US3172919A

US3172919A - Preparation of alkylnaphthalene concentrates

Info

Publication number: US3172919A
Authority: US
Publication date: 1965-03-09
Anticipated expiration: 1982-03-09

Description

March 9, 1965 P. F. HAGERTY ETAL 3,172,919

PREPARATION OF ALKYLNAPHTHALENE CONCENTRATES Filed June 8, 1961 FPrifmonI Raffinate U Ul' r a :2 Phase lst Ehxtract l9 Feed .J l P use ,Reject Phase IO l3 i l Secondary Furfural 2nd Extract Hexflne Phase Secondary Furfural R ject Phase lsf Extract Phase 2nd Extract Hexane J I phase INVENTORS P. FRANK HAGERTY ESAROLD F. TSE Br. JAY SURRENA ATTORNEY Unitd States 3,172,919 PREPARATEUN F ALKYLNAPHTHALENE C(DNCENTRATES This invention relates to the preparation of alkylnaphthalene concentrates which are suitable feed stocks for conversion to naphthalene by high temperature dealkylation.

Gas oils derived from hydrocarbon cracking processes which are either thermal or catalytic are composed generally of non-aromatic hydrocarbons, monocyclic aromatics and dicyclic aromatics. The latter are mainly alkylnaphthalenes such as mono-, di-, and trimethylnaphthalenes and, in smaller quantity, the ethylnaphthalenes. The aromatic hydrocarbon content of cracked gas oils usually lies Within the range of 30-80% by volume with the amount depending upon the particular operation in which the gas oil has been produced.

It is known that naphthalene can be produced from the alkylnaphthalenes by high temperature dealkylation in the presence of hydrogen. Processes for effecting this reaction non-catalytically generally require a temperature in the range of 1200-1400 F. When a catalyst such as cobalt molybdate is used, a somewhat lower temperature can be employed, for example, ll00l200 F. In utilizing cracked gas oil as a source of alkyl aromatics for feed to such dealkylation processes, a problem is presented in the preparation of a suitable alkylnaphthalene concentrate as feed stock. It is important that the feed have a low content of non-aromatics as well as a reduced content of monocyclic aromatics, for the reason that these components crack rapidly at the high temperature employed and a highly exothermic reaction is encountered. The presence of substantial amounts of these components which are not precursors for naphthalene formation, and particularly the presence of the non-aromatics, tends to make the reaction uncontrollable. For the process to operate properly, it is highly desirable that the feed be a dicyclic aromatic concentrate and that it contain as low a content of non-aromatics as possible.

The present invention provides an economical procedure for processing cracked gas oil to produce dicyclic aromatic concentrates which are particularly suitable as feed to such dealkylation operations. According to the invention, a fraction derived from cracked gas oil and boiling mainly in the range of 440l5 F. is first countercurrently extracted with a furfural solvent in limited amount but suflicient to extract essentially all of the dicyclic aromatics. Most of the non-aromatics and a portion of the monocyclic aromatics remain in the raffinate phase and are removed. The extract phase contains essentially all of the dicyclic aromatics, a major part of the monocyclic aromatics and also a substantial but minor amount of the non-aromatics. The extract phase is then treated with a C C saturated hydrocarbon, such as hexane, in a manner whereby essentially all of the non-aromatics and a portion of the monocyclic aromatics are displaced therefrom, being replaced by the C C saturated hydrocarbon. However, prior to such treatment it is essential that the extract phase be diluted with more furfural solvent Within a limited proportion range as hereinafter specified. Omission of this dilution step will vitiate the treatment with the C -C saturated hydrocarbon and result in failure to achieve the desired displacement of the non-aromatics. By first diluting with atent furfural in the proper amount and then treating with hexane in proper amount, a product can be obtained which contains nearly all of the dicyclic aromatics and essentially none of the non-aromatics'that were present in the feed. This product is eminently suitable for conversion to naphthalene by high temperature dealkylation.

The invention is more specifically described with reference to the accompanying drawing in which FlGURE 1 is a schematic illustration of one embodiment of the invention and FIGURE 2 is a schematic illustration of another embodiment.

