PRODUCTION, CHARACTERIZATION AND FUEL PROPERTIES OF ALTERNATIVE DIESEL FUEL FROM PYROLYSIS OF WASTE PLASTIC GROCERY BAGS

PLASTIC WASTE : A TIME BOMB TICKING FOR INDIA

Source : Status report on municipal solid waste management by CPCB

Source : The Hindu , dated: April 4, 2013

PLASTICS : DEFINITION

Plastics are a generic group of synthetic or natural materials, composed of high-molecular chains whose sole or major element is carbon.

A plastic material is (Society of Plastics Industry) any one of a large group of materials consisting wholly or in part of combinations of carbon with oxygen, hydrogen, nitrogen, and other organic or inorganic elements which, while solid in the finished state, at some stage in its manufacture is made liquid, and thus capable of being formed into various shapes, most usually through the application, either singly or together, of heat and pressure.’

PLASTICS : CLASSIFICATION

PYROLYSIS : DEFINITION

Pyrolysis, also termed thermolysis (Greek : pur = fire; thermos = warm; luo = loosen), is a process of chemical and thermal decomposition, generally leading to smaller molecules.

It differs from combustion in that it occurs in the absence of air and therefore no oxidation takes place.

PYROLYSIS OF PLASTICS AND RUBBER

In its simplest definition pyrolysis is the degradation of polymers at high temperatures under non oxidative conditions to yield valuable products (e.g. fuels and oils).

Pyrolysis can be conducted at various temperature levels, reaction times, pressures, and in the presence or absence of reactive gases or liquids, and of catalysts.

Plastic pyrolysis proceeds at low ( < 400⁰C ), medium (400⁰C - 600⁰C) or high temperature ( >600⁰C).

The pressure is generally atmospheric. Sub atmospheric operation, whether using vacuum or diluents, e.g. steam, may be selected if the most desirable products are thermally un-stable, e.g. easily re-polymerizing, as in the pyrolysis of rubber or styrenics.

PYROLYSIS : ADVANTAGES OVER ALTERNATE PLASTIC TREATMENT PROCESSES

It can deal with plastic waste which is otherwise difficult to recycle and it creates reusable products with unlimited market acceptance.

As feedstock recycling and pyrolysis is not incineration there are no toxic or environmentally harmful emissions.

The major advantage of the pyrolysis technology is its ability to handle unsorted, unwashed plastic. This means that heavily contaminated plastics such as mulch film (which sometimes contains as much as 20% adherent dirt/soil) can be processed without difficulty.

COMMERCIAL PYROLYSIS PROCESSES FOR WASTE PLASTICS.

PLASTICS SUITABLE FOR TREATMENT

CLASSIFICATION OF POLYETHYLENE

1. HIGH DENSITY POLYETHYLENE (HDPE)

2. MEDIUM DENSITY POLYETHYLENE (MDPE)

3. LOW DENSITY POLYETHYLENE (LDPE)

Source : Feedstock Recycling and Pyrolysis of Waste Plastics: Converting Waste Plastics into Diesel and Other Fuels Edited byJ. Scheirs and W. Kaminsky 2006 John Wiley & Sons, Ltd ISBN: 0-470-02152-7

STRUCTURE OF THE SYSTEM

COMMERCIAL PLASTIC PYROLYSIS PROCESSES

1. THERMOFUEL PROCESS

2. SMUDA PROCESS

3. POLYMER-ENGINEERING PROCESS (CATALYTIC DEPOLYMERIZATION)

4. ROYCO PROCESS

5. REENTECH PROCESS

6. HITACHI PROCESS

7. CHIYODA PROCESS

8. BLOWDEC PROCESS

9. CONRAD PROCESS

THERMOFUEL PROCESS In the Thermofuel process, plastic waste is first converted to the molten state and then ‘cracked’ in a stainless steel chamber at temperatures in the range 350–425⁰C under inert gas (i.e. nitrogen).

The hot pyrolytic gases are condensed in a specially designed two-stage condenser system to yield a hydrocarbon distillate comprising straight- and branched-chain aliphatic, cyclic aliphatics and aromatic hydrocarbons.

The resulting mixture is essentially equivalent to regular diesel.

Source : Feedstock Recycling and Pyrolysis of Waste Plastics: Converting Waste Plastics into Diesel and Other Fuels Edited byJ. Scheirs and W. Kaminsky 2006 John Wiley & Sons, Ltd ISBN: 0-470-02152-7

SMUDA PROCESS The Smuda pyrolysis process developed by Dr Heinrich W. Smuda is a continuous process where the mixed plastic feedstock is fed from an extruder into a stirred and heated pyrolysis chamber

The extruder acts as an airlock to exclude oxygen and also to preheat and melt the polymer, so less energy input is required in the main chamber.

The pyrolysis vessel operates at a constant level of 60% and the headspace is purged with nitrogen gas. A layered silicate catalyst (5–10% by vol) is added to the plastic melt to give a catalytic cracking reaction.

The fuel from the Smuda process is both transportation-grade diesel (85%) and gasoline (15%).

Photograph of Smuda stirred-tank reactor (left) and bottom of distillation column (right).(Copyright. Scheirs)

CHARACTERIZATION AND PROPERTIES OF ALTERNATE DIESEL FUEL

PRODUCTION OF TEST FUEL Thermochemical conversion of plastic grocery bags (HDPE) to oils were conducted using a pyrolysis batch reactor in triplicate.

Pyrolysis was performed in a Be-h desktop plastic to oil system containing a 2 L reactor and oil collection system using approximately 500 g of plastic grocery bags each time.

