1. INTRODUCTION

Pyrolysis is a
chemical reaction involving molecular breakdown of larger molecules into
smaller molecules in the presence of high temperature. Pyrolysis has been
derived from two Greek words “pyro” – fire and “lysis” – separating.
Pyrolysis, a type of thermolysis, commonly observed in organic
materials exposed to high temperatures involves irreversible simultaneous
change of chemical composition and physical phase.
It is one of the processes involved in charring
wood, in absence of oxygen for the synthesis of coal, starting at 200–300°C
(390–570°F).13

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Plastic, the
synthetic material made from a wide range of organic polymers such as
polyethylene, poly vinyl chloride, nylon, etc., which can be molded into shape,
while soft, and then set into a rigid or slightly elastic form. An important
property attributed to plastics is plasticity, which is the general property
of the materials to irreversibly deform without breaking. Polymers of plastic
are often made up of carbon and hydrogen and sometimes of oxygen, nitrogen,
sulfur, chlorine, fluorine, phosphorous, or silicon. 2

 

Three forms of plastics are: thermoplastics,
thermosets and bio-plastics.

 

Thermoplastics soften when heated and harden on cooling. More than 80
percent of plastics are thermoplastics, examples of which include:  High density polyethylene (HDPE), Low density
polyethylene (LDPE), Polyethylene terephthalate (PET), Polypropylene (PP),
Polyvinyl chloride (PVC) 2

 

Thermosets are hardened by a curing process and cannot be re-melted or
re-molded. Examples of thermosets include: Polyurethane (PU), Epoxy, Phenolics
and Unsaturated polyesters. 2

 

The following processes can produce bio-plastics:

•Conversion of plant sugars into plastic

•Production of plastics inside
micro-organisms

•Growing plastics in corn and other crops 2

 

According to the
report of Central Pollution Control Board (CPCB) in 2016, it was seen that the
packaging and polyvinyl chloride (PVC) pipe industry is growing at the rate of
16-18% per year. In the day to day practices we use different kind of plastics
goods and its demand is rapidly increasing from domestic use to industrial
applications. The demand for the plastic goods is growing at an annual rate of
22%. According to the plastic production data of 2014-15, 6533.157 thousand
metric tons was produced. The National consumption of plastic is as shown in
Table 1 from the year 1996 to 2007. The domestic consumption is expected to
touch 20 million Metric tons by 2020. 5, 8

 

Table 1

S.
No.

Year

Consumption
(Tons)

1.

1996

61,000

2.

2000

3,00,000

3.

2001

4,00,000

4.

2007

8,500,000

Source: Central Pollution Control Board

 

The per capita
consumption of plastic in India doubled from 4 kg in 2006 to 8 kg in 2008 and
12 kg in 2016, and would touch the global average of 27 kg per person by 2020,
according to plastic and polymers industry representatives. Among the factors
driving the consumption growth of plastics is increasing in packaging, infrastructure,
agriculture, automotive, healthcare and FMCG segments. 6, 8

Although plastics
are desirable commodities which provide enormous economic benefits to the
society, the non-biodegradability of it has made their disposal a serious
environmental concern. The littering of these wastes has resulted in a general
deterioration of hygiene in urban areas as well as threat to the biodiversity
both on land and marine region.

The present
paper highlights the process by which waste plastics like polyethylene and
polypropylene which account for 60 % of the plastics being consumed can be converted
to gasoline, diesel or aromatics as described. The process is completely
environment friendly as no toxic substances are evolved. The process has the
potential of augmenting the high value petroleum products as well as providing
an environmentally sound method for their disposal. Adoption of this process
can help in keeping the urban and semi-urban areas free from plastics. 7

 

 

 

 

 

 

 

 

2. EXPERIMENTAL PROCEDURE

 

 

Figure 1: Fabricated Reactor (Photo Captured In Lab)

 

Firstly, the
reactor was assembled, insulated properly with asbestos sheets and insulation
ropes to minimize the heat losses as shown in Figure 1. Initially, the
temperatures profile was worked out to set the maximum temperature of the
reactor to 500°C by regulating the voltage from the dimmer stat at 160 V. Thus,
the maximum temperature of reactor under different conditions of voltage and
time was obtained. The data obtained during this calibration was utilized for
controlling the reactor temperature and maintaining it during the actual
operation run. The reactor was then subjected to trial runs for optimizing the
process parameters.