Referring first to FIGURE 1, a feed stock derived from catalytic gas oil and having a boiling range of 440515 F. and an aromatic content'of, for example, 54% by volume is introduced through line 10 into the bottom of a countercurrent contactor 11. Furfural solvent, herein referred to as primary furfural, is introduced to the top of the columnthrough line 12 and flows downwardly therein countercurrent to the feed. The term furfural solvent as used herein refers to furfural itself or furfural containing dissolved water in any amount up to saturation at the temperature of the extraction operation. Column 11 should be operated at a temperature in the range of 10150 F. and more preferrably l10 F. In this operation-it is important that the amount of primary furfural fed tothe column be such that, on a volume basis, its ratio to the total aromatics in the feed lies in the range of 0.75:1 to 7:1 and more preferably 1:1 to 2:1. Under these conditions the extract phase, which is withdrawn from the column through line 13 and is herein referred to as the 1st extract phase, will contain essentially all of the dicyclic aromatics, while the raifinate phase, which is removed via line 14, will contain a major proportion of the non-aromatics and some of the monocyclic aromatics The 1st extract phase in line 13 is admixed with an appropriate amount of additional furfural solvent, herein referred to as secondary furfuraljfed through line 15, and the mixture is sent to the top of a second column 16. It is important'that the amount of secondary furfural used be in the range of 0.15 to 2.5 volumes-per volume of extract (i.e., gas oil hydrocarbons) in the extract phase and more preferably in the range of 0.25 to 1.25 vols/vol.

A C C saturated hydrocarbon or mixture of such hydrocarbons is fed to the bottom of column 16 through line 17 and therein passes upwardly in contact with the downfiowing extract phase. Any parafiinic or naphthenic C C hydrocarbon or mixture'thereof can be used for this purpose. The C -C hydrocarbon material can contain a minor amount, for example, up to 10% by volume of aromatic components such as benzene and toluene. In the present description hexane will be considered as the saturated hydrocarbon employed. Again,

it is important that the amount of hexane be regulated within a specific range, namely, from 0.5 to 2.0 vols. per vol. of extract in the 1st extract phase fed to the top of column 16. More preferably, this ratio is in the range of 0.751.1 vols/vol. The temperature of this operation can be in the range of 1015()" F., more'preferably 70ll0 F., and it most preferably is about the same as the temperature used for the extraction in column 11. Contact of the hexane in the amount specified with the 1st extract phase causes most of the hexane to dissolve in the furfural and displace the non-aromatics therefrom along with a part of the monocyclic aromatics. There is Withdrawn from the top of the column through line 19 a reject phase which contains essentially all of the nonaromatics that were present in the 1st extract phase and only a small amount of the hexane used. From the base of the column a 2nd extract phase is removed through line 18. This material contains nearly allof the dicyclic aromatics that were present in. the feed, generally less than 50% of the monocyclic aromatics that were present and essentially none of the non-aromatics.

To illustrate the operation of the process more specifically, data are tabulated below to show a material balance (weight basis) for an operation in which it is assumed that 100 lbs. of gas oil feed fraction, 116 lbs. of primary furfural, 59.2 lbs. of secondary furfural and 35.3 lbs. of hexane are introduced per unit time. Each column is a contactor of the rotating disc type and is operated at a temperature of approximately 100 F.

From the data tabulated, it can be seen that, upon distillation of the 2nd extract phase to remove hexane and furfural, the extract product obtained will be composed of about 65 dicyclic aromatics and 35% monocyclic aromatics. It can also be seen that only about 13% of the hexane used appears in the reject phase. Hence the operation in column 16 is mainly not a countercurrent extraction by means of hexane but rather a displacement of undesirable hydrocarbons from the ex tract phase and replacement thereof by the hexane.

By way of contrast, when the introduction of secondary furfural is omitted with the other flow rates the same as specified in the table, essentially no separation is effected in column 16 and the materials withdrawn through

lines

19 and 18 have about the same composition as the 1st extract phase except for the hexane added.

FIGURE 2 illustrates a modification of the process in which the first column (not shown) is operated in the same manner as described above but the second column 20 is operated with a stripping section at the top. The secondary furfural from line 21 is split into two streams with part flowing to the top of the column and the remainder being introduced through line 22 into the 1st extract phase which passes through line 23 to an intermediate level in column 20. Hexane is fed to the bottom through line 25. The amount of furfural introduced through line 22 should be at least by volume based on the extract in the 1st extract phase. The portion of the column above line 23 constitutes a stripping section in which the reject phase is countercurrently contacted with the remainder of the secondary furfural. This type of operation tends to give a still higher recovery of dicyclic aromatic in the 2nd extract phase removed from the base of the column through line 24.

