US3055825A

US3055825A - Process for the treatment of hydrocarbon oils

Info

Publication number: US3055825A
Application number: US783166A
Authority: US
Inventors: Weigert C Buningh; Have Cornelis D Ten
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1958-01-03
Filing date: 1958-12-29
Publication date: 1962-09-25
Anticipated expiration: 1979-09-25
Also published as: NL97060C; FR1228067A; BE574399A; NL223748A

Description

3,055,825 PROCESS FOR THE TREATMENT OF HYDROCARBON OILS Weigert C. Buningh and Cornelis D. Ten Have, Amsterdam, Netherlands, assignors to Shell Oil Company, a corporation of Delaware No Drawing. Filed Dec. 29, 1958, Ser. No. 783,166 Claims priority, application Netherlands Jan. 3, 1958 21 Claims. (Cl. 208-254) This invention relates to a process for removing nitrogen compounds from hydrocarbon oils. More particularly, it relates to a process for removing nitrogen compounds from hydrocarbon oils containing olefins by means of solid adsorbents.

Almost all petroleum crude oils contain small amounts of various nitrogenous compounds which are found in varying concentrations in the fractions and products produced from such crudes. These nitrogen-containing compounds have been identified as consisting of aryl and alkyl amines, derivatives of pyridine, pyrroles, pyrazoles, and quinolines. When these compounds are present in hydrocarbon oil fractions such as lubricating oils, fuel oils, diesel oils, jet fuels, and gasolines, they may cause deposit or laquer formations in the systems in which they are used. Moreover, such nitrogen compounds have been found to contribute to instability during storage and the formation of sludge, gum, and dark color. To avoid the adverse effects of which nitrogenous compounds contribute, it is frequently desirable to remove them.

Many processes have been used and suggested for the removal of nitrogen compounds from hydrocarbon oils, among which are extraction with sulfuric acid, ion exchange, hydrotreating, and other means of removal by solid adsorbents. However, none of the means heretofore known have been entirely successful and the removal of nitrogen compounds from petroleum hydrocarbons is not widely practiced in the United States. The heretofore most promising of these processes has been hydrotreating of the hydrocarbon over a catalyst which is selective to Ward denitrification. However, in the case of gasolines containing olefins, this process has the severe disadvantage that a significant octane number loss is incurred by the partial hydrogenation of the high-octane olefinic components. Sulfuric acid extraction has also been used with some frequency. However, this process has been found to contribute to greater gum formation in the ex-.

because of the difficulty in desorbing the adsorbed ma-' terials and regenerating the expensive adsorbents effectively,.and further because of excessive regeneration time requirements.

.It' is. therefore an object of this invention to provide an improved process for theremoval of nitrogen compounds from hydrocarbon oils. It is a further object to provide a process for the removal of nitrogen compounds from hydrocarbon oils by means of an easily regenerated. It is a still further object of the invertsolid adsorbent. tion to provide a non-corrosive process for removal of nitrogen compounds from hydrocarbon oils. Another object is to provide a process for theremoval of nitrogen compounds from hydrocarbon oils in which olefinic con- Patented Sept. 25, 1962 ire stituents of the oils are not adsorbed or polymerized. Yet another object of the invention is to provide an adsorptive process for the removal of nitrogen compounds from hydrocarbons in which the regeneration of the adsorbent is sufficiently rapid and complete as to permit the carrying out of the process in a continuous manner. The foregoing objects will be apparent from the detailed description of the invention.

The present invention is an improved process for the removal of nitrogenous compounds from hydrocarbon oils which comprises passing the hydrocarbon which contains nitrogen compounds through a solid adsorbent, which has been pre-wetted with a polar organic liquid, until the adsorbent is saturated with nitrogenous compounds, and desorbing the nitrogen compounds, regenerating the adsorbent, and pre-wetting the adsorbent in a single operation by passing through it a mixture of polar organic liquid and water.'

The process according to this invention may be applied to various hydrocarbon oils containing nitrogenous compounds. However, it is particularly advantageous for the removal of dissolved organic nitrogen compounds from hydrocarbon oils containing olefins, such as gasolines and gas oils obtained by thermal or catalytic cracking or by thermal reforming. This process may also be applied to oil which has been obtained from oil-bearing shale by exposing it to heating. The process is also useful for removing organic nitrogen compounds from distillation products obtained in the working up of tar, e.g., crude benzene fractions. The starting materials are preferably fractions which have already been subjected to conventional pre-refining.

