Decomposition characteristics of residue from the pyrolysis of polystyrene waste in a fluidized-bed reactor

Effective treatment of residue generated from the pyrolysis of polystyrene wastes has been one of the important factors in the recovery of styrene monomer and oil from polystyrene wastes. Depending on the experimental conditions, the yields of oil and styrene monomer are considerably decreased in the presence of residue. Here the residue was decomposed effectively in a catalytic fluidized-bed reactor. Nitrogen and silica sand were used as a fluidizing gas and a bed material, respectively. Effects of catalyst, temperature and gas velocity on the characteristics of decomposition of the residue were examined. It was found that the residue could be decomposed to oil or chemicals effectively by means of a catalytic fluidized-bed reacting system. The yields of oil and individual chemicals and the composition of the products were dependent upon the operating variables such as reaction temperature, catalyst and gas velocity.     

Activation of olive-seed waste residue using CO2 in a fluidized-bed reactor

Physical activation of olive-seed waste residue was carried out under N₂/CO₂ atmosphere in a fluidized-bed reactor system. The effects of activation temperature, activation time and particle size on both yield and quality of the prepared products were studied. The quality was measured in terms of iodine number and adsorptive capacity towards methylene blue dye. In general, it was found that higher activation temperature, longer activation time and smaller particle size produced a higher quality activated carbon. The products were compared to a commercial grade activated carbon prepared by steam activation process. Samples of 0.71–0.85 mm particle size activated at 900°C and activation time greater than 60 min were superior to the commercial carbon. Similar results were obtained for similar samples activated at 800°C and activation times greater than 60 min. A kinetic model was applied to the data. A first order reaction kinetics was found to fit the experimental data well. The value of the rate constant for activation was found to be 0.65 s⁻¹.     

Sensitivity analysis of a batch polymerization reactor

The sensitivity of model output variables for a batch polymerization reactor to uncertainties in the kinetic parameters and initial conditions is studied. Differential equations that describe the time variation of sensitivity coefficients for the batch reactor are derived. Numerical integration of the sensitivity equations reveals that the system output responses are very sensitive to parameter variations especially when the polymerization exhibits an autoacceleration of the reaction rate.     

An optimization study on the pyrolysis of polystyrene in a batch reactor

The pyrolysis process of polystyrene (PS) has been investigated to find optimal temperature profiles which minimize the reaction time and the reaction energy required for a given conversion in a batch reactor. Assuming that the fragmentation of PS in pyrolysis is described by the mechanism of random and/or specific degradations, we used a continuous kinetic model for solving three moment equations to determine the transient change of molecular weight distributions (MWD) of the polymers. We then converted this independent-variable minimization problem using a coordinate transformation to a dependent-variable minimization problem that yields the optimal temperature profiles as its solution. The optimization results obtained in this study encompass the cases of different objective functions which cover minimum reaction time, minimum energy consumed, or any combination of these. It has turned out that maintaining the reaction temperature constant at an optimal level is the best solution in this optimization problem. An economic cost function also has been introduced as the third objective function to be minimized in addition to the reaction time and the reaction energy. This new function can serve as a convenient measure to judge the performance of the pyrolysis process minimizing the involved cost.     

Distribution and characteristics of pyrolysis products from automobile shredder residue using an experimental semi-batch reactor

