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BROMINE RECOVERY FROM THE PLASTICS FRACTION OF ...

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THE PLASTICS FRACTION OF WASTE FROM ELECTRICAL AND ELECTRONIC EQUIPMENT (WEEE) CONTAINING BROMINATED FLAME-RETARDANTS COULD POTENTIALLY BE PROCESSED TO CLOSE ...

BROMINE RECOVERY FROM THE PLASTICS FRACTION OF WASTE OF

    ELECTRICAL AND ELECTRONIC EQUIPMENT (WEEE) WITH STAGED

    GASIFICATION

    aabHarold Boerrigter, André B.J. Oudhuis, and Lein Tange

    a Energy research Centre of the Netherlands (ECN), Unit ECN Biomass, P.O. Box 1, 1755 ZG Petten,

    the Netherlands, Phone +31-224-564591, email boerrigter@ecn.nl

    b DSBG, Verrijn Stuartlaan 1c, 2288 EK Rijswijk, the Netherlands, email tangel@eurobrom.dsbg.com

    The plastics fraction of Waste from Electrical and Electronic Equipment (WEEE) con-taining brominated flame-retardants could potentially be processed to close the bro-mine loop at the End-of-Life. Staged-gasification, comprising pyrolysis (550?C) and high temperature gasification (>1230?C), is a process suitable for this purpose. In test runs with two plastics WEEE fractions in the ECN installation 'Pyromaat' bromine was recovered by 'wet' alkaline scrubbing of the syngas. Utilising auxiliary gases resulted in higher percentages of volatised bromine (of >96%, compared to 81% without auxil-iary gases). The produced scrubber solutions are free of contaminating organic com-pounds ('tars') and may contain ~95% of the bromine in the feed.

1. INTRODUCTION

    The consumption of electrical and electronic equipment (EEE) within the European Union has increased from 5.8 million tons per year in 1980 to 13.6 million tons in 2000, which relates to an increase of 134% over the twenty-year period [1]. The total waste of electrical electronic

    equipment (WEEE) is amounting to 4.4 millions tons in 2000 [1,2]. In a sustainable society

    the need for virgin materials and fossil fuels should be minimised. To realise this, waste must be optimally converted into energy and products [3].

     In the Netherlands, currently Mirec and Coolrec recycle WEEE - this recycling is compa-rable to the recycling of cars and white goods due to the similarity in composition (see Fig-ure 1). For WEEE ~75% of the material is recovered to be used as recycled feedstock. This fraction comprises glass, wood, and mainly the Ferrous and non-Ferrous metals. The non-Ferrous metals comprise aluminium, copper, and smaller amounts of the valuable noble-metals gold, silver, and palladium. In a mixed WEEE stream the plastics fraction accounts for ~20%. The plastics contain some minor amounts of metals and other components due to the non-optimal separation [2]. ECO-impact studies have demonstrated that there is a limit of 15 to 18% of this plastics waste that can be mechanically recycled with environmental benefits. Further mechanical recycling requires relatively many efforts that annul the environmental gain [4]. This means that the majority of the remaining waste must be recycled by other tech-niques.

    ? ECN Biomass page 1 of 6

    Figure 1. Breakdown of Cars & White Goods and WEEE into fractions for mechani-

    cal recycling, feedstock recycling, energy recovery, and the residue [3].

    Approximately 12% of the plastics used in EEE contains flame-retardants, in most cases comprising brominated flame-retardants (BFRs). The major applications of BFRs in EEE are brown goods, office equipment, and printing circuit boards. The more frequently used poly-mer for brown goods is HIPS (High Impact Polystyrene). HIPS is generally associated with the BFR decabromodiphenyl ether (DECA). Housing of office equipment is generally associ-ated with the BFR's tetrabromobisphenolA (TBBA) and octabromodiphenyl ether (OCTA) or brominated epoxy oligomers (produced from TBBA). The element antimony (Sb) is generally added to BFR's as a synergist to improve the flame-retardant behaviour of EEE plastics. A (mass) relation of 3-4 to 1 for Br and Sb is typical for flame-retardants [2] except in Printed Circuit boards.

     Recycling of plastics WEEE, containing BFRs, means preferably feedstock recycling of bromine, antimony, the valuable metals, and recovery of the energy content. Combustion, gasification, and pyrolysis-based technologies have in principal the possibility to realise this. In 2000 ECN Biomass performed a study in which eight processes were evaluated on the suitability for the feedstock recycling of bromine and antimony, with energy recovery [3]. It was concluded that four processes are in principle able to process WEEE, of which staged gasification is the "best available technology" (although with minimal operational experi-ence) [3].

     As continuation, the technical feasibility had to be assessed of using bromine salts pro-duced in the selected thermal processes as feedstock for the bromine industry to close the loop. For this purpose, a staged-gasification test in the ECN Biomass bench-scale ‘Pyromaat’

    installation was performed. Bromine was recovered from the syngas by wet alkaline scrub-bing. Experimental data was acquired on bromine partitioning in the process for mass and ? ECN Biomass page 2 of 6

    Table 1. Ultimate analyses of the two tested WEEE materials.

