Removal and recycling of catalysts in chlorinated pricess streams

A catalyst, such as FeCl.sub.3, useful in the production of chlorinated hydrocarbons such as 1,1-dichloroethane is removed from the effluent of a process reactor and recycled. Hydrochloric acid is removed from the process stream resulting in the catalyst present in the process stream in solution precipitating out of solution. Then it can be removed from the process stream by conventional separation techniques. Alternatively, the catalyst present in the process stream as a solid, without the removal of HCl, is separated from the liquid present by means of a cyclone and recycled. In both cases, the catalyst retains its catalytic activity.

BACKGROUND OF THE INVENTION 
This invention relates to the treatment of chlorinated hydrocarbon process 
streams to remove and recycle metallic impurities such as ferric iron. 
Chlorinated hydrocarbons possess various utilities as, for example, 
solvents and pesticides and as intermediates in organic synthesis. 
A number of valuable chlorinated hydrocarbons such as 1,1-dichloroethane, 
1,2-dichloroethane, 1,1,2,2-tetrachloroethane, and 1,1,1-trichloroethane, 
ethyl chloride and analogous chlorinated derivatives of higher 
hydrocarbons such as propane or butane are commonly made by liquid phase 
catalytic hydrochlorination or chlorination of the corresponding 
unsaturated precursor such as ethylene, vinyl chloride or vinylidene 
chloride. Metallic halides, particularly ferric chloride, are often the 
catalysts in these processes. However, the removal of ferric iron or other 
metallic contaminants that result from the use of these catalysts has been 
a long-standing problem. The presence of metalic ions, particularly in the 
form of ferric chloride catalysts, during the flashing and recovery of the 
desired chlorinated hydrocarbons causes dehydrochlorination of the desired 
chlorinated hydrocarbons and subsequent polymerization of the resulting 
unsaturated products. This results in the production of tars which must be 
disposed of as hazardous wastes. 
Various techniques have been proposed to remove the ferric iron or other 
metallic contaminants from chlorinated hydrocarbon process streams. Soviet 
Union Pat. No. 530,877 discloses the use of a reducing agent such as 
reduced iron, stannous chloride, or cuprous chloride to reduce Fe(III) to 
Fe(II) to facilitate the precipitation of the iron. U.S. Pat. No. 
4,533,473 describes the removal of metallic contaminants by contacting the 
process stream with a dilute aqueous solution of a mineral acid in which 
the contaminant is generally soluble. The contaminant can then be removed 
with the dilute mineral acid. Other patents, such as U.S. Pat. No. 
4,412,086 and U.S. Pat. No. 4,307,261, describe the use of hydrocarbon 
oils which are less volatile than the desired products and in which ferric 
iron is less soluble to separate the ferric iron from the desired 
products. The more volatile hydrocarbons are removed by flashing or 
fractional distillation and the iron and less volatile oils are left 
behind. The iron is not soluble in the remaining hydrocarbon oil and 
precipitates out and can then be separated. 
These techniques are not without problems. The catalyst recovered generally 
has lost most or all of its catalytic activity. Further, the processes 
necessary to remove the iron or other catalysts frequently require 
multiple steps and the building and maintenance of special equipment. 
Thus, what is needed is a method of removing the ferric iron or other 
metallic contaminants from chlorinated hydrocarbon process streams that is 
simple, efficient and economical and that retains the iron in a form with 
its catalytic activity either unchanged or minimally changed so that the 
catalyst may be recycled. 
SUMMARY OF THE INVENTION 
The present invention is such a process for the recycling of a catalyst, 
useful in reactions for the production of chlorinated hydrocarbons, which 
is present in a liquid process stream with the chlorinated hydrocarbon 
products and other components, comprising 
(a) separating the catalyst present as a solid from the liquid process 
stream; and 
(b) returning the separated catalyst to the process reactor. 
It is surprising that the activity of the catalyst is not affected to a 
significant extent by this process.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
In a preferred embodiment of this invention, the process stream component 
in which the catalyst is most soluble in removed from the process stream 
prior to separating the solid catalyst from the liquid process stream. The 
removal of this process stream component results in the separation of a 
larger portion of the catalyst from the liquid process stream. 