As the adsorbent for this invention, various high surface area adsorption compounds may be used so long as they possess at least moderate base exchange capacity and a high surface area. change capacity of at least 15 mini-equivalents per grams and a surface area of at least 100 M /gram are preferred. Examples of suitable adsorbents are silicaprior to treatment of the nitrogenous hydrocarbons there with. As a result of the pretreatment, the adsorbent retains its full capacity to adsorb organic nitrogen compounds. Moreover, the catalytic etfect of the adsorbent upon the polymerization of the unsaturated compoundsis prevented by the polar organic liquid adsorbed on the surface of the adsorption agent. It is preferred to use for the pretreatment of the adsorbent a polar organic liquid which has an adsorptive affinity for the adsorbent approximately equal to that of the organic nitrogen compounds which are to be removed. Furthermore, it should be at least partially soluble in hydrocarbons. Fifty percent solubility of the polar organic liquid in hydrocarbons is preferred and complete solubility is particularly preferred. An adsorptive agent pretreated in the above manner can thus be regenerated and pretreated simultaneously by means of the polar organic liquid with which the adsorption agent must be pretreated.

The adsorbent may be pretreated with various polar organic liquids or mixtures thereof having approximately equal adsorption affinity for the adsorbent as the organic nitrogen compounds to be removed. Suitable for this purpose are dialkyl ketones, esters of fatty acids, dialkyl ethers, cyclic ethers, alkanols, alkanediols, and monoethers thereof. Examples of some of the specific compounds which may be used are acetone, butanone, ethyl Adsorbents having a base ex-' acetate, diethyl ether, diisopropyl ether, dioxane, methanol, ethanol, isopropyl alcohol, ethylene glycol, 2-ethoxyethanol, and diethylene glycol mono-methyl ether. In order that the adsortpive afiinity of the polar organic liquid approximate that of the nitrogen compounds, it is preferred that it contain not more than six carbon atoms per molecule. In the case of dialkyl ketones, it is preferred that they contain less than six carbon atoms per molecule. Acetone is particularly preferred as the pretreating fluid for practicing this invention.

Organic nitrogen compounds contained in hydrocarbon oils, e.g., catalytically cracked gasoline, are effectively recovered by means of the foregoing adsorbents which have been pretreated by any of the above polar organic liquids or their mixtures until the adsorbent becomes saturated, which point may readily be detected by an increase in the amount of nitrogenous compounds in the treated hydrocarbon oil. The adsorbent may be regenerated effectively and rapidly by first contacting it with a mixture comprising equal parts by volume of water and the pretreating polar organic liquid and subsequently with the polar pretreating liquid alone. These liquids may be passed down through the adsorbent to effect the regeneration. Any hydrocarbon oil still present in the adsorbent is expelled by the mixture of water and pretreating liquid. It is a unique and highly advantageous characteristic of this invention that during the regeneration step the water is elutriated immediately after the residual gasoline. The pretreating liquid, e.g. acetone, containing the desorbed nitrogen compound then follows. As a result, the acetone need not come into contact with the elutriated hydrocarbon oil. The hydrocarbon oil and water may, of course, be separated simply by settling into two phases. Thus removal of nitrogen compounds from hydrocarbons, including the residual gasoline which is present in the adsorption zone at the time of the regeneration cycle may be effected without the necessity of distilling the treated product. The regeneration may be effected merely by contacting the adsorbent with the polar liquid alone. After treatment of the adsorbent with polar organic liquid, following the desorbing operation in which water was also used, the adsorbent is again ready for use. The nitrogen compounds may be recovered from the polar organic liquid by fractionation of the elutriated mixture.

