Hamburg procedure

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The Hamburger method (also BP Chemicals Pyrolysis Process) is a method of fluidized bed pyrolysis for the chemical recycling of plastic materials , biomaterials, and similar materials. It has been developed at the University of Hamburg since the 1970s by Professors Hansjörg Sinn and Walter Kaminsky . The aim is to obtain valuable products that can be used as raw materials in the chemical or petrochemical industry. The plastic is decomposed in a fluidized bed reactor at temperatures between 300 ° C and 900 ° C with the exclusion of oxygen.

Input materials

The Hamburg process is primarily used to recycle plastics. However, wood , straw , bamboo , sewage sludge , oil shale or tanker residues can also be used.

Plastics

It can be both pure plastics, as well as plastic mixtures, such as. B. occurs in household waste to be pyrolyzed. Pure plastics such as polymethyl methacrylate (PMMA), polytetrafluoroethylene (PTFE) or polystyrene (PS) are suitable for the recovery of monomers (reversal of the polymerization ). The pyrolysis of PMMA at 450 ° C and PTFE between 600 ° C and 650 ° C enables well over 90% of the monomer to be recovered. Since PMMA is a mass-produced plastic and the resulting monomer, methyl methacrylate (MMA), is relatively expensive, the Hamburg process can cover costs here. PTFE is only a small waste material, which makes it difficult to recycle it economically. Styrene , around 75% of which can be recovered from PS at 520 ° C, is a cheap raw material, so that it is difficult to achieve cost-covering recovery here too.

In the case of polyolefins such as polyethylene (PE) or polypropylene (PP), the recovery of the monomers is only possible to a limited extent. The monomers ethylene and propylene are always formed during the pyrolysis of polyolefins , but other products are preferred depending on the temperature range. In the lower temperature range (400 ° C - 600 ° C) mainly waxes are produced. In contrast, at higher temperatures (approx. 750 ° C) the chains are broken down further and aromatics such as benzene , toluene and xylenes are formed.

The use of plastic mixtures always results in an inconsistent product mixture that is best suited for incineration . The problem here are plastics such as polyvinyl chloride (PVC) or polyester , which can form corrosive and sublime products that are able to damage the system.

Other input materials

Biomaterials are another possible input. The highest oil yield is achieved at a temperature of around 475 ° C. In addition to an oil with a high water content, there is always between 10% and 40% charcoal. In addition to many phenolic products, the oil contains a number of aromatic substances . Today, this oil is often used as a smoke flavor ( liquid smoke ) because, in contrast to classic smoking, it does not contain any polycondensed aromatics that are considered carcinogenic.

Fluidized bed pyrolysis can also be used to separate inorganic and organic substances. It can be z. B. in the case of oil shale, separate oil and rock.

Technical implementation

The Hamburg process is a continuously operating fluidized bed pyrolysis. Here, a is fluidized from below through a porous plate ( fluidization base ) whirled (fluidized). Quartz sand is usually used as the vortex . However, catalytically active materials, e.g. B. zeolites can be used if they have sufficient thermal stability and hardness . The fluidizing gas used is nitrogen or pyrolysis gas (gas that is created during pyrolysis and is returned to the reactor after the separation of condensable products - circular operation). However, water vapor can also serve as fluidizing gas, which leads to a slight oxidation of the products. The use of oxygen is excluded because it is a pyrolysis and not a combustion. This is why heating is also carried out indirectly using burners or electrically. The pyrolysis products are not mixed with combustion products.

The use of a twin screw feed for the material to be pyrolyzed is characteristic. The first screw is used for metering, while the second screw conveys the material directly into the hot fluidized bed and the decomposition takes place immediately ( flash pyrolysis ). The reaction time is in the range of a few seconds. After pyrolysis, the products are cooled and separated in several steps.

Application examples

In Grangemouth ( Scotland ), BP has been operating a plant since 1998 , which has been expanded to 25,000 t / a over the years. It is operated with local plastic waste at a temperature between 400 ° C and 450 ° C.

From 1984 to 1988, a demonstration plant for the pyrolysis of plastic waste and tires was in operation in Ebenhausen . A tire pyrolysis plant was also in operation in the GDR from 1984 to 1989 .

literature

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