US2464576A - Process for the removal of mercaptans from petroleum distillates with an aqueous alkaline reagent containing lignin and the regeneration of the spent alkaline reagent - Google Patents

Description

Patented Mar. 15, 1949 PROCESS FOR THE REMOVAL OF MERCAP- TAN 8 FROM PETROLEUM DISTILLATES WITH AN AQUEOUS ALKALINE REAGENT CONTAINING LIGNIN AND THE REGENER- ATION OF THE SPENT ALKALINE REAGENT Robert R. Hibbard, Lorain, and Franklin Veatch, Cleveland, Ohio, asalgnors to The Standard Oil gohrlnpany, Cleveland, Ohio, a corporation of N o Drawing 10 Claims.

This invention relates to the treatmentoi' hydrocarbons to remove sulfur constituents normally present, and has specific reference to the removal of mercaptans from petroleum distillates.

The treatment of petroleum distillates, such as gasoline, to remove sulfur compounds stems from the objectionable character of such compounds, particularly from the standpoint of odor. It is desirable to "sweeten" the distillate by removal of sulfur constituents in the nature 01 free sulfur, hydrogen sulfide, mercaptans and thio compounds either by conversion to less objectionable suliur-containlng compounds, or by actual removal from the petroleum distillate.

It has long been known that sulfur compounds can be extracted from a hydrocarbon distillate to a great extent by washing with an aqueous solution of alkali, such as caustic soda. The more acidic compounds such as hydrogen sulfide go into solution readily, and their removal presents little problem.

Petroleum cllstillates commonly contain mercaptans in concentrations of from 0.001 to 0.1%, expressed as weight percent of mercaptan sulfur. The mercaptans are weakly acidic, and are often only partially removed by the alkali wash, so that the amount of mercaptans remaining present in the petroleum distillate is above the critical limit for a so-called "sweet gasoline. This may be explained by the following equilibrium equation oi mercaptans in a hydrocarbon distillate treated with an aqueous alkali solution:

+M H RSH RSH T: Its-+11 RSM V Dissolved in Dissolved in Ionized in Saponiiled hydrocarbon (l) alkali (2) alkali (3) in alkali It will be apparent that the concentration of m'ercaptans in the hydrocarbon phase can be kept at a desired low level if the equilibrium (1) is shifted by rendering the mercaptans more soluble in the alkali phase, or by maintaining a low concentration of mercaptans (either ionized or as mercaptides) in the alkali phase.

It has been proposed heretofore to facilitate mercaptan removal from hydrocarbon distillates by the addition of compounds to the alkali solution which renders the mercaptans more soluble therein, and then removing the dissolved mercaptans when the alkali solution is spent" or Application April 18, 1946, erlal No. 683,237

(Cl. lac-29) has absorbed mercaptans to an extent that its mercaptan-removing action is lessened. The latter has been accomplished, for example. by stripping the mercaptans from the spent alkali solution with steam, by treating the alkali solution with a solution of elemental sulfur or polysulfldes, by oxidizing the mercaptans with air, and by other known methods of mercaptan separation. The rate of oxidation of mercaptans in spent alkali solutions by treatment with air can be accelerated by adding suitable catalysts to the solution. Metallic oxidation catalysts and tannicacid have been proposed for this purpose.

In accordance with the present invention. it has been discovered that mercaptan reduction in hydrocarbons is effectively increased by using lignin in the aqueous alkali solution that is used to treat the hydrocarbon distillate, the alkali being treated with oxygen or an oxygen containing gas, such as air, at some stage during the process.

The process may be a single stage process, i. e., the hydrocarbons may be treated with the llgnincontaining alkali in the presence of oxygen. The presence of the iignin assists in causing the solution of mercaptans in the caustic shifting equilibrium (l) to the right. The presence of the lignin also assists the oxygen in converting mercaptides to oxidation products, further shifting equilibrium (2) and (3) to the right. Generally the process is carried out in two steps in a coinmercial operation in which the lignin-containing caustic is contacted with the mercaptan-containing hydrocarbon, and the mercaptan-contalning and lignin-containing caustic is treated with oxygen to convert the mercaptans to oxidation products. The two-step process is preferred and will be referred to hereinafter in describing the invention.

