GB1575053A - Low temperature pyrolsis of polyolefins to give liquid and gaseous hydrocarbons - Google Patents

Description

(54) LOW TEMPERATURE PYROLYSIS OF POLYOLEFINS TO GIVE LIQUID AND GASEOUS HYDROCARBONS (71) We, BASF AKTIENGESELLSHAFT, a German Joint Stock Company of 6700 Ludwigshafen, Federal Republic of Germany, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following Statement: As part of the art of high temperature pyrolysis, it has been disclosed to degrade polyolefins pyrolytically by means of indirectly heated rotary furnaces or screws, at about 5000 C; this process requires relatively long residence times, and the reaction products obtained comprise about 90% of an oil and about l0% of a gas.The pyrolysis can be carried out at somewhat lower overall temperatures, e.g. 300 initially and 500"C later, if it is in the form of a twostage process, or if the pyrolysis is carried out under reduced pressure. In hydrocracking, ie. in decomposing the polyolefins in hydrogen under superatmospheric pressure, eg. at 10 bars pressure, degradation can, again, be effected down to about 400"C (cf. Hj. Sinn, "Recycling der Kunststoffe", ChemieIng.-Techn., 46 (1974), 579-589, and T. Takesue, Kagaku Kogyo, 23 (1972), 536-542).

Processes in which the pyrolytic decomposition of the polyolefins is carried out in a salt melt, consisting, for example, of 1 part of magnesium chloride and 2 parts of potassium chloride, at from 600 to 8000 C, or simultaneously with a reaction with organic chlorine compounds, have also been disclosed. Furthermore, processes have been disclosed in which the pyrolysis is carried out in a fluidized bed, with sand as the bed material and nitrogen, steam or cracked gas as the fluidizing medium; in this case gaseous products are formed in a yield of about 65% of the polyolefin employed, accompanied by only about 33% of liquid, in particular cyclic, hydrocarbons, a relatively high proportion of valuable aromatic compounds being obtained by a particular flow system of the reaction gases (cf. Hj. Sinn, 1.c.; I.

Menzel, Thesis Abstracts, Chemie-Ing.

Techn., 46 (1974), 607).

A disadvantage of all high temperature pyrolysis processes is that the decomposition temperature is from 400 to 900"cm in particular from 600 to 8000C, and/or that a high proportion of gaseous pyrolysis products is formed.

The catalytic cracking of higher hydrocarbons, eg. heavy oils and paraffins, by means of inorganic chlorides, especially aluminum chloride, to give low hydrocarbons, in particular liquid hydrocarbons, has also been disclosed, a principal advantage of this method over high temperature pyrolysis being the substantially lower cracking temperatures, which are at most about 300"C. (cf. Georg Kränzlein, "Aluminiumchloride in der Organischen Chemie", Verlag Chemie, Berlin, 1939, chapter XIX "Cracken", pages 200/201; the published description of German Patent Application p 47,112 D; L.A. Potolovsky and G. S.

Spektor "Cracking Industrial Paraffin", The Journal of Applied Chemistry of the USSR, 28 (1955), English translation, 729-733).

Finally, it is known that dissolved polyolefins, eg. polyethylene, are degraded by 5% by weight of aluminum chloride at 1300C until a waxy consistency is reached, ie. relatively extensive degradation is achieved (cf.

Wayne L. Carrick "Reactions of Polyolefins with Strong Lewis Acids*', Journal of Polymer Science; Part A-1, 8 (1970), 215-223).

It would be desirable if the following objectives could be achieved.

I) to degrade relatively high molecular weight polyolefins (in contradistinction to heavy oils or paraffins) pyrolytically; II) to effect pyrolysis at the lowest possible temperature; III) to obtain exclusively gaseous and liquid hydrocarbons (i.e. no waxy hydrocarbons) as the degradation products; IV) to obtain a very high proportion of liquid degradation products; and V) to obtain liquid degradation products which contain as high a proportion as possible of hydrocarbons which may be used as automotive fuels.

If these objects were achievable by a technically simple method, two substantial advantages would result, namely not only a contribution to the protection of the environment (by destruction of polyolefin scrap) but also a countermeasure to the energy crisis (by obtaining an automotive fuel).

We have found that good results may be achieved by means of a low temperature process for the pyrolysis of hydrocarbon material, wherein a normally solid plasticlike polyolefin, especially a polyethylene, preferably having a melt index (determined by the method of ASTM D 1238-62 T) of from 0.1 to 0.25 g/10 minutes (under Condition E = 1900/2.16 kg) or of from 1.7 to 2.3 g/10 minutes (under Condition F = 1900/21.6 kg), mixed with from 5 to 12, especially from 8 to 10, % by weight (based on the polyolefin) of an inorganic halide as pyrolysis catalyst, is agitated in the molten state at from 150 to 300"C, and the normally liquid gaseous hydrocarbons thereby produced are isolated.

