High-density hydrocarbon fuels, as important components of jet fuels, are one of factors capable of deciding the performances of spacecraft, and the fuels may be mono-component hydrocarbon compound or mixtures comprising a plurality of hydrocarbon compounds. The fuels can be used in engines of turbojets, ramjets and rockets. Developments in the aerospace engineering have put forward high requirements on this kind of high-density fuels: on one hand, the high-density fuels are required to provide more propulsion kinetic energy under the circumstance that the volumes of fuel tanks are given, i.e., the fuels have higher density and higher volume caloric values; on the other hand, the high-density fuels are further required to have good low temperature flow ability.
Naphthalene-derived alkanes have a bicyclic fused-ring structure that is very stable, and thus they can be used as stabilizers in fuels, to inhibit thermal decomposition of the fuels. Naphthalene-derived alkanes are commonly prepared from coal-based compounds. Decalin is one of the naphthalene-derived alkanes, having a density of 0.88 g/mL, an ice point less than −30° C., and a net combustion caloric value higher than 37.4 MJ/L, and thus it, due to the good stability to heat and oxygen, is a predominant component of high-density jet fuels, for example, JP-900. Alkyl-substituted naphthalene-derived alkanes have good low-temperature flow ability and high thermal stability, while keeping high density.
Bicyclic fused-ring alkanes (e.g., naphthalene-derived alkanes) in the art are usually prepared by a two-step process or by a multi-step process. In the first step, selected raw materials, such as cycloalkenes or cyclitols, are used to synthesize unsaturated bicyclic compounds or oxygen-containing bicyclic compounds by the C—C coupling reaction. The corresponding product, after being purified by separations, undergoes the reaction in the second step, that is, under severe conditions, the unsaturated bicyclic compounds or the oxygen-containing bicyclic compounds undergo hydrogenation or deoxygenation to produce bicyclic fused-ring alkanes (such as naphthalene-derived alkanes). The prior art process involves the following defects:
1. The reaction operations are complex, and the yield of the corresponding product is low. For example, Zhang et al. (see ACS Sustainable Chem. Eng., 2016, 4 (11), 6160-6166) prepares the decalin with cyclopentanol as the raw material according to the following steps: the cyclopentanol is first catalytically dehydrated to produce cyclopentene that is purified by separation; then, the cyclopentene is catalytically alkylated to produce a precursor of decalin and other fuels, the precursor being purified by separation; at last, the precursor is hydrogenated under high pressure to produce decalin; the yield of the target product decalin is only 55.3%.
2. A C—C coupling reaction will produce a bicyclic fused-ring product and a linear bicyclic product, and accordingly, the final product obtainable after the hydrogenation also includes a bicyclic fused-ring alkane and a linear bicyclic alkane, wherein the bicyclic fused-ring alkane is the desirable target product. However, the molar ratio of the target product to the linear bicyclic alkane cannot be effectively controlled. Said bicyclic fused-ring product is meant to that the two rings share the same one C—C bond on a ring; said linear bicyclic product is meant to that the two rings are connected by one C—C bond that is not on a ring.
3. The hydrogenation reaction will highly require the catalyst and the associated apparatus used therein. For example, hydrogenating a unsaturated bicyclic compound, such as naphthalene, shall undergo a two-stage high-pressure hydrogenation process: in the first stage, the naphthalene is intermediately hydrogenated to produce tetralin, and a majority of sulfur present in the raw material is removed; in the second stage, the tetralin is deeply hydrogenated to produce decalin; in the process, the deep hydrogenation step of the tetralin is severe, and the temperature as required by the hydrogenation stage is high. In the hydrogenation steps, commonly-used catalysts include nickel catalysts, platinum-molybdenum catalysts, platinum-aluminum catalysts and nickel-aluminum catalysts; while the hydrogen gas pressure in the reaction is different according to different catalysts and reaction conditions as used therein, the pressure as required by the reaction is generally high, usually higher than 6 MPa, and even up to 20 MPa. In general, when the hydrogen gas pressure is lower than 6 MPa, the full hydrogenation will be hardly accomplished.
In the prior art, there are some processes for preparation of naphthalene-derived alkanes by hydrogenating naphthalene or naphthalene substitutes. However, the raw materials for these processes are naphthalene or naphthalene substitutes which are primarily derived from coal tar, a byproduct of coking, and from petroleum distillations, and they have few sources, which limits the scale industrial production of the naphthalene-derived alkanes. In addition, the aforementioned defects in the item 3 are still involved.
The Chinese patent with the application number 2017107835706 discloses a method for the preparation of an alkyl-substituted naphthalene-derived alkane. However, the method involves the following defects: a. catalysts used therein are required to have anacidity-H0 of greater than 12.3, and a working temperature of at most 120° C.; b. in the reaction, coking is severe, which results in rapid decrease of the activity of the catalyst; c. the yield of the product naphthalene-derived alkanes is low, generally 75% or below.
In order to overcome the aforementioned defects, the invention is proposed.