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On the use of hydrogen donors for partial upgrading of heavy petroleum Laura O. Alemán-Vázquez, Pablo Torres-Mancera, Jorge Ancheyta, and Joel Ramírez-Salgado Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b01656 • Publication Date (Web): 06 Oct 2016 Downloaded from http://pubs.acs.org on October 9, 2016

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On the use of hydrogen donors for partial upgrading of heavy petroleum Laura O. Alemán-Vázquez, Pablo Torres-Mancera, Jorge Ancheyta*, Joel Ramírez-Salgado Instituto Mexicano del Petróleo. Eje Central Lázaro Cárdenas Norte 152, Col. San Bartolo Atepehuacan, México City, 07730, MEXICO Corresponding author: E-mail: [email protected]

Abstract The huge energy required to overcome the high-pressure drop in pipelines due to the high viscosity of heavy crude oils has motivated the development of technologies to improve the flow properties of these heavy hydrocarbons, such as friction reduction, viscosity reduction and in situ upgrading. It has been reported that a series of H-donors has been used to upgrade heavy oil for their transportation (low viscosity and high API gravity). Virtually any organic compound with a low oxidation potential can serve as a useful hydrogen donor. The low oxidation potential enables the transfer of hydrogen(s) from the donor to the substrate under mild reaction conditions. The choice of donor is based on the nature of the reaction, its availability and solubility in the reaction medium. Keywords: Hydrogen donors; heavy oil, viscosity 1. Introduction The future use of petroleum will likely be centered on heavy oils, including heavy crude oil, extra-heavy crude oil and refinery residues. Heavy oil differs from conventional crude oil, because the former has low hydrogen-to-carbon ratio and high content of heteroatoms (e.g., nitrogen, sulfur) and metals concentrated in the asphaltene fraction. Heavy oil and bitumen are characterized by having high viscosity (i.e. resistance to flow) and high density (low API gravity) compared with conventional oil.

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It has been widely recognized that heavy oil exhibits two main problems: transportation and processing. Both issues can be solved by means of upgrading technologies either partial or total. The most used technologies for upgrading of heavy oil are based on hydrogen addition and carbon rejection. The most representative hydrogen addition based technology is catalytic hydroprocessing while delayed coking belongs to the carbon rejection family. In the case of the hydrogen addition route, most of the options include a catalytic process that can operate in fixed-bed, moving-bed, ebullated-bed or slurry-phase reactors, except hydrovisbreaking that is a thermal process. Another approach for hydrogen addition is the use of hydrogen donors, which are chemical compounds that can easily transfer the hydrogen to the heavy oil. There is a variety of hydrogen donors reported in the literature which differ in the capacity for donating hydrogen, cost, degradation conditions particularly temperature, etc. Some hydrogen donors have been tested with model compounds and mixtures of them, while only a few are used for improving the quality of hydrocarbon streams. Processing the heavy oil requires firstly its transference from the production centers to the refiners or upgraders. To do so, the viscosity of the heavy oil needs to be reduced to a value that assures its transportation, e.g. 250 cSt at 100°F. The viscosity reduction is mainly done by dilution with lighter crude oils or distillates as well as by heating. The basic hypothesis of this contribution is that thermal or catalytic cracking assisted by hydrogen donors is useful in the selective processing of high molecular weight entities presented in coal or heavy oils (asphaltenes). As result, an effective viscosity reduction will be achieved, since the amount and properties of macromolecules are determinant in the crude oil properties related to transport by pipelines

1-5

. In consequence, partial upgrading

of heavy oil is enough aiming at diminishing viscosity to meet standards to allow for its transportation, given that higher levels of conversion and yields along with substantial removal of contaminants are not necessary. Hence, the use of hydrogen donors is also an option to solve the problem of heavy oil transportation, which can be more attractive from technical and economical points of view.


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A review of literature reports on the use of hydrogen donors for assisting thermal processes has been performed. The results are discussed in terms of types of H-donors, reaction mechanisms, properties, and applications. The aim is to foreseeing the application of technologies based on hydrogen donors for reducing the viscosity of heavy oils to allow them to be transported. 2. Methods of partial upgrading of heavy crude oils The transportation of extremely viscous liquids, such as heavy and extra-heavy crude oils through pipelines, presents many difficult problems even when pressures near the maximum permissible for standard pipe and pumping equipment are used. As the dominant transport fluid property, high viscosity crude oil puts great challenges to oil production, refining and transportation through wells and pipeline. Pipelines are the most economical and safest option for transportation of large volumes of crude oil. The most common key specifications to ensure adequate flow rates are: API gravity ≥ 16 °API and viscosity ≤ 250 cSt at 100 °F 6, 7. There are different techniques by which it is intended to help the transport of heavy and extra heavy oils through pipelines8: a. Friction reduction b. Viscosity reduction c. In situ upgrading 2.1 Friction reduction Friction reducers are additives that modify fluid rheological properties to reduce the friction created within the fluid as it flows through small-diameter pipelines. The viscous drag, wall friction and pressure drop in the pipeline are much higher in heavy oil compared with conventional light oils. The drag is the result of stresses at the wall due to fluid shearing causing a drop in fluid pressure. When higher flow rates are needed, fluid deformation is higher and shear stresses increase, thus more pressure must be applied to maintain the flow at the same average velocity. However, specifications of pipeline design may limit the pressure that can be employed or rise substantially the investment costs.


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The frictional drag present in laminar flow conditions cannot be changed unless the physical properties of the circulating fluid is altered. The commercial friction reducing agents do not change the properties of the fluid and consequently only act effectively in turbulent flow conditions. In the majority of the pipelines, the flow is of turbulent type. Therefore, friction reducing agents can give good results in most of the pipelines: drag reduction additives and core annular flow. 2.2 Viscosity reduction Viscosity reduction is focused on trying to understand the mechanisms by which the viscosity of a heavy or extra heavy oil is reduced for producing a transportable hydrocarbon. The approaches for transporting heavy crude oil by viscosity reduction are: dilution of heavy oil with light hydrocarbon fractions, upgrading, use of flow improvers, heating of subsea pipelines and formation of oil-in-water emulsions (O/W emulsions) by means of a surfactant. The most used methods for viscosity reduction are: 1) Increase of temperature (heating), which is one of the widely used and preferred methods to reduce the viscosity of heavy oils since the 30’s. However, heating the oil to increase its temperature includes a considerable amount of energy and cost. Another disadvantage is the higher corrosion problems due to temperature increase. Heating the pipeline induces changes in the rheological properties of the oil, which can result in instability of the fluid and a large number of heating stations to reduce heat losses along the pipeline, thus increasing the cost due to most of the transmission lines use insulating material to maintain the high temperatures and reduce heat loss to the surroundings. 2) Addition of lighter liquid hydrocarbons to the heavy oil (dilution). It is well-known that the lower the viscosity of the diluent, the lower the viscosity of the mixture. The formation of stable inverse emulsions that promote an important viscosity reduction and pressure drops is a technological alternative for improving the fluidity of heavy crude oils. The emulsion stability is strongly affected by the nature of interfacial films and the surfactant (or biosurfactant) adsorption mechanisms. An important aspect to be taken into account in this approach is that water must be removed from oil before 4 ACS Paragon Plus Environment

