Md. Azhar Uddin

Degradation of polyethylene and polypropylene into fuel oil by using solid acid and non-acid catalysts

The thermal and catalytic degradation of plastic polymers, polyethylene (PE) at 430°C and polypropylene (PP) at 380°C into fuel oil were carried out by batch operation. The catalysts employed were acid-catalysts silica–alumina (SA-1, SA-2), zeolite ZSM-5 and non acidic mesoporous silica catalysts (silicalite, mesoporous silica gel and mesoporous folded silica (FSM). The yields of product gas, liquid and residues; recovery rate of liquid products, and boiling point distribution of liquid products by catalytic degradation were compared with those of non-catalytic thermal degradation. The present work is divided into three sections: (1) a study of effect of catalytic contact mode and (2) a study of effect of types of catalysts on plastic degradation, and (3) the evaluation of catalysts during the degradation of PE and PP by repeating batch operation. For PP degradation in liquid phase contact with SA-1, the yield of liquid hydrocarbons was obtained with 69 wt.%, and the boiling point (bp) of the oil ranged between 36 and 270°C, equivalent to the bp of normal paraffins n-C6 to n-C15. The liquid products from catalytic degradation have a carbon number distribution very similar to commercial automobile gasoline. For vapor phase contact, the yield of liquid products was much lower (54%) and the rate of liquid recovery (or formation) was much slower. Catalysts possessing strong acid sites such as zeolite ZSM-5 accelerated the degradation of PP and PE into gases which resulted in low liquid yields. For FSM, which possesses no acid sites, the initial rates of PP and PE degradation into liquid were as fast as that over an acid catalyst (SA-1) and the liquid yields were higher. The liquid products from catalytic degradation over FSM have a carbon number distribution similar to a mixture of kerosene and diesel oil. Upon repeated use SA-1 deactivated very rapidly due to coke deposition on the catalyst, whereas FSM deactivated much more slowly. These findings concerning the FSM catalyst strongly suggest that the mesopores surrounded by the silica sheet may act as reservoir for radical species and the radical species accelerate the degradation of plastic melt.

Thermal decomposition of flame-retarded high-impact polystyrene

The thermal decomposition of four high-impact polystyrene (HIPS) samples containing brominated flame retardants has been studied. Decabromodiphenyl ether (Br10-DPE) and decabromodibenzyl (Br10-DB) were used as flame retardants and two samples contained antimony trioxide (Sb2O3) synergist besides the brominated additives. The thermal decomposition of HIPS samples was studied by thermogravimetry/mass spectrometry (TG/MS), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and pyrolysis-mass spectrometry (Py-MS). It was established that the brominated additives themselves do not change the decomposition temperature of polystyrene (PS). However, Sb2O3 reduces the thermal stability of the samples indicating that Sb2O3 initiates the decomposition of the flame retardants and PS. Water and styrene products were detected during the first stage of decomposition from HIPS samples containing Sb2O3. Nevertheless, the majority of PS decomposes at a higher temperature. The two brominated flame retardants decompose by different pathways. The scission of CC bonds, resulting in the formation of bromotoluenes, is the most important reaction of Br10-DB additives. In contrast, Br10-DPE decomposes by an intermolecular ring closure pathway producing brominated dibenzofurans (DBF).

Basic study on a continuous flow reactor for thermal degradation of polymers

Abstract A continuous flow reactor for thermal degradation of polymer such as polyethylene (PE), polypropylene (PP) and polystyrene (PS) was operated at the feed rate of 0–1.5 kg h −1 in order to investigate the characteristics of the continuous flow operation and the thermal degradation behavior of polymers. Rate studies on thermal degradation of polymers were made at various temperatures and under a steady state. The activation energies, calculated on the basis of the rate of volatilization, were 221, 216 and 208 kJ mol −1 for thermal degradation of PE, PP and PS, respectively. These activation energies indicate that a chemical reaction takes a role of rate controlling step in this reactor system. By continuous flow operation, polymers were converted to the liquid product with high yield of 93.6–96.2, 96.1–99.1 and 99.9 wt.% for PE, PP and PS. The liquid products consisted of a wide spectrum of hydrocarbons distributed C 4 –C 30 . Thermal degradation by continuous flow operation is a suitable technique for converting plastic polymers into liquid hydrocarbons which could be used as feed stock materials. Based on the observed information, a macroscopic mechanism was proposed. The thermal degradation of polymers consists of two distinct reactions which simultaneously occur in the reactor. One is a random scission of links which causes a molecular weight reduction of the raw polymer, and the other is a chain-end scission of CC bonds, which causes the generation of the volatile product. The chain-end scission takes a place at the gas–liquid interface in the working reactor.

Thermal degradation of polyethylene mixed with poly(vinyl chloride) and poly(ethyleneterephthalate)

Thermal degradation of plastics such as polyethylene (PE), poly(vinylchloride) (PVC), poly(ethyleneterephthalate) (PET) and their mixtures (PE + PVC and PE + PET) was studied at 430 °C by batch operation to analyse the conversion of waste plastics into fuel oil. A visual inspection of the inside of the reactor was made and the macroscopic process of degradation was monitored. Products of degradation were classified into three groups: gases, liquids and residues in the reactor. The degradation of PE produced liquid products which consisted of C5-C25 fraction of hydrocarbons with a yield of 70 wt%. On the other hand, the degradation of PVC produced only 4.7 wt% liquid products which consisted of C5-C20 fraction of hydrocarbons and the degradation of PET produced no liquid products. The effect of mixing PVC and PET with PE on the yield and compositions of liquid products was investigated. The addition of either PVC or PET to PE decreased the overall liquid products yield; however, it promoted the degradation of PE into low molecular weight liquid hydrocarbon products.

