PARTⅡ GASIFICATIONGENERATION OF H2 GAS FROM SOLID BASED POLYMERWASTES MECHANICALLY MILLED WITH Ni AND Ca
William Tongamp *1, Qiwu Zhang 2, Atsushi Shibayama 1, Fumio Saito 2
1

Faculty of Engineering & Resource Science, Akita University
1-1 Tegata-Gakuen machi, Akita 010-8502, Japan
2
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University
2-1-1, Katahira, Aoba-Ku, Sendai 980-8577, JapanE–mail: wtongamp@gipc.akita-u.ac.jp
Abstract:This paper discusses a process developed to produce high purity hydrogen gas fromsolid based hydrocarbons or polymers such as plastic wastes or biomass in a two–step process
at temperatures below 600 °C. Polyethylene [–CH2–]n (PE), polyvinyl chloride[–CH2–CHCl–]n (PVC), Polystyrene [–CH2–CH(C6H5)–]n, Poly(vinyl alcohol)[–CH(OH)CH2–]n, cellulose C6(H2O)5 as sample hydrocarbon based compounds were firstprepared by milling with Ni(OH)2 or Ni–doped LDH to provide Ni as catalyst for C–C bondrupture and Ca(OH)2 or CaO to provide Ca for CO2 or CO adsorption. In the second stage, themilled products were heated in He/Ar gas environments and product gases generated between
400–700 °C were evaluated for optimum conditions of hydrogen generation.
Results for all samples investigated showed that the addition of Ni and Ca to the samples
and sufficient milling allowed high gas generation mainly composed of H2 and CH4, CO, CO2
during heating at temperatures from 400–600 °C. Carbon oxides (CO2, CO) were fixed as
CaCO3 and hydrogen gas with purity >95% and CO/CO2 concentrations <0.5% were achieved.
The process offers a novel approach to treat solid waste hydrocarbon based polymer bytransforming it into hydrogen.
1. Introduction
Production of hydrogen which is a valuable raw material for chemical and petrochemicalindustry and as a clean energy for combustion has received greater attention in recent. It is
usually achieved by the steam reforming of hydrocarbons with the assistance of catalyst andadsorbents. Generation of hydrogen from hydrocarbon based compounds and derivatives iswell known and can be achieved by the steam reforming process with water Eq. (1) or byoxygen in the partial oxidation process Eq. (2), and product CO further participating inwater–gas shift reaction for hydrogen Eq. (3) [1–4].

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CnHm + nH2O = nCO + (n+1/2m)H2
CnHm + O2 = n/2CO + (n+1/2m)H2
CO + H2O = CO2 + H2

(1)
(2)
(3)

Steam reforming is most efficient and industrially applied process for hydrogenproduction. Among many catalysts (Rh, Ru, Pd, Pt, Cu, Co) offered in steam reforming
reactions for C–C bond rupture in hydrocarbons, Ni is the most often used due to its low costand high activity [2–4]. CaO and LDHs as CO2 adsorbents is discussed in literature [5–8].
Although the steam reforming process has been successfully applied for industrial
production of hydrogen from natural gas, there exists difficulty for direct application of thisprocess for solid samples, particularly hydrocarbon–contained solid wastes or biomass
samples. Gasification of the solid wastes may be one effort to produce gases which are usedagain for steam reforming to replace natural gas. Direct pyrolysis of the solid wastes to emithydrogen will become possible if catalyst can be fully dispersed among the solid wastes.
Recently we reported such a process to convert PE, PVC, PS, cellulose into hydrogen [9–12]
by milling with Ca(OH)2 or CaO and Ni(OH)2 or Ni–doped LDH and heating the milled
sample at temperatures in the range of 400–600 °C. Ni is fully dispersed among the samples
and reduced into Ni–metal during heating operation, which works as catalyst to facilitate
release of hydrogen and Ca to fix carbon oxides allowing production of hydrogen gas.
2. Experimental
PE, PVC, PS, PVA, cellulose, CaO, Ca(OH)2 and Ni(OH)2 chemical reagents used as
starting materials were supplied by Wako Chemicals–Japan and the Ni–doped LDH wasprepared by a mechanochemical route [12–14]. A 3.0 g sample mixture was milled by aplanetary ball mill (Pulverisette – 7, Fritsch, Germany), which has two mill pots (45 cm3 innervolume each) made of ZrO2 with 7x15 mm diameter ZrO2 balls. Milling time in this work wasranged from 30–120 min and mill speed from 300–700 rpm. Each polymer was mixed withCa at equal molar ratio to fix carbon content and catalyst at varying amounts. Characterization
by a set of analytical methods of X–ray diffraction (XRD), infrared spectroscopy (FT–IR),
thermogravimetry–mass spectroscopy (TG–MS) and gas chromatography (GC) wereperformed on the milled and heated samples to monitor the process.
3. Results and discussion
3.1 PE[–CH2–]n–Ca(OH)2–Ni(OH)2/Ni–doped LDH sample systems
TG/MS analysis of gaseous products up to 700 °C showed H2, CH4, CO, CO2, H2O with
H2 patterns dominant between 400–500 °C, reaching maximum at 430 °C. H2 concentration>95% was obtained for a mixture (6:14:1 = C:H2O:Ni) sample and the concentration of COand CO2 was kept below 0.5%. H2 concentration dropped to between 60–90% when mole
H2O was reduced to 12, 10, 7 moles resulting in an increase in CH4 concentration to over 25%,- 130 -PARTⅡ GASIFICATION
however, concentration of CO and CO2 was consistently below 0.5% of gases collected. The
intensity and concentration of H2 gas generated increased as milling progressed from 10–60
min, mill speed from 300–700 rpm. Analysis of solid product after heating at 500 °C by XRDand TG–DTA showed that over 80% of the heated sample was CaCO3 indicating that over80% H2 gas has been generated from PE sample. Water molecules in both hydroxides assist inwater–gas shift reaction for H2 gas generation with CaO as adsorbent for fixing CO2 and Ni as
catalyst assisting C–C bond rupture.

