Method for producing non-carcinogenic aromatic process oil

Abstract

The present invention relates to the chemical or petroleum-processing industry and can be used in the production of petroleum plasticizers for synthetic rubber and tyres. In the method for producing non-carcinogenic aromatic process oil, containing a PCA extract of less than 3.0% according to the IP-346 method, said method comprising purifying the oil fractions of petroleum with selective solvents and separating the extract, additionally processing the extract with a polar solvent and producing a raffinate as the end product, the polar solvent used is a mixture of dimethylsulphoxide and Nmethylpyrrolidone, which is used for preliminary processing of the extract, wherein, after the preliminary processing, the mixture of extract and polar solvent is filtered, divided and the light phase is sent to the additional processing of the extract with the polar solvent, and the heavy phase is sent to a polar solvent regeneration stage. The ratio of dimethylsulphoxide to N-methylpyrrolidone in the mixture is within the range of 1:0.1-0.5. The ratio of polar solvent to extract in the additional processing stage is within the range of 1.5-2.5:1. The ratio of polar solvent to extract in the preliminary processing stage is within the range of 0.1-0.3:1. The technical result consists in increasing the efficiency of the process by preventing the formation of an intermediate layer in the extractor column, by reducing the ratio of solvent:extract, and, as a consequence, by increasing the productivity of the plant, simplifying the process of drying the solvent, and eliminating a paraffin-naphthene solvent, which substantially simplifies the regeneration of extractant from the raffinate solution.

Claims

1. A process for producing non-carcinogenic aromatic process oil containing less than 3.0% of a PCA extract according to method IP-346, the process comprising the steps of: (a) refining a petroleum oil fraction with a solvent and extracting residual and distillate extracts from the refined fraction; (b) mixing the residual and distillate extracts with a polar solvent comprising a mixture of dimethyl sulphoxide and N-methylpyrrolidone, wherein a weight ratio of dimethyl sulphoxide to N-methylpyrrolidone is in a range of 1:0.1-0.5; (c) filtering a mixture of the extracts and the polar solvent formed in step (b) to provide (i) a light fraction comprising partially refined petroleum oil extracts and (ii) a heavy fraction comprising an extraction solution; (d) treating the light fraction with the polar solvent to produce a raffinate; and (e) regenerating the polar solvent with use of the heavy fraction.

2. The process according to claim 1, wherein a weight ratio of the polar solvent to the light fraction in step (d) is within a range of 1.5-2.5:1.

3. The process according to claim 1, wherein a weight ratio of the polar solvent to the residual and distillate extracts in step (b) is within a range of 0.1-0.3:1.

Description

DETAILED DESCRIPTION OF THE INVENTION AND BRIEF DESCRIPTION OF THE DRAWINGS

(1) A plant for producing non-carcinogenic aromatic process oil consists of a mixer 1 connected to a heat exchanger 2 and filter 3. The filter 3 is connected to a phase separator 4 connected to the bottom of extraction column 5 provided with a contact device 6. The top of extraction column 5 is connected to a heat exchanger 7. In the bottom of the column an interface level controller 8 is installed.

(2) The method for producing non-carcinogenic aromatic process oil is carried out as follows. By refining petroleum oil fractions and deasphaltizate with polar solventsphenols, N-methylpyrrolidone or furfurol by the known methods extractsresidual and distillate ones are recovered.

(3) The selective refining extract of petroleum oil fractions in a stream (V) through the heat exchanger 2 is directed in a stream (IV) to the mixer 1 for pretreatment. In the heat exchanger 2 the extract is heated by the known methods to the desired temperature (70-110 C.). A polar solventa mixture of dimethyl sulphoxide and N-methylpyrrolidone in the weight ratio of from 1:0.1 to 0.5 is directed to the mixture in a stream (III). The ratio of the polar solvent and the extract in the pretreatment step is in the range of from 0.1 to 0.3:1. Mixing carries out at a temperature of the column bottom equal to 70-110 C. The mixture may be chosen from standard industrially manufactured mixing devices providing sufficiently mixing petroleum extracts and polar solvents. From contacting an extract and polar solvent at the phase interface boundary coagulation (flotation) of very small inclusions of high carbon compounds and contaminations of mineral origin into larger particles takes place. Further the mixture of the extract and polar solvent in a stream (VI) is directed to the filter 3, wherein the separation of particles formed by mixing takes place. Filtering is carried out by the known methods providing the recovery of solid particles having a size less than 20 m, at a preferably temperature of 70-110 C. The filtrate in a stream (VIII) is periodically removed from the filter by the known methods and is directed to bitumen. Further the filtered mixture of the extract and polar solvent in a stream (VII) is provided to the separation to the phase separator 4 to produce a light phase (a partially refined petroleum oil fraction extract) and a heavy phase (an extraction solution). The phase separator 4 may be chosen from industrially manufactured gravity separators, centrifugal separators and liquid separators of other types providing sufficiently separating the light and heavy phases. The light phase in a stream (IX) is directed to the bottom of the extraction column 5 to additional treatment, the heavy phase in a stream (X) is directed to the step of regenerating the polar solvent. The extraction column 5 comprises a contact device 6 provided by the known method (disc rotor or regular packing, or dumped packing) to provide the efficient weight exchange and has gravity zones in the bottom and top to separate the light (raffinate) and heavy (extraction) phases. The column diameter and height depend on the desired capacity and number of theoretical plates to allow the best separation of components of the original extract.

