Behaviour of tetralin in coal liquefaction: Examination in long-run batch-autoclave experiments

The decomposition of tetralin in the presence and absence of coal was investigated in batch-autoclave experiments. The effect of temperature, atmosphere and reaction time on tetralin dehydrogenation, isomerization and hydrocracking was studied. At 400 and 450 °C, coal accelerates the formation of 1 - methylindan and n-butylbenzene (as primary products) changing the tetralin into compounds with reduced hydrogen donor capacity. The 1 -methylindan and n-butylbenzene are subsequently (hydro)-cracked to smaller products. At low hydrogen pressure the conversion of tetralin into naphthalene and hydrogen becomes considerable, making uncertain the calculation of hydrogen transfer from the tetralin to the coal on the basis of tetralin/naphthalene ratios.     

高温下工业NiW/Al2O3催化剂上萘的加氢饱和反应

在中压固定床中,高温条件下研究了工业NiW/Al2O3催化剂上硫化氢气氛中反应温度、反应压力和空速对萘加氢饱和反应过程的影响。实验结果表明,在液时空速为10—30 h-1,氢油体积比为800,高反应温度区320—380℃的实验条件下,萘加氢主要生成四氢萘和十氢萘,而进一步加氢裂化产物较少;提高反应温度,萘转化率和四氢萘的收率下降,加氢裂化产物略有升高,表明高温不利于芳环的加氢饱和;提高加氢反应压力,萘的转化率和四氢萘的芳环加氢程度提高;综合反应结果,提出了高温条件下萘加氢的简化可逆连串反应途径。     

Thermal dissociation of tetralin between 300 and 450 °C

Most studies of the hydrogenation of coal in hydrogen-donor solvents involve the reaction of hydrogen with coal slurried in tetralin, with or without catalysts. Reaction schemes proposed usually ignore the possibility of the contribution of products of the thermal breakdown of tetralin itself. In the work presented below tetralin was heated for various periods at temperatures between 300 and 450 °C without hydrogen or coal, and the products were analysed by capillary chromatography. The main products formed were naphthalene and the tetralin isomer 1-methyl indan. Tetralin did not disproportionate to naphthalene and decalin, although this has been suggested in the literature as a mechanism for the formation of the naphthalene usually observed. Naphthalene was produced, at temperatures as low as 350 to 400 °C, by dehydrogenation of the saturated ring. This ring also rearranged to give 1-methyl indan, and at higher temperatures broke open to yield alkyl benzenes. This cracking of the saturated ring was found to enhance the naphthalene formation.     

Hydrogenolysis and hydrocracking of the carbon-oxygen bond. 2. Thermal cleavage of the carbon-oxygen bond in guaiacol

Low-rank coals and their precursors contain, in addition to aromatic hydroxy groups, aromatic methoxy groups. In the present work a model compound, guaiacol, is used for the study of the behaviour of the carbon-oxygen bonds under thermolytic conditions. The thermolysis of guaiacol is studied in tetralin, naphthalene and without solvent under hydrogen or nitrogen pressure at 578–618 K. The compound is homolytically converted by first-order kinetics. The major product is pyrocatechol. Phenol, o-cresol, methyl catechols and methyl guaiacols are also formed. When tetralin is present it reacts in a molar ratio of 1:4 with guaiacol to form naphthalene. The source of hydrogen when tetralin is not present is guaiacol itself because molecular hydrogen does not participate in the reaction. The kinetics and reaction mechanism are discussed.     

Elucidation of hydrogen mobility in coal under reductive atmosphere using a tritium tracer method

Hydrogen exchange reaction of three Argonne coals (Illinois No. 6, Upper Freeport and Pocahontas #3) and Wandoan coal with tritiated gaseous hydrogen were performed at several temperatures. Hydrogen exchange reaction was performed in a flow reactor packed with 0.4 g of coal and 0.05 g of catalysts under the following conditions: pressure 15 kg/cm², temperature 200, 250, 300 °C, carrier gas H₂ or N₂ 5 ml/min. When a pulse of [³H]H₂ was introduced into a coal in H₂ carrier gas at several temperatures, the delay of [³H]H₂ pulse observed increased with increasing the reaction temperature and decreased with increasing coal rank. Further in the reaction of tritiated coals with gaseous hydrogen at constant temperature, the hydrogen exchange rate was estimated from the release rate of [³H]H₂. The apparent hydrogen exchange rate at 200 °C was higher than that at 250 °C. This shows that the hydrogen with low reactivity came to participate in the reaction at high temperature. When the reaction of tritiated coal with gaseous hydrogen was performed during heat treatment, one, two or three peaks of tritium concentration were observed in the outlet of the reactor depending on temperature (200, 250 or 300 °C, respectively) at which tritium was incorporated into coal initially. It was suggested that there were at least three kinds of hydrogen with different reactivity in coal.     