    Average composition WEEE mix1 TV backplates

    [wt%, dry]

    C 69.6 81.2

    H 6.6 7.2

    N 2.49 1.1

    F 0.30 ~

    S 0.11 0.03

    Cl 2.64 1.6

    Br 1.60 3.1

    ash 10.6 1.33

    O (by difference) 6.12 4.47

    Sb [g/kg] 2.7 24.0

    LHV [MJ/kg] 31 38

    energy balance calculations. This paper describes the results of the staged-gasification test with a focus on the production of a bromine solution and the fate of bromine.

2. EXPERIMENTAL

    Two plastics fractions of WEEE were tested: "WEEE mix1" and "TV backplates". The compo-sitions are shown in Table 1, although the remark should be made that the variations of the composition can be quite large, even within the fractions. The fractions were provided by EBFRIP and are representative for existing industrial material streams. The two materials tested have a relatively high bromine content (of 1.6 and 3.1 wt%, respectively) compared to other plastics WEEE fractions.

     The ECN unit ‘Pyromaat’ is a lab-scale staged-gasification installation with a capacity of 5 kg/h. The process layout is comparable to the full-scale installations that are marketed by the Dutch company Gibros PEC. The basic process layout with the functional units of the ‘Py-

    romaat’ is shown in Figure 2. In the test runs 1.2 to 1.5 kg/h feed material was introduced into the externally heated pyrolysis reactor equipped with a rotating coil. Upon pyrolysis at 550?C (residence time >15 min) the material decomposed in a tar-rich gas and solid residue (char). The plastics WEEE fractions contain large amounts of the halides bromine and chlorine, that upon pyrolysis were released as mainly HBr and HCl, and to a lesser extent Br and Cl. Part 22

    of the bromine and chlorine remained (inorganic) bound in the char [5]. Besides the halide

    compounds, the pyrolysis gas comprised CO, H, CO, HO, CH, CH, BTX (benzene, tolu-2224xy

    ene, and xylenes), and tars (heavier organic compounds).

     After the reactor the char is collected in a closed container. The gases flow into the high temperature gasifier (i.e. tar cracker) that was operated at temperatures >1230?C to break-down all the tars. The fuel gas from the gasifier existing of CO, H, CO, and HO was 222

    scrubbed with an aqueous NaOH solution (initial pH >10) in the wet scrubber to remove all the HBr and HCl from the gas. The scrubber consists of a pump, a filter to remove dust and soot from the water, and a buffer tank. The syngas leaving the scrubber was combusted in a ? ECN Biomass page 3 of 6

    Bromine recovery

    via NaBr

    Figure 2. Impression of the 'Pyromaat' with the material flows, gas flows, and

    analysis points indicated.

    closed combustion chamber while NH was injected into the flared gas to neutralise small 3

    amounts of halide compounds present in the gas.

3. RESULTS OF TEST RUNS

    The high carbon content of the plastics WEEE (70 and 81 wt%, respectively, for WEEE Mix1 and TV backplates) gave rise to the formation of large amounts of soot (i.e. pure carbon dust).

    The high soot loads of the gas give rise to the risk of blocking of the pipe connecting the py-rolysis reactor and the gasifier (Figure 2), which would have resulted in pressure build-up in the reactor. Short test runs were carried out to minimise fouling and deposited soot was re-moved between the runs. Furthermore, fouling was minimised by the addition of auxiliary gases to the system

     In test run #1 with WEEE Mix1 as feed without auxiliary gases, 19 wt% of the bromine and 31 wt% of the chlorine remained inorganically bound in the char phase (Table 2). Espe-cially calcium (Ca), present in the feed in 10 g/kg as CaCO, is known to form stable halide 3

    salts. The halides volatised mainly as HBr and HCl and, possibly, to minor extent as Br and 2

    Cl. Furthermore, part of the halides was volatilised with antimony as the (mixed) halide salts 2

    SbX (SbBr, SbBrCl, SbBrCl, and SbCl that all boil at ~280?C [6]). The volatilisation ac-33223

    counts for the low recovery of antimony in the char. The higher percentage of chloride recov-ered in the char compared to bromine might be explained by the higher stability of the inor-ganically bound chlorides compared to the bromides. In contact with water in the scrubber all these antimony compounds hydrolyse to the antimony trioxide SbO and dissolve [3]. 23

     In the WEEE Mix1 test run #2 auxiliary gases were used and the char production was ~30% lower. The decreased recovery of antimony is in line with the lower char flow (one-third ? ECN Biomass page 4 of 6

Table 2. Char flow in different test runs and recovery of the halides and antimony in the char.

