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BACKGROUND OF THE INVENTION
In U.S. Pat. Nos. 3,479,395, 3,637,515, 3,668,239, 3,689,535, 3,715,388,
3,715,389, 3,743,672, 3,789,065, 3,907,874, 3,985,795, 4,045,477 and
4,073,876 there is disclosed processes for the preparation of vicinal
glycol esters by the liquid phase oxidation of an olefin, such as ethylene
or propylene in a carboxylic acid medium, such as acetic acid using a
tellurium catalyst and a source of halide ions.
The present invention is directed to an effective method of recovering the
tellurium from vicinal glycol ester solutions produced, for example, by
such above described processes and containing tellurium in the form of
soluble inorganic tellurium compounds and organotellurium compounds.
Because of the high reactivity of tellurium, in combination with a halide
source when used as a catalyst as in the above reaction its combination
with organic compounds such as the carboxylic acids and olefins employed
very frequently results in the formation of organo-tellurium compounds,
such as tetra and divalent alkyl tellurium halides, tellurium carboxylate
compounds and the compounds described for example in an article by Jan
Bergman, Kemisk Tedskrift, Vol. 88 (11) pp. 62-3, 1976, Sweden, entitled
New Production Process for Ethylene Glycol as well as other soluble
tellurium compounds which remain in solution with the glycol ester
reaction product. In such reaction, a portion of the tellurium catalyst
such as tellurium dioxide, etc. is itself or in combination with the
halide source, converted to one or more organotellurium compounds. The
type and number of organotellurium compounds which may be formed is a
function of the reaction conditions to produce the vicinal glycol ester
such as time, temperature, carboxylic acid and any solvent which might be
employed. In addition, at least some of the inorganic tellurium compounds
used as catalysts or formed in the reaction, such as tellurium
tetrabromide, may also remain in solution with the glycol ester product.
Because of the cost and toxicity of tellurium, it is essential that as much
of the tellurium be recovered from the glycol ester reaction product as is
possible and from the inorganic or organotellurium compounds in a form
suitable for reuse as a catalyst.
There is no known prior art which describes the removal and recovery of
soluble inorganic or organotellurium compounds from a vicinal glycol ester
product by adsorption on granular activated carbon and prepared by the
tellurium catalyzed acetoxylation of olefins.
SUMMARY OF THE INVENTION
This invention relates to a process for the removal and recovery of
tellurium from organic solutions containing soluble inorganic or organic
tellurium compounds. More specifically, the present invention concerns a
process for the granular activated carbon adsorption of tellurium
compounds from glycol ester solutions obtained from the tellurium
catalyzed liquid phase reaction of an olefin, molecular oxygen and an
aliphatic monocarboxylic acid in the presence of a halide ion as described
for example in any of the aforementioned United States patents the
processes of which are incorporated herein by reference. The crude vicinal
glycol ester products produced by such processes, which may contain one or
more soluble organotellurium compounds as well as soluble inorganic
tellurium compounds, are percolated through, or intimately contacted with,
granular activated carbon to adsorb the soluble tellurium compounds
leaving a tellurium-free vicinal glycol ester reaction product which may
be processed to recover the ester product and by products and any
undesirable or unrecoverable material burned, if desired for fuel value
without loss of valuable tellurium. The tellurium may be recovered from
the activated carbon by washing with for example, acetic acid followed by
purging with a mineral acid such as hydrochloric, nitric, etc. and/or with
steam. The tellurium enriched wash solution may be subjected to stripping
or distillation to remove water and recover acid leaving a tellurium
compound concentrate or residue which may be treated to recover the
tellurium in a form suitable for reuse in the vicinal glycol ester
synthesis reaction.
Advantages provided by the process of the present invention, are (1) it is
an adsorption process and therefore not dependent upon differences in the
relative volatilities of the tellurium and non-tellurium containing
components of the glycol ester tellurium-containing solutions as would be
associated with possible distillation recovery methods and (2) there is no
dependence upon relative solubilities of the tellurium and non-tellurium
containing components as related to possible liquid-liquid extraction
methods of recovery.
