US3168451A - Control process in the recovery of naphthalene from alkylnaphthalene by distillation - Google Patents

Description

Feb. 2, 1965 A. J. GORAND 3,163,451

CONTROL. PROCESS IN THE RECOVERY OF NAPHTHALENE FROM ALKYLNAPHTHALENE BY DISTILLATION Filed May 9, 1901 2.23m R W 222 2 1 m m m W mm mm m J A mm L D v E m L. L A Q mm/a EH mm! w. om r 35 wucmu O: 0 2:88 =2 E 2 II. l l N= m 3 m 2m @Vli. mm F o 8 wm r o H II II cozouwm u 0 0 20 2 .ll up ow mm .0 0220 0 mm mm a :2 a; 8m 3.3m 2 5 m United States Patent 3,168,451 CONTROL PRQCESS IN THE RECGVERY 0F NAPHTHALENE FROM ALKYLNAPHTHA- LENE BY DISTHLLATION Alfred J. Gorand, Ridley Park, Pa, assignor to Sun Oil Company, Philadelphia, Pa, a corporation of New Jersey Filed May 9, 1961, Ser. No. 108,861 4 Claims. (Cl. 2tl239.5)

In the production of naphthalene by dealkylation of alkylnaphthalenes, the product is distilled to separate naphthalene from alkylnaphthalenes which are also contained in some amount in the product. The overhead from the distillation is advantageously cooled by indirect heat exchange with boiler feed water, with evolution of steam from the water. Supplemental cooling and condensing, with separation of gas and vapor, and distillation to separate gasoline-range hydrocarbons from naphthalene are then provided by the overhead-processing equipment.

In such systems, the possibility of temporary failure of boiier feed water supply is one which must be taken into account, for the sake of safety. Ordinarily, such failure would result in a rise in temperature in the distillation column, and in the evolution of abnormally large quantities of vapor to be handled by the overhead-processing equipment. The provision of overhead-processing equipment having capacity large enough to handle these quantities of vapor is expensive, particularly in view of the problems of solidification that are presented by the high-melting materials that are contained in the condensed-ring aromatic hydrocarbon mixtures. The alternative of venting large quantities of aromatic hydrocarbons to the atmosphere is also to be avoided, because of the pollution and loss-of-product factors. The problem is aggravated by the fact that sound principles of plant design usually dictate the provision of heat conservation means whereby the heat supplied to the distillation column cannot be discontined, in the vent of boiler feed water supply failure for example, without shutting down the lant.

P The present invention, however, provides safety and product-conservation measures whereby the plant can continue to operate through a period of temporary failure of boiler feed water supply, or other circumstance causing abnormally high temperatures in the distillation column, without generating abnormally large quantities of vapor to be handled by the overhead-processing equipment.

The invention will be further described with reference to the attached drawing, which is a schematic flow sheet of one embodiment of the invention.

Referring to the drawing, catalytic cycle oil is introduced into distillation zone 10 through line 12. A methylnaphthalenes distillate suitable for demethylation to naphthylene is withdrawn through line 14. A higher boiling distillate suitable for use as subsequently described is withdrawn through line 16. Typically, the line 14 distillate has boiling range about 420 to 480 F., and the line 16 distillate has boiling range about 480 to 650 F. The monomethylnaphthalenes boil at about 465 to 470 F. and are contained in the line 14 distillate. The dimethylnaphthalenes boil at about 500 to 515 F., and these and higher boiling materials are largely concentrated in the line 16 distillate.

The methylnaphthalenes distillate is introduced into extraction zone 18, where it is subjected to conventional solvent extraction to separate non-aromatic constituents of the methylnaphthalenes as undissolved rafl'lnate, which is removed through line 243, from solution of aromatic constituents including the methynaphthalenes in the solvent, e.g. furfural. The extraction indicated in zone 20 may in- 3,163,451 Patented Feb. 2, 1965 ice clude the use of a second solvent for the non-aromatic constituents of the feed-stock for the extraction.

