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Co-coking of coal with pitches and waste plastics
FUEL PROCESSING TECHNOLOGY EL.SINTER
Fuel Proce\sin_c Technology
50 (1997) 17% I X3
Co-coking of coal with pitches and waste plastics G. Collin ‘.*, B. Bujnowska h-‘, J. Polaczek
’
Received IX October 1995: accepted 2 I August I996
Abstract Liquid-phase co-themolysis of waste plastics (e.g. polystyrene. polycarbonate, polyurethane, polyvinyl chloride, tire rubber, unsaturated polyester resin, melamine-phenol formaldehyde resin, polyethylene, polyamide, polyethylene terephthalate, phenol formaldehyde resin) with coal-tar pitch at temperatures up to 400°C yielded gases, pyrolysis oils, and high-melting pitches (reaction pitches). Thermogravimetric analysis of these pitches showed that they were thermally stable up to the plastic temperature range of coals. Hence, the reaction pitches could be used as reactive additives for weak-coking coals to improve their coking properties. 0 1997 Elsevier Science B.V. Kc~uord.c:
Liquid-phase co-thermolysis: Reaction pitches
1. Introduction Coal-tar pitch is a multicomponent mixture of medium and higher molecular condensed aromatic hydrocarbons and heterocyclic compounds [ 11. In liquid-phase thermolysis experiments it has been shown that the main reaction pathways in the thermal chemistry of medium-sized pitch constituents are dehydrogenative polycondensation and subsequent intramolecular dehydrocyclization of oligoaryls initially formed releasing atomic hydrogen radicals [2]. Hence, at higher temperatures, coal-tar pitch can act as a hydrogen-donor solvent. Co-carbonization of low-rank coking coals and coal blends with coal-tar pitch as the hydrogen-donor additive has been found to improve the coking properties of coals and the quality of resulting cokes significantly 13-51. Thus, in the
Corresponding author
’ Deceased 037%3820/97/617.00 0 1997 Elsevier Science B.V. All rights reserved. P/I sO~7x-~~?o~9~)olo~~-s
Milling
Reaction
Distillation 7
8%
Toluene Ethylbenzene
16 %
f?+ Z2-tar
Pit&-j
50 % Polystyrene
--_I
Cumene
5%
Other Hydrocarbons
1%
Reaction Pitch Fig.
I. Co-thermolysis
of polystyrene
with coal-tar pitch (1:
70 %
I ).
of a 2:l mixture of a low-rank gas-flame coal and a low-volatile steam coal, the addition of coal-tar pitch improved the coke strength and the abrasion of the resulting cokes which were measured in the Micum drum [6-S]. Attempts have been made to achieve similar hydrogen transfer effects by co-coking coal with synthetic polymers. e.g. waste plastics, instead of pitch. These attempts have not been successful because on the one hand most thermoplastics decompose below the plastic temperature range of coals and on the other hand most elastomers and thermosets cannot be liquified at all, so that solvolysis of coal macerals by hydrogen transfer cannot occur. Therefore, attempts have been made first to convert the synthetic polymers by liquid-phase thermolysis with coal-tar pitch yielding reaction pitches (RP) which can then be used as reactive additives in co-coking with coal. Thus, a 1:l mixture of polystyrene and normal coal-tar pitch (softening point Ring and Ball (R and B) about 90°C) was thermally autoclaved in the liquid phase at 370” up to 400°C under the resulting pressure of up to 30 bar (Fig. I) [9]. This treatment yielded about 70% RP (softening point R and B 130°C) and about 30% distillate. The main volatile reaction product was ethylbenzene, indicating hydrogen transfer from coal-tar pitch to the primary thermolysis product styrene monomer. In this experiment 40% of the polystyrene fed was converted to non-volatile compounds in RP. case
2. Experimental Mixtures of coal-tar pitch and several types of plastics were treated under atmospheric pressure at reaction temperatures between 215 and 400°C and reaction times between 1.5 and 6 h (Fig. 2). The yield of non-volatile compounds from waste plastics in the resulting RP was determined by weighing the distillation residue at 350°C substracting the content of coal-tar pitch (50% of the entire mixture) and dividing by the weight of the added plastic (50% of the entire mixture). The yield of non-volatile compounds was lowest with 6% in the case of polystyrene (injection-molding waste). Coal-tar pitch itself was almost stable up to 350°C resulting in a yield of 99.5% under test conditions. The other waste plastics tested were polycarbonate (PC, CD production waste). polyurethane (PU, rubber waste). polyvinyl chloride (soft PVC, Pb-stabilized),
G. C&in
% 100
et al. / Fuel Processing Technology 50
Yield
T
of non-volatile compounds from waste plastic in “Reaction Pitch”
98 -
76 -
68 52 44
0 Reaction temp. (“C) Reaction time (h) Softenin point (“C3
f 1997) 179-184
PS
PC
300
350
215 250
350
4
4
3
2
5
1215
05
>215
103
76 .. . .
