US2296096A - Acid-treating process - Google Patents

Description

Patente'd Sept. 15, 1942 ACID-TREATING APROCESS Russell F. Dorsch, San Antonio, Tex., assignor, by mesne assignments, to The V'Iexas Company, New York, N. Y., a corporation of Delaware Application November 2, 1940, Serial No. 364,027

(Cl. 19d-40) 4 Claims.

This invention relates to a process for treating petroleum hydrocarbon oils with acids to remove sulfur and gum-forming constituents. invention particularly relates to a simpliiied and improved process whereby both sulfur-containing straight run and cracked naphthas may be treated efciently with sulfuric acid.

In considering the treatment of petroleum hydrocarbon oils with sulfuric acid to remove sulfur and gum-forming constituents it is important to make a distinction between oils obtained by straight run distillation and those obtained as a result of a cracking operation. Straight run oils are relatively free from hydrocarbons which tend to polymerize in the presence of sulfuric acid and therefore these oils may be treated with strong sulfuric acid in relatively 4large amounts so as to reduce the sulfur content of the oils to as low a point as possible. Severe acid treatment of straight run oils with attendant reduction in sulfur content is advantageous because it increases the susceptibility of the oils to tetraethyl lead. Of course, the amo-unt of acid used in the treatment of straight run oils is limited by the advantages gained through further sulfur reduction; beyond a certain point the use of additional acid becomes uneconomical. On the other hand, cracked oils, which are usually fractions obtained by distillation from the product of a cracking operation, should be treated carefully with sulfuric acid since otherwise the losses due to polymerization will be excessive. l

It is conventional to prepare gasolines from petroleum hydrocarbon Vmixtures containing straight run and cracked naphthas in varying proportions, `When the naphthas are obtained from high sulfur crudes, acid treatment of both straight run and cracked naphthas is usually resorted to. At times the two naphthas have been mixed prior to acid treatment, This is not satisfactory because an acid treatment strong enough to produce the desired effect on the straight run `naphtha causes `excessive polymerization of the cracked naphtha, while weak acid treatment does not reduce the sulfur content sufiiciently. p

To solve this problem a so-called two-acid prccess has been employed. Inthis process an acid such as recovered 9S per cent to 100 per cent sulfuric acid is used for the treatment of the straight run naphtha and a weaker acid such as recovered, so-called 66 B. (about 93 per cent)` acid is used for the cracked naphtha. Although this process is reasonably satisfactory it is difficult to operate, particularly in relatively small The and erosion of the pipes and valves.

refineries. In controlling the flow of/acid to both the `straight run and cracked naphthas, jets wherein the naphtha ilows through a restricted oriceand the acid is pulled into the stream due to the suction created have been used. In order that the acid should be proportioned properly it is important that the acid flow to the jet at a relatively high velocity, which requires that the pipe carrying the acid be of small diameter. To illustrate this problem, in the treatment of typical straight run and cracked naphthas, of the order of three pounds of 98 per cent acid per barrel of straight run naphtha and 21/2 pounds of 66 B. acid per barrel of cracked naphtha are required. Where less than 100 barrels per hour of each naphtha is charged, for example, it is necessary thatrthe acids flow to the jets in small streams. For economic reasons the acids used in this process are recovered black acids which contain impurities such as coke and also a proportion of inorganic salts such las sodium sulfate. When flowing such acids in small pipes, clogging of the `pipes and valves occurs, requiring shutting down to clean out the equipment. Also, accurate control of the flow is diilicult because of corrosion The twoacid process has another disadvantage which is particularly applicable to the treatment of cracked naphtha. To avoid overreaction, the time o f `reaction must be short but the sulfuric acid-should Vbe dispersed thoroughly through the naphtha. Due to the small volume of acid used adequate mixing of the acid and cracked naphtha is difficult in the time permitted.

Thepresent invention provides a process which is free from the foregoing and other disadvantages Vof lthe processes previously employed for the acid treatment of both straight run and cracked petroleum hydrocarbon oils. In line with the terminology used above, the process may be termed a one-acid process since only a single acid is 'employed for the treatment of both the straight Vrun an-d the cracked oil. The process comprises introducing all the acid required for the treatment of both oils into the straight run oil and then using the acid sludge from the straight run treatment for the treatment of the cracked oil. It has been discovered that suilicient acid may be introduced into the straight run oil to produce excellent results on this oil and at the same time produce a straight run sludge which is capable of effecting the desired purification of the cracked oil, no other acid treatment being required.

