This invention relates to an improved method for recovering 2,6-dimethylnaphthalene
by crystallization from a mixture containing 2,6-dimethylnaphthalene and organic
components formed during the preparation or isolation of 2,6-dimethylnaphthalene.
More particularly, this invention relates to a method for recovering 2,6-dimethylnaphthalene
from a mixture containing dimethylnaphthalenes, wherein the composition of the
mixture is adjusted to provide for efficient crystallization of the 2,6-dimethylnaphthalene.
Background of the Invention
2,6-Dimethylnaphthalene is a preferred feedstock for preparing 2,6-naphthalenedicarboxylic
acid. 2,6-Naphthalenedicarboxylic acid is a useful monomer for the preparation
of high performance polymeric materials. For example, 2,6-naphthalenedicarboxylic
acid, or its methyl ester, can be reacted with ethylene glycol to prepare poly(ethylene-2,6-naphthalate)
(PEN). Fibers and film manufactured from PEN have improved strength and superior
thermal properties relative to other polyester materials. Films made from PEN demonstrate,
for example, superior resistance to gas diffusion and particularly to the diffusion
of carbon dioxide, oxygen and water vapor. Because of its exceptional properties,
PEN is especially suitable for applications such as food and beverage containers,
particularly for so-called "hot-fill" food and beverage containers, tire cord,
magnetic recording tape and electronic components.
Although 2,6-naphthalenedicarboxylic acid can be prepared by a number
of processes, perhaps the most preferred because of cost and efficiency, is the
liquid phase oxidation of 2,6-dimethylnaphthalene. A suitable method for oxidizing
2,6-dimethylnaphthalene to 2,6-naphthalenedicarboxylic acid is described, for example,
in U.S. Patent 5,183,933 to Harper et al. Although feedstocks other than 2,6-dimethylnaphthalene,
for example 2,6-diethylnaphthalene or 2,6-diisopropylnaphthalene, can be oxidized
to 2,6-naphthalenedicarboxylic acid, 2,6-dimethylnaphthalene is preferred because
it is lower in molecular weight compared to 2,6-diethyl- or 2,6-diisopropylnaphthalene
and, therefore, less 2,6-dimethylnaphthalene (by weight) is required to prepare
a specified weight amount of 2,6-naphthalenedicarboxylic acid.
While 2,6-dimethylnaphthalene is present in certain refinery streams,
for large scale use it is preferable to manufacture 2,6-dimethylnaphthalene starting
with simple, readily available and inexpensive starting materials. One such process
for manufacturing 2,6-dimethylnaphthalene is disclosed in Lillwitz et al., U.S.
Patent 5,198,594. The process for preparing 2,6-dimethylnaphthalene disclosed therein
is called the "Alkenylation. Process," which comprises reacting o-xylene with butadiene
in the presence of a zero-valent alkali metal to form orthotolylpentene (OTP).
The alkali metal-promoted reaction of an alkylaromatic with a conjugated diene
such as butadiene to form an olefinically substituted aromatic is referred to as
an alkenylation reaction. The OTP is subsequently cyclized to form 1,5-dimethyltetralin
(1,5-DMT), the 1,5-DMT is dehydrogenated to 1,5-dimethylnaphthalene (1,5-DMN)
and the 1,5-DMN is isomerized to the desired 2,6-dimethylnaphthalene (2,6-DMN).
The overall process is summarized in equations (1) through (4) below.
In the alkenylation process for preparing 2,6-dimethylnaphthalene,
the isomerization of 1,5-dimethylnaphthalene typically produces not only the desired
2,6-dimethylnaphthalene, but also a mixture of other hydrocarbon components such
as 1,6- and 1,7-dimethylnaphthalenes and 1- and 2-monomethylnaphthalenes and various
trimethylnaphthalenes. Additionally, other processes for preparing 2,6-dimethylnaphthalene
and methods for isolating 2,6-dimethylnaphthalene from refinery streams generally
require recovering the 2,6-dimethylnaphthalene from a mixture containing other
hydrocarbons. In order to have a cost-effective process for preparing 2,6-dimethylnaphthalene,
it is necessary to efficiently isolate the 2,6-dimethylnaphthalene from the mixture
of hydrocarbons produced by the isomerization reaction, the hydrocarbon mixtures
produced by other processes for preparing 2,6-dimethylnaphthalene, or mixtures
produced during the processes for isolating 2,6-dimethylnaphthalene from refinery
streams. The art, therefore, needs a simple and cost effective method for recovering
valuable 2,6-dimethylnaphthalene from a mixture containing 2,6-dimethylnaphthalene
and other hydrocarbon components. The present invention provides such a method.
Methods for isolating 2,6-dimethylnaphthalene from mixtures of hydrocarbons
are known. For example, U.S. Patent 3,806,552 to Oka et al., discloses that the
separation of 2,6-dimethylnaphthalene from the isomerization reaction product can
be easily carried out by cooling the isomerization reaction product to a proper
temperature and separating the precipitated crystals, or by adding a suitable solvent
to the isomerization reaction product, cooling the solution and separating the
precipitated crystals. A number of suitable solvents are disclosed therein. U.S.
Patent 3,775,496 to Thompson et al., discloses that selective crystallization has
been used to separate DMN (dimethylnaphthalenes) from each other, citing U.S.
