Sulfur Removal And Phenol Separation From Oils By Acid-Base Interaction

Oil products, i.e., gasoline, diesel, coal tar oil, other coal liquid, etc, are mainly produced by petroleum refining and coal processing. They are important source of energy and chemicals. The fuel oils stemmed from petroleum have large amount of thiophenic sulfurs, and these S-containing oils results in increasingly severe environmental problem, e.g., the weather with smog, PM2.5 pollution, and acidic rain. Thus, the technology of oil desulfurization is quite crucial. For the coal tar oils derived from coal, meanwhile, they have a lot of valuable chemicals that are regarded as materials of organic chemical industry. Among the process, the separation of phenolic compounds from coal tar oil shows commercial value and application prospective.For the desulfurization of fuel oils, traditional hydrodesulfurization (HDS), which shows severe condition, octane number loss, and difficulty in desulfurizing low S-content oils, has hardly met the current demand of sulfur limit. The non-HDS technologies are widely studied and used, including adsorptive desulfurization (ADS), extractive desulfurization (EDS), and oxidative desulfurization (ODS). Based on Lewis acid-base interaction, ADS, EDS, and ODS for model and real oils were investigated in this thesis.First, this thesis studied ADS performance of four Lewis acids AlCl3, FeCl3, ZnCl2, and CuCl for 3-methyl thiophene (3-MT), benzothiophene (BT), and dibenzothiophene (DBT). The results showed that AlCl3 and FeCl3 had good desulfurization performance, and that thiophenic compounds showed the adsorptive activity order of 3-MT> BT> DBT. Further, AlCl3 can strongly interact with 3-MT, showing the S-capacity of 141 mgS/g in n-octane oil and 123 mgS/g in the oil containing 25 wt%toluene. Meanwhile, AlCl3can adsorb BT as well, accompanying with the oligomerization of BT itself. The oligomerization was proven to be beneficial to the BT removal. For DBT, AICl3 cannot adsorb it from oils effectively. Ultimately, hard and soft acids and bases theory was used to analyze the desulfurization mechanism in this system. It was found that thiophenic compounds were both hard and soft bases. The a-lone pair electron on S-atom was the region of hard base, the π-electron system of aromatic ring was the region of soft base, and the electron density of hard or soft region referred to the basicity of corresponding part.Then, the method of softening hard acid AlCl3 by alkyl halides was proposed to improve the desulfurization performance of AlCl3 (hard acid) for DBT (soft base). It was found that t-C4H9Cl, n-C4H9Cl, t-C4H9Br, and n-C4H9Br can soften AlCl3, and that some viscous liquids containing carbonium ion formed during the process. These liquids were named as carbonium pseudo ionic liquids (CPILs). The CPIL like t-C4H9Cl-AlCl3 included (CH3)3C+and dissolved AlCl3. For (CH3)3C+, the central C+was the hard acid region, and the plane formed by three groups of-CH3 was the soft acid region. Accordingly, CPIL could extract thiophenic sulfurs by both hard-hard and soft-soft interactions. The results indicated that CPIL can surprisingly desulfurize the model oil with or without toluene:three sulfurs were thoroughly removed by small amount of extractant within 20 min. With the complexing extraction processing, thiophenic compounds were partially alkylated. Moreover, CPIL can desulfurize the oils with complex composition (model gasoline and real oil). Sulfurs in light oil can be completely eliminated by CPIL; meanwhile, above 93%of sulfurs in heavy oil can be removed as well.Meanwhile, the method of hardening thiophenic sulfurs (soft bases) was proposed. Acetyl chloride (AC), propionyl chloride (PC), and butyryl chloride (BC) and Lewis acids AlCl3 can provide-C=O group to thiophenic compounds via Friedel-Crafts acylation, and the thiophenic sulfurs with-C=O group were adsorbed more readily by hard acid AlCl3. This method was named as acylation desulfurization (ACDS). The results showed that