We have found that the low temperature pyrolysis process of the invention proves particularly successful if aluminum chloride is employed as the inorganic halide.

We have further found that the process according to the invention is particularly economical if the heat required to maintain the pyrolysis reaction is provided by combustion of the normally gaseous hydrocarbons resulting from the pyrolysis.

With regard to the materials used in the new process the following details are to be noted: a) Suitable polyolefins for pyrolysis include the conventional plastic-like polyolefins, eg. polypropylene, poly-n-butene, poly- i-butene, polymethylpentene and, in particular, polyethylene. It is self-evident that for economic reasons polyolefin scrap or offspecification polyolefins will be employed virtually exclusively.

b) Suitable inorganic halides include the halides of the elements of the 3rd group and the 4th period of the periodic table of the elements; as far as the 4th period is concerned, it is above all the halides of the metals having the electron- configuration of the 3d sub-group which are suitable. The chlorides, above all aluminum chloride, are particularly suitable halides.

c) The normally liquid hydrocarbons formed in the pyrolysis in general account for up to 80% by weight of the polyolefin; they essentially have carbon numbers of from 5 to 14, particularly from 6 to 12, ie.

a composition which corresponds to an automotive fuel mixture.

d) The normally gaseous hydrocarbons formed in the pyrolysis in general account for up to 20% by weight of the polyolefin; they essentially have carbon numbers of from 2 to 5, particularly 3 or 4, and can be combusted or be converted to alkanes, particularly isobutane and propane.

Apart from the special requirements of the invention, the new process as such can be carried out with the conventional equipment and procedures for liquid phase pyrolysis, so that further details are superfluous. What may be mentioned is that, for example, stirred kettles have proved suitable equipment in which to carry out the actual pyrolysis, and that it is advantageous to introduce the inorganic halide, in the form of a powder, into the fused polyolefin whilst stirring and excluding moisture.

Heated screw-type machinery, in which the polyolefins are degraded as they move forward and the volatile degradation products are removed, whilst the non-volatile constituents formed in the pyrolysis are discharged at the end of the screw, is particularly suitable.

EXAMPLE Shredded scrap polyethylene, having a melt index (determined by the method of ASTM D 1238-62 T) of 2.0 g/10 minutes (under Condition F = 1900/21.6 kg) is fused in a heated stirred kettle having a conventional downstream fractionating unit, the amount of scrap used being such that the kettle is about one-third filled with melt. When the melt has reached a temperature of 200"C, 9% by weight (based on polyethylene) of aluminum chloride are added, after which the mixture is stirred for 140 minutes at this temperature.

The fractionating device downstream from the stirred kettle is operated so as to isolate a fraction of normally liquid hydrocarbons of boiling range from 20 to 1850 C, and the normally gaseous hydrocarbons. The liquid fraction accounts for 77% by weight (based on polyethylene employed) and the gaseous fraction for 19% by weight (based on polyethylene employed). The remainder consists of residues.

A gasoline-like automotive fuel can easily be produced from the liquid fraction.

WHAT WE CLAIM IS: 1. A low temperature process for the pyrolysis of hyrocarbon material, wherein a normally solid plastic-like polyolefin, mixed with from 5 to 12% by weight (based on the polyolefin) of an inorganic halide as pyrolysis catalyst, is agitated in the molten state at from 150 to 300"C and the nor

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   liquid hydrocarbons (i.e. no waxy hydrocarbons) as the degradation products; IV) to obtain a very high proportion of liquid degradation products; and V) to obtain liquid degradation products which contain as high a proportion as possible of hydrocarbons which may be used as automotive fuels.

   If these objects were achievable by a technically simple method, two substantial advantages would result, namely not only a contribution to the protection of the environment (by destruction of polyolefin scrap) but also a countermeasure to the energy crisis (by obtaining an automotive fuel).

   We have found that good results may be achieved by means of a low temperature process for the pyrolysis of hydrocarbon material, wherein a normally solid plasticlike polyolefin, especially a polyethylene, preferably having a melt index (determined by the method of ASTM D 1238-62 T) of from 0.1 to 0.25 g/10 minutes (under Condition E = 1900/2.16 kg) or of from 1.7 to 2.3 g/10 minutes (under Condition F = 1900/21.6 kg), mixed with from 5 to 12, especially from 8 to 10, % by weight (based on the polyolefin) of an inorganic halide as pyrolysis catalyst, is agitated in the molten state at from 150 to 300"C, and the normally liquid gaseous hydrocarbons thereby produced are isolated.

