The Effect of Acidity on Olefin Aromatization over Potassium Modified ZSM-5 Catalysts

The preparation of light alkenes by the gas phase oxidative cracking (GOC) or catalytic oxidative cracking (COC) of model high hydrocarbons (hexane, cyclohexane, isooctane and decane in the GOC process and hexane in the COC process) was investigated in this paper. The selection for the feed in the GOC process was flexible. Excellent conversion of hydrocarbons (over 85%) and high yield of light alkenes (about 50%) were obtained in the GOC of various hydrocarbons including cyclohexane at 750°C. In the GOC process, the utilization ratio of the carbon resources was high; CO dominated the produced CO _X (the selectivity to CO₂ was always below 1%); and the total selectivity to light alkenes and CO was near or over 70%. In the COC of hexane over three typical catalysts (HZSM-5, 10% La₂O₃/HZSM-5 and 0.25% Li/MgO), the selectivity to CO _X was hard to decrease and the conversion of hexane and yield of light alkenes could not compete with those in the GOC process. With the addition of H₂ in the feed, the selectivity to CO _X was reduced below 5% over 0.1% Pt/HZSM-5 or 0.1% Pt/MgAl₂O₄ catalyst. The latter catalyst was superior to the former catalyst due to its perfect performance at high temperature, and with the latter, excellent selectivity to light alkenes (70%) and the conversion of hexane (92%) were achieved at 850°C (a yield of light alkenes of 64%, correspondingly).     

Production of lower alkenes and light fuels by gas phase oxidative cracking of heavy hydrocarbons

The gas phase oxidative cracking (GOC) and non-oxidative pyrolysis of heavy hydrocarbons were investigated, with decalin (decahydronaphthalene) and tetralin (tetrahydronaphthalene) as the model compounds for naphthenic hydrocarbon and aromatic hydrocarbon, respectively. Unlike pyrolysis, the ring rupture of decalin or tetralin molecule and the decoking ability of system were significantly enhanced due to the introduction of O₂ in GOC. For GOC of decalin, both the lower alkenes and the light fuels were obtained. At lower temperatures the light fuels mainly contained alkyl benzene, alkyl cyclohexane and isoparaffins, while it was rich in BTX (benzene, toluene and xylenes) at higher temperatures. A 38.9% yield of lower alkenes and 48.0% yield of light fuels (BTX mass content: 59.9%) at 100% decalin conversion were obtained under the conditions of 800 °C and decalin / O₂ = 0.5. For GOC of tetralin, both the dehydrogenation and the cracking reactions dominated the reaction routes, resulting in a high mass content of alkyl naphthalene and alkyl benzene in the light fuels. The estimation of O₂ distribution in the products demonstrated that O₂ participated primarily in the oxydehydrogenation reactions at low temperatures, while mainly in the partial oxidation reactions at high temperatures to produce CO_x (x = 1, 2).     

Study on pyrolysis of oil sludge with microalgae residue additive

The pyrolysis of oil sludge (OS) with microalgae residue (MR) additive was conducted with a TGA and a tube furnace. The pyrolysis process of OS with the MR additive can be divided into three stages: 1) water evaporation, 2) the release of light groups of hydrocarbon compounds, the cracking of heavy groups, and carbon decomposition, and 3) minerals decomposition. With the MR addition ratio increasing, the yield of oil and gas increased, and oil to gas ratio increased during OS pyrolysis. The MR addition improved the quality of pyrolysis oil and gas from OS pyrolysis. The proportion of light oil increased from 38 % with a 5 % MR addition ratio to 45 % with a 30 % addition ratio. Major components of pyrolysis gas included H₂, CO, CO₂, and C_xH_y. With the increase of the MR blending ratio, CO and CO₂ contents increased, while H₂ and C_xH_y contents decreased. Adding MR favoured the transformation of heavy hydrocarbons (C₆₊), resulting in a high content of light hydrocarbons. This work can help promote massive synergistic treatment of OS and microalgae biomass.