Three sets of
experiments were performed at 4800C temperature with mixed plastic
feed consisting of HDPE and LDPE as shown in Figure 5. The first set was
carried out without any catalyst, the second set was carried in the presence of
porcelain beads as shown in Figure 6 and the third set with copper mesh as
shown in Figure 7. It was observed that the condenser did not require low
temperature cooling, as the vapours started solidifying at room temperature by
itself in the first two experimental sets except the third experimental set. As
a result, water condensers were used for cooling the vapour products from the
third set of experiment. The 1st air condenser was maintained at
higher temperature while the 2nd condenser was maintained at room
temperature which was followed by an optional water condenser. This type of
cooling arrangement helps in collecting the products properly. The experimental
setup is as shown in Figure 2.

 

 

Figure 2: Reactor assembly

 

 

Inference:

 

The experiment
took 45 minutes on an average to reach the reaction temperature of 480°C once
the heater was started. The product was collected from the condenser line. The
operation continued until an appreciable amount of product was collected. When
the vapors stopped coming out of the reactor, the heating was stopped.

It was observed
that very high pour point products were obtained. Even at the room temperature
this product appeared to be waxy in nature.

The products
obtained from all the three sets of experiments were waxy in nature and were
then subjected to simple distillation while closely monitoring the distillation
temperatures and appearance of the material in the distillation flask. When the
material in the distillation flask appeared little darker and thicker, the
heating was stopped, and the flask was allowed to cool. The distillate
collected appeared to be clean yellowish liquid product and the material left
in the flask looked like grease. The distillate was also subjected to
fractional distillation to recover gasoline range and gas-oil range
hydrocarbons.

The simple
distillation assembly arranged is as shown in the Figure 3:

 

 

Figure 3: Simple distillation assembly (photo captured
in lab

 

The
difference in the appearance of the raw product, distilled product and greasy
residue is as shown in Figure 4.

 

 

 

 

 

Figure 4: Product before and after distillation and
greasy residue obtained

 

The distilled
products obtained from the fractional distillation of all three sets of
experiments were subjected to tests such as ASTM distillation, Aniline point,
Pour point, Conradson Carbon Residue, Redwood and Kinematic viscosity, API
gravity, Flash and Fire point, Bromine number, etc, for determining the
characteristics of the products obtained as depicted in Table 2 for Cracked
Product, Table 3 for Gasoline fraction and Table 4 for Gas oil fraction and
were compared with the ASTM standards as shown in Table 5 and 6 for Gasoline
and Gas oil fractions respectively.

 

 

 

 

3. RESULTS
AND DISCUSSION

 

A. First set
of experiment – Thermal Cracking:

Material
Balance (Overall weight basis):

 

Feed: 350 gm HDPE flakes + 50 gm LDPE
flakes

Total recovery in ml – 370 ml from 400
gm feed

Total recovery in gm – 352 gm liquid
product from 400 gm feed

FEED = LIQUID
PRODUCT + (VAPOUR LOSSES + RESIDUE)

Figure 5: Raw Feed
(HDPE + LDPE)
(HDPE +LDPE)
 

400 gm = 352 gm + 48 gm                                               

The distillate
obtained had boiling range (44- 372oC) in ASTM distillation.

 

 

Temperature (oC)

% Distillate

44

IBP

105

10

125

20

160

30

194

40

206

50

230

60

260

70

282

80

320

90

372

94

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Graph 1: ASTM Characteristics of Thermal product

 

Gasoline:

 

The Gasoline fraction obtained was pale yellow in
colour and in the boiling range 35-209oC

 

Temperature (oC)

% Distillate

35

IBP

84

10

112

20

121

30

129

40

136

50

152

60

161

70

170

80

188

90

209

94

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Graph 2: ASTM Characteristics of Thermal Gasoline

 

 

 

 

 

 

 

 

Gas oil

 

The gas oil
fraction obtained was reddish yellow in colour and in the boiling range 45-350oC.

Temperature (oC)

% Distillate

45

IBP

102

10

158

20

235

30

260

40

285

50

295

60

315

70

318

80

350

83

­

 

 

 

 

 

 

 

 

 

 

 

 

Graph 3: ASTM Characteristics of Thermal Gas oil

 

B. Second set
of experiment – Cracking in presence of porcelain beads

Material
Balance (Overall weight basis):

Feed: 350 gm HDPE flakes + 50 gm LDPE
flakes

Catalyst: 60 gm acid activated
porcelain beads.

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 6:
Porcelain Beads

 

Total recovery in ml – 400 ml from 400
gm feed

Total recovery in gm – 380 gm liquid
product from 400 gm feed

The distillate obtained
was of boiling range (38- 350oC) in ASTM distillation.

