Ajay K. Dalai

Production of H2 and medium Btu gas via pyrolysis of lignins in a fixed-bed reactor

Lignins are generally used as a low-grade fuel in the pulp and paper industry. In this work, pyrolysis of Alcell and Kraft lignins obtained from Alcell process and Westvaco, respectively, was carried out in a fixed-bed reactor to produce hydrogen and gas with medium heating value. The effects of carrier gas (helium) flow rate (13.4–33 ml/min/g of lignin), heating rate (5–15°C/min) and temperature (350–800°C) on the lignin conversion, product composition, and gas yield have been studied. The gaseous products mainly consisted of H2, CO, CO2, CH4 and C2+. The carrier gas flow rate did not have any significant effect on the conversion. However, at 800°C and at a constant heating rate of 15°C/min with increase in carrier gas flow rate from 13.4 to 33 ml/min/g of lignin, the volume of product gas decreased from 820 to 736 ml/g for Kraft and from 820 to 762 ml/g for Alcell lignin and the production of hydrogen increased from 43 to 66 mol% for Kraft lignin and from 31 to 46 mol% for Alcell lignin. At a lower carrier gas flow rate of 13.4 ml/min/g of lignin, the gas had a maximum heating value of 437 Btu/scf. At this flow rate and at 800°C, with increase in heating rate from 5 to 15°C/min both lignin conversion and hydrogen production increased from 56 to 65 wt.% and 24 to 31 mol%, respectively, for Alcell lignin. With decrease in temperature from 800°C to 350°C, the conversion of Alcell and Kraft lignins were decreased from 65 to 28 wt.% and from 57 to 25 wt.%, respectively. Also, with decrease in temperature, production of hydrogen was decreased. Maximum heating value of gas (491 Btu/scf) was obtained at 450°C for Alcell lignin.

Modeling of methanol to olefins (MTO) process in a circulating fluidized bed reactor

Abstract Methanol is obtained commercially from natural gas. However, production of light olefins such as ethylene, propylene, etc. from natural gas is higher value-added gas conversion option and therefore, the conversion of methanol to olefins is of industrial importance. In the present work, this process is simulated in a circulating fluidized bed (CFB) reactor at 450°C and at atmospheric pressure. The simulation combined the kinetic model with SAPO-34 as the catalyst and the core-annulus type hydrodynamic model. The modeling studies indicated that the selectivity towards ethylene increased significantly with increase in coke deposit on the catalyst. This was attributed to the ‘cage effect’ of the coke on the catalyst. However, the increase in coke deposit on the catalyst also decreased the methanol conversion. At 5xa0wt% coke on the catalyst, the methanol conversion and C 2 +C 3 light olefin selectivity were optimum at 90 and 75xa0wt%, respectively. The influence of the exit geometry such as smooth exit, abrupt exit and exit with a projected end, on the solids hold-up and thereby on the methanol conversion and light olefin yield were also studied. As the exit geometry varied from smooth to exit with projected end, the methanol conversion increased due to the increased solids hold-up in the riser correspondingly increasing the light olefin yield. The simulator also predicts the flow characteristics within the CFB.

Correlation of electrical properties and performance of OCM MOx/Na2WO4/SiO2 catalysts

Abstract The electrical conductivity and catalytic performance of MOx/Na2WO4/SiO2 catalysts in oxidative coupling of methane (OCM) are measured and correlated. M is V, Cr, Mn, Fe, Co or Zn. In this study, for the first time, the conductivity of the catalyst powder was measured under the OCM conditions as well as in oxygen. A definite correlation between the catalytic performance, the electrical conductivity under the OCM conditions, and the band gap of metal oxide constituent of the catalysts is observed. Manganese oxide (MnOx with the lowest band gap) on Na2WO4SiO2 with the highest electrical conductivity shows the best catalytic performance.