Patents 3,485,885; 3,541,175; 3,590,091 and 3,594,436. U.S. Patent 3,541,175 discloses
a process for isolating 2,6-dimethylnaphthalene, and it discloses that crystallization
may be carried out in a scraped cooling crystallizer. British Patent 1,345,479
discloses that 2,6-dimethylnaphthalene can be isolated by crystallization. As an
example, 2,6-DMN is crystallized from a mixture containing 35.3 mol.% 2,6-DMN,
36.8% 1,6-DMN, 8% 1,5-DMN, 7.7% 1,7-DMN and 4.2% low-boiling point and high boiling
Other method for obtaining 2,6-dimethylnaphthalene by crystallization
are disclosed in US-A-3,153,676 and US-A-3,590,091.
US-A-3,153,676 discloses a method for obtaining 2,6-dimethylnaphthalene
from a mixture containing 2,7-dimethylnaphthalene and various low-melting components,
by crystallization at 0-30°C.
US-A-3,590,091 describes a method for the recovery of 2,6-dimethylnaphthalene
from mixtures containing 2,7-dimethylnaphthalene at a temperature range of -50
to 70°C. The crystallization is carried out at a temperature at which the 2,6-/2,7-dimethylnaphthalene
eutectic mixture is soluble in the liquid present.
Summary of the Invention
The present invention provides improved procedures for crystallizing
2,6-dimethylnaphthalene according to the following two variants.
According to the first variant, there is provided a method for preparing
crystalline 2,6-dimethylnaphthalene comprising crystallizing in a scraped-wall
crystallizer apparatus at crystallization temperature t degrees Celsius (T degrees
Fahrenheit), a mixture of low melting components, LM, having melting points of
21°C (70°F) and below, and high melting components, HM, including 2,6-dimethylnaphthalene,
having melting points above 21°C (70°F), such that:
(5a) HM / (LM)< 0.03 (T-50) + A
(5b) HM / (LM)< 0.054 (t-10) + A
where HM is the total weight percent of high melting components, including 2,6-dimethylnaphthalene,
in the mixture, and LM is the total weight percent of low melting components in
the mixture, t is the temperature in degrees Celsius and T is the temperature of
the crystallization in degrees Fahrenheit, and where A is a value no more than
Brief Description of the Figures
Figure 1 shows in graphical form preferred parameters for operating
the method of this invention.
Figure 2 is a flow diagram showing a preferred embodiment for operating
the method of this invention.
Detailed Description of the Invention
We discovered that 2,6-dimethylnaphthalene can be effectively crystallized
in a scraped-wall crystallization apparatus provided the weight ratio of high melting
components (HM), which includes 2,6-dimethylnaphthalene, to low melting components
(LM) in the mixture being crystallized is as follows:
(5a) HM / (LM) < 0.03 (T - 50) + A or(5b) HM / (LM) < 0.054 (t -10) + A
where t is the temperature in degrees Celsius and T is the temperature, in degrees
Fahrenheit, used for the crystallization and A is no more than about 1.0. We have
determined that when the ratio of HM/LM is outside of this range, the scraped-wall
crystallizer cannot effectively crystallize the 2,6-dimethylnaphthalene. Specifically,
the mixture being crystallized forms a solid mass that clings to the scraping device
in the crystallizer and the crystallizer becomes inoperable. In contrast, when
the crystallization operation is conducted within the operable range of equation
(5), the product exiting the scraped-wall crystallizer is in the form of a slurry
of crystalline 2,6-dimethylnaphthalene in the crystallization mother liquor. Additionally,
we have determined that the weight ratio of high melting components to low melting
components in the mixture subjected to crystallization can be adjusted to the desired
composition by utilizing the light boiling components (lights) that are produced
during the preparation or isolation of 2,6-dimethylnaphthalene. These lights, for
example, can comprise the mixture of components having a lower boiling point than
the dimethylnaphthalenes, and which components are produced during the process
steps for preparing 2,6-dimethylnaphthalene using the alkenylation process. Instead
of removing these lights, we have determined that the amount of lights present
during the crystallization of the 2,6-dimethylnaphthalene can be adjusted by, for
example, fractionation prior to crystallization. The composition produced thereby
provides for the efficient crystallization of 2,6-dimethylnaphthalene, particularly
when a scraped-wall crystallizer apparatus is used to conduct the crystallitation.
In equation (5) above, T is preferably in the range of (10 - 65°C) 50 to about
150°F, more preferably 15 - 60°C (60 to about 140°F).
The method of this invention is advantageously used to isolate 2,6-dimethylnaphthalene
produced by the alkenylation process. As described hereinabove and summarized
in Equations (1) to (4) hereinabove, the alkenylation process comprises four basic
chemical reaction steps. In the first step, the alkenylation reaction, o-xylene
is reacted with butadiene to produce an orthotolylpentene (OTP). The OTP formed
is actually a mixture of 5-OTP-1 and cis- and trans-5-OTP-2. A suitable method
for preparing orthotolylpentene is disclosed in Lillwitz et al., U.S. Patent 5,198,594;
other methods are disclosed in U.S. Patents 3,766,288 and 3,953,535 to Shima et
al. The specification of these three patents are hereby incorporated by reference.