The invention may be more readily understood from the following illustrative examples:

Example I Silica gel was wetted with acetone. In order to prevent an undesirable rise in temperature and if possible to fill all pores with acetone the silica gel was immersed in acetone. Twenty grams of the silica gel thus wetted were introduced into a vertical glass tube having an inside diameter of 17 mm. There was introduced into the top of the tube a gasoline obtained by catalytic cracking of a mineral oil and having a boiling range of from 40 C. to 205 C. The gasoline was previously made doctor-sweet by a treatment with a dilute aqueous caustic solution followed by an air solutizer sweetening treatment as described in British patent specification No. 775,015, the treated gasoline having a content of nitrogen compounds of 6.5 milli-equivalents per litre, viz. 0.0116% by weight (calculated as nitrogen). The gasoline was passed through the tube at the rate of 450 cc. per hour. The gasoline issuing from the tube was substantially free from nitrogen. After approximately 2500 cc. of gasoline had been passed through the tube the silica gel was found to be saturated with nitrogen compounds, from appearance of nitrogen compounds in the effluent gasoline.

The silica gel was then regenerated. In order to expel the gasoline present in the tube, 50 cc. of a 1:1 by volume mixture of acetone and water were first passed through the tube. Following the gasoline, water issued from the tube. These liquids could be readily separated. Nitrogen-containing acetone, containing 0.8 milliequivalent of nitrogen per gram of silica gel then flowed from the tube. Hence 11.2 mg. of nitrogen had been bound and subsequently eluted, per gram of silica gel. After the treatment with the mixture of acetone and water, 50 cc. of acetone were passed through the tube, as a result of which the silica gel was again ready for use.

After five cycles of nitrogen removal and regeneration, the capacity of the silica gel was found to have been only slightly reduced. Originally this capacity Was 0.8 milliequivalent of nitrogen per gram of silica gel. After regenerating five times, 0.5 milli-equivalent of nitrogen could be adsorbed per gram of silica gel. After regenerating 15 times, the capacity was still 0.5 milli-equivalent of adsorbed nitrogen per gram of silica gel.

Example 11 Twenty grams of silica gel having a particle size of 0.2-1 mm. diameter were introduced into a vertical tube having an inside diameter of 17 mm. The height of the silica gel bed was 12 cm. The silica gel had been previously immersed in ethyl acetate.

A gasoline obtained by catalytic cracking, boiling be tween 40 C. and 205 C. and pretreated in the same manner as described in Example I, was passed into the top of the tube at the rate of 450 cc. per hour. This gasoline had a nitrogen content of 0.0116% by weight. The gasoline flowing from the tube was substantially free from nitrogen.

After 3,000 cc. of gasoline had been passed through, the bed was found to be saturated with nitrogen compounds.

The silica gel bed was again prepared for further use by passing cc. of ethyl acetate through the bed. The gasoline and the nitrogen compounds adsorbed on the silica gel were washed out by the ethyl acetate. From the collected mixture of nitrogen compounds, gasoline and ethyl acetate it was possible to separate the ethyl acetate from the nitrogen compounds by distillation.

Example III Twenty-five grams of silica-alumina gel having a particle size of approximately 0.2 mm. were introduced into a vertical tube having an inside diameter of 17 mm. This silica-alumina had been used as a catlyst in a cracking plant for the production of cracked gasoline. The height of the bed formed was 12 cm. The catalyst had been previously immersed in acetone.

A gasoline obtained by catalytic cracking and boiling between 40 C. and 205 C. was passed into the top of the tube at the rate of 450 cc. per hour. This gasoline had a nitrogen content of 0.0116% by weight. After the treatment the gasoline was substantially free from nitrogen.

After 1,000 cc. of gasoline had been passed through the bed was found to be saturated with nitrogen compounds.

The bed was again prepared for further use by passing 90 cc. of acetone through it. The gasoline and the nitrogen compounds adsorbed on the silica-alumina was washed out. From the collected mixture of nitrogen compounds, gasoline and acetone it was possible to separate the acetone from the nitrogen compounds by distilation.

Example IV Twenty grams of silica gel having a particle size of 0.21 mm. diameter, previously immersed in acetone, are introduced into a vertical tube having an inside diameter of 17 mm., to a bed height of 12 cm.

A light gas oil obtained by catalytic cracking, having a gravity of 34.8" API, and boiling between 198 C. and 343 C. is passed into the top of the tube at the rate of 325 cc. per hour. This gas oil has a nitrogen content of 0.015% by weight. The gas oil flowing from the tube is substantially free from nitrogen until after 2,100 cc. of light gas oil are passed through the bed.

The silica gel is again prepared for further use by passing through the tube 50 cc. of a mixture of acetone and water in the ratio by volume of 1: 1. The gas oil issues from the tube followed by the water and the two are readily separated by settling. The nitrogen-containing acetone then flows from the tube, from which mixture the acetone is removed by distillation. Approximately 20 cc. of acetone are then passed through the column to pre-wet the adsorbent for another adsorption cycle.

