DE3300673A1 - METHOD AND DEVICE FOR THE PYROLYTIC DECOMPOSITION OF POLYMERS - Google Patents

Description

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The invention relates to a method and an apparatus
for the pyrolytic decomposition of polymers, preferably
for the production of heating oil and other useful products from atactic polypropylene.

The ever-increasing accumulation of waste from polymer material as by-products of industrial processes and the like has a clearly recognized need for the elimination of the these substances, preferably with a simultaneous economic Mutzen, produced.

1G Most of the polymer waste is due to its low content useful as fuel. However, many high and medium molecular weight polymers are at room temperature semi-solid, such as atactic polypropylene, and consequently difficult to convey and atomize and thus for direct combustion in conventional burners cannot be used. It is a wide variety of thermal decomposition methods These polymeric wastes are known in lower molecular weight fragments to make them easier to handle and use as heating oil or raw materials for industry

to be able to. Examples of such methods are contained in U.S. Patents 3,829,558, 3,832,151, or k 151,216. A main problem with the known processes is that deposits of by-products, in particular carbon-containing materials, form on the heat exchange surfaces of the thermal reactors. These deposits limit and reduce the efficiency of the noise exchange surfaces and require work to be carried out every step of the way or periodic shutdown of the system for cleaning. The uneven heating of conventional ovens increases this problem, as hot spots are often found on the intestinal exchange surfaces along the path of the waste material to be thermally decomposed.

occur, causing the formation of carbonaceous deposits favor. The remedies suggested for this, such as lower reaction temperatures or removal of carbon-rich fractions of the material to be decomposed could not sufficiently solve the problem to enable a continuously operating process.

The invention is based on the object of a system for Pyrolytic decomposition of polymer material into fragments with lower molecular weight, in the case of hot spots (hot spots) avoided in the reactor system and the formation of uneven carbonaceous deposits is largely prevented.

According to the invention, this object is achieved by the features of Characteristic of claim 1 solved.

By using a heated fluidized bed as a heat source for the pyrolytic decomposition a uniform Heating of the reactor lines achieved, which can be controlled relatively easily, so that the carbonaceous deposits are reduced and a uniform starting product is obtained.

In a preferred application of the invention, polymeric Waste materials such as atactic polypropylene in one heated tank melted to a viscosity at which it under absolute pressures ρ preferably between 3, * + 5 and 17.25 bar can be pumped. The molten material passes through thermally insulated pipes at least one Reactor line, preferably two or more, preferably helical reactor lines, supplied in which it is in Absence of oxygen thermally decomposes, i.e. it is pyrolyzed to form fragments with a lower molecular weight than that of the molecules of the starting material. The response time depends on the dimensions

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solutions of the reactor lines and the flow rate of the polymer material. The fluidized bed heats the reactor lines and the polymers flowing through them to precisely adjustable temperatures. The pyrolysed product passes from the reactor lines into a separator, for example a flash distillation apparatus, the polymer fragments being separated into groups essentially according to their molecular weight. In the case of atactic polypropylene, which has been ^{heated to about 42G 0} C for a period of about 1D minutes, the main products are heating oil IMr. 6 and IMr. 2 as well as some lighter gaseous fuels, which are preferably used to supply the burners for heating the real melt tank and the fluidized bed.

About carbon deposits on the walls of the reactor pipes to eliminate, an oxygen-containing gas, preferably air, to be passed through these lines, which enables the deposits to burn off. The resulting heat is partly dissipated by a fluidized bed, so that no overheating of the reactor walls can occur. In order to enable a continuous working method, it is expedient to provide at least two reactor lines, one of which is always in operation, while the other is cleaned.

The invention is explained in more detail below with reference to the drawing, in which a system is shown schematically for thermal decomposition of atactic polypropylene is shown.