Automobile shredder residue (ASR) generated by end-of-life vehicles, comprises more than 20% of a new vehicle by weight. Significant amounts of polymers in ASR, such as Poly Propylene (PP), Poly Ethylene (PE), Acrylonitrile Butadiene Styrene (ABS), Ethylene Propylene Ethylidene Nobomene (EPDM), rubber, Polyethylene Terephthalate (PET), Poly Amide (PA), and Poly Vinyl Chloride (PVC), can be used as energy or chemical sources, whereas other components, such as tires, rubber, glass, wood, sand/dust, and heavy metals inhibit the recycling of ASR. In many countries, landfill use of ASR is regulated, so landfill costs have increased, as has inappropriate disposal; sending ASR to landfills will be needed to be regulated in Korea. Pyrolysis has been suggested as an economically feasible recycling and recovery technique for ASR in Korea and other advanced countries. Before such technology is implemented, the characteristics of pyrolyzed products should be investigated. Shredded samples from the facility were collected, and calorific value, elemental analysis, and leaching tests were performed to determine ASR characteristics. Pyrolysis experiments were conducted at five different temperatures, 400, 500, 600, 700, and 800 °C, and the product distributions of gas, tar, and char were investigated. The optimal temperature for ASR pyrolysis, in terms of yield efficiency, was found to be 600 °C. The mean calorific value was also found to be higher in this case; thus, ASR can be treated as an auxiliary fuel. During pyrolysis, there were high ignition losses of light and heavy fluff, due to the presence of organic materials. The leaching concentrations of all tested heavy metals were found to be within the Korean guideline values. In terms of carbon number distributions, pyrolysis of ASR at 600 °C was optimal. For further utilization of pyrolysis products as fuel, the characteristics of char, oil, and gas were investigated with an experimental batch reactor.     

Continuous pyrolysis of waste tyres in a conical spouted bed reactor

Continuous pyrolysis of scrap tyres has been carried out in a conical spouted bed reactor and the results (yields, composition of the volatile fraction and carbon black properties) have been compared with those obtained operating in batch mode in a previous study. Continuous operation in the 425-600 °C range gives way to a yield of 1.8-6.8 wt.% of gases, 44.5-55.0 wt.% of liquid fraction (C₅-C₁₀ range hydrocarbons, with a maximum yield of limonene of 19.3 wt.% at 425 °C), 9.2-11.5 wt.% of tar and 33.9-35.8 wt.% of char. The main differences between the continuous and batch processes are in the yield of light aromatics, which is higher in the continuous process, and in that of the heavy liquid fraction or tar, which is higher in the batch process. These are the advantages of the continuous process, although hydrogenation of the liquid fraction is required even in this case in order to use it as fuel. The high yield of limonene, the flexibility in the operating conditions and the capacity for a continuous removal of the residual carbon black from the reactor are the advantages of conical spouted bed technology. The excellent performance of the conical spouted bed reactor for the tyre pyrolysis process is due to the solid cyclic movement, the good contact between phases, the high heating rate and the reduced residence time of the volatile products.     

The analysis of a batch electrochemical reactor with continuously recirculating electrolyte

An analysis has been made to describe the variation of reactant concentration with time in an electrochemical reactor through which a batch of electrolyte is continuously recirculated, the electrochemical reaction being mass transfer controlled. Application of the analysis has been made to a hypothetical copper electrowinning process employing a parallel plate electrochemical cell.     

Molten waste plastic pyrolysis in a vertical falling film reactor and the influence of temperature on the pyrolysis products

Molten plastics are characterised with high viscosity and low thermal conductivity. Applying falling film pyrolysis reactor to deal with waste plastics can not only improve heat transfer efficiency, but also solve the flow problem.In this work, the pyrolysis process of molten polypropylene(PP) in a vertical falling film reactor is experimentally studied, and the influence of heating temperature on pyrolysis products is discussed. It has been found that with the temperature increases from 550 ℃ to 625 ℃, the yield of pyrolysis oil decreases from 74.4 wt%(± 2.2 wt%) to53.5 wt%(±1.3 wt%). The major compositions of the pyrolysis oil are C_9, C_(12) and C_(18), and β-scission reactions are predominant. The content of the light fraction C_6-C_(12) of pyrolysis oil is 69.7 wt%. Compared with other pyrolysis reactors, the yield of oil from vertical falling film pyrolysis reactor is slightly higher than that from tubular reactor,equal to that from rotary kiln reactor, and slightly lower than that in medium fluidised-bed reactor.     

