Inhibition of 141b decomposition

Details Inhibition of 141b decomposition Inhibition of 141b decomposition

1997-11-25

2001-05-22

Manoharan, Virginia (Department: 1764)

Distillation: processes, separatory

Addition of material to distilland to inhibit or prevent...

C159SDIG001, C159SDIG002, C203S086000, C202S267100, C570S177000, C570S178000

Reexamination Certificate

active

06235161

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method of inhibiting the formation of unsaturated carbon compounds and other unwanted by-products formed during the heating of 1,1-dichloro-1-fluoroethane (“141b”), especially as it relates to the separation of 141b from a liquid mixture containing 1,1,1,2-tetrachloroethane (“130a”) and, if present, 1,1,1-trichloroethane (“140a”) via distillation.
BACKGROUND OF THE INVENTION
The hydrochlorofluorocarbon 141b is a replacement for trichlorofluoromethane (“11”) as a foam blowing agent. As shown by Brooks et al. in U.S. Pat. No. 4,949,479 (the entire specification of which is hereby incorporated by reference), however, the manufacture of 141b from 140a and hydrogen fluoride (“HP”) results in the formation of vinylidene chloride (“1130a”) and other unsaturated by-products and acids, principally HCl. Because of similar boiling points, 141b (b.p. 32 C) and 1130a (b.p. 31 C) cannot be readily separated by distillation. Thus, Brooks et al. teach the use of a photochlorination step to convert the 1130a in the 141b product stream to the higher boiling 130a (b.p. 130.5 C), then distillation of the photochlorinated liquid mixture to separate the low boiling 141b from the higher boiling liquids such as 130a (and possibly 140a unless it has been removed upstream). However, it is found that 1130a and acid (primarily HCl with lesser amounds of HF) are reformed in the distillation column and distill overhead with the 141b product. While the acid can be removed from the product by selective adsorption or reaction, such as by passing the acidic 141b through a bed of potassium hydroxide, it is undesirable since it is an added step. Reformation of the 1130a is more difficult, however, because as noted above it has nearly the same boiling point as the desired 141b product. Thus, yet another post-treatment would be required to remove the 1130a unless its formation in the distillation column can be inhibited. The same problem is presented when 141b is formed by the reaction of 1130a and HF [as taught, for example, by Henne et al., JACS 65, 1271 (1943)], resulting in a product stream containing 141b and 1130a.
SUMMARY OF THE INVENTION
A method is provided for inhibiting the formation of unsaturated carbon compounds during the heating of 141b (alone or as a liquid mixture containing 130a or both 130a and 140a), which method comprises conducting said heating (a) in the presence of an effective amount of an inhibitor selected from a dialkylhydroxylamine where the alkyl groups have 1 to 4 carbons such as methyl, ethyl, propyl, or butyl [preferably diethylhydroxylamine (“DEHA”)]; an epoxide (or cyclic oxide) having 3 to 6 or 10 to 30 carbons such as alpha-pinene oxide (“APO”), 1,2-hexadecene oxide (“HO”), butylene oxide (“BO”), limonene monoxide, limonene dioxide, methyl epoxy soyate, propylene oxide, dicyclopentadiene dioxide alcohol, isoprene oxide, glycidyl isopropyl ether, 1,4-dioxane, or an epoxidized alpha olefin such as C
10
H
20
O, C
12
H
24
O, or C
16
H
32
O (preferably APO, HO, or BO); a free radical scavenger having at least two double bonds and a boiling point greater than that of 141b such as alpha-methyl-stirene (“AMS”), limonene or one of its optical isomers such as d-limonene (“DL”), alloocimene, or isoprene (preferably AMS or DL); a phenol, the phenyl group of which can be unsubstituted or substituted at one or more of the ring positions with substituents separately selected from alkyl (such as methyl, ethyl, isopropyl, butyl), alkoxy (such as methoxy, ethoxy, propoxy, isopropoxy), nitro, halo (such as F, Cl, or Br), alkylamine salt (such as —N(CH