The hydrocarbon material treated may be any containing mercaptans. Generally they are from petroleum sources and the materials most commonly treated are distillates, such as naphthas, gasoline, kerosene, etb.

Lignin is readily available as icy-products of processes involving the separation of ceilulosic from non-cellulosic substances, such as the waste liquors from chemical wood pulping processes.

aqueous alkali solution directly, or the lignin content may be isolated from the waste liquors by acid precipitation and then added to the caustic solution. Lignin derivatives, such as the disodlum salt or other alkali metal salts, may be employed satisfactorily. Standardized grades of llgnln are presently available commercially and it may be desirable to employ lignin of a uniform reproducible grade in carrying out the present invention.

The alkali solution to be used may be any of those normally employed for such purposes, such as caustic soda, caustic potash, alkali metal carbonates, and other equivalent alkali compounds. The concentration of the caustic may be any concentration which will remove merca'ptans to the desired extent. the preferred concentration being between 5 B. to 25 as. (about 3 to 20%), the optimum strength being to in aqueous solution.

The lignin constituent may be employed in an amount sufficient to facilitate mercaptan removal, concentrations of 0.5 to 10% being suitable, and amounts of 2 to 4% by weight of the caustic solution being optimum.

In carrying out the method of the present inmention, it is preferred to prewash the hydrocarbon distillate with caustic to remove the more readily removable sulfur constituents, such as free sulfur and hydrogen sulfide, thus avoiding undue sulfur contamination of the caustic containing lignin, employed in the separation of the mercaptans. The mercaptan extraction is eflected at temperatures at which the mercaptans pass readily to the caustic phase, temperatures between F. and 200 F. being preferred and best results being obtained with a temperature approximating 100 F.

The mercaptan extraction with aqueous alkali solution, in a two-step operation, may be accomplished in any known way. In practice, it has been found desirable to employ suillcient caustic to extract the mercaptans to the desired extent, for example, 10 to 1000 volumes oi caustic with 100 volumes of hydrocarbon distillate, carrying the liquids through a single stage or a counter current multi-stage extraction process, as desired, to effect removal of the mercaptans from the hydrocarbon distillate.

Suitable additives to aid in solution of the mercaptans in the caustic, other than the lignin, may be employed. It has been found that advantageous results are obtained by allowing natural cresol and xylol, components normally present in the hydrocarbon, to build up in concentration in the caustic.

Oxidation of the mercaptans in the spent caustic containing the lignin may be accomplished in any known manner, such as by passing oxygen or an oxygen-containing gas through the caustic solution. Advantageous results may be obtained by use of superatmospheric pressures, although the advantages of the invention are not limited to employment of this expedient. Pressures from atmospheric to 250 lbs. sq. in, have been employed satisfactorily.

The temperature at which the mercaptan oxidation step may be carried out should be such as to accomplish removal of the mercaptans and a temperature of between 50 F. and 200 F. is satisfactory, desirable results being obtained with a temperature of 125 F.

The following experimental data substantiates the effectiveness of lignin to facilitate the removal of mercaptans from the caustic. In carrying out 4 the experiments, "Induiin A" is a commercially available lignln product obtained by acidifying the waste liquor from a sulfate and soda paper pulp process, whereas "Indulin C" is the disodium derivative of "Indulin A."

[All values in mine] Mercaptan Sulfur per Liter oi Caustic Liguln Additive in l5% NaOH Moral tan Initial ono. ftcr Oxidation Mercanlb Min Rate Per ton Cone. Treatment Min.

with Air None 8. 3 4. 2 27 4% "lndulin A" 8.3 1.3 .45 4% "lndulln C 8.3 0.0 .55 N one e o. 1.1 .7 .027 4% "Induiin C". I. l .18 .002

Mermptan Sulfur in Hgdrocarbon istillates Merca tan Lignln Additive in 15% Noon Initial Mercaptan Extraction Per cent Per cent None 5% "lndulin C 0. 041

The above data show the efl'ectivcness of llgnln in facilitating the action of the caustic in removing mercaptans from a hydrocarbon distillate such as gasoline.