Fig 1 TG–DTA and TG–MS profiles of (a) PE/Ca(OH)2/Ni(OH)2 (6:6:1) and (b) PE/LDH(1:0.05) mixtures prepared by milling for 60 min at 700 rpm and heated under helium flow of300 ml.min-1.
A mixture of PE and Ni–doped LDH milled for 1 h followed by heating produced
gaseous products mainly consisted of H2, CH4, CO, CO2 with H2 concentration over 80%
between 450–550 °C, showing almost similar results for PE milled/mixed with Ni(OH)2 isindicated in Fig. 1 [12].
Tab. 1

Total gaseous product generation and composition analysis of gas constituents fordifferent sample systems at 400–550 °C.
Sample system

Tot. gas (%)(H2, CH4, CO, CO2)

Gas conc. (%)
H2CH4COCO2

PE–Ca(OH)2–Ni(OH)259.4

94.6

5.3

0.2

0.0

PE–Ca(OH)2–(Ni–LDH)

49.4

80.6

15.2

2.9

1.3

PVC–CaO–Ni(OH)2

28.4

95.4

3.9

0.5

0.2

PS–Ca(OH)2–Ni(OH)2

11.7

95.8

3.1

1.0

0.3

PVA–Ca(OH)2–Ni(OH)2

31.3

98.8

1.1

0.1

0.1

Cellulose–LiOH–Ni(OH)2

52.9>97<4.0<0.5<0.5- 131 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
3.2 PVC–Ca(OH)2–Ni(OH)2 sample system
Analyses by thermogravimetry–mass spectroscopy (TG–MS) and gas chromatography(GC) showed H2, CH4, CO and CO2 as main constituents. The results clearly show thataddition of Ni(OH)2 to provide nickel as catalyst and CaO as adsorbent to fix CO2 and HClgases generated during heating, assisted in clean H2 generation with concentration near 90%
at temperatures between 450–550 °C. Analyses of solids after heating by X–ray diffraction
and TG–DTA techniques showed both CaOHCl and CaCO3 as main phases in the product[10].
3.3 PS / PVA–Ca(OH)2–Ni(OH)2 sample system
Analysis of the gaseous products by TG–MS, Gas–chromatography, and solid products
by TG–DTA and XRD show that CO2 gas was fixed as CaCO3 at temperatures between
350–600 °C allowing generation of H2 gas with concentrations >95% for PS and >98% for
PVA . The results in this study show that milling of solid based hydrocarbon compounds withnickel and calcium hydroxides allows dispersion of nickel to hydrocarbon surfaces andfacilitates C–C bond rupture in polymer(s) during heating at temperatures below 500 °C, atthe same time calcium adsorbs CO2.
CaCO3(a)CaO

CaCO3(a)Ca(OH)2Ni(OH)2Ni

1 minCaONi

30 min(i)60 min60 min(No Ni(OH)2))

1020(ii)
3040
2q / degree

5060

10Ni

2030402q / degree

5060Fig. 2. XRD patterns of (a) PE/Ca(OH)2/Ni(OH)2 (6:6:1) mixture prepared by milling fordifferent times and heated at 500 °C for 120 min under helium gas; (b) PS/Ca(OH)2/Ni(OH)2(1:8:1) mixture; (i) product after milling for 60 min and, (ii) milled product heated at 500 °C
under argon gas atmosphere.
Representative results in Fig. 2 show that carbon oxides (CO2 and CO) released fromdecomposition of the polymers and / or solid hydrocarbon based compounds during heating isfixed as CaCO3 allowing generation of high purity hydrogen gas.
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3.4 Cellulose–LiOH–Ni(OH)2 sample system
For this system, LiOH was used in place of Ca but for the same purpose to adsorb CO2
released allowing generation of clean hydrogen gas. Use of Ni(OH)2 and Ni(COOH)2 wereobserved as to give higher hydrogen nyield as compared to Ni–metal [11].
4. Conclusion
The results in the study investigating milling of solid based hydrocarbon compounds orpolymers such as PE, PVC, PS, PVA, cellulose with Ca compounds (CaO, Ca(OH)2) and Nicompounds (Ni(OH)2, Ni–doped LDH) followed by heating at temperatures below 550 °C canallow generation of high purity hydrogen gas.
This shows both Ca and Ni offered as adsorbent/catalyst and water moles offered byhydroxides and LDH could allow water–gas shift reactions to proceed. Carbon oxides wereclearly fixed by Ca and Li suggesting a separate gas separation process could be avoided inthis process. More work is in progress to evaluate this process for further development byconsidering regeneration of adsorbents and catalysts and evaluation of costs in milling andheating operations.
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