This process possesses several important advantages. As noted above, severe acid treatment of straight run oils is desirable. In the present process an excess of acid is used on the straight run oil and yet the economy of the process is not reduced. As a matter of fact the process involves important savings over the processes referred to above. Thus, the total amount of acid required is less than a process where separate acids are used. Since only one acid is used, the amount of acid flowing in the one streamis increased, thereby simplifying control of this flow. Control of the operation of the process is also simplied because the acid introduced is dependent upon the requirements of the cracked oil rather than the requirements of both oils. The straight run acid sludge, which is introduced into the cracked naphtha, occupies a relatively large volume, and, as a result, the flow of this sludge may be easily controlled and difculty due to clogging may be avoided. Also the rate of dispersion of the acid in the cracked oil is irnproved, apparently because the hydrocarbons present in Ithe straight run sludge facilitate thorough mixing of the acid with the oil.

In order that the invention may be understood more fully reference should be had to the drawing, the single figure of which represents diagrammatically a suitable system for carrying out the process of the invention in a continuous manner. Since the process is especially adapted for use in the combined treatment of sulfur-containing straight run and cracked naphthas, the following description is particularly concerned with such oils. Referring to the drawing, straight run naphtha is forced by a pump I into a line 2 leading into the system. From the line 2 the naphtha enters a mixing jet 3 wherein it is contacted with strong sulfuric acid, such as recovered 98 per cent black acid, flowing from acid storage vessel 4 through line 5 in a manner described more fully below. A line 6 conducts the mixture of acid and naphtha into a mixer 'I which may be of any suitable construction, such as a pipe mixer, for example, and from the mixer the mixture flows through line 8 into the lower portion of a settler 9. In this settler straight run acid sludge settles to the bottom and is removed as rapidly as formed through a line IIJ leading to the cracked naphtha system. The treated straight run naphtha passes from the top of settler 9 into a line II, through which it is conducted into admixture with cracked naphtha containing acid sludge. Cracked naphtha is forced into the system by means of pump I2 and passes through line I3 leading to a mixing jet I4, which is similar to mixing jet 3. In mixing jet I 4 the cracked naphtha is mixed with straight run acid sludge and the resulting mixture passes through line I into mixer I6 and thence through line I'I leading to settler I 8. Line II carrying acid-treated straight run naphtha leads into line I'I, and the mixture of straight run naphtha, cracked naphtha, and acid sludge, therefore,l passes into settler I8 where the sludge settles and is drawn off. From this settler the combined naphthas are passed to a caustic washing system, and to any further treatment desired.

The flow of acid into the straight run naphtha line is conveniently accomplished in the apparatus disclosed by proceeding as follows: Connecting line 2 and line 5 there is disposed a line 20. This line is provided with two valves, 2| and 22, and a flow-meter 23.v As the process is usually operated, the pressure in the naphtha line is greater than the pressure on the acid at the point line 5 joins with line 20. With valves 2I and 22 open no acid would flow to the jet. However, by opening both of the valves in line 5 and partially closing valve 22 the ow of naphthav in line 20 is controlled so that a regulated mixture of naphtha and acid flows to the jet 3, the total amount of liquid entering this jet through line 5 being determined by the naphtha flow through the jet from line 2. This method of introducing the acid is convenient because it increases the Volume of liquid flowing to the jet. However, this method forms no part of the` present invention and is disclosed and claimed in the application of Eddins W. McNealy, led of even date herewith. If desired, the acid may flow directly into the naphtha line` from the acid storage vessel. Also the straight run naphtha may be passed through a body of acid from which the sludge is continuously withdrawn.

