US3579599A

US3579599A - Process for extract-separation of aromatic hydrocarbons

Info

Publication number: US3579599A
Application number: US776728A
Authority: US
Inventors: Yoshiro Ito; Tamotsu Ueno; Takashi Nakano; Kazuo Okamoto
Original assignee: Japan Gas Chemical Co Inc
Current assignee: Japan Gas Chemical Co Inc
Priority date: 1967-11-21
Filing date: 1968-11-18
Publication date: 1971-05-18
Anticipated expiration: 1988-05-18
Also published as: NL6816604A; NL163202C; GB1238474A; BE724148A; SU416934A3; FR1604275A; DE1810029A1

Abstract

A PROCESS FOR EXTRACT-SEPARATING AROMATIC HYDROCARBONS HAVING LARGER BASICITY INTO A HYDROGEN FLUORIDE PHASE BY ALLOWING AN EXTRACTING AGENT CONSISTING OF HYDROGEN FLUORIDE AND BORON TRIFLUORIDE TO COME IN CONTACT WITH A MIXTURE CONTAINING TWO OR MORE AROMATIC HYDROCARBONS HAVING DIFFERENT BASICITY FROM EACH OTHER. MORE PARTICULARLY, A PROCES FOR EXTRACT-SEPARATING AROMATIC HYDROCARBONS IN A

HIGH YIELD AND PURITY WITHOUT SUBSTANTIALLY REFLUXING SAID AROMATIC HYROCARBON HAVING LARGER BASICITY, HERETOFORE CONSIDERED A NECESSITY, BY FEEDING EXTRACTING AGENT CONSISTING OF HF AND BF3, AND DILUENT IN HIGHLY PRECISE AMOUNTS ACCORDING TO A PREDETERMINED CORRELATION.

Description

May 18, 1971 YQSHlRQ rro EI'AL 3,579,599

PROCESS FOR EXTRACT-SEPARATION 0F AROMATIC HYDROCARBONS Filed Nov. 18, 1968 3 Sheets-Sheet 1 May 18, 1971 Filed Nov. 18, 1968 3 Sheets-Sheet 2 OIO May 18, 1971 Filed Nov. 18, 1968 YOSHIRO ITO PROCESS FOR EXTRACT-SEPARATION OF AROMATIC HYDROCARBONS 3 Sheets-Sheet 3 United States Patent O 3,579,599 PROCESS FOR EXTRACT-SEPARATION OF AROMATIC HYDROCARBONS Yoshiro Ito, Tarnotsu Ueno, Takashi Nakano, and Kazuo Okamoto, Kurashiki-shi, Japan, assignors to Japan Gas- Chemical Company, Inc., Tokyo, Japan Filed Nov. 18, 1968, Ser. No. 776,728

Claims priority, application Japan, Nov. 21, 1967,

42/ 74,896 Int. Cl. Ctl7c 7/10 Int. Cl. 260674 Claims ABSTRACT OF THE DISCLOSURE A process for extract-separating aromatic hydrocarbons having larger basicity into a hydrogen fluoride phase by allowing an extracting agent consisting of hydrogen fluoride and boron trifluoride to come in contact with a mixture containing two or more aromatic hydrocarbons having different basicity from each other. More particularly, a process for extract-separating aromatic hydrocarbons in a high yield and purity without substantially refluxing said aromatic hydrocarbon having larger basicity, heretofore considered a necessity, by feeding extracting agent consisting of HF and BF and diluent in highly precise amounts according to a predetermined correlation.

CROSS-REFERENCE TO RELATED APPLICATIONS This invention is an improvement of a copending application, Ser. No. 555,168 (date of application: June 3, 1966). The object of said copending application is given below:

A process for continuously extract-separating m-xylene from a mixture of xylenes containing m-xylene and at least one xylene isomer (inclusive of ethylbenzene) other than m-xylene comprising the steps of charging said xylene mixture, reflux m-xylene, diluent, BF, and liquid HF into an m-xylene extractor, and extracting m-xylene in a continuous countercurrent extraction method, characterized by selectively extracting m-xylene from said xylene mixture under such selected operating conditions of said extractor as the mole ratio of BF /HF in the HF extract withdrawn from said m-xylene extractor, that is, the concentration of xylene, in the hydrocarbon phase at the HF extract withdrawal section (final stage), and Brn, that is, the mole ratio of m-xylene/BF in the HF extract, will substantially satisfy the 'y-flm correlation on 'y-flm shown by such a diagram as FIGS. 24.

