US2220138A - Purification of hydrocarbons - Google Patents

Description

Nov. 5, 1940. f w. R, woon 2,220,138

PURIFICATION OF HYDROCABBONS v Filed June l0, 1938 HOLVALLQVBH PUR\F\ED LIQLHD HYDROCAR BON 33 SEPARATOR SOLUTION oF swRoNG ALKALI BOLVALLDVBH LIQUID HYDRocARBoN FREE oF H25 SEPARATOR' SOLUTION OF WEAK ALKAL\ Z O (D E 98 :fr w Q. S

INVENTOR MMM/ff@ ATTORNEYS Patenti-,rl Nev. s, 1940 PUItIFICATIQN F HYDROCARBONS wllllm nobel-a wood, Louisville, xy., asslxnor to The Girdler Corporation, Louisville, Ky., a

corporation of Delaware Applicatloninne 10, 1938, Serial N o. 212,929

3 Claims. (CL 196-32) 'Ihis invention relates to the treatment of hydrocarbon compounds in liquid state for'the removal of sulfur compounds therefrom.

The sulfur impurities commonly'found in hy- 5 drocarbons particularly those obtained from petroleum oils, may include hydrogen 'sulilde l which vmay be that derived from the original petroleum oil or asa result of certain reactions employed in the refining processes, and particularly in the cracking process. Hydrogen sulilde is of a strongly acidic nature and may be removed from such hydrocarbon liquids by reacting it with an agent of 'an alkaline nature. However, the reaction between a strongly acidic u material such as hydrogen sulfide, and a strongly alkaline inorganic material such as caustic soda or the like, results in a relatively stable by-product from which the hydrogen sulfide cannot be readilyremoved in gaseous form to regenerate the alkaline reagent.

Other sulfur compounds commonly found in such hydrocarbon liquids are mercaptans, which are of a weak acidic character and form readily decomposable compounds with 'alkaline treating agents. 'I'he by-product resulting from the rehas reacted with the hydrogen sulfide cannot be readily regenerated for reuse. If a weak alkaline agent be employed which will react with the hydrogen sulde to form a readily decomposable 40 by-product, it will not necessarily react with all of the weakly acidic mercaptans. Thus, if a strong inorganic alkali be employed no cyclic system can be employed, since large quantities cf sodium sulfide, which .cannot be regenerated are formed when soda is used as the alkaline material, and if a weakly alkaline agent be employed there is no assurance of complete removal lof the mercaptans.

It has been proposed in the Bottoms Reissue Patent 18,958, to use alkaline amines for removing sulfur compounds from gaseous mixtures, and in a cyclic system, and this has proved very eilicient and satisfactory in commercial practice, but due to the special problems involved in the treatment of liquid hydrocarbons it has not been thought practicable to employ such alkaline amlhesin the treatment of. lliquid hydrocarbons.

Although alkaline amines of the concentration recommended in the Bottoms reissue patent, 5

' namely about 50%; are not practical for remov- 'lution and the liquid therefore becomesproporing sulfur compounds from liquid hydrocarbons,

it has now been discovered that hydrogen sulfide may be effectively and satisfactorily removed by the use of an alkaline amine of com- 10 paratively low concentration, and circulated in a cyclic system with regeneration and liberation of the sulfur compound.

It has been further discovered that where the liquid hydrocarbon contains both hydrogen sul- 15 de and mercaptans, the hydrogen sulfide may be first removed by an alkaline -amine ilowing in a cyclic system with regeneration, and that thereafter the mercaptans may be removed byl a stronger alkaline reagent, which due to the weak acidic character of the mercaptans, may be readily regenerated so that the alkaline reagent may here also ow in a cyclic system with regeneration.

By using two separate closed treating cycles employing basic agents and operating in succession on the liquid hydrocarbon these sulfur compounds may be removed without the development of stable by-products, and with regeneration of the basic agents in both cycles. 'I'he strongly acidic sulfur compound is removed by the solution of a weakly alkaline compound, andthe weakly acidic sulfur compound is removed by a solution of a strongly alkaline compound.

