Method for diamondoid extraction using a solvent system

A method for extracting diamondoid compounds from a hydrocarbonaceous fluid such as natural gas, that contains diamondoid compounds is disclosed. The hydrocarbonaceous fluid is mixed with a first solvent in which diamondoids are at least partially soluble. The resulting mixture is separated into a vapor stream and a diamondoid-enriched solvent stream. The vapor stream is then countercurrently flowed past a second solvent in a multistage contacting device, so that a diamondoid-depleted vapor stream and a second diamondoid-enriched solvent stream are created. The diamondoid-enriched solvent streams can be recycled and either added to the first solvent or removed if they are highly saturated with diamondoid compounds.

FIELD OF THE INVENTION 
The present invention relates generally to the production of 
hydrocarbonaceous fluids that contain diamondoid compounds. More 
specifically, this invention provides a method for extracting diamondoid 
compounds from a hydrocarbonaceous fluid such as a natural gas stream, 
using a solvent system. 
BACKGROUND OF THE INVENTION 
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 a larger 
problem. The presence of diamondoid compounds in natural gas has been 
found to cause plugging in the process equipment requiring costly 
maintenance downtime to remove. 
A publication by W. J. King entitled "Operating Problems in the Hanlan Swan 
Hills Gas Field," (SPE No. 17761, 1988), discloses a method for removing 
diamondoid deposits from an aerial inlet cooler using solvents. 
U.S. Pat. Nos. 4,952,747; 4,952,748; and 4,952,749, all issued to Alexander 
et al. and are all hereby incorporated by reference. Patent No. '748 
teaches a method of extracting diamondoids from a gas stream by mixing the 
gas stream with a solvent. Further extraction by means of a silica gel is 
also disclosed. Patent '747 adds a heat exchange process. Patent '749 
teaches a method of diamondoid extraction that requires contacting the gas 
stream with a porous solid such as a zeolite whereby the zeolite absorbs 
some of the diamondoids. 
U.S. Pat. No. 5,019,665, issued to Partridge et al. discloses a method for 
concentrating diamondoid compounds that exist in a solvent, during a 
refinery process. A solvent that is enriched in diamondoid compounds is 
contacted with a shape-selective catalyst under refinery conversion 
conditions to prevent conversion of the diamondoid compounds and to yield 
a solvent that is now concentrated with the isolated diamondoid compounds. 
However, none of the above methods teaches the use of a multi-stage 
contacting device, whereby the diamondoid enriched fluid is flowed 
countercurrently past a suitable solvent. The prior work is therefore 
limited in the attempts at diamondoid extraction. There is therefore a 
need for an efficient, economic procedure to safely extract diamondoid 
compounds from hydrocarbonaceous fluids such as a natural gas stream. 
SUMMARY OF THE INVENTION 
The present invention is surprisingly successful in providing a method for 
extracting diamondoid compounds from a hydrocarbonaceous fluid such as 
natural gas, using a solvent system. It is especially useful at natural 
gas production facilities. 
A hydrocarbonaceous fluid containing a recoverable concentration of 
diamondoid compounds is provided and is mixed with a first solvent in 
which diamondoid compounds are at least partially soluble. The conditions, 
such as temperature and pressure, of the mixture are controlled to 
maintain at least a portion of the mixture in the liquid phase. The 
mixture is then separated, under the controlled conditions, into a vapor 
stream and a diamondoid-enriched solvent stream. 
A second solvent in which diamondoid compounds are at least partially 
soluble is flowed countercurrently in a multistage contacting device past 
the vapor stream so that the vapor stream contacts the second solvent to 
create a diamondoid-depleted vapor stream and a second diamondoid-enriched 
solvent stream. Conditions including temperature and pressure of the 
second solvent are controlled to maintain at least a portion of the second 
diamondoid-enriched solvent stream in the liquid phase. The 
diamondoid-depleted vapor stream is now separated from the second 
diamondoid-enriched solvent stream. 
Either or both of the diamondoid-enriched solvent streams may be recycled, 
so that they are at least partially saturated with diamondoid compounds. 
Either or both of the diamondoid-enriched solvent streams may be recycled 
by adding to the first solvent in controlled amounts, and controlled 
amounts of the diamondoid-enriched solvent streams can be removed. 
