Isocyanate production procedure

Details Isocyanate production procedure Isocyanate production procedure

2001-05-31

2003-10-28

Barts, Samuel (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Isocyanate esters

Reexamination Certificate

active

06639101

ABSTRACT:

FIELD OF THE INVENTION
This invention refers to a procedure to produce isocyanates through the catalytic thermal decomposition of carbamates.
BACKGROUND OF THE INVENTION
Isocyanates are compounds with one or more —NCO functional groups, appropriate as raw materials widely used to produce polyurethanes, polyureas, etc., which are manufactured industrially on a large scale.
Isocyanates are mainly produced industrially from the reaction of amines with phosgene. However, the procedures that use phosgene have handling problems, since it is a highly toxic product, hydrogen chloride is produced as a by-product in large quantities and the use of highly sophisticated materials is required to avoid corrosion. This is why the industry is attempting to develop efficient isocyanate production procedures that avoid the use of phosgene as raw material.
One of these procedures is based on the thermal decomposition of carbamates. It is known that isocyanates can be obtained by heating liquid carbamates without catalysts (JP 1135753 A, U.S. Pat. No. 5,789,614). However, without catalysts, the speed of the thermal decomposition is generally limited and when the temperature is raised to speed up reaction time, by-products with high molecular weight are formed and yield tends to fall.
The use of several catalysts has been suggested in order to increase reaction speed and reduce the forming of by-products. Recommendations have been made to use elements from zinc, copper, aluminium, titanium and carbon groups (except carbon) and their oxides (JP 57158747 A), rare earths, antimony or bismuth and their oxides (JP 57159751 A), boron and derivatives of arsenic, antimony and quaternary ammonium salts (JP 57158746 A), synthetic boron, aluminium, silicon, tin, lead, antimony, zinc, yttrium, lanthanum, titanium, zirconium, niobium, wolfram or iron oxides (U.S. Pat. No. 5,326,903). All these procedures to produce isocyanates through the catalytic thermal decomposition of carbamates have the disadvantage associated to the forming of heavy by-products with high boiling points and slow reaction speeds. The application for European patent EP 672653 suggests a procedure to produce isocyanates through the thermal decomposition of carbamates in the presence of sulphonic acids or their alkaline metal salts. Although this patent application mentions high reaction speeds and high isocyanate yields, the catalysts used are not soluble in the reaction media and the separation or elimination of the a products of this reaction is difficult and costly.
COMPENDIUM OF THE INVENTION
The invention faces the problem of developing a procedure for the industrial manufacture of isocyanates. The solution provided by this invention is based on the catalytic thermal decomposition of the relevant carbamates using natural or synthetic silicates as catalysts.
One purpose of this invention, therefore, is a procedure for the production of isocyanates, through the catalytic thermal decomposition of the relevant carbamates, using natural or synthetic silicates as catalysts.
The procedure provided by this invention is a simple and economic process which obtains isocyanates with a small number of by-products with a high molecular weight, and high reaction speed, selectivity and yield, using low-cost catalysts which are easily separated from the reaction media by conventional methods, such as filtration or centrifuging, which lead to a simple and economic purification process for the isocyanates.
DETAILED DESCRIPTION OF THE INVENTION
The invention provides a procedure to produce isocyanates from carbamates by catalytic thermal decomposition, from here on the invention procedure, characterised in that it uses natural or synthetic silicates as catalysts.
In the sense used in this description, the term “isocyanate” includes all compounds that include at least one —NCO functional group. The isocyanates that can be obtained by the invention procedure include mono-, di- and polyisocyanates.
The carbamates that can be used in the invention procedure are compounds that include at least one —NHCOO— functional group, and can include saturated or unsaturated aliphatic groups, allylcyclical groups or aromatic groups. In a particular embodiment, the carbamates than can be used as raw material in the invention procedure correspond to the general formula:
R
1
—(NHCOOR
2
)
n
wherein
R
1
and R
2
, independently, identical or different, represent alkylic groups, alkylidene, alkenyl, allylcyclical groups, di-radicalic allylcyclical groups, aromatic groups, arylalkylic groups or di-radicalic aromatic groups; n is a whole number equal to 1, 2, 3 or 4.
The alkylic groups include methyl, ethyl, propyl, butyl, pentyl, hexyl, acryloyloxyethyl, 2-(methacryloyloxy)-ethyl, 2-dimethylamineoethyl, 3-dimethylamine-n-propyl, 2-methoxyethyl, 3-methoxybutyl groups, etc. The alkylidene groups include divalent acyclical groups such as the ethylidene, propylidene, butylidene, pentamethylene, hexamethylene groups, etc. The alkenyl groups include the propoenyl, butenyl, pentenyl groups, etc. The allylcyclical groups include the cyclopentyl, cyclohexyl, and cyclooctyl groups, etc. The di-radicalic allylcyclical groups are bivalent allylcyclical groups such as the 1,4-cyclohexylidene group. The aromatic and arylalkylic groups include the phenyl, tolyl, xylyl, naphthyl, biphenyl, anthanyl groups, etc. The di-radicalic aromatic groups are bivalent aromatic groups such as the 4,4′-methylen-bis-phenylene group. This list is not exhaustive, but merely informative.
These organic groups can contain other functional groups that are inert for isocyanates as substitutes, such as halogens, alcoxy, nitro, etc.
Examples of carbamates that can be used for the invention procedure include aliphatic carbamates such as 1,4-bis(methoxycarbonylamine)butane, 1,6-bis(methoxycarbonylamine)hexane, etc.; allylcyclical carbamates such as 1,3- or 1,4-bis(methoxycarbonylamine-methyl)benzene; 2,4′- or 4,4′-bis(methoxycarbonylamine)diphenylmethane, 4,4′-bis(methoxycarbonylamine)biphenyl, 1,5- or 2,6-bis(methoxycarbonylamine)naphthalene, etc.
The invention procedure can be carried out with a single carbamate or a mixture of 2 or more carbamates.
According to a particular embodiment of the invention procedure, the catalytic thermal decomposition of the carbamates is carried out in the presence of a solvent that is inert in the presence of isocyanates. The solvents that can be used in the invention procedure include aliphatic, allylcyclical and aromatic hydrocarbons, halogenated aromatic hydrocarbons, esters, ketones, ethers, etc. These solvents include alkanes such as hexane, decane, tetradecane, etc.; alicyclical hydrocarbons such as cyclohexane, cyclooctane, cyclododecane, decalin, etc.; aromatic hydrocarbons such as benzene, toluene, xylene, biphenyl, naphthalene, benzyltoluene, tetralin, pyrene, diphenyl-methane, triphenylmethane, phenylphthalene, etc.; esters such as dibutyl phthalate, dioctyl phthalate, diisodecyl phthalate, etc.; ketones such as methylethylcetone, aceto-phenone, etc.; and esters such as anisol, diphenylether, etc.
The quantity of solvent to be used is not critical and can vary between 0.05 and 100 times the weight of the carbamate used, preferably between 0.5 and 10 times its weight.
The temperature of the thermal decomposition of the carbamates is between 150° C. and 300° C., preferably between 200° C. and 275° C. When the reaction temperature is below 150° C., reaction time is very slow and inappropriate for an industrial process. Reaction temperatures over 300° C. are not preferred because undesirable quantities of by-products are formed.
Reaction can take place at reduced pressure or levels higher than atmospheric pressure. The choice of pressure basically depends on the solvent and reaction temperature selected. Reaction time is chosen depending on the kind of carbamate, solvent, reaction temperature and pressure and the type and quantity of the catalyst to be used. Any expert can select the best possible reaction conditions in each case by simple trials.
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