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any further processing or refining. By minimizing the water level in oil, corrosion is reduced, which maximizes the use of pipelines by eliminating severe operational problems. Hence, this transport strategy should involve both the formation and breaking of emulsions and removal of water from oil after being transported and before the crude oil is refined. 2.3 In situ upgrading The objective of in situ upgrading is to increase the mobility of the heavy crude oil and bitumen by reducing their viscosity to improve recovery or production as well as transportation via pipelines. This reduces refining severity and its environmental impact. The implementation of in-situ upgrading significantly reduces energy consumption since the heat from the steam injection is used to produce and upgraded oil. First at all, in-situ processes are difficult to control and monitor, which prevent them from being applied widely. In situ upgrading is achievable during thermal recovery methods such as ISC (Insitu combustion), SAGD (Steam Assisted Gravity Drainage), CSS (Cyclical Steam Stimulation or Huff-and-Puff), THAI (Toe to Heel Air Injection) and CAPRI (Catalytic Upgrading Process in situ). The upgrading is achieved due to the heavy molecules splitting into smaller molecules thermally. These thermal cracking reactions in situ reduce the viscosity of the heavy oil by a high order of magnitude, thereby improving flow and production8. The partial upgrading process is usually performed in two stages: Hydrocracking and hydrotreating. In the upgrading process, metals catalyze the hydrogenation reaction. Since asphaltenes and resins are the major constituents of heavy oils, these components present the highest impact on the method selection9, 10. 3

Fundamentals 3.1 Thermodynamics of hydrogen donation

Hydrogen donors must be capable of releasing hydrogen in an activated state to the reaction medium at the temperature and pressure employed. In a first approach, hydrogen donor supply useful hydrogen to the reaction medium by dehydrogenation and then the donor remains in its dehydrogenated form as byproduct. This description corresponds to donors applied in absence of hydrogen in gas phase as in carbon rejection technologies. On the other hand, as soon as the donors release hydrogen, a regeneration to the original 5 ACS Paragon Plus Environment

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hydrogenated state of the hydrogen donor by catching molecular H2 from gas phase by chemical reaction is desirable. In this second approach, by means of hydrogenationdehydrogenation cycles, a continuous hydrogen supply by hydrogen donors is possible. This explanation corresponds to hydrogen donors applied in hydrogen addition technologies where gas phase hydrogen is available. Both approaches provide activated hydrogen released from the hydrogen donor, in consequence, hydrogenation reactions are heightened, the amounts of free radical are lessened and thus formation of coke is inhibited. Where coke is defined as a carbonaceous solid material of high molecular weight, obtained as a solid byproduct during thermal processing by aromatic ring condensation reactions. To assure the functioning of hydrogen donor in a cyclical way, the hydrogenationdehydrogenation reaction must be near reversibility, i.e. it should be used at a temperature in which coexistence of quantitative amounts of reactants and products is stablished. For a given reaction, reversibility is located at a temperature where equilibrium constant is about 1, implying that ln(Ke) must be around zero. Figure 1 shows the chemical reaction schemes for the system consisting of decalin, tetralin, and naphthalene, these compounds may be interconverted by hydrogen addition or removal. Most of the hydrogen donors reported in the literature are based on this system, being tetralin the compound most frequently used. Based on the Van’t Hoff equation, equilibrium constants at different temperatures were computed using ∆Go, ∆Ho and Cp data published by Poling et. al. 11, the next equations were employed: ௗ௟௡௄ ௗ்

∆ு

= ோ் మ

(1) ்

∆‫ ܪ∆ = ܪ‬଴ + ‫׬‬ଶଽ଼ ∆‫ܶ݀݌ܥ‬

(2)

‫ ܣ = ݌ܥ‬+ ‫ ܶܤ‬+ ‫ ܶܥ‬ଶ + ‫ ܶܦ‬ଷ

(3)

The behavior of thermodynamic equilibrium constants for the gas phase dehydrogenation of cis-decalin, trans-decalin and tetralin as function of temperature is depicted in Figure 2. The reversibility of hydrogenation-dehydrogenation reactions is stablished at different temperatures; around 330oC for trans-decalin to tetralin, at 292oC for cis-decalin to tetralin and for decalin to naphthalene at 209oC. It is interesting to highlight that despite cis-decalin and trans-decalin are quite similar compounds the temperature of complete reversibility differs near 40oC. The calculation of thermodynamic equilibrium parameters in real processes is complicated due to several factors: large number of compounds, complex 6 ACS Paragon Plus Environment

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network of parallel and consecutive reactions, liquid-phase equilibrium distribution, etc. Nonetheless,

based

on

thermodynamic

equilibrium

for

tetralin

hydrogenation-

dehydrogenation, it can be hypothesized that to assure the completeness of hydrogenationdehydrogenation cycles a hydrogen donor should be used at a specific process conditions, where the temperature is particularly important. The temperature at which Ke=1 for hydrogenation of several compounds containing single and double aromatic rings are shown in Tables 1 and 2. The values were estimated based on equilibrium data previously published 12. 3.2 Reaction mechanism of hydrogen donation Most of the hydrogenation transfer mechanisms when using hydrogen donors are poorly understood. In terms of electronegativity, hydrogen occupies a central position among all the elements of the periodic table. Hydrogen has a value of 2.1 of Pauling electronegativity, which is between fluoride (4.0) and many metals (0.9 to 1.5). Therefore, in reactions involving hydrogen transfer, it may appear as a proton, an atom, or hydride, depending on the reactants and conditions. In many reactions with hydrogen donors, it may not be easy to determine how the hydrogen is transferred 13. Atomic hydrogen is a powerful reducing agent, but readily dimerizes to impractical molecular hydrogen. There are various ways to create conditions under which atomic hydrogen can be generated or in which hydrogen atoms may be transferred from a donor molecule to an acceptor substrate 14. The hydrogen transfer observed from hydrogen donors during fragmentation of coal structures or hydrocarbon molecules sometimes is referred as hydrogen shuttling without a detailed explanation of the molecular phenomena 15-26, perhaps due to the fact that the exact mechanism has not been completely elucidated. The functioning of hydrogen donor solvents during thermal processes can be analyzed based on the cracking of hydrocarbons by free radical mechanism. Below is described the cracking mechanism using general equations to represents the different reaction steps, where all the subscripts i, j, k, l, n, m, are integers.


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1. Initiation step. Homolytic thermal scission of some C-C bonds of hydrocarbon species contained in petroleum or coal yielding free radicals. The general reaction is represented as follows: ‫ܥ‬௞ ‫ܪ‬ଶ௞ାଶ ⇄ ሾ‫ܥ‬௜ ‫ܪ‬ଶ௜ାଵ ሿ ∗ +ൣ‫ܥ‬௝ ‫ܪ‬ଶ௝ାଵ ൧ ∗

(4)

where ݇ = ݅ + ݆. 2.

