JP4520095B2 - Waste plastic treatment method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a waste plastic processing method for effectively using plastic waste.
[0002]
[Prior art]
In recent years, a large amount of plastics has been discarded as industrial waste or general waste, and its treatment has become a serious social and environmental problem. As disposal methods of this waste plastic, landfill, simple incineration, thermal recycling and material recycling are known.
[0003]
In thermal recycling, waste plastic is oiled or gasified and used as fuel. For example, there is a method in which waste plastic is heated in a hydrogen-donating solvent such as hydrogenated anthracene and hydrocracked to make oil. It is disclosed (see Patent Document 1).
[0004]
[Patent Document 1]
JP-A-7-138576
In material recycling, waste plastics can be recycled into other useful chemicals. For example, the latter can be decomposed and vaporized by gallium-containing silicate catalyst. A method for recovering benzene, toluene and xylene (BTX) has been disclosed (see Patent Document 2).
[0006]
[Patent Document 2]
Japanese Patent Laid-Open No. 2001-316517
[Problems to be solved by the invention]
In the landfill, not only useful components are not recovered, but since plastic has a low bulk density, a large landfill site is required, which is also not environmentally preferable.
[0008]
Incinerated, the plastic tends to break the combustion furnace to issue a high heat by combustion, also, there is a problem of generation of NO _x.
[0009]
Thermal recycling is mainly a method of thermally decomposing plastics at 300 to 800 ° C. to obtain oil, but undecomposed residues are generated at low temperatures and coking troubles are generated at high temperatures. In addition, the quality of the pyrolysis oil produced is poor, and there are problems such as thermal stability and generation of gum during storage.
[0010]
There are various methods for material recycling, but there is a problem that a large amount of various by-products are produced and the yield of BTX is low (see Patent Document 2). In addition, waste plastics containing a large amount of chlorine also have a problem that a gallium-containing silicate catalyst (cyclization catalyst) is poisoned by released hydrogen chloride, chlorine, etc. during pyrolysis and vaporization.
[0011]
An object of the present invention is to obtain a useful component such as benzene, toluene, and xylene (BTX) from a waste plastic in a high acquisition amount, thereby providing a highly effective method of using the waste plastic.
[0012]
[Means for Solving the Problems]
As a result of intensive studies to develop a method for effectively using waste plastics, the present inventors have come to focus on a method for converting to BTX, and various methods for obtaining BTX from waste plastic in a high yield. investigated. As a result, waste plastic is heated and liquefied in a monocyclic or polycyclic aromatic compound such as tar, and hydrogen is added thereto to cause a hydrogenolysis reaction, and the reaction product is present in the presence of a cyclization catalyst. It was found that at least one of benzene, toluene and xylene can be obtained in a high amount by reacting under the following conditions.
[0013]
That is, the present invention provides at least one catalyst selected from iron, iron oxide, and iron sulfide by adding hydrogen to a liquid monocyclic or polycyclic aromatic compound containing chlorine-containing waste plastic that has been liquefied by heating. And a hydrocracking reaction, and the reaction product is reacted in the presence of a cyclization catalyst to produce at least one of benzene, toluene and xylene. is there.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The waste plastic may be any plastic as long as it can be liquefied by heating at about 200 to 350 ° C. and can generate low molecular weight hydrocarbons by hydrocracking reaction. This is not limited to thermoplastic resins, but also includes thermosetting resins. The main objects are polyolefin resins such as polyethylene, polypropylene and polystyrene. Since polyvinyl chloride, polyvinylidene chloride, and the like generate hydrogen chloride by heating, it is preferable to treat the generated hydrogen chloride gas by carrying out heating liquefaction in a sealed structure. The waste plastic may be a plastic alone or a composite with an inorganic substance that does not melt at a heating liquefaction temperature such as metal or glass. Specific examples include waste automobiles, waste home appliances, waste OA equipment, and shredder dust obtained by crushing and treating them.
[0015]
The liquefaction of the waste plastic may be due to thermal decomposition as well as melting of the waste plastic by heating. The temperature of the waste plastic which is heated and liquefied is about 150 to 500 ° C, usually about 200 to 350 ° C, preferably about 200 to 300 ° C.
[0016]
This liquefaction may be performed prior to mixing with the monocyclic or polycyclic aromatic compound, but it is more convenient to dissolve the waste plastic into the monocyclic and polycyclic aromatic compounds after mixing. It is.