The pyrolysis reactor has two heating zones (upper and lower); the upper and lower temperatures were set to 420 and 440 °C, respectively. Once the reactor reached the set temperatures, a reaction time of 2 h was employed from that point on.

Vapors produced as a result of pyrolysis were condensed over water as plastic crude oil (PCO). The upper oil layer was separated and weighed. The reactor lid was opened once the temperature was below 50 °C to remove the remaining residual solid material and weighed separately.

The PCO thus obtained after pyrolysis of waste plastic grocery bags was distilled into four fractions (b190; 190–290; 290–340; and 340+°C equivalent of motor gasoline (MG), diesel#1 (PPEH-L), diesel #2 (PPEH-H) and VGO respectively.

CHEMICAL CHARACTERIZATION OF PLASTIC OIL FRACTIONS

1. Gas chromatography–mass spectroscopy (GC–MS)

An Agilent DB-35MS column (30 m × 0.320 mm; 0.25μmfilm thickness) was used with a helium flow rate of 0.509 mL/min. The temperature program began with a hold at 30 °C for 10 min followed by an increase at 1 °C/min to 195 °C, then 35 °C/min to 330 °C, which was held for 1 min. The injector and column transfer line heater were both set to 340 °C. The detector inlet and MS quadropole temperatures were 220 and 150 °C, respectively. The injection volume was 1μL.

RESULTS :-

The principal constituents in PPEH-L and PPEH-H were quantified by GC–MS, as depicted by a representative chromatogram.

In agreement with the NMR results, both samples were comprised of a series of saturated and unsaturated hydrocarbons.

The test demonstrated that both fuels were composed of a mixture of hydrocarbons. However, PPEH-H contained heavier constituents GC–MS results further revealed that PPEH-L contained 43.6% (peak area) of compounds containing one or more double bonds (olefins), while PPEH-H contained 28.2% of such olefin peaks.

2. Simulated distillation by GC–FID The boiling point distribution of PCO fractions was obtained by performing simulated distillations.

The analysis was performed on 1% (w/w) sample solutions in dichloromethane using an HP 5890 Series II FID gas chromatograph equipped with a temperature programmed vaporizer injector.

RESULT :-

The boiling point distribution of PCO fractions was obtained using high temperature GC–FID.

.As boiling point and MW distribution of PCO were similar to petroleum fractions and contained negligible heteroatom content, therefore, it is speculated that these PCOs will be compatible with petroleum crude oil for refining in a conventional refinery.

(contd.)

Simulated distillation of a plastic crude and its four fractions.

3. Size exclusion chromatography (SEC) analysis

Molecular weight (MW) distributions were determined by SEC.

SEC analysis was carried out on a on a Waters (Milford, MA) Styragel HR1 SEC column (7.8 mm × 300 mm), Waters 2414 RI detector, and THF as mobile phase (1.0 mL/min).

The resulting chromatographic data was processed using Matlab software to provide the weight-average MW (Mw) and polydispersity index (PDI).

RESULTS :-

Comparison to the MW obtained for ULSD (Mw of 131 with max MW of 299 g/mol) revealed greater similarity to PPEH-L than PPEH-H. For most of the PCO fractions polydispersity index (PDI) ranged between 1.33 and 1.65, thus indicating a narrow distribution of MWs for these fractions compared to the ULSD exhibiting a higher PDI (2.08).

4. NMR and FT-IR spectroscopy Chemical functionality information was obtained by analyzing the fractions using Fourier-Transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopies.

Samples were dissolved in CDCl3(Cambridge Isotope Laboratories, Andover, MA) and all spectra were acquired at 26.9 °C. Chemical shifts (δ) are reported as parts per million (ppm) from tetramethylsilane based on the lock solvent.

RESULTS :-

Compositional analysis by NMR spectroscopy revealed the presence of aromatic, olefinic and paraffinic protons in PPEH-L and PPEH-H

Aromatics comprised 1.0 and 0.6% of the overall proton content of PPEH-L and PPEH-H, respectively.

Unsaturated protons (aliphatic olefins) constituted 5.4% and 2.6% of PPEH-L and PPEH-H, respectively.

The remainder of the content of PPEH-L (94.0%) and PPEH-H (96.8%) was composed of aliphatic saturated hydrocarbons.

No oxygenated species such as carboxylic acids, aldehydes, ketones, ethers, or alcohols were detected by either 1H or 13C NMR spectroscopies.

Properties of PPEH and comparison to ULSD PPEH-L showed excellent cloud point and pour point values. There was significant improvement over the conventional ULSD.

PPEH-H, with its greater content of higher-melting longer-chain paraffinic constituents relative to PPEH-L and ULSD, provided CP (4.7 °C), CFPP (3.7 °C) and PP (4.0 °C). The 1:1 PPEH-L/H blend, representative of summer grade ULSD, yielded cold flow properties (CP−5.9 °C, CFPP−6.0 °C, and PP −8.3 °C) intermediate to those of the neat materials.

The plastic derivative fuels were found to have reduced stability. The presence of unsaturated constituents was speculated as the reason for the reduced stabilities of PPEH-L and PPEH-H versus ULSD.

CONCLUSIONS Pyrolysis of HDPE waste plastic grocery bags followed by distillation resulted in a major liquid hydrocarbon product (PPEH-L).

Also obtained was a heavier boiling fraction (290–340 °C) equivalent of diesel#2 from distillation of the crude pyrolysis product, PPEH-H.

ThermoFuel is a truly sustainable waste solution, diverting plastic waste from landfills, utilizing the embodied energy content of plastics and producing a highly usable commodity that is more environmentally friendly than any conventional distillate.

The result of this process is claimed to be a virtually nonpolluting, (100%) synthetic fuel that does not require engine modification for maximum efficiency.

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