In this alkenylation reaction, o-xylene in the liquid phase is reacted with 1,3-butadiene
in the presence of a catalytic amount of an alkali metal. Typically, an excess
molar amount of o-xylene is used in order to reduce the amount of high molecular
weight by-products that are formed resulting from the reaction of more than one
molecule of butadiene per molecule of o-xylene. For example, 1,3-butadiene can
be reacted with about 1.1 to about 20 moles of o-xylene per mole of 1,3-butadiene,
in the liquid phase, at a temperature of 93 - 160°C (about 200°F to about 320°F)
and at a pressure of about 1 atmosphere to about 3 atmospheres to form a product
mixture comprising orthotolylpentene. The reaction is suitably catalyzed by an
alkali metal such as potassium or a mixture of potassium and sodium, preferably
NaK. The amount of alkali metal is 1 to 10,000 parts by weight per million parts
by weight of o-xylene. After the alkenylation reaction, the reactive alkali metal
can be quenched with, for example, water or an alcohol, and the excess o-xylene
is removed to produce a concentrate containing the desired orthotolylpentene.
The concentrate can be fractionated to remove materials having boiling points higher
and/or lower than orthotolylpentene to form a purified form of orthotolylpentene.
However, the concentrate containing components having a lower and higher boiling
point than orthotolylpentene can also be used directly in the cyclization step.
In the cyclization step of the alkenylation process, the orthotolylpentene
is cyclized using a catalyst to form 1,5-dimethyltetralin. Methods for cyclizing
orthotolylpentene, as well as suitable catalysts, are disclosed in U.S. Patents
5,034,561; 5,030,781 and 5,073,670, to Sikkenga et al., the specifications of which
are hereby incorporated by reference. Other processes for cyclizing orthotolylpentene
to dimethyltetralin are disclosed, for example, in U.S. Patents 3,775,498; 3,775,496
and 3,840,609, the specifications of which are hereby incorporated by reference.
The cyclization reaction can be conducted using either a gaseous or liquid phase
reaction. A preferred method for cyclizing orthotolylpentene to 1,5-dimethyltetralin
uses an acidic molecular sieve catalyst such as a low-acidity, ultrastable crystalline
aluminosilicate zeolite Y in the hydrogen form having a silica-to-alumina bulk
molar ratio of at least about 12, a unit cell size no greater than 24.3 Angstroms,
a sodium content of no more than about 0.4 weight percent sodium or, in terms
of sodium oxide, a sodium oxide -to-alumina bulk molar ratio in the range of 0.001:1
to 1:1. The cyclization reaction comprises maintaining the orthotolylpentene in
the liquid phase at a temperature of 120°C to 350°C, at a pressure, for example,
of 0.05 to 0.5 atmospheres, to form a reaction mixture comprising the 1,5-dimethyltetralin.
The weight ratio of orthotolylpentene to the molecular sieve cyclization catalyst
is suitably 1000:1 to 10:1. The mixture produced by the cyclization reaction can
be used directly for the next reaction in the alkenylation process; alternatively,
the reaction product mixture from the cyclization reaction can be fractionated
to remove light and/or heavy components and thereby prepare a concentrate of 1,5-dimethyltetralin.
In the next step of the alkenylation process, the mixture produced
by the cyclization reaction, or the concentrate prepared by fractionating the
product from the cyclization reaction, is dehydrogenated to prepare 1,5-dimethylnaphthalene.
This dehydrogenation can be accomplished using either a gas phase reaction or
a liquid phase reaction. Suitable methods and catalysts for conducting such a dehydrogenation
reaction are disclosed in U.S. Patents 5,118,892; 5,189,234; 3,775,498 and 3,781,375,
the specifications of which are hereby incorporated by reference. A preferred
method comprises contacting the 1,5-dimethyltetralin in the gas phase with a suitable
dehydrogenation catalyst such as a catalyst comprising alumina, 0.05 to 5.0 weight
percent platinum or palladium, no more than about 0.14 weight percent halide, and
0.10 to 2.0 weight percent alkali metal, all weight percents based on the weight
of the catalyst at a temperature of 315 - 482°C (about 600 to about 900°F) a pressure
of 10.1 kPa - 2.02 MPa (about 0.01 atmosphere to about 25 atmospheres), and at a
weight hourly space velocity of 0.1 hr-1 to 20 hr-1. The
mixture produced by the dehydrogenation reaction can be used directly in the isomerization
reaction; alternatively, it can be fractionated to remove lower boiling components
and/or higher boiling components, for example, those formed during the dehydrogenation
reaction. The product from the dehydrogenation reaction, either in fractionated
or unfractionated form, is isomerized over a suitable catalyst to form a mixture
of dimethylnaphthalenes, including the desired 2,6-dimethylnaphthalene. Suitable
methods for isomerizing 1,5-dimethylnaphthalene are disclosed, for example, in
U.S. Patents 4,962,260; 4,950,825; 3,775,498; 3,781,375; 3,855,328 and 3,957,896,
the specifications of which are hereby incorporated by reference. A suitable method
for isomerizing 1,5-dimethylnaphthalene comprises contacting 1,5-dimethylnaphthalene
in the liquid phase at a temperature in the range of 200°C to 420°C with an acidic
isomerization catalyst. For example, the catalyst can comprise either an acidic
ultrastable crystalline y-zeolite having a silica-toalumina molar ratio of from
4:1 to 10:1, having pore windows provided by twelve-membered rings containing oxygen
and a unit cell size of from about 24.2 to about 24.7 angstroms, or beta-zeolite.
The product from this isomerization reaction contains 2,6-dimethylnaphthalene.