-
-
PE
PA
PET
300
380
250 400
300
300
2
:
1.5 5
2
2
117
101
215
115
250
>215
74 ...
I -
-
TR
84 -
UP MPF Mix
-
i I PU PVC
84 -
98 -
88 -
350 3
-
3
350
-
PF Pitch 350 4 101
(R&W
Fig. 2. Co-thermolysis of waste plastics with coal-tar pitch (1: I ).PS = polystyrene (injection molding waste): PC = polycarhonate (CD production waste); PU = polyurethane (rubberwaste); PCV = polyvinyl chloride (soft, Pb-stabilized); TR = tire rubber: UP = unsaturated polyester resin; MPF = melamine-phenol formaldehyde resin; Mix = mixed waste plastics; PE = low-density polyethylene; PA = polyamide-6 (injection molding waste); PET = polyethylene terephthalate (used bottles); PF = phenol formaldehyde resin (mineralfilled); Pitch = coal-tar pitch.
tire rubber (TR), unsaturated polyester resin (UP), melamine-phenol formaldehyde resin (MPF), mixed waste plastics (Mix), low-density polyethylene (PE), polyamide-6 (PA, injection-molding waste), polyethylene terephthalate (PET, used bottles), phenol formaldehyde resin (PF, mineral-filled). In the following order PC < PU < PVC < TR < UP < MPF < Mix < PE < PA < PET < PF, increasing yields of non-volatile compounds from waste plastic in RP were formed. 100
80
g?
- 60 E .o, 2 40
c
_.__
PVC
-.-.-Pitch
_--__-_._-~_
0’ 60
_.. 121.
+ PVC
150
240
330
510 420 Temperature
(,,,,_, - , ..........-lT.7 . . ..4_,__...___...; I _ L
600 690 (“C)
~~~
780
Fig. 3. Thermogravimetric analyses of PVC, coal-tar pitch, and PVC/pitch temperature of the TGA apparatus (heating rate 10 Kmin-’ ).
870
960
mixture (1:l).
Temperature
=
IX’
80 8 60 E .‘J 3al 40
~~~ I
- Pitch 2. _ l:IYI k;yyhbonate Polycarbonate
0 60
Fig. 4. Thermogravimetric Temperature = temperature
-L___
150
240
,
330
~~~~~_~~~
420 510 Temperature
600 (“C)
690
780
870
960
analyses of polycarbonate (PC). coal-tar pitch. and PC/pitch of the TGA apparatus (heating rate IO K min. ’).
mixture
(I:
I ).
Thermogravimetric analysis of coal-tar pitch, waste plastics and their 1: 1 mixtures showed higher residuals than those calculated from the results of the single components the evolution of volatiles from coal-tar (Figs. 3-5). At a heating rate of 10 Kmin-’ pitch alone started at about 200°C. The main thermolysis reaction occurred between 300 and 500°C. The yield of residue in the form of pitch coke was about 30%. At 300°C the yield of residue was about 80% under these test conditions. Under the same test conditions the Pb-stabilized soft PVC showed two reaction steps: firstly in the temperature range between about 240 and 400°C with a residue yield of 33%, secondly in the temperature range between about 480 and 550°C with a residue yield of 2 1%. The 1: 1 mixture of PVC with coal-tar pitch reacted at temperatures as low as about 100°C to yield HCl. The residue yield was 66% after the first reaction step at about 420°C and after the second reaction step 52% at 565°C. For the PC waste the curve of the thermogravimetric analysis showed an almost complete destruction in the narrow
20”.
