A. L. Cukierman

CO2 gasification of Argentinean coal chars: a kinetic characterization

Abstract A kinetic characterization of the CO 2 gasification of chars from Argentinean low-rank coals, subbituminous (SB) and high volatile bituminous (HVB), is performed by isothermal thermogravimetry. Temperatures in the range 1173–1433 K and CO 2 concentrations among 50% and 70% v/v are employed. Experimental data obtained for both chars for the whole range of experimental conditions explored were satisfactorily described by a single master curve. Reactivity differences between chars are discussed in terms of carbon content, microporosity and crystallinity of the char carbonaceous part. In addition, potential catalytic effects of inherent minerals on chars gasification reactivity are examined by demineralizing the chars. For the subbituminous char, catalytic effects due to mineral matter content are detected up to 1333 K, whereas at higher temperatures they become considerably less pronounced. For the bituminous char, reactivity seems to depend more on structural and textural features than on catalysis over the whole range of operating conditions. Intrinsic gasification rates for both chars are properly represented by the well-known random capillary and random pore models (RPM). Recent models based on modifications introduced to the latter are also applied and kinetic data description is discussed.

Effect of pyrolysis temperature on composition, surface properties and thermal degradation rates of Brazil Nut shells

Changes in chemical and surface characteristics of Brazil Nut shells (Bertholletia excelsa) due to pyrolysis at different temperatures (350 degrees C, 600 degrees C, 850 degrees C) were examined. For this purpose, proximate and ultimate analyses, physical adsorption measurements of N2 (-196 degrees C) and CO, (25 degrees C) as well as samples visualisation by scanning electronic microscopy (SEM) were performed. Appreciable differences in the residue characteristics, depending markedly on the pyrolysis temperature, were observed. Release of volatile matter led to the development of pores of different sizes. Progressive increases in micropore development with increasing pyrolysis temperature took place, whereas a maximum development of larger pores occurred at 600 degrees C. Furthermore, kinetics measurements of Brazil Nut shells pyrolysis from ambient temperature up to 900 degrees C were performed by non-isothermal thermogravimetric analysis. A model taking into account the significant changes in the residue during pyrolysis, through an increase in the activation energy with temperature and solid conversion, were found to properly fit the kinetics data over the wide range of degradation investigated.

Arundo donax cane as a precursor for activated carbons preparation by phosphoric acid activation.

Canes from Arundo donax, a herbaceous rapid-growing plant, were used as precursor for activated carbon preparation by phosphoric acid activation under a self-generated atmosphere. The influence of the carbonization temperature in the range 400-550 degrees C and of the weight ratio phosphoric acid to precursor (R = 1.5-2.5) on the developed porous structure of the resulting carbons was studied for 1 h of carbonization time. Surface properties of the activated carbons were dependent on a combined effect of the conditions employed. Carbons developed either with R = 1.5 over the range 400-500 degrees C, or with R = 2 at 500 degrees C exhibited surface areas of around 1100 m2/g, the latter conditions promoting a larger pore volume and enhanced mesoporous character. For both ratios, temperature above 500 degrees C led to reduction in porosity development. A similar effect was found for the highest ratio (R = 2.5) and 500 degrees C. The influence of carrying out the carbonization either for times shorter than 1 h or under flowing N2 was also examined at selected conditions (R = 2, 500 degrees C). Shorter times induced increase in the surface area (approximately 1300 m2/g), yielding carbons with smaller mean pore radius. Activated carbons obtained under flowing N2 possessed predominant microporous structures and larger ash contents than the samples derived in the self-generated atmosphere.

Potentiality of lignin from the Kraft pulping process for removal of trace nickel from wastewater: effect of demineralisation.

An industrial raw Kraft lignin was investigated to ascertain its potential use for removal of trace Ni(II) ion from wastewater by using dilute solutions (0.34-1.7 mM) as models. The effect of demineralisation on its metal sorption ability was examined by employing acid pre-treated samples. Under fixed pre-established equilibrium conditions, the raw lignin exhibited a lower effectiveness than the demineralised one, with the latter attaining an almost complete removal of Ni(II) ions. For both lignins, sorption kinetics was properly described by a pseudo-second order rate model. Equilibrium isotherms were also determined and adequately represented by conventional two-parameter models. The higher nickel sorption capacity for the demineralised lignin compared to the raw sample was consistent with enhancements in the negative magnitude of zeta potential, sodium sorption capacity, and content of phenolic hydroxyl groups occasioned by the acid pre-treatment. Accordingly, demineralisation appears as a readily convenient strategy to improve the behaviour of industrial Kraft lignin for potential use as a biosorbent of trace nickel from polluted water.