The system has a heated melt tank 10 which is connected to a pump 14 by means of a line 12. The pump 14 feeds into a line 16 from which two separate supply lines 18 and 18 ¹ extend, each of which is a

Product inlet valve 19 bzui. 19 ' and lead to a reactor tube 20 or 20'. The actuator tubes 20 and 20 'are preferably arranged helically and in a fluidized bed fan 22 which has a jacket 2k which is provided at its lower end with a divider plate 26 which separates the fluidized bed zone 30 from a lower heating chamber 2Θ . The heating chamber 2S is provided with a burner 32 which heats air which rises through the distributor plate 26 into the fluidized bed zone 30. In the fluidized bed zone 30 there is arranged a fluidized bed of solid particles which are suspended in the hot gas flowing upwards and form a fluidized mass 33 which transfers the heat to the submerged reactor tubes 20 and 20 '. The air passes from the furnace 22 through a line 3U into a separator 36, preferably a cyclone, which separates entrained particles and releases the gas into the atmosphere. From the reactor tubes 20 and 20 ', the cleavage product passes via lines 37 and 37' into a separator 38, for example a flash distillation apparatus. One line U2.

connects the lower part of the separator 38 to a cooler kk, from which fission products with a higher molecular weight pass to a first storage container kG. In addition, the separator 38 is connected via a line kB to a condenser 50 which has a first outlet line 52 for gaseous products of low molecular weight and a second outlet line 5k for liquid products of medium molecular weight. These outlet lines 52, 54 lead to second and third storage containers 56 and 57, respectively.

In a preferred application of the invention, atactic Polypropylene, a partially crystalline substance that is solid or semi-solid at room temperature and consists of one Mixture of waste by-products that are produced in the

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Production of polypropylene incurred by thermal decomposition in heating oils IMr. 6 and no. 2 and other usable materials are broken down. Here, the atactic Polypro pylene waste Uird of a polypropylene plant in the melting tank 1D collected and DÜI ^ t to about ⁰ C 2DD heated until it becomes liquid at a pressure between 3 ρ, £ * 5 and 7.25 bar in the reactor tubes 2D and 20 'to be pumped. In these tubes the atactic polypropylene is heated to a temperature which is sufficient to break CC bonds in the waste material and to produce the desired products. This takes place at around * + 20 ^a C over a certain period of time. The products are made at about 25 ^D C is normally about 90 wt.% Of ^F lüssigen and about 10% of gaseous fuels and are conveyed from the reactor tubes to the separator 38, in which the liquid fractions in EIIen heavy (highly viscous) part and a mixture of light (low-viscosity) parts and the remaining gases' is divided. The latter is fed to the condenser 50, where the light components condense and then passed into the container 56, while the remaining gases are fed to the container 57. These gases are preferably used to supply the burners for heating the melting tank 10 and the flow cell 33.

Although the extremely precise and uniform heating through the fluidized bed the amount of carbonaceous Deposits on the ends of the reactor tubes are considerable reduced, it cannot be avoided that in the long run these deposits prevent heat transfer from the fluidized bed gradually decrease to the material in sen reactor tubes. In order to remove these deposits and still enable continuous operation, the Reactor tubes 20 and 20 'separately with polymer material bzm.

charged with an inert gas and air. The latter serves to to burn out the reactor tubes.

This burnout is achieved in the system shown in that the supply of atactic polypropylene to the reactor tube 20 is interrupted by closing the product flow valve 19 and an inert gas, preferably nitrogen, is supplied by opening a flushing inlet valve 60, which is the polypropylene contained in the tubes and / or fission products removed. Immediately thereafter, a product outlet valve 62 is closed in order to interrupt the flow to the separator 38, and a flushing outlet valve Gk is opened so that the flushing gas is released into the atmosphere or into the heating chamber 28 for the purpose of combustion of approximately na: h Pyrolysis products. Then an air inlet valve 66 is opened to introduce oxygen-containing gas into the reactor tube 20, whereby a rapid combustion of the carbonaceous deposits takes place which are present in the reactor tube 20 after the purging n ^ 3 ^. The flushing inlet valve 60 can be closed in order to accelerate the combustion by increasing the amount of oxygen present. The heat of combustion would normally cause excessive temperatures which in typical systems could damage or destroy the reactor walls. The fluidized bed, however, absorbs some of the heat, so that overheating of the reactor tubes due to the heat of combustion of the carbonaceous deposits is avoided.