The following example illustrates the operation of the process for the treating of about 74 barrels per hour of straight run naphtha containing about 0.l2 per cent total sulfur, and about barrels per hour of cracked naphtha prepared by thermal cracking and containing about 0.22 per cent sulfur. The straight run system is adjusted so that the pressure on pump I is 60 to 80 pounds per square inch and valve 22 is adjusted so that about '7 pounds of recovered 98 per cent sulfuric acid are fed into the jet 3 for each barrel of straight run naphtha. This amount of acid is substantially in excess of the amount that would be introduced were the acid to be used for the treatment of the straight run naphtha alone. The resulting mixture is then passed through the mixer 'I and into the settler 9, the contact time, calculated from the time the mixture leaves the jet until it enters the settler, being about 46 seconds. The straight run acid sludge is removed from the settler 9 as rapidly as it is formed and is introduced into the cracked naphtha line through jet I4. The pressure on the cracked naphtha pump I2 is also about 60 to 80 pounds per square inch. In the jet I4 the cracked naphtha is joined by the acid sludge in the proportions of about 4.7 pounds of acid sludge for each barrel olf cracked naphtha. This sludge Weighs about twice as much as an amount of recovered 93 per cent acid having the same value as an acid treating agent. Further due to the larger flow and hydrocarbons contained in the sludge, the flow is not subject to becoming clogged and the sludge is quickly and eiciently mixed or dispersed with the cracked naphtha. The mixture of cracked naphtha and straight run sludge is passed through mixer I6 and then into line II where it is joined by the acid treated straight run naphtha from settler 9. 'Ihe straight run naphtha serves to cool the mixture and reduce the se- Verity of the action of the acid on the cracked naphtha. In settler I8 sludge settles out and is withdrawn, and the combined naphthas are passed to a caustic wash and are further treated to obtain a iinished gasoline. The time of contact between the straight run acid sludge and the cracked naphtha, calculated from the time of mixing the two in jet I4 until the cornbined naphthas and sludge enter settler I8, is about 31 seconds. The nished gasoline obtained from this process contains less than 0.1% sulfur.

From the foregoing description it will be seen that all the acid enters the process through the straight run system. Thus, the straight run naphtha is treated with all the acid used, an

amount in excess of that employed on this naphtha where the straight run and cracked naphthas are treated separately. Also, it is necessary to control only one acid flow. Since at all times the straight run naphtha is contacted with suicient acid to reduce the sulfur content to the desired point, the determination of the amount of acid required may be made solely by reference to the effect on the cracked naphtha.

It will be understood that in operating the present process the conditions will be adjusted in accordance with the relative amounts of straight run and cracked oils treated. In some cases, where a relatively small amount of cracked oil is treated, it may be advisable not to employ all the straight run sludge for treatingthis oil, but instead to conduct a part of this sludge out of the system separately.

Since changes may be made in the process l above described without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. In the process for acid treating both straight run and cracked hydrocarbon oils to remove sulful and gum-forming constituents, the improvement which comprises contacting the straight run petroleum hydrocarbon oil with sulfuric acid to form an acid-treated straight run petroleum hydrocarbon oil and a straight run acid sludge, and mixing the straight run acid sludge with the cracked petroleum hydrocarbon oil, whereby there is produced acid-treated cracked petroleum hydrocarbon oil, the sulfuric acid contacted with the straight run petroleum hydrocarbon oil being the only acid employed in the process.

2. In the process for acid treating both straight run naphtha and cracked naphtha to remove sulfur and gum-forming constituents, the improvement which comprises contacting the straight run naphtha with sulfuric acid to produce an acid-treated straight run naphtha and a straight run acid sludge, and mixing the straight run acid sludge with the cracked naphtha, whereby there is produced acid-treated cracked naphtha, the sulfuric acid contacted with the straight run naphtha being the only acid employed in the process and the amount of this acid being regulated in accordance with the acid requirements of the cracked naphtha.

3. In the process for acid treating both straight run naphtha and cracked naphtha to remove sulfur and gum-forming constituents, the improvement Which comprises contacting the straight run naphtha with sulfuric acid of about 98 per cent strength to produce an acid-treated straight run naphtha and a straight run acid sludge, and mixing the straight run acid sludge with the cracked naphtha, whereby there is produced acidtreated cracked naphtha, the sulfuric acid contacted with the straight run naphtha being the only acid employed in the process and the amount of this acid being regulated in accordance with the acid requirements of the cracked naphtha,

4. The continuous process for acid treating both straight run naphtha and cracked naphtha which comprises continuously flowing sulfuric acid of about 98 per cent strength into contact with a ilowing body of the straight run naphtha to produce an acid-treated straight run naphtha and a straight run acid sludge, continuously separating the straight run acid sludge from the acidtreated straight run naphtha as rapidly as formed, and continuously flowing the straight run acid sludge into contact with a flowing body of the cracked naphtha, whereby there is produced acid-treated cracked naphtha, the acid contacted with the straight run naphtha being the only acid employed in the process and the amount of this acid being regulated in accordance with the acid requirements of the cracked naphtha.

RUSSELL F. DORSCH.

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