3
)
3
+
Cl
−
), acyl (—C(O)R where R is alkyl), acyloxy (—OC(O)R where R is alkyl), cyano, hydroxy, phenyl which is unsubstituted or substituted as above, the alkyl portion of such substituents generally being lower alkyl of 1 to 4 carbons, and wherein two adjacent positions of the phenyl group can have substituents which are joined to form a fused aromatic ring as in naphthol (preferred phenols being 2,6-di-t-butyl-4-methylphenol and 4-methoxyphenol); or a 1,4-benzoquinone which can be unsubstituted or substituted at each of the aromatic ring positions with substituents separately selected from those listed for phenol (the preferred benzoquinone being unsubstituted); or (b) in a vessel made of a nickel alloy.
This method is particularly applicable to separation of 141b from a liquid mixture containing 130a (and, optionally, 140a) in a distillation column. If an inhibitor is used, it is added to the bottom (or “reboiler” section) of the column. If the column is made of a nickel alloy, use of an inhibitor is not necessary.
DETAILED DESCRIPTION OF THE INVENTION
In one embodiment of the invention it has now been found that the presence of the aforementioned inhibitors inhibits the formation of unsaturated carbon compounds such as 1130a and acids such as HCl and HP during the heating of 141b, such as occurs when a liquid mixture comprising 141b, 130a, and, optionally, 140a is heated in a distillation column to separate low boiling compounds such as 141b from higher boiling compounds such as 130a (and 140a, if present).
When added to a distillation column, the inhibitor should be added to the bottom or reboiler section of the column where the temperature is highest, typically on the order of from about 75 F to about 200 F (preferably about 90-160 F). The temperature at the top of the column is typically about 20 degrees lower than that at the bottom. Adding the inhibitor to the feed stream to the column, as opposed to the column bottom, has been found to be ineffective.
The inhibitor is generally fed to the column at a rate sufficient to maintain a level of inhibitor in the bottoms stream exiting the column of from about 500 to about 5000 ppm, more typically from about 1500 to about 3500 ppm.
This embodiment is illustrated in Examples 1-5 below (where percents are weight percent unless otherwise noted). Examples 1-3 employ a conventional carbon steel column.
In a second embodiment it has now been found that the use of nickel alloys such as Nickel, Monel, Inconel, Hastelloy, or Carpenter 20 for the vessel in which the heating or distillation is conducted is effective to inhibit the formation of acids and 1130a without the use of inhibitors. Inconel and Hastelloy alloys are particularly preferred. Exclusion of air from such processes also assists in the inhibition. This embodiment is illustrated by Example 5 and 6.


REFERENCES:
patent: 3142708 (1964-07-01), Young
patent: 3763017 (1973-10-01), Yves et al.
patent: 4178316 (1979-12-01), Schultz et al.
patent: 4422913 (1983-12-01), Larsen et al.
patent: 4948479 (1990-08-01), Brooks et al.
patent: 4954330 (1990-09-01), Ziegenhain
patent: 4960580 (1990-10-01), Gumprecht
patent: 4975156 (1990-12-01), Wismer
patent: 5105035 (1992-04-01), Wang et al.
patent: 5120461 (1992-06-01), Logsdon et al.
patent: 5122294 (1992-06-01), Logsdon et al.
patent: 5126067 (1992-06-01), Swan et al.
patent: 5135680 (1992-08-01), Crooker et al.
patent: 5169995 (1992-12-01), Crooker et al.
patent: 5200431 (1993-04-01), Dattani et al.
patent: 5306850 (1994-04-01), Darago
patent: 5531867 (1996-07-01), Crooker et al.
patent: 5567281 (1996-10-01), Crooker et al.
patent: 5656137 (1997-08-01), Brooks et al.
patent: 0 472 391 A1 (1992-02-01), None
patent: 53-46804 (1978-12-01), None
patent: 2-215738 (1989-02-01), None

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