Preferably, the product from the isomerization contains at least about 20, more
preferably at least about 35 weight percent 2,6-dimethylnaphthalene. In addition,
depending on the conditions used for the isomerization, and whether or not prior
fractionation steps were used to remove high boiling and low boiling components
from the product mixtures produced during the preceding alkenylation, cyclization,
dehydrogenation and isomerization steps, the product mixture produced by the isomerization
reaction can contain in addition to the dimethylnaphthalenes, 1 to 20 weight percent
of light, low boiling components (lights), 0.5 to 5 weight percent of various
trimethylnaphthalenes and 0.5 to 5 weight percent of the heavy, high boiling components
(heavies). By light, low boiling, we mean that the boiling point of the component
is lower than the boiling point of 2-methylnaphthalene. Thus the light, low boiling
components (lights) have a boiling point lower than 260°C (about 500°F), preferably
lower than about 243°C (470°F), at atmospheric pressure. By heavy, high boiling,
we mean having a boiling point greater than the boiling point of any of the dimethylnaphthalenes,
more preferably greater than the boiling point of the trimethylnaphthalenes. Thus,
the heavy, high boiling components (heavies) have a boiling point greater than
271°C (about 520°F) at atmospheric pressure. In addition to the above, the product
produced by the isomerization reaction can contain various other dimethylnaphthalenes
in addition to the desired 2,6-dimethylnaphthalene. Such dimethylnaphthalenes
include one or more of 1,6- and 1,7-dimethylnaphthalene, preferably at least 1,6-dimethylnaphthalene,
and typically about 40 to about 80 weight percent of such other dimethylnaphthalenes.
As described hereinabove, instead of removing the light, low-boiling
components prior to crystallizing the 2,6-dimethylnaphthalene, they can be included,
in variable amounts, in the mixture fed to the crystallizer in order to improve
the crystallization of the 2,6-dimethylnaphthalene. The amount of lights included
in the mixture fed to the crystallizer apparatus is an amount that provides for
the efficient crystallization of 2,6-dimethylnaphthalene, suitably at least about
5 weight percent of the total mixture crystallized, preferably at least about 7
weight percent, and most preferably at least about 10 weight percent of the total
mixture subjected to crystallization. Preferably no more than about 25 weight percent
of the mixture subjected to crystallization is lights.
In addition to the amount of lights present in the mixture crystallized,
the relative amounts of the other components in the mixture affects the crystallization
of the 2,6-dimethylnaphthalene. As stated hereinabove, the weight ratio of high
melting components, HM, to low melting components, LM, must be:
(5a) HM / (LM) < 0.03 (T -50) + A or(5b) HM / (LM)< 0.054 (t-10) + A
wherein the high melting components have melting points above about 21°C (70°F)
and can include, for example, 2,6-dimethylnaphthalene, 1,5-dimethylnaphthalene,
2,7-dimethylnaphthalene and 2-methylnaphthalene (2-MN). The low melting components
include, for example, 1,6-dimethylnaphthalene, 1,7-dimethylnaphthalene, 1-methynaphthalene
and other light boiling components, the trimethylnaphthalene fraction and the
heavy boiling components. The value of A is no greater than 1.0, more preferably
no greater than 0.9. Most preferably, A is 1.0 to 0.9. Thus, we have found that
a mixture containing the composition X shown below could not be crystallized in
a scraped-wall crystallizer to isolate 2,6-dimethylnaphthalene at a crystallization
temperature of 21°C (70°C) whereas, the composition Y shown below was successfully
crystallized at 29°C (85°F) to yield 2,6-dimethylnaphthalene in high yield and
purity using a scraped-wall crystallizer apparatus to conduct the crystallization.
As shown below, the feed X has a HM/LM ratio of 1.6 and at a crystallization temperature
of 21°C (70°F), equation (5) is not satisfied where A is 1.0. Composition Y, however,
has a HM/LM value of 1.2 and at a crystallization temperature 85°F, equation (5)
is satisfied where A is 1.0.
COMPOSITION (WT.%) COMPONENT X Y Z Lightsa4.00.77.2 2-MN0.90.63.1 1-MN0.30.51.1 1,5-DMN126.96.36.199 1,6-DMN33.041.427.6 2,6-DMN41.439.043.5 1,7-DMN0.81.81.4 2,7-DMN188.8.131.52 Heavies184.108.40.206 Cryst. Temp. °C (°F)21 (70)29 (85)21 (70) HM/LM220.127.116.11 0.03(T-50) +1.01.62.01.6 HM/LM < 0.03 (T-50) + 1.0 CRYSTALLIZEDNoYesYes 2,6-DMN (Yield, %/Purity, %)inoperable75.6/9977.8/97.5
a Other than 1-MN
Thus, it is not only the quantity of the light boiling components
in the mixture that provides for efficient crystallization, but the weight ratio
of high melting components to low melting components and the crystallization temperature.
At times, the ability to adjust the ratio of high melting components to low melting
components is not feasible unless the adjustment is made by altering the level
of light boiling components, i.e., a type of low melting component, in the feed
mixture to the crystallizer. For example, mixture Z in the table above, which mixture
contained more lights than mixture X, was effectively crystallized in a scraped-wall
crystallizer apparatus providing 2,6-dimethylnaphthalene in good purity and high
yield. Using the lights to assist in the crystallization of 2,6-dimethylnaphthalene
is advantageous because it does not introduce extraneous components into the process
stream, which would occur if a solvent were used. After crystallization, and after
the desired crystalline 2,6-dimethylnaphthalene is separated from the mother liquor,
the mother liquor, which contains the light and heavy components, can be fractionated
into its various components. One or more of such fractions can be recycled to the
isomerization or crystallization step if desired, or one or more can be purged
from the process and used, for example, as fuel.