It is an object of this invention therefore to provide a process for the
substantial recovery of valuable tellurium from tellurium-containing
vicinal glycol ester solutions and the ultimate purification of the glycol
ester.
It is another object of this invention to provide a process for the
recovery of tellurium in a form suitable for recycle and reuse as a
catalyst for the synthesis of vicinal glycol esters by the liquid phase
oxidation of an olefin in an aliphatic carboxylic acid medium.
It is a further object of this invention to recover contained tellurium
values from tellurium-containing vicinal glycol ester solutions utilizing
an activated carbon to absorb the soluble tellurium compounds from the
solutions and to recover the tellurium from the activated carbon for
conversion to a form suitable for recycle and resue in the vicinal glycol
esters synthesis process.
These and other objects and advantages of this invention will become
apparent from the description of the invention which follows and from the
claims.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the present invention, a vicinal glycol ester solution
containing soluble tellurium compounds, as for example, an ethylene glycol
ester solution obtained by reacting under liquid phase oxidative
conditions, ethylene, molecular oxygen and an aliphatic monocarboxylic
acid such as acetic acid at a temperature of from about 80.degree. C. to
200.degree. C. in the presence of an effective amount of a tellurium
catalyst such as tellurium dioxide in combination with a source of halide
ions such as hydrobromic acid, is contacted with granular activated carbon
by percolation of the tellurium-containing glycol ester solution through a
bed of the carbon or is intimately slurried with the carbon to adsorb the
contained soluble tellurium compounds leaving an essentially tellurium
free vicinal glycol ester reaction product which may then be processed by
conventional methods to recover the desired vicinal glycol ester product
and by-products. The activated carbon containing the tellurium compound
adsorbate is then subjected to an acid wash followed by purging with steam
and/or a mineral acid to desorb the tellurium compounds from the activated
carbon and form tellurium-containing wash solution. The
tellurium-containing wash solution is then stripped or distilled to remove
water and the acids leaving a tellurium compound concentrate or residue.
The tellurium compound concentrate or residue containing various tellurium
compounds may be treated to recover the tellurium in catalytically useful
form. One method is to convert the tellurium, in the presence of air or
oxygen, to tellurium dioxide at temperatures of from about 600.degree. C.
to 1000.degree. C. preferably 700.degree. C. to 950.degree. C. and recover
the TeO.sub.2 from the effluent reactor stream by cooling to collect the
TeO.sub.2.
Tellurium per se, which may be present in the crude vicinal glycol ester
reaction product is insoluble and may be and is preferably recovered,
along with any other insoluble tellurium compounds, by filtration prior to
treatment of the reaction product with activated carbon to remove the
soluble tellurium compounds.
The amount and type of tellurium compounds in the crude vicinal glycol
ester reaction product will generally depend on the type and amount of
tellurium compound and halide ion source employed to produce the glycol
ester as well as the reaction conditions and ester being produced. Thus
the amount of soluble tellurium in the form of inorganic tellurium
compounds and/or organotellurium compounds can range from about 0.25
percent to 1.5 percent or more by weight of the glycol ester produced, for
example, by the processes as set forth in U.S. Pat. Nos. 3,668,239 and
3,715,389 noted above.
The carboxylic acids employed to prepare the vicinal glycol esters are
generally used as solvent as well as to supply the moiety for the
subsequent ester produced and are preferably the lower aliphatic
monocarboxylic acids containing 1 to 4 carbon atoms, especially acetic
acid, although other inert solvents such as water, tetrahydrofuran,
dioxane, etc. may be employed in the process in addition to the
monocarboxylic acid reactant. The separation and recovery of the soluble
tellurium compounds by employing activated carbon according to the present
invention, is not dependent upon the concentration of the carboxylic acid
reactant-solvent, the major component, in addition to the ester and glycol
products produced. The reaction product or effluent reaction product
stream should be fluid enough to pass through or be able to be filtered
from the activated carbon employed. Generally, the concentration of the
carboxylic acid should be in the range of between 10 and 90 weight percent
and preferably in the 20 to 40 weight percent range.
