RU2065473C1 - Method of oil fraction selective refining - Google Patents

Abstract

FIELD: oil refining. SUBSTANCE: oil fraction is added to middle part of extractor and contacted with solvent which is added to its upper part in the presence of antisolvent. The latter is added to bottom part of extractor followed by solvent regeneration from raffinate and extractive solutions and raffinate and extract were obtained. Raffinate is distilled off and vapor zone is isolated and after cooling the first part of raffinate and liquid phase were obtained. Part of the first fraction is cooled to temperature not exceeding that at raffinate solution outlet from extractor top and added to extractor between raw and antisolvent addition. Remained part of liquid phase is removed as the second raffinate fraction. EFFECT: improved method of oil refining. 9 tbl, 2 dwg

Description

 The invention relates to the field of chemical technology and can be used in liquid extraction processes, in particular in the oil refining industry in installations for the purification of oil fractions by selective solvents such as phenol, furfural, N-dimethylpyrrolidone and others.

 A known method for the selective purification of oil fractions [1] is carried out by countercurrent contacting of the raw material (oil fraction) with a solvent (phenol) supplied to the upper zone (part) of the extractor. The closest in technical essence and the achieved effect to the proposed method, that is, the prototype, is a method for the selective purification of oil fractions by countercurrent contacting of raw materials (F) introduced into the middle part of the extractor with a solvent (S) introduced into the upper theoretical stage in the presence of an anti-solvent (phenolic water, C) supplied to the lower theoretical stage of the extractor, followed by regeneration of the solvent from the extract and raffinate solutions (Sr and St, respectively) in the regenerator blocks tion (2) to obtain a raffinate (r) and extract (e) [1] (Appendix 1).

 The main disadvantage of this method is the relatively low selection of raffinate. In addition, there are no reserves for increasing the efficiency of the liquid extraction process in industrial apparatus because of the small amounts of raffinate solution (risicle) in the zone below the input of raw materials ("distant" part of the extractor).

 The main objective of the present invention is to increase the selection of raffinate in the selective purification of oily oil fractions and obtain two fractions of raffinate.

 This goal is achieved by the fact that in the selective purification of oil fractions by countercurrent contacting of the raw material introduced into the middle part of the extractor with a solvent introduced into the upper theoretical stage of the extractor, in the presence of an anti-solvent fed to the lower theoretical stage of the extractor, followed by regeneration of the solvent from the extract and of raffinate solutions in regeneration units and obtaining raffinate and extract, the raffinate obtained after regeneration of the solvent is heated, subjected to the distillation process, the vapor phase is condensed, cooled and the first raffinate fraction is obtained, and part of the liquid phase is cooled to a temperature not exceeding the temperature at the outlet of the raffinate solution from the extractor, and introduced into the extractor in the form of recirculate to the second theoretical stage, counting from the bottom, between the input of raw materials and an anti-solvent, a second raffinate fraction is obtained from the remaining portion of the liquid phase.

 The introduction of recirculate into the extractor between the inputs of the feedstock and the anti-solvent allows for selective redistribution of the feed components and solvent associated with their different mutual solubility in the interacting counter flows of raffinate and extract solutions. As a result of this redistribution, there is an additional extraction of valuable raw materials from the extract solution entering the lower part of the extractor from the feed zone, and an increase in the selection of raffinate in terms of the weight of the feedstock.

 Due to the fact that at each theoretical (equilibrium) stage there is a mutual mass transfer of components between the interacting phases to the state of phase equilibrium, in the proposed method, the extract solution of the penultimate stage contains a certain amount of valuable raw materials, the loss of which is unacceptable.

 By acting on this solution with an anti-solvent (phenolic water), it is possible to isolate valuable hydrocarbons in the composition of the raffinate solution leaving the last step. This explains the choice of the place where the recirculate is introduced into the extractor, namely between the inputs of the raw material and the anti-solvent.

 The proposed method is implemented in a full extraction column (extractor), that is, consisting of a concentration part (above the input of raw materials), a feed zone and a distant part (below the input of raw materials). In contrast to the prototype, the claimed method enhances the efficiency of the distillation of the extractor by feeding recirculate between the inputs of the raw material and the anti-solvent, which allowed to increase the selection of raffinate.

