Narendra N. Bakhshi

Preparation and characterization of bio-diesels from various bio-oils.

Methyl, ethyl, 2-propyl and butyl esters were prepared from canola and linseed oils through transesterification using KOH and/ or sodium alkoxides as catalysts. In addition, methyl and ethyl esters were prepared from rapeseed and sunflower oils using the same catalysts. Chemical composition of the esters was determined by HPLC for the class of lipids and by GC for fatty acid compositions. The bio-diesel esters were characterized for their physical and fuel properties including density, viscosity, iodine value, acid value, cloud point, pure point, gross heat of combustion and volatility. Methyl and ethyl esters prepared from a particular vegetable oil had similar viscosities, cloud points and pour points, whereas methyl, ethyl, 2-propyl and butyl esters derived from a particular vegetable oil had similar gross heating values. However, their densities, which were 2 7% higher than those of diesel fuels, statistically decreased in the order of methyl approximately 2-propyl > ethyl > butyl esters. Butyl esters showed reduced cloud points (-6 degrees C to -10 degrees C) and pour points (-13 degrees C to -16 degrees C) similar to those of summer diesel fuel having cloud and pour points of -8 degrees C and -15 degrees C, respectively. The viscosities of bio-diesels (3.3-7.6 x 10(-4) Pa s at 40 degrees C) were much less than those of pure oils (22.4-45.1 x 10(-4) Pa s at 40 degrees C) and were twice those of summer and winter diesel fuels (3.50 and 1.72 x 10(-4) Pa s at 40 degrees C), and their gross heat contents of approximately 40 MJ/kg were 11% less than those of diesel fuels (approximately 45 MJ/kg). For different esters from the same vegetable oil, methyl esters were the most volatile, and the volatility decreased as the alkyl group grew bulkier. However, the bio-diesels were considerably less volatile than the conventional diesel fuels.

Production of hydrocarbons by catalytic upgrading of a fast pyrolysis bio-oil. Part I: Conversion over various catalysts

The upgrading of a fast pyrolysis bio-oil was studied with different catalysts in a fixed bed micro-reactor. The catalysts were HZSM-5 (average pore size, 0.54 nm), H-Y (0.74 nm), H-mordenite (0.67 nm), silicalite (0.54 nm) and silica-alumina (3.15 nm). The experiments were carried out at atmospheric pressure, 1.8 and 3.6 weight hourly space velocity, and a temperature range of 290–410°C. The products were char, coke, gas, tar, residue, water and an organic distillate fraction (ODF). The objective was to obtain high yields of hydrocarbons in the ODF. The yields of hydrocarbons (based on the amount of bio-oil fed) were 27.9 wt% with HZSM-5, 14.1 wt% with H-Y, 4.4 wt% with H-mordenite, 5 wt% with silicalite and 13.2 wt% with silica-alumina. It was interesting to note that whereas HZSM-5 and H-mordenite produced more aromatic than aliphatic hydrocarbons, H-Y, silicalite and silica-alumina produced more aliphatic than aromatic hydrocarbons. The main aromatic hydrocarbons were toluene, xylenes and trimethylbenzenes. The liquid aliphatic hydrocarbon content consisted mostly of C6-C9 hydrocarbons. Alkylated cyclopentene, cyclopropane, pentane and hexene were the main aliphatic hydrocarbons. In most of the runs, doubling the space velocity from 1.8 to 3.6 h−1 resulted in decreased coke, char and gas formation and increased ODF yields. On the other hand, deoxygenation and hydrocarbon formation decreased.

Production of hydrocarbons by catalytic upgrading of a fast pyrolysis bio-oil. Part II: Comparative catalyst performance and reaction pathways

Abstract Catalysts, namely, HZSM-5, H-mordenite H-Y, silicalite and silica-alumina which were used for the upgrading of Pyrolysis bio-oil in Part I of this study were examined for their relative performance in the production of organic distillate fraction (ODF), hydrocarbon formation and minimization of char, coke and tar formation. A catalyst effectiveness criterion based on yield and selectivity for each product was defined and correlated with the performance of each catalyst. Amongst the five catalysts studied, HZSM-5 was the most effective catalyst for the production of ODF, overall hydrocarbons and aromatic hydrocarbons. Also, it provided the least coke formation. Silica-alumina catalyst was most effective for minimizing the char formation and H-Y catalyst was superior in minimizing tar formation as well as maximizing the production of aliphatic hydrocarbon. Reaction pathways were proposed for the conversion of bio-oil. It was postulated that bio-oil conversion proceeded as a result of thermal effects followed by thermocatalytic effects. The thermal effects produced separation of bio-oil to light organics and heavy organics and polymerization of bio-oil to char. The thermocatalytic effects produced coke, tar, gas, water and the desired organic distillate fraction. Deoxygenation, cracking, cyclization, aromatization, isomerization and polymerization were the main thermocatalytic reactions.

