US2378216A - Conversion of hydrocarbons - Google Patents

Description

Filed Sept. 28, 1942 NNN,

tba

Patented June 12, 1945 CONVERSION HYDROCABBQNS Vladimir Haensel and Bernard S. Friedman, Chicago, Ill., assignors to Universal Oil Products Company, Chicago, Ill., a corporation of Dela- Wale Application September 28, 1942, Serial No. 459,939

11 Claims.

This invention relates to the conversion of hydrocarbons and more particularly to va combination oi interdependent and cooperative steps whereby a hydrocarbon mixture comprising essentially parafllns and oleilns is separated into a second mixture of isoparafflns and oleilns and this second mixture is subjected to alkylation to produce a saturated high antiknock distillate. This distillate is substantially saturated in character and is of high antiknock value. The major portion of this distillate boils within the range of gasoline and is particularly suitable for use in aviation gasoline.

In the alkylation of isoparamns by olens, it is essential that an excess of isoparafiins be present in the reaction zone in order to minimize undesirable polymerization reactions and also because the presence of an excess of isoparaillns has been found to yield alkylation products o f higher antilmock properties. The ratio of isoparamns to olefins is usually within the range of 3:1 to as high as 20:1 or, in certain cases, even higher. l

In addition, experiments have shown that the presence of substantial amounts of normal paraillns in the alkylation zone has a deleterious eilect upon the alkylation reaction. Further, the presence of such large amounts of normal parafflns increases the size of the alkylation equipment and thus adds considerably to the cost of alkylation plants. Also, this presence of large quantities of normal paraiiins in the alkylation zone creates a heavy burden on the subsequent fractionation equipment of the process. In the alkylation processes heretofore proposed, the products from the alkylatlon zone comprise principally alkylate, normal parains and excess isoparaiilns, and entails fractionation and distillation equipment of considerable expense in order to eect separation of these products. It is a particular feature of'the present invention that this excessive cost of fractionation is greatly reduced by the combination of interdependent steps disclosed herein.

According to the present invention, the charging stock, comprising essentially a mixture of oletlns and paraiilns, is subjected to extraction in the presence of a particular separating agent which has been found to have a high capacity, that is, it will dissolve large proportions of the hydrocarbons and, in addition,.it has a high selectivity-that is, it will dissolve the oleiins preferentially tothe parafilns. The extract phase, comprising principally the olens and separating agent, is subjected to treatment with an isopar- (Cl. 26o-683.4)

aln in order to release the oleilns and to thereby produce a mixture oi.' isoparaiiin and oleflns for the subsequent alkylation step of the process. Another particular feature of the present invention is that the quantity of oleflns absorbed by the separating agent and the oleflns released by contact with the isoparaiilns are balanced to produce an isoparailin-oleiln mixture of the correct composition required for optimum alkylation. 'I'hese results are achieved by the use of the particular separating agent and the particular combination of interdependent steps disclosed herein.

In one specific embodiment the present invention comprises subjecting an olen-parafln mixture to extraction with a separating agent comprising essentially a phosphoric acid solution of silver phosphate, separating an extract phase from a' raillnate phase, contacting the extract phase with an isoparamn in order to separate an isoparain-oleiin mixture in which the ratio of isoparamns to olefin is within the range of 3:1 to :1, subjecting said isoparailin-olefln mixture .to alkylation in the presence of an alkylation catalyst,vfractionating the products of said alkylation to separate afraction comprising principally isobutane and recycling said fraction to the process.

'Ihe invention will be further explained in connection with theaccompanying drawing which 30 illustrates a ilow diagram of one method in which the process may be conducted. However, it is not intended to limit the invention to the particular flow as shown in the drawing.

In order to simplify the further explanation of the invention the following description will be limited to the treatment of a butane-butylene charging stock. The butane-butylene fraction charged to the process will usually vary in its composition of normal butane, isobutane, normal butylene and isobutylene, as well as in the minor quantities of the lower and high boiling compounds, depending upon the source from which it is obtained and upon the method by which it is recovered. It is understood that the invention is not limited to the treatment of butane-butylene mixtures but that the invention is applicable to the treatment of other mixtures containing olens and parail'lns which are suitable, after treatment in the early stages of the present combination process, for alkylation in the subsequent stage of the process. Y

Ii the charging stock contains'suliur or sulfur compounds, the charging stock is preferably given a preliminary treatment in order to remove the 56 sulfur therefrom. Usually a caustic wash will be sumcient to remove the hydrogen sulfide but, if necessary, a. more severe treatment may be employed.