In addition to using lights to adjust the HM/LM ratio, the 1,5-dimethyltetralin
(1,5-DMT) produced in the second step of the alkenylation process can also be
used. This component, which has a melting point of less than 21°C (70°F), is also
highly suitable because it does not add extraneous materials to the process. When
used, the amount of 1,5-DMT in the mixture crystallized is suitably at least about
2 wt.% of the mixture crystallized, preferably at least about 5 wt.% and more preferably
at least about 7 wt.%.
The lights (i.e., light, low boiling components) useful in the method
of this invention comprise a complex mixture of compounds and where such mixture
is produced during the manufacture or isolation of 2,6-dimethylnaphthalene. Preferably,
the lights comprise a mixture of organic compounds which mixture has a boiling
point lower than the boiling point of 2-methylnaphthalene, and more preferably
where they are obtained by fractionating the mixture produced in the alkenylation
process subsequent to the isomerization step where 1,5-dimethylnaphthalene is isomerized
to 2,6-dimethynaphthalene. The lights mixture has a melting point below 70°F,
and thus is a low-melting component. These lights typically contain o-xylene, 1-methyl-2-pentylbenzene,
5-orthotolylpentene-1, 5-orthotolylpentene-2, 1,5-dimethyltetralin, 1,6-dimethyltetralin,
other dimethyltetralin isomers, and 1-methylnaphthalene.
As described hereinabove, the method of this invention is also useful
for isolating, by crystallization, 2,6-dimethylnaphthalene from other sources or
produced by other synthetic routes. For example, the method of this invention can
be used to crystallize 2,6-dimethylnaphthalene isolated from fractions obtained
from the catalytic or thermal cracking of petroleum, such as the dimethylnaphthalene
portion separated by distillation from recycle oil in the FCC process. The method
of this invention can also be used to isolate 2,6-dimethylnaphthalene from dimethylnaphthalene-containing
fractions obtained from coal tar. The method of this invention can also be used
to isolate, by crystallization, 2,6-dimethylnaphthalene produced via the method
disclosed in U.S. Patents 5,008,479; 5,023,390; and 5,068,480.
The crystallization apparatus most suitable for crystallizing 2,6-dimethylnaphthalene
according to the method of this invention is a scraped-wall type crystallizer.
In these types of crystallization apparatus spring-loaded scraper blades, typically
manufactured from a flexible, polymeric material having resistance to high temperatures,
resistance to chemical attack, and good wear resistance and lubricity (for example,
nylon, Teflon®, Torlon®, such as Torlon® 4301 or 4302, or Hydlar®),
-rotates within a crystallization drum while the polymeric scraper blades "scrape"
the inside wall of the crystallization drum. The outside of the crystallization
drum is equipped with cooling jackets to cool the liquid being crystallized to
the desired crystallization temperature while the blades in the scraped-wall crystallizer
scrape along the inside cylindered walls of the crystallization drum. The scraped-wall
crystallizer suitably contains a separate pumping device to maintain the contents
of the crystallization drum well mixed. Suitable scraped-wall crystallizers are
available from Victoria Machine Works, Victoria, Texas. Two or more scraped-wall
crystallizers can be used in series, each operating at successively decreasing
temperatures, and where the feed to the second comprises a slurry produced in the
first crystallizer. A double-pipe scraped-wall crystallizer can also be used along
with the drum-type scraped-wall crystallizer. While scraped-wall crystallizers
are preferred for the method of this invention, other crystallization apparatus
can be used, for example, a draft tube crystallizer. However, with these other
crystallizers, a lower HM/LM ratio will likely be necessary, i.e., where A is
no more more than about 0.6. The crystallization method disclosed herein can be
conducted in a batch or continuous manner.
Detailed Description of the Figures
Figure 1 is a graph showing the operating range for the method of
this invention. The region below the line termed "operable," identifies the various
crystallization temperatures and ratios of HM/LM that can be used at such temperatures
to provide for the efficient crystallization of 2,6-dimethylnaphthalene in a scraped-wall
crystallizer. In Figure 1, the line establishing the operable reaion corresponds
to the equation:
(5a) HM / (LM) < 0.03 (T - 50) + A or(5b) HM / (LM) < 0.054 (t -10) + A
Figure 2 is a flow diagram representing a preferred embodiment for
operating the method of this invention. In Figure 2, the dotted lines represent
optional process steps that can be operated individually or in any combination.
In this preferred embodiment, butadiene and o-xylene are reacted in a liquid phase
reaction using a molar excess of o-xylene relative to butadiene and catalyzed by
a metallic sodium-potassium (NaK) catalyst. In the next process step, the excess
o-xylene is removed, typically by distillation, and is recycled to the alkenylation
reaction mixture. The orthotolylpentene (OTP) separated from the o-xylene is either
sent directly to the cyclization reactor in the Cyclization Step or subjected to
a Separation Step A, typically distillation, to remove components having a boiling
point lower and/or higher than about the boiling point the OTP, thereby forming
an OTP concentrate. The OTP is subsequently cyclized to 1,5-dimethyltetralin (1,5-DMT)
in the Cyclization Step using a suitable cyclization catalyst, and where the cyclization
can be conducted in either liquid or gas phase mode. The 1,5-DMT produced from
the Cyclization Step is either sent directly to the Dehydrogenation Step or first
subjected to a Separation Step B, typically distillation, where components having
a boiling point lower and/or higher than about the boiling point of 1,5-DMT are
removed. In the Dehydrogenation Step, the 1,5-DMT is dehydrogenated to 1,5-dimethylnaphthalene
(1,5-DMN) in either a liquid phase or gas phase reaction using a suitable dehydrogenation
catalyst. The product mixture from the Dehydrogenation Step is sent directly to
the Isomerization Step or subjected to a Separation Step C, typically distillation,
where the materials having a boiling point lower and/or higher than about the boiling
point of 1,5-dimethylnaphthalene are removed. The product 1,5-dimethylnaphthalene
from the Dehydrogenation Step is isomerized in the Isomerization Step in either
a gas or liquid phase reaction using a suitable isomerization catalyst to form
a mixture of dimethylnaphthalenes, including the desired 2,6-dimethylnaphthalene.