Controlled amounts of the second diamondoid-enriched solvent stream can be 
added to the first recycled diamondoid-enriched solvent stream. 
The above and other embodiments, objects, advantages, and features of the 
invention will become more readily apparent from the following detailed 
description of the invention, which is provided in connection with the 
accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
In accordance with the present invention, a new improved method for 
extracting diamondoid compounds from a hydrocarbonaceous fluid using a 
solvent system has been developed. 
Referring to FIG. 1, a preferred embodiment of the present invention is 
schematically illustrated. A hydrocarbonaceous fluid 11 (such as a natural 
gas stream) that contains diamondoid compounds is withdrawn from a 
wellhead 13 at high pressure. Pressure is then reduced to a desired 
pressure, typically about 900 to 1400 psig by means well known in the art. 
A first solvent 15, in which diamondoids are at least partially soluble is 
mixed with the hydrocarbonaceous fluid 11. Such solvents are known in the 
art, and include diesel fuel, toluene, and xylene. 
The conditions of the mixture, including temperature and pressure are 
controlled by means well known in the art so that at least a portion of 
the mixture remains in the liquid phase. Solvent mixing rates of about 2 
to 6 gallons per minute at natural gas flow rates of 10 to 15 million 
standard cubic feet per day are known to be effective for diamondoid 
sorption. The optimum rate at which the first solvent 15 is added to the 
hydrocarbonaceous fluid to minimize solvent costs while preventing 
diamondoid deposition in downstream process equipment may be determined by 
one of ordinary skill in the art, with a reasonable amount of trial and 
error. 
The mixture of hydrocarbonaceous fluid 11 and first solvent 15, which is 
now under controlled pressure and temperature conditions, next flows to a 
separator 17 where it is flashed to form a vapor stream 19 and a now 
diamondoid-enriched solvent stream 21. The separator 17 may comprise any 
suitable vapor-liquid separation device known to those skilled in the art 
of process equipment design. Diamondoid-enriched solvent stream 21 can be 
recycled and re-mixed with said first solvent 15 in a diamondoid solvent 
tank 23. It is preferable that the recycled diamondoid-enriched solvent 
stream be at least partially saturated with diamondoid compounds. 
In another embodiment of the present invention, controlled amounts of a 
fresh solvent (such as more of the first solvent) are added to the first 
recycled diamond-enriched solvent stream, and controlled amounts of the 
first recycled diamondoid-enriched solvent are removed. 
In the preferred embodiment, vapor stream 19 is flowed into a multistage 
contacting device 25. It is desireable, though not necessary, to flow the 
vapor stream 19 into the lower portion of the contacting device 25. A 
second solvent 27, in which diamondoid compounds are at least partially 
soluble, is then flowed countercurrently past the vapor stream 19 in the 
contacting device 25, so that the vapor stream 19 contacts the second 
solvent 27 to create a diamondoid-depleted vapor stream 29 and a second 
diamondoid-enriched solvent stream 31. The conditions of the second 
solvent 27 are controlled (including temperature and pressure) to maintain 
at least a portion of the second diamondoid-enriched solvent stream 31 in 
the liquid phase. An absorber column of various types known in the 
production process design art makes a particularly suitable multistage 
contacting device 25. The second solvent 27 may be identical to the first 
solvent 15. 
The diamondoid-depleted vapor stream 29 is then separated from the second 
diamondoid-enriched solvent stream 31. The diamondoid-depleted vapor 
stream 29 is now purified of diamondoid compounds to the degree that it 
can then be flowed to a pipeline or storage facility. The second 
diamondoid-enriched solvent stream 31 can now be added, in controlled 
amounts that can be determined by one of ordinary skill in the art, to the 
first recycled diamondoid-enriched solvent stream, either in addition to 
said first solvent, or instead of said first solvent. The second 
diamondoid-enriched solvent stream 31, if saturated with diamondoid 
compounds, can be removed by a means known to anyone of ordinary skill in 
the art of production process design. 
While a preferred embodiment of the invention has been described and 
illustrated, it should be apparent that many modifications can be made 
thereto without departing from the spirit or scope of the invention. 
Accordingly, the invention is not limited by the foregoing description, 
but is only limited by the scope of the claims appended hereto.