Refining process

The discovery of the process for the separation of tantalum and niobium using fluorination marked, in fact, the beginning of the development of the chemistry and technology of tantalum and niobium in general, and initiated the development of complex fluoride compound chemistry in particular. 

Two main methods exist for the production of tantalum and niobium from the mineral raw material. The first method is based on the chlorination of raw material, followed by separation and purification by distillation of tantalum and niobium in the form of pentachlorides, TaCl5 and NbCl5 [24, 29]. Boiling points of tantalum and niobium pentachlorides (236°C and 248°C, respectively) are relatively low and are far enough apart to enable separation by distillation. 

Two types of chlorination processes are used for the different kinds of raw material. The first process is a reductive process by which oxide-type raw materials in the form of ores or concentrates are chlorinated. The essence of this process is the interaction with chlorine gas in the presence of coal or other related material. 

Chlorination of ferroalloys (ferroniobium-tantalum) is a more economical and simple alternative [30]. The process is performed on a sodium chloride melt that contains iron trichloride, FeCL. Chlorine is passed through the melt yielding NaFeCfi, which interacts as a chlorination agent with the Fe-Nb-Ta alloy. Chlorination of ferroalloys allows for the production of pure tantalum and niobium pentachlorides, which are used further in the production of high purity oxides and other products. 

The performance of different types of chlorination processes is discussed comprehensively in overview [31]. It should be mentioned that carbon tetrachloride can also be applied successfully in the chlorination of rare refractory metal oxides, including tantalum oxide. 

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A knowledge of these compounds is important because they often have undesirable attributes, e.g., unpleasant odor, the SO2 formed by combustion, catalyst poisoning. There are a number of refining processes to eliminate sulfur compounds. 

Following certain refining processes like catalytic cracking, sizeable amounts of nitrogen can appear in light cuts and cause quality problems such as instability in storage, brown color, and gums. 

The determination of the elemental composition of a petroleum cut is of prime importance because it provides a quick means of finding out the quality of a given cut or determining the efficiency of a refining process. In fact, the quality of a cut generally increases with the H/C ratio and in all cases, with a decrease in hetero-element (nitrogen, sulfur, and metals) content. 

For many years the development of refining processes and the formulation of gasolines has centered around the octane number. It is therefore appropriate to explain briefly what is the current situation and what are the prospects in this area. 

Finally, it is by means of synergy between the refining processes and the combustion techniques that the emissions of NO due to industrial installations can be minimized. 

Since the discovery of petroleum, the rational utilization of the fractions that compose it has strongly influenced the development of refining processes as well as their arrangement in refining flowsheets. 

Properly speaking, steam cracking is not a refining process. A key petrochemical process, it has the purpose of producing ethylene, propylene, butadiene, butenes and aromatics (BTX) mainly from light fractions of crude oil (LPG, naphthas), but also from heavy fractions hydrotreated or not (paraffinic vacuum distillates, residue from hydrocracking HOC). 

Here again, this is not a refining process, properly speaking. Partial oxidation is one of the processes for the ultimate conversion of heavy residues, asphalts, coke and even coal. 

Catalytic cracking is a key refining process along with catalytic reforming and alkylation for the production of gasoline. Operating at low pressure and in the gas phase, it uses the catalyst as a solid heat transfer medium. The reaction temperature is 500-540°C and residence time is on the order of one second. 

Heinrich, G., R. Bonnifay, J.-L. Mauleon, M. Demar and M.A. Silverman (1993), Advances in FCC design. Parts 1 and 11 . Refining process services Seminar, Amsterdam. 

Separation of Fatty Acids. Tall oil is a by-product of the pulp and paper manufacturiag process and contains a spectmm of fatty acids, such as palmitic, stearic, oleic, and linoleic acids, and rosia acids, such as abietic acid. The conventional refining process to recover these fatty acids iavolves iatensive distillation under vacuum. This process does not yield high purity fatty acids, and moreover, a significant degradation of fatty acids occurs because of the high process temperatures. These fatty and rosia acids can be separated usiag a UOP Sorbex process (93—99) (Tables 8 and 9). 

Many of the impurities are much lower than the values shown in Table 3, but these analytical lower limits are typical and more than sufficient for all but special appHcations. Zirconium content can be from 0.01 to 4.5%, and is typically 0.5—2%, but this is a function of how far the separation process was carried, not a function of the reduction or refining processes. 

Hafnium tetrabromide [13777-22-5], HfBr, is very similar to the tetrachloride in both its physical and chemical properties. Hafnium tetraiodide [13777-23-6], Hfl, is produced by reaction of iodine with hafnium metal at 300°C or higher. At temperatures above 1200°C, the iodide dissociates to hafnium metal and iodine. These two reactions are the basis for the iodide-bar refining process. Hafnium iodide is reported to have three stable crystalline forms at 263—405°C (60). 

Immobile hydrocarbon sources requite refining processes involving hydrogenation. Additional hydrogen is also requited to eliminate sources of sulfur and nitrogen oxides that would be emitted to the environment. Resources can be classified as mostiy consumed, proven but stiU in the ground, and yet to be discovered. A reasonable estimate for the proven reserves for cmde oil is estimated at 140 x 10 t (1.0 x 10 bbl) (4). In 1950 the United States proven reserves were 32% of the world s reserve. In 1975 this percentage had decreased to 5%, and by 1993 it was down to 2.5%. Since 1950 the dominance of... 

Fig. 12. Flow diagram of a fumace-ketde and/or aH-ketde lead refining process.

Refining Processes. AH the reduction processes yield an impure metal containing some of the minor elements present in the concentrate, eg, cadmium in 2inc, or some elements introduced during the smelting process, eg, carbon in pig iron. These impurities must be removed from the cmde metal in order to meet specifications for use. Refining operations may be classified according to the kind of phases involved in the process, ie, separation of a vapor from a Hquid or soHd, separation of a soHd from a Hquid, or transfer between two Hquid phases. In addition, they may be characterized by whether or not they involve oxidation—reduction reactions. 

Steelmaking. Steelmaking is the most economically important slag refining process (see Steel). Pig iron contains up to 4% carbon, 1% manganese, 1%... 

It is frequendy advantageous to favor rapid disengagement of HCl by operating the reaction in an inert solvent such as an alkane. The pure triesters are recovered by a multistep refining process (Fig. 5). 

Conventional Refining Process. The conventional refining process is based on complex selective dissolution and precipitation techniques. The exact process at each refinery differs in detail (12—14), but a typical scheme is outlined in Figure 2. 

Refining Process Handbook," Hydrocarbon Process., 121 (Sept. 1978). 

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