In practicing either of the above-described embodiments, it is preferred to use furfural solvent which contains water and more preferably which is substantially saturated with water at the temperature of operation. It has been found that the presence of water in the solvent lowers its capacity for monocyclic aromatics while leaving the capacity for dicyclic aromatics substantially unaffected. Hence the use of water in the primary and secondary furfural results in obtaining a dicyclic aromatic concentrate of higher purity without reducing the recovery of dicyclic aromatics. Thus, under conditions comparable to those used for obtaining the data tabulated above but using furfural saturated with water, the dicyclic aromatic content of the extract product typically can be raised from 65% to 75-85% with the recovery of the dicyclic aromatics still being 100%.

Ne claim:

1. Method of preparing an alkylnaphthalene concentrate suitable for high temperature dealkylation to naphthalene which comprises.

(a) countercurrently extracting a gas oil fraction boiling mainly in the range of 440-515 F. and comprising alkylnapthalenes, monocyclic aromatics and nonaromatics with furfural solvent at a temperature in the range of 10150 F., the ratio of solvent to the total aromatics in the charge fraction being in the range of 0.75:1 to 7:1 on a volume basis;

( b) separating an extract phase from a rafiinate phase;

(c) diluting the extract phase with furfural solvent in amount of from 0.15 to 2.5 volumes of diluent solvent per volume of extract in the extract phase;

(0.) countercurrently contacting the diluted extract phase at a temperature in the range of 10-150 F. with saturated hydrocarbon of the C -C range in amount of 0.5 to 2.0 volumes of said saturated hydrocarbon per volume of extract in the extract phase, whereby said saturated hydrocarbon mainly dissolves in the diluted extract phase and displaces therefrom non-aromatics and a minor amount of the monocyclic aromatics to form a reject phase containing said displaced non-aromatics and monocyclic aromatics and only a minor proportion of said saturated hydrocarbon;

(e) removing the reject phase;

(f) removing a furfural phase containing most of the alkylnaphthalenes and most of the C C saturated hydrocarbon; and

(g) separating alkylnaphthalene concentrate from said furfural phase.

2. Method according to claim 1 wherein said furfural solvent is furfural substantially saturated with water.

3. Method of preparing an alkylnaphthalene concentrate suitable for high temperature dealkylation to naphthalene which comprises:

(a) countercurrently extracting a gas oil fraction boiling mainly in the range of 4405 15 F. and comprising alkylnaphthalenes, monocyclic aromatics and non-aromatics with furfural solvents at a temperature in the range of 70-1 10 F., the ratio of solvent to the total aromatics in the charge fraction being in the range of 0.75:1 to 2:1 on a volume basis;

(b) separating an extract phase from a raftinate phase;

(0) diluting the extract phase with furfural solvent in amount of from 0.25 to 1.25 volumes of diluent solvent per volume of extract in the extract phase;

(d) countercurrently contacting the diluted extract phase at a temperature in the range of 70-1 10 F. with saturated hydrocarbon of the C -C range in amount of 0.5 to 1.1 volumes of said saturated hydrocarbon per volume of extract in the extract phase, whereby said saturated hydrocarbon mainly dissolves in the diluted extract phase and displaces therefrom non-aromatics and a minor amount of the monocyclic aromatics to form a reject phase containing said displaced non-aromatics and monocyclic aromatics and only a minor proportion of said saturated hydrocarbon;

(e) removing the reject phase;

(f) removing a furfural phase containing most of the alkylnaphthalenes and most of the C -C saturated hydrocarbon; and

g) separating alkylnaphthalene concentrate from said furfural phase.

4. Method according to claim 3 wherein said furfural solvent is furfural substantially saturated with water.

5. Method according to claim 4 wherein said contacting of the diluted extract phase with said saturated hydrocarbon is at approximately the same temperature as said extracting of a gas oil fraction with furfural solvent.

