INTRODUCTION 27

5 SOME FEASIBLE PROCESSES

A brief survey is given of a number of processes that have been used in Europe forplastics pyrolysis. At present, all of these projects have been mothballed. The most relevantinitiatives are according to [15] :1. Hamburg University Pyrolysis Process, high-temperature pyrolysis of mixed plastics,

using a uid bed reactor. Demonstration plant at Ebenhausen has not survived shake-down, due to various operating problems.

2. BASF low-temperature pyrolysis of mixed plastics, using a battery of stirred tankreactors for liquefaction.

3. BP low-temperature pyrolysis of mixed plastics, using a uid bed reactor.4. Veba Oil hydrogenation technologies.

5.1 PILOT AND INDUSTRIAL PLANT OPERATION

5.1.1 Hamburg University, Ebenhausen

A plant operating according to the Hamburg University pyrolysis process was built atEbenhausen, with a capacity of 5000 tonnes per year. The feasibility of converting poly-olens by pyrolysis was successfully demonstrated, with yields from PE/PP mixtures oftypically 51% (m/m) gas, 42% (m/m) liquids and the balance unaccounted for. However,the gas to liquids ratio is very sensitive to pyrolysis temperature. Since gas and oil are themajor pyrolysis products, economic viability crucially depends on the price of crude oil.Under present conditions, protability and economic viability are unsatisfactory at thissmall scale of operation.

5.1.2 BASF, Ludwigshafen

The BASF feedstock recycling process was designed to handle mixed plastic waste, assupplied by the DSD (Duales System Deutschland) green dot packaging collection system.A large pilot plant, with a substantial capacity of 15 000 tonne/yr, was started up inLudwigshafen in 1994. At that time DSD estimated the total volume of mixed packagingplastics available for feedstock recycling at around 750 000 ton/yr. BASF offered to erecta full-scale industrial plant with a capacity of 300 000 ton/yr, but decided in 1996 to shutdown the pilot plant, since no agreement could be reached on a guaranteed long-termwaste supply and a gate fee sufcient to cover the costs.

In the BASF process, plastic waste is converted into petrochemical products in a three-stage process. Before feeding, the plastics are shredded, freed from other materials andagglomerated, to improve handling and enhance the density. In the rst stage, the plasticsare melted and liqueed in an agitated tank. The gaseous hydrochloric acid, evolving fromPVC at temperatures up to 300C, is absorbed in a water washer, and further processedto aqueous hydrochloric acid, to be reused in other BASF production plants.

In a second stage, the plastic oil was fed into a tubular cracker reactor, heated at over400C and thus cracked into compounds of different chain lengths, forming petrochemicalraw materials. The oils and gases thus obtained are separated in a third stage, resultingin the production of naphtha, aromatic fractions, and high-boiling oils. About 2030%of gases and 6070% of oils are produced and subsequently separated in a distillationcolumn.

28 A. BUEKENS

Pre-treatmentPlastic Liquefactionand cracking Separation

HCI

Gases

Oils

High boilers,residues

Figure 1.1 Schematic representation of the BASF pyrolysis process. (Reproduced bypermission of TNO)

The naphtha produced by the feedstock process is treated in a steam cracker, and themonomers (e.g. ethylene, propylene, butadiene) are recovered. These raw materials arethen used for the production of virgin plastic materials. High-boiling oils can be processedinto synthesis gas or conversion coke and then be transferred for further use. All theseproducts have outlets in the local BASF production plants.

During two years of trial operation, the pilot plant demonstrated its suitability. Althoughthe process can be considered proven, it is at present neither used by BASF, nor elsewherein Germany, because the quantities of plastic waste and dump fee needed for the plant tobe economically viable are not available in Germany (Figure 1.1).

The process products are:

HCl, which is either neutralized, or processed in a hydrochloric acid production plant; naphtha to be converted into monomers in a steam cracker; various monomers, which can be used for the production of virgin plastic materials; high-boiling oils, to be processed into synthesis gas or conversion coke; process residues, consisting typically of 5% minerals and metals, e.g. pigments or

aluminium can lids.

Processing plastic waste by the BASF process would have required a gate fee of160/tonne for a plant with a capacity of 300 000 tonne/yr and a fee of 250/tonne for aplant capacity of 150 000 tonne/yr [15].

5.1.3 BP, Grangemouth

In the early 1990s BP Chemicals rst tested technology for feedstock recycling, usinga uid bed cracking process. Research on a laboratory scale was followed (1994) bydemonstration at a continuous pilot plant scale (nominal 50 kg/hr) at BPs Grangemouthsite, using mixed waste packaging plastics. The technology was further developed withsome support from a Consortium of European companies (Elf Atochem, EniChem, DSM,CREED) and from APME. In 1998, BP Chemicals, VALPAK and Shanks & McEwan, setup a joint project (POLSCO), to study the feasibility of a 25 000 tonne/yr plant, includinglogistics infrastructure for supplying mixed plastics from Scotland. The project was seenas a remedy to the expected UK shortage in recycling capability, required to comply withEU and UK Packaging and Packaging Waste Directive.

