Study On Direct Catalytic Cracking Of High Tan Crude Oil

Along with increasing of crude oil's price, cost of crude oil is getting higher and higher and refinery's profit drops unceasingly. In the world, resources of high total acid number (TAN) crude oil are rich, and the price is lower than high quality crude oil. Refineries can obtain high profits if they processing high TAN crude oil. However, high TAN crude oil is the typical inferior crude oil with high TAN, high density, high viscosity, high carbon residue and high metal content. Processing high TAN crude oil can cause apparatus'serious corrosion. Moreover, content of light fraction is low and quality of VGO and VR is inferior in high TAN crude oil. These limit the processing of high TAN crude oil widely. Uses of FCC to process high TAN crude oil can not only avoid apparatus'corrosion, but also optimize product distribution, improve product quality, reduce processing line and save processing cost. So direct catalytic cracking of high TAN crude oil were studied in this paper.Firstly, thermal and catalytic conversion experiments of naphthenic acids were carried out in the fixed bed microreactor apparatus. The experimental results indicated that thermal decarboxylation rate was slow, and the decarboxylation ratio was low. Reaction temperature was the dominant influential factor of the thermal decarboxylation. Catalytic decarboxylation effect of naphthenic acids was remarkable. Influences of catalysts to catalytic decarboxylation ratio were indistinct. But catalytic decarboxylation products were different over various catalysts. Catalytic decarboxylation ratios of naphthenic acids over CORH and LTB-2 were 100% approximately. This ratio were not be affected by the reaction conditions, and CO was dominant catalytic decarboxylation product. Catalytic decarboxylation ratios of naphthenic acids overγ-Al2O3,MgO and CaO were lower slightly than that over CORH and LTB-2, and CO2 was dominant catalytic decarboxylation product. Although CaO and MgO are the basic oxides, decarboxylation mechanisms over these basic oxides are different. Catalytic decarboxylation was primary over MgO. Over CaO, there was not only catalytic decarboxylation, but also neutralization decarboxylation. The product of neutralization decarboxylation over CaO was calcium naphthenate. In addition, the straight running hydrocarbons can not affect the catalytic decarboxylation of naphthenic acids.Molecular simulation's results showed the catalytic decarboxylation mechanisms of different type naphthenic acids were different over Bronsted acid site. If the carboxyl group connected to the naphthene directly, there are two reaction pathways. Opening ring firstly and then decarboxylation is the domaint reaction pathway. If the carboxyl group connected to the naphthene through alkyl chain, catalytic decarboxylation mechanism was similar to the carbonium ion reaction mechanism. The bond orders changed after ketonic oxygen contacted to the Bronsted acid site. Bond ofβposition broke to produce methanoic acid, and then the methanoic acid decomposed to CO and H2O. Adsorptive capacities of naphthenic acids and basic nitrogen-containing compounds in porous channels of zeolites were different. Combining capacities of basic nitrogen-containing compounds and zeolites were higher than that of naphthenic acids. As a result of the steric effect, adsorptive capacities of small molecular compounds in porous channels of zeolites were even more.Although the quality of Sudanese Dar high TAN crude oil was inferior, it was very easy to catalytic crack because of the paraffin performance. Conversion was above 90% and liquid yield was above 80% at the condition of reaction temperature of 460℃, residence time of 1.15s and ratio of catalyst to oil of 6. Content of propylene and butylenes in LPG surpassed 80%. Olefins content in gasoline was under 40%. Because carbon residue was more than 8%, coke yield of Sudanese Dar high TAN crude oil was high in catalytic cracking process. Commercial test for catalytic cracking of Sudanese Dar high TAN crude oil verified the research results in laboratory, and more superior product distribution was obtained. Single-through conversion of the crude oil was very high, so recycle oil and slurry oil didn't need to reprocess. However, high coke yield made the carbon burning load of regenerator to increase greatly. This changed the heat distribution of reaction reproduction system. Heat to warm up the air that needed to burning coke was the main heat consumption. As a result of the existence of distillation diesel in crude oil, quality of the catalytic cracking diesel from Sudanese Dar high TAN crude oil was better than traditional catalytic cracking diesel, and the acidity was also qualified.Economic analyses for various processing schemes of Sudanese Dar high TAN crude oil indicated that direct catalytic cracking had the best economic efficiency. Total cost of the products was more 350 yuan/t than that of tranditional processing scheme, and was more 428 yuan/t than that of delayed coking scheme. Although energy consumption of catalytic cracking process was higher than that of delayed coking process and tranditional processing scheme, gross profit was more than 317 yuan/t and 315 yuan/t. If including the costs of various demulsifier, defoamer, corrosion inhibitor and labour, the profit difference would further increase.