PET
-.-.-Pitch+ PET ,1 _i -. 60
Fig. 5. Thermogravimetric mixture (1:l). Temperature
150
240
330
510 420 Temperature
600 690 (“C)
780
870
960
analyses of polyethylene terephthalate (PET). coal-tar pitch, and PET/pitch = temperature of the TGA apparatus (heating rate IO Kmin-’ ).
temperature range between 420 and 590°C with a yield of 28% residue and a yield of 22% at 900°C. PET decomposed almost completely in the temperature range of about 420 and 600°C. while the I:1 mixture with coal-tar pitch gave a residue yield of about 80% at 420°C and about 55% at 600°C. Hence, the RP of the co-thermolysis of coal-tar pitch with thermoplastics were in general more thermostable than the single components. Lab-scale co-coking experiments showed that the RP reacted with Silesian weak-coking coal and their blends within their plastic temperature range of about 370-470°C and improved their coking properties in a way similar to coal-tar pitch itself. The cokes had increased mechanical strength and optical anisotropy.
3. Conclusions 1. Liquid-phase co-thermolysis of synthetic polymers and plastic wastes with coal-tar pitch at temperatures from 200 up to 400°C yields reaction pitches (RP) which could be used as reactive additives in the coal-coking process. 2. The addition of the RP to weak-coking coals and coal blends could improve their coking properties and yield cokes with increased mechanical strength and optical anisotropy. 3. Co-coking of coal with RP from the co-thermolysis of waste plastics with coal-tar pitch could be a worthwile future technology for the conversion of mixed plastic wastes together with weak-coking coal blends to yield high-strength metallurgical cokes and chemical feedstocks in already existing conventional coke-oven plants. 4. In Memoriam Professor Dr. had.Ing. Bozena Bujnowsta (1938-1995). Professor B. Bujnowska received degrees of PhD and DSc at the Technical University of Wroclaw, Poland. She worked in the Institute of Chemistry and Technology of Petroleum and Coal of Technical University for 35 years. The main topics of her research were: flotation of hard coals and their petrographic constituents, formed coke - properties and structure, the nature of coking coals. the role of the plastic stage in the formation of coke permeability of coal plastic layers: the preparation of coke blends, pitch as a component in coking blends, and utilization of plastic waste in the coking process. Professor B. Bujnowska was the author or coauthor of 55 papers published in Polish and foreign journals and of a monograph, “Chemistry and Physics of Coal”. She presented many papers at Polish and international conferences. Professor B. Bujnowska received grants from the Humbold Foundation which enabled her to work in the Laboratories of Prof. H. Hoberg, Prof. H. Hammer. Prof. M. Wolf and Prof. K. Hedden. Prof. Bujnowska had a long and satisfying cooperation with Dr. G. Collin. from the Laboratory of Ruttgerswerke. The results of research of Prof. B. Bujnowska are a great contribution to coal science and technology. Under the supervision of Prof. Bujnowska, 30 M.Sc. degrees and one PhD degree were prepared.
1 had worked with Prof. B. Bujnowska for several years. She was a true academic and scientific worker and a dedicated teacher. Stefan Jasienko
Acknowledgements The authors gratefully thank Professor St. Jasienko, Wrodaw, Professor Castrop-Rauxel, and Professor W. Klose, Kassel, for useful discussions.
M. Zander.
References [I] [2] [3] [4] [5] [6] [7] [8] [9]
G. Collin and H. HGke, Tar and pitch, Ullmanns Encycl. Ind. Chem. (5th ed.), A26 (1995). Yl- 127 M. Zander and G. Collin, Fuel, 72 (1993) 1281-1285. H. Spengler, W. Weskamp and G. Collin. Cokemaking Int., 3 (I 99 I ) 25-29. B. Bujnowska and G. Collin, Cokemaking Int.. 6 (1994) 25-31. G. Collin and B. Bujnowska, Carbon, 32 (1994) 547-552. W. Weskamp, W. Rhode, W. Stewen and F. Orywal, Gliickauf, 118 (1982) 264-267. W. Weskamp, W. Stewen and D. Habermehl, Ghickauf, 119 (IY83) 1079-1083. W. Weskamp, W. Rhode, W. Stewen and D. Habermehl, Gliickauf. 121 (1985) 1090- 1094. Rltgerswerke AG. DE 30 37 829, 1980.