Chain propagation steps. Free radicals reactions: 2.1. Hydrogen transfer reaction. Converting a molecule into a new free radical by removal of a hydrogen atom by reaction with a free radical. ሾ‫ܥ‬௜ ‫ܪ‬ଶ௜ାଵ ሿ ∗ +‫ܥ‬௟ ‫ܪ‬ଶ௟ାଶ ⇄ ‫ܥ‬௜ ‫ܪ‬ଶ௜ାଶ + ሾ‫ܥ‬௟ ‫ܪ‬௟ାଵ ሿ ∗

(5)

2.2. Radical decomposition. Breaking of a free radical into a new radical and an olefin. ሾ‫ܥ‬௡ ‫ܪ‬ଶ௡ାଵ ሿ ∗⇒ ൣ‫ܥ‬௡ି௠ ‫ܪ‬ଶሺ௡ି௠ሻାଵ ൧ ∗ +‫ܥ‬௠ ‫ܪ‬ଶ௠

(6)

where ݊ ≥ 4, and 2 ≤ ݉ < ݊ 2.3. Radical addition. Corresponds to the reverse radical decomposition reaction in which an olefin and a free radical yield a larger free radical. ‫ܥ‬௠ ‫ܪ‬ଶ௠ + ሾ‫ܥ‬௟ ‫ܪ‬ଶ௟ାଵ ሿ ∗⇒ ൣ‫ܥ‬௠ା௟ ‫ܪ‬ଶሺ௠ା௟ሻାଵ ൧ ∗

(7)

where ݉ ≥ 2 2.4. Radical isomerization. Shifting atoms or group of atoms to another position. The equation represents the conversion of a primary into a secondary free radical. ሾ‫ܥ‬௡ ‫ܪ‬ଶ௡ାଵ ሿ ∗⇄ ൣ‫ܥ‬௠ ‫ܪ‬ଶ௠ାଵ − ‫ܥ‬ሶ ‫ ܪ‬− ‫ܥ‬௡ି௠ିଵ ‫ܪ‬ଶሺ௡ି௠ሻିଵ ൧

(8)

where ݊ ≥ 2, and ݉ ≤ ݊ − 2 3. Termination. Reaction between free radicals yielding stable products. ሾ‫ܥ‬௜ ‫ܪ‬ଶ௜ାଵ ሿ ∗ +ൣ‫ܥ‬௝ ‫ܪ‬ଶ௝ାଵ ൧ ∗⇄ ‫ܥ‬௞ ‫ܪ‬ଶ௞ାଶ

(9)

where ݅ + ݆ = ݇ Taking into account that hydrogen donor is aimed at assisting hydrogen supply, the immediate role of hydrogen donor is heighten the hydrogen transfer step leading to capping of free radicals and consequently a concomitant diminishing of the rest of the chain propagation steps due to the fall of free radicals concentration. A free radical mechanism involving tetralin as hydrogen donors during coal liquefaction proposed by Curran et. al. 27 is summarized below:


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‫ → ܯ‬2ܴ ∗

Initiation:

ܴ ∗ +‫ܥ‬ଵ଴ ‫ܪ‬ଵଶ → ܴ‫ ܪ‬+ ሾ‫ܥ‬ଵ଴ ‫ܪ‬ଵଵ ሿ ∗

Hydrogen transfer 1:

(10) (11)

Disproportionation:

‫ ∗ ܪ‬+‫ܥ‬ଵ଴ ‫ܪ‬ଵଶ → ‫ܥ‬ଵ଴ ‫ܪ‬ଵ଴ + ‫∗ ܪ‬

(12)

Hydrogen transfer 2:

ܴ ∗ +‫ܥ‬ଵ଴ ‫ܪ‬ଵଶ → ሾ‫ܥ‬ଵ଴ ‫ܪ‬ଵଵ ሿ ∗ +‫ܪ‬ଶ

(13)

Termination:

ܴ ∗ +ሾ‫ܥ‬ଵ଴ ‫ܪ‬ଵଵ ሿ ∗→ ܴ‫ ܪ‬+ ‫ܥ‬ଵ଴ ‫ܪ‬ଵ଴

(14)

Where M is the coal extract, R* represents general radical species, C10H12 is tetralin, and C10H10 is dihydonaphtalene. Interestingly, the final dihydronaphthalene is also a hydrogen donor capable to work in a similar scheme to tetralin, but yielding naphthalene as final byproduct. The role of hydrogen donors according to the free radical mechanism is the transference of a hydrogen atom between donor species and acceptor species (equations 5, 11 or 13). Several types of hydrogen donor species are included in Table 3, whereas the acceptor species are hydrocarbon free radicals produced by cracking of molecules contained in the processing coal or crude oil (equations 4 or 10). Additional hydrogen transfer mechanisms has been postulated. A summary of possible mechanisms was published by McMillen et al.28, they analyzed five modes of hydrogen transfer: concerted H2- transfer, reverse radical-disproportionation (RRD), hydrogen atom elimination-addition, 3-step hydrogen transfer and radical hydrogen-Transfer (RHT). Hydrogen donation is considered an important mechanism by which hydrogen is transferred from the donor to the oil. In theory, a good hydrogen donor solvent must diminish the rate of retrogressive reactions by capping free radicals. The quality of the hydrogen donor affects the relative rates of the progressive and retrogressive reactions. Good hydrogen donors such as tetralin enhance the relative rates of the progressive reactions while poor hydrogen donors such as napthalene promote retrogressive reactions. Reaction mechanisms of tetralin can be extrapolated to other varieties of hydrogen donors, whose base structure is similar to the tetralin 29-31. Hydrogen transfer between free radicals and hydrogen donor represented by reaction (11) is the base of the functioning of hydrogen donors. The rewritten reaction to include the transitional state is: ܴ ∗ +‫ → ܪܦ‬ሾ‫ܦ ∙ ܪ ∙ ܣ‬ሿ → ‫ ܪܣ‬+ ‫∗ ܦ‬

(15) 9

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Due to instability of free radicals involved, the experimental determination of thermodynamic parameters is difficult. Accordingly, some theoretical and empirical attempts to estimate activation barriers for this reaction have been published

32, 33

. It was

found that the lowest activation energy for hydrogen abstraction from several hydrogen donors to stabilize methyl and ethyl radicals corresponds to allylic hydrogen at α position. 3.3 Model molecules as hydrogen donors •

Tetralin

Tetralin is the simplest model compound of hydroaromatic hydrocarbons, which forms the basis of most of the hydrogen donors, however it degrades at high temperatures. The following routes have been suggested for degradation of tetralin 34,35: a. Saturated ring rupture and removal of gaseous fragments: ethylbenzene, ethylene, benzene and toluene b. Tetralin

degradation

by

intramolecular

saturated

ring

opening,

with

dehydrogenation by formation of 2-methylindene. This compound decomposes at the same temperature than tetralin and produces indene and methane c. Tetralin degradation in naphthalene by direct dehydrogenation Many of these transfer reactions of hydrogen atom proceed through radical mechanisms, for example, high temperature disproportionation of naphthalene, 1,2-dihydronaphthalene and 1,2,3,4–tetrahydronaphthalene. There have been many explanations on the activation of hydrogen. For instance, Figure 3 shows the direct activation of the H-H bond by direct collision with the free radicals of the bulk (liquid or may be solid) having sufficient energy. •

Decalin

Unlike tetralin, decalin (decahydronafthalene) undergoes thermal cracking that produces large amount of monoaromatics and gases (such as methane and ethylene) at temperatures of 700-950°C. The thermal cracking of decalin begins with the rupture of one of its rings in alkyl-cyclic compounds. These are subject to dealkylation, dehydrogenation and secondary rupture to form fragments with 4 and 5 atoms, which are precursors of aromatics

36

.