     

Formation of ilmenite-type CoTiO3 on TiO2 and its performance in oxidative dehydrogenation of cyclohexane with molecular oxygen

Ilmenite-type CoTiO₃ supported on TiO₂ was prepared and their catalytic activities were tested for oxidative dehydrogenation of cyclohexane to produce benzene. The catalyst was characterized by XRD, FE-SEM, HR-TEM, XPS, TPR and XANES. XRD reveals the formation of ilmenite-type CoTiO₃ on TiO₂. The catalyst showed 87.8% cyclohexane conversion with 89.2% benzene selectivity at 450 °C in a continuous fixed bed down flow reactor at atmospheric pressure. The influence of different reaction parameters like temperature, gas hour space velocity (GHSV), Co loading was studied in detail.     

Production of hydrocarbons by pyrolysis of methyl esters from rapeseed oil

The pyrolysis of a mixture of methyl esters from rapeseed oil has been studied in a tubular reactor between 550 and 850°C and in dilution with nitrogen. A specific device for the condensation of cracking effluents was used for the fractionated recovery of liquid and gaseous effluents, which were analyzed on-line by an infrared analyzer and by gas chromatography. The cracking products in the liquid effluent were identified by gas chromatography/mass spectrometry coupling. The effects of temperature on the cracking reaction were studied for a constant residence time of 320 ms and a constant dilution rate of 13 moles of nitrogen/mole of feedstock. The principal products observed were linear 1-olefins,n-paraffins, and unsaturated methyl esters. The gas fraction also contained CO, CO₂, and H₂. The middle-chain olefins (C₁₀–C₁₄ cut) and short-chain unsaturated esters, produced with a high added value, had an optimum yield at a cracking temperature of 700°C.     

煤快速热解固相和气相产物生成规律

利用能有效避免二次转化反应的高频炉热解装置对3种不同变质程度的煤进行了600～1200℃条件下的快速热解,考察了在煤热解最初阶段焦产率、焦-C产率、热解气产率、热解气4种主要组分H₂、CO、CH₄和CO₂的比例以及热解气热值随煤阶和热解温度的变化规律。结果表明,焦的产率和焦-C的产率均随煤阶的升高而升高,热解气的产率随煤阶的升高而降低;热解温度的提高能显著降低煤焦和焦-C的产率并提高热解气的产率。热解气组分以H₂相似文献   

Characteristics of hemicellulose,cellulose and lignin pyrolysis

The pyrolysis characteristics of three main components (hemicellulose, cellulose and lignin) of biomass were investigated using, respectively, a thermogravimetric analyzer (TGA) with differential scanning calorimetry (DSC) detector and a pack bed. The releasing of main gas products from biomass pyrolysis in TGA was on-line measured using Fourier transform infrared (FTIR) spectroscopy. In thermal analysis, the pyrolysis of hemicellulose and cellulose occurred quickly, with the weight loss of hemicellulose mainly happened at 220–315 °C and that of cellulose at 315–400 °C. However, lignin was more difficult to decompose, as its weight loss happened in a wide temperature range (from 160 to 900 °C) and the generated solid residue was very high (∼40 wt.%). From the viewpoint of energy consumption in the course of pyrolysis, cellulose behaved differently from hemicellulose and lignin; the pyrolysis of the former was endothermic while that of the latter was exothermic. The main gas products from pyrolyzing the three components were similar, including CO₂, CO, CH₄ and some organics. The releasing behaviors of H₂ and the total gas yield were measured using Micro-GC when pyrolyzing the three components in a packed bed. It was observed that hemicellulose had higher CO₂ yield, cellulose generated higher CO yield, and lignin owned higher H₂ and CH₄ yield. A better understanding to the gas products releasing from biomass pyrolysis could be achieved based on this in-depth investigation on three main biomass components.     

Parametric study of pyrolysis and steam gasification of rice straw in presence of K<Subscript>2</Subscript>CO<Subscript>3</Subscript>

