US2543575A - Method of fractionating chlorinated hydrocarbons - Google Patents

Description

Patented Feb. 27, 1951 METHOD OF FRACTIONATIN G CHLORIN- ATED HYDROCARBONS Clarence C. Harvey and Clarence M. Neher, Baton Rouge, La., and Julian Dorsky, assignors to Ethyl Corporation,

Pittsburgh, Pa., New York, N. Y.,

a corporation of Delaware No Drawing. Application November 17, 1948, Serial No. 60,636

2 Claims. 1

This invention relates to a method of fractionating in ferrous equipment a mixture of chlorinated hydrocarbons obtained from the chlorination of ethane.

Chlorine derivatives of ethane include ethyl chloride, 1,1 and 1,2-dichloroethane, 1,l,1 or 1,1,2- trichloroethane, and more highly chlorinated derivatives such as tetrachloroethane and the pentaor hexachlorocompounds. The most important, commercially, of these chloroethanes is ethyl chloride. Ethyl chloride can be made by the substitution chlorination of ethane, directly reacting ethane and chlorine. When such a reaction is carried out, the other chloroethanes mentioned above are also produced in varying quantities depending upon the ratio of chlorine and ethane fed to the chlorination reactor.

Such a product mixture must be separated into the particular compounds desired. The preferred method of making such a separation is by fractionation in a multiple plate tower. Heretofore, it has been neither feasible nor practical to fractionate such mixtures in iron or steel fractionating columns. The ferrous equipment appears to exert a catalytic effect on the mixture being fractionated and as a result, the desired products are degraded in two respects. Free acid and undesirable color are both formed at .the elevated temperature required for the fractionation. Commercial requirements for chloroethanes include rigid color and acidity standards. The obtaining of either a colorless or an acid free product alone is not sufficient. To be commercially saleable the product must be substantially both colorless and acid free.

It is possible to obtain a satisfactory product by fractionating mixtures of chloroethanes in expensive alloy or non-ferrous equipment. However the high investment requirement for fractionating towers of these materials, has been an important factor in preventing widespread commercial adoption of the ethane chlorination process. It is obvious that it would be highly desirable to conduct the fractionation in equipment made from less expensive materials such as iron and steel.

It is therefore an object of this invention to provide a method wherein products of an ethane chlorination can be fractionated in ferrous fractionating columns without product degradation. Another object is to prevent the tendency of ferrous materials to promote decomposition of chlorinated ethanes at distillation conditions. A more specific object is to minimize or prevent both acid formation and discolorations of chloroethanes at distillation conditions.

We have found a limited group of organic compounds which prevent both objectionable discoloration and acidity formation in ferrous fractionating equipment at temperatures between 180 and 300 F. and at pressures between atmospheric and 100 pounds per square inch, gauge. These materials, hereafter called stabilizers, are: triamylamine, tributylamine, 2-amino-2-methyl-l-propanol, diethylaminoethanol, quinoline, ethanolamine, propylamine, tripropylamine, diethylamine, diethylthiourea. These compounds are effective at concentrations as low as 0.001 weight per cent of the mixture. A preferred concentration range is from 0.005 to 0.02 weight per cent. A concentration of about one part per ten thousand (0.01 weight per cent) is satisfactory for most purposes.

The above compounds are all nitrogen containing organic compounds. However, it can not be assumed that any nitrogenous organic compound is satisfactory for the dual purpose of preventing color and acidv formation. Surprisingly, certain other nitrogenous organic compounds similar in structure to the above limited group were not effective for the dual purpose, but were found to be deficient either with respect to preventing color formation, acid formation or both. For example, although diethyl thiourea is effective in both respects, use of urea allowed formation of about 24 times as much acid, as well as severe discoloration. Diethylene triamine did not prevent discoloration, whereas diethylamine was excellent for both acid and color prevention. Quinoline, a heterocyclic nitrogen compound, was found to be a good stabilizer for the dual purpose. On the other hand, other heterocyclic nitrogen containing compounds such as melamine were ineffective in preventing acid formation. It is interesting to note that an aryl amine, such as triphenyl amine and aniline did not prevent color formation although aryl amines are described as effective stabilizers in the prior art.

To further illustrate the surprising nature of our invention, when 0.01 per cent by weight of quinoline was added to a chlorinated ethane mixture and tested in the presence of iron at a temperature of about 265 F., the acidity was reduced by 84 per cent as compared in a similar test without any stabilizer. By contrast, in a comparable test using a compound closely related to quincline, namely melamine, the acidity was reduced only by 42 per cent, which reduction was entirely unsatisfactory for a commercial and saleable product.