 In addition, in the proposed method with the same initial positions (loading; temperature; composition of raw materials, solvent and antisolvent; number of theoretical steps) with a prototype phenol content in the extract solution is higher, which indicates greater efficiency of the process of selective purification of oil fractions. The increase and alignment of the mass internal flows of the raffinate solution in steps (apparatus height) leads to a more efficient interaction of the internal flows both in existing industrial extractors, especially those working at reduced feed rates, and in newly designed devices.

 Distillation of the raffinate obtained after regeneration of the solvent from the raffinate solution allows to obtain two fractions of the raffinate. The first fraction of the raffinate, depending on the distillation conditions, can be used as an additive to diesel fuel, a raw material for secondary processes (reforming, catalytic cracking, etc.), a concentrate of high molecular weight paraffin hydrocarbons and for other purposes. The second fraction of the raffinate serves to obtain a base base of oils. In case of industrial need, the method involves mixing these two fractions to obtain a basic base of oils.

 The set of distinguishing features described above provides new technical properties of the proposed method: it increases the selection of raffinate due to the organization of a higher efficiency of the distillation part and especially in the case of industrial machines at low loads, increases the phenol content in the extract solution, increases and evens out mass internal flows raffinate solution according to the steps (height) of the extractor, it becomes possible as a result of distillation of the raffinate to obtain two fractions of the raffinate, one of which can be applied for various purposes, and the second to obtain a basic base of oils.

 In FIG. 2 (application) presents a schematic diagram of the proposed method. It includes two main elements: an extractor (1) with a total number of theoretical (equilibrium) purification steps equal to five, as applied to the process of selective purification of oil raw materials with phenol, and an apparatus (4) for distilling the raffinate removed from the regeneration unit (2) of the raffinate solution.

 Raw materials (F) are supplied to the third, theoretical top contacting stage (in principle, several feed-in feeds can be provided for different stages), a solvent (phenol, S) is fed countercurrently to the upper part of the extractor (to the first theoretical stage), and to create risicla to the fifth theoretical stage is supplied with an anti-solvent (phenolic water, C). Between the feedings of the feedstock and the anti-solvent, recycle (P) is fed to the fourth theoretical stage. Extract solution E-5 is discharged from the bottom of the extractor, after the phenol (Se) is isolated from it in the regeneration unit (2), extract (e) is obtained, which is mainly undesirable components extracted with the solvent from the feedstock. From the top of the extractor, the raffinate solution (R-1) is discharged and enters the regeneration unit (2), where after separation of the solvent (Sr) from it, raffinate (r) is obtained. The regenerated solvent (Sr and Se) is returned to the extractor (1). The raffinate (r) is heated in a heat exchanger (3) and fed to the distillation apparatus (4), where vapor and liquid phases are obtained. The vapor phase, the fraction of selection (distillation) of which is d, is condensed and cooled in a condenser-cooler (6) and the first raffinate fraction (r1) is obtained. Part of the liquid phase is cooled in a condenser-refrigerator (5) to a temperature not exceeding the temperature at the outlet of the raffinate solution from the extractor, and introduced into the extractor in the form of recirculate (P) to the fourth stage, and from the remaining part of the liquid phase, a second raffinate fraction (r2 ) The first and raffinate fractions are oil fractions purified from undesirable components.

 To test the effectiveness of the proposed method on the example of selective purification of oil fractions with phenol, studies were conducted on a computer (electronic computer) adiabatic countercurrent multistage liquid extraction. Several series of calculations were carried out: the first corresponds to the known method (prototype), the rest to the proposed method.

 Preliminary laboratory studies have shown that the effectiveness of industrial extractors for the selective purification of various oil fractions is equivalent to three to five theoretical steps. In this regard, when cleaning the fourth oil fraction with phenol, a scheme with five theoretical stages, that is, with more stringent conditions, when it comes to increasing the yield of raffinate, was chosen as a prototype.

 There are two types of distillation [2] simple distillation (single partial evaporation of a liquid mixture) and rectification. The use of the rectification process is certainly more effective for the qualitative separation of raffinate than simple distillation. In this regard, to convincingly demonstrate the solution of the goals of the proposed method, as an example, a scheme with a single partial evaporation of the raffinate was selected as the worst case of separation of the initial mixture (raffinate).