Chemistry of Texas lignite liquefaction in a hydrogen-donor solvent system

To study the nature of chemical cleavage and resultant product transfer from solid lignite phase to liquid phase, autoclave (300 cm³) experiments have been carried out at pressures ranging up to 34 MPa and temperatures of 380–390 °C. The charge to the autoclave was freshly mined wet lignite, tetralin and hydrogen or helium. To obtain an indication of the reaction mechanisms underlying the liquefaction process, liquid and gas samples from the reactor at different time intervals were analysed. The gas samples were analysed by use of a multi-column, multi-valve automated gas Chromatograph, a system specially fabricated for coal-derived gas analysis. The liquid sample was filtered through Millipore filters and separate into three fractions by gel permeation chromatography. Fraction 1 is mostly colloidal carbon and high-molecular-weight species which cannot be separated on a g.c. Fractions 2 and 3 were analysed by gas chromatography — mass spectrometry (g.c.-m.s.). Fraction 2 represents the liquid products released from lignite and fraction 3 is mostly the tetralin and tetralin-derived products. Gel permeation chromatography (g.p.c.) followed by gas chromatography (g.c.) was used to devise a method for monitoring the extent of liquefaction. The production of carbon dioxide is at a maximum before the liquefaction reactions are at a significant rate. The source of carbon dioxide appears to be the carboxylic groups in lignite. The liquefaction reactions consume hydrogen from tetralin which undergoes dehydrogenation to form naphthalene. Once the lignite has undergone depolymerization, the tetralin to naphthalene conversion slows down. The continued heating of lignite conversion products in excess of tetralin does not appear to alter the molecular size distribution of the liquid product. The distillable fraction of lignite-derived liquid is composed of various alkylated phenols and aromatics and alkanes, and they are formed simultaneously.     

Pyrolysis of hydrocarbon mixtures characteristic of coal: Application to dibenzyl mixture

Thermal cracking of dibenzyl dissolved in two solvents, tetralin and decalin, has been studied in a flow reactor, in the presence of steam, under atmospheric pressure and at temperatures between 600 and 750 °C. The nature of the products obtained depends upon the structure of the hydrogen-donor agent, but is independent of the structure of dibenzyl. Valuable products such as ethylene and a benzene, toluene and xylene (BTX) mixture, obtained by a β-scission reaction with a monomolecular mechanism, are predominant when decalin is used as solvent. The dehydrogenation of tetralin to naphthalene precedes cracking reactions of the bimolecular type, which lead to significant production of hydroaromatics such as indene. Cracking of dibenzyl, followed by hydrogen transfer from the solvent to the radicals formed, leads to toluene irrespective of the chemical nature of the hydrogen donor.     

Pyrolysis mechanism of pitch for carbon fiber using tritium tracer method

Tritium has been introduced into three coal tar pitches and a naphthalene pitch by two methods, one by isotope exchange with tritiated water using Pt/Al₂O₃ catalyst, and the other by hydrogenation with tritiated gaseous hydrogen using Ni-Mo/Al₂O₃ catalyst. The tritium-labelled pitches were carbonized up to 1000°C under nitrogen atmosphere. The release behaviors of hydrogen and tritium during the carbonization of tritiated pitches were investigated by comparing the rates of dehydrogenation and detritiation. The results indicate that the hydrogen introduced into the pitch by the isotope exchange is released more rapidly than the original hydrogen in the pitch while the hydrogen introduced into the pitch by the isotope addition is slightly more difficult to release relative to the original hydrogen in the pitch during the pyrolysis of the pitch. Moreover, it was clarified that the extent of development of optically anisotropic texture of the pitch is related not to the hydrogen exchange ratio but to the rate of hydrogen release during pyrolysis.     

Liquefaction of coal in hydrogen-donor and non-donor vehicles

Coal, slurried with tetralin, and heated rapidly to 400 °C, was converted to benzene-soluble, liquid products through a reaction path which appears to involve thermal cleavage of chemical bonds in the coal (so-called depolymerization). Free radicals formed pyrolytically were stabilized in the early stages by autogenous hydrogen transfer, and in later stages by abstraction of hydrogen from the hydrogen-donating tetralin (which was converted to dihydronaphthalene and then to naphthalene). Vitrinite of the coal particles became almost completely soluble in pyridine after 5 min reaction, and dispersed in the vehicle (tetralin) within about 10 min. Reaction in non-donor vehicles (naphthalene, dodecane) resulted in dispersion, but ‘repolymerization’ formed a benzene-insoluble material. Hydrogen transfer from tetralin increased exponentially with increased conversion of the coal to benzene-soluble material. Negligible influence of particle size (below 2–3 mm) implies that mass transfer is not a rate-limiting factor. High-volatile c bituminous coal and coals of lower rank converted at about the same rate and to the same extent (given equivalent petrographic compositions); approximately two-thirds of the ultimately achievable conversion occurs within 20 min. Higher-rank coals converted at a lower rate. Oxidation of the coal was deleterious to ultimate conversion.     

