Catalytic Dewaxing for Lube Oil Production

Abstract

The selective cracking of long-chain normal paraffin's of medium neutral raffinate, derived from a lube oil-phenol extraction unit, by the catalytic dewaxing technique over H-ZSM-5 and NiMo-H-mordenite catalysts was studied. The runs were conducted to produce lube oils with acceptable cold flow properties. The influences of zeolite types, metals loading, and operating reactor temperatures (290°C–475°C) can have a great effect on cracking high pour point n-paraffins into lower ones, and hence a reduction in pour points. An increase in temperature (between 290°C and 375°C) increased wax conversion (percent dewaxing) on H-ZSM-5 compared with NiMo-H-mordenite catalysts due to its higher cracking activity. As a result, large amounts of C₁-C₄ gases and C₅-170°C naphtha were produced. The low pour point lube oils produced from catalytic dewaxing over H-ZSM-5 compared with NiMo-H-mordenite catalyst indicates that the former was more selective for removing wax components than the later. On the other hand, high concentrations of aromatics were obtained on both catalysts, since the waxy paraffins are converted to lower boiling products. The reduction in dewaxed pour points (Δpp) was observed to be in the range of 38°C–42°C over H-ZSM-5, compared to 37°C–40°C over NiMo-H-mordenite at the same reaction temperature ranges (290°C–375°C), but NiMo-H-mordenite has advantages at higher temperature ranges (above 375°C) in pour point reduction (Δpp range: 41°C–42.5°C). The addition of bimetallic components to the mordenite-catalyst enhances its activity, and the rate of normal paraffin cracking was increased due to the hydrogenolysis activity of the active metals. This means that the bimetallic H-mordenite catalyst has the advantage over H-ZSM-5 in its refining activities (hydrodesulfurization HDS] and hydrodenitrogenation HDN]) under the tested operating conditions. These results may be attributed to shape-selective discriminating behavior due to differences in zeolite pore openings (i.e., 6.5 × 7.0 Å for mordenite and 5.3 × 5.6 Å for ZSM-5). In other words, a combination of isomerization and selective cracking reactions of high n-paraffins may occur during the dewaxing process using NiMo-H-mordenite catalyst. The influences of process parameters (temperature, pressure, and liquid hourly space velocity LHSV]) on the relations between wax conversion to maintain maximum low pour points and maximum dewaxed oil yields or minimum yields of the least desired gases were optimized to produce dewaxed lube oils of acceptable characteristics.