the AC-AICI3 had strong desulfurization activity:thiophene (T), BT, and DBT in model oils were completely removed within 20 min. The excellent ACDS of AC-AlCl3 was ascribed to the acylation that introduced-C=O group to sulfurs. This reaction increased the basicity of thiophenic sulfurs, improved their basic hardness, and accordingly enhanced the S-adsorption by strong and hard AlCl3. Further, the S-capacity of AlCl3 varied with AC adding to toluene-containing oils. With AC adding, the S-capacity of AlCl3 for T slightly decreased and approximately remained 120 mgS/g. For BT, the S-capacity of AlCl3 increased first and then decreased, showing the maximum data 75.4 mgS/g. For DBT, the S-capacity of AlCl3 continually grew with AC adding, showing the data from 0 to 27.3 mgS/g. Moreover, ACDS was also effective for real oil, showing the sulfur removal of above 84%and the S-capacity of 56.6 mgS/g.Further, the catalytic mechanism of Lewis-Bransted complex acid for ODS of thiophenic sulfurs was studied. Lewis acids (BF3, SnCl4, FeCl3, and ZnCl2) and Bransted acid (CH3COOH) were deemed as catalytic system, and Cr(VI) or Mn(VII) were selected as oxidant. DBT, BT, and T in model oils were oxidized and removed. In this complex acid system, Lewis acid was the core of, improving the Bransted acidity of complex acid by complexation with O atom of CH3COOH, enhancing the dissolution of Cr(VI), and catalyzing the S-oxidation. DBT was oxidized to its sulfone; whereas, BT and T were oxidized to some complicated products due to the oxidation of double bonds besides the oxidation of S-atom. The bond order and π-orbital electron occupancy of corresponding compounds containing double bond were calculated by quantum chemical method. The double bond reactivity of those compounds showed the order of benzene< toluene, DBTO2< DBT< T<BT <BTO2< TO2< cyclohexene. Finally, varying content and species of Lewis acid can adjust the acidity of complex acid successfully and thus control the S-oxidation selectivity effectively.For phenol separation from coal tar oil, conventional alkali washing method produces waste alkali, has complicated process, and costs a lot. In this thesis, phenol in oil was tried to be separated by chemical adsorption on the basis of acid-base interaction. AlCl3, hexamethylenetetramine (HMT), and triazole were used to adsorb phenol from model oils by Lewis acid-base interaction or H-bonding. The adsorptive behavior were experimentally investigated and theoretically analyzed. The results showed that the selected sorbents can adsorb phenol from model oil. HMT had best adsorption performance for phenol, showing the capacity of above 3500 mg/g, oil-insoluble property, and easy recycling. Thus, HMT was a highly effective sorbent for phenol. AlCl3 adsorbed phenol by strong Lewis acid-base interaction, the interaction energy was-111.5 kJ/mol, and thus sorbent was hard to be reused. Triazole was oil-soluble and showed relatively low adsorbance for phenol. Further, naphthalene and BT did not interfere with phenol adsorption on HMT, but accelerated the adsorption due to weak interaction between HMT or phenol and naphthalene or BT. The activation energy of adsorption reduced with naphthalene and BT adding. However, quinoline greatly hindered the adsorption of phenol on HMT. The adsorbance of HMT decreased to below 1000 mg/g. This phenomenon was ascribed to the fact that the quinoline showed strong interaction with phenol, and the interaction energy was-31.2 kJ/mol.Finally, two desulfurization systems regarding Lewis acid (AlCl3 and Cu(Ⅰ)-Y zeolite) were technically and financially estimated on the basis of experimental data obtained. The obtained data indicated that the two system selected were technically feasible, and that each had its own merits. AlCl3 system can inexpensively deal with oils containing Ts; meanwhile, Cu(Ⅰ)-Y zeolite system can cheaply treat oils with BTs. According to the financial evaluation of the two systems, both were financially feasible and could industrially scale up.