Fuel Proce\sin_c Technology
50 (1997) 17% I X3
Co-coking of coal with pitches and waste plastics G. Collin ‘.*, B. Bujnowska h-‘, J. Polaczek
’
Received IX October 1995: accepted 2 I August I996
Abstract Liquid-phase co-themolysis of waste plastics (e.g. polystyrene. polycarbonate, polyurethane, polyvinyl chloride, tire rubber, unsaturated polyester resin, melamine-phenol formaldehyde resin, polyethylene, polyamide, polyethylene terephthalate, phenol formaldehyde resin) with coal-tar pitch at temperatures up to 400°C yielded gases, pyrolysis oils, and high-melting pitches (reaction pitches). Thermogravimetric analysis of these pitches showed that they were thermally stable up to the plastic temperature range of coals. Hence, the reaction pitches could be used as reactive additives for weak-coking coals to improve their coking properties. 0 1997 Elsevier Science B.V. Kc~uord.c:
Liquid-phase co-thermolysis: Reaction pitches
1. Introduction Coal-tar pitch is a multicomponent mixture of medium and higher molecular condensed aromatic hydrocarbons and heterocyclic compounds [ 11. In liquid-phase thermolysis experiments it has been shown that the main reaction pathways in the thermal chemistry of medium-sized pitch constituents are dehydrogenative polycondensation and subsequent intramolecular dehydrocyclization of oligoaryls initially formed releasing atomic hydrogen radicals [2]. Hence, at higher temperatures, coal-tar pitch can act as a hydrogen-donor solvent. Co-carbonization of low-rank coking coals and coal blends with coal-tar pitch as the hydrogen-donor additive has been found to improve the coking properties of coals and the quality of resulting cokes significantly 13-51. Thus, in the
Corresponding author
’ Deceased 037%3820/97/617.00 0 1997 Elsevier Science B.V. All rights reserved. P/I sO~7x-~~?o~9~)olo~~-s
Milling
Reaction
Distillation 7
8%
Toluene Ethylbenzene
16 %
f?+ Z2-tar
Pit&-j
50 % Polystyrene
--_I
Cumene
5%
Other Hydrocarbons
1%
Reaction Pitch Fig.
I. Co-thermolysis
of polystyrene
with coal-tar pitch (1:
70 %
I ).
of a 2:l mixture of a low-rank gas-flame coal and a low-volatile steam coal, the addition of coal-tar pitch improved the coke strength and the abrasion of the resulting cokes which were measured in the Micum drum [6-S]. Attempts have been made to achieve similar hydrogen transfer effects by co-coking coal with synthetic polymers. e.g. waste plastics, instead of pitch. These attempts have not been successful because on the one hand most thermoplastics decompose below the plastic temperature range of coals and on the other hand most elastomers and thermosets cannot be liquified at all, so that solvolysis of coal macerals by hydrogen transfer cannot occur. Therefore, attempts have been made first to convert the synthetic polymers by liquid-phase thermolysis with coal-tar pitch yielding reaction pitches (RP) which can then be used as reactive additives in co-coking with coal. Thus, a 1:l mixture of polystyrene and normal coal-tar pitch (softening point Ring and Ball (R and B) about 90°C) was thermally autoclaved in the liquid phase at 370” up to 400°C under the resulting pressure of up to 30 bar (Fig. I) [9]. This treatment yielded about 70% RP (softening point R and B 130°C) and about 30% distillate. The main volatile reaction product was ethylbenzene, indicating hydrogen transfer from coal-tar pitch to the primary thermolysis product styrene monomer. In this experiment 40% of the polystyrene fed was converted to non-volatile compounds in RP. case
2. Experimental Mixtures of coal-tar pitch and several types of plastics were treated under atmospheric pressure at reaction temperatures between 215 and 400°C and reaction times between 1.5 and 6 h (Fig. 2). The yield of non-volatile compounds from waste plastics in the resulting RP was determined by weighing the distillation residue at 350°C substracting the content of coal-tar pitch (50% of the entire mixture) and dividing by the weight of the added plastic (50% of the entire mixture). The yield of non-volatile compounds was lowest with 6% in the case of polystyrene (injection-molding waste). Coal-tar pitch itself was almost stable up to 350°C resulting in a yield of 99.5% under test conditions. The other waste plastics tested were polycarbonate (PC, CD production waste). polyurethane (PU, rubber waste). polyvinyl chloride (soft PVC, Pb-stabilized),
G. C&in
% 100
et al. / Fuel Processing Technology 50
Yield
T
of non-volatile compounds from waste plastic in “Reaction Pitch”
98 -
76 -
68 52 44
0 Reaction temp. (“C) Reaction time (h) Softenin point (“C3
f 1997) 179-184
PS
PC
300
350
215 250
350
4
4
3
2
5
1215
05
>215
103
76 .. . .
