Fuel 90 (2011) 2334–2339

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Fuel

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Short communication

Hydrogen production by catalysed pyrolysis of polymer blends

P. Bober a,⇑, A. Orinák b, R. Orinaková b, P. Zamostny c, J. Ladomersky a, A. Fedorková d

a Faculty of Ecology and Environmental Sciences, Technical University in Zvolen, T.G. Masaryka 24, 960 53 Zvolen, Slovakiab Faculty of Sciences, Institute of Chemistry, University of P.J. Šafárik, Moyzesová 11, 041 54 Košice, Slovakiac Faculty of Chemical Technology, Institute of Chemical Technology Prague, Technická 5, 166 28 Prague 6, Dejvice, Czech Republicd Department of Analytical Chemistry, Faculty of Science, Comenius University, Mlynska Dolina, 842 15 Bratislava 4, Slovakia

a r t i c l e i n f o

Article history:Received 19 March 2009Received in revised form 27 January 2011Accepted 1 February 2011Available online 16 February 2011

Keywords:PyrolysisGCCatalysisMethane to hydrogen conversion

0016-2361/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.fuel.2011.02.001

⇑ Corresponding author.E-mail address: bober.peter9@gmail.com (P. Bober

a b s t r a c t

Differently composed mixtures of HDPE and PMMA were pyrolysed at 700 �C and 815 �C in pyrolysisreactor. It was directly coupled with gas chromatography/mass spectrometry (GC/MS). On line pyrolysisGC/MS was applied in analysis of hydrogen, methane and carbon monoxide yielding in polymer blendspyrolyzate with/without metal (Ni,Co) coated particles, tested as a methane to hydrogen conversion cat-alysts supporting additives. They were prepared by electrochemical deposition of Ni and Co on the smalliron particles surface. Maximum hydrogen production was confirmed at the highest pyrolysis tempera-ture (815 �C), and the highest HDPE contents in the blends mixture. Higher content of the PMMA in themixture led to higher production of CO and lower hydrogen contents in pyrolyzate. Nickel and cobalt con-taining additives affected production of hydrogen and other components at both 700 �C and 815 �C pyro-lysis temperatures. An effect of different heat distribution between metal particles and polyblendsoccurred and affected hydrogen production. Application of pyrolysis gas chromatography in hydrogenproduction from polyblends represents an important tool to model future technological outputs as wellsimultaneous hydrogen production and CO, CO2 elimination. Moreover, catalysis assisted conversion ofmethane to hydrogen can improve final hydrogen content in pyrolyzate. Effectivity of pyrolysis hydrogenproduction was determined by its quantification based on analytical calibration.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

The demand for energy and its resources is increasing day byday due to the rapid outgrowth of population and urbanization.As the major conventional energy resources like coal, petroleumand natural gas are at the verge of getting extinct, polymer wastecan be considered as one of the promising environment friendlyrenewable energy options [1].

Pyrolysis represents a unique and reliable method to studythermal degradation processes of the polymers or wastes. Originalis application in modeling of hydrogen production from differentsources. Thermal degradation during pyrolysis undergoes in innertatmosphere (nitrogen and none carbon dioxide, as greenhouse gas,formed. From this reasons pyrolysis can be applied in hydrogentechnologies.

The increase of a pyrolysis temperature at the thermal polymersdegradation causes the increase of an amount of the hydrocarbongases and the decrease an amount of oil/wax [2]. The hydrocarbongases, extracted from the pyrolysis of polypropylene, polyethylene,

ll rights reserved.

).