Free radicals in coal and coal conversions. 8. Experimental determination of conversion in hydroliquefaction

The results of conversion determinations on the products from Powhatan No.5 coal liquefied in an autoclave and in a high-pressure, high-temperature e.s.r. cavity are reported. Oil, asphaltene and preasphaltene yields, and overall conversion have been determined for Powhatan No.5 coal samples liquefied in tetralin, SRC-11 heavy distillate, and naphthalene at temperatures from 400 to 480 ° C in both reactor systems. The concept of reaction severity is introduced and used to formalize the relation between the effect of temperature and reaction time on oil yield and conversion. Oil is the predominant product in liquefaction in tetralin or naphthalene, asphaltene is the major product of liquefaction in SRC-II heavy distillate. Retrogressive reaction (THF-insoluble product formation) becomes severe when SRC-II heavy distillate is the liquefaction solvent and residence time of >10 min are used at temperatures >450 °C. Preasphaltenes appear to be the only intermediate species in Powhatan No.5 liquefaction.     

四氢萘催化脱氢反应动力学的研究

四氢萘在Ni Mo/Al_2O_3、Fe_2O_3、FeS_2上常压脱氢是典型的连串可逆反应,1,2-二氢萘及微量的1,4-二氢萘是反应的中间产物.脱氢反应速度随四氢萘分压提高和氢分压下降而提高.对二氢萘反应性能的考察表明它具有比四氢萘和萘高得多的反应活性,能迅速地催化转化为萘和四氢萘.氢加快二氢萘的加氢是它阻滞四氢萘脱氢的主要原因.各种催化剂对四氢萘脱氢、二氢萘转化和萘高压加氢都具有基本相同的活性顺序.根据可逆连串表面反应的历程及表面吸附的二氢萘为非常活泼的反应中间体的假设,作者推导了动力学模型,计算得到各反应物在Ni Mo/Al_2O_3、Fe_2O_3、Fe_2O_3/Al_2O_3上表面吸附常数和表面反应速率常数,并进行模拟计算.理论计算与实验能很好地吻合,证明了模型的合理性.模型及参数也进一步解释了一些实验事实.     

Liquefaction mechanism of Wandoan coal using tritium and 14C tracer methods: 1. Liquefaction in 3H and 14C labelled solvent

Liquefaction of Wandoan coal using a ³H labelled tetralin solvent which contains a small amount of ¹⁴C labelled naphthalene has been studied at 400 °C under an initial hydrogen pressure of 5.9 MPa, in the presence or absence of NiMoAl₂O₃ catalyst. The amounts of ³H and ¹⁴C transferred from the solvent to the products were measured as liquefaction progressed. The reaction pathways in the presence and absence of the catalyst were discussed and their reaction rate constants were calculated. According to the mass balances of hydrogen and ³H, in the absence of catalyst, tetralin provided coal with hydrogen atoms, and the degree of hydrogen exchange between coal and solvent was small. The catalyst decreased the hydrogen addition from solvent to coal and increased that from gas to coal.     

Steam cracking of coal-derived oils and model compounds: 1. Cracking of tetralin and t-decalin

Cracking of tetralin and t-decalin has been investigated in the temperature range between 700 and 850 °C and with residence times between 0.08 and 0.4 s. Most of the tetralin is dehydrogenated to yield 1,2-dihydronaphthalene and naphthalene. Other main products are indene and styrene, whereas t-decalin is predominantly cracked into ethylene and BTX aromatics. The kinetics of decalin decomposition can be described by a first-order irreversible reaction, whereas the behaviour of tetralin has to be expressed in terms of a reversible reaction. The overall activation energies are determined.     