This invention is based on the discovery that separation of aromatic hydrocarbons in a high yield and purity is possible without reflux of m-xylene a step heretofore been considered indispensable.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a process for extract-separating high basicity aromatic hydrocarbons into a hydrogen fluoride phase by allowing an extracting agent consisting of hydrogen fluoride and boron trifluoride to contact a mixture containing two or more aromatic hydrocarbons having ditferent basicity from each other.

This invention is applicable to a process for extract separating m-xylene from C aromatic hydrocarbon fraction; a process for extract-separating mesitylene from C aromatic hydrocarbon fraction; or a process for extractseparating aromatic hydrocarbons having a high boiling point from a mixture of xylenes and aromatic hydrocarbons having the high boiling point.

For the extract-separation of such aromatic hydrocarbons, this invention provides a process for separating Patented May 18, 1971 aromatic hydrocarbons in a higher yield and purity than ever before without the refluxing heretofore considered necessary.

When considered from a diiferent viewpoint, this invention is an improvement over the aforementioned process for extract-separating aromatic hydrocarbons. This improvement eliminates the necessity of recovering excessive diluent and installing auxiliary equipment related to the reflux, and, accordingly, increases the capacity of the extracting system and reduces utility requirements, for its operation.

DESCRIPTION OF THE PRIOR ART There have been numerous experiments conducted to selectively extract a constituent of aromatic hydrocarbons by employing BF -HF extracting agent, and those considered most closely related to this invention are US. Pat. 2,521,444, US. Pat. 2,727,078, and US. Pat. 2,848,- 518. Although US. Pat. 2,521,444 (Brooke et a1.) relates to a process for separating an isomeric mixture of lower dialkylbenzenes by employing BF -HF extracting agent, a number of extractors are utilized connected in series and into each of them BF -HF extracting agent is fed. This process is, however, considered primitive. US. Pat. 2,727,- 078 (Shoemaker) relates to a process for separating mxylene from an isomeric mixture of xylenes by employing BF -HF extracting agent, however, the characteristic of this process lies in forming a complex mixture of mxylene and at least one xylene isomer other than m-xylene, with BF in HF to which m-xylene and diluent are added, thereby selectively decomposing complex mixtures of other isomers, leaving m-xylene as the only complex form. It is to be noted that in this process addition of m-xylene is an absolutely necessary factor. US. Pat. 2,848,518 (Fragen) describes the total system related to a process for separating each constituent from a mixture of xylenes but description of said extraction process is extremely simple and covers no more than what is already described hereabove.

SUMMARY OF THE INVENTION Accordingly, this invention relates to a process for extract-separating high basicity aromatic hydrocarbons into a hydrogen fluoride phase by allowing an extracting agent consisting of hydrogen fluoride and boron trifluoride to contact with a mixture containing two or more aromatic hydrocarbons having different basicity from each other, characterized by extract-separation of aromatic hydrocarbons without substantially refluxing aromatic hydrocarbons to be extracted. Furthermore, this invention, employing as raw material C aromatic hydrocarbon fraction (referred to as C fraction hereinafter) containing m-xylene and at least one, xylene isomer other than mxylene, and feeding said C fraction, diluent, BF and liquid HF to an m-xylene extractor, relates to a process for extract-separating m-xylene in a continuous countercurrent extraction, characterized by continuous extractseparation of m-xylene from said C fraction containing m-xylene and at least one xylene isomer other than mxylene without substantially refluxing m-xylene under such operating conditions of said extractor as the mole ratio of BF HF in the HF extract withdrawn from said m-xylene extractor, 'y, that is, the concentration of xylene in the hydrocarbon phase at the HF extract withdrawal section (final stage), and pm, that is, the mole ratio of total mxylene/BF in the HF extract, will substantially satisfy the correlation shown by such a 'y-flm correlation diagram as FIGS. 24.

DEFINITION OF THE TERMS To define the terms used in this invention, the term C aromatic hydrocarbon fraction referred to in the specification means C aromatic hydrocarbon fraction obtained by separating from a petroleum constituent containing aromatic hydrocarbons, Which was obtained by catalytic reforming, thermal cracking of petroleum or from a tar constituent containing aromatic hydrocarbons, normally contains m-xylene, o-xylcne, p-xylene and ethylbenzene as principal constituents and a small amount of benzene, toluene, etc.