The present invention may be used in any process for the production of 
chlorinated hydrocarbons which has the following characteristics: 
(1) a liquid process stream is present; 
(2) said process stream is contaminated with a Friedel-Crafts catalyst such 
as FeCl.sub.3 or AlCl.sub.3 ; 
(3) said catalyst, if soluble, is soluble in a component of the process 
stream other than the desired product; and 
(4) said component can be removed from the process stream without removing 
the desired product. 
Examples of such processes include the preparation of 1,2-dichloroethane 
from ethylene and chlorine; the preparation of 1,1-dichloroethane from 
vinyl chloride and HCl; the preparation of 1,1,2,2-tetrachloroethane from 
ethylene and HCl; the preparation of ethyl chloride from ethylene and HCl; 
and the preparation of 1,1,1-trichloroethane. 
The precise characteristics of the process for the preparation of the 
chlorinated hydrocarbons are not crucial to the practice of this invention 
and will change depending on the particular chlorinated hydrocarbon being 
produced. The liquid process stream from which the catalyst is removed may 
be the effluent from the reactor of a single stage process or a 
multi-stage process. It may be at any temperature, pressure and rate of 
flow at which the process of the present invention may be practiced and 
the most preferred conditions will vary depending on the nature of the 
components of the process stream and on the reactor design and can be 
readily selected by one skilled in the art. 
The catalyst to be removed from the process stream may be any 
Friedel-Crafts catalyst useful in the processes described herein. It is 
preferred that the catalyst be a metallic halide and more preferred that 
the catalyst be AlCl.sub.3 or FeCl.sub.3. In the most preferred embodiment 
of the invention, the catalyst is FeCl.sub.3. The amount of catalyst that 
is present in a chlorinated hydrocarbon process stream will, of course, 
vary depending on the particular process being practiced. The process of 
this invention is effective for process streams containing any amount of 
catalyst from about 1 part per million (ppm) by weight up to about 1 
weight percent catalyst based on the weight of the reaction mixture. It is 
preferred that the catalyst be present in an amount of at least about 4 
ppm by weight and no more than about 500 ppm by weight. It is more 
preferred that the catalyst be present at at least about 50 ppm and no 
more than about 100 ppm by weight. 
The catalyst is normally not soluble in the reaction product, but is 
soluble in contaminants present in the process stream. Examples of such 
contaminants include HCl, which is present as a reactant or by-product, 
and water. In a preferred embodiment, HCl is the contaminant to be 
removed. 
The removal of some or all of the contaminants in which the catalyst is at 
least partially soluble causes the catalyst to precipitate from the 
solution. The amount of contaminants to be removed from the process stream 
is any amount which will cause a sufficient portion of the catalyst to 
precipitate from the solution to reduce the amount of catalyst present in 
the tarpot to a sufficient level so that the amount of tars formed therein 
is significantly lowered. It is preferred that at least about 50 weight 
percent of the total contaminant is removed. It is more preferred that at 
least about 75 weight percent is removed and it is most preferred that at 
least about 90 weight percent of the total contaminant is removed. 
In the process of this invention, the contaminants are removed from the 
liquid process stream by vaporizing the contaminants while leaving the 
desired product in the liquid phase. This can be accomplished by raising 
the temperature of the process stream, lowering the pressure of the 
process stream or a combination of both or by other separation techniques 
known to the art. It is preferred to vaporize the contaminants by rapidly 
lowering the pressure in the process stream. The pressure can be lowered 
any amount which will result in the contaminants being vaporized. It is 
preferred that the pressure be decreased to a pressure no more than 70 
percent of the original pressure. It is more preferred that the pressure 
be decreased to a pressure no more than about 50 percent of the original 
pressure. It is most preferred that the pressure in the process stream be 
lowered to a pressure which is about 30 percent of the original pressure. 
This pressure decrease is preferably accomplished in a relatively short 
period of time. It is preferred that the pressure drop occur in no more 
than one second. It is more preferred that the pressure drop occur in less 
than 0.1 second. Any means for lowering the pressure that results in a 
pressure drop sufficient to vaporize the contaminants is operable in the 
practice of the process of this invention. Examples of suitable techniques 
include valves, restricting orifices, small piping or equipment such as 
heat exchangers. It is preferred to use a valve to lower the pressure. 