The aromatic extract, after conventional removal of solvent by means not shown, followed by heating by means not shown, including indirect heat exchange as subsequently described and passage through a fired heater, is introduced through line 22 into reaction zone 24, Wherein it is subjected to a known thermal or catalytic de methylation reaction, which may be preceded by a known hydrodesulfurization reaction. The demethylation product withdrawn through line 26 contains naphthalene, including that produced in the demethylation; methylnaphthalenes, including some unreacted material and some partial dealkyiation products of dimethylnaphthalenes for example; and some higher boiling material. Typically, the product contains about 40 to 65% naphthalene, and 35 to 60% higher boiling aromatic hydrocarbons.

The demethylation product is typically passed in indirect heat exchange not shown with the line 22 feed to the demethylation, and/or with other streams requiring heating, thereby to cool the product to a suitable temperature for further treatment as subsequently described. The demethylation product is introduced into separator 48; gas is removed from the latter through line 50, and liquid demethylation product, at 150 F. for example, is removed through line 52. The efiluent 52 is heated for example to 520 F, typically by indirect heat exchange not shown with the line 26 product, and the heated material is introduced through line 54 into distillation zone 56. Overhead, comprising naphthalene and gasoline-range components of the demethylation product, is Withdrawn through line 53 at 492 F. for example, and introduced into indirect heat exchanger 60. Boiler feed water is introduced into exchanger 60 through line 62, and steam is generated therefrom by the heat of the line 58 overhead, and the steam is withdrawn through line 64. The cooled overhead is passed through line 66 into separator 68, which is heated by steam coils to prevent solidification of high-melting components of the overhead. Vapor is withdrawn through line 71), and liquid is Withdrawn and returned to tower 56 as reflux through line 71.

The line 70 vapors are cooled in condenser 72, of conventional water-cooled type, and the eifiuent is introduced through line 74 into separator 76. Uncondensed vapor and gas are removed through line 78, and liquid is removed through line and introduced into distillation zone 32, from which gasoline-range hydrocarbons are removed as overhead through line 84, and naphthalene is removed as residue and as a product of the process.

The distillation zone 56 is operated for example with a temperature and pressure at the bottom thereof of about 550 F. and 20 p.s.i.g. Heat is supplied to the column 56 by removing liquid from a tray near the bottom through means not shown, heating the liquid, for example by indirect heat exchange not shown with the line 26 demethylation product, and returning the heated liquid through means not shown to a tray near the bottom of column 56.

Residue is withdrawn from column 56 through line 92 and introduced into distillation zone 94, from which a methylnaphthalenes stream is removed as overhead through line 96, for recycle to reaction zone 24 or for other use, and a higher-boiling residue is removed through line 98.

In column 56, in one embodiment, a thermocouple or other temperature-responsive device is provided, and signals generated by such device are transmitted through connections 102 and 104 to valve 106 in line 17. When the temperature detected by the device 100 exceeds a certain level, e.g., 575 F., or some other temperature in the range from 560 to 620 F. for example, the valve 106 is opened, and higher-boiling distillate from zone 10 is area r51 introduced through lines 16 and 108, or through lines 16,. 110 and 54, into column 56. The actual level of introduction of the distillate into column 56 may vary widely, and the two alternative locations indicated in the drawing are merely illustrative. In general, the location may be anywhere above the bottom of the column 56, though preferably not below the level of feed introduction through line 54. It is not essential that the distillate be introduced into column 56, and the distillate may instead be contacted with the line 58 overhead in a separate vessel not shown; however, it is preferred that the distillate be introduced into the column 56.

In another embodiment, the valve 106 is operated by pressure-responsive device 112, rather than by tempera-- ture-responsive device 109. When the pressure detected by the pressure-responsive means exceeds a given level, e.g., 2O p.s.i.g., or some other pressure within the range from 15 to 50 p.s.i.g. for example, the signal which is generated actuates valve 106 through connections 114 and 194, and the line 16 distillate is introduced into column 56 in the manner previously described. If desired, both temperature-responsive and pressurea'esponsive actuation may be employed, so that the valve 196 is opened it either the temperature or the pressure exceeds a certain level.