Preliminary study on mechanism of naphthalene hydrogenation to form decalins via tetralin over Pt/TiO2

To clarify the mechanism of naphthalene hydrogenation to cis- and trans-decahydronaphthalene (decalins) via tetrahydronaphthalene (tetralin), the rate of naphthalene hydrogenation was compared with those of tetralin and tetralin containing 3–10 mol% naphthalene over a TiO₂-supported Pt catalyst. Tetralin was hydrogenated to decalins readily, while the naphthalene hydrogenation did not take place under the same reaction conditions (433 K and 2.96 MPa). When 3–10 mol% naphthalene was added to tetralin, the rate of hydrogenation decreased clearly with an increase of naphthalene content. The observation suggests that naphthalene interacts with surface metals strongly and prevents the hydrogenation of tetralin.     

Reaction mechanism of coal hydrogenation 4. Effect of catalyst type

Japanese Taiheiyo coal was hydrogenated in naphthalene or tetralin under 10 MPa hydrogen using three types of catalyst of varying activities: stabilized nickel, iron dust (from steel-making converter) plus sulphur and cobalt-molybdenum on alumina support. In naphthalene, conversion (calculated from the pyridineinsoluble residue) and hydrogen consumption decreased with catalyst activity, in the order: Ni 〉 Fe 〉 Co-Mo 〉 no catalyst. In tetralin, conversion and hydrogen consumption was in the same order as in naphthalene, and the ratio of the amount of hydrogen consumed from gaseous hydrogen to that transferred from tetralin also had a similar tendency. This result supports the finding that the catalyst accelerates the direct hydrogenation of coal by gaseous hydrogen.     

Aspects of the chemistry of donor solvent coal dissolution. The hydrogen-deuterium exchange reactions of tetralin-d12 with Illinois No. 6 coal,coal products and related compounds

The exchange of hydrogen and deuterium atoms between Illinois No. 6 coal and tetralin-d₁₂ and naphthalene-d₈ has been studied at 400 °C. These exchange reactions are readily reversible and the evidence suggests that the same kinds of hydrogen atoms exchange with tetralin as with naphthalene. The influence of illinois No. 6 coal, selected coal products and other compounds representative of the structural elements in Illinois No. 6 coal on the rate of the exchange reaction between diphenylmethane and tetralin-d₁₂ has been studied also. The results indicate that the exchange reaction is initiated by compounds which have labile linkages or reducible structures but not by the weak acids or weak bases. The reactions are initiated by single-bond homolyses and by molecule-induced homolyses.     

Reaction mechanism of coal hydrogenation: 1. Two-ring solvent system

Taiheiyo coal was hydrogenated in naphthalene, tetralin and decalin under 10 MPa (initial pressure) of hydrogen or nitrogen with stabilized nickel as catalyst at 400 °C for 15 min. Preasphaltene, asphaltene and oil conversions and the conversion of the solvents were measured. The hydrogen absorbed by coal from molecular hydrogen and from the donor solvent was calculated. The main reaction route appears to be the direct hydrogenation of coal by molecular hydrogen, with the side reaction via solvent by molecular hydrogen occurring only slightly, when an active catalyst such as stabilized nickel is present.     

氢能载体十氢萘制氢表观动力学

十氢萘是一种储氢密度很高的氢能载体,通过催化脱氢反应可将储存在十氢萘中的氢气释放出来。本文考察了用于制氢的十氢萘液相脱氢反应,在Pt负载的活性炭颗粒催化剂(Pt/AC)上可获得约47%的脱氢转化率;浓度分布显示十氢萘脱氢为分别生成萘及四氢萘的平行反应。在温度290~335℃、压力0.7~1.3MPa、搅拌转速1000r/min的条件下,在间歇高压釜中考察了十氢液相催化脱氢动力学,建立了脱氢反应表观动力学模型,对十氢萘脱氢实验数据进行非线性拟合,得到十氢萘脱氢表观动力学模型参数,生成萘及四氢萘的表观活化能分别为116.27kJ/mol、114.38kJ/mol。经统计检验,结果表明所建立的十氢萘催化脱氢表观动力学模型和参数估值是可靠的。     

反应条件对萘饱和加氢的影响

在固定床反应器中,采用Ni/γ-Al2O3加氢催化剂,考察了反应温度、压力和空速对萘转化率、四氢萘和十氢萘选择性、十氢萘反顺质量比的影响规律,并进一步考察了两种不同构型(反式和顺式)十氢萘产物的选择性生成。结果表明,反式和顺式十氢萘的总选择性可达95%以上,萘的转化率可达100%;较佳工艺条件为:空速0.6～6.0 h-1,反应温度210～250℃,压力不低于5.4 MPa。根据反顺质量比随空速、温度和压力的变化趋势,做了进一步的考察,结果显示,在保持十氢萘总选择性高于97%的前提下,可实现反式与顺式十氢萘各自的高选择性生成,反顺质量比可取得高值8.70和低值0.86。