-
-
PE
PA
PET
300
380
250 400
300
300
2
:
1.5 5
2
2
117
101
215
115
250
>215
74 ...
I -
-
TR
84 -
UP MPF Mix
-
i I PU PVC
84 -
98 -
88 -
350 3
-
3
350
-
PF Pitch 350 4 101
(R&W
Fig. 2. Co-thermolysis of waste plastics with coal-tar pitch (1: I ).PS = polystyrene (injection molding waste): PC = polycarhonate (CD production waste); PU = polyurethane (rubberwaste); PCV = polyvinyl chloride (soft, Pb-stabilized); TR = tire rubber: UP = unsaturated polyester resin; MPF = melamine-phenol formaldehyde resin; Mix = mixed waste plastics; PE = low-density polyethylene; PA = polyamide-6 (injection molding waste); PET = polyethylene terephthalate (used bottles); PF = phenol formaldehyde resin (mineralfilled); Pitch = coal-tar pitch.
tire rubber (TR), unsaturated polyester resin (UP), melamine-phenol formaldehyde resin (MPF), mixed waste plastics (Mix), low-density polyethylene (PE), polyamide-6 (PA, injection-molding waste), polyethylene terephthalate (PET, used bottles), phenol formaldehyde resin (PF, mineral-filled). In the following order PC < PU < PVC < TR < UP < MPF < Mix < PE < PA < PET < PF, increasing yields of non-volatile compounds from waste plastic in RP were formed. 100
80
g?
- 60 E .o, 2 40
c
_.__
PVC
-.-.-Pitch
_--__-_._-~_
0’ 60
_.. 121.
+ PVC
150
240
330
510 420 Temperature
(,,,,_, - , ..........-lT.7 . . ..4_,__...___...; I _ L
600 690 (“C)
~~~
780
Fig. 3. Thermogravimetric analyses of PVC, coal-tar pitch, and PVC/pitch temperature of the TGA apparatus (heating rate 10 Kmin-’ ).
870
960
mixture (1:l).
Temperature
=
IX’
80 8 60 E .‘J 3al 40
~~~ I
- Pitch 2. _ l:IYI k;yyhbonate Polycarbonate
0 60
Fig. 4. Thermogravimetric Temperature = temperature
-L___
150
240
,
330
~~~~~_~~~
420 510 Temperature
600 (“C)
690
780
870
960
analyses of polycarbonate (PC). coal-tar pitch. and PC/pitch of the TGA apparatus (heating rate IO K min. ’).
mixture
(I:
I ).
Thermogravimetric analysis of coal-tar pitch, waste plastics and their 1: 1 mixtures showed higher residuals than those calculated from the results of the single components the evolution of volatiles from coal-tar (Figs. 3-5). At a heating rate of 10 Kmin-’ pitch alone started at about 200°C. The main thermolysis reaction occurred between 300 and 500°C. The yield of residue in the form of pitch coke was about 30%. At 300°C the yield of residue was about 80% under these test conditions. Under the same test conditions the Pb-stabilized soft PVC showed two reaction steps: firstly in the temperature range between about 240 and 400°C with a residue yield of 33%, secondly in the temperature range between about 480 and 550°C with a residue yield of 2 1%. The 1: 1 mixture of PVC with coal-tar pitch reacted at temperatures as low as about 100°C to yield HCl. The residue yield was 66% after the first reaction step at about 420°C and after the second reaction step 52% at 565°C. For the PC waste the curve of the thermogravimetric analysis showed an almost complete destruction in the narrow
20”.