In one embodiment, at least a portion of the line 955 residue is introduced into vessel 99, cooled to a suitable temperature, e.g., 150 to 250 F., and maintained there as a source of absorber oil until such time as it is needed. It is then passed, with the aid of pumping means not shown, actuated by means 1% or 11 .2, through lines 161 and 17 into column 56, upon opening of valve 106. The line 98 residue constitutes in such case an alternative source of the oil for introduction into the column in response to a condition of abnormally high temperature. This embodiment has the advantage that the line 98 residue is essentially entirely aromatic, and its use avoids the introduction of non-aromatic components which results from the use of the line 16 distillate.

In another embodiment, at least a portion 92 residue, which is essentially entirely aromatic, from column 56 is introduced through line 93 into receiver $9, for subsequent use, after cooling to a suitable temperaof the line .2

4t porary heat imbalance, while avoiding evolution of abnormally large amounts of vapor.

The absorber oil which is used in the invention is an oil higher boiling than the alkylnaphthalenes which are normally in the line 92. residue but which are vaporized when the temperature in column 56 rises above a given level and would be removed in the line 58 overhead if the absorber oil were not introduced. Preferably, the absorber oil contains components boiling above 525 F., and more preferably at least of such components. The absorber oil preferably contains 50 to wt. percent of .aromatic hydrocarbons. Suitable sources of absorber oil are the line 16 distillate and the line 92 and line $8 residues as illustrated in the drawing.

The temperature at which the absorber oil is introduced into column 56 is not critical, though relatively low temperatures result of course in a quicker return of the column to suitable operating temperature. in typical plant operations, it is convenient to introduce the distillate at a temperature in the range from room temperature to 250 F., but other temperatures may be used in some cases.

The amount of the absorber oil which is introduced into column 56 as a result of the opening of the valve 106 depends upon the magnitude of the heat imbalance which the distillate is introduced to correct. Preferably the valve 106 is automatically closed when the temperature I and/ or pressure in column 56 fall again to a suitable operating level. The introduction of feed into column 56 through line 54 usually continues during the introduction of the absorber oil into the column.

The introduction of the absorber oil into tower 56 will usually be effective to prevent the pressure in tower 56 from 1151111; to an unsafe level. However, a pressure relief valve not shown may be provided as an additional safety measure. Such valve may open for example at 75 p.s.i.g. and discharge to the atmosphere or to a receiver not shown.

ture, e.g., to 250 F., as a source of absorber oil for I introduction through line 17 into column 56 upon opening of valve 106. However, the line 98 residue is preferred to the line 92 residue as a source of such absorber oil.

The absorber oil which, in periods of abnormally high temperature, is introduced through line 17 into column 56, absorbs certain higher-boiling components of the demethylation product. In ordinary operation of column 56, those components are removed in the line 92 residue, but in the event of abnormally high temperature in column 56, these components would, in the absence of the introduction of the absorber oil, be removed in the line 58 overhead. The introduction of the absorber oil pre- A rupture disc may advantageously be provided in the system by which the absorber oil is supplied to the tower 56 upon opening of the valve 106. Such disc, e.g., in line 108 or line 119, is ruptured upon opening of the valve 106 and subjected to the elevated pressure resulting from such opening. Prior to such opening, the disc prevents leakage of absorber oil into the normal operating streams; this is particularly beneficial where the absorber oil contains a substantial amount of nonaromatic material which would be undesirable in the normal operating streams. When the condition of abnormally high temperature has been corrected by addition of absorber oil, and the valve 136 has again been closed, shutting off the absorber oil supply, the rupture disc can be replaced. This may be done while the plant is on stream, by using a pair of rupvents the higher-boiling components from being removed in the overhead, and thereby prevents those higher-boiling components from being lost or from overloading the overhead-processing equipment.

The absorber oil containing absorbed higher-boiling components passes out of column 56 through line 92 and into tower 94. The absorbed components are removed as overhead through line 96, and all or a part of the absorber oil is removed as residue through line 98.

During the introduction of the absorber oil through line 17 into column 56, the overheads from columns 56 and 94 are similar to those obtained in normal operation, and the residues from columns 56 and 94 contain components of the absorber oil, in addition to the normal components. Thus, by designing these columns for the handling of this additional residue, operation which is normal in other respects can be preserved through a temture discs in parallel, as known in the art, one disc being in service while the other is being replaced.