Study of pyrolysis kinetics of Alberta oil sand by thermogravimetric analysis

The kinetics of the thermal decomposition of Alberta oil sand has been investigated by thermogravimetric analysis (TGA) for the study of oil sand pyrolysis characteristics. The TGA experiments were carried out at four different heating rates of 10, 20, 30, 40 °C/min up to 900 °C to verify weight variation and reaction temperature. The activation energy of the thermal decomposition of Alberta oil sand obtained from the kinetic analysis was similar to that of the previous researches. Also, bitumen was extracted by solvent (toluene, THF (tetrahydrofuran)) and analyzed. Extracted bitumen was analyzed by using proximate analysis, ultimate analysis, heavy metal analysis, heating value, asphaltenes, API, SIMDIS, density, TLC, and molecular weight. The analyses of the extracted bitumen were similar to those of heavy residue.     

The analysis of an isothermal batch electrochemical reactor with a secondary cathodic reaction

An analysis has been made to examine the effect of a constant applied electrolysing voltage on the performance of an isothermal batch electrochemical reactor in which the rate of the cathodic reaction is limited by mass transfer of a reactant to the electrode surface, a simultaneous secondary reaction occurring at higher cathode potentials.Numerical solutions are presented for a hypothetical process study to show how average production rates for various percentage conversions of reactant are influenced by the magnitude of the electrolysing voltage and the corresponding electrical energy requirement. The most noticeable effect is that the electrical energy requirements for a given production rate are very strongly influenced by both the degree of conversion of reactant and by the extent to which the secondary reaction occurs.     

Coal pyrolysis and gasification in a fluidized bed thermogravimetric analyzer

The kinetics and modelling of coal gasification were studied in the newly developed fluidized bed thermogravimetric analyzer. The total weight loss obtained from the fluidized bed reactor and the total gas product are in general agreement. The presented model for the micro‐fluidized bed reactor encompasses the kinetics of coal pyrolysis as well as the gasification reactions. For coal pyrolysis, the resulting activation energies for the individual gases were 34.7 to 59.8 kcal/mol. These values are 19 to 21 % lower than those found in the literature for similar coals. This decrease of the activation energies of the endothermic pyrolysis reactions is attributed to a gradient of temperature of 185 to 209 °C. The obtained activation energy for the CO shift reaction is 46.6 kcal/mol, increasing by 20 % from the one used in the literature. This increase of the activation energy of such a mildly exothermic reaction represents an equivalent of 170 °C gradient of temperature. The effects of temperature on the yield and the composition of the gas product are studied. Experimental results and equilibrium data are also compared. The model shows reasonably good agreement with the experimental results, except for the water gas shift reaction.

     

Co-pyrolysis characteristics of typical components of waste plastics in a falling film pyrolysis reactor

Waste plastics mainly come from MSW and usually exist in the form of mixed plastics. During the co-pyrolysis process of mixed plastics, various plastic components have different physicochemical properties and reaction mechanisms. Considering the high viscosity and low thermal conductivity of molten plastics, a falling film pyrolysis reactor was selected to explore the rapid co-pyrolysis process of typical plastic components (PP, PE and PS). The oil and gas yields and the compositions of pyrolysis products of the three components under different ratios at pyrolysis temperatures were analyzed to explore the co-pyrolysis characteristics of PP, PE, and PS. The study is of great significance to the recycling of waste plastics.     

Fuels by pyrolysis of waste plastics from agricultural and packaging sectors in a pilot scale reactor

