved into its components in a gas 
chromatograph which analyzed the product to contain 10 parts of diamondoid 
in 90 parts of hydrocarbon liquid. The chromatographic analysis of the 
feed mixture is shown in FIG. 3. The diamondoid containing product was 
then resolved in a thermal diffusion apparatus. The thermal diffusion 
apparatus included two concentric tubes approximately five (5) feet in 
length sized such that the outside diameter of the inner tube exceeded the 
inside diameter of the outer tube by approximately 0.006 inch. Thus the 
space between the two surfaces was approximately 0.003 inch. The inside 
diameter of the outer tube and the outside diameter of the inner tube were 
each approximately two (2) inches. The inner tube was maintained at a 
temperature of about 78.degree. F. by flowing cooling water through the 
length of the inner tube. The outer tube was maintained at a temperature 
of about 148.degree. F. by electric resistance heating. 
The diamondoid containing product mentioned above was then allowed to 
equilibrate in the thermal diffusion apparatus for a period of about 20 
hours. The product was then sampled by withdrawing the top and bottom 10 
volume percent from the thermal diffusion apparatus. The bottom 10% 
contained more than 20 weight percent diamondoid compounds as shown by 
chromatographic analysis in FIG. 4. The top 10% predominately contained 
normal paraffins as shown by chromatographic analysis in FIG. 5. 
Changes and modifications in the specifically described embodiments can be 
carried out without departing from the scope of the invention which is 
intended to be limited only by the scope of the appended claims.