Ali Y. Bilgesü

Flash pyrolysis of polystyrene wastes in a free-fall reactor under vacuum

Abstract Plastic waste minimization and recycling are important for both economical and environmental reasons. In this flash pyrolysis study, polystyrene wastes were degraded in a free-fall reactor under vacuum to regain the monomer. A set of experiments varied the temperature between 700 and 875°C and determined its effects on the phase yields, the benzene, styrene, toluene, and naphthalene distribution of the liquid output and C1–C4 content of the gaseous output. The liquid yield maximized around 750°C and the styrene yield at 825°C. In general, operating at higher temperatures lessened the solid residue and increased the gaseous yield and total conversion. Employing waste particles in four size ranges, a second set of runs indicated that the finer the waste particles fed the higher the gaseous yield and total conversion. This recycling method can be made more promising if the feed particles are allowed more time for degradation and the removal of the primary products speeded up thereby preventing their decomposition. Ways are suggested to obviate these residence time problems.

Production of oxalic acid from sugar beet molasses by formed nitrogen oxides.

Production of oxalic acid from sugar beet molasses was developed in a series of three reactors. Nitrogen oxides formed were used to manufacture oxalic acid in the second and third reactor. Parameters affecting the reaction were determined to be, air flow rate, temperature, the amount of V2O5 catalyst and the concentrations of molasses and H2SO4. The maximum yields in the second and third reactors were 78.9% and 74.6% of theoretical yield, respectively. Also, kinetic experiments were performed and the first-order rate constants were determined for the glucose consumption rate. Nitrogen oxides in off-gases from the final reactor were absorbed in water and concentrated sulphuric acid and reused in the following reactors giving slightly lower yields under similar conditions. In this novel way, it was possible to recover NO(x) and to prevent air pollution. Meanwhile, it was possible to reduce the unit cost of reactant for oxalic acid production. A maximum 77.5% and 74.1% of theoretical yield was obtained by using the absorption solutions with NO(x).

Desulphurization of coals by flash pyrolysis followed by magnetic separation

Abstract Removal of inorganic sulphur from a Turkish lignite (Tuncbilek) by flash pyrolysis and magnetic separation was investigated. Pyrite is slightly paramagnetic, however, its paramagnetism is not sufficient to affect the separation from coal. Depending on the pyrolysis temperature pyrite, FeS 2 , converts to a variety of iron sulfides, among which the ferrimagnetic pyrrhotite, Fe 7 S 8 , forms at 973 K. In this study, the highest rate of sulphur removal was observed at 923 K. For the particle size of −0.1 mm, a 35% sulphur reduction was achieved by flash pyrolysis and this reduction was further enhanced to 48% by magnetic separation.

Flash Vacuum Pyrolysis of Low Density Polyethylene in a Free-Fall Reactor

Polyethylene (PE) is the principal component of postconsumer plastic wastes. It is important to develop chemical techniques to decompose PE with a view to recycling and production of compounds that are valuable as fuel or industrial raw materials. The most common reactors in polymer pyrolysis are fluidized-bed types. Free-fall reactors do not suffer the disadvantages of fluidized beds related to inert gas employment. This flash pyrolysis study has shown that low density polyethylene (LDPE) can be continuously degraded in a free-fall reactor under vacuum to give a product quality superior to other methods. The total conversion (i.e., the sum of liquid and gas yield) is 43% at 875°C when the feed is 150–75 μm LDPE particles. Over 99% of the gaseous product is C1 to C4, the ethylene monomer exceeding 64%. The bulk of the liquid product is paraffinic; 96% of which is below C40, while over 55% is C12–C20. As is known, C12–C20 hydrocarbons are essential raw materials for the production of fatty acids, fatty alcohols, and detergents. Reduction in operation temperature down to 750°C causes the total conversion to fall from 40% to 25%. This is accompanied by a slight increase (from about 64% to 67%) in the ethylene monomer yield. Thus higher temperatures should be preferred. On the other hand, indications are that lowering the particle size down to −75 μm favorably influences the total conversion, with a gain of about 20%.

USE OF CYCLOHEXANE AS SOLVENT IN THERMAL DEGRADATION OF LOW DENSITY POLYETHYLENE WASTES

Thermal degradation of low density polyethylene (LDPE) wastes was investigated in this study as a step in chemical recycling. The effects of the degradation temperature, the solvent–LDPE ratio, and the reaction time were researched in the respective ranges 375–450°C, 0:1–6:1, and 30–120 min. Experiments at a cyclohexane:LDPE ratio of 6:1 showed that up to 425°C the solid residue decreased whereas the liquid yield and the total conversion increased. There were no significant changes thereafter. Solventless degradation at 425°C gave the weight percentages of 4.7, 75.6, and 19.7 for solid, liquid, and gaseous products, respectively. The use of cyclohexane as a solvent brought about approximately 20% gain in liquid yield and diminished the solid residue to negligible levels. Alkanes, alkenes, and cycloalkanes were the identified compounds in the light liquid products of degradation. The solvent reacted with the products. Reactions between alkanes and alkenes also contributed to cyclization that increased with temperature. The gas chromatography analyses identified methane and C2–C4 in the gaseous products. Reaction time tests showed unimportant changes in yield figures.

KINETIC PECULIARITY OF CO-PRODUCTION OF BENZENE AND NAPHTHALENE FROM AROMATIC MIXTURES BY THERMAL HYDRODEALKYLATION

ABSTRACT The kinetic peculiarity of aromatic and non-aromatic hydrocarbons under co-production process conditions of benzene and naphthalene from pyrolysis gasoline or other industrial aromatic mixtures through thermal hydrodealkylation was experimentally investigated. In these experiments, various model mixtures of such pure hydrocarbons as benzene, toluene, naphthalene, 1-, 2-methylnaphtalenes and n-heptane were used as raw materials, and under thermal hydrodealkylation conditions, conversion kinetics of these hydrocarbons and their effects to each other were studied. According to the experimental results obtained, the conversion rates in descending order are as n-heptane > 1-methylnaphthalene (1-MN) > 2-methylnaphthalene (2-MN) > toluene. N-heptane considerably accelerates the hydrodealkylation reactions of both toluene and 1-MN and 2-MN. While 1- MN and 2-MN increase the rate of toluenes conversion to some extent, toluene can prevent their conversion. Furthermore, n-heptane has an increasing impact on the reaction rate of benzenes conversion into biphenyl. At temperature of 625°C and in a long contact time (60 s or more) almost all of n-heptane is converted into mostly alkanes, C1–C3 gases.