The mixture produced by the Isomerization Step is directed to a Separation Step
D, typically distillation, where a portion of the lights and at least a portion
of the heavies can be removed. The resulting molten mixture containing DMN isomers
is directed to the Crystallization Step where the mixture is cooled to crystallize
the desired 2,6-dimethylnaphthalene in a crystallization apparatus. After the
crystallization, which is preferably conducted in a scraped-wall crystallizer or
two or more scraped-wall crystallizers in series, at a temperature in the range
of 10-65°C (about 50 to about 150°F), more preferably 15-60°C (60 to 140°F), the
crystalline 2,6-dimethylnaphthalene is separated from the crystallization mother
liquor in Separation Step E using a solid-liquid separation device such a centrifuge,
filter, settling tank, etc. The recovered 2,6-dimethylnaphthalene can be subjected
to additional purification procedures, if desired, such as washing, crystallization
from a melt of the product at a temperature higher than the temperature used in
the Crystallization Step, recrystallization from a solvent such as a low molecular
weight carboxylic acid such as acetic acid, a low molecular weight alcohol including
methanol, ethanol, isopropanol and the like, or a low boiling hydrocarbon such
as hexane, octane, nonane, a mixture of low boiling hydrocarbons, or a combination
of such purification procedures. The mother liquor recovered from the crystallization
of the 2,6-dimethylnaphthalene contains lights, 2-methylnaphthalene, a mixture
of dimethylnaphthalenes including 2,6-dimethylnaphthalene that was not crystallized,
a mixture of trimethylnaphthalenes, and various heavy components that have boiling
points higher than about the boiling points of the trimethylnaphthalenes. The mother
liquor can be separated in Separation Step F, preferably by fractional distillation,
into lights, the dimethylnaphthalenes and the heavies. The lights can be recycled
to the Crystallization Step. The dimethylnaphthalenes isomer fraction, as shown
in Figure 2, is preferably recycled to the Isomerization Step. Some of the dimethylnaphthalene
fraction may also eliminated after Separation Step E in order to prevent a build-up
of 2,7-dimethylnaphthalene. Some or all of the heavies are removed from the overall
process and are disposed as fuel or sold as by-product.
In the method of this invention, the composition of the mixture in
the Crystallization Step in Figure 2, is such that the equation.
(5a) HM / (LM) < 0.03 (T - 50) + A or(5b) HM / (LM) < 0.054 (t-10) + A
is satisfied, where HM, LM and T are described hereinabove, and A is no greater
than 1.0. In the method of this invention, the HM/LM ratio is efficiently adjusted
by adjusting the content of the lights in the mixture sent to the Crystallization
Step. The adjustment in the amount of lights is preferably made during the Separation
Step D shown in the Figure 2 where the product from the Isomerization Step is subjected
to a separation procedure, preferably one or more fractionations, where lights
and heavies are removed from the product formed during the Isomerization Step.
In this fractionation step, the amount of lights and heavies included in the material
sent to the Crystallization Step can be adjusted to meet the requirements of equation
(5). Lights from each of Separation Steps A-C can optionally be added to the Crystallization
Step in order to have the composition that is crystallized conform to equation
(5) hereinabove. Although not depicted in Figure 2, 1,5-DMT product produced in
the Cyclization Step can be added to the mixture crystallized in the Crystallization
Step. As discussed hereinabove, 1,5-DMT is a low melting component and can be used
to adjust the HM/LM ratio so that it meets the requirements of equation (5).
The following examples (of which Examples 2 and 6 are comparative)
will serve to further illustrate the method of this invention; however, they are
not intended to limit the scope thereof.
Feed mixtures corresponding to that shown in the following Tables
1 and 2 were crystallized at the temperatures indicated in the tables using a
scraped-wall crystallization apparatus as described hereinabove. The crystallizer
had a volume of 5 gal. and the scraper had Teflon® blades scraping the crystallizer
wall. The feed mixtures used for the crystallization runs reported in the tables
were prepared by the alkenylation process. As shown, the feed mixtures contained
various amounts of lights or 1,5-dimethyltetralin as some of the low melting components.
The feed materials were processed through the scraped-wall crystallizer in a continuous
manner. Samples were analyzed by gas chromotography to determine their composition.
Also, the scraped-walled crystallizer used for these experiments was equipped with
a viewing port to allow for the observation of the internals of the crystallizer
to see if there was an unusual or excessive build-up of rime. Each crystallization
run lasted approximately 16 hours.
As the results in Tables 1 and 2 show, when the HM/LM ratio for the
crystallization feed at crystallization temperature T in degrees Fahrenheit was
less than the value (0.03 (T-50) + A), the crystallization was successful in the
scraped-wall crystallizer producing 2,6-dimethylnaphthalene in high yield and purity.
