EP0639631B1 - Process for preparing syngas - Google Patents

Abstract

Plastic wastes are thermally cracked to give predominantly liquid products and the cracking products are converted into synthesis gas by partial oxidation.

Description

The invention relates to a method for converting Plastic waste in synthesis gas that is used as a raw material for chemical syntheses can be used.

One of the most pressing environmental problems faced by experts faces is the disposal of waste, including plastic ones. So far many times practiced storage of such materials in a mixture with other waste in landfills has proven questionable proven because they have long-term exposure to Groundwater and soil not taken into account. By Storage in special landfills tries to avoid such environmental pollution to prevent, but because appropriate Unloading sites are only available to a limited extent stand, the solution to the task of making the waste environmentally neutral eliminate, actually only in the future postponed.

Therefore, efforts have recently been made many times, procedures to develop the waste for processing. You are not just protecting the environment to the goal, but often the extraction of usable Products from their intended purpose no longer substances to be fed directly.

Refurbishing used or not type-appropriate Plastics as a recyclable source material in most cases fails because of waste plastics contain different material composition. It is easy to see that such mixtures generally do not recondition to an original material to let. The separation of the mixtures into parts of the same material nature fails because of the Difficulty identifying the individual components. But also from waste of identical plastics only in exceptional cases the original material in its original form Quality can be regained because of the necessary chemical and / or physical treatment steps the molecular structure of the polymers and so that their original properties are changed.

Plastic waste can only be burned without special precautions should be discarded if it is ensured that no pollutants in the Environment. This requirement is only in exceptional cases given, because they often contain chlorine, but also components containing sulfur or nitrogen as well as heavy metals that are undesirable during combustion Products of combustion. Dedusting and Flue gas scrubbing, if necessary special combustion devices, are then indispensable. Delivery and dosage problems can also occur if the Waste non-combustible and non-melting foreign substances contains. Furthermore, economic reasons argue against high-quality finishing products of petrochemical raw materials like their raw materials, namely petroleum and petroleum products, to burn.

Instead of burning them, you no longer have usable ones Plastics also split thermally. The developed for this Procedures are varied. So you get by breaking down polyethylene at 400 to 450 ° C Gasoline-kerosene mixture (C.A. Vol. 76, 1972, 158024 q). This process can also be carried out in the presence of nickel catalysts be carried out (Chem. Ind. XXIII, 1971, 630). The splitting of carbon-containing organic waste synthetic or predominantly synthetic origin is carried out according to the process of EP-A-291 698 under hydrating Conditions and gives predominantly hydrocarbon fractions in the gasoline and medium oil (diesel oil) boiling range. Waste from plastic and rubber are being re-used the process described in DE-C-2 205 001 thermally at 250 to 450 ° C in the presence of one at the reaction temperature split liquid auxiliary phase. Arise over 90% liquid hydrocarbons and only in subordinate ones Amounts of soot.

One of the primary goals of thermal processing is the conversion of plastics into liquid fuels, which are easily conveyed and dosed and in the combustion air can be distributed homogeneously to a smoke and ensure soot-free combustion. A previous one Use of the hydrocarbons e.g. as a solution, Extraction or cleaning agents are not excluded.

A major disadvantage of the known methods is the need to comply with the plastics Temperatures and dwell times very largely dismantle. Furthermore, they require an expensive one Separation of those often contained in the plastics Solids such as inorganic or organic pigments, Opacifiers and fillers.

The invention has for its object plastic waste to convert into technically usable raw materials. Here, solids are incorporated into the plastics concentrated and free of organic components accumulate, so that they are environmentally friendly can be disposed of.

This object is achieved by a manufacturing method of synthesis gas from plastic waste. It is characterized in that the waste thermally predominantly split into liquid products and the liquid Fission products due to partial oxidation in synthesis gas be transferred.