    Feed / Condition WEEE Mix1 (#1) WEEE Mix1 (#2) TV backplates

    Feed flow [kg/h] 1.19 1.19 1.20

    Char flow [kg/h] 0.45 0.30 0.14

    Char as fraction from feed [-] 0.38 0.25 0.12

    Recovery in Char

    Bromine (Br) 19% 3.5% 2.3%

    Chlorine (Cl) 31% 7.4% 2.5%

    Antimony (Sb) 3.7% 2.5% 0.6%

    lower). However, the effect on the halide recovery in the char is much bigger, i.e. that is ap-

    proximately 5 times lower. The auxiliary gases lead to locally higher temperatures in the ma-terial and resultantly in more volatilisation of the halides as HBr and HCl. In the test run with TV backplates only <3 wt% of the halides and antimony remained in the char. This is a result of the combination of the low calcium content in the feed, a low char production, and the utili-sation of auxiliary gases.

    The syngas containing most of the halides (81 to >96 wt% bromine and 69 to >97 wt% chlo-rine) was scrubbed with a NaOH solution in the 'wet' scrubber. After the experiments the vol-umes of the two scrubber solutions of the WEEE Mix1 and TV backplates tests were concen-trated. Both concentrated solutions were analysed to check on the presence of organic com-pounds in the water, i.e. possible tar residues. In both solutions no organic compounds were present: Dissolved Organic Carbon concentration DOC = 0 mg/kg (suspended soot was re-moved by filtration prior to analysis). Due to the absence of oxygen in the syngas it is ex-pected that the concentration of possibly present dioxins and furans is at least twelve times lower than in the case of combustion of the materials [7].

4. CONCLUSION

    Staged-gasification test runs were performed with two plastics WEEE fractions: WEEE MIX1 and TV backplates. Upon pyrolysis of these material a lot of soot is formed that ultimately may result in blockage of the installation. Auxiliary gases were used to minimise soot forma-tion and fouling. The use of auxiliary gases resulted furthermore in lower char flows, and as result, higher percentages of bromine (and chloride) and antimony that were volatilised. For WEEE MIX1 the bromine volatilisation increases from 81 to >96 wt% upon, while for TV backplates the volatilisation is >97 wt%. When using auxiliary gases the partitioning of the elements to the gas phase is favoured, which allows higher recovery rates in the wet alkaline scrubber. Recovery of ~95% of the mass of bromine in the feed can be achieved based on a scrubber efficiency of 99%. The gasifier was operated at temperatures >1230?C to destruct all tars, therefore, the water of the scrubber remained free of contamination with organic compounds.

? ECN Biomass page 5 of 6

    In conclusion, it was shown that staged gasification is a very suitable technique to produce bromine solutions by wet alkaline scrubbing, although processing plastics from WEEE brings about specific technical issues. By applying auxiliary gases the bromine partitioning can be pushed to the gas phase and due to the high-temperature gasifier no organic contamination of the water will take place. Due to the feeding of pure plastics from WEEE it is possible to produce a highly concentrated bromine stream. With staged-gasification it is possible to re-cover 10-30 kg bromine from 1000 kg plastics from WEEE.

    The next activity is the testing within the bromine industry of the produced bromine solutions for recovery of the bromine to close the loop. Furthermore, the optimal process layout and operational conditions have to be determined and an assessment made of the technical and economical feasibility of bromine recycling with staged-gasification.

ACKNOWLEDGEMENTS

    The work described in this paper was sponsored by the European Brominated Flame Retar-dant Industry Panel (EBFRIP), a sector group of the European Chemical Industry Council (CEFIC). The authors acknowledge H. Bodenstaff and R.W.A. Wilberink for performing the staged-gasification experiments and J. Kuipers for performing the chemical analysis.

5. REFERENCES

    1. APME report, Plastics, a material of innovation for the electrical and electronic industry -

    Insight into consumption and recovery in Western Europe 2000, Spring 2001.

    2. European Brominated Flame Retardants Industry Panel Recovery of bromine & antimony

    from waste electrical & electronic equipment containing bromine in the European Union,

    PB Kennedy & Donkin Limited report, BECCH074.1071, May 1999.

    3. Boerrigter, H. Implementation of thermal processes for feedstock recycling of bromine

    and antimony, with energy recovery, from plastics waste of electrical and electronic

    equipment (WEEE). Phase 1: Literature survey/status update, evaluation, and ranking of

    combustion, gasification, and pyrolysis based technologies, Energy research Centre of

    the Netherlands (ECN), Petten, The Netherlands, ECN-C--00-104, November 2000. 4. (a) APME Summary Report, Separated mixed plastics waste as a fuel source, 1997. (b)

    APME Summary Report (TNO study), Accessing the eco-efficiency of plastics packaging

    waste recovery, No 8034/GB/01/00, January 2000.

    5. Chien, Y.-C.; Wang, P.H.; Lin, K.-S.; Huang, Y.-J.; Yang, Y.W. Chemosphere 40 (2000)

    383-387.

    6. Handbook of Chemistry and Physics, Lide, D.R. (ed.), 71st ed., CRC, 1990-1991. 7. Pekárek, V.; Grabic, R.; Marklund, S.; Punčochář, M.; Ullrich, J.: Effects of oxygen on

    formation of PCB and PCDD/F on extracted fly ash in the presence of carbon and cupric

    salt, Chemosphere 43 (2001) 777-782.

    ? ECN Biomass page 6 of 6

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