Also, the term xylene isomers other than m-xylene includes ethylbenzene in addition to o-xylene and pxylene.

The term raflinate means a hydrocarbon phase remaining without being extracted into the HF phase in the extractor, and when extracting m-xylene from C aromatic hydrocarbon fraction, it means a mixture of C aromatic hydrocarbon substantially not containing m-xylene, diluent added in the course of extracting mxylene, a very small amount of HF, BF benzene, toluene, etc. Accordingly, the diluent, a very small amount of HF, BF etc. are removed through distillation of the raflinate, and residual C aromatic hydrocarbon fraction is obtained.

The term extract product means aromatic hydrocarbons to be extracted in the HF extract. The term extrac means the sum of extracting agent and extract product.

BRIEF DESCRIPTION OF THE DRAl/VINGS FIG. 1 is a highly simplified flow sheet to illustrate the principle of extraction. FIG. 2 shows the -fim at temperature C. as BF HF in parameter between m, signifying correlation the mole ratio of m-xylene/B'F in the HF extract and y, signifying the concentration of xylene in the hydrocarbon phase at the HF extract withdrawal section (final stage). FIG. 3 illustrates the same relation shown in FIG. 2 at C., and FIG. 4 also illustrates the same relation shown in FIG. 2 at +15 C.

DESCRIPTION OF THE PREFERRED EMBODIMENT This invention provides an efiective process for selectively extracting a certain specific hydrocarbon from a mixture of more than two aromatic hydrocarbons having diflerent basicity from each other. The process is also effective for extract-separating mesitylene from a mixture current extracting system 1, and at the same time, hydrogen fluoride and boron trifluoride are fed through pipe 3 and pipe 4 respectively to the top of the extractor 1, and countercurrent contact of the HF-BF phase and C fraction phase is allowed to take place in the extractor. In this instance, diluent is fed into the extractor 1 through pipe 5 to improve its selectivity, and furthermore, a portion of extract-separated high purity m-xylene is fed back as reflux to the extractor 1 through pipe 6. The extract and rafiinate are withdrawn from the extractor 1 through pipe 8 and pipe 7, respectively. Above process has been considered normal with the prior art. The inventors have already discovered that in order to extract into the HF extract the sum of the m-xylene in the feed C fraction and reflux m-xylene, that is, the entire amount of m-xylene to be fed into the m-xylene extractor, without substantially leaving any residual m-xylene in the raflinate, it is necessary to feed HF, BF diluent, and extract product in such a proportion as will substantially satisfy a highly precise correlation, that is, the correlation shown in FIGS. 24 (Ser. No. 555,168).

The inventors have advanced further with the study to extract-separate m-xylene from the C fraction, utilizing such correlation as mentioned above, and as a result, discovered an unexpected fact that the reflux of m-xylene, heretofore considered as absolutely necessary in the extract-separation of high purity m-xylene, is not always necessary, and on the basis of this discovery have developed this invention.

Namely, in the process heretofore employed, the amount of reflux is at a reflux ratio of 0.54, while in this invention without substantially refluxing means a reflux ratio of 0.2 or less (including 0.0). The reflux ratio is a value meaning the value of said amount of reflux divided by the value of the total amount of extract product in the HF extract withdrawn from the extractor minus the amount of reflux to be fed back to the extractor as reflux.

Next, Table 1 shows the result of measurement of mxylene/BF mole ratio in the HF extract in both cases using pure m-xylene only and using pure m-xylene and a known quantity of diluent added to the system. As diluent, n-hexane is employed and the measured temperature is 0 C.

TABLE 1 m-Xylene m-Xylene nrXylene in m-Xylene in HF in hydrohydrocarbon Feed, Feed, BF ab- BF lfeed dissolved (mole) carbon phase/total m-xylene n-hexane Feed, HF sorbed in Parameter. m-xylene in HF BE in HF phase hydrocar- No. (mole) (mole) (mole) HF (mole) BFs/HF (mole) (mole) (mole) Bin (mole) bon I L 290 3. 0. 099 0. 0288 0. 077 0. 129 1. 30 0. 217 0. 0628 0. 168 0. 434 2. 00 0. 311 0. 0903 0. 241 0. 672 2. l6 0. 496 0. 1440 0. 385 1. 20 2. 41 0. 546 0. 1580 0. 425 1. 29 2. 3