The pyrolysis of waste plastics (so called chemical recycling) is one perspective way of their utilizations, but the end product properties are a key point of the industrial leading of processes. In this paper a pilot scale pyrolysis process has been investigated. Waste plastics were decomposed in a tube reactor at 520 °C, using hourly feed rate of 9.0 kg. Raw materials were selectively collected wastes from agricultural and packaging industry. For supporting the more intensive cracking of CC bonds of main polymer structure a commercial ZSM-5 catalyst was tested in concentration of 5.0%. Products were separated into gases, gasoline, light and heavy oil by distillation. Plastic wastes could be converted into gasoline and light oil with yields of 20–48% and 17–36% depending on the used parameters. The gas and liquid products had significant content of unsaturated hydrocarbons, principally olefins. In the presence of ZSM-5 catalyst the yields of lighter fractions (especially gasoline) could be considerably increased and the average molecular weight of each fraction has decreased. Gasoline had C₅–C₁₅ hydrocarbons, while light oil had C₁₂–C₂₈. The used catalyst has promoted the formation of i-butane in gases and affected the composition of both gasoline and light oil. Properties of products are advantageous for fuel-like applications, and they are able to increase the productivity of refinery. On the other hand the possibility for further utilization of products from pyrolysis basically was affected by the source and the properties of raw materials. Waste polyethylene from agricultural consisted of some elements from fertilizers (N, S, P and Ca), which could not be removed from the surfaces of raw materials by pre-treatment (e.g. washing). In that case significant concentration of N, S, P and Ca can be measured in all products, but the catalyst has decreased the concentration of impurities. Gasoline, light oil and heavy oil were nitrogen free and sulphur content was below 12 mg/kg in hydrocarbons obtained by the pyrolysis of polypropylene waste from packaging.     

Synthesis of char,bio-oil and gases using a screw feeder pyrolysis reactor

In this study, char, bio-oil and gases were synthesized with a continuous pyrolysis process from residual plants consisting of Cogongrass and Manilagrass at temperatures in the range of 400–550°C, with a feed rate of 150, 350, and 550 rpm (r min^?1). The product yield calculation showed that the liquid yield was highest at 53.56%, at 350 rpm. After separation of the bio-oil from liquid phase, the bio-oil was found to have components of approximately 33.38%, of which the solid yield (char) was highest at 27.35%, at 350 rpm, and the gas yield was highest at 43.60%, at 150 rpm. This indicates that biomass from residual plants materials produced good yields because of low solid and gas yields while having high liquid yield.     

Investigation on pyrolysis of Moroccan oil shale/plastic mixtures by thermogravimetric analysis

Thermal degradation processes for a series of mixtures of oil shale/plastic were investigated using thermogravimetric analysis (TGA) at four heating rates of 2, 10, 20 and 50 K min^− 1 from ambient temperature to 1273 K. High density polyethylene (HDPE), low density polyethylene (LDPE) and polypropylene (PP) were selected as plastic samples. Based on the results obtained, three thermal stages were identified during the thermal degradation. The first is attributed to the drying of absorbed water; the second was dominated by the overlapping of organic matter and plastic pyrolysis, while the third was linked to the mineral matter pyrolysis, which occurred at much higher temperatures. Discrepancies between the experimental and calculated TG/DTG profiles were considered as a measurement of the extent of interactions occurring on co-pyrolysis. The maximum degradation temperatures of each component in the mixture were higher than those of the individual components; thus an increase in thermal stability was expected. In addition, a kinetic analysis was performed to fit thermogravimetric data. A reasonable fit to the experimental data was obtained for all materials and their mixtures.     

Comparison of a block-flow reactor and thermogravimetric analysis in the steam gasification of different types of carbon

A new type of reactor for carbon reactivity measurements, the so called block-flow reactor (BFR) is compared with the more common thermogravimetric analysis (TGA) for the carbon-steam reaction. It is shown, that BFR is particularly suitable for fast kinetic measurements at negligible burn off variations and for the determination of initial effects, which gives complementary information with respect to TGA measurements. This is illustrated by steam gasification results of typical examples of a commercial coal, wood and activated carbon. In BFR, highly porous pure activated carbon shows an initially lower reactivity compared with stable values determined by TGA. Coke and carbonised fir show a high initial reactivity, which disappears on heating under reaction conditions. When the reactivities have stablized the results of BFR and TGA are consistent and agree well with literature values. The reactivity per unit surface area is approximately equal for the three carbons studied. Initial catalytic effects of nickel appear to be very different for the various carbons and can be determined reliably by BFR measurements.     