The term plastic waste in the sense of the new process is very broad. It closes uniform Substances and mixtures of substances of whatever origin and Composition a. According to their thermal behavior the wastes are derived from thermoplastic or thermoset Plastics. To the plastic waste include used plastics for packaging purposes served or as materials, e.g. in construction, electrical or textile industry, in machine and vehicle construction, have been used or for everyday items, processed like household and sports equipment or toys had been. Plastic waste is also bad batches and residues and residues from production and Processing. Plastic waste can therefore be short Designate plastic material that does not regenerate or another economic exploitation leaves. Waste can be processed using the new process e.g. process the following plastics: polyolefins, Vinyl resins such as polyvinyl chloride, polyvinyl acetate and Polyvinyl alcohol, also polystyrenes, polycarbonates, Polymethylene oxides, polyacrylates, polyurethanes, polyamides, Polyester resins as well as hardened epoxy resins. Especially the process with thermoplastic is simple Perform plastics.

According to the invention, the feed material from which is rough Impurities such as metals, glass and ceramic materials were mechanically separated, thermally to low molecular weight Dismantled fragments. Are basically all known processes for this process step suitable, the preferred liquid and only in subordinate Amount of gaseous decomposition products and / or soot surrender. The cleavage of the polymeric compounds can in In the presence or absence of hydrogen. There is also a subsequent hydrogenation of the cleavage products possible; however, it is not the sub-step thermal pretreatment of the waste is absolutely necessary, to work under hydrating conditions. The Choosing the most suitable for the thermal degradation of plastics The process therefore largely depends on the particular Circumstances.

The depolymerization of plastic waste does not only result to easily dosed and homogeneous, liquid products. In particular, it also has a dechlorination in the Plastic waste, which often contains chlorine Plastics. The halogen is called Hydrogen chloride split off from the gaseous Degradation products are washed out in a known manner. The Liquid fission products only contain chlorine in small amounts Quantities tolerable in the subsequent gasification are.

Thermal treatment has proven to be particularly suitable of plastic waste at temperatures between 250 and 450 ° C using one at the reaction temperature proven liquid auxiliary phase (see. DE-C-2 205 001). This auxiliary phase is used in particular to transfer the Heat on the feed materials in the cracking reactor. About that it also promotes thermal degradation in that it in many cases the starting materials swell like a gel leaves. Such substances are successfully used as an auxiliary phase applied, the waste products used and the Fission products at the given reaction temperature at least partially solve. Natural have proven themselves or artificial waxy hydrocarbons, further Polyglycols and especially the liquid degradation products the plastic waste itself.

The dismantling of the waste to be processed is promoted by that you mechanically before thermal splitting crushed. In addition, he can add more suitable Catalysts are accelerated. So you can Waste containing mainly polyolefins in the presence of manganese, vanadium, copper, chrome, molybdenum or tungsten compounds easily at elevated temperature split into small molecules. The catalytic Effective metals can already be found in plastics are in the form of additives, so that their addition is unnecessary.

The high-molecular feedstocks are converted in conventional reactors, e.g. in closed, with a stirring kettle provided. Usually you work in one step. Especially when develop aggressive gases when processing waste, it is recommended that the splitting process two or to carry out in several stages, the split in the individual Stages generally not at the same temperature, but with increasing temperatures from level to level is operated. This is how it is with chlorine containing polymer proved to be useful, water-moist Plastics first at moderate temperature, the not yet leading to the HCl elimination, to dry one corrosive stress on the reactor materials to avoid aqueous hydrogen chloride. Only after the Drying, the temperature is increased so far that as a result of the cleavage of the polymers hydrogen chloride forms. The dechlorination can be done in an additional Level by further increasing the temperature and the dwell time are completed. The gradually Thermal degradation of chlorine-containing polymeric substances allows, by choosing the reaction temperature, the fission products producing aggressive gases preferred in to enrich the first gap stage, so that in the subsequent Separation of gases harmful to the environment only part of the fission products of a cleaning device must be fed. However, it should be emphasized that even plastic waste, the chlorine on a scale of about 5 wt .-%, according to the invention Process converted into liquid fission products whose chlorine content is only a few 100 ppm is.

The fission products boil in the area of raw gasoline (Naphtha) and the middle distillates and also own the Viscosity of these petroleum fractions. You can therefore be pump with conventional devices.