(4) To the top of the extraction column 5 through the heat exchanger 7 in a stream (XI) a mixture of dimethyl sulphoxide and N-methylpyrrolidone in the weight ratio of 1:0.1 to 0.5 is fed. In the heat exchanger 7 the solvent mixture is heated to the temperature allowing temperatures at the top of column 5 within the range of from 80 to 120 C., the temperature of the column 5 bottom is 70-110 C. The ratio of polar solvent and extract in the additional treatment step is in the range of 1.5 to 2.5:1.

(5) From the bottom of the column 5 through the phase interface controller 8 in a stream (XIII) an extraction solution containing dimethyl sulphoxide, N-methylpyrrolidone, polycyclic aromatic hydrocarbons, resins and asphaltenes is withdrawn. From the top of the column in a stream XII a raffinate solution containing refined petroleum, N-methylpyrrolidone and dimethyl sulphoxide escapes. On completing the process the solvents are separated from the raffinate and extract by the known methods (underpressure distillation, reextraction). The raffinate is used as a process oil (plasticizer). The extract may be used as a component of fuel oil, in the production of bitumen and for some other purposes.

(6) As a polar solvent a mixture of dimethyl sulphoxide and N-methylpyrrolidone in the weight ratio of from 1:0.1 to 0.5 is used.

EXAMPLE 1

Comparative

(7) For extraction a column consisting of two glass shells having a diameter of 25 mm filled with a metal packing was used and having heating and cooling jackets.

(8) The temperature in the column was maintained by means of two thermostats one of which heated the upper heat exchanger and the upper shell, the other onethe lower shell and the lower heat exchanger.

(9) The extract obtained by solvent refining deasphaltizate with phenol containing 8.9% polycyclic aromatic hydrocarbons (PCA) according to the IP-346 method and 33.5% of aromatic carbon C.sub.a was fed by a dosing pump through the heat exchanger to the bottom of the extraction column. dimethyl sulphoxide (DMSO) was provided by a dosing pump through the heat exchanger to the top of the extraction column in the DMSO:extract weight ratio of 2.0:1. The temperature at the top of the column was 115 C., at the bottom of the column100 C.

(10) From the bottom of the column a raffinate solution containing refined petroleum and DMSO was withdrawn. From the bottom of the column through the phase interface controller an extraction solution containing DMSO, an extract of PCA and resins was withdrawn. At the phase interface level gradual accumulation of the intermediate layer is noticeable, the operation regime of the column is broken, the quality of refined petroleum degrades, that is why the dosages of the extract and DMSO had to be lowered by 30% for a month.

(11) After stripping the solvents refined petroleum used as a plasticizer, and the extract containing PCA with three and more aromatic rings and resins which is a side product are produced. The produced non-carcinogenic aromatic process oil was analyzed for the content of a PCA extract and the content of aromatic carbon C.sub.a.

(12) The content of the PCA extract was determined by the IP-346 method. The determination is carried out by extracting an oil sample dissolved in cyclohexane with dimethyl sulphoxide followed by recovering PCA from the solution by means of cyclohexane and 4% aqueous sodium chloride solution and stripping cyclohexane from PCA by a rotary evaporator.

(13) The content of aromatic carbon C.sub.a was determined by the ASTM D 2140 method. The method consists in measuring the refraction index at 20 C., density at 20 C., and kinematic viscosity at 37.8 C. Further, according to the obtained measuring results the refraction intercept and weight-viscosity constant are calculated. Then according to the refraction intercept and weight-viscosity constant values on a diagram the content of aromatic carbon C.sub.a is determined.

