CA1184948A - Producing solvent-grade methyl-naphthalene - Google Patents

Abstract

ABSTRACT
PRODUCING SOLVENT-GRADE METHYL-NAPHTHALENE
A methylnaphthalene-containing coal tar dis-tillation fraction which has already been extracted with base to remove tar acids is treated by three ex-tractions to remove tar bases and impurities which have or form color or odor. No final distillation is required. The first extraction is with about 70-85%
sulfuric acid, the second with about 90-100% sulfuric acid and the third with aqueous base such as about 2-25%
sodium hydroxide. The resultant methyl-naphthalene is suitable for dye-carrier and other solvent applications.

Description

DL'SCRI P'~IO~`I
P~ODI~CINC; SOLVENT-GRADE~ E'.L'HYL~ P~
BAC~GROUtiD Ol; THE I~1VE:~'l'IO~`~
.. . . . _ The present invention relates to the pro-duction of solvent-grade methyl-napththalene from a coal tar fraction, and especially to such processes wherein color-free solvent-grade methyl-naphthalene is producec1 in an extraction process without a final distillation step.
While ~,lany valuable chemicals are known to be contained in coal tar, the recovery of these chelnicals from complex mixtures is frequently so complicated or involves so much energy consumption as to become uneconomical. Accor~ingly, many available chemioals in coal tar are left in low value products such as creosote, or are used as fuel Methyl-naphthalenes are a kno~n group of coal tar components found in distillation fractions boiling between 230C and 27QC. Methyl-naph-thalenes are known to be useful as fiber swelling agents and as dye carriers. For such solvent applications, methylnaphthalenes can be diluted with other similarly boiling hydrocarbons such as biphenyl to extend their usefulness, but should be free of tar bases such as quinolirle and isoquinoline and should not have or produce color or odor upon standiny.
One known method o~ pro~ucinq solvent-3rade methyl-napththalene includes extraction of a coal t~r distillation fraction (e.y. ;23Q-270C) with a~ueous sodium hydroxide to remove tar acicls (e.~. phenols an~

cresols), followed by extraction ~lith ~ilute acid (e.~J.
10 20~ H2SO4) to remove Inost tar bases and rJrodlJce a raffinate high in methyl-naphthalene and other hydro-carbons such as biphenyl. If the rafEinate is used directlv, or after only further base an.~ ter extrac-tions, it is unsat.isfactory as a swellin~J solv*nt or di'G
carrier because of color and oc3Or formatiorl. Thfse problems have previously been avoided by extl-r.ic~t.i.n~J the raffinate with di.lute soclium hydroxi(-~e ancl ~herl clistill-ing the product over NaO~I flakes. Such a~ditiona.ldistillation increases the cost of the product, however, because of increase ca~ital and energy usage U.S. Patent 3,412,168 to Mascantonio et al.
(1965! discloses a five-step process for producing high purity monomethyl-naphthalenes from a coal tar distil-lation fraction containing methyl~naphthalenes, tar bases, tar acids and other materials boiling between 230C and 270OC or between 230C and 250~C. The first four steps are extractions:
(1) with 10-50~ sulfuric acid below 80C,

(2) with 90-100~ sulfuric acid between 150C
and 190~,

(3) with 10-50% aqueous sodium hydroxide, and

(4) with water.
The final step is a distillation to produce a distillate between 235CC and 247~C comprising at least 90~ mono-methyl-naphthalenes.
While the process of U.S. Patent 3,412,168 does produce mono methyl-naphthalenes of high purity, it has the disadvantages of producing a solid polymeric material in the second extraction and also of requirin~
high temperature for both the second extraction and the final distillation. Furthermore, in conductin~ a final distillation to remove undesirable impurities, it also removes hydrocarbons such as biphenyl which are desira~ly left in the methyl-napthalene fraction if it is to be used as a dye carrier or for other solvent applications.

