Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2002-04-17
2004-04-13
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C570S172000
Reexamination Certificate
active
06720466
ABSTRACT:
FIELD OF THE INVENTION
The invention finds applicability in 1,1,1,3,3-pentachloropropane production.
BACKGROUND OF THE INVENTION
There is a need in industry to produce halohydrocarbons that are environmentally safe as a replacement for certain halogenated chemicals that deplete the ozone layer.
Prior Art
1,1,1,3,3-Pentachloropropane (HCC240f) can be obtained by the addition reaction of carbon tetrachloride and vinyl chloride. For example, Kotora et.al. (Journal of Molecular Catalysis, Vol.77, 51-60 (1992)) added carbon tetrachloride to vinyl chloride in a batch reaction using either cuprous chloride or tetrakis(acetonitrile)copper(I) perchlorate catalyst and n-butylamine as co-catalyst. They obtained about a 97-98% yield by these methods. Zil'berman et.al. (J.Org.Chem.USSR (Engl.Transl.), Vol. 3, 2101-2105 (1967) CAS [68(10):40147p]) used a ferrous chloride hydrate catalyst with isopropanol solvent to make a product mixture containing only 81 wt % HCC240f, together with several higher molecular weight telomers. Both of these batch methods involved aqueous wash steps for the product purification. Neither method is adaptable to a continuous process in which the catalyst is to be recycled.
Rygas et.al. (U.S. Pat. No. 5,902,914, May 11, 1999) described a continuous process for the production of haloalkanes, including HCC240f, which includes catalyst recycle and purification steps. For example, carbon tetrachloride and vinyl chloride are (A) reacted in the presence of a catalyst and a cocatalyst to produce a haloalkane product stream. This stream is (B) flash-distilled” to produce a first stream comprising unreacted feed material and the cocatalyst and a second stream containing a haloalkane product and the catalyst. The second stream from (B) is then (C) filtered to remove the catalyst, and the filtrate is (D) distilled to purify the haloalkane product. Step (D) may be carried out in the presence of metal chelating agents, such as tributylphosphate, which may act to improve the distillation yield. Their preferred catalyst/cocatalyst systems were cuprous chloride/tert-butylamine or iron powder/hexamethylphosphoramide.
However, this scheme will not work for the catalyst system described herein. In our invention, the catalyst is ferrous chloride (produced in situ from the reaction of ferric chloride and iron metal), and the cocatalyst is tributylphosphate. Tributylphosphate, being a very high-boiling substance, will not go overhead in a flash distillation such as step (B) of Rygas et.al. Further, a filtration step such as step (C) is of no value for our system, since the catalyst components ferrous chloride and ferric chloride are soluble in the reactor effluent, and even more soluble in the bottoms stream from an initial distillation step.
Rygas et.al. (U.S. Pat. No. 6,187,978 Feb. 13, 2001) have also described another process for the production of haloalkanes. For example, they disclose a process in which carbon tetrachloride may be reacted with vinyl chloride in the presence of an iron-containing compound and tributylphosphate to produce a product stream. Then, in separation scheme (A), the reactor product stream may be distilled into a top stream comprising volatile reactants that are recycled, and a bottom stream that contains the HCC240f product and the catalyst complex. This bottom stream may be further distilled into a second top stream comprising the desired product, and a second bottom stream containing the catalyst complex, which is recycled. Alternatively, in separation scheme (B), the reactor product stream may be distilled into a top stream that contains the desired product and a bottom stream that contains the catalyst components. This bottom stream may be recycled, while the top stream may be distilled into a second top stream containing volatile reactants, which are recycled, and a second bottom stream, which contains the desired halocarbon product.
But separation scheme (A) would subject the catalyst components to two distillation steps before they are recycled into the reactor. Each distillation step stresses the catalyst components, causing degradation. In a process based on the reaction of carbon tetrachloride with vinyl chloride in the presence of iron chlorides and tributylphosphate, such as that described herein, the catalyst degrades by a process of chemical reactions that increase in extent with temperature, time, and catalyst concentration. The bottoms stream from the first distillation of scheme (A) is large, since it contains the desired product of the reaction. This means that the equipment used for both distillation steps of scheme (A) must be large, and the residence times in both stills must be relatively long. The catalyst components are recovered as the bottoms from the second still, where the temperature is high, the catalyst concentration is high, and the liquid residence time is long.
Separation scheme (B) is better, since the catalyst is recovered and recycled as the bottoms from the first tower. Even so, this first tower is necessarily large, since it handles the whole product load, going overhead, and so the liquid residence time is long. If one wishes to recover most of the product, then the concentration of catalyst components in the bottoms of the first tower is high, and the temperature is high. These conditions again promote rapid degradation of the catalyst. Furthermore, the reaction of the invention results in the production of two main undesired byproducts—1,1,1,3,5,5-hexachloropentane (HCC470jfdf) and 1,1,3,3,5,5-hexachloropentane (HCC470nfaf). These components, being less volatile than the desired HCC240f (b.p. 179 C), tend to stay with the catalyst components, which are either non-volatile, or have very high boiling points (tributylphosphate boils at 289 C.). Therefore, if the bottoms of the first tower are recycled, this stream carries with it a considerable amount of the hexachloropentane byproducts. These components, in the recycle stream, are harmful to the desired reaction in two ways: first, they dilute the reactants, thereby reducing the reaction rate. Second, they can react with vinyl chloride, thus consuming valuable feedstock, and produce further undesired by-products.
What is needed is a method of recovering the HCC240f, free of the hexachloropentane byproducts, which minimizes the stress placed on the catalyst components, and which separates, as much as possible, the catalyst components from the hexachloropentanes.
Wilson et al (U.S. Pat. No. 6,313,360) is directed to a process for the production of 1,1,1,3,3-pentachloropropane by reacting carbon tetrachloride (CCl
4
) and vinyl chloride in the presence of a catalyst mixture (organophosphate solvent, iron metal and ferric chloride). The process of the herein disclosed invention in superior to that of the Wilson et al in that the conditions employed are more economic and the activity of the catalyst is maintained to a far greater degree.
The prior art (Wilson et al) describes a single-stage catalyst recovery system. In prior art processes high temperature and long residence time tend to cause degradation of the catalyst. The inventors have found that by adding a second distillation step and modifying the conditions of the first distillation step a surprisingly high percentage of the desired product (1,1,1,3,3-pentachloropropane) can be recovered in pure form and the catalyst is maintained in exceptionally useful form.
The inventors have succeeded in producing a much more highly concentrated catalyst recycle stream than that embodied in U.S. Pat. No. 6,313,360. They have also succeeded in recovering a significantly higher percentage of the 1,1,1,3,3-pentachloropropane produced. Based on the prior-art work, in lab and pilot plant, the inventors have unexpectedly retained significant amounts of active catalyst in their recycle process.
OBJECTS OF THE INVENTION
A main object of the invention is to produce a process that will maximize the recovery of the catalyst.
A further object of the invention is to perform the process under relatively mild conditions.
A si
Dawkins John L.
Klausmeyer Rodney L.
Weller James J.
Wilson Richard L.
Armstrong, Kratz, Quintos Hanson & Brooks, LLP.
Price Elvis O.
Richter Johann
Vulcan Chemicals a division of Vulcan Materials Company
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