It is not intended that the process of the resent invention be limited to certain conditions of temperature and pressure hereinbefore described, for the many variations possible in carrying out the invention will be apparent to those skilled in the art.

We claim:

1. In a method of improving hydrocarbons the step of contacting a mercaptan-containing hydrocarbon distillate in the liquid phase with an aqueous alkaline reagent having lignin dissolved therein.

2. In a'method of improving hydrocarbons the step of contacting a mercaptan-containing hydrocarbon distillate in the liquid phase with an aqueous alkaline reagent having lignin dissolved therein in the presence of oxygen.

3. In a method of improving mercaptan-containing hydrocarbon distillate in liquid phase by treating the same with an aqueous alkaline reagent, the step of contacting a mercaptan-contaming aqueous alkaline reagent with oxygen in the presence of lignin dissolved therein, whereby the aqueous alkaline reagent may be recycled ior reuse in further treating said hydrocarbon.

4. In a method oi improving hydrocarbons the steps of contacting a mercaptan-containing hydrocarbon distillate in the liquid phase with an 5 aqueous alkaline reagent having lignin dissolved therein to remove mercaptans from the hydrocarbon, and treating the mercaptan-containing and lignin-containing alkaline reagent with oxygen to remove mercaptans from the reagent. whereby the aqueous alkaline treating reagent may be recycled to the hydrocarbon treating step.

5. In a method of improving hydrocarbons the steps of contacting a mercaptan-contalning hydrocarbon distillate in the liquid phase with an aqueous alkaline reagent having lignin dissolved therein, separating the hydrocarbon from the alkaline reagent containing the mercaptan, to remove mercaptans from the hydrocarbon, and treating the mercaptan-containing and lignincontaining alkaline reagent with oxygen to remove mercaptans from the reagent, said lignin having been obtained from a sulfate and soda pulp process, whereby the aqueous alkaline treating reagent may be recycled to the hydrocarbon treating step.

6. In a method of improving hydrocarbons the steps of contacting a mercaptan-containing hydrocarbon with an aqueous caustic solution having lignin dissolved therein, separating the hydrocarbon from the caustic solution containing the mercaptan, to remove mercaptans from the hydrocarbon, and treating the mercaptan-containing and lignin-containing caustic solution with oxygen to remove mercaptans from the reagent, said lignin having been obtained from a sulfate and soda pulp process, whereby the aqueous alkaline treating reagent may be recycled to the hydrocarbon treating step.

7. In a method of improving hydrocarbons containing sulfur compounds, comprising contacting a hydrocarbon distillate in the liquid phase with a first alkaline solution to remove free sulfur and hydrogen sulfide constituents normally present. and contacting the distillate with a second aqueous alkaline solution having liznin dissolved therein, said lignin having been obtained from av sulfate and soda pulp process.

ii. In a method of improving hydrocarbons the step of contacting a mercaptan-containing hydrocarbon distillate in the liquid phase with an aqueous alkaline reagent having lignin dissolved therein, said lignin having been obtained from a sulfate and soda paper pulp process.

9. In a method of improving hydrocarbons the step of contacting a mercaptan-containing hydrocarbon distillate in the liquid phase with an aqueous alkaline reagent having lignin dissolved therein, in the presence of oxygen, said lignin having been obtained from a sulfate and soda pap r Dull process.

10. In a method of improving mercaptan-containing hydrocarbon distillate in liquid phase by treating the same with an aqueous alkaline reagent, the step of contacting a mercaptan-containing aqueous alkaline reagent with oxygen in the presence of lignin dissolved therein, said lignin having been obtained from a sulfate and soda paper pulp process, whereby the aqueous alkaline reagent may be recycled for reuse in further treating said hydrocarbon.

ROBERT R. HIBBARD. FRANKLIN VEATCH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,015,038 Pevere Sept. 17, 1935 2,272,594 Bender Feb. 10, 1942 2,315,530 Loyd Apr. 6, 1943 2,317,054 Henderson et al. Apr. 20, 1943 2,389,771 Bond Feb. 20, 1945 2,413,945 Bolt Jan. '7, 1947 OTHER REFERENCES Gordon et al., Chlorine as a Deodorant Pulp Manufacture," Paper Trade Journal. April 28. 1938, pages 81-85.