The activated carbon which may be employed in the process of the invention
is an amorphous form of carbon which generally has a surface area ranging
from about 300 to 2000 m.sup.2 /g. and is usually a dense, hard and
regenerable granular activated carbon intended for packed bed adsorption
application. The pore structure of such carbons are generally controlled
to provide a broad range of pore sizes with the larger pore sizes being
predominant. Such activated carbons may be prepared from a variety of
materials of animal, vegetable or mineral origin such as bone char, wood,
hard and soft coal, lignite, coconut shells, coke and petroleum residues.
The preparation of activated carbon including some liquid phase and vapor
phase applications appears in the Kirk and Othmer, Encyclopedia of
Chemical Technology, 2nd Edition, Volume 4, pp. 149-157. Typical of the
activated carbons commercially available which may be employed in the
process of the present invention are for example, (1) "Nuchar WV-G"
prepared from bituminous coal and sold by Westvaco, Chemical Division and
having an iodine number (minimum of 1050, a particle size (U.S. Sieve
Series) of approximately 12.times.40, an apparent density of 27.5
lb./ft..sup.3 and a surface area (nitrogen BET method) of 1100 m.sup.2 /g.
and (2) Type "SGL", "CAL" and "OL" granular carbons prepared from
bituminous coal and sold by the Calgon Corporation having iodine numbers
(minimum) of 900, 1000, and 1000, particle size of approximately
8.times.30 mesh, 12.times.40 mesh and 20.times.50 mesh, apparent densities
of 30, 27.5 and 28.1 lb./ft..sup.3, and a surface area (N.sub.2, BET
method) of 950-1050, 1000-1100, and 1000-1100 m.sup.2 /g. respectively.
The tellurium adsorption process of this invention may generally be carried
out at temperatures of from about ambient to temperatures of about
95.degree. C. and preferably between about 15.degree. C. and 30.degree. C.
Higher or lower temperatures may be employed but are limited by the
volatility of the lowest boiling components in the reaction solution to be
treated and the freezing point of the reaction solution or the temperature
at which the viscosity increase inhibits proper flow through or intimate
mixture with the activated carbon respectively.
After the crude tellurium compound containing vicinal glycol ester solution
has been treated with the activated carbon to essentially remove the
soluble tellurium compounds and separated therefrom it may be processed by
any known method to recover the ester product. The activated carbon with
the tellurium compounds adsorbed thereon is then treated to recover the
tellurium. A preferred method is to acid wash the carbon with a carboxylic
acid similar to the ester moiety of the crude vicinal glycol ester
processed to remove any entrained ester product and then purge the carbon
with steam and/or a mineral acid to desorb the tellurium from the carbon.
The wash-purge solution containing the recovered tellurium compounds is
then stripped or distilled to remove contained water and acid leaving a
tellurium compound concentrate or residue. The tellurium compound
concentrate containing various tellurium compounds is then combusted as
hereinabove described to recover the tellurium in catalytically useful
form.
Although the process of the present invention will be directed to the
treatment for the removal and recovery of tellurium compounds from a crude
vicinal glycol ester solution which is an ethylene glycol diacetate
solution containing tellurium compounds as well as other by-products and
produced by the liquid phase oxidation of ethylene and acetic acid with
molecular oxygen in the presence of tellurium dioxide and hydrobromic acid
as set forth in U.S. Pat. No. 3,715,389, it is not intended that the
process be limited to such ethylene glycol diacetate solution and those
skilled in the art will recognize that the present process is broadly
applicable to the treatment of other vicinal glycol ester solutions such
as ethylene glycol diformate, dipropionate, dibutyrate, diisobutyrate,
etc. as well as the propylene glycol diesters, 2,3-butandiol diesters,
etc. which have been prepared, for example, by the tellurium catalyzed
processes as described in the above noted U.S. patents.
The following Examples are provided to illustrate the recovery of tellurium
compounds from a glycol ester solution in accordance with the principles
of this invention but are not construed as limiting the invention in any
way except as indicated by the claims.