A parametric study of pyrolysis and steam gasification of rice straw (RS) was performed to investigate the effect of the presence of K₂CO₃ on the behavior of gas evolution, gas component distribution, pyrolysis/gasification reactivity, the quality and volume of synthetic gas. During pyrolysis, with the increase in K₂CO₃ content in RS (i) the instantaneous CO₂ concentration was increased while CO concentration was relatively stable; (ii) the yield of CO₂ and H₂ increased on the cost of CH₄. During steam gasification of RS, with the increase in K₂CO₃ content in RS (i) the instantaneous concentration of CO₂ and H₂ increased while instantaneous concentration of CO and CH₄ decreased; (ii) the yield of CO₂ and H₂ production and total yield increased; and (iii) yield of CO and CH₄ production followed the order: 9% K₂CO₃ RS<6% K₂CO₃ RS<raw RS<3% K₂CO₃ RS<water-leached RS. Water-leached RS showed the highest pyrolysis reactivity, while stream gasification reactivity was proportional to K₂CO₃ content in RS. The results of this study reveal that the presence of K₂CO₃ during pyrolysis and steam gasification of RS effectively improves production of H₂ rich gas.     

热分解气氛对流化床煤热解制油的影响

在循环流化床锅炉上耦合流化床热解反应器既可提供电力又副产热解油,明显提高煤的利用价值。在这个过程中,热解反应器通常利用自身产生的热解气作为流化介质。本文考察了模拟热解气反应气氛对流化床煤热解拔头制取热解油产率的影响,并利用TG-FTIR分析了焦油官能团组成及随TG温度的变化。针对锅炉用烟煤的实验结果表明：采用热解气作为反应气氛时焦油产率最大,相对无水无灰基煤达13%。反应气氛中H₂和CO₂的存在不利于焦油生成,但CO 和CH₄的加入提高了焦油产率;H₂的加入有利于焦油中酚羟基、羧基类化合物生成,同时也促进了脂肪族化合物的裂解;CH₄的存在可以提高焦油中单环芳烃、脂肪族及酚羟基类化合物的含量。     

An integrated catalytic approach for the production of hydrogen by glycerol reforming coupled with water-gas shift

Reaction kinetics measurements of glycerol conversion on carbon-supported Pt-based bimetallic catalysts at temperatures from 548 to 623 K show that the addition of Ru, Re and Os to platinum significantly increases the catalyst activity for the production of synthesis gas (H₂/CO mixtures) at low temperatures (548–573 K). Based on this finding, we demonstrate a gas phase catalytic process for glycerol reforming, based on the use of two catalyst beds that can be tuned to yield hydrogen (and CO₂) or synthesis gas at 573 K and a pressure of 1 atm. The first bed consists of a carbon-supported bimetallic platinum-based catalyst to achieve conversion of glycerol to a H₂/CO gas mixture, followed by a second bed comprised of a catalyst that is effective for water-gas shift, such as 1.0% Pt/CeO₂/ZrO₂. This integrated catalytic system displayed 100% carbon conversion of concentrated glycerol solutions (30–80 wt.%) into CO₂ and CO, with a hydrogen yield equal to 80% of the amount that would ideally be obtained from the stoichiometric conversion of glycerol to H₂ and CO followed by equilibrated water-gas shift with the water present in the feed.     

Thermogravimetric characteristics and pyrolysis kinetics of Giheung Respia sewage sludge

Sewage sludge acquired from Giheung Respia treatment facility was characterized and converted into gas, bio-oil and char by pyrolysis. The rate of conversion as a function of temperature was obtained from differential thermogravimetric analysis (DTG) for different heating rates. The activation energy calculated from data selected conversions shows that the activation energy decreased with increasing conversion up to 10%, steadily increased from 10 to 70%, and substantially increased from 70 to 90%. Depending on the level of conversion, the values of activation energies varied between 181 and 659 kJ/mol. The gas product obtained in the experiment at 450 °C, 20 min mainly included CO₂ (30%), CO (23%) and CH₄ (17%). The product yields of gas, oil and char were systematically studied by changing the pyrolysis temperature and residence time.     