6. Method of preparing an alkylnaphthalene concentrate from a cracked gas oil which comprises the steps of (a) countercurrently extracting a gas oil fraction boiling mainly in the range of 44-0515 F. and comprising alkylnaphthalenes, monocyclic aromatics and 5 6 non-aromatics with furfural solvent at a temperature (1) removing a furfural phase containing most of the in the range of 10-150 F., the ratio of solvent to alkylnaphthalenes and most of the C -C saturated the total aromatics in the fraction being in the range hydrocarbon; and of 0.75:1 to 721 on a volume basis; (g) separating alkylnaphthalene concentrate from said (1)) separating an extract phase from a raffinate phase; 5 furfural phase.

(c) diluting the extract phase with additional furfural 7. Method according to claim 6 wherein said furfural solvent in amount of from 0.15 to 2.5 volumes of solvent is furfural substantially saturated with Water. diluent solvent per volume of extract in the extract 8. Method according to claim 6 wherein said extract- P ing temperature is in the range of 70-110" F.

( countercull'ently Contacting the diluted eXtYaPt 10 9. Method according to claim 8 wherein the amount P at appmximately the Same temPerature as m of the C -C saturated hydrocarbon is 0.5 to 1.1 volsaid extracting step, with saturated hydrocarbon of umes the C C range in amount of 0.5 to 2.0 volumes of said saturated hydrocarbon per volume of ex- Ref r c Cit d b th E i tract in the extract phase, whereby said saturated 15 hydrocarbon mainly dissolves in the diluted extract UNITED STATES PATENTS phase and displaces therefrom non-aromatics and a 10,54 8/40 Tijmstl'a 208-327 minor amount of the monocyclic aromatics to form 2,419,039 4/47 Scarth 208323 a reject phase containing said displaced non-.aro- 2,489,042 1/49 Medcalf et a1. 260-674 matics and monocyclic aromatics and only a minor 20 2,928,788 3/60 Jezl 208-323 proportion of said saturated hydrocarbon; (e) removing the reject phase; ALPHONSO D. SULLIVAN, Primary Examiner.

Claims

1. METHOD OF PREPARING AN ALKYLNAPHTHALENE CONCENTRATE SUITABLE FOR HIGH TEMPERATURE DEALKYLATION TO NAPHTHALENE WHICH COMPRISES: (A) COUNTERCURRENTLY EXTRACTING A GAS OIL FRACTION BOILING MAINLY IN THE RANGE OF 440-515*F. AND COMPRISING ALKYLNAPHTHALENES, MONOCYCLIC AROMATICS AND NONAROMATICS WITH FURFURAL SOLVENT AT A TEMPERATURE IN THE RANGE OF 10-150*F., THE RATIO OF SOLVENT TO THE TOTAL AROMATICS IN THE CHARGE FRACTION BEING IN THE RANGE OF 0.75:1 TO 7:1 ON A VOLUME BASIS; (B) SEPARATING AN EXTRACT PHASE FROM A RAFFINATE PHASE; (C) DILUTING THE EXTRACT PHASE WITH FURFURAL SOLVENT IN AMOUNT OF FROM 0.15 TO 2.5 VOLUMES OF DILUENT SOLVENT PER VOLUME OF EXTRACT IN THE EXTRACT PHASE; (D) COUNTERCURRENTLY CONTACTING THE DILUTED EXTRACT PHASE AT A TEMPERATURE IN THE RANGE OF 10-150*F. WITH SATURATED HYDROCARBON OF THE C5-C8 RANGE IN AMOUNT OF 0.5 TO 2.0 VOLUMES OF SAID SATURATED HYDROCARBON PER VOLUME OF EXTRACT IN THE EXTRACT PHASE, WHEREBY SAID SATURATED HYDROCARBON MAINLY DISSOLVES IN THE DILUTED EXTRACT PHASE AND DISPLACES THEREFROM NON-AROMATICS AND A MINOR AMOUNT OF THE MONOCYCLIC AROMATICS TO FORM A REJECT PHASE CONTAINING SAID DISPLACED NON-AROMATICS AND MONOCYCLIC AROMATICS AND ONLY A MINOR PROPORTION OF SAID SATURATED HYDROCARBON; (E) REMOVING THE REJECT PHASE; (F) REMOVING A FURFURAL PHASE CONTAINING MOST OF THE ALKYLNAPHTHALENES AND MOST OF THE C5-C8 SATURATED HYDROCARBON; AND (G) SEPARATING ALKYLNAPHTHALENE CONCENTRATE FROM SAID FURFURAL PHASE.