BRIEF DESCRIP'rION OF THE INVE~JT10~1 The present invention includes a process for producing solvent-grade methyl-nar~hthalene without further distillation from a base-extracted coal tar ~is-tillation fraction containin-J methylnaphthalene~-"
biphenyl, indole and at least one additional tar bas selected from the group consi~stirl~J o~ guinoline and isoquinoline. It .should be appreciated that such base-extracted coal tar distillation fractions arQ frequently produced as a by-product of naphthalene production and thus involve no new equipment or energy consumption beyond that already expended. The process cornprises the steps.
(a) extracting said base-extracted coal tar distillation fraction with aqueous sulfuric acid of concentration between about 70 and 85 weight percent to produce a first aqueous extract and a first organic raffinate substantially free of additional tar bases.
(b) extracting said first organic raffinate with concentrated sulfuric acid of a concentration between about 90 and 100 weight percent to produce a second aqueous (acid) extract and a second organic raffinate substantially free of color and of indole and additional tar bases; and (c) extracting said second organic raffinate with aqueous base to produce a third aqueous extract and a third organic raffinate which contains methyl-naphthalenes and biphenyl and is substantially free of colored, color-forming and odor-forming impurities.
The conditions of the first extraction of the process of the present invention enable sufficiently large quantities of tar bases to be removed from tlle organic layer in the first step for the first organic raffinate to contain only low levels of tar bases.
Accordingly, the use of strong sulfuric acid in the second extraction does not produce solid mateL-ials, but rather removes substantially all tar bases an~ color bodies into a liquid aqueous layer ullder mild tempera-ture conditions and eliminates the contribution of such tar bases to color and odor formation in the final product. Once residual acidic components, includirlg residual sulfuric acid and any sulfonates, are rernov~d in the third extraction, the final product is substan-tially color and odor-free without requiring a final distillation.
DETAILED DESCRIPTIOi~ OF T~IE INVE~`lrr'IV~I
The base~extracted coal tar dicitill~ltiorl fraction used as starting material in the present inven-tion can be a material normally ~ound as a by-product o naphthalene production. In naphthalene prod~ction, a coal tar distillation fraction of fairly broad boiling point range (170 275C) is extracted with base such as aqueous caustic to remove tar acids such as phenol, cresols and the li~e (which tar acids can be sprung from the aqueous layer by addition of acid.) The base-extracted coal tar distillation fraction is then generally distilled to recover naphthalene as the major product, and a fraction boiling higher than napthalene 2t3 as a by-product. This higher boiling fraction gener~lly contains a high proportion of methyl-naphthalenes, but also contains hydrocarbons such as bipllenvl, naphtnalene and acenaphthene, tar bases such as ~uinoline, iso~uino-line and indole, some residual tar acids such as 2,6 xylenol and miscellaneous other components SUCIl as dibenzofuran. Because of the difficulty of recovering useable materials from this higher boiling fraction, it is normally blended in cresote or used as fuel. At times, tar bases have been recovered from this higher boiling fraction by extraction with ~ilute acid, but the raffinate organic layer is ~enerally still unsuitable for most applications because of color formation.
While this conventional higher boilin~ com-ponent may be used in the present process, it is also contemplated to increase the hydrocarbon content of this material by raising the maximum boiling point of the orginial distillation fraction so as to include greateL-amounts of hydrocarbons such as fluorene, acenaphthene and bip~enyl in the distillation fraction. These hi~her-boiling materials Will be unaffected b~ b~se extrac~ion and by distillation to recover nd~ht~lal~-~ne, arl~ will he present with the methyl-naphthalene~s in the higher S boiling fraction which is a by~product o~ nar~tha)~-rlf production. Representative compositions o~ the b~:lSe-extracted coal tar distillation fraction u~ (l in the present invention are given in l~able 1, t~elow.
In the first step oE the present inventi-)n, the based-extracted coal tar di~stillation fraction is extracted with aqueous sulfuric acid of concentration between about 70 and 85 weight percent. This extraction is preferrably conducted at about room temperature with some internal heat generation caused by reactions such as neutralization and sulfonation which may take place.
It is preferred to use sufficient aqueous sulfuric acid to effectively neutralize and extract the tar base con-tent of the base-extracted coal tar distillation frac-tion. It is more preferred to use ei~her stoichiometric amounts of acid or a slight excess, so as to ensure removal of most of the tar bases and produce a first organic raffinate substantially free of the common tar bases such as quinoline and isoquinoline and also pre-ferably having reduced indole content. If the sulruric acid îs of a concentration much below 70 weight percent, it is less effective to remove indole in this first extrac.ion, more corrosive to most materials of con-struction and more awkward because of higher requir~d volumes of acid phase. If it is of a concentration much above ~5 weight percent, it tends to polymerize the indole and form a solid material that complicates liquid-liquid separation. FurthermoreJ while the first step may be conducted at tem~eratures as high as 80C~
it is preferred to operate below about 50C and more preferrably near about room temperature so as to mini-mize reaction such as sulfonation and polymerization of the indole and because ther~ is no advantage gained by heating. The first aqueous lextract will contain sulfat*