polystyrene, polyethylene terephthalate and polyvinyl chloride,consist mainly of the alkanes (methane, ethane, propane, butane)about 80% and the alkenes (ethylene, propylene, butylene) about10–20% [3]. The extract of gaseous H2, obtained by a plasticpyrolysis at 500 �C, presented 0.13% (polyethylene), 0.13% (poly-propylene), 0.17% (acrylonitrile butadiene styrene), 0.24% (polysty-rene) and 0.52% (polyethylene terephthalate) [4]. The pyrolysisdegradation of HDPE in fluidized bed reactor produced 0.4(w/w)% of H2 at 685 �C, 1.2% (w/w) at 780 �C, until 1.8% (w/w) at850 �C. The pyrolysis temperature as well as the freeboard temper-ature have a great influence on the process and affect the productdistribution and gas composition due to the secondary reactions inthe freeboard. At around 780 �C the gas production stabilizes. Thetemperature also affects the composition of the gas phase, since anincrease in H2, CH4 and C2H4 yields is observed [2]. Very importantprocedure for improved hydrogen production is co-pyrolysis withbiomass. It leads to maximum production of light liquids atoptimum temperature. The origins of both biomass and plastichad significant influences on the co-pyrolysis products/distribu-tion. In some cases non-additive effects were observed [5–7]. Inter-esting in hydrogen production seems to be two steps pyrolysis:thermal degradation of plastics followed with catalytic steamreforming of pyrolysis gases and vapours [8]. At higher pyrolysis

P. Bober et al. / Fuel 90 (2011) 2334–2339 2335

temperatures (over 700 �C) increases also amount of methane ingaseous phase. Its catalytic conversion to hydrogen improves con-tents in gaseous phase.

Different monometallic and bimetallic catalysts were studied atthe decomposition of the gaseous and liquid hydrocarbons onhydrogen and carbon products [9,10] Especially Ni catalysts hadthe high catalytic activity in hydrogen conversion and produce car-bon nanofibers and nanotubes at the temperature range of 500–700 �C. Using Ni catalyst at 60–70% (w/w) conversion of CH4 pro-duced 80% (w/w) of H2 in the temperature range 700–800 �C[11]. The noble metals (Pt, Rh, Pd) were used as the supportingsubstances to improve the thermal stability and the activity of me-tal catalyst.

Some of bimetallic catalysts consisting of Fe, Ni, Pd, Cu metalsproduced the higher amount of H2 than the monometallic catalysts[12–15]. Using binary Fe-M (M = Pd, Mo or Ni) catalysts with sup-port of alumina oxide at catalytic dehydrogenating of CH4 and tem-perature 700–800 �C more than 80% (w/w) H2 was obtained[16,17].

Of the thermodynamics aspect decomposition of the liquid car-bons is more preferable to the decomposition of CH4, as there is re-quired 1.5–2 times less energy to make a unit volume of H2.

Besides the metallic catalysts a variety of carbon materials ofdifferent origins and structures, including of activated carbon(AC), carbon black (CB), microcrystalline graphite and nanostruc-tured carbons have been used. Using AC catalyst at (propane,methane, gasoline) decomposition at temperature 880–920 �C pro-duced 80% of H2. However, pyrolysis gas contained lower concen-tration of H2 (in average 70%) by using CB catalyst [18].

The objective of the present study has been to analyze the effectof metal coated iron particle containing additives and polymercomposition in polyblends on the pyrolyzate composition obtainedby pyrolysis of PMMA and HDPE over samples of metal additives(powdered particles with electrolytic deposited Ni and Co coat-ings). Study was focused on hydrogen contents of gas fraction ofpyrolyzate in relation to variations in HDPE/PMMA ration in blendsand on the yields of the most important compounds (CO, CO2 andCH4) occurred in each system. A detailed comparison is made withresults obtained by other authors under similar or different exper-imental conditions that may contribute to a better understandingof the potential of the catalytic pyrolysis process as a promisingpolyethylene recycling process, hydrogen production and carbonoxides elimination.

2. Material and methods

2.1. Standards and chemicals

For optimized production of hydrogen by pyrolysis degradationwe used following chemicals and samples: polyblends – polyethyl-ene (HDPE) and poly(methyl methacrylate) (PMMA) in the rate of4:1 and 1:4. Both polymers purchased from Alfa Aesar (Karlsruhe,Germany). Samples of metal additive (powder particles withelectrolytic deposited metal coating) composed of additive no. 42(Ni – 43%, Co – 26.3%, Fe – 30.7%), additive no. 44 (Ni – 17%, Co –6%, Fe – 77%). A high level controlled electrochemical metal platingof the homogeneous, uniform and adhesive Ni–Co micro-layer onFe micro-particle powder substrate was performed in the stirredheterogeneous system (SHS). Perfect homogeneity, uniform, evenand adhesive metallic coating of the product and a high level con-trol of the overall process are the main advantages of electrochem-ical metal plating of the powder substrate in the SHS. Solid metallicparticles are dispersed by a mechanical stirring of the electrolyte.The dispersed particles intermittently come into the contact witha solid electrode to be charged and thereby coated with a metallic

layer. This electrochemical reactor system possesses variousadvantages, in particular a significantly larger reaction area andenhanced mass transport. In the optimal case, every particle ofthe powder will be coated by the plating metal(s) thus ensuringa high homogeneity of the final product.