It has been further discovered that by the use of dilute solutions containing less than 30% of the `amine base, and preferably in the form of monoethanolamine, the amine solution saturated with hydrogen sulfide will have a lower viscosity than the fresh solution, and a ready separation of the saturated solution from the liquid hydrocarbon can Foe effected. Furthermore, the solution containing hydrogen suliide has a higher `specific gravity than the fresh so- 45 ti'onatelyl heavier than the liquid hydrocarbon which also assists in the separation. Furthermore, the solution saturated with hydrogen sulde has a greater surface tension than the fresh solution and therefore less tendency to emul- 50 sify. Heretofore danger of emulsication of Vorganic alkaline materials with the liquid hydrocarbons has been` considered an obstacle to the usev of such materials. Thus, the results obtained by the use of airline solutions of comapparatus utilizing difference in speciiic gravity` or the separator Il. 60

paratively low concentration are contrary to prior teachings to the effect that the emcient operation required relatively concentrated solutions of about 50% or more oi the amine.

'I'he present process may be carried out in various types of apparatus. In the accompanying drawing there is shownsomewhat diagrammatically a type of apparatus which may be employed. The liquid hydrocarbon, for instance a prime cut naphtha or a virgin naphtha, may be delivered througha pipe I0 into a mixing chamber Il in which it is thoroughly mixed with an amine solution which is immiscible therewith, and delivered through the pipe I2. The two liquids may iiow in the same direction and intermixing may be eiected in Aany suitable manner, as for instance by bailles or by mechanical agitation, or by means effecting repeated changesin the direction of iiow through the mixer. The amine will react with the hydrogen suliide and the mixture of liquid hydrocarbon. and amine saturated with hydrogen suli'lde may pass out through the pipe I3 to any suitable form of separator Il. The separation may be eilected by the difference in specific gravities of the two liquids, and by a mere settling process, or the separator may be in the form oi.' a centrifuge or any other type oi for effecting separation. The lighter liquid hydrocarbon free. of hydrogen sulfide may be drawn oi from the top of the separator through the pipe I5, and into the second stage of the'process in the event that it contains mercaptans, but ii it is free of mercaptans the liquid hydrocarbon free of hydrogen sulfide may be delivered from the pipe I5 through the pipe I6 to any desired point of disposal.

'I'he solution of the relativelyweak amine saturated with hydrogen sulde may be returned from the separator Il through a pipe I'I into a reactivator I8 where the liquid is heated or subjected tojsub-atmospheric pressure, to remove the hydrogen sulfide in gaseous form through the vent I9. 'I'he reactivator may be of the `type shown in the Bottoms patent above referred to. Thereactivated and puriiied amine solution may be delivered through a pipe 20 by means oi' a pump 2| and back through the pipe I2 entering the mixing chamber II, and this pipe I2 may include -a cooler I2' for removing the heat imparted to the liquid by the heating coil I8 in the reactivator I8.

It is unnecessary to employ any `ash drums or the like iorl preventing the liquid hydrocarbon from entering the reactivator I8, since it is not necessary to conduct the process at elevated temperatures or pressures, and no loss of the amine results .from vvaporization in the reactivator I8 Thus a very economical process results.

Assuming that .the liquid hydrocarbon to be treated contains both hydrogen suliide and mercaptans, the liquid hydrocarbon may be treated as above described by the amine solution which will remove the highly acidic hydrogen suliide without removing appreciable quantities of the weakly acidic mercaptans, most of which will remain in the liquid hydrocarbon passing through the outlet pipe I5.

The liquid hydrocarbon may then be delivered to the second phase of the process which may be carried ,out by apparatus very similar to that employed in the rst phase. The liquid hydrocarbon'free of hydrogen sulfide, and containing the mercaptans, will ilow through the pipe 38 to amixing chamber-3l whereitismixcdwltha solution oi' any strongly alkaline inorganic material entering through the' pipe 32. The strongly alkaline material may be a 15% solution ot caustic soda, which is immiscible therewith and which 5 will react with the mercaptans, and the mixture of the alkaline solution saturated with mercaptans and the liquid hydrocarbon may be delivered through a pipe 3l to a. separator 3l. The two liquids will separate byl gravity in the separator 1o 3l, or may be separated mechanically by a omtrifuge, and the purined liquid hydrocarbon will be delivered through the pipe 35. The alkaline solution saturated with the mercaptans may be drawn on through the pipe 31 and delivered to 15 a reactivator 38 heated by 'a coil 3l'. 'I'he mercaptans will be volatilized and delivered in gaseous form through the vent 38, and the reactivated alkaline solution returned through the pipe Il Vand pump 4I to the pipe 32 which may contain 20 a cooler 32'.