salts or sulfuric acid addition salts o~ the tar bas~
If desired, the tar bases can be recovere~ th~refrot,-, ~,y neutralizing this first aqueous extract with c~ustic c~r other inorganic bases, forming an organic layer contain-ing tar bases. The tar bases r,lay be se~arated on~ frovanother in conventional fashion as descri~,e~, for exaJn-ple~ in U.S. Patent Nos. 2,456,77~ to ~ngel (1~45);
2,510,875 to Engel (1946); 2,618,639 to Stas;e (1951) and 2,391,270 to Reimers (1943).
The first organic raffinate frol,l tlle fir~;t extraction is then extracted with sulfuric acid of con~
centration between about 90 and 100 weight percent.
This concentrated sulfuric acid effectively rernoves tne remaining indole. Because, however, the indole content of the first organic raffinate is relatively lo~, the second aqueous (acid) extract produced in the second step does not have a sludge or polymeric layer, but rather contains the indole in a dissolved form such as its sulfate or a sulfonate. Some other undesirable impurities such as 2,6-xylenol may also be removed by the strong acid treatment. It has been found that, when the first organic raffinate from the first step is directly washed with base and/or water, it still con-tains color and odorforming impurities. By contrast, the second step using concentrated sulfuric acid appears to remove these impurities, even under mild conditions.
The aqueous extract ~rom the second extrac-tion contains indole in dissolved forms. While this aqueous extract may be neutralized and an organic layer formed therefrom, it is generally not desirable to tr~
to recover valuable products from the second organic layer.
The second organic raffinate is then extracted with aqueous base such as 2-25 weight percent sodiun~
hydroxide, to remove any sulfonates or excess sulfuric acid left from the first two extractions into a third aqueous layer or third aqueous extract. The remaining organic material, the third organic raffinate, will then contain methyl-naphthalen~s and ~inhenyl (E~lu~ s~
amounts of naphthalene, acenaphthene and sirnilar hyrJro-carbons) and he color stable. It is ~)referred to assur~=
complete separation of the third orcJanic raf f ir1ate ~ro the third aqueous extract by use of a coa1esc~r or ~-,y passing the third oryanic raLfinate containincJ dispers~d a~ueous phase through a material such as alumlnum o~id~
or anhydrous sodium or magneslum sulfate, which rernoves the aqueous phase. It is not preEerr~1 to leave an~
traces of aqueous phase in the third organic ra~inate, since undesired side products such as sulfonates may still form over time.
In practising the invention, it is possible to wash the second organic raffinate with water between the second and third extractions. This removes some of the excess acid from the first and second extractions and thus reduces the quantity of aqueous base required to neutralize any acid in the second organic raffinate.
Because, however the density of the organic phase at each point is close to that of water, any water washin~
produces two phase that separate only slowly, requiring long residence times or the use of a coalescer. For similar reasons, base strengths above 5~ are preferred so that the density of the third aqueous extract is in-creased. Similarly, the third organic raffinate may bewashed with water to remove entrained base or salts.
Additional water washing between the first and second extraction may be practiced, but is generallv not preferred, since it tends to dilute the acid strength during the second extraction, and thus requires more acid to r,laintain the desired 90-lO0 weight percent strength.
The present invention is illustrated by the following examples, which are not intended to be lir~iting.
Instead, various additions, deletions and modifications may be made tllerein without departing from the spirit and scope of the present invention as set forth by claims that follow.

EXA~PL~
Several useful methylnar,hthal*ne-containin~
fractions froin coal tar extraction (after extraction with aqueous base and further distillation to recover naphthalene) were analyzed by gas chromatoyraphy. The analyses are indicated in Table 1.
T~BrJE I
Methyl Naphthalene Fractions From Coal Tar r)istiLlation COMPONE~ S A B C ~ E
_ Naphthalene 6.3 5.6 4.9 15.8 ~.0 2-~ethyl naphthalene 43.7 47.1 30.4 33.4 47.2 l~Methyl naphthalene 19.8 19.8 13.1 16.7 18.8 Quinoline 10.9 12.0 11.2 7.2 9.2 Isoquinoline 5.1 4.4 3.5 5.8 4.5 Biphenyl 5.6 4.7 8.7 ~.0 4.7 Indole ; 5.3 5.2 5.3 3.8 4.8 Dibenzofuran <1.0 <1.0 5.6 <1.0 1.3 Acenaphthene <1.0 <1.0 7.4 2.4 2.1 Indene 1.0 <1.0 <1.0 <1.0 ~1.0 Benzofuran <1.0 <1.0 <1.0 <1.0 <1.0 Lights* <1.0 <1.0 <1.0 <1.0 <1.0 *Material boiling below 170C
EXA~IPLE 1 Step a) 500 g of a methyl naphthalene frac-tion (B, See table 1) were mixed with 100 g of 75% H2SO
solution in a 1 liter beaker and stirred vigorously using an over-head agitator for 30 minutes. After settling, the two phases were separated in a 1 liter separatory funnel, and the top organic ~hase weighed 370g and had the composition given in Table ~. The color of the organic phase was dar]c bluish violet, vir-tually the same as that of the startin~ material.