Effect of diluent size on the performance of a micro-scale fixed bed multiphase reactor in up flow and down flow modes of operation

The comparative behaviors of a micro-scale fixed bed multiphase reactor in up flow and down flow modes of operation were studied for hydrodesulfurization of atmospheric gas oil over a commercial catalyst. The experiments for the two modes of operation were conducted for a wide range of diluent size and other process variables such as liquid hourly space velocity and hydrogen/gas oil ratio. The results showed that the down flow mode of operation using 0.19 mm size of diluent could be used for generating reliable and meaningful data. On the other hand, the use of up flow mode of operation is restricted only for higher space velocities even while using 0.19 mm size of diluent. The results also indicated that the performance of the up flow mode of operation was poor at higher hydrogen/gas oil ratio. This change in performance is pronounced when higher size of diluent was used with the catalyst. In contrary, the hydrogen/gas oil ratio had minimum effect on the performance of the reactor for down flow mode of operation.

Preparation of activated carbon from Canadian coals using a fixed-bed reactor and a spouted bed-kiln system

Abstract Several western Canadian coals (Bienfait lignite, Roselyn, Montgomery, Atlas-Century and Egg Lake subbituminous coals, and Coal Valley and Smoky River bituminous coals) were activated with steam to produce granular activated carbons. Activation times and temperatures were 0.5–4.0 h and 650–850°C. The iodine number was used as a primary indicator of product quality. Activated carbons having iodine numbers of ≥ 500 mg g−1 carbon were produced from each coal except Smoky River. Bienfait lignite was found to be relatively reactive, the highest iodine number developed being 545 at a yield of 29 wt% and at 650°C. Products from Montgomery and Atlas-Century coals showed iodine numbers of 620 and 579 at yields of 36 and 37 wt% respectively, at 700°C. When activated at 650°C for 3 h, Roselyn coal gave a product with an iodine number of 730. The products from Coal Valley coal, the least reactive, had an iodine numbers which increased from 370 on activation at 650°C for 2 h to 571 on activation at 760°C for 1.0 h, the product yield decreasing from 59 to 45 wt%. The high ash of the products, 23–67 wt%, limits their quality. The performances of fixed-bed and spouted bed-kiln reaction systems were compared by analyses of the properties of the products from Coal Valley coal. The fixed-bed system generally gave products with higher sorptive capacities under operating conditions which caused higher carbon burnoff.

Activation of Canadian coals in a fixed-bed reactor and an internally stirred horizontal kiln

Activation of a lignite, a subbituminous coal and a high-volatile bituminous coal was studied using a fixed-bed reactor and an internally stirred horizontal kiln (ISHK), the latter being designed to control dusting problems encountered in handling finely divided coal. The properties of the activated carbons were determined by measuring iodine, methylene blue and phenol numbers, specific surface areas, bulk density, mercury and nitrogen porosities and ash and mineral contents. The lignite, activated at lower temperatures (∼700°C) in the ISHK system, developed a surface area of ∼500 m2 g−1 with most of the adsorptive surface associated with micropores of radii 700 m2 g−1 and a methylene blue number of 175, higher values than the best obtained with the lower-rank coals. The activation temperature needed to achieve these results with this higher-rank coal is ∼150 K higher than that for the low-rank coals.

Thermal characteristics of synthetic sodium zeolites prepared with silica from rice-husk ash