However, decalin can serve as hydrogen donor at high temperatures. Due to the excellent


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thermal stability at high temperatures, decalin has applications as fuel in the area of aviation. Trans-decalin has been reported with potential endothermic fuel jets or cooling fluid on surfaces and air. The final product of hydrogen transfer reactions for both tetralin and decalin is naphthalene; naphthalene is one of the major products in the thermal cracking in samples containing tetralin or decalin. The effectiveness of the H-transfer is substantially high in tetralin than in decalin. This is because the benzyl radical of tetralin is more stable than the tertiary radical formed by H-substraction of decalin. Considering reaction rates of firstorder decomposition, decalin shows higher hydrogen value as compared with tetralin. •

Naphthalene

In hydrogenation reaction (Figure 4) naphthalene is easy to hydrogenate to 1,2,3,4tetrahydronaphthalene (tetralin), which can promote with some difficulty the hydrogenation of isomers (cis- and tans-) of decahydronaphthalene (decalin) as observed in Figure 6. Cracking reactions of low molecular weight compounds may occur and are undesirable. Valuable compounds are obtained from the hydrogenolysis reactions/ring opening, whose compounds are of high molecular weight, (mainly alkyl-cyclohexenes, alkylbenzenes, metilindanes and methylindenes, and spirodecane) which have high cetane number. •

Aromatics

Concerning the formation of aromatic hydrocarbons, it can be stated that the presence of an aromatic ring in the structure of the starting reactant influences the direct formation of hydrogenation ring. Reactions only affect the aromatic type formed: C10 monoaromatic mainly from ring opening reactions, C6-C9 aromatic light from cracking reactions, C10 aromatic intermediates from hydrogen transfer reactions that favor the formation of diaromatics and heavy aromatic compounds receiving a contribution of the above reactions and mainly from alkylation and disproportionation. The π radicals involving delocalized electrons of polynuclear aromatic hydrocarbons are stable and maintained during storage of the oil. These radicals, by slow condensation reaction, could gradually lead to the formation of pitch; however, the addition of


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molybdenum naphthenate or other hydrogen donors, decreases the content of free radicals in the medium, slowing down all reactions, particularly condensation reactions (Figure 5). •

Pyrene

It is observed that the hydrogen donors and aromatic polycondensates interact synergistically improving coal conversion. This is explained by tetralin and pyrene. Due to the combined effect, plus the hydropyrene that is present in the coal-pyrene-tetralinhydrogen system, at 427 °C the synergistic effect (30 wt % tetralin and 70 wt % pyrene) has shown the highest bituminous coal conversion

37

. Undoubtedly, the pyrene has high

ability to accept the evolved hydrogen tetralin until the formation of hexapyrene. The hydrogenation rate gradually decreases as the hydrogenation level grows, and the hydrogenation of the last ring becomes difficult (Figure 6) 38. In addition to polycondensed aromatic molecules, oxygen containing compounds also have been tested as hydrogen donors. By cracking of model compounds, it was found that hydrogen donor capacity follows the order: furans < phenol < ketones < aldehydes < ethers. In the research, the transference of hydrogen from the hydrogen donor was evidenced by using deuterium tracer compounds 39. 3.4 Hydrogen donor ability Several attempts to measure the ability to donate hydrogen during coal liquefaction of a chemical compound have been performed. A hydrogen donor parameter is defined based on one or several of the next parameters: solubility, polarity, chemical reaction tests, mass spectrometry, structural parameters, spectroscopic features obtained from 1H and 13C NMR 40-57

.

In most of the cases the parameters are defined for specific chemical compounds, even so those based on chemical composition and/or spectroscopic data can be applied to complex mixtures like the present in oil derived solvents. Some illustrative examples of estimation of hydrogen donor capacity are given below: − A method to measure the solvent effect during liquefaction of sawdust based on tetralin as chemical probe was developed by Li et al 40: Solvent Impact Index (SII):

ܵ‫= ܫܫ‬

ఈబ ିఈభ ఈబ


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Where αo represents the tetralin conversion with toluene as inert reference solvent, and α1 is the tetralin conversion in the tested hydrogen donor solvent. They indicated good agreement between SII and sawdust conversion and yield. − The Solvent Hydrogen Donor Index (SHDI) was defined for liquefaction solvents composed by complex hydrocarbon mixtures

41

. Creosote oil derived solvents was

used as hydrogen donors and two Australian coal samples to test the parameter. The SHDI is obtained from 1H spectroscopic data as follows: ܵ‫ܪ = ܫܦܪ‬ௗ ∗ %‫ܪ‬ Where Hd is the quotient of the integrated intensity taken between 2.65 and 2.8 ppm and the total integrated intensity, and %H is the weight percent of hydrogen in the sample. A match between SHDI and coal conversion in most of the results was obtained. − By means of de-hydrogenation of coal-derived solvents using sulfur as hydrogen acceptor and spectrospic NMR data, Aiura et al. measured the amount of transferable hydrogens 42. − A proposal to determine the performance of solvents during coal liquefaction is based on a reaction test of a solvent and benzoyl peroxide followed by NMR spectroscopy. A set of four indices is determined; the donor index, the efficiency index, the scavenger index and the recycle index 43. In spite of the several attempts to measure the hydrogen donor ability of either a specific compound or a given oil-derived solvent, there is no a universal tool for quantify this parameter. This is due probably to the fact that the hydrogen donation during thermal cracking reactions in a complex multiphase reaction system is strongly dependent on the process conditions, particularly the type feed (coal, bitumen, heavy crude oil, etc.) and also on the temperature and pressure which strongly affect the hydrogenation-dehydrogenation equilibria of the hydrogen donating species. Most of the fundamental studies and methodologies to quantify transfer donor ability were performed during the 80s. With the advent of theoretical computational tools and modern characterization techniques, new insights to decipher the exact mechanism of hydrogen donation and to compute the hydrogen donor ability could be achieved, especially for asphaltene evolution during upgrading processes. 4

Types of hydrogen donors


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Virtually any organic compound with a low oxidation potential can serve as a useful hydrogen donor. The low oxidation potential enables the transfer of hydrogen(s) from the donor to the substrate under mild reaction conditions. The choice of donor is based on the nature of the reaction, its availability and solubility in the reaction medium. Alcohols, hydrazine, cyclic olefins and hydroaromatics have been employed as hydrogen donors for the transfer hydrogenation of various functional groups. Table 1 shows the most common chemical species of different types of hydrogen donors that have been used so far 39, 58, 59. Some hydrogen donors or hydrogen transfer solvents are polycyclic compounds free of carbonyl groups, type naphthene-aromatic or naphthenic, which are dehydrogenated. They transfer hydrogen atoms to heavy hydrocarbon oil, reducing its viscosity and increasing its API gravity, minimize the polymerization reactions of the heavy molecules via free radical mechanism (prevent coke formation). Various technologies where hydrogen donors are used are reported in the literature

60,61

. The rate of hydrogenation is susceptible to control

by selecting the hydrogen donor agent. However, by using non-catalytic systems will not be possible to achieve high cracking and hydrogenation levels. The final process should be determined based on the required final product quality. The use of hydrogen donor solvents was mentioned at first time in 1933, in the hydrogenation of coke for the treatment of oil residue, the first patent was registered in 1947. Afterward some other patents are reported on the application of hydrogen donor agents. Carlson et al.