Catalytic conversion of canola oil to fuels and chemicals: roles of catalyst acidity, basicity and shape selectivity on product distribution

Studies were performed at atmospheric pressure in a fixed-bed microreactor at temperatures of 400 and 500°C over HZSM-5, silicalite, silica, silica-alumina, γ-alumina, calcium oxide and magnesium oxide catalysts to determine the various roles of catalyst acidity, basicity and shape selectivity on canola oil conversion and product distribution. Results showed that the initial decomposition of canola oil to long chain hydrocarbons and oxygenated hydrocarbons was independent of catalyst characteristics. However, subsequent decomposition (secondary cracking) of the resulting heavy molecules into light molecules (gas or liquid) appeared to be greatly enhanced by the amorphous and non-shape selective characteristics of the catalyst (as in silica-alumina, γ-alumina and silica). In contrast, a high shape selectivity in a catalyst (as in HZSM-5 and silicalite catalysts) permitted a mild secondary cracking resulting in a low gas yield and a high organic liquid product yield. On the other hand, it was interesting to observe that the presence of basic sites in a catalyst (as in calcium oxide and magnesium oxide) strongly inhibited secondary cracking. This resulted in the production of high yields of residual oil and low gas yields. The production of C2C4 olefins, n-C4 hydrocarbons and aromatic hydrocarbons of unconstrained sizes, which reflected thermal effects on the overall reaction scheme, were predominant in amorphous and non-shape selective catalysts. On the other hand, the formation of C2C4 paraffins, branched chain and total C4 hydrocarbons as well as aromatic hydrocarbons of constrained sizes (C7C9) which were predominant in the shape selective catalysts showed that, apart from the products formed due to thermal effects, the type, structure and sizes of other products are determined principally by the shape selective characteristic of the catalyst.

Catalytic conversion of a biofuel to hydrocarbons: effect of mixtures of HZSM-5 and silica-alumina catalysts on product distribution

Abstract The potential for producing hydrocarbons from the conversion of biofuels has been the focus of attention in recent years. In a preliminary study, we observed that it was possible to produce various types of liquid hydrocarbons and also to dramatically change the hydrocarbon content from aromatic to aliphatic by mixing silica-alumina and HZSM-5 catalysts in different proportions. In the present work, an in-depth study was undertaken in order to investigate the effect of various mixture compositions of silica-alumina and HZSM-5 on the yield and selectivity for liquid hydrocarbons. The biofuel used in the present study was produced by the rapid thermal processing of maple wood. The runs were performed in a fixed-bed microreactor operating at atmospheric pressure, 1.8–7.2 WHSV and 330–410°C. It was interesting to observe that for all catalyst mixtures, the optimum yields of organic liquid product (OLP) and total hydrocarbons were obtained at 370°C. The HZSM-5 content ( H f ) of the catalyst mixtures ranged between 0 and 40 wt.%. The catalysts were thoroughly characterized by the following techniques: X-ray powder diffraction, temperature-programmed desorption with ammonia, FT-IR and NMR spectroscopy and measurement of their BET and pore sizes. The yield of OLP increased with H f and ranged between 13 and 27 wt.% of the biofuel feed. Aliphatic hydrocarbons were the main products (37–77 wt.% of OLP), followed by aromatic hydrocarbons (2–38 wt.% of OLP). At low H f (below 10 wt.%), the main effect of HZSM-5 was to increase the extent of cracking and thereby increase the aliphatic hydrocarbon production. At H f > 10, a combination of cracking followed by shape selectivity resulted in the production of aromatic hydrocarbons at the expense of aliphatic hydrocarbons. The results were analyzed statistically in order to determine which factors (namely HZSM-5 content in the catalyst ( H f ), space velocity, temperature and their interactions) were mainly responsible for the formation of OLP and its hydrocarbon content. The results showed that all three factors affected the OLP yields rather significantly. However, the aliphatic hydrocarbon yield was mostly affected by the space velocity and H f , and the aromatic hydrocarbon yield was significantly affected by temperature and H f . A regression surface response model was used to relate the yields of these products with the above-mentioned factors.