Referring' to the drawing, the charging stock is introduced to the process through line I and is directed into primary extractor or zone 2, which may be of any suitable type in order to effect the desired contact of the charge with the separating agent. Thus. this zone may take the form of one or more zones which may or may not contain packing material such as gravel, clay, synthetically prepared composites, etc., and/or fractionating means such as baille plates, bubble trays or the like. In the particular case illustrated in the drawing, countercurrent flow of .hydrocarbons and separating agent is shown, although it is understood that concurrent flow may also be utilized.

Referring again to the drawing, the separating agent may be introduced through line 3 to zone 2 and, after the operation of the process has commenced, the separating agent may comprise all or a portion thereof which is recycled within the process in a manner to be hereinafter described in detail.

The separating agent of the present invention comprises a phosphoric acid solution of silver phosphate. Experiments indicate the best results are obtained when employing high concentrations of silver phosphate. However, the concentration of the silver phosphate is limited by the concentration of the phosphoric acid. On the other hand, the concentration of the phosphoric acid is limited since the undiluted acid is too viscous and also since the undiluted acid tends to catalyze undesired reactions. Thus. for example, it has been found that phosphoric acid solutions of greater than 95 percent concentration are too viscous for practical use at ordinary temperatures. Therefore, according to the present invention, the phosphoric acid solution should be below 95 percent concentration and preferably below 90 percent concentration.

Effective separating agents have been prepared comprising 30 percent silver phosphate and 70 percent by weight of phosphoric. acid of 85 percent concentration. Likewise, effective separating agents have been prepared comprising 18 percent silver phosphate and 82 percent by weight of phosphoric acid. of 67.5 percent concentration. In general, it is preferred to utilize as high a concentration of the acid as is satisfactory in connection with the particular separation desired and also to use as high a concentration of the silver phosphate as may be dissolved therein. In most cases the concentration of phosphoric acid should be above 50 percent.

'I'he silver phosphate-phosphoric acid solution may be prepared in any suitable manner. One convenient method is to mix the required amount of silver phosphate in a concentrated phosphoric acid solution and then add the necessary amount of water in order to yield a separating agent of the desired concentration. On the other hand the phosphoric acid may be diluted prior to the addition of the silver phosphate.

The temperature employed in primary extractor 2 will depend upon the particular compounds being treated and may range from subatmospheric up to 150 F., or more. In general the temperature should be below 150 F., in order to avoid undesired reactions which will occur at the higher temperatures. Although atmospheric, subatmospheric or superatmospheric pressures may be employed, it is generally preferred to employ sumcient superatmospheric pressure in order to maintain the hydrocarbons in substantially liquid phase.

The hydrocarbons and separatingagent are then allowed to settle in either extractor 2 or in other zones into an extract phase and a raillnate phase. In multiple stage operations, the railinate phase may be contacted with further quantities of the separating agent in order to finally recover substantially all ofthe oleiins contained in the charging stock. The extract phases may then be combined and directed through line l into secondary extractor 5.

The raffinate phase or phases may be withdrawn from the upper portion of extractor 2 through line 6 and treated to separate the separating agent from the hydrocarbons. This may take any convenient form and the separating agent may be recycled, by well-known means not illustrated, to the extract step of the process. The saturated hydrocarbons are then directed into isobutane column 1 wherein they are fractionated in order to separate isobutane from normal butane. 'I'he normal butane is removed through line 8 to storage or any desired further treatment or use. The isobutane is removed through line 8 and a portion thereof may be withdrawn from the process. while all or at least the remaining portion is directed through line l0 into secondary extractor 5. Line Il is provided for the introduction of additional isobutane, if required.

Secondary extractor 5 is usually operated within the same range of conditions heretofore specii'led in connection with primary extractor 2, that is, temperatures of below about F., and sumcient superatmospheric pressure to maintain the hydrocarbons in substantially liquid phase. It is believed that a complex is formed between the olens and the separating agent and that this complex is in equilibrium in the extract phase. By contacting the isoparafns with the extract phase, this equilibrium is disturbed and the oleiins are released. from the solution in order to maintain the new equilibrium established. Thus, a very eiective and ready separation of the oleiins is accomplished in an improved manner.