T~BLE 2 Components Methyl nar~hthalene Fractions, cornpoitic)n Before ~r~-at- After AEter After A~ter ment step(a) step(b % % ~ ~ ~
Lights* <1.0 <1.0 <1 0 ~.1.0 <1.0 Indene <1.0 <1.0 <1.0 ~1.0 ~1.0 Benzofuran <1.0 <1.0 <1. n < 1 . o cl.o ~laphthalene5.5 6.7 6.~ 6.~ 6.~
2-Methyl 47.1 56.7 57.9 60.0 60.0 naphthalene l-Methyl 19.8 23.8 24.2 '4.2 24.2 naphthalene Quinoline 12.0 N.D N.D ll.D ~.D
15 Isoquinoline ~.4 N.D N.D ll.D ~I.D
Biphenyl 4 7 5.3 5.9 5.9 5.9 Illdole 5.2 0.4 ~.D N.D N.D
Acenaphthene <1.01.3 1.4 1.~ 1.4 Dibenzofuran <1.01.0 <1.0 <1.0 <1.0 * Material boiling below 170C
N.D. = none detectable Step b) The organic raffinate (300 g) fror.
step (a~ was mixed with 30 g of 98% H2SO4 and stirred vigorously in a 700 mL beaker using an overhead stirrer.
After 10 minutes of agitation, the mixture was allowed to settle in a separatory funnel. The dark reddish-colored acid phase was separated from the top oryanic phase (287 g) in a separatory funnel. The organic raf-finate was clear with a light red~ish tinge due to dis-persed acid phase. Gas chromatographic analysis (seeTable 2) showed that no detectable amount of indole was present, besides quinoline and isoquinoline, which were removed completely in step (a).
Step c) 100 g of the organic phase from step (b) was mixed with 20 g of a 10% aqueous so~ium hydro~-ide solution in a 250 mL separatory funnel and shaken vigorously for 2 minutes. After settliny, the colorless organic layer at the top was separated from the bottom caustic phase. Gas chromatogra2hic analysis (sec '~a~le 2) showed virtually no dif~erence in the composition of the organic phase before and after th~ casutic wash.
The organic raffinate was color-free, with a sliyht haz~
due to finely dis~ersed aqueous ~hase ~r~sent.
Step d) 95 ~ of the color-free or-~anic E~ha;e from step (c) was placed in a ~50 mL Erlenmeyer 1ack and 5 9 of anhydrous magnesium sulfate was add~d to i~
and stirred over a magnetic stirrer fvr 10 rninutes. on filtering a very clear and colorless oryanic li~uid (94 g) was obtained. Gas chrornatographic analysis showed virtually no change in compositlon (Ta~le 2).

500 g of the same rnethyl naphthalene fraction (B, table 1) was stirred with 150 g of 75% H2SO4 as in example 1. The top organic phase on separation and gas chromatography analysis showed no detectable amounts of quinoline, isoquinoline and also indole. The organic phase was still dark-colored as in example 1.
mreatment of the organic phase with 96~ H2SO~
(5:1 organic to acid by weight) and subsequent separa-tion as in example 1 furnished an organic phase identi-cal to the one in example 1. On mixing with a 20~
aqueous sodium hydroxide solution (5Ol organic to acid by weight) and phase separation a color-free organic raffinate was obtained, having virtually identical composition as in example 1.
~ he slightly hazy liquid was allowed to stand over alumina (20-1 organic to alur,~ina by weight), and the product obtained after filtration was color-free and clearO
EXAMPLE_3 500 g of a different methyl naphthalene frac-tion (C, table 1) was shal;en viyorously with lQ~ mL of 85% H2SO4 in a 1 liter separatory funnel for 2 minutes.
The dark colored aqueous phase was drawn off from the bo~tom and the organic phase in the separatory funnel was treated with 35 mL of 98~ H~SO~ and a~ain sha~en vigorously. After 2 ~inutes of shaking it was allo~,Jed to settle and the lower acid phase was run o~.
To the organic phase in the separatory funnel was added 100 mL of 10~ llaOI~ solution and shakcn vi-j-orously for one minute and the mixture allo~/ed tosettle. After running of~ the causkic phase froln thr bottom, the slightly hazy or(Janic phas( was run ollt through a bed of anhydrous sodium sul~te (10 fJ~. ~
clear and colorless methyl naphthalene fractiorl (355 ~) was collected, which contained no detectable amollnts quinoline, isoquinoline and indole.