62

used tetralin as hydrogen donor, which is dehydrogenated to naphthalene

and the residue is converted to products of low boiling point with low coke and dry gas formation. A typical hydrogen donating agent is decalin, which proceeds in a hydrogenation reaction in equilibrium with tetraline and naphthalene. Separation of these compounds results difficult, therefore its recovery from the reaction bulk is complicated due to its high solubility in hydrogenated reagents, and thus solvents for extraction are required. Another disadvantage of some hydrogen donors is that one-step of external hydrogenation of the inactive donor (activation) is required. Hydrogenation can be conducted over a suitable catalyst and problems typically arise from catalyst deactivation by coke formation 14 ACS Paragon Plus Environment

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and metal deposition. Others types of H-donor are those where prior hydrogenation is not necessary. Hydrogenation reactions are not favored by limited availability of hydrogen to be transferred to the liquid before initiating the reaction and by the use of low hydrogen partial pressure. However, the hydrogenation reactions can be preferred by the use of hydrogen donor agents that can reversibly hydrogenate-dehydrogenate in the reaction mixture in a cyclical way. Therefore, when hydrogen donors are used in a hydrogenation reaction of a particular molecule, balance hydrogenation-dehydrogenation of the hydrogen donor agent generates an additional amount of hydrogen atoms to the reaction medium, favoring the hydrogenation of the substrate. Polynuclear aromatics, e.g. pyrene, fluoranthene, and basic nitrogen compounds such as quinoline and benzoquinolines, which are constituents of various petroleum refinery streams, can function as hydrogen transfer agents

63-65

. Some authors have used tetralin,

decalin and naphthalene as hydrogen donors obtaining improved API gravity, viscosity and distillate yields 66. The use of hydrogen donor in liquid phase, such as tetralin or decalin is well known; however, these compounds are expensive and difficult to recover and reuse. The more active hydrogen donors in liquid phase appear to be principally alcohols, hydroaromatics, cyclic ethers and occasionally formic and ascorbic acids. Examples of materials suitable as hydrogen transfer solvents that are easily thermally hydrogenated and dehydrogenated include: pyrene, fluoranthene, anthracene, benzanthracene, dibenzanthracene, perylene, coronene, and benzopyrene, as well as their nitrogen analogs such as quinoline, benzoquinoline, acridine, azapyrene, and their hydrogenated derivatives. Mixtures of suitable hydrogen transfer solvents can be used as well as mixtures of hydrogen transfer solvents and other solvents containing at least 15 wt. % 65. Compared with the catalytic approaches that use molecular hydrogen, hydrogen donors have real advantages and potential. Molecular hydrogen has low molecular weight and therefore high diffusion capacity, and is readily combustible that has considerable risks especially to large scale. Using hydrogen donors avoids these difficulties, since no pressure vessels and simple stirring of the solution are usually required. 15 ACS Paragon Plus Environment

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In the presence of manganese at elevated temperatures, a process for the total or partial hydrogenation of polynuclear aromatic compounds (phenanthrene, pyrene, naphthalene) with hydrogen is described. Partially hydrogenated resulting products are useful as hydrogen donors in the thermal cracking process 67. The hydrogenation of unsaturated copolymers such as polybutadiene, polyisoprene and polydiene-styrene block copolymers has been reported without addition of hydrogen gas which are dissolved in a solvent selected from the group consisting of hexane, toluene, cyclohexane, and tetrahydrofuran

68

. A hydrogen donor compound is selected from the

group consisting of formic acid, formates, phosphoric acid, phosphonates, cyclohexene and indoline in the presence of a VII Group metal catalyst, especially supported of palladium catalyst

69

. A recycling method for polymer materials comprising a material

depolymerization by heating is used in the presence of a hydrogen donor material and a strong base 70. Some hydrotreating processes use at the same time hydrogen donor and catalyst. Conversion of coal and heavy hydrocarbons to lighter products (low molecular weight) is done by hydrocracking in the presence of a hydrogen donor (tetralin) and solvent hydrogen donor which include C10 -C12 tetrahydronaphthalenes, C12 and C13 acenaphthenes, di, tetraand octahydroanthracenes of boiling point higher than 200 °C. The feed was converted in the presence of an alkali metal catalyst prepared by heating at a temperature higher than 427 °C and hydrogenation catalyst consisting of cobalt, molybdenum, nickel, tungsten and mixtures thereof. Hydrogen-donor solvent is used in concentration between 1.2 and 3.0 wt% 71,72. The hydrogen donors may also be strongly aromatic streams, such as product from the fractionator bottoms or recycled gasoil from the catalytic cracking unit, tar pyrolysis plant, or coking plants 73,74. A process for catalytic hydroconversion of coal by a metal compound in the presence of hydrogen donor solvents have been described in patents

75,76

. Preferred metal compounds

are molybdenum naphthenate as the catalyst precursor at temperature below 350 °C. Suitable aromatic hydrogen donor solvents include hydrogenated creosote oil, hydrogenated intermediate product streams from catalytic cracking of petroleum feedstock, 16 ACS Paragon Plus Environment

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coal-derived liquids which are rich in indane, C10 to C12 tetralins, decalins, biphenyl, methylnaphthalene,

dimethylnaphthalene,

C12

and

C13

acenaphthenes

and

tetrahydroacenaphthene (Table 3). Coal derived products showed enough stability as to be used as hydrogen donor solvents in subsequent processes such as catalytic and thermal cracking, including viscosity reduction and coking, with improved yields of liquid and reduction of coke. Hydrogenation of pericondensed aromatics behaves very reactive as a hydrogen donor solvent; H2S can then play a role as a catalyst for the transfer of H (it is not clear how the H2S can encourage the transfer of H). Hydrogenation may capture free radicals in the solution or participate in partial hydrogenation of pericondensed aromatics, playing the role of hydrogen donor solvent. By comparing compositional changes in the reacted solvents, and assuming pseudo first order kinetics, it was possible to rank various hydroaromatics contained in the hydrotreated creosote oil according to their effectiveness in donating hydrogen. Octahydrophenantrene, tetralin and tetrahydrophenanthrene have low rate of hydrogen donation, and they have a propensity for isomerization 77. Moreover, the naphthalene may be hydrogenated catalytically with tetralin and recycled, note that the paraffins and naphthenic compounds with one ring are hydrogen transfer agents ineffective and condensed compounds with naphthene ring such as decalin are most effective. A mixture of naphthenic condensed ring and aromatic compounds are recommended. In tetralin only naphthenic hydrogens are activated by the adjacent aromatic rings and are sufficiently non-reactive to minimize coke selectivity and gas produced during the thermal cracking. The most active donors for liquid systems are mainly alcohols, hydroaromatic, cyclic ethers and formic and ascorbic acid occasionally; while in for liquid-solid systems they are: cyclohexane phosphinic acid and phosphinates, and indoline. The tri-alkylsilanes and trialkystanan have proven to be good type of homogeneous or heterogeneous hydrogen donors 78. Table 1 summarizes the chemical structure of several hydrogen donors.