The contaminants, after being vaporized, are removed from the process 
stream. The way in which the contaminants are removed is not critical so 
long as the contaminants leave the process stream while the desired 
products and the catalyst remain in the process stream. It is preferred to 
remove the contaminants by means of a vent and in such a way that the 
contaminants, if valuable, are not lost. 
The pressure in the process stream as it leaves the reactor may be left 
unchanged or may be increased by pumping or other means prior to the 
removal and recycling of the catalyst by the practice of this invention. 
Similarly, the rate of flow in the process stream may be left unchanged or 
modified by pumping or other means prior to the removal and recycling of 
the catalyst by the practice of this invention. The practice of this 
invention does not require special pressure or pumping conditions other 
than that the conditions be such that the process stream is in the liquid 
phase and the contaminants may be selectively removed by vaporization. 
Within this limitation, the pressure and pumping conditions may be 
optimized to meet the requirements of the overall process for the 
preparation of the chlorinated hydrocarbons. It is preferred that the 
pressure be at least about 0 psig and no greater than about 100 psig. 
Any temperature at which the components of the process stream, with the 
exception of the catalyst, are in the liquid phase and the contaminants in 
which the catalyst is most soluble may be vaporized is operable in the 
practice of this invention. The preferred temperature ranges will depend, 
at least in part, on the particular chlorinated hydrocarbon being produced 
and the process by which it is produced. It is most preferred that the 
temperature of the process stream be unchanged from what it would be in 
the absence of this invention. That is, it is most preferred that the 
process of recycling the catalyst be conducted at the temperature at which 
the process stream would normally exist. 
Removal of the process stream contaminants in which the catalyst is most 
soluble causes the catalyst to precipitate out of solution. It is 
preferred that the catalyst originally be present both in solution and in 
colloidal form. Thus, when the catalyst in solution precipitates out of 
solution, it precipitates onto the colloidal catalyst already present and 
increases the size of the catalyst particles to a point where the catalyst 
can be removed from the process stream for returning to the process 
reactor for recycling by conventional techniques for the separation of 
solids and liquids. Examples of such methods include filtration, 
centrifugation and use of a cyclone. It is preferred to separate the solid 
from the liquid by means of a cyclone. The amount of catalyst removed from 
the process stream and recycled may be any amount which will reduce the 
catalyst present in the process stream so as to decrease the formation of 
tars in the tarpot by an amount essentially equal to the percent of 
catalyst removed. As an example, if 85 weight percent of the catalyst is 
removed, the formation of tars will be decreased by about 85 weight 
percent. It is preferred that at least about 50 percent on a weight basis 
of the catalyst is removed resulting in a decrease in tar formation of 
about 50 weight percent. It is more preferred that at least about 75 
weight percent of the catalyst is removed resulting in a decrease in tar 
formation of about 75 weight percent and it is most preferred that at 
least about 90 percent is removed resulting in a decrease in tar formation 
of about 90 weight percent. 
When the removal of less than about 50 weight percent of the catalyst will 
provide a satisfactory reduction in the formation of tars under process 
conditions, such removal may be obtained without the removal of the 
process stream component in which the catalyst is most soluble. Under many 
process conditions, some of the catalyst will be present in solid form and 
a significant portion of this catalyst may be removed by the practice of 
this invention. In particular, a significant portion of the catalyst may 
be removed by using a cyclone to separate the solid and the liquid. It is 
preferred that at least about 25 weight percent of the catalyst is removed 
without the removal of the process stream component in which the catalyst 
is most soluble. This results in a 25 weight percent decrease in tar 
formation. It is more preferred that at least about 35 weight percent is 
removed resulting in about a 35 percent decrease in tar formation and most 
preferred that at least about 50 weight percent is removed resulting in a 
decrease in tar formation of about 50 percent. 