In the Examples which follow the ethylene glycol diacetate solution was
obtained by taking the effluent from a tellurium oxide catalyzed
conversion of ethylene with acetic acid, hydrobromic acid, 2-bromoethyl
acetate and oxygen as described in U.S. Pat. No. 3,715,389. The crude
ethylene glycol diacetate solution after filtration to remove insoluble
components contained approximately 24.74 percent acetic acid, 0.86 percent
hydrobromic acid, 1.25 percent bromoacetic acid, 0.36 percent soluble
tellurium as tellurium compounds, 5.0 percent water, 61.79 percent acetate
and formate esters of ethylene glycol and diethylene glycol and 6.0
percent of unidentified high molecular weight by-product material.
EXAMPLE 1
20 grams of the crude ethylene glycol ester solution containing 0.36
percent total soluble tellurium was percolated through a 0.5 inch diameter
glass column containing a 6 inch bed of 12.times.40 mesh activated carbon
("Nuchar WV-G", of Westvaco Chemical Division--a bituminous coal derived
activated carbon described hereinabove), followed by an acetic acid wash
to remove entrained product. X-ray analysis of two 10 gram samples of
activated carbon treated effluent showed that the total soluble tellurium
of the crude solution was reduced from 0.36 percent to 0.02 percent and
0.05 percent in the first and second 10 gram fractions respectively. The
average percent tellurium value of the effluent represented a 93 percent
tellurium removal.
EXAMPLE 2
237.6 grams of the crude ethylene glycol ester solution containing 0.36
percent (0.855 grams total soluble tellurium was percolated through a 0.75
inch diameter glass column containing 20 grams of 12.times.40 mesh
activated carbon ("Nuchar WV-G" sold by Westvaco, Chemical Division).
Table 1 below shows that 97 percent of the solution was recovered with a
tellurium content of 156 ppm as compared to 3600 ppm in the crude
solution. A total of 0.807 grams of tellurium was retained on the
activated carbon showing a capacity of approximately 1 g. tellurium/25
grams of activated carbon. After percolation the carbon was washed with
acetic acid to remove entrained product.
TABLE 1
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Fraction No.
Weight (gms.)
Tellurium %
Tellurium (gms.)
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1-16 166.09 0.010 --
17 10.51 0.03 .00315
18 10.63 0.04 .00425
19 11.22 0.05 .00561
20 10.10 0.14 .01414
21 22.06 0.04 .00882
230.61 total .03597 total.sup. (1)
Acetic Acid
Wash 57.49 0.02 .01150
Total gms. Te Charged
0.85536
Total gms. Te in Effluent
0.04747
Total gms. Te Retained
0.80789 gms./20 gms. carbon
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.sup.(1) equals 0.0156 percent Te in effluent.
EXAMPLE 3
The procedure of Example 1 was repeated using a 6 inch bed of 20.times.50
mesh activated carbon (Type "OL" granular carbon of the Calgon
Corporation, Activated Carbon Division, a bituminous coal derived from
activated carbon described hereinabove). X-ray analysis of two 10 gram
samples of the activated carbon treated effluent showed that the total
soluble tellurium of the crude solution was reduced from 0.36 percent to
0.012 percent and 0.018 percent in the first and second 10 gram fractions
respectively. The average percent tellurium value of the effluent
represents a 95 percent tellurium removal.
EXAMPLE 4
The 20 gram of activated carbon employed in Example 2 and containing the
tellurium compound adsorbate and retained in the glass column was washed
with 50 grams of acetic acid followed by a 40 gram nitric acid (95
percent) wash and a steam purge at 100.degree. C. to desorb the tellurium
compounds from the carbon and reactivate the carbon and form a
tellurium-containing wash solution. The tellurium-containing wash solution
was distilled at a temperature of from 80.degree. C. to 120.degree. C. to
remove contained water and acid leaving a tellurium compound concentrate
which was further treated by heating to a temperature of 850.degree. C. in
the presence of air to convert the tellurium contained in the concentrate
to tellurium dioxide which was recovered by cooling the effluent
air-TeO.sub.2 stream to collect the TeO.sub.2.
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