The differential thermal analysis and thermogravimetric data on the synthetic sodium zeolite species NaX, Pc, HS, Z-21 and analcime, prepared with silica from rice-husk ash, are presented. The DTA curves revealed the presence of an initial endotherm for dehydration, followed by an exotherm at around 800 to 850°, representing the structural change and dissociation of all these species, except in the case of zeolite Z-21. For the latter, the initial endotherm was followed by an endotherm in the 900° region. The structural changes inferred on the basis of the DTA curves were confirmed by X-ray diffraction analysis.ZusammenfassungDifferentialthermoanalytische und thermogravimetrische Daten von den synthetischen, unter Verwendung von Reisschalenasche als Siliciumdioxidquelle hergestellten Na-Zeolithen NaX, Pc, HS, Z-21 und Analcim werden angegeben. Die DTA-Kurven zeigen anfangs einen der Dehydratisierung zuzuschreibenden endothermen Peak, dem bei 800–850° ein exothermer folgt, der auf den Zusammenbruch der Zeolithstruktur zurückzuführen ist. Nur im Falle von Z-21 tritt dieser exotherme Peak erst bei 900° auf. Die mittels DTA festgestellten strukturellen Veränderungen wurden röntgendiffraktometrisch verifiziert.РезюмеДизельные топлива с р азличным содержание м вокса были исследова ны усовершенствованны м методом дифференци ального термического анализ а (ДТА), согласно стандартным тестовы м методам. Из ДТА-кривы х были измерены следующие п араметры: начало температурно го пика, максимум темп ературного пика и площадь пика. Ис следовано изменение этих парам етров в зависимости о т таких стандартных характе ристик дизельных топлив, как температу ры помутнения, застыв ания, закупорки фильтра на холоду и содержанием воска и найдена для ни х линейная корреляци я. Коэффициенты коррел яции были вычислены согласно установлен ным уравнениям, котор ые были также использованы д ля определения стандартных парамет ров других образцов д изельного топлива на основе их Д ТА-кривых. Пределы точности усо вершенствованного м етода ДТА найдены удовлетвори тельными.

Studies on chlorided Pt/Al2O3 catalysts: preparation, characterization and n-butane isomerization activity

A series of chlorided Pt/Al2O3 (both γ and η) catalysts were prepared and characterized for various physicochemical properties. The chloride content of the catalysts was found to increase with chloride treatment time up to a certain level and then decrease owing to prolonged exposure at high temperature. The surface area and pore volume of the catalysts were decreased by chloride treatment. The activity of the prepared catalysts were tested in n-butane isomerization. The platinum content of the catalysts was found to have no effect on catalytic activity up to 0.2 wt% whereas the chloride content of the catalyst strongly influenced the activity and a >20-fold increase in activity was observed on chloriding Pt/Al2O3 catalysts. The catalyst activity was found to be directly related to its acidity.

Use of Stable Isotope Ratios to Determine the Origin of Coke Formed in Gas Turbines

Coke deposits can form in compression equipment on natural gas transmission lines. These deposits are a result of incomplete combustion due to poor fuel gas quality or incorrect equipment design and/or operation. There is an isotopic “signature” which is carried over from the fuel gas into the coke if incomplete combustion occurs, allowing the origin of the coke deposit to be identified. The use of a continuous flow gas chromatograph isotope ratio mass spectrometer (GC/IRMS) provides a convenient method for determining the isotopic composition of the components in the fuel gas. These ratios can then be used to identify if a correlation exists with the 13 C/12 C ratio of the coke sample. Previous projects in 1999 and 2000 demonstrated that the coke deposits found within gas turbines could be closely related to the incomplete combustion of the fuel gas. One outcome of that work was determining the value for having a good understanding of stable isotope signatures for gas entering the pipeline system. In 2000, fuel gas samples were obtained from various areas in the Alberta TransCanada collection system, their isotope ratios were measured and then used to produce coke. This work substantiated previous project work, reinforcing the isotopic relationship between coke and the source material. Current work is to produce a model to quantitatively relate the various components of the source material to coke deposits. This model could then be used as a tool to enhance the performance of the gas turbines. Detailed investigation into the sensitivity of stable carbon isotope measurements for identifying the source of coke deposits for a complete range of TransCanada fuel gas mixtures is presented.Copyright

Production of hydrogen and medium btu gas via pyrolysis of a Kraft lignin in a fixed-bed reactor

Lignins are generally used as a low grade fuel in the pulp and paper industry. In this work, pyrolysis of a Kraft lignin obtained from Westvaco was carried out in a fixed-bed reactor to produce hydrogen and gas with medium heating value. The effects of carrier gas (helium) flow rate (13.4-33 ml/min/g lignin), heating rate (5-15/spl deg/C/min) and temperature (350-800/spl deg/C) on the lignin conversion, product yield and the product gas composition were studied.