When the solid catalyst is separaed from the liquid process stream 
containing primarily the chlorinated hydrocarbon product, the amount of 
liquid going with the catalyst to be recycled may vary depending on the 
overall process requirements. It is preferred that the ratio of the liquid 
and solid catalyst being returned to the reactor for recycling to the 
liquid going on to the next stage of the process range from about 3:1 to 
about 1:12. It is more preferred that this ratio range from about 2:1 to 
about 1:3. It is most preferred that the ratio be about 1:1. The amount of 
liquid going with the catalyst to be recycled may be controlled by the use 
of a valve or choice of cyclone size. It is preferred that it be 
controlled by means of a valve. 
The catalyst being recycled maintains a high degree of catalytic activity. 
It is preferred that the catalyst maintain at least about 50 percent of 
the activity it had prior to being separated from the process stream and 
returned to the reactor for recycling. It is more preferred that the 
catalyst maintain at least 75 percent of its activity and most preferred 
that it maintain at least about 90 percent of its activity. 
A more thorough understanding of this invention may be obtained by 
reference to FIG. 1 which outlines a process for the liquid phase reaction 
of hydrogen chloride and vinyl chloride in the presence of a homogeneous 
FeCl.sub.3 catalyst to form 1,1-dichloroethane. It should be noted that 
the figure refers to a preferred embodiment of the invention and is 
presented to offer a better understanding of it, but the figure should not 
be interpreted as limiting the invention in any way. 
In FIG. 1, reactant streams 1 and 2 represent respectively the reactants, 
vinyl chloride and hydrogen chloride. Reactant stream 3 represents the 
catalyst, FeCl.sub.3. The liquid phase reactor is represented by 4. The 
process stream 6 is the effluent from the reactor 4 and contains 
1,1-dichloroethane, unreacted HCl and unreacted vinyl chloride, all in the 
liquid phase. FeCl.sub.3 is also present both in solution and as colloidal 
iron. It is present at a level of approximately 500 ppm (parts per 
million). The rate of flow of process stream 6 is about 70 gallons per 
minute and its temperature is about 50.degree. C. The pressure in the 
process stream 6 is increased to about 100 psig from the about 55 psig in 
the reactor 2 by means of a pump 5 in the process line 6. The pressure in 
the process stream 6 is rapidly reduced to about 35 psig by means of a 
valve 7 and HCl and vinyl chloride are removed from the process stream as 
vapors by means of a vent 8 through process line 9. This results in the 
removal of about 75 weight percent of HCl. Since the FeCl.sub.3 is soluble 
in HCl and less soluble in 1,1-dichloroethane, this results in more than 
95 percent on a weight basis of the FeCl.sub.3 present in the solution 
precipitating out onto the colloidal iron already present. Process stream 
10 now contains predominantly 1,1-dichloroethane and FeCl.sub.3 and enters 
a cyclone 11 where at least about 50 percent of the FeCl.sub.3 is removed 
as the bottoms and the overflow in process stream 12 of the cyclone 11 
contains 1,1-dichloroethane, a small amount of FeCl.sub.3, vinyl chloride 
and hydrogen chloride. The bottoms contain FeCl.sub.3 and 
1,1-dichloroethane which are recycled to the reactor 4 via process stream 
14. The amount of 1,1-dichloroethane leaving the cyclone 11 as bottoms is 
controlled by a valve 13. The rate of flow of the process stream 14 
containing the bottoms is about 5 to about 35 gallons per minute and its 
pressure and temperature are about 35 psig and about 55.degree. C. 
respectively. The FeCl.sub.3 recycled to the reactor 4 has virtually the 
same catalytic activity as fresh catalyst. The overflow stream 12 flows at 
a rate of about 65 gallons per minute. Its temperature is about 55.degree. 
C. and its pressure is about 35 psig. The 1,1-dichloroethane, small 
amount of FeCl.sub.3, vinyl chloride and hydrogen chloride in the overflow 
stream 12 enter a vessel 15 where the 1,1-dichloroethane is flashed 
overhead and removed in process stream 16 while the bottoms are removed 
through process stream 17 for disposal. 
The following examples are given to illustrate the invention, but should 
not be interpreted as limiting it in any way. Unless stated otherwise, all 
parts and percentages given are by weight. 