2- 0. 942 0. 233 3. 40 0. 294 O. 0864 0. 312 0. 503 I. 71 O. 439 0. 653 0. 469 0. 1380 0. 498 0. 727 1. 0. 125 0. 480 0. 682 0. 2003 0. 723 0. 790 1. 16 0. 152 0. 395

3 0. 658 0. 349 3. 4O 0. 145 0. 0426 0. 220 O. 172 1. 19 0. 486 0. 583 0. 294 0. 0865 0. 447 0. 399 l. 36 0. 259 O. 426 0. 415 0. 1221 0. 632 0. 518 1. 25 0. 140 0. 286 0. 586 0. 1725 0. 892 0. 580 0. 99 0. 078 0. 183

of C aromatic hydrocarbons, or for extract-separating a Here n and 'y are defined by the following formula: hydrocarbon having a high boiling point from a mixture to l a i v of xylene and aromatic hydrocarbons havmg said higher [3 3mm t c hydmfiarbons m HF extract (mole) boiling point. However, this invention is particularly ef fective in providing an industrial process for extractseparating m-xylene from the C fraction.

Accordingly, in the following general explanation, extract-separation of m-xylene from the C fraction is given as an example for simplifying the explanation and for easier understanding.

Referring to FIG. 1, the raw material C fraction is fed through pipe 2 into the center of the continuous counter- BE, in HF extract (mole) (flm: 5 in case where aromatic hydrocarbon is pure m-xylene) aromatic hydrocarbons in hydrocarbon phase 1: in equilibrium relation with HF extract (mole) aromatic hydrocarbons in hydrocarbon phase in equilibrium relation with HF extract (mole) diluent in hydrocarbon phase (mole) Also. the hydrocarbon phase means residual hydrocarbons not extracted in the HF extract phase (solution of aromatic hydrocarbons and diluent). FIGS. 2-4 show the relation obtained from the result related to m-xylene as the mole ratio of BF /HF in the HF extract as parameter between rim, that is, the mole ratio of m-xylene/BF in the HF extract and 7, that is, the concentration of C aromatic hydrocarbons in the hydrocarbon phase in equilibrium relation with the HF extract. FIG. 2, FIG. 3, and FIG. 4 show the value when the measured temperature is C., 20 C. and C., respectively. In other words, notwithstanding a change in temperature and diluent employed, the result showing the same tendency is obtainable. Furthermore, according to an experiment as above to determine dissolved amount of the C fraction containing different concentrations of m-xylene, [3 and 8m are substantially equal as long as the concentration of m-xylene in the HF extract (based on C aromatic hydrocarbon) is 94 mole percent or more. The diluent is substantially present in the C aromatic hydrocarbon phase and acts as diluent to the C aromatic hydrocarbon. As is clear from FIGS. 2-4, in case of m-xylene, ,Bm, that is, the mole ratio of m-xylene/BF in the HF extract, shows a value siginficantly deviated from 1 depending on the BF /HF mole ratio in the HF extract, and 'y, that is, the concentration of the aromatic hydrocarbons in the hydrocarbon phase.

The -Bm correlation such as those shown in FIGS. 2-4 is particularly important for selective extraction of m-xylene from the C fraction. Namely, in order to selectively extract m-xylene present in the C fraction as a high purity m-xylene complex, and simultaneously leave substantially no m-xylene in the rafiinate, it is necessary to select the addition amount of HF and BE; (or, for example, the mole ratio of BF /HF and the amount of BF so as to allow the total m-xylene fed into the m-xylene extractor to be extracted in the withdrawn HF extract. To obtain high purity m-xylene and residual C fraction consisting substantially of xylene isomers other than m-xylene, these ratios must be determined highly precisely.

In this invention, as the operating conditions of said m-xylene extractor, the BP /HF mole ratio of the with drawn HF extract must be first established within the range of 0.02-0.20, followed by determination of that is, the concentration of the aromatic hydrocarbon in the hydrocarbon phase at the HF extract withdrawal section (final stage). Should the BF /HF mole ratio be too low, the amount of needed HF would increase, hence increased amount of the extract subject to decomposition and increased heat load caused by the decomposition. Also, when the BF /HF mole ratio is increased, the pressure inthe' extractor will increase. For this reason, selection of the aforementioned range is desirable. The value of 'y is approximately 0.3 or less. Especially it-is known from our experience that when the reflux ratio is zero, the value of y becomes to 0.1 or less. Once these ratios are determined, fim, that is, the m-xylene/BF mole ratio in the HF extract, will be decided to substantially satisfy such 'y-fim equilibrium correlation as shown in FIGS. 2-4, and from value, this determined is the amount of BF to be charged into said m-xylene extractor. The amount of HP to be added can be easily determined from the aforementioned selected value of the addition amount of BF and from the aforementioned selected value of the BF /HF mole ratio in the HF extract.