Example V Twenty grams of silica gel having a particle size diameter of 0.2-1 mm. and pre-wet by immersion in diethyl ether are introduced into a vertical column, having an inside diameter of 17 mm., to a gel bed height of 12 cm.

A gasoline obtained by catalytic cracking and boiling between 40 C. and 205 C. is passed into the top of the tube at the rate of 450 cc. per hour. This gasoline had a nitrogen content of 0.0116% by weight. The gasoline flowing from the column is substantially free of nitrogen until over 2,500 cc. of gasoline have been passed through the bed.

The silica gel is prepared for further use by passing 75 cc. of diethyl ether through the bed. The gasoline and nitrogen compounds are desorbed from the silica gel and washed out by the diethyl ether. From the collected mixture of nitrogen compounds, gasoline and diethyl ether, it is possible to separate the diethyl ether from the nitrogen compounds by distillation.

Example VI A column 12 cm. in height is prepared from 20 grams of silica gel having a particle size diameter of 0.2-1 mm. and previously immersed in ethanol.

A catalytically cracked gasoline boiling between 40 C. and 205 C. and having a nitrogen content of 0.0116% by weight is passed through the column at the rate of 400 cc. per hour. The gasoline flowing from the column is substantially free of nitrogen. After 2,300 cc. of gasoline has been passed through, the bed is found to be saturated with nitrogen compounds.

By passing 85 cc. of ethanol through the bed, the gasoline and nitrogen compounds removed from the gasoline are desorbed and washed from the column. No further washing with ethanol is necessary and the column is regenerated and ready for further use.

Example VII Twenty grams of silica gel having a particle size diameter of 0.2-1 mm. and pre-wet by immersion in dioxane are introduced into a vertical tube, having an inside diameter of 17 mm., to a bed height of 12 cm.

A gasoline obtained by catalytic cracking and boiling between 40 C. and 205 C. is passed into the top of the tube at the rate of 400 cc. per hour. The effiuent gaso line, which had a nitrogen content of 0.0116% by weight prior to treatment by this process, is substantially free from nitrogen until after 3,000 cc. of gasoline have been passed through the bed.

The silica gel bed was prepared for further use by passing 90 cc. of dioxane through the bed of adsorbent. The gasoline and nitrogen compounds are thusly desorbed from the silica gel and washed out by the dioxane. The components of the elutriant wash liquid solution are then separated by distillation.

Since this invention is carried out in the liquid phase, the operating pressure has no substantial effect on the adsorption characteristics of the process. Therefore, the choice of operating pressures will be governed largely by pressure drop and throughput requirements.

It is, of course, known that temperature generally reduces the adsorptivity of a compound. However temperature also reduces the adsorptivity of the polar organic liquid to about the same extent. Therefore, since the relative adsorptivities of the components to be separated and the polar organic liquid determine the selectivity; and further, since their relative adsorptivities re-' main about the same, it may readily be seen that there is no marked shift in selectivity to be obtainned by varying the temperature of the process. Of course, extreme variations can significantly affect the relative adsorptivity and therefore it is preferred to carry out the process between about 20 C. and 60 C. However, successful operation is not limited to this range except as the relative adsorptivity of the polar organic liquid and nitrogen compounds to be removed may be changed thereby to the extent that the desired degree of selectivity is destroyed. The comparatively low temperatures at which this process may be carried out is, of course, advantageous in that it reduces further the risk of chemical conversion of the oil components when in contact with the adsorbent.

It will be recognized by those skilled in the art that the efiiuen't from the column must, during the nitrogen removal step, be equilibrated with the column. That is, the fluid being treated must be of sufficiently low viscosity that all of the nitrogen compounds have sufiicient residence time within the column to be diffused through the liquid hydrocarbon solute phase to the adsorbing surface. It is thus another effect of higher temperature, due to lower viscosity, that better establishment of equilibrium can take place. Oils having too high viscosity to allow proper diffusion of the nitrogen compounds may nevertheless be treated by this process by diluting them with a low viscosity solvent having a very low adsorptive affinity such as low molecular weight liquid paraflinic hydrocarbons, e.g., pentane. From this, it will also be understood that the space velocity of oil through the column must be sufficiently low to equilibrate the efliuent to the column of adsorbent in order to avoid incomplete removal of nitrogen compounds. It is generally preferred not to exceed-a liquid hourly space velocity of 60 volumes of oil per volume of adsorbent per hour. The short residence times, which characterize this process for the removal of nitrogen compounds, are additionally advantageous in that the likelihood of chemical conversion of the oil components when in contact with the adsorbent is even further reduced.