 The temperatures of the feedstock, solvent, anti-solvent, their costs, yield and composition of the raffinate and extract depend on the characteristics of a particular process and the requirements for the quality and yield of raffinate.

 The amount of raw material (fourth oil fraction), solvent (flooded phenol) and anti-solvent (phenolic water), their input temperature, as well as the number of theoretical stages in the extractor were the same for all series of calculations. The ratio of these flows, their compositions and temperatures are taken in accordance with the technological regime of industrial plants for the selective purification of the fourth oil fraction with phenol.

 One of the main elements of computer calculation of countercurrent adiabatic multistage liquid extraction is the calculation of activity coefficients, for the calculation of which the group contribution method was used. For this, based on a group and chemical analysis of the raw materials, the raw materials were presented in the form of a model mixture consisting of twelve components (paraffins, isoparaffins, naphthenes, single-ring, multi-ring aromatics and other individual hydrocarbons) plus two components phenol and water. Thus, the calculation of the phase equilibrium between the interacting flows at each theoretical stage was carried out for 14 components.

Initial data:
the amount of input raw material, kg 200
the amount of phenol introduced, kg 340
the amount of introduced phenolic water, kg 6
input temperature of raw materials, ^o With 67
phenol input temperature, ^o С 73
temperature of phenolic water input, ^o С 30
phenol water content, mass percent 2
phenol content in water, mass percent 9
mass ratio of phenol raw materials 1.7: 1.0
The examples show the results of computer calculations for each series of "experiments" after the five-stage system reaches stationary mode, which was confirmed by the material balance (general and by components) of the process, the constancy of the quality and yield of raffinate and extract, as well as the constancy of internal liquid flows by mass and temperature profile in steps.

 The main parameters that have a decisive effect to achieve the goal of increasing the selection of raffinate by the proposed method are the quantity and temperature of the recirculate fed to the fourth stage.

To quantify the effect of each of these determining parameters on increasing the yield (selection) of the raffinate r, a large series of calculations ("experiments") were carried out on a computer with a wide variation in the values of these parameters for a given system. The amount of recycle was varied from 0 (prototype) to 200 kg, and its temperature was from 30 to 70 ^o C. Also, to study the effect of the composition of the recycle, the proportion of the distillate d raffinate r was varied from 4 to 14 wt.

 When implementing the proposed method in an industrial plant, it will be necessary to make the optimal choice of temperature and the amount of recirculate introduced into the extractor. It should be noted, in turn, that the amount of recirculate introduced into the extractor will depend not only on its temperature, but also on the specific parameters of the technological regime of purification, the physical nature and properties of both the raw material to be purified and the solvent. The operation mode of the distillation apparatus will be determined by the technical requirements for the quality of the fractions of raffinates r1 and r2.

 Example 1. The first series of "experiments" (computer calculations) was aimed at studying the prototype, that is, the known method for the selective purification of oil fractions. The following results were obtained that characterize the method for the selective purification of oil fractions by countercurrent contacting of the feed with phenol supplied to the upper part of the extractor in the presence of phenolic water (anti-solvent), followed by regeneration of phenol and obtaining raffinate and extract.

The selection of the raffinate r, wt. 68,2
The phenol content in the raffinate solution, wt. 16,2
The phenol content in the extract solution, wt. 80,4
The delamination factor for the first stage, molar 0.849
The delamination factor for the fourth stage, molar 0,989
The delamination factor for the fifth step, molar 0,944
The density of raw materials F at 20 ^o C, kg / m ³ 950,4
The refractive index of raw materials F at 20 ^o With 1,531205
The density of the raffinate r at 20 ^o C, kg / m ³ 877,2
The refractive index of the raffinate r at 20 ^o With 1.486510
The density of the extract e at 20 ^o C, kg / m ³ 949,6
The refractive index of the extract e at 20 ^o With 1,530774
Example 2. A large series of computer calculations ("experiments" was aimed at studying the extractor according to the proposed method, characterized in that the raffinate obtained after solvent regeneration is heated, subjected to a distillation process, the vapor phase is condensed, cooled and the first raffinate fraction is obtained, and part of the liquid phase is cooled to a temperature not exceeding the temperature at the outlet of the raffinate solution from the extractor, and introduced into the extractor to the second theoretical stage, counting from the bottom, between the input of the raw material and the anti-solvent, from avsheysya portion of the liquid phase obtained second fraction a raffinate.

 tables 4 to 9 (see the appendix) presents a part of the results of the calculations that demonstrate the possibility of achieving the goals and advantages of the proposed method compared to the prototype.