However, when the value of HM/LM was not less than (0.03 (T-50) + A), the crystallizer
Feed Components (wt.%) Crystallization Run # 1 2 3 4 5 6 "Lights"a24.024.035.37.20.74.0 2-MN18.104.22.168.10.60.9 1-MN22.214.171.124.10.50.3 1,5-DMN126.96.36.199.513.39.2 1,6-DMN6.56.55.027.641.233.0 2,6-DMN55.755.741.843.539.041.4 1,7-DMN0.50.50.21.41.80.8 2,7-DMN0.70.70.66.12.49.3 Heavies0.10.10.12.50.41.0 CONDITIONS HM/LMb°C2.02.01.31.51.21.6 Crystallization Temp.°C (°F)29 (85)21 (70)21 (70)21 (70)29 (85)21 (70) 0.03 (T-50) + 1.0*○188.8.131.52.62.11.6 RECOVERY OF 2.6-DMN FROM CRYSTALLIZATION Yield of 2,6-DMN, wt.%77.0Inoperable66.777.875.6Inoperable Purity of 2,6-DMN, wt.%97.9NA97.797.599.0NA
a Lights other
than 1-MN produced during the preparation of 2,%dimethylnaphthalene by the alkenylation
process. Lights have a boiling point below about 470°F, at atmospheric distillation
pressure.b Weight ratio of high melting (HM) components, i.e.,
1,5-DMN, 2,6-DMN, 2,7-DMN and 2-MN, in feed mixture to low melting (LM) components,
i.e., 1,6-DMN, 1,7-DMN,1-MN and other lights, and heavies.*○
The numerical values in this
row of the table correspond to the relationship 0.054 (t-10) + 1.0 where t is expressed
in degrees Celcius.
Feed Components (wt.%) Crystalllzatlon Run #7 8 9 10 1,5-DMT38.8184.108.40.206 "Lights" a220.127.116.11.6 2-MN0.20.20.22.0 1-MN0.10.10.10.9 1,5-DMN18.104.22.168.6 1,6-DMN22.214.171.1247.3 2,6-DMN47.741.841.843.0 1,7-DMN0.30.30.31.2 2,7-DMN0.60.50.56.2 Heavies0.10.40.42.6 CONDITIONS HM/LMb1.00.80.81.4 Crystallization Temp.,°C (°F)21 (70)21 (70)10 (50)21 (70) *0.03 (T-50) + 1.01.61.61.01.6 RECOVERY OF 2.6-DMN FROM CRYSTALLIZATION Yield of 2,6-DMN, wt.%67.867.571.076.6 Purity of 2,6-DMN, wt.%99.999.999.995.4
a Lights other than 1-MN and 1,5-DMT
produced during the preparation of 2,6-dimethylnaphthalene by the alkenylation process.
Lights have a boiling point below about 470°F, at atmospheric distillation pressure.b Weight ratio of high melting (HM) components, i.e.,
1,5-DMN, 2,6-DMN, 2,7-DMN, and 2-MN in feed mixture to low melting (LM) components,
i.e., 1,6-DMN, 1,7-DMN, 1-MN and 1,5-DMT and other lights, and heavies.* see footnote to Table I
Verfahren zur Gewinnung von kristallinem 2,6-Dimethylnaphthalin umfassend ein
Kristallisieren in einem Kratzwand-Kristallisationsapparat bei einer Kristallisationstemperatur
T von einer Mischung niedrigschmelzender Komponenten, LM, mit Schmelzpunkten von
70°F und darunter, und hochschmelzender Komponenten (HM), welche 2,6-Dimethylnaphthalin
einschließen, mit Schmelzpunkten über 21°C (70°F), so daß
(5a) HM / (LM) < 0,03 (T - 50) + A
(5b) HM / (LM)< 0,054 (t - 10) + A
wobei HM die Gesamtgewichtsprozente hochschmelzender Komponenten, welche 2,6-Dimethylnaphthalin
einschließen, in der Mischung sind, und LM die Gesamtgewichtsprozente niedrigschmelzender
Komponenten in der Mischung sind und wobei t die Temperatur der Kristallisation
in Grad Celsius ist (T ist die Temperatur der Kristallisation in Grad Fahrenheit)
und A nicht mehr als ca. 1,0 ist.
Das Verfahren nach Anspruch 1, wobei die Mischung durch einen Alkenylierungsprozeß
hergestellt wird, welcher umfaßt: Alkenylieren von o-Xylol mit 1,3-Butadien in
Gegenwart eines Alkalimetalls, um ortho-Tolylpenten zu bilden, Cyclisieren von
ortho-Tolylpenten, um 1,5-Dimethyltetralin zu bilden, Dehydrieren des Dimethyltetralins,
um eine Mischung zu bilden, welche 1,5-Dimethylnaphthalin umfaßt, und Isomerisieren
des 1,5-Dimethylnaphthalins, um die Mischung zu bilden, welche 2,6-Dimethylnaphthalin
Das Verfahren nach Anspruch 2, wobei die hochschmelzenden Komponenten, HM,
2,6-Dimethylnaphthalin, 1,5-Dimethylnaphthalin, 2,7-Dimethylnaphthalin und 2-Methylnaphthalin
umfassen, und die niedrigschmelzenden Komponenten, LM, die Schweren, die während
des Alkenylierungsprozesses erzeugt wurden, die Leichten, die während des Alkenylierungsprozesses
erzeugt wurden, und 1,6- und 1,7-Dimethylnaphthalin umfassen.
Das Verfahren nach Anspruch 2, wobei die niedrigschmelzenden Komponenten 1,5-Dimethyltetralin
Das Verfahren nach Anspruch 2, wobei die niedrigschmelzenden Komponenten die
Leichten umfassen, die während des Alkenylierungsprozesses erzeugt wurden, und
wobei die Mischung, die in dem Kratzwand-Kristallisationsapparat kristallisiert
wurde, wenigstens ca. 5 Gewichtsprozent der Leichten enthält.