Nonlinear control of a batch ester-interchange reactor

Nonlinear control algorithms using feedback input-output linearization and sliding mode control are applied to a lab-scale batch ester-interchange reaction system. Batch ester-interchange reaction requires no overshoot of reaction temperature in earlier stage of reaction and tight temperature control throughout the reaction to keep uniform quality of the final product and to prevent variation of the amount of the byproduct such as diethylene glycol at each batch. Through experimentation we find that the nonlinear controller of input-output linearization algorithm shows better control performance both at setpoint tracking and disturbance rejection than the conventional PID controller. Further, sliding mode control algorithm is supplemented and simulated to show that it improves robustness against plant-model mismatch.     

Electrochemical removal of cadmium using a batch undivided reactor with a rotating cylinder electrode

The performance of an undivided electrochemical batch reactor with a rotating cylinder electrode under potentiostatic control is examined for the removal of cadmium from a sodium sulfate solution containing 500 ppm Cd(II) at pH ? 7. The effect of hydrogen evolution as a side cathodic reaction on the figures of merit of the reactor is analysed. The best results were obtained for a cathode potential of ?0.9 V against the saturated calomel electrode. With an angular velocity of 1500 rpm the space time yield and the normalized space velocity were 0.66 mol m^?3 s^?1 and 3.9 h^?1 respectively, while the fractional conversion was 67.3% with a current efficiency of 66.7%. The surface morphology of the deposits as a function of the applied potential is also reported. © 2001 Society of Chemical Industry     

Investigation of thermochemical conversion of biomass in supercritical water using a batch reactor

This study focused on gasification of biomass and a biomass model compound. Data are presented that show the presence of supercritical water enhances gasification efficiency, as it participates as both a solvent and a reactant. It is established that biomass gasification efficiencies are in the same range for all types of biomass. The thermodynamic changes of state are functions of elemental composition, not biomass species. The oxidation state of carbon atom of biomass is a key variable in determining the changes in enthalpy during both conventional combustion and supercritical water gasification. The oxidation state of the feed (together with the reaction conditions that influence the degree to which water participates as a reactant) also determines the vapor product composition.Decomposition reactions to vapor products are rapid and complete at high temperature (?550 °C), catalytic mediation is not required. Temperature and residence time are important operating parameters for SCW gasification. Less important are the pressure of gasification (in the range of 40-67 MPa) and the presence of catalyst. The vapor yield, gas composition, the carbon and hydrogen balance of SCW gasification are functions of gasification temperature, residence time and biomass load (concentration).     

The treatment of sulfate-rich wastewater using an anaerobic sequencing batch biofilm pilot-scale reactor

This paper presents the results from 92 cycles of an anaerobic sequencing batch biofilm reactor containing biomass immobilized on inert support (mineral coal) applied for the treatment of an industrial wastewater containing high sulfate concentration. The pilot-scale reactor, with a total volume of 1.2 m³, was operated at sulfate loading rates ranging from 0.15 to 1.90 kgSO₄²⁻/cycle (48 h — cycle) corresponding to sulfate concentrations of 0.25 to 3.0 gSO₄²⁻ l^− 1. Domestic sewage and ethanol were utilized as electron donors for sulfate reduction. Influent sulfate concentrations were increased in order to evaluate the minimum COD/sulfate ratio at which high reactor performance could be maintained. The mean sulfate removal efficiency remained between the range of 88 to 92% at several sulfate concentrations. Temporal profiles along the 48 h cycles were carried out under stable operation at sulfate concentrations of 1.0, 2.0 and 3.0 gSO₄²⁻ l^− 1. Sulfate removal reached 99% for cycle times of 15, 25, and 30 h, and the effluents sulfate concentrations were lower than 8 mgSO₄²⁻ l^− 1. The results demonstrate the potential applicability of the anaerobic configuration for the biological treatment of sulfate-rich wastewaters.