 The presented information about the results of the study of the prototype (application, table 1 3) and the method under consideration (table 4 9) allow us to make the following generalizations. The conducted studies confirm the fundamental possibility of increasing the yield (selection) of raffinate by the considered method. In particular, in the studied area, the influence of two determining factors on the increase in raffinate yield is shown: the amount and temperature of the recirculate (P) fed to the extractor (Table 4 and Table 5).

The selection of raffinate r increases to 13.1 wt. compared with the prototype with an increase in the supply of recirculate from 0 to 200 kg with a fixed temperature of 50 ^o C (table 4).

The selection of raffinate r increases to 15.3 wt. and up to 12.0 wt. (table 5), respectively, for the lower (30 ^o C) and upper (60 ^o C) temperatures of the recirculate. However, it should be noted that the increase in the selection of raffinate compared with the prototype begins when the quantities of recirculate in excess of 16 kg

The increased selection of raffinate under the influence of these factors (temperature and amount of recirculate) can be explained, in particular, by an increase in the temperature gradient along the height of the extractor (table 8) compared with the prototype (table 3). So, if for the prototype the temperature difference between the first and fifth steps is 2.7 ^o C, then for the method under consideration it varies from 3 ^o C to 19.5 ^o C, and there is an increase in the temperature gradient with an increase in the amount of recirculate supplied to the extractor at set temperature (table. 8).

 An increase in the temperature gradient contributes to more efficient cleaning during the extraction process: improved process selectivity, increased selection of valuable raw materials, etc. A significant decrease in temperature at the fourth and fifth steps is an additional source of creation of a risicle in the lower part of the extractor, which significantly improves the operation of the zone located below the input raw materials and contributes to an increase in the selection of raffinate with increasing supply of recirculate to the extractor.

 An important characteristic of gravitational type extractors is the difference in the densities of the oncoming flows of the raffinate and extract solutions interacting with each other in steps (apparatus height). Due to the small density difference Δρ in the distant part of industrial extractors operating according to the known method (prototype), ablation is observed together with the extract solution of the raffinate solution in the dispersed phase, which clearly reduces the yield of valuable raw materials in the raffinate.

 In the proposed method, there is an increase in the density difference between the raffinate and extract solutions, which is the driving force of the process of separation of the interacting phases in the extractor.

So for the prototype, the density difference Dr at the fourth stage is 0.4 kg / m ³ , and for the proposed method 85 kg / m ³ at a fixed flow rate of recirculate 120 kg (table 9). A noticeable increase in the density difference between the raffinate and extract solutions of Dr and in the middle part of the extractor (Table 9), which certainly contributes to an improvement in the efficiency of gravitational extractors. In particular, in industrial extraction apparatuses operating according to the proposed method, a decrease in the ablation of risicles is expected, especially in the area below the input of raw materials.

 The rationale for the selection of the limits of temperature change of the recirculate in the proposed method. The upper (maximum) temperature of the recirculate is the temperature of the raffinate solution (R-1), which is removed from the top of the extractor. If the temperature of the recirculate is higher than the accepted one, this will entail a complication of the pumping circuit of the recirculate: it is necessary to install an additional heater (heat exchanger) in parallel with the refrigerator, which will increase the cost of the process and energy consumption, complicate the process control, reduce the temperature gradient of the extractor (reduce the selectivity of the process ) and etc.

 The lower (lowest) value of the temperature of the recirculate is ambiguous and is determined by the conditions under which sufficient fluidity of the flow is ensured, which in turn depends on the nature of the raw material, solvent, and thermophysical properties of the recirculate, in particular, such as viscosity, density, pour point, heat capacity, etc. .