Das Verfahren nach Anspruch 3, wobei die Leichten Komponenten mit Siedepunkten
unter dem Siedepunkt von 2-Methylnaphthalin, das in dem Mischung vorhanden ist,
umfassen, und die Schweren Komponenten mit Siedepunkten über dem Siedepunkt von
jedem der Dimethylnaphthaline in der Mischung umfassen.
A method for recovering crystalline 2,6-dimethylnaphthalene comprising crystallizing
in a scraped-wall crystallizer apparatus at crystallization temperature T, a mixture
of low melting components, LM, having melting points of 70°F and below, and high
melting components (HM), including 2,6-dimethylnaphthalene, having melting points
above 21°C (70°F) such that:
(5a) HM / (LM)< 0.03 (T -50) + A or(5b) HM / (LM) < 0.054 (t-10) + A
where HM is the total weight percent high melting components, including 2,6-dimethylnaphthalene,
in the mixture, and LM is the total weight percent of low melting components in
the mixture and where t is the temperature of the crystalization in degrees Celsius
(T is the temperature of the crystallization in degrees Fahrenheit), and A is no
more than 1.0.
The method of Claim 1 wherein the mixture is prepared by the alkenylation process
comprising, alkenylating o-xylene with 1,3-butadiene in the presence of an alkali
metal to form orthotolylpentene, cyclizing orthotolylpentene to form 1,5-dimethyltetralin,
dehydrogenating the dimethyltetralin to form a mixture comprising 1,5-dimethylnaphthalene,
and isomerizing the 1,5-dimethylnaphthalene to form the mixture comprising 2,6-dimethylnaphthalene.
The method of Claim 2 wherein the high melting components, HM, comprise 2,6-dimethylnaphthalene,
1,5-dimethylnaphthalene, 2,7-dimethylnaphthalene and 2-methylnaphthalene and the
low melting components, LM, comprise heavies produced during the alkenylation
process, lights produced during the alkenylation process, and 1,6- and 1,7-dimethylnaphthalene.
The method of Claim 2 wherein the low melting components include 1 ,5-dimethyltetralin.
The method of Claim 2 wherein the low melting components comprise lights produced
during the alkenylation process and wherein the mixture crystallized in the scraped-wall
crystallizer contains at least about 5 weight percent lights.
The method of Claim 3 wherein the lights comprise components having boiling
points less than the boiling point of 2-methylnaphthalene present in the mixture,
and heavies comprise components having boiling points higher than the boiling point
of any of the dimethylnaphthalenes in the mixture.
Procédé de récupération de 2,6-diméthylnaphtalène cristallin comprenant la
cristallisation dans un appareil de cristallisation à paroi raclée à une température
de cristallisation T, d'un mélange de composants à bas point de fusion, LM, ayant
un point de fusion de 21°C (70°F) et inférieur, et de composants à haut point de
fusion (HM) incluant le 2,6-diméthylnaphtalène, ayant un point de fusion supérieur
à 21°C (70°F), de telle sorte que :
(5a) HM/LM < 0,03 (T - 50) + A
(5b) HM/LM < 0,054 (t - 10) + A
où HM est le pourcentage en poids du total des composants à haut point de fusion,
incluant le 2,6-diméthylnaphtalène, dans le mélange, et LM est le pourcentage en
poids du total des composants à bas point de fusion, dans le mélange et où t est
la température de cristallisation en °C (T est la température de cristallisation
en °F), et A ne dépasse pas environ 1,0.
Procédé suivant la revendication 1, dans lequel le mélange est préparé par
le traitement d'alcénylation comprenant l'alcénylation d'o-xylène avec du 1,3-butadiène
en présence d'un métal alcalin pour former un ortho-tolylpentène, la cyclisation
de l'ortho-tolylpentène pour former la 1,5-diméthyltètraline, la déshydrogénation
de la diméthyltétraline pour former un mélange comprenant du 1,5-diméthylnaphtalène
et l'isomérisation du 1,5-diméthylnaphtalène pour former le mélange comprenant
Procédé suivant la revendication 2, dans lequel les composants à haut point
de fusion, HM, comprennent le 2,6-diméthylnaphtalène, le 1,5-diméthylnaphtalène,
le 2,7-diméthylnaphtalène et le 2-méthylnaphtalène, et les composants à bas point
de fusion, LM, comprennent des produits lourds obtenus pendant le traitement d'alcénylation,
des produits légers obtenus pendant le traitement d'alcénylation, ainsi que le
1,6-diméthylnaphtalène et le 1,7-diméthylnaphtalène.
Procédé suivant la revendication 2, dans lequel les composants à bas point
de fusion comprennent la 1,5-diméthyltétraline.
Procédé suivant la revendication 2, dans lequel les composants à bas point
de fusion comprennent les produits légers obtenus pendant le traitement d'alcénylation
et dans lequel le mélange cristallisé dans le cristallisoir à paroi raclée contient
au moins environ 5% en poids de produits légers.
Procédé suivant la revendication 3, dans lequel les produits légers comprennent
des composants ayant un point d'ébullition inférieur au point d'ébullition du 2-méthylnaphtalène
présent dans le mélange, et les produits lourds comprennent des composants ayant
un point d'ébullition supérieur au point d'ébullition de l'un quelconque des diméthylnaphtalènes
présents dans le mélange.