In this invention, when the amount of reflux is decreased, the ratio of the diluent to be fed against the extract product withdrawn from the extract Withdrawal section wil be inevitably increased. This is defined as D by the following formula:

amount of diluent to be fed into extractor (mole) D varies somewhat depending upon the concentration of the extract product in the raw material; however, when there is absolutely no reflux (that is to say when the reflux ratio is zero), D is appropriate in the range of 0.7-10 with a 1-5 range being most desirable. When the reflux ratio is 0.2, D may be 0.5 or above.

The diluent is removed as raflinate. Stable substances that do not substantially dissolve in extracting agent but form a uniform phase with ratfinate can be used as diluent, for example, aliphatic saturated hydrocarbons such as propane, n-butane, i-butane, n-pentane, and n-hexane; alicyclic saturated hydrocarbons such as cyclopentane, and cyclohexane; or halogenated hydrocarbons such as carbon tetrachloride. When carbon tetrachloride is used, the top and bottom positions of the raffinate and the extract are normally reversed. An extraction temperature of -20-+30 C. and pressure of 1-20 kg./cm. g. are used in the extractor. The amount of hydrogen fluoride to be fed is 1.8-25 mole against one mole of the raw material aromatic hydrocarbon, while the abount of boron trifluoride is about 0.7-1.5 moles against one mole of the extract product in the raw material aromatic hydrocarbon. It is desirable to select the mole ratio of boron trifluoride/ hydrogen fluoride within the range of 002-020. The types of extracting tower suitable for use include such as a packed tower, perforated plate tower, perforated plate pulse tower, extractor equipped with stirrer, and mixer settler.

As mentioned above according to this invention, high basicity aromatic hydrocarbons of high purity can be extract-separated in an extremely high yield without substantially refluxing the extract product. As this invention does not require reflux of the extract product, the amount of extract product at the extract withdrawal section is de creased, thereby decreasing the amount of feed diluent. As mentioned earlier, this decreases need for recovering excessive diluent and for installing the auxiliary equipment needed in connection with the reflux, nor will there be any substantial increase in the theoretical number of plates necessary for extraction, and significant benefits such as increased capacity of the extractor are obtained.

EXAMPLE 1 Extracting agent Substance supplied HF 2 BF;

Benzene Toluene Raw material Diluent Exsupplied supplied tract;

Raninate o-Xylene Total of aromatic hydrocarbons n-H exane 297 3 No'rE.Unit=mole/hour.

The theoretical number of plates of the extraction tower was 7.5.

REFERENCE EXAMPLE 1 When 39 (mole/hour) of m-xylene (98%) (reflux ratio: 0.2) is fed into the extract withdrawal section, using the same amount of diluent as used in Example 1, the theoretical number of plates is 6.7 and the mole ratio of boron trifluoride/raw material will also be increased by 3%, while the extracting capacity of said equipment will be decreased by 4%, hence, there is practically no difference between Example 1 and Reference Example 1. On the other hand, when the amount of reflux is set at 97 (mole;/hour) (reflux ratio: 0.5), the theoretical number of plates is 6.6 and the mole ratio of boron trifluoride/raw material will increase by 14%. In this instance, an increase in the amount of heat necessary for the recovery of the diluent and cooling of the reflux m-xylene is 50 times or more of the amount of heat required to cool the C fraction and n-hexane to 5 C. from room temperature an enormous increase in utility requirements. Also, the extraction capacity will be decreased by 15%. Furthermore, with the reflux m-xylene (reflux ratio: 1.0) being set at 194 (mole/hour), the theoretical number of plates remains practically unchanged at 6.6, While the boron trifiuoride/raw material mole ratio goes up by about 20% with the extraction capacity reduced by about 30%, necessitating still more utilities.