Leave hydrocarbons formed during the splitting the reactor partly as vapors mixed with Hydrogen chloride and small amounts of other fission gases like carbon monoxide, hydrogen, nitrogen and ammonia. They are made from the gaseous mixture by partial Condensation obtained as an ash-free condensate. It is one for further processing, e.g. on naphtha, suitable raw material. The gas phase containing hydrogen chloride can e.g. be converted into about 30% hydrochloric acid.

The remaining part of the fission product, which is the total Ash contains, is discharged liquid and alone or mixed with other raw materials, e.g. Naphtha, with Water vapor and oxygen converted to synthesis gas.

This reaction can also be carried out by known methods respectively. Processes that are particularly suitable include: problem-free separation of the ashes and their extraction without foreign admixtures allowed. The solution to this task requires the highest possible carbon turnover in the Reactor to discharge soot along with the ashes avoid. Furthermore, for the raw gas, the liquid ash carries special cooling devices. Proven has the immediate cooling with water in one Quench cooler or one of radiation cooler and convection cooler existing system. Close the cooling stage water washes, in the last ash residue removed become. The ash can be stored in landfills or in metals be worked up.

A process that is particularly relevant to pollutant avoidance the claims outlined above is sufficient, e.g. in EP-A-0 515 950. It is characterized in that the feed oxidized under conditions that lead to the formation of about 0.1 up to about 0.3% by weight of carbon black, based on the in the form of Carbon used hydrocarbons. This way of working can also be successfully applied to the Conversion of waste products from plastic waste into Use carbon monoxide-hydrogen mixtures. In this Case is the carbon content of the depolymerized Plastics reference value for the soot content. Its height is in a known manner about the amount of oxygen supplied set, moreover, the use recommend a specially designed burner (see e.g. EP-B-0 095 103). The gasification itself takes place at temperatures between 1100 and 1500 ° C and a pressure of 1 up to 10 MPa. That the gasification reactor with a temperature from 1300 to 1500 ° C leaving raw gas contains in addition Soot in the specified amount of metals and / or metal compounds in liquid form. It will initially be in one Radiation cooler pre-cooled to 500 to 1000 ° C, one temperature range, in which the metallic contaminants solidify without substantial contact with the cooler wall. Some of the solid particles settle in the water sump of the radiation cooler and are discharged from there. For further cooling to 150 to 300 ° C, preferably 260 to 280 ° C, you can manage the rest Portions of fine metal particles and soot particles Raw gas in a convection cooler. Because of the gas contaminants already carried in the radiation cooler are frozen, they affect the effectiveness of the Convection cooler by laying the flow paths and No deposits on the exchange surfaces. The almost The solids are completely separated by washing of the gas with water. This substep of the process is conveniently with the help of wet separators State of the art e.g. packed towers sprinkled with water, which if necessary also in connection with Venturi scrubbers can be applied. The ashes are mechanically removed from the wash water Separation, e.g. Filtration, won.

The carbon monoxide / hydrogen mixture obtained by gasifying the depolymerized plastic waste can be used directly as a starting material for chemical reactions, for example for oxosynthesis. Depending on the composition of plastic waste, the C / H ratio of their fission products is lower than that of heavy fuel oils, the common raw material for synthesis gas production. The CO / H ₂ ratio of 1: 1 required for certain applications (eg in the oxo process) is therefore not always achieved. In order to reduce the hydrogen content, a hydrogen-rich fraction can be separated from the solid-free raw gas in a membrane system, which is burned or worked up by conversion to pure hydrogen. Of course, the gas mixture as a whole can also be converted into hydrogen by conversion.

The figure shows the new process in the form of a block diagram. Plastic waste is broken down thermally in the depolymerization stage at temperatures which, depending on the process, are in the range of 200 to 500 ° C to liquid products, the flowability of which corresponds roughly to that of heavy heating oils at the same temperature. The depolymerization is accompanied by the splitting off of hydrogen chloride from chlorine-containing plastics, the hydrogen chloride is washed out with water from the reaction product and worked up in a known manner, for example to 30% crude acid. In special cases, the hydrogen chloride can also be neutralized in an alkaline wash. The splitting is followed by gasification, ie the partial oxidation of the depolymerized waste with oxygen in the presence of water vapor. Chlorine-carbon compounds remaining in low concentrations in the cleavage product do not impair this process step. The CO / H ₂ mixture resulting from the gasification is washed to remove solids and HCl with water, to which alkaline reagents such as alkali metal carbonate or hydroxide have optionally been added. To produce synthesis gas with a specific CO / H ₂ ratio that differs from the composition of the raw gas, the raw gas is passed through a membrane filter.