By means of the present process liquid hydrocarbons may be treated without requiring a. prior gasiiication stage, .and the puriiication may becarried out at low temperature and at a low cost. It is not necessary to employ high treating temperatures, which is frequently found necessary in the treating of gaseous hydrocarbons where there is present the danger of condensation.

The process is very economical, due to the i'act 30 that little, if any, of the amines or alkaline solutions are lost, and there is no appreciable amount of hydrocarbon lost in the solution going to the reactivator. This is due in large measure to the use of a relatively low concentration of amine-35 instead of the higher concentration heretofore disclosed for the treatment of mixed gases.

Reference has been made to monoethanolamine as the preferred weakly alkaline material. The term amineas used in this case is intended to 40 include any of the other amines or analogous organic bases dened in the Bottoms patent above referred to as an amine selected from the group `consisting of aliphatic and cycloparaiiin amines,

'and which is free from carboxyl or carbonyl 45 groups, and which has a boiling point not substantially below 100 C. l Any of these may be employed within the scope of the present invention. The amine employed is preferably an aliphatic amine, and preferably one including a hydroxyl group, such amines being known as allqlol amines. Y

In the speciiic example given there is reference to the use of naphtha, but any other appropriate type of liquid hydrocarbon which has a distinctly different 'speciiic gravity from the alkaline solution may be employed, such for instance, as kemsene, gasoline, or the like. Furthermore, the invention may be employed in the treatment of hydrocarbons in liquid state under pressure con- 00 ditions suiiicent to maintain normally gaseous hydrocarbons in liquid condition during the pln'iflcaton of the same. As will be apparent, othery iorms and arrangements of apparatus may be made for carrying out the invention without departing from the scope of the same.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. The process of removing sulfur compounds 7o from liquid hydrocarbons and separately recovering weakly acidic sulfur compounds and strongly acidic sulfur compounds in gaseous form, which includes first mixing the hydrocarbon in a liquid State with a solution containing not more than 30% alkylol amine and insuiliciently basic to react in a substantial measure with mercaptans and other lweakly acidic sulfur compounds in said hydrocarbon, but suihciently basic to react with hydrogen sulde and other strongly acidic sulfur compounds therein, separating said hydrocarbon and said solution, thereafter mixing said hydrocarbon in a liquid state with a solution of an alkali suiliciently basic to react in substantial measure with mercaptans and other weakly acidic sulfur compounds in said hydrocarbon, separating said hydrocarbon and said second mentioned solution, and separately heating said solutions to liberate therefrom the strongly acidic sulfur compounds and the weakly acidic sulfur compounds in gaseous form and regenerate the solutions.

2. The process of removing sulfur compounds from a hydrocarbon in a liquid state, which includes maintaining a cyclic flow of a solution containing not over 30% of an alkylol amine through a contact chamber, a separator and a heated regenerator, maintaining a separate cyclic ow of a solution of a strong alkali through a contact chamber, a separator and a heated regeneratorand circulating a hydrocarbon in liquid 26 state through said contact chamber and separator of the :Erst cycle, and then through the contact chamber and separator of the second cycle, to separate the strongly acidic sulfur compounds from the hydrocarbon in the rst cycle and weakly acidic sulfur compounds from the hydrocarbon in the second cycle and to deliver the strongly acidic sulfur compounds and the weakly acidic sulfur compounds in gaseous form and separately from said heated regenerators.

3. The process of purifying hydrocarbons in a liquid state and recovering hydrogen sulfide and mercaptans separately in gaseous form, which includes passing the liquid hydrocarbon in contact with a solution of an alkylol amine of a concentration not over 30%, to thereby remove from the liquid hydrocarbon the hydrogen sulde present, separating the liquid hydrocarbon from the solution, mixing the liquid hydrocarbon with a solution of a strong alkali to thereby remove the mercaptans, separating the hydrocarbon from said last mentioned solution, and separately heating said solutions to separate therefrom the hydrogen sulilde and the mercaptans in gaseous form and regenerate said solutions.

wnmAM ROBERTS woon.

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