Pyrolysis of tire powder: influence of operation variables on the composition and yields of gaseous product

The pyrolysis of tire powder was studied experimentally using a specially designed pyrolyzer with high heating rates. The composition and yield of the derived gases and distribution of the pyrolyzed product were determined at temperatures between 500 and 1000 °C under different gas phase residence times. It is found that the gas yield goes up while the char and tar yield decrease with increasing temperature. The gaseous product mainly consists of H₂, CO, CO₂, H₂S and hydrocarbons such as CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, C₄H₈ and C₄H₆ with a little other hydrocarbon gases. Its heating value is in the range of 20 to 37 MJ/Nm³. Maximum heating value is achieved at a temperature between 700 and 800 °C. The product distribution ratio of gas, tar and char is about 21:44:35 at 800 °C. The gas yield increases with increasing gas residence time when temperature of the residence zone is higher than 700 °C. The gas heating value shows the opposite trend when the temperature is higher than 800 °C. Calcined dolomite and limestone were used to explore their effect on pyrolyzed product distribution and composition of the gaseous product. It is found that both of them affect the product distribution, but the effect on tar cracking is not obvious when the temperature is lower than 900 °C. It is also found that H₂S can be absorbed effectively by using either of them. About 57% sulfur is retained in the char and 6% in the gas phase. The results indicated that high-energy recovery could not be achieved if fuel gas is the only target product. In view of this, multi-use of the pyrolyzed product is highly recommended.     

Pyrolysis of used sunflower oil in the presence of sodium carbonate by using fractionating pyrolysis reactor

Pyrolysis of used sunflower oil was carried out in a reactor equipped with a fractionating packed column (in three different lengths of 180, 360 and 540 mm) at 400 and 420°C in the presence of sodium carbonate (1, 5, 10 and 20% based on oil weight) as a catalyst. The use of packed column increased the residence times of the primer pyrolysis products in the reactor and packed column by the fractionating of the products which caused the additional catalytic and thermal reactions in the reaction system and increased the content of liquid hydrocarbons in gasoline boiling range. The conversion of oil was high (42–83 wt.%) and the product distribution was depended strongly on the reaction temperature, packed column length and catalyst content. The pyrolysis products consisted of gas and liquid hydrocarbons, carboxylic acids, CO, CO₂, H₂ and water. Increase in the column length increased the amount of gas and coke–residual oil and decreased the amount of liquid hydrocarbon and acid phase. Also, increase of sodium carbonate content and the temperature increased the formation of liquid hydrocarbon and gas products and decreased the formation of aqueous phase, acid phase and coke–residual oil. The major hydrocarbons of the liquid hydrocarbon phase were C₅–C₁₁ hydrocarbons. The highest C₅–C₁₁ yields (36.4%) was obtained by using 10% Na₂CO₃ and a packed column of 180 mm at 420°C. The gas products included mostly C₁–C₃ hydrocarbons.     

Thermal degradation mechanism of poly(ether imide) by stepwise Py–GC/MS

The thermal degradation of poly(ether imide) (PEI) was studied through a combination of thermogravimetric analysis and stepwise pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) techniques with consecutive heating of the samples at fixed temperature intervals to achieve narrow temperature pyrolysis conditions. The individual mass chromatograms of various pyrolysates were correlated with pyrolysis temperatures to determine the pyrolysis mechanism. The major mechanisms were two‐stage pyrolysis, involving main‐chain random scission, and carbonization. In the first stage, the scission of hydrolyzed imide groups, ether groups, and isopropylidene groups produced CO+CO₂ and phenol as the major products and was accompanied by chain transfer of carbonization to form partially carbonized solid residue. In the second pyrolysis stage, the decomposition of the partially carbonized solid residue and remaining imide groups formed CO+CO₂ as the major product along with benzene and a small amount of benzonitrile. The yield of CO+CO₂ was the largest fraction in the total ion chromatogram of the evolved gas mixtures. Hence, the thermal stability of the imide group was identical to the maximum thermogravimetry loss rates in the two‐stage pyrolysis regions. Afterward, carbonization dominated the decomposition of the solid residue at high temperatures. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1151–1161, 2001     

生物质快速热解制油试验及流程模拟

使用自主研发的流化床热解反应器对生物质热解制油进行实验研究,通过对不同实验温度450、500、525、550、580、610℃下得到的目标产物进行分析,得到了反应温度对生物油产率的影响规律。实验表明：550℃时,最大液体产率为42.5%（质量）;实验得到的不可冷凝气体的组分以CO、CO₂、CH₄和H₂为主,气相产物产率约为37.7%（质量）。在实验基础上,利用Aspen Plus流程模拟软件,建立了生物质热解制油工艺模拟流程,模拟分析了热解温度对生物油产率的影响,结果表明该模型能准确模拟实际热解过程,具有较好的适用性和可靠性。     