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Methods for measuring hydrogen donor concentration and relative reactivity were developed by Ken Gould et al. 79 using a chemical dehydrogenation agent, 2-3-dichloro-pbenzoquinone (DDQ). It forms strong charge transfer complexes with polynuclear aromatics. Because the moles of unreacted DDQ equals the moles of dehydrogenated product formed, and the moles of donatable hydrogen in the feed equals two times the moles of DDQ reacted. The grams of donatable hydrogen per 100 g of sample and the hydrogen percent that is donatable could be calculated. Figure 7 shows DDQ abstraction of two donor hydrogens per molecule. Resulting hydrogen donor relative reactivities show that tetralin was not an ideal hydrogen donor, 1,2,3,4-tetrahydriquinoline is a super-reactive hydrogen donor, being 50 times higher than tetraline. Dihydrophenantren is less reactive. Langer

80

and Chen et al.

74

used certain crude oil fractions as hydrogen donors. Some

fractions available in refinery process streams are relatively rich in compounds with condensed aromatic rings such as alkyl naphthalenes, anthracenes and fenantracenos alkyl. Partial hydrogenation of these fractions produces compounds that transfer hydrogen easily to the residue in the same way as tetralin, which is a relatively expensive compound. West Texas fractions showed that the refining streams contain up to 70% of compounds with 12% naphthene rings and aromatic ring structures. Hence, some crude oil fractions and also coal derived streams can be considered as hydrogen donor solvents, where the hydrogen donating species are designated as natural hydrogen donors. 5

Applications of hydrogen donors for upgrading processes

5.1

Visbreaking

Visbreaking is a well-known technology based on the thermal cracking applied to oil residua. The reduction of viscosity is the target pursued in the process, but also some additional distillate yields are obtained. In a simple description, atmospheric or vacuum residua are heated at temperatures ranging from 450 to 510oC during short residence time to prevent excess coke production, thus the low residua conversion obtained is normally enough as to meet requirements 81,82. Visbreaking becomes more efficient when the process is operated under hydrogen atmosphere achieving high yields and product quality (hydrovisbreaking).


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The main differences

between visbreaking and hydrovisbreaking are that in

hydrovisbreaking, some hydrogen is consumed (from 0.2 to 0.4 wt%), whereas in visbreaking, a small amount of hydrogen is produced (~ 0.05 wt%). Hydrovisbreaking has the following advantages over normal visbreaking 61,74, 80: a)

The conversion of distillate is higher by 5 to 10 wt%

b)

The quality of the residue is much better

c)

The H/C ratio is higher and the density and viscosity are even lower

Accordingly, the presence of hydrogen donor is beneficial in the process since improving hydrogenation and suppressing coke formation are desirable. In this regard, several hydrogen donors derived from streams containing multi-ring hydroaromatic components have been used as additives to improve the results obtained by visbreaking processes

83-87

. Most of the published results showed reduction of viscosity,

higher liquid yields and diminishing of the amount of coke production, but a comprehensive explanation of the hydrogen donors functioning is not normally included. A hypothesis indicates that due to hydrogen shuttle between asphaltene and hydrogen donors a better performance of visbreaking in presence of hydrogen donors is achieved compared with the conventional one 83. 5.2

Direct coal liquefaction

Direct coal liquefaction (DCL) refers to the conversion of coal to liquid hydrocarbons. The earliest version of the process consists of the dissolution of coal in a given solvent al high temperature and pressure followed by thermal cracking of the dissolved coal. Later, improved processes were developed by including hydrogen and catalysts. The liquid product derived from processed coal is recycled as solvent for coal dispersion and transportation. Nonetheless, sometimes external solvents are employed, ranging from specific compounds to oil derived streams. Between 1960 and 1990, various processes for coal liquefaction were developed, they can be broadly classified as one stage or two stage processes

88

, a list of these technologies is presented in Table 1. It is possible to upgrade

coal and petroleum-derived oils simultaneously in the so-called “co-processing”, some of the listed processes were designed with this purpose, and some of the rest can be adapted for co-processing.


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It is recognized that the solvent employed in the DCL processes affects the amount and quality of products 89-91. Indeed, at relatively low temperature conditions the solvent act as a hydrogen donor, and some processes include the re-hydrogenation of the recycle solvent. Several studies have been reported aimed at determining the effect of catalyst, solvent or both

92-98

. Tetralin is probably the most-tested hydrogen donor solvent, a brief review of

coal liquefaction in presence of catalyst and tetralin has been lately published 99. The majority of research studies and technological developments involving hydrogen donors have been performed around direct coal liquefaction processes. Hence most of the advances relates to the role of hydrogen donors during the processes and the mechanism of hydrogen donation arises mainly from DCL. 5.3 Aquathermolysis Aquathermolysis is a process comprising the thermal cracking of extracting oil during steam stimulation. In brief, superheated steam is injected into the oil reservoir, and the oil is recovered after a soak period. The aim of the process is to stimulate crude oil production and allow for its transportation by reduction of viscosity. The process is based on the breaking of chemical bonds; C-C, C-O and specifically the C-S of organosulfur compounds with production of gases (CH4, CO2, H2, and H2S). Higher profit from the process are obtained by using catalysts and hydrogen donors. Different types of catalysts have been reported: water-soluble liquids

113,114

100-104

, oil-soluble

104,105

, mineral

106-109

, dispersed

110-112

. Often, catalysts are used along with hydrogen donor solvents

, and ionic

108, 110, 115-117

.

Experimental evidence of the efficiency of hydrogen donors in the catalytic aquathermolysis process is summarized in two reviews recently published 118, 119. 6

Concluding remarks

Piping of heavy oil is expensive due to the elevated resistance found in the flow of these oils. Since this resistance has its origin in the heavy oil composition, the most successful methods to improve the pipeline flow properties of heavy oils aim at modifying the oil microstructure. It is necessary to develop technologies at low cost and easy to use to help the oils in their transportation through pipelines. In situ upgrading has received wide attention in the last few years, though its field operation requires substantial technological improvement.