It is a further advantage of the process of this invention that the amount of polar organic liquid (washing liquid) required to desorb the removed nitrogen compounds is small, thus significantly decreasing the initial capital expense and solvent costs for the commercial practice of the invention. It is of interest to note that the amount of washing liquid required is substantially unaffected by the ratio of adsorbent to treated oil, and is primarily a function of the amount of adsorbent. It is preferred to use a minimum of about 1 ml. of washing liquid per gram of adsorbent, still better at least 2 ml. Greater degrees of er tectiveness of desorption may be obtained at even higher ratios, however, such ratios in excess of about 3 ml. per gram unduly increase the cost of solvent, solvent recovery, and equipment. v

t is a very attractive feature of the process of the invention that the regeneration of the adsorption is very rapid as well as complete. The regeneration period is much shorter than the adsorption period and hence is not a limiting factor in the practice of the process of a cyclic process. Thus, the process may be carried out on a continuous feed basis with only two adsorber columns in parallel one of which is regenerated while the other is adsorbing. However, because of the rapidity with which the regeneration is completed, it is not necessary to resort to intermittent operation of the adsorbers. The process may be carried out continuously, for example in a vessel having fixed inlet and outlet nozzles above and below a rotating bed of adsorbent. Conversely, a vessel having a fixed bed of adsorbent with rotating inlet and outlet nozzles can also be used. It is, of course, to be understood that the practice of the invention is not limited to fixed bed operation wherein the liquid is passed through the adsorbent, but may be adapted to other modes of operation, such as placing the adsorbent in the liquid to be treated and then separating the adsorbent from the treated liquid by filtration or other liquid-solids separation means.

We claim as our invention:

1. A process for the removal of dissolved organic nitrogen compounds from liquid hydrocarbons by contacting the liquid hydrocarbon with the entire body of a solid adsorbent having adsorptive surfaces pre-wet with a polar organic liquid having an adsorptive afiinity for the solid adsorbent approximately equal to the adsorptive afiinity for the adsorbent of the dissolved organic nitrogen compounds to be removed and in which said polar organic liquid is an organic compound containing oxygen, selected from the group consisting of dialkyl ketones, alkyl esters, dialkyl ethers, cyclic ethers, alkanols, alkanediols, and alkanediol monoethers, separating the hydrocarbons from the adsorbent and adsorbate comprising at least a portion of the nitrogen compounds, desorbing the adsorbate nitrogen compounds from the adsorbent, and regenerating and pre-wetting the adsorbent for further use with at least one milliliter of said polar organic liquid per gram of adsorbent.

2. The process of claim 1 in which the adsorbent is a high surface area inorganic compound containing oxides of metals selected from the group consisting of silicon and aluminum.

3. The process of claim 2 in which the adsorptive agent is silica gel.

4. The process of claim 2 in which the adsorptive agent is alumina.

5. The process of claim 1 in which the polar organic liquid is a dialkyl ketone having less than six carbon atoms per molecule.

6. The process of claim 5 in which the polar organic liquid is acetone.

7. The process of claim 1 in which the polar organic liquid is a fatty acid alkyl ester having no more than six carbon atoms per molecule.

8. The process of claim 7 in which the polar organic liquid is ethyl acetate.

9. The process of claim 1 in which the polar organic liquid is a dialkyl ether, having no more than six carbon atoms per molecule.

, 10. The process of claim 9 in which the polar organic liquid is diethyl ether.

11. The process of claim 9 in which the polar organic liquid is diisopropyl ether.

12. The process of claim 1 in which the polar organic liquid is a cyclic ether having no more than six carbon atoms per molecule.

13. The process of claim 12 in which the polar organic liquid is dioxane.

14. The process of claim 1 in which the polar organic liquid is an alkanol having no more than six carbon atoms per molecule.