Reactive separation of ethylene from the effluent gas of methane oxidative coupling via alkylation of benzene to ethylbenzene on ZSM-5

Separation of ethylene from the effluent gas of oxidative coupling has been a challenging issue for several years. In a combined process of oxidative coupling and reforming of methane, reactive separation of ethylene via alkylation of benzene to ethylbenzene (EB) is a promising option. Ethylene was successfully converted to the useful chemical intermediate EB using ZSM-5. Yields of EB up to 90% were found at more than 95% conversion and more than 90% selectivity at 360 °C. Methane and ethane present in the feed were not converted and can be used for steam reforming in the proposed reaction concept. None of the additional components present in the effluent gas of oxidative coupling (CO, CO₂, CH₄, C₂H₆ and H₂O) influences activity or selectivity of the alkylation catalyst. Stability of ZSM-5 is also not influenced by the added components, with the exception of water, which even increases stability.     

Characterization of pyrolysis products of harbolite and Avgamasya asphaltites: comparison with solvent extracts

The products of pyrolysis at 525 and 840 °C of two asphaltites from South-Eastern Turkey have been analysed and compared with the bitumen obtained by solvent extraction. The yield of oil product is reasonably similar for all three treatments, with gas (hydrogen, ethene, C₁C₄ alkanes and hydrogen sulphide) being liberated during pyrolysis. Greater percentages of alkanes with shorter chain lengths (along with some alkenes), and of pentane-soluble aromatic oils with reduced molecular masses, are generated during pyrolysis, at the expense of asphaltenes. The extra alkanes are generated partly by the cracking of aromatic side-chains and also from kerogen. Pyrolysis reduces the number of sulphur linkages in the oil, but nitrogen- and oxygen-containing structures are liberated from kerogen during heating.     

Gas evolution during oil shale pyrolysis. 1. Nonisothermal rate measurements

The rate of evolution of CH₄, CO, CO₂, H₂, C₂ hydrocarbons, and C₃ hydrocarbons during pyrolysis of Colorado oil shale between 25 and 900 °C is reported. All experiments were performed nonisothermally using linear heating rates varying from 0.5 to 4.0 °C min^?1. Hydrogen is the major noncondensable gas produced by kerogen pyrolysis. The amount of H₂ released is influenced, via the shift and Boudouard reactions, by the CO₂ evolved from mineral carbonates. Lesser amounts of C₁, C₂, and C₃ hydrocarbons are produced. On the basis of heat content, however, the combined C₁ to C₃ hydrocarbons contribute twice as much as H₂ to the heating value of the pyrolysis gas. The evolution of H₂ and CH₄ involves processes that are interpreted as a ‘primary’ pyrolysis of the kerogen to generate oil, and a higher temperature ‘secondary’ pyrolysis of the carbonaceous residue. The CO formed is a product of the Boudouard reaction; nearly complete conversion of the carbon residue to CO via this reaction is observed.     

Catalytic production of olefins using natural halloysite nanotubes

The production of C₂-C₄ olefins by deep catalytic cracking and the thermocontact pyrolysis of vacuum gas oil, commercial-grade cottonseed oil, and a vacuum gas oil-cottonseed oil 90: 10 mixture in the temperature range of 600–800°C is studied using natural halloysite extracted from kaolinite fields in the form of aluminosilicate sheets rolled in nanotubes. It is found that in the deep catalytic cracking of vacuum gas oil at 600°C using halloysite as a catalyst, the gain in the yield of ethylene is 6.4–10.1 wt %, compared to yields of this product when using ZSM-5 catalyst. Adding 10% commercial-grade cottonseed oil to the vacuum gas oil further increases the yield of ethylene by 2.2 wt % with a simultaneous 3.3 wt % rise in the yield of propylene. The cracking of pure cottonseed oil under identical conditions yields ethylene and propylene of 16.1 and 9.2 wt %, respectively. The possibility of using halloysite nanotubes as a heating surface for the thermal pyrolysis of the above feedstocks at temperatures of 700–800°C in order to obtain yields of C₂-C₃ olefins exceeding those of identical products in industry, and of reusing halloysites in the thermoconversion of the studied feedstocks via their complete regeneration, is confirmed.     

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.