 Both a decrease in temperature and an increase in the amount of recirculator introduced into the extractor simultaneously contribute to an increase in the yield of raffinate, however, an increased selection of raffinate can lead to a deterioration in its quality characteristics (Table 6). When implementing the proposed method in industrial plants, it will be necessary to make the optimal choice of temperature and amount of the raffinate solution introduced into the extractor, based on a technical and economic analysis. However, it must be emphasized that the quality of the raffinate r, satisfying the technical requirements, is the determining criterion for the final selection of the analyzed two determining factors.

 It should also be noted that the amount of raffinate solution introduced into the extractor will depend not only on its temperature, but also on the specific parameters of the technological mode of the extraction process, the physical nature and properties of the raw material to be purified, as well as the maximum (permissible) total load of flows along the extractor’s cross section, features for existing equipment.

 An analysis of the data presented in tables 2 and 7 shows that the amount of extract solution in the fourth and fifth theoretical stages decreases with an increase in the amount of recirculate supplied to the extractor. At the same time, there is an increase in the flows of the raffinate solution and, accordingly, due to this, an increase in the total flows at each stage with the exception of the 5th (lower) stage. This indicates that the recirculate extracts a large proportion of valuable components from the extract solution (K-3), while a smaller fraction remains on the share of the anti-solvent. The total load of the extractor in the counter interacting flows of raffinate and extract solutions increases significantly with increasing amount of recirculate.

 In the proposed method, the distant, lower part of the extractor is "more efficiently earned" by feeding recirculate.

 The increased total load of the internal flows along the steps will allow to efficiently carry out the extraction process on existing industrial equipment, especially on that which currently operates at low capacities.

 An analysis of the effect of the amount of recirculated feed to the extractor at a given temperature (Table 4) shows an improvement in the efficiency (for example, selectivity) of the liquid extraction process. So, with an increase in the supply of recirculate, in addition to the main increase in the selection of raffinate, the phenol content in the extract solution increases to 4.7%. In addition, delamination factors (Fi), which are the ratio of the amount of extract solution to the amount of the initial mixture (Fi Ei / (Ei + Ri ) for each step, tend to decrease.

 Analysis of the calculation results for a given system shows that in order to increase the selection of raffinate, it is necessary to supply recirculate of about 32 kg or more. However, for other systems (various types of raw materials, temperature conditions, mass ratios of phenol raw materials, etc.), this value of the recycle can change.

 The proposed method allows to obtain two raffinates. The first raffinate t1 can have a multi-purpose purpose (a component of diesel fuel, raw materials for secondary oil refining processes, raw materials for the petrochemical industry, raw materials for the production of low melting paraffins, etc.). The second raffinate r2 is used to obtain a base oil base. In the case of distillation of the raffinate r by distillation, it becomes possible to control the quality of the raffinate r1 that meets the technical standards for use in the respective abovementioned purposes.

 The implementation of the proposed method in industrial plants is quite simple and does not require significant costs.

 Thus, as shown by the results of studies, the use of the proposed method for the selective purification of oil fractions will significantly increase the selection of raffinate and get two fractions of raffinate.

Bibliographic data
1. Chernozhukov N.I. Oil and gas processing technology. M. Chemistry, 1966, p. 114 (analogue), p. 134-136 (prototype).

 2. Kasatkin A.G. Basic processes and apparatuses of chemical technology. M. Chemistry, 1971, p. 496. TTT1 TTT2 TTT3

Claims (1)

 A method for the selective purification of oil fractions by countercurrent contacting of raw materials introduced into the middle part of the extractor with a solvent introduced into the upper part of the extractor in the presence of an anti-solvent supplied to the lower part of the extractor, followed by regeneration of the solvent from raffinate and extract solutions to obtain raffinate and extract, characterized in that the raffinate is subjected to distillation with the release of the vapor phase, after cooling which receive the first fraction of the raffinate, and the liquid phase, part of which is cooled they are pressed to a temperature not exceeding the temperature at the outlet of the raffinate solution from the top of the extractor, and introduced into the extractor between the inputs of the raw material and the anti-solvent and the remaining part of the liquid phase is withdrawn in the form of a second raffinate fraction.

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