Iron powder (type ASC-200) prepared by a pressure wateratomization process (Mannesmann) was used as a material forthe electrolytic coating by nickel and cobalt. The particle size frac-tion (63–100) lm was used. The geometric surface area, differentfrom the real surface area, was determined by BET analysis.Specific surface area of Fe spheres for granulometric fraction(63–100) lm was 95.2 cm2 g�1.

A thermostatic electrolytic cell with separated cathodic com-partment formed by cylindrical vessel with textile net diaphragm(mesh size about 0.04 mm) was used. The suspension formed by5 g of Fe powder and of electrolyte (75 ml) in cathodic compart-ment was held in fluidized state by intensive circular stirring(800 rpm) during galvanostatic electrolysis for 30 min withconstant current intensity 0.2 (additive no. 44) or 0.8 A (additiveno. 42). Sheet solid cathode (15 cm � 2.4 cm � 2 mm; workingarea = 15.84 cm2) and anode were made from stainless steel. Cath-ode was placed near the wall of the cylindrical cell. The powdermaterial was introduced into the cathodic compartment of the cell.

The iron powder was chemically activated by etching in reduc-ing agent (10% solution of hydrazine dihydrochloride) for 5 min be-fore electrolysis. The plating electrolyte consisted of 0.69 M NiSO4,0.125 M CoSO4 and 0.26 M NaCl (adjusted to pH = 2).

The content of deposited Ni and Co was determined afterdissolution in nitric acid by Atomic Absorption Spectrometry(AAS) PERKIN-ELMER 420.

HDPE and PMMA, each separately specially were mechanicallyhomogenized in porcelain mortar. Consequential sample of polybl-ends (after mixing) weighted approximately to 50 mg. By this pro-cess were prepared four 4 samples in the ratio HDPE:PMMA = 4:1and next four 4 samples in the ratio HDPE:PMMA = 1:4. These sam-ples were undergo qualitative and quantitative Py-GC/MS analysisof hydrogen content as well contents of other constituents. Forconstruction of calibration graph we used standard stuff gaseoushydrogen from sampling bag. Advanced filling and dischargingwere repeated. That the volume of gaseous hydrogen within ap-proach 100% concentration of gaseous hydrogen. Hydrogen con-tents have been calculated based on equation: p � VH2 = nH2 � R � T,where VH2 is calibrated and determined hydrogen content inblends pyrolyzate. From this equation a mass of hydrogen has beenexactly calculated as others parameters were constant and known.Weight percentage was calculated:

WH2 ¼mH2P

mi100%

where mH2 = weight of H2,P

mi = summary weight of H2, CH4 a CO,the same calculation is for wCH4 and wCO.

2.2. Methods, instrumentation and determination conditions

Component analysis of hydrogen, methane and carbon monox-ide in pyrolyzate of polyblends was performed with GC/MS – QP2010 connected to A/D converter and personal computer withcompetent software equipment. Device consisted of two basicparts: the chromatograph GC 2010 with mass spectrometric detec-tor (MSD).

Chromatographic separation was performed on column Molsi-eve 5 A with stationary phase thickness 30 lm, column internaldiameter 0.32 mm and column length 40 m. As a carrier gas hasbeen helium utilized at pressure 59 kPa and total flow12.9 mL/min. Temperature of injector was 60 �C, initial pyrolyzertemperature was 150 �C and increased to 700 �C and 815 �C by

2336 P. Bober et al. / Fuel 90 (2011) 2334–2339

polyblends analysis. Temperature of column was 60 �C, 40 flowcolumn, 0.90 mL/min and column temperature program:60 �C/20 min.