Instead of synthesis gas, hydrogen can also be obtained from the raw gas. For this purpose, it is converted, the resulting CO ₂ / H ₂ mixture is sent to a chemical wash and separated into CO ₂ and H ₂ in a pressure swing absorption stage.

example

Recycled packaging material made of plastic with a content of 2.5% by weight of water and 3.3% by weight of chlorine is suspended in a liquid auxiliary phase, which was obtained by thermal splitting of plastic waste, and to separate the water at about 130 ° C. heated. The plastic suspension is then transferred to the cleavage reactor, in which the feed material is depolymerized at about 350 ° C. and has a residence time of about 4 hours. Gaseous fission products are cooled to about 30 ° C and fed to an appropriate absorption system for the separation of hydrogen chloride. The liquid depolymerizate has the following composition. C. = 84.3% by weight H = 12.0 " N = 0.4 " S = 1.3 " ash = 2.0 "

It contains 300 mg Cl / l, has a density of 920 kg / m ³ and a viscosity of 404 mPa. s (at 90 ° C).

Part of the liquid fission product is used as an auxiliary phase (suspension medium) for the thermal fission of further plastic waste, the rest is partially oxidized to water gas. For this purpose, the depolymerizate is reacted with oxygen and water vapor in a known manner at about 1400 ° C. and a pressure of 4 MPa. To generate 1000 Nm ² CO / H ₂ mixture, 400 kg depolymerizate, 325 Nm ³ oxygen and 110 kg steam are required. The raw gas contains 43.8 vol% CO, 48.6 vol% H ₂ and 6.6 vol% CO ₂ ; the CO / H ₂ ratio is about 0.9.

Claims (11)

1. A process for the preparation of synthesis gas from plastic wastes, which comprises thermally cracking the wastes predominantly to give liquid products and transforming the liquid cracking products by partial oxidation into synthesis gas.
2. The process as claimed in claim 1, wherein the thermal cracking is carried out at temperatures between 250 and 450°C, using an auxiliary phase liquid at the reaction temperature.
3. The process as claimed in claim 2, wherein the liquid auxiliary phase is composed of the liquid degradation products of the plastic wastes.
4. The process as claimed in one or more of claims 1 to 3, wherein the thermal cracking is carried out in the presence of catalysts.
5. The process as claimed in one or more of claims 1 to 4, wherein, in particular, if chlorine-containing plastic wastes are present, the thermal cracking is carried out in two or more stages, the temperature increasing from stage to stage and, by choice of the temperature, the majority of the hydrogen chloride resulting as a cracking product being formed in the first stage.
6. The process as claimed in one or more of claims 1 to 5, wherein the partial oxidation of the liquid cracking products is carried out at temperatures between 1100 and 1500°C and at a pressure of 1 to 10 MPa.
7. The process as claimed in one or more of claims 1 to 6, wherein the partial oxidation is conducted in such a way via the amount of oxygen added that about 0.1 to about 0.3% by weight of soot is formed, based on the liquid cracking products.
8. The process as claimed in one or more of claims 1 to 7, wherein the crude gas leaving the gasification reactor is first cooled in a radiant cooler to 500 to 1000°C and is then cooled in a convection cooler to 150 to 300°C.
9. The process as claimed in one or more of claims 1 to 8, wherein the cooled gas is scrubbed with water and the ash suspended in the scrubbing water is thereupon separated off.
10. The process as claimed in one or more of claims 1 to 9, wherein the purified gae is fed to a membrane filter unit to establish a desired CO/H₂ ratio.
11. The process as claimed in one or more of claims 1 to 9, wherein the purified gas is fed to a converter.

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