The use of isobutane or other isoparains which are to be subsequently alkylated as the stripping medium in this step of the process, is of prime importance since it eliminates any further fractionation of the mixture of isoparaiiin and olefin, and this is one of the particular features of the present invention.

Another important advantage of this method of operation is that it eliminates the necessity of heating the extract phase to high temperatures in order/to separate the oleflns. Heating to high temperatures may cause polymerization or hydration reactions which are undesired in the particular process of the present invention.

The silver phosphate-phosphoric acid solution is removed from extractor 5 through line l2 and all or a portion thereof may be withdrawn from the process. Preferably, however, the greater portion of this solution is recycled by way of lines I2, I3 and 3 to extractor 2 for further use in the process.

The isobutane-olen mixture is withdrawn through line il from the upper portion of extractor 5 and, as a particular feature of the present invention, .this stream has a composition of isoparafn to olefin within the range of 3:1 to 20:1 and in most cases the ratio. of isoparaiiin .to olen will be within the range of 5:1 to 10:1.

,avaaie This stream is then directed through line Il into alkylation zone II.

Alwlation zone il may comprise any of the well-known forms oi' alkylation equipment suitable for obtaining intimate contact between the hydrocarbon reactants and the alkylation catalyst under controlled conditions of temperature,

`pressure and time of contact. Any suitable alkylatlon catalyst may be employed, the preferred catalysts being hydrogen fluoride, sulfuric acid and phosphoric acid, although these catalysts are not necessarily equivalent in their activity in eiecting the desired reaction. Under certain circumstances, metal halides and particularly aluminum chloride may be utilized as the catalyst. The present invention is not limited to any particular catalyst and, even in certain cases. where it is desired to effect the reaction by purely thermal means. the catalyst may be omitted. Although not illustrated in the drawing, when a mineral acid catalyst in liquid condition is employed, suitable means will, of course, be provided for the introduction and withdrawal of the catalyst. Likewise, it is within the scope of the invention to recycle all or a portion of the catalyst within the alkylation zone or to regenerate the catalyst prior to such recycle.

The exactftemperature and pressure to be employed in the alkylation reaction will, of course, depend upon the catalyst. When utilizing hydrogen fluoride catalysts, the temperatures employed are usually within the range of about 50 F., to about 200 F., and preferably between about 60 F., to about 125 F. Usually sufilcient pressure is employed to maintain the reactants in liquid phase, although it is within the scope of the invention to utilize .vapor or. mixed phase operations when desired.

The alkylation products are directed through line I 8 into debutanizing column I1. As a particular feature of the present invention, the products being introduced into zone I1 will comprise principally alkylate and excess isobutane. Thus, a simple debutanizing operation will effect the desired operation in order to evolve and remove the isobutane from the liquid alkylate. In contrast, in the absence of the features ofthe present invention, the products from the usual alkylation process contains varying proportions of normal butane in addition to the isobutane and alkylate. This then requires rather expensive fractionating equipment for accomplishing the desired separation.

The liquid alkylate is withdrawn from zone I1 through line 'I8 and usually will be rerun in a separate zone to eiect the recovering of gasoline or gasoline fractions of the desired end boiling point. f

The separated isobutane is withdrawn from the upper portion of the zone I'I and all or a portion thereof may be removed from lthe process through line I9. Preferably, however, at least a. portion of the isobutane will be recycled to the alkylation step by way of lines and 2 I. In case other components are present in suilcient quantity in the isobutane stream withdrawn from zone I1, it is within the scope of the invention to direct all or a portion of this stream through lines 22 and 8 into isobutane column 1. Likewise, when desired, all or a portion of the isobutane stream may be directed through lines 20 and I0 to secondary extractor 5.

The following example is vintroduced for the purpose of further illustrating the nature of the invention and is not intended to unduly limit A butene-butylene fraction containing 20 percent of butylenes is subjected to extraction at a temperature of about 100 F.,- with a separating agent comprising 30 percent by weight of silver phosphate and 70 percent by weight of 85 percent phosphoric acid. The extract phase is then contacted with isobutane suiilcient to separate most of the dissolved olefin and to yield an iscparailin-oleiln mixture in which the ratio of isobutane to oleiln is 10: 1. The isoparafhn-olefin mixture-is then subjected to alkylation at a temperature of abou-t 100 F., in the presence of hydrogen fluoride catalyst. The products are fractionated to separate alkylate from isobutane, a portion of 'the isobutane being recycled to the isobutane column and the remaining portion being supplied to the secondary extractor. The alkylate is further fractionated to separate a fraction having a 300 F., end boiling point and this latter fraction is of high antiknock value nd particularly suitable for use in 'aviationgaso- We claim as our invention:

1. A process for preparing an isoparailln-olerln fraction relatively free "of normal paraffin, which comprises contacting a hydrocarbon fraction containing olens and normal and isoparaiilns with a phosphoric acid solution of silver phosphate under conditions such that there is formed an olefin extract phase containing said solution and said olens in the proportion at least approaching that of an equilibrium mixture of the two components, separating the extract phase from the parailln or ramnate phase and contacting an isoparamn with said extract phase under conditions such that equilibrium in the extract phase is disturbed and the olens released therefrom.

2. The process defined in claim 1 further characterized in that the amount oi' isoparailln con- 40 tacted with said extract phase is in excess of the raflinate phase into a normal parafnn part and an isoparailin part and contacting an isoparaln including the isoparailln separated from the ramnate phase with said extract phase under conditions such that equilibrium in the extract phase is disturbed and the olei'ins released therefrom.

4. A process for preparing an isobutane-butene fraction relatively free of normal butane which comprises contacting a C4 hydrocarbon fraction containing butenes and normal and isobutanes with a phosphoric acid solution of silver phosphate under conditions such that there is formed a butene extract phase containing said solution and said butenes in the proportion at least approaching that of an equilibrium mixture of the two components. separating the extract phase comprises contacting a C4 hydrocarbon fraction containing butenes and normal and iscbutanes with a phosphoric acid solution oi.' silver pliesphate under conditions such that there is formed a butene extract phase containing said solution and said butenes in the proportion at least ap-` proaching that of an equilibrium mixture of the two components, separating the extract phase from the butane or ramnate phase, separating said rafiinate phase into a normal butane part and an isobutane part and contacting isobutane including that separated from said ramnate phase with said extract phase under conditions such that equilibrium in the extract phase is disturbed and the olefins released therefrom.`

6. The process deilned in claim 5 further characterized in that the amount of isobutane contacted with said extract phase is in excess oi.' the amount of normal and isobutane in said C4 fraction.

7. A process for preparing an isobutane-butene fraction relatively free of normal butane, which comprises contacting a C4 hydrocarbon fraction containing butenes and normal and isobutanes with a phosphoric acid solution of silver phosphate, at a temperature below about 150 F. and under a superatmospheric pressure sumcient to maintain the C4 hydrocarbons in substantially liquid phase, thereby forming an extract phase containing butenes and said solution in the proportion at least approaching that of an equilibrium mixture of the two components, separating the extract phase from the butane or raiiinate phase, separating said raillnate phase into a normal butane part and an isobutane part and extracting the butenes from said extract phase at a temperature below about 150 F. by contacting therewith isobutane including isobutane from said raflinate phase, in suillcient amount to disturb the equilibrium in the extract phase and release the butenes therefrom.

8. A process which comprises contacting a C4 hydrocarbon fraction containing butenes and normal and isobutanes with a phosphoric acid solution o! silver phosphate under conditions such that there is formed a butene extract phase conavaria taining said solution and said butenes in the proportion at least approaching that of an equilibrium mixture of the two components, separating the extract phase fromV the butane or raiiinate phase, stripping the butenes from said extract phase by contacting therewith isobutane includlng that separated from said railinate phase in an amount suillcient to disturb the equilibrium in the extract phase and release the butenes therefrom, subjecting the resultant isobutanebutene traction to alkylation in the presence of an alkylating catalyst different in composition than the silver phosphate solution, separating unreacted isobutane from the products of alkylation and returning the isobutane thus separated t0 the olefin stripping step.

9. A process for preparing an isoparailn-olen fraction relatively free of normal parailln which comprises contacting a. hydrocarbon fraction containing oleiins and normal and isoparaiiins with a phosphoric acid solution of silver phosphate under conditions such that oleiins are absorbed in the extract phase, separating the resultant extract phase from the raflinite phase and contacting an isoparaiiin fraction relatively free of normal paraiiins with said extract phase to extract oleiins from the latter.

10.- A process for preparing an isoparain-olen fraction relatively free of normal paraffin which comprises contacting a hydrocarbon fraction containing olens and normal andisoparains with a phosphoric acid solution ot silver phosphate under conditions such that olens are absorbed l VLADIMIR. HAENSEL. BERNARD S. FRIEDMAN.

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