NO171921B - PROCEDURE FOR MANUFACTURING NORMALLY LIQUID HYDROCARBON PRODUCTS FROM PLASTIC MATERIAL - Google Patents

Description

The present invention relates to a method for producing a normal liquid hydrocarbon product, which i.a. is useful as a raw material for the manufacture of gasoline, from plastic material.

As the amount of manufactured plastic has grown in recent years, disposal of plastic scrap has become a growing problem. Although various thermal decomposition methods have been proposed as potential solutions to the disposal problem, they are however inconvenient in that the formation of a significant amount of coke and waxy materials, which tend to adhere to the inner wall of the reaction vessel, cannot be avoided. Consequently, it has not been possible to put these methods into practical use when disposing of commonly used types of plastic.

The present invention provides a method for the production of a liquid hydrocarbon product including C5-C22~hyclrocartons" comprising thermal decomposition of a plastic material in the molten, liquid phase in the presence of an inorganic, porous particulate material and catalytic conversion of the vaporous product that is thereby generated in contact with a zeolite, characterized in that the catalytic conversion is carried out at a temperature in the range between 200 and 350°C, and that a zeolite is used which has a restriction index in the range between 1 and 12.

The plastic material used in the method according to the invention can be any polymer or copolymer of an ethylenically unsaturated monomer, including aromatic species, such as polystyrene and polyethylene terephthalate, although halogen-containing polymers and copolymers should be avoided. Preferably, the material is a polyolefinic plastic material, especially polyethylene, polypropylene and polybutylene (including copolymers and mixtures containing this as an essential component). Since the present method is specifically designed for the disposal of scrap plastic, the plastic material used can assume a wide variety of forms, such as films, layers and shaped objects, although films and layers are preferred. These materials, after being pulverized by means of suitable devices, are fed continuously to a thermal cleavage reactor by means of an extruder, while heating them to a liquid or molten state.

The thermal splitting step in the method according to the invention is carried out with the plastic material in a molten, liquid phase. The temperature used in the thermal decomposition step is preferably 390-500°C, more preferably 400-450°C, and the pressure is preferably atmospheric pressure. It is preferred to supply the plastic material to the thermal decomposition step continuously, so that the level of the molten, liquid phase in the fission reactor is kept substantially constant. The thermal fission reaction is preferably carried out under stirring and in the presence of an inorganic porous particulate material. Although there is no particular limitation as to the nature and size of the inorganic porous particulate material, provided that does not deform or degrade, it is usually preferred to use porous particulate material having a size of 1-10 mm. Illustrative examples of suitable porous particulate materials are natural zeolites, bauxite and red clay (the residue remaining after the removal of aluminum from bauxite).The porous particulate feed the rial may show some cleavage activity, although this should be lower than that of the zeolite catalyst used in the subsequent catalytic conversion step.

Use of the inorganic particulate material facilitates heat transfer during thermal cracking, inhibits sticking of coke to the reactor vessel, and lowers the boiling point of the vapor product that is formed, thereby facilitating the supply of the vapor product to the catalytic conversion step, and the quality and yield of the final the produced hydrocarbon oil is improved. The amount of the inorganic particulate material is preferably at least 5 wt-#, but may be up to 200-400 wt-#, of the molten material in the reaction vessel.

The paraffin-rich, vaporous product formed in the thermal cracking step is then fed to a catalytic conversion unit containing a zeolite having a restriction index between 1 and 12. The term restriction index is defined e.g. in the U.S. Patent No. 4,016,218. Examples of suitable zeolites include ZSM-5 (see U.S. Patent No. 3702886), ZMS-11 (see U.S. Patent No. 3709979), ZMS-12 (see U.S. Patent No. 3832449), ZSM-23 (see U.S. Patent No. 4076842), ZSM-35 (see U.S. Patent No. 4,016,245), and ZSM-48 (see U.S. Patent No. 4,375,573), although ZSM-5 is preferred. The zeolite is normally used in its hydrogen form, although it may contain a metal such as platinum. The zeolite is also usually combined with a binder, such as aluminum oxide, and produced as particles having a size of 0.1-10 mm.

The catalytic conversion reaction is normally carried out at atmospheric pressure, at a weight room velocity per hour of 0.8-0.85,' and a temperature of 200-350°C, preferably of 250-340°C. Operation at such a low temperature is unexpected and not only brings economic benefits, but also inhibits unwanted side-reactions.

Application of the zeolite in the second cleavage stage not only allows a reduction of the cleavage temperature and continuous operation, but also improves the quality and yield of the product. Aging of the zeolite catalyst has been found to be relatively slow, and the present method can be carried out with a zeolite catalyst which has been regenerated after use in this or another reaction.

The resulting product is a low pour point hydrocarbon oil that demonstrates the occurrence of not only the cleavage reaction but also isomerization reactions. The absence of high molecular weight substances in the product can also be determined.