   We have found that the low temperature pyrolysis process of the invention proves particularly successful if aluminum chloride is employed as the inorganic halide.

   We have further found that the process according to the invention is particularly economical if the heat required to maintain the pyrolysis reaction is provided by combustion of the normally gaseous hydrocarbons resulting from the pyrolysis.

   With regard to the materials used in the new process the following details are to be noted: a) Suitable polyolefins for pyrolysis include the conventional plastic-like polyolefins, eg. polypropylene, poly-n-butene, poly- i-butene, polymethylpentene and, in particular, polyethylene. It is self-evident that for economic reasons polyolefin scrap or offspecification polyolefins will be employed virtually exclusively.

   b) Suitable inorganic halides include the halides of the elements of the 3rd group and the 4th period of the periodic table of the elements; as far as the 4th period is concerned, it is above all the halides of the metals having the electron- configuration of the 3d sub-group which are suitable. The chlorides, above all aluminum chloride, are particularly suitable halides.

   c) The normally liquid hydrocarbons formed in the pyrolysis in general account for up to 80% by weight of the polyolefin; they essentially have carbon numbers of from 5 to 14, particularly from 6 to 12, ie.

   a composition which corresponds to an automotive fuel mixture.

   d) The normally gaseous hydrocarbons formed in the pyrolysis in general account for up to 20% by weight of the polyolefin; they essentially have carbon numbers of from 2 to 5, particularly 3 or 4, and can be combusted or be converted to alkanes, particularly isobutane and propane.

   Apart from the special requirements of the invention, the new process as such can be carried out with the conventional equipment and procedures for liquid phase pyrolysis, so that further details are superfluous. What may be mentioned is that, for example, stirred kettles have proved suitable equipment in which to carry out the actual pyrolysis, and that it is advantageous to introduce the inorganic halide, in the form of a powder, into the fused polyolefin whilst stirring and excluding moisture.

   Heated screw-type machinery, in which the polyolefins are degraded as they move forward and the volatile degradation products are removed, whilst the non-volatile constituents formed in the pyrolysis are discharged at the end of the screw, is particularly suitable.

   EXAMPLE Shredded scrap polyethylene, having a melt index (determined by the method of ASTM D 1238-62 T) of 2.0 g/10 minutes (under Condition F = 1900/21.6 kg) is fused in a heated stirred kettle having a conventional downstream fractionating unit, the amount of scrap used being such that the kettle is about one-third filled with melt. When the melt has reached a temperature of 200"C, 9% by weight (based on polyethylene) of aluminum chloride are added, after which the mixture is stirred for 140 minutes at this temperature.

   The fractionating device downstream from the stirred kettle is operated so as to isolate a fraction of normally liquid hydrocarbons of boiling range from 20 to 1850 C, and the normally gaseous hydrocarbons. The liquid fraction accounts for 77% by weight (based on polyethylene employed) and the gaseous fraction for 19% by weight (based on polyethylene employed). The remainder consists of residues.

   A gasoline-like automotive fuel can easily be produced from the liquid fraction.

   WHAT WE CLAIM IS: 1. A low temperature process for the pyrolysis of hyrocarbon material, wherein a normally solid plastic-like polyolefin, mixed with from 5 to 12% by weight (based on the polyolefin) of an inorganic halide as pyrolysis catalyst, is agitated in the molten state at from 150 to 300"C and the nor

   mally liquid and normally gaseous hydrocarbons thereby produced are isolated.
2. 2. A process as claimed in claim 1, wherein aluminum chloride is employed as the inorganic halide.
3. 3. A process as claimed in claim 1 or 2, wherein the heat required to maintain the pyrolysis reaction is provided by combustion of the normally gaseous hydrocarbons resulting from the pyrolysis.
4. 4. A process as claimed in any of claims 1 to 3, wherein the polyolefin has a melt index of from 0.1 to 0.25 g/10 minutes (under condition E = 1900/2.16 kg).
5. 5. A process as claimed in any of claims 1 to 4, wherein off-specification or scrap polyethylene is used as the polyolefin.
6. 6. A process as claimed in any of claims 1 to 5, wherein a pyrolysis temperature of 180 to 220"C is used.
7. 7. A process as claimed in any of claims 1 to 6, wherein from 8 to 10% by weight of the inorganic halide (based on the polyolefine) is used.
8. 8. A low temperature process for the pyrolysis of a polyolefin carried out substantially as described in the foregoing Example.
9. 9. Normally liquid hydrocarbons when obtained by a process as claimed in any of claims 1 to 8.