Temperature (oC)

% Distillate

38

IBP

120

10

165

20

208

30

235

40

270

50

285

60

295

70

330

80

350

85

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Graph 4: ASTM Characteristics of Porcelain product

Gasoline

 

Temperature (oC)

% Distillate

48

IBP

65

10

88

20

105

30

115

40

123

50

132

60

144

70

150

80

165

90

175

95

189

96

The Gasoline fraction obtained was pale yellow in
color and in the boiling range 48-189oC

 

 

 

Graph 5: ASTM Characteristics of Porcelain Gasoline

 

Gas oil

 

The gas oil
fraction obtained was reddish yellow in color and in the boiling range 50-340oC.

Temperature
(oC)

%
Distillate

50

IBP

65

10

205

20

220

30

240

40

260

50

275

60

285

70

305

80

325

90

340

95

 

Graph 6: ASTM Characteristics of Porcelain Gas Oil

 

 

 

 

 

 

 

 

 

 

 

 

 

 

C. Third set of experiment – Cracking in presence of
Copper mesh

Material
Balance (Overall weight basis):

Feed: 350
gm HDPE flakes + 50 gm LDPE flakes

Catalyst:
Total 6 meshes of acid activated copper of 10 gm each.

 

 

 

 

 

 

 

 

 

 

 

 

Figure 7:
Copper Mesh

 

Total recovery in ml – 420 ml from 400
gm feed

Total recovery in gm – 399 gm liquid
product from 400 gm feed

FEED = LIQUID
PRODUCT + (VAPOUR PRODUCT + RESIDUE)

400 gm = 399 gm
+ 1 gm

In
this procedure, the yield obtained is 99.75 % i.e. 399 g.

The distillate obtained was of boiling range (52-
360oC) in ASTM distillation.

Temperature (oC)

% Distillate

52

IBP

80

10

110

20

150

30

195

40

235

50

255

60

275

70

305

80

330

90

360

95

 

Graph 7: ASTM Characteristics of Copper product

 

Gasoline

The Gasoline fraction obtained was pale yellow in
color and in the boiling range 35-209oC

Temperature (oC)

% Distillate

35

IBP

74

10

100

20

110

30

125

40

134

50

142

60

155

70

165

80

185

90

209

94

 

                               

Graph 8: ASTM Characteristics of Copper Gasoline

 

Gas oil

The gas oil fraction obtained was reddish yellow in
color and in the boiling range 35-344oC.

 

 

 

Temperature (oC)

% Distillate

35

IBP

204

10

220

20

240

30

274

40

288

50

305

60

310

70

320

80

344

82

 

Graph 9: ASTM Characteristics of Copper Gas oil

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CHARACTERISTICS
OF PRODUCTS OBTAINED FROM THREE SETS OF EXPERIMENTS

 

Table
2 : Cracked Product

 

Sr no.

Test Properties

Thermally Cracked

Porcelain Catalyst

Copper Catalyst

1

Colour

Black

Reddish
Brown

Yellowish
Brown

2

Density
( g/cm3)

0.7944
(33oC)

0.7856
(32oC)

0.7729
(36oC)

3

Specific
Gravity

0.8548
(33oC)

0.7763
(32oC)

0.7637
(36oC)

4

API
Gravity (oAPI)

34.0310
(33oC)

50.7749
(32oC)

53.7699(36oC)

5

Viscosity
(cst)

5.1465
(34oC)

3.6255
(31oC)

3.324(32oC)

6

CCR
(%)

0.375

0.001

0

7

Pour
Point ( oC)

13

10

19

8

Cloud
Point ( oC)

17

19

25.5

9

Flash
Point (oC)

75

35

35

10

Aniline
Point (oC)

80

80

56

11

Copper
Corrosion Characteristics

Not
worse than 1a

Not
worse than 1a

Not
worse than 1a

12

TAN
(mg
KOH/g sample)

1.0601

0.7886

1.0549

13

Bromine
Number

9.4653

9.9577

9.7828

14

Drop
melting point of distillation residue (0C)

54

54

51

 

 

 

 

 

 

 

 

 

Table
3: Gasoline Fraction

 

Sr no.

Test Properties

Thermally Cracked

Porcelain Catalyst

Copper Catalyst

1

Density
( g/cm3)

0.7561
(34oC)

0.7538
(33oC)

0.7519
(35oC)

2

Specific
Gravity

0.8292
(34oC)

0.8287
(33oC)

0.8266
(35oC)

3

API
Gravity (oAPI)

39.1454
(34oC)

39.2517
(33oC)

39.6831(35oC)

4

Viscosity
(cst)

0.7215
(34oC)

0.7085
(32oC)

0.6851
(35oC)

5

Pour
Point ( oC)

Not
obtained upto
 -25oC

Not
obtained upto -25oC

Not
obtained upto -25oC

6

Cloud
Point ( oC)

5.4

3

2

7

Flash
Point (oC)

35

35

35

8

Copper
Corrosion Characteristics

Not
worse than 1a

Not
worse than 1a

Not
worse than 1a

9

TAN
(mg
KOH/g sample)

1.0617

0.7854

1.0511

10

Bromine
Number

17.0762

16.6829

17.088

 

 

 

 

Table
4: Gas Oil Fraction

 

Sr no.