When all of the carbonaceous material has been burned out, pipe 20 is brought back into service by closing air inlet valve 66 and opening purge inlet valve 60 and purge outlet valve Gk and purging reactor tube 20 with nitrogen until all oxygen is removed. Then the valves

6 ^ and 60 closed and the product flow valve 19 again opened so that polymer material flow into the tube 20 can. Finally, the product outlet valve 62 is opened again, so that the reactor tube 20 is fully operational again is.

As previously mentioned, the other reactor tube 20 'remains fully operational during the burnout of the tube 20. When the reactor tube 20 is put back into operation, the tube 20 'can be burned out without affecting the mode of operation of the tube 20 by appropriately actuating the valves 19', 60 ¹ , 62 ·, 6 ^ 'and 66 · the same above in connection with the reactor tube 20 described method is used. Of course, more than two reactor tubes can also be provided and more than one of these tubes can also be burned out at the same time.

Claims (1)

Claims π. ^ Device for the pyrolytic decomposition of polymers into products with a lower molecular weight, g e k e π η is characterized by a) a fluidized bed which can be operated at pyrolysing temperatures and has at least one reactor line (20,2D ¹ ) and b) means (1U) for conveying polymer material through the reactor line (ZC, 20 '). 2. Apparatus according to claim 1, characterized by a Melting tank (10) for melting the polymer material before it is fed to the reactor line (2C, 20 '). 3. Apparatus according to claim 2, characterized by a pump (1U) for conveying the molten Falymer material through the reactor line (20,2O ¹ ). U. Device according to one of the preceding claims, characterized in that a plurality of reactor lines (20, 20 ¹ ) is provided, each of which has an independent, regulated supply of polymer material. Bank details: Hypobank Gauting Account No. 3750123448 (BLZ 700 280 01) JJUUD / 5. Apparatus according to claim U _1, characterized by first means (60,6D ¹ ) for the controlled supply of inert gas and additional means (66,66 ') for the controlled supply of an oxygen-containing gas to the or each reactor line (20, 20 ·). 6. Device according to one of claims 1 to 3, characterized through a separator (38) for dividing the pyrolyzed Polymer material in fractions. 7. Apparatus according to claim 6, characterized in that the Separate (38) is a flash still. 8. A method for pyrolysing polymer material, characterized in that that the polymer material is passed through a reactor line arranged in a fluidized bed, in which it heated to the pyrolysis temperature and broken down into fragments with a lower molecular weight. 5. The method according to claim 8, characterized in that the polymer material is melted prior to pyrolysis. 1D. Method according to claim 8 or 9, characterized in that the fragments of the polymer material after leaving the reactor line are separated according to their molecular weight will. 11. The method according to claim 8, characterized in that for Removal of carbon deposits on the walls the reactor line these deposits of oxygen at temperatures during which they burn, with at least part of the heat of combustion in the fluidized bed is discharged. 12. The method according to claim 11, characterized in that in the presence of several reactor lines in at least one An oxygen-containing gas for the purpose of cleaning Lüird leads, while in at least one other line; Polymer material is pyrolytically decomposed. 13. The method according to claim 12, characterized in that the reactor lines are purged with an inert gas before the deposits are exposed to oxygen. 1if. Method according to claim 13, characterized in that the reactor pipes after the l / burning of the carbonaceous Deposits can be flushed with an inert gas. 15. The method according to claim 13 or I **, characterized in that that nitrogen is used as the inert gas. 16. The method according to one or more of claims B to 15, characterized in that ice contains oxygen Gas air is used. 17. The method according to one or more of claims 8 to 16, characterized in that part of the pyrolyzed Product used as fuel for heating the fluidized bed and / or for melting the polymer material will. 1Θ. Applying the method according to one or more of the Claims B to 16, for the pyrolytic decomposition of atactic polypropylene. 19. Process for removing carbonaceous deposits von Dberf laugher., which are in a thermally conductive connection with a fluidized bed, characterized in that, that the deposits are heated to temperatures at which they burn in the presence of oxygen, that the deposits are exposed to oxygen and that some of the heat of combustion is dissipated into the fluidized bed to avoid overheating of the surfaces.