The invention claimed is:

1. In a distillation process wherein feed stock containing naphthalene and alkylnaphthalenes is distilled to obtain naphthalene as overhead and alkylnaphthalenes as residue, the improvement which comprises introducing into the distillation zone at the locus intermediate the feed point and overhead, when the temperature therein rises above a given level and lower boiling constituents of said alkylnaphthalenes are thereby vaporized, an absorber o-il containing at least 50% aromatic constitutents and having boiling range above that of said lower boiling constituents, thereby to absorp vapors of the latter in said absorber oil, removing absorber oil and absorbed lower boiling constituents, together with the higher boiling constituents of said alkylnaphthalenes, as residue, and discontinuing the introduction of said absorber oil when the temperature in the distillation zone falls below a given level.

2. In a distillation process wherein feed stock containing naphthalene and alkylnaphthalenes is distilled to ob- 5 tain naphthalene as overhead and allrylnaphthalenes as residue, the improvement which comprises introducing into the distillation zone at the locus intermediate the feed point and overhead, when the pressure therein rises above a given level and lower boiling constituents of said alkylnaphthalenes are thereby vaporized an absorber oil containing at least 50% aromatic constituents and having boiling range above that of said lower boiling constituents, thereby to absorp vapors of the latter in said absorber oil, removing absorber oil and absorbed lower boiling constituents, together with the higher boiling constituents of said alkylnaphthalenes, as residue, and discontinuing the introduction of said absorber oil when the pressure in the distillation zone falls below a given level.

3. Process for preventing excessive temperature increase during the distillation of a feed stock containing naphthalene and alkylnaphthalenes which comprises:

(1) passing said feed stock into a distillation zone at a temperature sufiicient to substantially vaporize mainly said naphthalene, (2) removing naphthalene in high concentration as an overhead stream, (3) removing aiirylnanhthalenes in high concentration as a residue stream, 4) introducing into said distillation zone at a locus intermediate to the feed point and overhead an absorber oil only when the temperature within said 5 zone increases abnormally above said temperature and lower boiling constituents of said alkylnaphthalenes are thereby vaporized to absorb vapors of the latter in said absorber oil,

(5) removing absorber oil and lower boiling constituents together with higher boiling constituents of said alkylnaphthalenes from said distillation zone, and

(6) discontinuing the introduction of said absorber oil only when the temperature within said zone decreases to said temperature.

4. Process according to claim 3 wherein said absorber oil contains at least 50 percent aromatic constituents and has a boiling range above that of said lower boiling constituents.

References Cited in the file of this patent UNITED STATES PATENTS 2,277,070 Carney Mar. 24, 1942 2,302,187 Carney Nov. 17, 1942 2,357,113 Houghland et a1 Aug. 29, 1944 2,364,341 Bright et al. Dec. 5, 1944 2,414,371 Fragen et a1 Jan. 14, 1947 2,508,434 Storment May 23, 1950 2,649,404 Reynolds Aug. 18, 1953 2,749,281 Ferro June 5, 1956 2,878,261 Broughton Mar. 17, 1959

Claims (1)

1. IN A DISTILLATION PROCESS WHEREIN FEED STOCK CONTAINING NAPHTHALENE AND ALKYLNAPHTHALENES IS DISTILLED TO OBTAIN NAPHTHALENE AS OVERHEAD AND ALKYLNAPHTHALENES AS RESIDUE, THE IMPROVEMENT WHICH COMPRISES INTRODUCING INTO THE DISTILLATION ZONE AT THE LOCUS INTERMEDIATE THE FEED POINT AND OVERHEAD, WHEN THE TEMPERATURE THEREIN RISES ABOVE A GIVEN LEVEL AND LOWER BOILING CONSTITUENTS OF SAID ALKYLNAPHTHALENES ARE THEREBY VAPORIZED, AN ABSORBER OIL CONTAINING AT LEAST 50% AROMATIC CONSTITUENTS AND HAVING BOILING RANGE ABOVE THAT OF SAID LOWER BOILING CONSTITUENTS, THEREBY TO ABSORP VAPORS OF THE LATTER IN SAID ABSORBER OIL, REMOVING ABSORBER OIL AND ABSORBED LOWER BOILING CONSTITUENTS, TOGETHER WITH THE HIGHER BOILING CON-

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