[0017]
The monocyclic or polycyclic aromatic compound is liquid in a state of containing waste plastic that has been heated and liquefied, and can generate at least one of benzene, toluene, and xylene by hydrogenolysis. Is. Examples of such aromatic compounds include monocyclic aromatic compounds such as toluene, xylene, and biphenyl, and polycyclic aromatic compounds such as naphthalene, anthracene, pyrene, fluoranthene, and compounds added to these alkyl side chains. There is. These do not need to be a single product, but are usually used in the state of a crude product or a crude product, that is, a mixture. Specifically, it is a tar produced as a by-product from a coke oven, a product obtained by removing a pitch from the tar, or an FCC residual oil produced as a by-product in an oil refining process. Tar contains a large amount of an aromatic compound, particularly biphenyl or fluoranthene, and produces BTX efficiently in the hydrocracking reaction, and also produces indene and fluorene as by-products. Therefore, indene, fluorene, and the like are preferable because they can be obtained separately and effectively used.
[0018]
The amount of the monocyclic or polycyclic aromatic compound used may be 50% or more with respect to the waste plastic, but is preferably about 100 to 200%. Even if it is used in a large amount, the effect is not changed, and the amount of heat for maintaining the reaction temperature in the hydrocracking reaction step increases, which is not preferable.
[0019]
The hydrocracking reaction of the waste plastic may be performed in a separate process from the liquefaction of the waste plastic, or may be performed in one process. Examples of the catalyst used for the hydrocracking reaction include iron catalyst and converter ash (Fe ₂ O ₃ ). In addition, iron sulfide is mentioned. These catalysts can be supported on a support such as alumina (Al ₂ O ₃ ) if necessary. When used as a granular material, the particle size may be normal and about 0.1 to 10 mm. The catalyst may be a fluidized bed, a fixed bed, a slurry bed or the like.
[0020]
The hydrogen source used in this reaction is not particularly limited, and may be generated in a reaction vessel in addition to hydrogen gas. In any case, it is preferable that the cost is low. For example, coke oven gas, hydrogen gas for petroleum refining, or the like can be used. The supply amount of hydrogen is about 0.05 to 5.0% by weight, preferably about 0.1 to 1.0% by weight, based on the total amount of waste plastic and tar.
[0021]
The hydrocracking reaction may be either a liquid phase or a gas phase. The reaction temperature is about 300 to 500 ° C, preferably about 350 to 450 ° C, and the pressure is about 10 to 200 atm, preferably about 20 to 70 atm. .
[0022]
After the hydrocracking reaction, the light component is cyclized to increase the BTX component. The heavy components will be used as fuel. Moreover, since exhaust gas contains a large amount of hydrogen and methane, it is used more effectively. The light component is mainly composed of propane, butane, heptane, hexane, octane, decane and the like in addition to the tar-derived fraction, and can be separated from the heavy component by, for example, distillation. This light cyclization reaction may be carried out in a separate step from the hydrogenolysis reaction, or in one step.
[0023]
The cyclization catalyst is supported by zeolite, for example, Na _x Al _x Si _96-x O ₁₉₂ (x ≦ 27), ZSM-5, ZSM-11, HZSM-5, or HZSM-11 carrying Ga, Zn or Cu. Gallium-silicate systems such as Ga-ZSM-5, Ga-HZSM-5, such as xM ₂ O.yGa ₂ O ₃ .zSiO ₂ .nH ₂ O (M: Na, K, etc.), Ni— Mo / Al ₂ O ₃ or the like can be used. These catalysts may be either a fluidized bed or a fixed bed, and the particle size when used in the form of particulates may be about 0.1 to 10 mm.
[0024]
The cyclization reaction may be either a liquid phase or a gas phase. The reaction temperature is about 350 to 700 ° C, preferably about 400 to 550 ° C, and the pressure is about 1 to 10 atm, preferably about 1 to 1.5 atm. .
[0025]
The reaction product is a mixture of hydrogen, methane, ethane, propane gas, naphthalene, anthracene, etc. in addition to BTX, and is appropriately separated depending on the intended use. For this separation, distillation or high-temperature separation operation is simple.