15. The process of claim 1 in which the polar organic liquid is an alkanediol having no more than six carbon atoms per molecule.

16. The process of claim 1 in which the polar organic liquid is alkanediol monoether having no more than six carbon atoms per molecule.

17. A process for the removal of dissolved organic nitrogen compounds from liquid hydrocarbons by contacting said liquid hydrocarbon with the entire body of a solid adsorptive agent, the adsorptive surfaces of which have been pre-wetted with acetone, wherein the removed nitrogen compounds are desorbed from the adsorptive agent, and said adsorptive agent is regenerated and prewetted for further use by first contacting said adsorbent with at least one milliliter of a mixture consisting of equal parts by volume of acetone and water per gram of adsorbent, and subsequently contacting said adsorbent with acetone.

18. The process of claim 17 in which the liquid which is to be treated is a nitrogen-containing hydrocarbon obtained by the thermal or catalytic cracking of higher boiling mineral oils.

19. The process of claim 18 in which the liquid hydrocarbon to be treated is a cracked gasoline.

20. A process for the removal of dissolved organic nitrogen compounds from liquid petroleum hydrocarbons by passing said liquid hydrocarbons in contact with and through the entire body of a solid adsorptive body in a column, the surfaces of said body being pre-wet with a polar organic liquid having an adsorptive aflinity for the body approximately equal to that of the nitrogen compounds and in which said polar organic liquid is an organic compound containing oxygen, selected from the group consisting of dialkyl ketones, alkyl esters, dialkyl ethers, cyclic ethers, alkanols, alkane diols, and alkanediol monoethers, separately removing the bulk of the sotreated hydrocarbons from the column, desorbing the adsorbate nitrogen compounds from the solid with a desorbent consisting essentially of the pre-wetting polar com pound, whereby the adsorbent is regenerated and prewetted for further use with at least 1 milliliter of the polar organic liquid per gram of adsorbent.

21. A process according to claim 20 wherein, following removal of the main bulk of the liquid hydrocarbons, pre-wetting polar liquid mixed with water is introduced into the column, polar liquid remaining on the adsorbent and water advancing through the adsorbent and passing out of the column, whereby remaining liquid hydrocarbons are swept out of the column, and thereafter introducing substantially anhydrous pre-wetting polar liquid, the total amount of said liquid on the adsorbent then being at least about 1 milliliter per gram of adsorbent.

References Cited in the file of this patent UNITED STATES PATENTS 2,728,715 Rampino Dec. 27, 1955 2,763,603 Skinner Sept. 18, 1956 2,779,718 Capell et al Jan. 29, 1957 2,925,379 Fleck et .al Feb. 16, 1960 2,925,380 Fleck et al Feb. 16, 1960

Claims

1. A PROCESS FOR THE REMOVAL OF DISSOLVED ORGANIC NITROGEN COMPOUNDS FROM LIQUID HYDROCARBONS BY CONTACTING THE LIQUID HYDROCARBON WITH THE ENTIRE BODY OF A SOLID ADSORBENT HAVING ADSORPTIVE SUSRFACES PRE-WET WITH A POLAR ORGANIC LIQUID HAVING AN ADSORPTIVE AFFINITY FOR THE SOLID ADSORBER APPROXIMATELY EQUAL TO THE ADSORPTIVE AFFINITY FOR THE ADSORBENT OF THE DISSOLVED ORGANIC NITROGEN COMPOUND TO BE REMOVED AND IN WHICH SAID POLAR ORGANIC LIQUID IS AN ORGANIC COMPOUND CONTAINING OXYGEN, SELECTED FROM THE GROUP CONSISTING OF DIALKYL KETONES, ALKYL ESTERS, DIALKYL ETHERS, CYCLIC ETHERS, ALKANOLS, ALKANEDIOLS, AND ALKANEDOIL NONOETHERS, SEPARATING THE HYDROCARBONS FROM THE ADSORBENT AND ADSORBATE COMPRISING AT LEAST A PORTION OF THE NITROGEN COMPOUNDS, DESORBING THE ADSORBATE NITROGEN COMPOUNDS FROM THE ADSORBENT, AND REGENERATING AND PRE-WETTING THE ADSORBENT FOR FURTHER USE WITH AT LEAST ONE MILLILITER OF SAID POLAR ORGANIC LIQUID PER GRAM OF ADSORBENT.