The catalytic effect of Red Mud on the degradation of poly (vinyl chloride) containing polymer mixture into fuel oil

Thermal and catalytic degradation of poly (vinyl chloride) (PVC) containing polymer mixtures, PVC/PE, PVC/PP and PVC/PS, into fuel oil was investigated. In the catalytic degradations, Red Mud (a waste from alumina production) was tested as both cracking and dechlorination catalyst. For comparison, γ-Fe2O3 as a chlorine sorbent and SA-1 (silica alumina) as a solid acid catalyst were also used. The effect of degradation conditions, such as nitrogen gas flow, stepwise pyrolysis, catalyst contact mode, on the dechlorination was also investigated. The use of N2 gas flow suppressed partially the reaction between HCl gas from the degradation of PVC and polymer degradation products. By stepwise pyrolysis, over 90% chlorine in the feed plastic was recovered as HCl gas. SA1 catalyst accelerated the rate of polymer degradation and lowered the boiling point of liquid products, but the chlorine content of oil over SA1 was also the highest. Red Mud (RM) and iron oxides sorbents showed good effect on the fixation of evolved HCl. However, they had no effect on the cracking of polymers. The oils derived from PVC containing pure polymer mixtures by thermal degradation contained a lower amount of chlorine than the oils obtained using RM and other catalysts. From this result we conclude that the formation of some organic chlorine compounds may be promoted by the interaction of the HCl and the catalysts.

Role of SO 2 for Elemental Mercury Removal from Coal Combustion Flue Gas by Activated Carbon

In order to clarify the role of SO 2 in the removal of mercury from coal combustion flue gas by activated carbon, the removal of Hg° vapor from simulated coal combustion flue gas containing SO 2 by a commercial activated carbon (AC) was studied. The Hg° removal experiments were carried out in a conventional flow type packed bed reactor system with simulated flue gases having a composition of Hg° (4.9 ppb), SO 2 (0 or 500 ppm), CO 2 (10%), H 2 O (0 or 15%), O 2 (0 or 5%), and N 2 (balance gas) at a space velocity (SV) of 6.0 × 10 4 h -1 in a temperature rang 60-100 °C. It was found that, for SO 2 containing flue gas, the presence of both O 2 and H 2 O was necessary for the removal of Hg° and the Hg° removal was favored by lowering the reaction temperature in the order of 60 > 80 > 100 °C. The presence of SO 2 in the flue was essential for the removal of Hg° by untreated activated carbon. The activated carbons pretreated with SO 2 or H 2 SO 4 prior to the Hg° removal also showed Hg° removal activities even in the absence of SO 2 ; however, the presence of SO 2 also suppressed the Hg° removal of the SO 2 -pretreated AC or H 2 SO 4 preadded AC.

Novel calcium based sorbent (Ca-C) for the dehalogenation (Br, Cl) process during halogenated mixed plastic (PP/PE/PS/PVC and HIPS-Br) pyrolysis

A calcium carbonate carbon composite sorbent (Ca-C) was prepared by using 90 wt% of calcium carbonate and 10 wt% phenol resin. The Ca-C sorbent was successfully utilised for the dechlorination and debromination process during halogenated (Cl, Br) mixed waste plastic (PP/PE/PS/PVC/HIPS-Br: 3∶3∶2∶1∶1) pyrolysis at 430 °C and produced halogen free liquid products.

Hydrogen production from algal biomass via steam gasification

Algal biomasses were tested as feedstock for steam gasification in a dual-bed microreactor in a two-stage process. Gasification experiments were carried out in absence and presence of catalyst. The catalysts used were 10% Fe₂O₃-90% CeO₂ and red mud (activated and natural forms). Effects of catalysts on tar formation and gasification efficiencies were comparatively investigated. It was observed that the characteristic of algae gasification was dependent on its components and the catalysts used. The main role of the catalyst was reforming of the tar derived from algae pyrolysis, besides enhancing water gas shift reaction. The tar reduction levels were in the range of 80-100% for seaweeds and of 53-70% for microalgae. Fe₂O₃-CeO₂ was found to be the most effective catalyst. The maximum hydrogen yields obtained were 1036 cc/g algae for Fucus serratus, 937 cc/g algae for Laminaria digitata and 413 cc/g algae for Nannochloropsis oculata.

FT-IR and XRD analysis of natural Na-bentonite and Cu(II)-loaded Na-bentonite.

Na-bentonite has been studied extensively because of its strong adsorption capacity and complexation ability. In this work, surface area, total pore volume, mean pore diameter, TG, DTA, FT-IR and XRD were carried out in order to reveal the characteristics of natural Na-bentonite. XRD and FT-IR of natural Na-bentonite (China) and Cu-loaded Na-bentonite as a function of Na-bentonite dosage and temperature using batch technique were characterized in detail, respectively.

Vapour phase catalytic hydrodechlorination of chlorobenzene over Ni–carbon composite catalysts

Abstract Ni–carbon composite catalysts were prepared by a modified carbothermal reduction method using ion exchange resins. The catalysts were characterised by N2 adsorption, X-ray diffraction and transmission electron microscope. The catalysts activities and selectivities were studied in the hydrodechlorination of chlorobenzene. The catalyst activities depend upon the carbothermal reduction temperature during preparation. These catalysts are found to be more stable and selective in this reaction even in the presence of HCl which is produced during the reaction.