[0029]
[Example 1 ]
The processing flow of the waste plastics is shown in Figure 1. In this treatment method, waste plastic and tar are put in the dissolution tank 1 and dissolved by heating, and the pressure is increased by the snake pump 2 and sent to the reaction tower 3. The reaction tower 3 is supplied with a hydrocracking catalyst (iron oxide), and part of it forms iron chloride, which helps fix chlorine in the waste plastic. Refined coke oven gas (COG) is blown from the bottom. The mixture of waste plastic and tar that has undergone hydrocracking reaction in the reaction tower 3 is sent to a high-temperature centrifuge 10, and chlorine in the waste plastic is removed as iron chloride. The mixture of waste plastic and tar from which chlorine has been removed is further sent to the simple distillation column 4. On the other hand, the exhaust COG that has passed through the reaction tower 3 is discharged from the top of the tower, merges with the light components discharged from the simple distillation tower 4, and sent to the catalytic reaction tower 5. The catalytic reaction column 5 is packed with a cyclization catalyst, and is converted into BTXs there.
[0030]
In the above processing flow, waste plastics are mainly made of polyethylene, polypropylene, polystyrene, and polyvinyl chloride, and the chlorine content is 4.1% by weight. In addition, coal tar from 230 to 350 ° C. is used as the tar. Waste plastic and tar are supplied to the dissolution tank 1 at 9.6 kg / hr and 14.4 kg / hr, respectively. In the dissolution tank 1, the waste plastic is dissolved (liquefied) at 200 ° C. Purified COG is composed of H ₂ 54% by volume, CH ₄ 30% by volume, CO 7% by volume, CO ₂ 2% by volume, N ₂ 3% by volume, C ₂ H ₂ 2% by volume, and other 2% by volume. , and the the reaction column 3 is supplied at a flow rate of 4.98Nm ³ / hr. As the catalyst, iron oxide (Fe ₂ O ₃ particles) obtained by calcining iron sulfate at 800 ° C. is used, and its supply amount is 3.0 kg / hr. The reaction temperature in the reaction tower 3 is 430 ° C., the pressure is 100 atm, and the reaction time (residence time) is 1 hour. The waste plastic and tar and the mixture of iron oxide and iron chloride that have undergone hydrocracking reaction in the reaction tower 3 are sent to the high-temperature centrifuge 10 at a flow rate of 27.3 kg / hr. The waste plastic / tar mixture from which iron particles have been removed is sent to a simple distillation column at 23.8 kg / hr. The light component discharged from the distillation column 4 and the exhaust COG discharged from the reaction column 3 are supplied to the catalytic reaction column 5 and subjected to a cyclization reaction to be converted into BTXs. The catalytic reaction tower 5 is filled with a gallium-containing zeolite-based cyclization catalyst (Ga-HZSM-5), and has a reaction temperature of 500 ° C. or higher and a reaction time (residence time) of 0.5 minutes. From the catalytic reaction tower 5, products in which BTXs are mostly occupied are discharged at 8.8 kg / hr.
[0031]
【The invention's effect】
According to the present invention, hydrogen of a waste plastic is used to hydrogenate a monocyclic or polycyclic aromatic compound used as a heating medium to increase BTX, and the waste plastic is also cyclized to increase BTX. As a result, the useful substance BTX can be efficiently obtained from inexpensive waste. If tar is used for this heat medium, indene, fluorene and the like can be obtained at low cost.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram schematically showing the configuration of an embodiment of the present invention.

Claims (3)

Hydrogen decomposition with liquid at least one catalyst selected from iron, iron oxide and iron sulfide by adding hydrogen to liquid monocyclic or polycyclic aromatic compounds containing chlorine-containing waste plastics liquefied by heating A method for treating waste plastic, characterized by reacting and reacting the reaction product in the presence of a cyclization catalyst to produce at least one of benzene, toluene and xylene. Hydrogen decomposition in a liquid monocyclic or polycyclic aromatic compound containing chlorine-containing waste plastic that has been heated and liquefied, and at least one catalyst selected from iron, iron oxide, and iron sulfide A method for treating waste plastic, characterized by reacting and removing chlorine, and reacting the reaction product in the presence of a cyclization catalyst to produce at least one of benzene, toluene and xylene. The method for treating waste plastics according to claim 1 or 2, wherein the chlorine-containing waste plastics contain polyvinyl chloride.

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