PET
-.-.-Pitch+ PET ,1 _i -. 60
Fig. 5. Thermogravimetric mixture (1:l). Temperature
150
240
330
510 420 Temperature
600 690 (“C)
780
870
960
analyses of polyethylene terephthalate (PET). coal-tar pitch, and PET/pitch = temperature of the TGA apparatus (heating rate IO Kmin-’ ).
temperature range between 420 and 590°C with a yield of 28% residue and a yield of 22% at 900°C. PET decomposed almost completely in the temperature range of about 420 and 600°C. while the I:1 mixture with coal-tar pitch gave a residue yield of about 80% at 420°C and about 55% at 600°C. Hence, the RP of the co-thermolysis of coal-tar pitch with thermoplastics were in general more thermostable than the single components. Lab-scale co-coking experiments showed that the RP reacted with Silesian weak-coking coal and their blends within their plastic temperature range of about 370-470°C and improved their coking properties in a way similar to coal-tar pitch itself. The cokes had increased mechanical strength and optical anisotropy.
3. Conclusions 1. Liquid-phase co-thermolysis of synthetic polymers and plastic wastes with coal-tar pitch at temperatures from 200 up to 400°C yields reaction pitches (RP) which could be used as reactive additives in the coal-coking process. 2. The addition of the RP to weak-coking coals and coal blends could improve their coking properties and yield cokes with increased mechanical strength and optical anisotropy. 3. Co-coking of coal with RP from the co-thermolysis of waste plastics with coal-tar pitch could be a worthwile future technology for the conversion of mixed plastic wastes together with weak-coking coal blends to yield high-strength metallurgical cokes and chemical feedstocks in already existing conventional coke-oven plants. 4. In Memoriam Professor Dr. had.Ing. Bozena Bujnowsta (1938-1995). Professor B. Bujnowska received degrees of PhD and DSc at the Technical University of Wroclaw, Poland. She worked in the Institute of Chemistry and Technology of Petroleum and Coal of Technical University for 35 years. The main topics of her research were: flotation of hard coals and their petrographic constituents, formed coke - properties and structure, the nature of coking coals. the role of the plastic stage in the formation of coke permeability of coal plastic layers: the preparation of coke blends, pitch as a component in coking blends, and utilization of plastic waste in the coking process. Professor B. Bujnowska was the author or coauthor of 55 papers published in Polish and foreign journals and of a monograph, “Chemistry and Physics of Coal”. She presented many papers at Polish and international conferences. Professor B. Bujnowska received grants from the Humbold Foundation which enabled her to work in the Laboratories of Prof. H. Hoberg, Prof. H. Hammer. Prof. M. Wolf and Prof. K. Hedden. Prof. Bujnowska had a long and satisfying cooperation with Dr. G. Collin. from the Laboratory of Ruttgerswerke. The results of research of Prof. B. Bujnowska are a great contribution to coal science and technology. Under the supervision of Prof. Bujnowska, 30 M.Sc. degrees and one PhD degree were prepared.
1 had worked with Prof. B. Bujnowska for several years. She was a true academic and scientific worker and a dedicated teacher. Stefan Jasienko
Acknowledgements The authors gratefully thank Professor St. Jasienko, Wrodaw, Professor Castrop-Rauxel, and Professor W. Klose, Kassel, for useful discussions.
M. Zander.
References [I] [2] [3] [4] [5] [6] [7] [8] [9]
G. Collin and H. HGke, Tar and pitch, Ullmanns Encycl. Ind. Chem. (5th ed.), A26 (1995). Yl- 127 M. Zander and G. Collin, Fuel, 72 (1993) 1281-1285. H. Spengler, W. Weskamp and G. Collin. Cokemaking Int., 3 (I 99 I ) 25-29. B. Bujnowska and G. Collin, Cokemaking Int.. 6 (1994) 25-31. G. Collin and B. Bujnowska, Carbon, 32 (1994) 547-552. W. Weskamp, W. Rhode, W. Stewen and F. Orywal, Gliickauf, 118 (1982) 264-267. W. Weskamp, W. Stewen and D. Habermehl, Ghickauf, 119 (IY83) 1079-1083. W. Weskamp, W. Rhode, W. Stewen and D. Habermehl, Gliickauf. 121 (1985) 1090- 1094. Rltgerswerke AG. DE 30 37 829, 1980.