Four gallons of tar fraction labeled material E in Table 1 was pumped into a static mixer system at 1600 mL/min mixing cocurrently with 250 mL/min of 75~
H2SO4. The series of static mixers used resulted in a residence time of 5.3 seconds and fluid velocities between 0.3 and 1.7 m/sec at various points along the series of mixers. The heat of reaction without external ~0 cooling resulted in a tem~eratur~e increase from 26C
to 60C over the lenyth of the mixer. After leaving the mixing sections the mixture was separated after 10-15 min settling time. This treatment using 20~ excess acid (over theoretical for removal of quinolines and indole) resulted in removal of essentially all of the quinolines and isoquinolines and left 0.44% indole in the raffinate.
After cleaning out the equipment the raffinate from the 75% acid treatment was pumped through the mix-ing system at 1600 mL/min cocurrently contacting 160 mL/
min of 98% H2SO4. The raffinate from this treatment after leaving a settler (5 min residence tirne) was pumped through a coalescer device to remove sli~ht entrained acid droplets.
After cleaning out the equipment again the clarified raffinate frolll the 98~ acid treatment was pumped through the mixing system at 1600 r,lL/min cocur-rently mixing Wit'l 160 mL/rnin of 10~ l~aOH to remove an sulfonates and residual acid. The raffinate after 5 49~E3 -12~
min settling was again passed through the coalescer device to remove slight entrained aqueo~s phase result-in~ in a clear product solution of light color and the following analysis naphthalene 7.1 2 methyl naphthalene 56.2~
1 methyl naphthalene 23.6%
Biphenyl 7.0 other 6.1

Claims (10)

WHAT IS CLAIMED IS:

1. A process for producing solvent-grade methyl-naphthalene without further distillation from a base-extracted coal tar distillation fraction containing methylnapthalenes, biphenyl, indole and at least one additional tar base selected from the group consisting of quinoline and isoquinoline, comprising the steps:
(a) extracting said base-extracted coal tar distillation fraction with aqueous sulfuric acid of concentration between about 70 and 85 weight percent to produce a first aqueous extract and a first organic raffinate substantially free of additional tar bases;
(b) extracting said first organic raffinate with concentrated sulfuric acid of a concentration between about 90 and 100 weight percent to produce a second aqueous extract and a second organic raffinate substantially free of color and of indole and additional tar bases; and (c) extracting said second organic raffinate with aqueous base to produce a third aqueous extract and a third organic raffinate which contains methyl-naphthalenes and biphenyl and is substantially free of colored, color-forming and odor-forming impurities.

2. The process of claim 1 wherein each of said extracting steps are conducted at a temperature below about 80°C.

3. The process of claim 1 wherein sufficient aqueous sulfuric acid is used to remove a major propor-tion of the indole present in said base-extracted coal tar distillation fraction from said first organic raffi-nate.

4. The process of claim 1 or 3 wherein said aqueous sulfuric acid is between about 75 and about 80 weight %.

5. The process of claim 1 wherein said con-centrated sulfuric acid is between about 95 and about 98 weight %.

6. The process of claim 1 wherein said third organic raffinate is passed through a solid material to remove traces of third aqueous extract.

7. The process of claim 1 or 6 wherein said third organic raffinate is washed with water.

8. The process of claim 1 wherein said second organic raffinate is washed with water before extraction by aqueous base.

9. The process of claim 1 or 8 wherein said aqueous base is between about 2 and about 25 weight %
sodium hydroxide.

10. The process of claim 1 or 8 wherein said aqueous base is between about 10 and about 20 weight %
sodium hydroxide.