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The advantages of technologies based on thermal processes assisted by hydrogen donors are: •

Increased distillate yields

•

Effective decrease in the amount of coke formed

•

The process could be either pure thermal or catalytic

•

Several chemical compounds can be used as hydrogen donors

•

The possibility of using oil fractions as hydrogen donor solvents when processing residua or extra-heavy crude oils

•

Availability of information about the hydrogen transfer capability of common hydrogen donors

Nonetheless, some drawbacks of hydrogen donors can also be outlined: •

Difficult recovery of liquid hydrogen donors from the product stream

•

Effectiveness strongly dependent on operating conditions (temperature and pressure), and type of feed

•

To warrant their cyclical hydrogen transfer perform external re-hydrogenation cycles may be required

•

To assure thermodynamic equilibrium of hydrogenation-dehydrogenation reactions, the control of the operation temperature must be considered

•

The exact mechanism of hydrogen transfer has not been completely elucidated

•

Scarce information on the impact of the using of hydrogen donors in the product distribution of crude oils, specifically on the content and characteristics of asphaltenes

References 1.

Puttagunta V. R.; Miadonye A., Oil and gas journal, 1993; 91; 71-73.

2.

Mullins O. C.; Sheu E.Y.; Asphaltenes: Fundamentals and applications, Springer science businessmen media, New York, 1995.

3.

Mack C., J. Phys. Chem., 1932; 36; 2901–2914.

4.

Speight J., Part. Oil & Gas Science and Technology, 2004; 59; 467-477.

5.

Altgelt K. H.; Harle O. L., Ind. Eng. Chem. Prod. Res. Dev., 1975; 14; 240–246. 21 ACS Paragon Plus Environment

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9.

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74. Chen, Q.; Ga, Y.; Wang, Z. X.; Guo, A. J. Petrol. Sci. and Tech., 2014; 32, 2506–2511. 75. Aldridge, C. L.; Bearden, R. US Patent Number 4,077,867. 1978. 76. Rudnick, L. R. US Patent Number 4,642,175. 1987. 77. Kuhlmann E. J.; Guptill R. P.; Jung, D. Y.; Zang, H. K. US Patent Number 4,476,009. 1984. 78. Joshi, J. B.; Pandit, A B.; Kataria, K. L.; Kulkarni, R. P.; Sawarkar, A. N.; Tandon, D.; Ram Y.; Kumar, M. M. Ind. Eng. Chem. Res. 2008; 47; 8960–8988. 79. Gould, K. A.; Wiehe, I. A. Energy Fuels. 2007; 21; 1199-1204. 80. Langer, A. W.; Stewart, J. Thompson, C. E.; White, H. T.; Hill, R. M. Ind. Eng. Chem. Process Des. Dev. 1962; 1; 309-312. 81. Speight J. G., Scientia Iranica C 2012; 19; 569-573. 82. Rana M. S., Sámano V., Ancheyta J., Díaz J.A.I., Fuel 2007; 86; 1216-1231. 83. Chen Q., Gao Y., Wang Z. X., Guo A. J., Petrol. Sci. & Tech 2014; 32; 2506-2511. 84. Deng W., Liu D., Zhou J., Que G., ACS Div. of Pet. Chem. Preprints, 48, 4, (2003), 341-343. 85. Del Bianco A., Garuti G., Pirovano C.and Russo R., Fuel 1995; 74; 756-760. 86. Del Bianco A., Panariti N., Prandini B., Beltrame P.L., Carniti P., Fuel 72; 1993; 8185. 87. Wang Q., Guo L., Wang Z-X, Mu B-Q., Wuo A-J, Liu H., J. of Fuel Chem. and Tech. 2012; 40; 1317-1322. 88. R. Kamal, “Technology Status Report: Coal Liquefaction”, Department of Trade and Industry, UK 1999. 89. Kamiya Y., Nagae S., Yao T., Hirai H., Fukushima A., Fuel 1982; 61; 906-911. 90. Kitahoka Y., Ueda M., Murata K., Ito H., Mikami K., Fuel 1982; 61; 919-924. 91. Sato Y; Yamamoto Y; Kamo T; Inaba A; Miki H; Saito I, Energy & Fuels V5 N.1 98102 v 5, n 1, p 98-102, January, 1991. 92. Khare, S.; Dell'Amico, M. Canadian J. of Chem. Eng. 2013; 91; 1660-1670. 93. Kamiya Y., Nagae S., Fuel 1985; 64; 1242-1245. 94. Li Q., Liu D., Song L., Wu P., Yan Z., Li M., Fuel 2016; 164; 94-98. 95. Kim K.H., Brown R.C., Kieffer M., Bai X., Energy Fuels 2014; 28; 6429-6437. 96. Shui H., Cai Z., Xu C., Energies 2010; 3; 155-170. 25 ACS Paragon Plus Environment

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97. Ikenaga N., Kan-nan S., Sakoda T., Suzuki T., Catal. Today 1997; 39; 99-109. 98. Kouzu M., Koyama K., Oneyama M., Aramaki T,, Hayashi T., Kobayashi M. Ito H., Hattori H., Fuel 2000; 79; 365-371. 99. Johannes I., Tiikma L., Luik H., Tamvelius H., Krasulina J., ISRN – Chemical Engineering 2012, Article ID 617363. 100. Clark P. D., Hyne J. B., Fuel 1984; 63; 1649-1654. 101. Clark P. D., Dowling N. I., Hyne J. B., Lesage K. L., Fuel 66 (1987) 1353-1357. 102. Clark P. D., Dowling N. I., Lesage K. L., Hyne J.B., Fuel 66 (1987) 1699-1702. 103. Clark P. D., Kirk M. J., Energy Fuels 8 (1994) 380-387. 104. Yufeng H., Shuyuan L., Fuchen D., Hang Y., Pet. Sci. 6 (2009) 194-200. 105. Fang H., Liu Y., Zhang L., Zhao X., Fuel 81 (2002) 1733-1738. 106. Fang H., Zhang Y., Zhong L. G., Energy Fuels 15 (2001) 1475-1479. 107. Siskin M., Brons G., Katritzky A. R., Balasubramanian M., Energy Fuels 4 (1990) 475-482. 108. Ovalles C., Vallejos C., Vasquez T., Rojas I., Ehrman U., Benitez J.L., Martínez R., Pet. Sci. Tecnol. 21 (2003) 255-274. 109. Fang H., Zhang Y., Lin Y., Fuel 2009; 83; 2035-2039. 110. Wei L., Hua Z. J., Wua Q. J., J. Fuel Chem. Technol. 2007; 35; 176-180. 111. Chen Y., Wang Y., Wu C., Xia F., Energy Fuels 2008; 22; 1502-1508. 112. Wang Y., Chen Y., He J., Li P., Yang C., Energy Fuels 2010; 24; 1502-1510. 113. Fang H.-F., Li Z.-B., Liang T., J. Fuel. Chem. Technol. 2007; 35; 32-35. 114. Fang Z.-X., Wang T.-F., He Y.-H., J. Fuel. Chem. Technol. 2009; 37; 690-693. 115. Liu Y., Fan H., Energy Fuels 2002; 16; 842-846. 116. Strusz O.P., Mojeisky T. W., Payzant J. D., Olah G A., Surya Prakash G. K., Energy Fuels 1999; 13; 558-569 117. Vallejos, C.; Vasquez, T.; Ovalles, C. US Patent Number 5,891,829. 1999. 118. Ovalles C., Rivero V., Salazar A., Catalysts 2015; 5; 286-297. 119. Ovalles C., Rengel-Unda P., Bruzual J., Salazar A., Fuel Chem Div Preprints 48 (2003) 59.


