The Research On Preparation Of High Octane Gasoline Component From Coal Tar Light Oil

Fluid Catalytic Cracking (FCC) Gasoline is the main components of domestic gasoline, the representative characteristics of which are high-sulfur, high-ene, low aromatic, what’s more, hydrodesulfurization (HDS) will also lead to a significant decline in octane number (RON) that is not high. At present, a large amount of methyl tert-butyl ether (MTBE) that is environmentally harmful was added to gasoline to increase its RON by refiners, beacuse the technologies for producing high-octane oil products(Reformate, Isomerization oil, Aromatization oil, et al) are relatively backward. A byproduct of coal chemical industry-coal tar light oil (CTLO), whose carbon atoms and distillation range is quite similar to gasoline, the dominant compounds are monocyclic aromatic hydrocarbons that have high octane number. Compared with the motor gasoline national standard V, CTLO could be used as excellent high aromatic and high octane gasoline blending component if the benzene, unsaturated hydrocarbons and heterocyclic compounds in it were effectively removed. The present method is also providing a new and efficient direction for high value-added utilization of CTLO, meanwhile, which also has far-reaching significance in promoting development of deep processing of coal tar.The whole component and heteroatom compounds of CTLO and the product oil were qualitatively and quantitatively analyzed by high-efficiency gas chromatography-mass spectrometry(GC-MS). The efficient conventional catalysts NiMo/η-Al2O3, CoMo/η-Al2O3, NiMo/γ-Al2O3 and CoMo/γ-Al203 were prepared by incipient-wetness impregnation method in paper. With CTLO as raw material, author has investigated the effects of the order of one-stage or two-stage hydrogenation process and distillation process upon the reaction in high pressure fixed bed reactor, the optimal hydro-upgrading process was obtained by comparing benzene, sulfur content, bromine value and octane number among several processes, on this basis, the process parameters were optimized. The adaptation of the four conventional catalysts in CTLO hydro-upgrading was investigated and the best one was screened according to some targets. The influences over the physical and chemical properties of modified catalysts by different phosphate loading were studied by means of N2-BET, XRD, H2-TPR and NH3-TPD. Furthermore, the structure-activity relationship for modified catalyst was investigated along with the activity evaluation reaction, the efficient catalysts matching the CTLO characteristics were screened finally. The high purity, high-octane gasoline blending component was obtained from CTLO by upgrading. The main contents and results are concluded as follows:1. With a byproduct of coal chemical industry-CTLO that has numerous aromatic and rarely olefins as raw material, to prepare high-octane gasoline blending component is absolutely feasible after hydro-upgrading via highly efficient hydrotreating catalyst in miniature high pressure fixed bed reactor.2. Taking into account benzene, sulfur content, bromine value, RON and the economic investment, one-stage hydrogenation-rectification can be used as the process for producing high-octane gasoline blending component from CTLO. On this basis, the process parameters were optimized:temperature is 300-340℃, pressure is 2.8-3.0 MPa; H2/Oil ratio is 700-900:1 and liquid hourly space velocity is 0.3-0.5 h-1, and they can be appropriately adjusted in accordance with their own objectives and requirements of raw materials and product features.3. The low-temperature reduction of catalyst was more improved by Ni, thus, a larger number of octahedrally coordinated Mo species was enhanced at the same time; The amount of middle-strong acid in Ni(Co)Mo/η-Al2O3 was larger than in Ni(Co)Mo/y-Al2O3; More number of octahedrally coordinated Mo species exist in η-Al2O3-supported catalysts, thence having more CoMoS phase in the form of higher activity Type II. Despite the sulfur content of product oil from NiMo/η-Al2O3 completely meets the requirements of motor gasoline national standard V, loss of octane number was excessive. The demand of the purpose of product and other indicators were fully considered, CoMo/η-A12O3 is closer to the requirements of CTLO because of that has special isomerization function over xylene. In addition,3-methylthiophene is most easily removed from CTLO; followed by the thiophene; 2-methylthiophene is the hardest.4. Phosphorus can not only improve metal dispersion over η-Al2O3, but also weaken the strong interaction between Mo and η-Al2O3. More importantly, the catalysts modified by appropriate phosphorus exhibit excellent performance of low-temperature reduction as confirmed by TPR as a result of increased octahedral Mo species. In addition, the results from NH3-TPD show that the addition of phosphate significantly alters the acidity of the catalyst, while the number of strong acid sites is reduced, the concentration of medium strength acid sites is progressively increased with increasing phosphate level, and its mechanism is the added phosphate changes the number of -OH and its acid strength. In this study the total acidity(0.5291 mmol/g) and the number of middle-strong acid were the largest when the catalyst was modified by 1.5 wt% phosphate.5. The rate-determining step for HDN under this system is the hydrogenation of the pyridine ring. The phosphate-added catalyst showed better activity of the hydrogenation reaction of naphthalene compared to the conventional catalysts, the generated tetralin acts as hydrogen-donating solvent in CTLO, thus it is beneficial to the deep HDS, HDN and HDO to a certain extent. The various advantageous effects of appropriate phosphorus upon HDS, HDN and HDO; however, the performance of catalyst was deteriorated by excessive phosphorus because AlPO4 was formed from the excess phosphate and Al2O3 and the specific surface was significantly reduced.6. Modified catalysts by P loading in the range 1.0-1.5 wt% can meet the requirements of CTLO, the result demonstrated excellent activity and stability of CoMoP1.0/η-Al2O3 and COMOP1.5/η-Al2O3 in the 360h stability test. Taking CoMoP1.5/η-Al2O3 as an example, the density(763 kg/m3), benzene content(0.07%) and sulfur content(7.2 mg/kg) of the product oil completely meet the requirements of motor gasoline national standard V; Furthermore, CTLO treated by the upgrading process can be used as high quality, high-aromatic and high octane gasoline component, in which nitrogen content is 0.058%, oxygen content is 0.021%, bromine number is 0.37 gBr/100g and RON is up to 105.3.