2.3. Quantification of solid and gaseous sample

Solid sample was applied in platinum sample boat. Aliquotquantity of prepared sample was weighted in platinum sampleboat by balance. Then it was applied special holder insert ininjector chaplet, in which temperature and pressure were beforealone by inserting zero. After installation holder together withplatinum sample boat we are again increase pressure and temper-ature of injector. Samples of gaseous hydrogen we are take away

Fig. 1. Hydrogen contents (w/w%) obtained from pyrolyzates of polyblends HDPE/PMM700 �C. Sample amount: 1 mg. (b) Formation of methane and (c) CO in pyrolyzate (give

from sampling pocket by help of injector squirt with volume1000 ll.

3. Results and discussion

The results obtained from Py-GC/MS analyses of HDPE/PMMApolyblends showed evident maximum hydrogen formation frommixture containing four part of HDPE and one part PMMA at815 �C pyrolysis temperature (Fig. 1). It is evident because HDPEdoes not contain any other atoms like oxygen, nitrogen or others.At 815 �C it was about 66.1% (w/w) of hydrogen yield more thanat pyrolysis temperature 700 �C. If ratio HDPE/PMMA has beenchanged to 1:4 a decrease in hydrogen evolution was about

A in different ratios without porous catalysts (a). Pyrolysis temperature 815 �C andn in peaks area counts in brackets).

P. Bober et al. / Fuel 90 (2011) 2334–2339 2337

83.8% at 700 �C. This fact confirmed also another results welldocumented with polyolefins production from polymer waste atlower pyrolysis temperature [19–21]. Importance of chemicalstructure of polymers and their blends at hydrogen production inpyrolyzate is also evident. The results showed again very impor-tant role of pyrolysis temperature for final polyblends degradationproducts formation (Fig. 1a). Methane production is dominant inthe same blends mixture as given in Fig. 1b. In dominant part ofPMMA containing polyblends methane contents significantly de-creases. If PMMA prevailed in mixture with HDPE an increase ofcarbon monoxide formation yielded while hydrogen contents de-creased (Fig. 1c). This simulates effect of polyblends compositionon final gaseous phase of pyrolyzate formation and how this affectshydrogen production. Now the effect of catalytic pyrolysis onmethane to hydrogen conversion has been applied by powdered

Fig. 2. Hydrogen (a), methane (b) and CO (c) evolution prognosis in gaseous phase of p

metallic materials as catalysts. The aim of application of thesematerials was to maximize the porosity and roughness using elec-trodeposition of Ni and Co on iron particles. We want to achievethe structure of ‘‘porous nickel’’ with the highest possible amountof Ni. With a higher concentration of nickel on the surface of Ni–Co–Fe particles increases the amount of reaction centers and thusthe conversion of hydrogen is higher.

Nickel can play an important role in methane conversion toform different forms of carbon (pyrolysis rest) and hydrogen yield.By this process a total hydrogen amount in gaseous phase in-creases. Electrochemical metal coatings deposition at powderedparticles enables preparation of different surfaces that can provecatalytic activity. It allows the challenge of catalysts preparationon which are independently tunable in metal particle size and sur-face properties. Metal coat is continuous and high content of Fe an

yrolyzate from different ratio polyblends and added powder catalysts no. 42 or 44.

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low content of Co detected in the beginning of electrochemicaldeposition can be associated with the surface of iron particle andcobalt deposited. In the pores of iron particle surface. Further in-crease in the cobalt and nickel content as well as decrease in ironcontent in the analyzed section corresponded to the coating filmonto the particle surface. On the inner side of the deposit was high-er content of cobalt, while nickel dominated on the outer side.From profiles of individual metals it is evident that the depositionof binary layer starts with the deposition of cobalt followed bysimultaneous co-deposition of both metals. In the last period ofthe electrolysis, deposition of nickel takes place mainly becauseof the decreasing content of cobalt but relatively constant contentof nickel in the plating bath when the nickel anode was used [22].