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Energy & Fuels

Table 1. Temperature for Ke=1 for single-ring aromatic hydrogenation Hydrogenation reaction Benzene + 3H2 ↔ ciclohexane Toluene + 3H2 ↔ methylcyclohexane Ethylbenzene + 3H2 ↔ ethylcyclohexane Propylbenzene + 3H2 ↔ propylcyclohexane Cumene + 3H2 ↔ isopropylcyclohexane n-Butylbenzene + 3H2 ↔ n-butylcyclohexane Cyclohexene + H2 ↔ cyclohexane Styrene + H2 ↔ ethylbenzene Styrene + 4H2 ↔ ethilcyclohexane o-Xylene + 3H2 ↔ 1,2-dimetilciclohexano p-Xylene + 3H2 ↔ 1,4-dimetilciclohexano m-Xylene + 3H2 ↔ 1,3-dimetilciclohexano 1,2,3-Trimethylbenzene + 3 H2 ↔ 1,2,3-trimethylcyclohexane 1,2,4- Trimethylbenzene + 3 H2 ↔ 1,2,4-trimethylcyclohexane 1,3,5- Trimethylbenzene + 3 H2 ↔ 1,3,5-trimetilciclohexano 1,2,3,5-Tetramethylbenzene + 3 H2 ↔ 1,2,3,5-tetramethylcyclohexane

T, oC [Ke=1] 302 295 285 277 336 273 548 739 405 252 257 270 269 241 251 226

Table 2. Temperature for Ke=1 for double-ring aromatic hydrogenation Hydrogenation reaction Naphthalene + 2H2 ↔ tetralin Tetralin + 3H2 ↔ trans-decalin Naphthalene + 5H2 ↔ trans-decalin Biphenyl + 3H2 ↔ cyclohexylbenzene Cyclohexylbenzene + 3H2 ↔ cyclohexylcyclohexane Biphenyl+ 6 H2 ↔ cyclohexylcyclohexane Phenanthrene + H2 ↔ dihydrophenantrene Phenanthrene + 2H2 ↔ tetrahydrophenantrene Phenanthrene + 4H2 ↔ octahydrophenantrene Phenanthrene + 7H2 ↔ perhydrophenantrene Indene+ H2 ↔ indane Indane+ 3H2 ↔ cis-hydrindane Acenapthalene + 2H2 ↔ tetrahidroacenaphthalene Acenafteno + 5H2 ↔ perhydroacenaphthene Fluorene + 3H2 ↔ cis-hexahydrofluorene Fluorene + 6H2 ↔ perhydrofluorene


T, oC [Ke=1] 248 217 229 268 252 260 153 223 221 226 530 229 225 189 213 188

Energy & Fuels

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Table 3. Types of hydrogen donor agents 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Structure

Name

Structure

Name

Structure

Name

Tetralin

Dibenzanthracene

Tetrahydroacenaphthene

Decalin

Pyrene

Benzoquinoline

Naphthalene

1,2,3,6,7,8-hexahydropyrene

1,2,3,4Tetrahydroquinoline

Toluene

Benzopyrene

Quinoline

Benzene

Methylnaphthalene

Indoline

Cyclohexane

Dimethylnaphthalene

Tetrahydrofuran

Perylene

Azapyrene

Tetrahydrofluoranthene

Coronene

Biphenyl

Alkyl-ester sulfonate copper

Anthracene

Arylamine

Syngas

1,4,5,8,9,10Hexahydroanthracene

Acridine

Metanol

1,2,3,4,5,6,7,8octahydroanthracen

1,1’-Binaphthyl

Etanol

9,10-dihydroanthrace

Dibenziltoluene

Acetone

9,10-Dihydrophenanthrene

Indane

Ethyl acetate

Phenanthrene

Acenaphthene

n-heptane

Benzanthracene

Fluoranthene

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Energy & Fuels

Table 4. Direct coal liquefaction technologies89 Single stage processes Country USA

Germany Japan

Two-stage processes

Process / Company SCR I, II / Gulf Oil EDS /Exxon H-Coal / HTI Conoco Zinc Chloride / Conoco Kohleoel / Ruhrkohle Imhausen NEDOL / NEDO

Country USA

UK

Japan

Germany

Process / Company CTSL / USDOE/HTI CSF / Consolidation coal Co Lummus ISTL / Lummus Crest Chevron coal liquefaction CCLP/ chevron Kerr-McGee ITSL / Kerr- McGee Amoco CC-TSL / Amoco Liquid solvent extraction (LSE) / British Coal corporation Supercritical Gas Extraction (SGE) / British Coal corporation Brown Coal Liquefaction (BCL) / NEDO Mitsubishi Solvolysis / Mitsubishi Heavy Industries Pyrosol / Saarbergwerke


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Figures caption

Figure 1. Hydrogenation-dehydrogenation scheme for decalin, tetralin, and naphthalene. Figure 2. Equilibrium constants for gas phase hydrogenation-dehydrogenation of the decalintetralin-naphthalene system. Figure 3. Tetralin degradation in naphthalene by direct dehydrogenation. Figure 4. Naphthalene hydrogenation reaction. Figure 5. Aromatic condensation to (a) biphenyl, (b) binaphthyl, and (c) formation of polyaromatic solid. Figure 6. Proposed network of pyrene hydrogenation: (A) pyrene, (B) 4,5-dihydropyrene, (C) 4,5,9,10-tetrahydropyren, (D) 1,2,3,6,7,8-hexahydropyrene, (E) 1,2,3,3a,4,5-hexahydropyrene, (F) 1,2,3,3a,4,5,5a,6,7,8-decahydropyrene and (G) perhydropyrene. Figure 7. DDQ abstraction of two donor hydrogens per molecule


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Energy & Fuels

H

H

trans-decalin H

+3H2 tetralin

+2H2 naphthalene

H

cis-decalin

Figure 1


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2


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+R•

+R•

-H

•

+R•

+ H•

,

+ H•

,

Figure 3


-H

+ R•

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Disintegration products with low molecular weight

cis-decalin H

3H2 H

2H2

Page 34 of 37


Hydrogenolysis products / ring opening / isomerization with high molecular weight

R

+

3H2

H

Hydrogenolysis products / ring opening / isomerization with high molecular weight

H R

+

+ …

trans-decalin

Figure 4



+ …

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Energy & Fuels

2

+ H2 (a)

+ H2

2

(b)

R• + Aromatic R-aromatic polyaromatics + solids R• + solids R-solids deposit/large particles

(c)

Figure 5


Energy & Fuels

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A

B

D

E

G

H

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C

F

Figure 6


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Energy & Fuels

OH

O Cl +

CN +

2 Cl

CN

CN

Cl

CN

2 OH

O Tetralin

Cl

DDQ

Naphthalene

Figure 7


DDQ-H2

Use of Hydrogen Donors for Partial Upgrading of ... - ACS Publications

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