COMATIVE EXAMPLE 1 
Determination of FeCl.sub.3 Particle Size in Reactor Effluent (Not an 
embodiment of the invention) 
Samples are taken from a 1,1-dichloroethane process stream feeding a tarpot 
by means of a sample line fitted with a Nupro.RTM. sintered metal filter. 
Three filters are used, having 2, 7 and 15 micron pore sizes respectively. 
In each instance, approximately 20 ml of filtered liquid is run into a 
tared 2-ounce bottle. A weighed amount, approximately 75 g, of 0.1N HCl is 
added to the bottle, it is shaken for 10 minutes and the FeCl.sub.3 is 
extracted into the aqueous phase. The sample is analyzed for iron by means 
of atomic absorption (AA). An unfiltered sample is simultaneously taken 
with each filtered sample and also analyzed for Fe by AA. The results 
obtained are presented in Table I below. 
TABLE I 
______________________________________ 
Fe Remaining in Filtered vs. Non-Filtered 
Samples 
Filter Size Fe Content 
Fe Removal 
(microns) (ppm) (%) 
______________________________________ 
2 89 28.9 
unfiltered 125 -- 
7 123 6.1 
unfiltered 131 -- 
15 113.5 9.2 
unfiltered 125 -- 
______________________________________ 
The information in Table I shows that, untreated, the particle size of the 
iron is quite small and that even with a 2 micron filter, only about 28.9 
percent of the iron can be removed by filtration. 
EXAMPLE 1 
Effect of Removal of HCl from Chlorinated Solvent Process Stream on the 
Particle Size of FeCl.sub.3 
Three unfiltered samples are taken from the process stream in the same 
manner as in Example 1 and analyzed for Fe by AA. Each sample is then 
allowed to stand with the bottle cap removed. A small nitrogen purge is 
placed on the head space to prevent the absorption of water from the 
atmosphere. HCl evolves from the solution as a vapor. At 15- and 75-minute 
intervals, the liquid in the bottles is sampled, filtered and analyzed for 
Fe by AA. Glass filters of 0.3 and 2.7 microns are used on the first two 
samples and a 5-10 micron filter paper is used on the last sample. The 
results of this experiment are shown in Table II below. 
TABLE II 
______________________________________ 
Fe Removal After Degassing HCl 
Filter Fe Fe 
Size Time Content Removal 
(microns) (min) (ppm) (%) 
______________________________________ 
0.3 0 65 -- 
0.3 15 2 97 
0.3 75 6 -- 
2.7 0 146 -- 
2.7 15 16 89 
2.7 75 37 -- 
5-10 0 125 -- 
5-10 15 25 80 
5-10 75 60 -- 
______________________________________ 
The above data shows that, about 15 minutes after the degassing of HCl, the 
Fe content of the samples can be decreased by 97 percent by filtration 
through a 0.3 micron filter and by almost 90 percent when using a 2.7 
micron filter. This shows that the removal of the HCl results in the 
particle size of iron increasing substantially so that it can be removed 
by conventional techniques. The increase in the amount of Fe present at 75 
minutes is probably due to the absorption of some water from the 
atmosphere into the solution thus increasing the solubility of iron and 
decreasing the ease of removing it from the solution. 
EXAMPLE 2 
Removal of FeCl.sub.3 Without removing HCl 
In a process for the production of 1,1-dichloroethane, the reactor effluent 
containing 1,1-dichloroethane, FeCl.sub.3, and HCl, at 50 psig and 
24.degree. C. is routed through a 10 mm cyclone. A 50 psi pressure drop is 
obtained across the cyclone and both the overflow and the underflow from 
the cyclone enter sample bottles at atmospheric pressure. The feed to the 
cyclone is 5.38 pounds/minute and the iron content as measured by atomic 
absorption is 116 ppm. The overflow from the cyclone is 2.51 pounds/minute 
and the iron content is 63 ppm. The underflow from the cyclone is 2.87 
pounds/minute and the iron content is 146 ppm. This indicates that the 
amount of iron removed and recycled is 45.7 percent and the amount of 
1,1-dichloroethane recycled is 53.3 percent.