In like manner the use of 0.01 per cent of diethylamine resulted in a water white product which can be readily marketed. In contrast, when 0.01

per cent of diethylenetriamine, a compound closely related to diethylamine, was used, the product had a dark. dirty discoloration making it entirely unsaleable. Furthermore. a nitrogen compound such as acetoxime when so tested effected no reduction in acidity and the final product was dark in color.

The exact mechanism of operation of the eifective stabilizers is not certain. Eflectiveness is not merely a function of ability to combine with hydrogen chloride, as has been theorized by prior workers in this field. Some of the nitrogenous compounds did prevent free acid formation but not discoloration. The converse is true in other instances. Furthermore taken alone, neither the prevention of decomposition of the products being fractionated nor elimination of corrosion of the ferrous equipment satisfactorily explains the phenomena of preventing both color and acid formation. It is believed that the effective stabilizers exert a passivating or deactivating action on the ferrous metals present, thereby preventing catalysis of reactions which would result in discoloration or in free acid release. However, the fact remains that there is no way of predicting wheth er or not a given nitrogenous organic compound will work. In most cases a given compound el ther works or it doesn't, i. e., there is no middle round.

Broadly. our invention comprises fractionatins in ferrous equipment any mixture of chlorine de rivatives of ethane resulting from ethane chlorination, in the presence of one or more of our stabilizers. The stabilizer may be added to the feed stream to the fractionating column, or to any other suitable point in the column. As most of the eifective stabilizers are liquids direct addition to the fractionating column or mixing with the feed stream thereto is a simple matter.

A specific embodiment of the invention comprises the fractionation of a mixture containing 52 parts by weight of ethyl chloride, 40 parts of dlchloroethanes, 7 parts of trichloroethanes and 1 part of tetrachloroethane. This is a typical stream from an ethane chlorination process, after the hydrogen chloride and non-condensible hy-,

belt and at a pressure of about 35 pounds per square inch, gauge. The mixture was fractionated thereby into a pure ethyl chloride overhead product and a bottom product containing the other components of the feed mixture. Each of these products was free from both acid and color formation.

Other embodiments of our invention are possible within the scope of the following claims.

We claim:

1. The process comprising fractionating a mixture of chloroe'thanes from an ethane chlorination reaction in a ferrous fractionating column with a reboiler temperature of about 230 F. and at a pressure of about 35 pounds per square inch in the presence of less than 0.02 weight percent of a nitrogenous organic compound selected from the group consistingof diethylamine, propylamine, tripropylamine, tributylamine, triamylamine, diethylaminoethanol, ethanolamine, 2- amino-2-methyl-1-propanol, diethylthiourea and quinollne.

2. The process comprising fractionally distilling. in a fractionating column having a ferrous metal surface in contact with the material being distilled, a mixture of chloroethanes produced by an ethane chlorination reaction, said distillation being eil'ected at a temperature between about 180 and 300 F. and under a pressure of between about atmospheric pressure and pounds per square inch gauge pressure, and said mixture having between about 0.001 and 0.02 per cent by weight of an added discoloration and acidity reducing compound selected from the class consisting of diethylamine, propylamlne, tripropylamine, tributylamine, triamylainine, diethylaminoethanol, ethanolamine, 2-amino-2-methyl-l-propanol, diethylthiourea and quinoline.

CLARENCE c. HARVEY. CLARENCE M. NEHER. JULIAN DORSKY.

REFERENCES CITED The following references are of record in the me of this patent:

UNITED STATES PATENTS Number Name Date 2,013,251 Missbach June 9, 1936 2,311,044 Petering Mar. 20, 1945

Claims (1)

1. THE PROCESS COMPRISING FRACTIONATING A MIXTURE OF CHLOROETHANES FROM AN ETHANE CHLORINATION REACTION IN A FERROUS FRACTIONATING COLUMN WITH A REBOILER TEMPERATURE OF ABOUT 230* F. AND AT A PRESSURE OF ABOUT 35 POUNDS PER SQUARE INC IN THE PRESENCE OF LESS THAN 0.02 WEIGHT PERCENT OF A NITROGENOUS ORGANIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF DIETHYLAMINE, PROPYLAMINE, TRIPROPYLAMINE, TRIBUTYLAMINE, TRIAMYLAMINE, DIETHYLAMINOETHANOL, ETHANOLAMINE, 2AMINO-2-METHYL-L-PROPANOL, DIETHYLTHIOUREA AND QUINOLINE.