Test Properties

Thermally Cracked

Porcelain Catalyst

Copper Catalyst

1

Density
( g/cm3)

0.8126
(34oC)

0.8109
(33oC)

0.8095
(35oC)

2

Specific
Gravity

0.8670
(34oC)

0.8666
(33oC)

0.8651
(35oC)

3

API
Gravity (oAPI)

31.7194
(34oC)

31.7825
(33oC)

32.8023
(35oC)

4

Viscosity
(cst)

3.5335
(34oC)

3.3572
(33oC)

3.2178
(35oC)

5

CCR
(%)

0.351

0.231

0.112

6

Pour
Point ( oC)

25

19

17

7

Cloud
Point ( oC)

32

25.5

24.7

8

Flash
Point (oC)

35

39

39

9

Aniline
Point (oC)

83

59

54

10

Copper
Corrosion Characteristics

Not
worse than 1a

Not
worse than 1a

Not
worse than 1a

11

TAN
(mg
KOH/g sample)

1.047

0.5257

1.065

12

Bromine
Number

9.7721

9.3961

9.4463

 

 

 

 

 

 

 

 

 

Figure 8: Final products as
obtained from the experiment

 

The figure above shows the following product (from
left to right):

·        
Obtained from Copper
Mesh

1.      
Crude oil

2.      
Gasoline

3.      
Gas oil

 

·        
Obtained from Porcelain
Beads

1.      
Crude oil

2.      
Gasoline

3.      
Gas oil

 

·        
Obtained from Thermal
Cracking

1.      
Crude oil

2.      
Gasoline

3.      
Gas oil

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ASTM
Standard Specifications:4

 

Table
5: Gasoline

 

Sr No.

Test Properties

Range

1

Density
( g/cm3) *

0.7-0.78

2

Specific
Gravity*

0.7-0.8

3

API
Gravity (oAPI) *

30-39

4

Viscosity
(cst) *

0.37-0.44

5

Pour
Point ( oC)

-40

6

Cloud
Point ( oC)

3

7

Flash
Point (oC)

45

8

Copper
Corrosion Characteristics

Not
worse than 1a

9

TAN
(mg KOH/g sample)

0.5

(*Note: At 60oF)

 

Table
6: Diesel

 

Sr No.

Test Properties

Range

1

Density
( g/cm3) *

0.83-0.87

2

Specific
Gravity*

0.81-0.89

3

API
Gravity (oAPI) *

30-42

4

Viscosity
(cst) *

2.6-4.1

5

CCR
(%)

0.2

6

Pour
Point ( oC)

-6

7

Cloud
Point ( oC)

6

8

Flash
Point (oC)

165

9

Aniline
Point (oC)

65-70

10

Copper
Corrosion Characteristics

Not
worse than 1a

11

TAN
(mg KOH/gsample)

0.5

(*Note: At 60oF)

 

4. CONCLUSION

 

Based on the
results obtained from the three sets of experiments performed it can be
concluded that the cracking of plastics is a viable way for the disposal of
plastic wastes, considering the environmental hazards posed by the generation
and consumption of huge amount of plastic waste. Since plastic is a petroleum
product and the energy lost in the form of plastic waste can be recovered back
to the energy contained as hydrocarbon liquids and gases by pyrolysis process.
This way the environment can be saved from the threat due to plastic wastes and
at the same time, to some extent, non-renewable source of energy (petroleum)
can be conserved. Therefore the conversion of plastic waste to liquid and
gaseous hydrocarbons can be used as a source of energy and/or as a feedstock
for petrochemicals which seems to be an environmentally and economically best
option available.

It is observed
that the product obtained from the cracking of plastic waste in the presence of
ceramic beads and copper is more stable than the thermally cracked product.
However, the product obtained from cracking of waste plastic in the presence of
ceramic beads is waxy in nature similar to the product that is obtained from
the thermal cracking of waste plastic. While the product obtained from the
cracking of waste plastic in the presence of copper mesh has higher yields, less
waxy nature and color stability compared to the products obtained from the
other two sets of experiments.

From these
observations, it appears that the cracking of plastic waste in presence of
copper mesh is most efficient process compared to thermal cracking and cracking
in presence of porcelain beads.

Author