It turns out that the hydrocarbon oil product contains only hydrocarbons with more than 22 carbon atoms in significant amounts. Consequently, the hydrocarbon oil product can be added directly to the gasoline blending pool. Gaseous by-products are also obtained by the present method, but these contain a significant proportion of valuable C3~C5 compounds.

The invention will be described below with reference to the attached drawing, which is a schematic illustration of an apparatus for carrying out a method according to an example of the invention.

Referring to the drawing, the thermal cracking reactor is generally indicated at 1 and includes a feedstock feed zone 2, a thermal cracking reaction zone 3 and a stirrer 4, mounted on top of zone 3. The feedstock feed zone 2 includes a screw feeder 5 which in turn feeds the plastic material to the top of the thermal fission reaction zone 3. Inside the themic fission reaction zone 3, a level gauge 6 is introduced to measure the height of the molten raw material, and a thermometer 7.

The top of the thermal cracking reactor 1 is connected to a catalytic reaction zone 8 which is filled with HZSM-5, which has a particle size of approx. 3 mm, in which a thermometer 9 is also introduced. The bottom of the thermal fission reactor 1 is equipped with a gas burner 10.

The thermal decomposition reaction zone 3 is kept at the desired operating temperature by means of the burner 10, while the catalytic reaction zone 8 is kept at the operating temperature by means of the heat capacity of the vaporous thermal decomposition product, although an external heating device (not shown) can also be used.

The effluent from the catalytic reaction zone 8 is supplied by means of a cooling pipe 12, equipped with a water cooling condenser 11 to oil storage containers 13 and 14 for collection.

In a practical embodiment, the apparatus shown in Figure 1 was constructed and operated as follows: (A) The screw feeder 5 was of the two-axis screw type and was operated at a temperature of 330 "C and a feed rate

of 680-706 g/h.

(B) The thermal fission reactor 1 was a cylindrical vessel with height 560 mm, diameter 105 mm and volume 4.85

litres. The thermal cleavage reaction zone 3, i.e. the molten liquid phase area of the reactor 1, had a height of 250 mm, was filled with 250 g of natural zeolite, produced in Kasaoka, Japan (particle size of about 0.5 mm) and was stirred at 8 op.

(C) The catalytic cracking reaction zone 8 was a cylindrical tower with a height of 300 mm, an inner diameter of 76 mm and

volume 1.36 liters and was filled with 613 g of ZSM-5 in hydrogen form.

The invention shall be described in more detail in the following examples.

EXAMPLE 1

Polyethylene film, obtained as urban waste, was collected and pulverized to a size of approx. 5 mm. The pulverized raw material was placed in the raw material supply zone 2, heated to melting in the screw feeder 5 and fed to the first stage, the thermal cleavage reaction zone. The vaporous product thereby formed was led to the second stage, the catalytic reaction zone 8, in which the catalytic conversion was carried out. The conditions used and the results obtained are summarized in the following table:

Analysis of a typical hydrocarbon oil product produced the following results:

Analysis of a typical gaseous by-product from the process gave the following results on a percentage basis of the entire gas component: H27.0; CH48.0; C2H44.5; C2H67.6;

C3H85.6; C3H619.9; i -C4<E>10 1.1;

n_c4H109'851_C4H824»551_C5<H>12 °»5;

n-C5H1211.5.

Typical material balances were as follows:

EXAMPLE 2

The procedure from the previous example was repeated with two separate feedstocks, one consisting of particulate polyethylene, and the other consisting of a particulate mixture of 90 wt # polyethylene and 10 wt # polystyrene. The results obtained are summarized as follows:

Claims (9)

1. Process for the production of a liquid hydrocarbon product comprising C5-C22"hydrocarbons, comprising the thermal decomposition of a plastic material in the molten, liquid phase in the presence of an inorganic, porous particulate material and catalytic conversion of the vaporous product thereby generated by contact with a zeolite, characterized in that the catalytic conversion is carried out at a temperature in the range between 200 and 350°C, and that a zeolite is used which has a restriction index in the range between 1 and 12. 2. Method according to claim 1, characterized in that the catalytic conversion of the vapor phase is effected at a temperature in the range between 250 and 340°C. 3. Method according to claim 1, characterized in that an inorganic, porous particulate material is used which has catalytic cleavage activity. 4. Method according to claim 3, characterized in that a naturally occurring zeolite is used as inorganic, porous particulate material. 5. Method according to any one of the preceding claims, characterized in that the thermal splitting of the liquid phase is effected at a temperature in the range between 390 and 500°C. 6. Method according to any one of the preceding claims, characterized in that the zeolite used in the catalytic conversion step is ZSM-5. 7. Method according to any one of the preceding claims, characterized in that a polyolefinic plastic material is used as plastic material. 8. Method according to claim 7, characterized in that a homo- or copolymer of ethylene, propylene or butene is used as polyolefinic plastic material. 9. Method according to any one of the preceding claims, characterized in that the liquid product of the catalytic conversion of the vapor phase consists essentially of hydrocarbons having a carbon number not exceeding 22.