The production of gasoline range hydrocarbons from Alcell® lignin using HZSM-5 catalyst

The conversion of a solvolysis lignin to useful chemicals and fuels was investigated using HZSM-5 catalyst. The study was carried out in a fixed bed reactor operating at atmospheric pressure, over a temperature range of 500°C–650°C, and weight hourly space velocities of 2.5 to 7.5 h−1. The major objective was to investigate the use of HZSM-5 catalyst in the production of both liquid and gaseous hydrocarbon products directly from the lignin. Conversion was high and ranged between 50% and 85% for the reaction conditions used. Using a WHSV of 5 h−1, the liquid product (LP) yield was 39 wt.% at 500°C but decreased to 34 wt.% at 600°C and then to 11 wt.% at 650°C. The highest yield of liquid product (43 wt.%) was obtained at 550°C with a WHSV of 5 h−1. In all the experiments, the liquid product mainly consisted of aromatic hydrocarbons (mostly benzene, toluene and xylene — with toluene dominating). The yield of toluene increased from 31 wt.% of the liquid product at 600°C (WHSV=2.5 h−1) to 44 wt.% at 650°C (WHSV=5 h−1). The total gas yield increased dramatically with increasing temperature but only moderately with increasing WHSV. The yields of the major components in the gas stream (propane, ethylene, propylene, carbon dioxide and carbon monoxide) were greatly affected by temperature.

Upgrading of Wood-Derived Bio-Oil Over Hzsm-5

Abstract The upgrading of a biol-oil obtained by the high-pressure liquefaction of aspen wood was studied over HZSM-5. A fixed-bed microreactor, operated at atmospheric pressure and in the temperature range 370–410°C was used. The oil was co-fed with diluents such as tetralin, steam and methanol. The upgraded product contained a large percentage of benzene, tolyene, xylene and other hydrocarbons as liquid. The amount of pitch in the product decreased by 70–80% wt from that in the oil. In all the experiments, the phenolic content of the bio-oil decreased whereas the amount of aromatic hydrocarbons increased significantly to a maximum value. The amount of gas product was usually less than 5% wt. At high temperatures, over 30% wt of the oil remained as coke on the catalyst. A reaction scheme is postulated based on the results.

Characterization and stability analysis of wood-derived bio-oil

Abstract The stability characteristics of a bio-oil, produced by the high pressure liquefaction of aspen wood were studied by observing the changes in its physical properties, composition and distillation characteristics with time. Distillation characteristics of the fresh bio-oil showed that maximum amount of organic distillate was obtained at 172 Pa and 200°C. This distillate fraction mainly consisted of aromatic, aliphatic and naphthenic hydrocarbons and oxygenated compounds such as phenols, furans, alcohols, acids, ethers, aldehydes and ketones. The bio-oil viscosity, and chemical composition were found to change substantially over time probably due to polymerization of some components. Upon storage, the concentration of aromatic hydrocarbons and phenols decreased while the concentration of aldehydes and ketones increased. Also, the oxygen content of the distillate decreased from 22.7 wt% for the fresh bio-oil to 18.8 wt% after 31 days. However, when the bio-oil was mixed with tetralin it was observed that the properties of the mixture remained unchanged with time. Tetralin was found to donate hydrogen leading to the improvement in bio-oil stability. A free radical mechanism is proposed to explain the effect of tetralin.

Kinetic modeling of the production of hydrogen from the methanol-steam reforming process over Mn-promoted coprecipitated Cu-Al catalyst

Abstract Kinetic studies were performed using a manganese-promoted coprecipitated Cu-Al catalyst at reaction temperatures in the range 170–250°C and space time ranging from 0.1 to 2.5 g cat h/mol CH3OH to examine the influence of catalyst and reaction temperature on the rate-controlling mechanism of the methanol-steam reforming process for the production of hydrogen. Results showed the existence of two reaction temperature-dependent kinetic regions, thus highlighting a thermodynamic constraint on the participation of the redox property of the catalyst in the reaction. It was interesting to observe that methanol dissociation by OH bond cleavage was the rate-determining step in the low reaction temperature region whereas in the high reaction temperature region, the rate-determining step switched to methyl formate hydrolysis. Empirical rate models as well as those based on the Langmuir-Hinshelwood approach using these rate-determining steps were developed for the two reaction temperature regimes. These models were able to describe the methanol-steam reforming process adequately for the respective temperature regimes.

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.