INTRODUCTION 29

Some preparation of the waste plastics feed is required before pyrolysis, including sizereduction and removal of most nonplastics. This feed is charged into the heated uidizedbed reactor, operating at 500C, in the absence of air. The plastics thermally crack tohydrocarbons, which leave the bed together with the uidizing gas. Solid impurities andsome coke either accumulate in the bed or are carried out as ne particles and capturedby cyclones.

The decomposition of PVC leads to HCl formation, which is eventually neutralized bycontacting the hot gas with solid lime, resulting in a CaCl2 fraction to be landlled. Theprocess shows very good results concerning the removal of chlorine. With an input of1% Cl, the products contain 10 ppm Cl, somewhat higher than the 5 ppm typical ofrenery use. Also, metals like Pb, Cd and Sb can be removed to very low levels in theproducts. Tests have shown that all hydrocarbon products can be used for further treatmentin reneries. The puried gas is cooled, condensing to a distillate feedstock, tested againstagreed specications before transfer to the downstream user plant. The light hydrocarbonpyrolysis gases are compressed, reheated and returned to the reactor as uidizing gas.Part of this stream could be used as fuel gas for heating the cracking reactor, but as itis olen-rich, recovery options were also considered. The ow scheme is illustrated inFigure 1.2.

The process ow diagram shows hydrocarbon recovery in two stages, since the heavyfraction becomes a wax at about 60C. Once recovered, the light and heavy fractions(about 85% by weight) could be combined together for shipment to downstream reneryprocessing if the plastic feed is passed on as hydrocarbon liquid to the downstream plants.The balance is gaseous at ambient temperature and could be used to heat the process. Inthis way nearly all of the plastic is used with just solids separated as a waste product.The gas has a high content of monomers (ethylene and propylene) with only some 15%being methane.

Conceptually, the process can run in self-sufcient heating mode. In this case, overallgas caloric requirement may need a small net export or import as the product gas quality

Plasticswaste

Limeabsorber

Reactor

Fuel gas

FilterHydrocarbon

Distillate feedstock

Figure 1.2 Schematic representation of the BP process. (Reproduced by permission ofTNO)

30 A. BUEKENS

varies with plastic feed specication and operating conditions. The other main utilitiesneeded are:

electrical power 60 kWh/tonne feed plastic; cooling water 40 m3/tonne feed plastic; steam 1.2 tonne/tonne feed.

All emissions are very low and should comply with local regulations.The cost of treatment depends on many factors such as scale, location, scope, required

preparation stages, and economic parameters used. Hence, comparison of the processes isdifcult. The investment costs of a plant of 25 000 tpa, located in Western Europe in 1998,were estimated as 1520 M. Under these conditions, a gate fee of some 250 /tonne isnecessary. For a 50 000-tpa plant this gate fee could be some 150 /tonne. These guresexclude the cost of collection and of preparation.

5.1.4 Veba Oil, Bottrop, Germany

From 1981 Veba Oil AG operated a coal-to-oil hydrogenation plant at Kohleol AnlageBottrop (KAB) in Germany, using the Bergius Pier coal liquefaction technology to convertcoal into naphtha and gas oil. In 1987 the plant was modied, applying Veba CombiCracking (VCC) technology to convert crude oil vacuum distillation residues into syntheticcrude. Since 1988 a share of the petroleum residue feedstock was substituted by chlorine-containing waste (containing, e.g. PCBs). In 1992/1993 a depolymerization unit was addedin front, to process exclusively mixed plastics waste from packaging, as collected by DSD.In 1998 some 87 000 tonnes were treated. DSD and Veba both agreed to terminate theircontract in 1999, instead of in 2003: hydrogenation was unable to compete economicallywith treatment in blast furnaces and with the SVZ process at Schwarze Pumpe.

The plant includes rst a depolymerization section and then the VCC section(Figure 1.3). In the rst section, the agglomerated plastic waste is depolymerized anddechlorinated at 350400C. The overhead product is partly condensed. The main part(80%) of the chlorine introduced evolves as gaseous HCl in the light gases and iswashed out, yielding technical HCl. The condensate, still containing some 18% of thechlorine input, is fed to a hydrotreater where the chlorine is eliminated together with thewater formed. The resulting chlorine-free condensate and gas are again mixed with thedepolymerizate for further treatment in the VCC section.

There, the depolymerizate is hydrogenated under high pressure (about 10 MPa) at some400450C, using a liquid phase reactor without internals. Separation yields a syntheticcrude oil, which may be processed in any oil renery. Light cracking products end up in theoff-gas and are sent to a treatment section, for removal of ammonia and hydrogen sulphide.A hydrogenated bituminous residue comprises heavy hydrocarbons, still contaminatedwith ashes, metals and salts. It is blended with coal for coke production (2 wt%).

The input specications for the plastic waste are:

particle size