Cadmium Uptake by Lignocellulosic Materials: Effect of Lignin Content

Abstract Two lignocellulosic materials with different lignin contents (18 and 42 %wt) and pure lignin (PL) were evaluated for their effectiveness in binding cadmium from dilute solutions in various concentrations. Maximum sorption capacities (X m), determined from equilibrium isotherms by applying the Langmuir model, indicated that PL (X m = 48.3 mg/g) and the sample with the larger lignin content (X m = 22.2 mg/g) showed a reasonable ability to uptake cadmium. An increasing relationship between X m and the samples lignin content was found, considering the tested materials together with others evaluated earlier under identical conditions. Pure lignin attained the highest value. Accordingly, the lignin content of lignocellulosic materials appears as an indicator of their ability to uptake cadmium. It could facilitate their screening for potential use as alternative cadmium sorbents from dilute wastewater. The effects of the samples dose and the solution pH on cadmium uptake also were investigated.

Pyrolysis of Biomass from Sustainable Energy Plantations: Effect of Mineral Matter Reduction on Kinetics and Charcoal Pore Structure

Abstract The effect of reducing mineral matter naturally present in sawdust from untreated poplar (Populus deltoide) wood and giant reed (Arundo donax) canes on pyrolysis kinetics was examined from comparative non-isothermal thermogravimetric measurements in the range 20–900°C, using raw and previously demineralized samples. Estimated kinetic parameters reflected changes caused by demineralization, especially in the low temperature range (up to ≈450°C), likely due to catalytic effects of the minerals. Pyrolysis of the demineralized biomasses also induced an enhanced development in pore structure of the resulting charcoal, favoring its potential use in adsorption applications and/or as an improved intermediate product for further conversion into activated carbons.

Thermochemical Conversion of Arundo Donax into Useful Solid Products

Physico-chemical characteristics of raw stems of giant reed (Arundo donax L.) and of the char obtained by pyrolysis at 500°C and 800°C under flowing N 2 , as well as char yield, were determined to examine features evolution and potential applications. The chars derived at both temperatures were found potentially suitable as solid bio-fuels. Char features and yield at the lower temperature were compared to those from pyrolysis of the stems pre-treated with a phosphoric acid solution under otherwise identical conditions. The acid treatment induced an enhanced char yield and a highly developed porous structure with surface properties similar to those characterizing activated carbons. Thermogravimetric analysis also showed substantial changes in pyrolytic behavior of the treated stems. They seem to be due to the catalytic action of the acid promoting degradation at lower temperatures compared to pyrolysis of the untreated stems.

Effectiveness Factor of Partially Wetted Catalyst Particles: Evaluation and Application to the Modeling of Trickle Bed Reactors

Abstract Trickle bed reactors are widely used in the petroleum industry, especially when processing heavy petroleum fractions, some of the applications being the hydrodesulfurization and hy-drocracking of heavy or residual petroleum fractions, hydrotreat-hg of lubricating oils, and other hydrogenation processes. In the chemical process industry the use of trickle bed reactors is not so widespread, although reactions such as the selective hydrogenation of acetylene, hydrogenation of alkyl anthraquinone, synthesis of butynediol, and oxidation of liquids with, air or oxygen are carried out. Extensive analysis of the advantages and disadvantages of this type of reactor has been presented in the literature [1–5].

On dynamic liquid holdup determination by the drainage method

A careful examination of the liquid drainage in packed-bed reactors using liquid superficial velocities characteristic of trickle flow regime and no gas velocity is both experimentally and theoretically carried out. True free-flowing or dynamic liquid holdups are determined in two different reactors packed with porous and nonporous particles employing several liquids. Dynamic liquid holdups are shown to be higher than those determined directly from total liquid drained volumes, which are usually reported when the drainage method is applied. It is found that a model of laminar liquid films properly addresses the influence of liquid superficial velocities and of liquid viscosity on the dynamic liquid holdup within the experimental conditions studied. A simple quantitative phenomenological model to describe the drainage kinetics is developed and is independently verified from experimental data. Satisfactory agreement is found for all the examined conditions.

Metal Ion Biosorption Potential of Lignocellulosic Biomasses and Marine Algae for Wastewater Treatment

The metal ion-binding abilities of six lignocellulosic biomasses obtained from agro-industrial products and sustainable plantations, as well as of two red and one green marine algal species, were examined in a comparative manner to ascertain their potential as biosorbents of heavy metals from low concentration wastewater. Dilute single-solute solutions of cadmium and nickel ions (≤ 1 mM) were used as models. All the biomaterials showed appreciable Cd(II) ion biosorption which was strongly dependent on the dosage used. The maximum Cd(II) ion biosorption capacities (XmL), as estimated from the experimental isotherms using the Langmuir model, indicated that the red algae (XmL= 0.26–0.52 mmol/g) and the lignocellulosic biomasses with larger lignin contents (XmL= 0.17–0.20 mmol/g) possessed the greatest potential. This behaviour also applied to Ni(II) ion biosorption, although the biomaterials proved to be less effective in this case, especially towards low dosage. Comparison of the Cd(II) ion equilibrium sorption by one of the lowest performing biomasses (sawdust from Arundo donax stems) with that for activated carbons developed from the same biomass under different atmospheres revealed that the biomass behaviour was similar to that of carbons activated by heating in inert or mildly oxidative atmospheres.