When higher amount of Ni containing additive (43% w/w, addi-tive no. 42) was introduced with polyblends sample directly intopyrolysis reactor, significant change of hydrogen production com-paring with additive no. 44 was confirmed at 700 �C (4:1) and815 �C (1:4) (Fig. 2a). HDPE/PMMA polyblends conversion in pres-ence of metal coated additives was dominant at 815 �C of pyrolysistemperature. The same effect of blends composition and pyrolysistemperature on hydrogen production was observed as in the caseof only polymers applied. Hydrogen yield decreased significantlywith pyrolysis temperature and HDPE contents decrease. Gener-ally, catalyst no. 42 effects hydrogen production in the case of allpolyblends tested (Fig. 2b). Fig 2b. shows proposed catalytic effectof additive no. 42 on effective methane to hydrogen conversion(methane contents lowering) at 815 �C pyrolysis temperature.From Fig. 2c it is evident effect of additive no. 44 at CO contentlowering in pyrolyzate mixture 4:1 HDPE/PMMA (815 �C) but noaffecting of methane conversion to hydrogen. Promising resultsshowed catalytic function of metal coated powders no. 42 onmethane to hydrogen conversion at higher pyrolysis temperatureand no. 44 on CO decrease and methane yield increase in pyrolyz-ates from HDPE/PMMA 4:1 at both temperatures applied. Theseprocesses could be also influenced by other metals (Fe, Co) pre-sents in additive no. 44. Detailed surface structure of additives ap-plied is shown at Fig. 3. Decrease in hydrogen production fromcatalytic pyrolysed polyblends (Fig. 2a) compared to those withoutthe additives (Fig. 1a) is not significant and it is caused by differentheat transport in polyblends mixture containing metal particles(additives) and so different heat consumption to main polyblendsdegradation process (it can be incomplete). Optimal sample poly-mer/catalysts composition will be studied in the futureexperiments.

Fig. 3. Optical micrograph of Ni coated Fe powder particles; cross-section. Grainsize: 45–63 lm with nickel.

The main impact of this research article was in the study ofpolymer blends degradation and methane to hydrogen conversionby two polymer ratios, pyrolysis temperature and effect of Ni/Cocoated metal particles with proposed catalytical function. In the fu-ture research we would like to apply newly prepared nanostruc-tured surface based catalysts to improve hydrogen content ingaseous phase. Application of reaction kinetics to declare processesof optimum hydrogen production will be also necessary.

4. Conclusion

Pyrolysis gas chromatography coupled with mass spectrometryhas been used in hydrogen analysis from thermal degradation oftwo polymer blends (HDPE/PMMA) in different ratios and with/without Ni/Co coated powder particles. Pyrolysis temperature ef-fect in hydrogen conversion was compared at two temperatures700 �C and 815 �C. Dominant effect of pyrolysis temperature wasconfirmed at 815 �C in comparison with degradation at pyrolysistemperature 700 �C. Average perceptual increase hydrogen weightwas observed at pyrolysis temperature 815 �C presented by 66.1%(w/w). Impact of HDPE:PMMA ratio on hydrogen conversion frompolyblends was monitored by results comparison betweenHDPE:PMMA = 4:1 and HDPE:PMMA = 1:4. Maximum hydrogenproduction from polyblends was registered at pyrolysis tempera-ture 815 �C and ratio HDPE:PMMA = 4:1. PMMA content in blendmade carbon monoxide and methane contents higher. Ni/Co con-taining additives with proposed catalytic activity on hydrogen con-version from methane showed partial effect when higher Nicontents containing catalyst affecting methane decrease in gaseousphase and its conversion into hydrogen. This is in good correlationwith many other results documented in literature. Cobalt coatedsurface with higher iron contents supported production of CH4,conversion to hydrogen has not been documented. Electrochemicalmetal deposition offers simple methods for powder particles sur-face composition modulation for optimum methane to hydrogenconversion from waste, plastic polyblends, etc. Future research willbe oriented to optimizing the blends–catalyst mixture to minimizeheat transport effect, carbon rest determination as well nanostruc-ture supported catalytic function introduction.

Acknowledgement

The authors thank for the financial support of the research bythe Grant VEGA 1/0011/11 and 1/0134/10 of the Slovak GrantAgency.

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