EXAMPLE 2 Using the same equipment as described in Example 1, the raw material C fraction containing 35%of m-xylene is fed to conduct countercurrent extraction under normal pressure and at +5 C. The results obtained are as shown in the following table. As diluent, n-pentane is employed without reflux.

EXAMPLE 3 The raw material C -C fraction containing 20% of 1,3,5-trimethyl benzene was fed so as to allow countercurrent contact to take place under normal pressure and at 8 C., all other conditions being identical with those described in Example 1. The results obtained are as follows Extracting Raw agent material Diluent Ex- Rath- Substance supplied supplied supplied tract nate HF 691 2 B F 61 1 Ethyl benzene 0 6 p-Xylene 0. 1 45 m-Xylene- 11 125 o-igene. It i. .1 0. 2 4O 1 ime bsnz enefli 56.7 0. 2

Total of aromatic hydrocarbons 284 68 215 n-Hex ane 227 225 NOTE.Unit =mole/hour.

We claim:

1. A process for continuous countercurrent extractseparation of aromatic hydrocarbons into a hydrogen fluoride phase, comprising:

contacting a mixture of two or more aromatic hydrocarbons having diiferent basicity from each other with an extracting agent consisting of hydrogen fluoride and boron trifiuoride at a temperature of from about 20 C. to +30 C., and

maintaining a reflux ratio up to 0.2.

2. The process of claim 1 wherein extraction is conducted with a BF /I-IF molar ratio of the HF extract of from 0.02 to 0.20, the concentration 7 of aromatic hydrocarbons in the hydrocarbon phase at the HF extract withdrawal section of the extractor employed has a value of less than 0.3, and the mole ratio B of the total m-Xylene/BF extract in the HF extract, will substantially satisfy a curve represented by the -5 correlation given in FIG. 2, wherein BF HF is the parameter.

3. The process of claim 1 wherein extraction is conducted with a BF /HF molar ratio of the HF extract of from 0.02 to 0.20, the concentration 7 of aromatic hydrocarbons in the hydrocarbon phase at the HF extract withdrawal section of the extractor employed has a value of less than 0.3, and the mole ratio B of the total mxylene/BF extract in the HF extract, will substantially satisfy a curve represented by the -5 correlation given in FIG. 3, wherein BF /HF is the parameter.

4. The process of claim 1 wherein extraction is con-. ducted with a BF /HF molar ratio of the HF extract of from 0.02 to 0.20, the concentration 7 of aromatic hydrocarbons in the hydrocarbon phase at the HF extract withdrawal section of the extractor employed has a value of less than 0.3, and the mole ratio B of the total mxylene/BF extract in the HF extract, will substantially satisfy a curve represented by the 7-13 correlation given in FIG. 4, wherein BF /HF is the parameter.

5. The process of claim 1, wherein the aromatic hydrocarbon mixture comprises a mixture of C aromatic hydrocarbons.

6. The process of claim 5, wherein the aromatic hydrocarbon mixture comprises a mixture of C aromatic hydrocarbons and the extract product is substantially m-xylene.

7. The process of claim 1, wherein the BF /HF mole ratio is from 0.02 to 0.20.

8. The process of claim 1, wherein the molar ratio of HF charge to the aromatic hydrocarbon mixture is from 1.8 to 25.

9. The process of claim 1, wherein the molar ratio of BF /extract product is from 0.7 to 1.5.

10. The process of claim 1, wherein the aromatic hydrocarbon mixture comprises a C aromatic hydrocarbon mixture,

the extract product is substantially 1,3,5-trimethylbenzene, the molar ratio of BF-,/ HF is from 0.02 to 0.20, the molar ratio of HF charge to the aromatic hydrocarbon mixture is from 1.8 to 25,

the molar ratio of BF;,/ extract product is from 0.7 to

1.5, and

the molar ratio of a diluent charge to the extract product is from 0.5 to 10.

References Cited UNITED STATES PATENTS 2,532,276 12/1950 Birch et a1. 2,848,518 8/1958 Fragen.

CURTIS R. DAVIS, Primary Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 579 599 Dated y 18 a 1971 Yoshiro Ito et a1.

Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, Table 1, under the heading "In-Xylene in hydrocarbon phase (mole) and referring to No. 2, "0.125" should read 0.215 Column 7, line 5, "(mole;/hour)" should read (mo1e; hour) Signed and sealed this 25th day of April 1972.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Commissioner of Patents Attesting Officer