Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Reexamination Certificate
2001-03-16
2002-10-15
Silverman, Stanley S. (Department: 1754)
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
C588S253000, C588S253000, C588S253000
Reexamination Certificate
active
06465707
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of hydrolytic treatment of halogenous, organic waste material, in particular halogenous plastic waste such as PVC (polyvinyl chloride). By the method the waste material is transformed to different fractions which are all environmentally safe and/or which can be recycled in an environmentally safe manner. Furthermore the treatment is economically advantageous due to the valuable halogen-free organic compounds obtained as decomposition products.
BACKGROUND ART
The disposal of halogenous, organic waste material, including in particular halogenous plastics such as materials containing polyvinyl chloride (PVC), polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride or polytetrafluoroethylene (PTFE), is a difficult task usually causing environmental problems. Thus the combustion of halogenous, organic waste materials results in noxious combustion products. Under unfavourable combustion conditions dioxins, which are very toxic, may be generated, and usually hydrohalic acids, such as HCl, are released which pollute the environment and may cause serious damage to the equipment used due to corrosion.
WO 96/29118 (NKT) discloses a method of dry pyrolysis treatment of PVC-containing material, in which the material in a decomposition step is heated in a reaction zone in a closed system without addition of water to a temperature between 150 and 750° C., preferably 250-350°, in the presence of a halogen-reactive compound selected among alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates and alkaline earth metal carbonates and mixtures thereof so as to establish a controllable autogenous pressure substantially above atmospheric pressure, in a sufficiently long reaction time to convert essentially all halogen present in the waste material to alkali metal halide or alkaline earth metal halide, said closed system preferably also comprising a condensation zone, where water vapour and volatile compounds liberated from the water material are condensed. The residue obtained in the decomposition step is washed with water, and the soluble and insoluble parts of the residue are separated. By the method the halogen is removed from the waste material without causing uncontrolled emission of hydrohalic acids to the environment. WO 96/29118 does not describe how the pyrolysis can be performed so as to ensure that the decomposition of the chlorine-free part of the PVC molecules results in a high yield of chlorine-free organic compounds which are liquid at normal ambient conditions and which in a conventional manner can be separated to a number of useful desirable products.
U.S. Pat. No. 5,324,817 (Saleh et al.) discloses a process for dehydrochlorinating PVC by heating the PVC in deoxygenated liquid water at temperatures from about 200° C. up to the critical temperature, at which the water can be maintained as a liquid phase. This process is not particularly effective, as only a maximum of about 90% by weight of the chlorine is removed from PVC. The treatment is preferably carried out at a pH up to 7, that is in the acidic range, the use of acid-resistant equipment thus being required. This publication does not either disclose the formation of valuable chlorine-free organic compounds by the decomposition process.
U.S. Pat. No. 5,386,055 (Lee et al.) describes a process for depolymerising polymers by partial oxidation at supercritical or near supercritical conditions for water. By the process the polymer is preferably rapidly brought to a temperature above the critical temperature of water (374° C.) by directly contacting the polymer with supercritical water and thus raising the temperature of the treated mixture substantially instantaneously and eliminating char formation. The treatment is carried out for a period of time ranging from three seconds to about one hour, thus preventing a too drastic decomposition causing formation of CO
2
and H
2
O, the object being to decompose polymers to the original monomers for recycling. Thus, to a certain extent also dimers, trimers and oligomers are produced. If the polymer is PVC, the object of the process is thus to decompose this to vinyl chloride. From the FIGS. 3, 4, 7 and 8 it appears that not only vinyl chloride, but also other low boiling chlorinated hydrocarbons including dichloroethylene, chloroethane, dichloroethane and dichloropropane are prepared. Preparation of valuable halogen-free organic. compounds is not suggested.
U.S. Pat. No. 5,315,055 and U.S. Pat. No. 5,728,909 (Butcher) both disclose a method for depolymerising polymeric material by alkali fusion, wherein a molten reaction mixture is prepared comprising a basic material, a copper source and said polymeric material, and maintaining the molten mixture at a temperature sufficient to reflux said molten mixture for sufficient time to depolymerise said polymeric material. This process is performed at atmospheric pressure and without addition of process water, the process being carried out in a melt. The said patents do not show how to obtain halogen-free decomposition products having a large quantity of valuable organic compounds.
WO 98/08880 (3M) discloses a method of dehydrofluorinating a fluoropolymer whereby an aqueous emulsion of the fluoropolymer is mixed with a basic compound and then heated to 40-100° C. in 3 minutes to 100 hours. The resulting material is described as a dehydrofluorinated fluoropolymer which indicates that the polymer backbone is not decomposed by such treatment below 100° C. Thus the material is in itself a polymer and not a mixture of valuable organic compounds which are liquid at normal ambient conditions.
JP published patent application No. 50,109,991 (Fujikura) discloses treatment of PVC at 160-300° C. in a basic aqueous solution exemplified by heating 22 g PVC, 16 g NaOH, 400 ml water and 5 ml 70% aqueous ethylamine solution at 200° C. in one hour. By this treatment the dechlorinated polymer material will not be decomposed to give a high yield of a mixture of valuable organic compounds which are liquid at normal ambient conditions. U.S. Pat. No. 3,826,789 (Yokokawa) discloses heat treatment of PVC in a basic aqueous solution. The temperature is stated to be from about 180° C. to about 300° C. but according to column 4, lines 6-8, the preferred reaction conditions are heating at 190 to 250° C. in 30 minutes to about 5 hours. Yokokawa does not suggest to adjust the conditions in order to obtain valuable organic compounds which are liquid at normal ambient conditions and which can be recycled. On the contrary the dechlorinated material is burned in a combustion furnace, cf. column 4, lines 34-39.
U.S. Pat. No. 5,608,136 (Maezawa et al.) discloses a method of pyrolytic decomposition of PVC. The treatment is carried out at a relatively high temperature in the range 300 to 600° C. and the dechlorinated pyrolysis product includes heavy compounds which can be condensed by cooling to 200-350° C. and recycled to the pyrolysis step, an oil fraction which is used as fuel and furthermore about 10 parts by weight of a gas which after cleaning in an exhaust gas treatment unit is burned with a burner for post-treatment (column 22, lines 17-20, column 43 and 44, Experiments 98 and 99, and Table 7). Thus both high molecular weight compounds and low molecular weight gaseous compounds occurs in the pyrolysis product which therefore has to be further fractionated and treated.
As appears from the above several approaches have been made to dispose of halogenous, organic waste material such as PVC in an environmentally acceptable manner and an number thereof involves a treatment with heat in the presence of a basic compound and with or without the presence of water. However, although the known methods in a more or less efficient manner can transform the halogen content into environmentally acceptable halides they are both complicated and expensive and not all the reaction products are environmentally safe or can be recycled in an environmentally safe manner.
It has now surprisingly been foun
Nave Eileen E.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Silverman Stanley S.
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