(14) The properties of the produced non-carcinogenic aromatic process oil are given in Table 1.

EXAMPLE 2

(15) In a cylindrical apparatus with a stirrer and heating jacket at a temperature of 100 C. for 30 min there was mixed 3000 g of extract (the kinematic viscosity at 100 C. according to the ASTM D 445 is 21.6 mm.sup.2/s, the content of the PCA extract according to the IP-346 method is 8.9%, the content of aromatic carbon C.sub.a is 33.5%) and 600 g of a mixture of DMSO and NMP in a weight ratio of 1:0.1. The weight ratio of polar solvent and extract in the step of pretreatment is 0.2:1. The resulted mixture at a temperature of 100 C. was filtered through a metal filter having a pore size of not more than 20 m.

(16) The filter was loaded into the heated cylindrical underflow apparatus for full stratifying at a temperature of 100 C. After dividing the heavy phase was separated and sent to the regeneration of the polar solvent, the light phase was sent to the additional treatment of the extract with the polar solvent.

(17) The thus treated extract (without solvent separation) was further refined by the extraction method according to Example 1 with a mixture of dimethyl sulphoxide and N-methylpyrrolidone in the weight ratio of 0.1:1 in the extraction column under the following conditions: the temperature of the column bottom is 115 C., the weight ratio of polar extract and extract in the pretreatment step is 1.8:1, the total weight ratio of polar extract and extract in the pretreatment step and additional treatment step is 1.9:1. The polar solvent was separated from the non-carcinogenic aromatic process oil by the distillation method at a lower pressure (pressure 5 mbar, temperature 180 C.). The produced non-carcinogenic aromatic process oil was analyzed for the content of a PCA extract and the content of aromatic carbon C.sub.a.

(18) For the time of the continuous operation (during a month) an inconsiderable formation of an intermediate layer was noticeable, no decreasing the dosages was required.

(19) The results of additional treatment of the extract with polar solvents are given in Table 1.

EXAMPLES 3-6

(20) The process of preparation and additional treatment was carried out according to Example 2 of the description. The weight ratio of dimethyl sulphoxide and N-methylpyrrolidone in the mixer was varied within the range of 1:0.08-0.6. The results of refining the extract with polar solvents are given in Table 1.

(21) TABLE-US-00001 TABLE 1 Polar solvent/extract Yield of non- Composition of ratio in carcinogenic Content of polar solvent additional aromatic PCA extract aromatic Example DMSO/NMP treatment process oil, % content, % carbon Ca, % 1 1:0.sup. 2.0:1 90 3.2 27.8 (comparative) 2 1:0.1 1.8:1 89 2.9 27.4 3 1:0.08 1.8:1 90 3.1 27.8 4 1:0.3 1.8:1 88 2.7 26.5 5 1:0.5 1.8:1 87 2.7 25.9 6 1:0.6 1.8:1 85 2.7 24.6

(22) As seen from Table 1, when the dimethyl sulphoxide:N-methylpyrrolidone ratio in the mixture is less than 1:0.1 the resulted product does not meet the requirements for the indicator the PCA extract content according to the IP-346 method and is more than 3.0% (Example 3). When the dimethyl sulphoxide and N-methylpyrrolidone ratio in the mixture is more than 1:0.5 (Example 6) the extraction selectivity of polycyclic aromatic hydrocarbons reduces, consequently the carbon content of aromatic ring of less than 25% resulting thereby in deteriorating the properties of vulcanized rubbers of butadiene-styrene rubber (in particular, deteriorating protector coupling with wet asphalt), as well as the yield of final product decreases. In the prototype example a step of preliminary preparation of the extract is absent and the extraction column gradually is blocked with mechanical impurities.

EXAMPLES 7-11

(23) The process of preparation and additional treatment of the extract was carried out according to Example 2. The weight ratio of polar solvent and extract in the additional treatment step was varied within the range of 1.4-2.6:1.

(24) The results of refining the extract with polar solvents are given in Table 2.

(25) TABLE-US-00002 Polar solvent/extract Yield of non- Composition of ratio in carcinogenic Content of polar solvent additional aromatic PCA extract aromatic Example DMSO/NMP treatment process oil, % content, % carbon Ca, % 7 1:0.2 1.4:1 90 3.2 28.0 8 1:0.2 1.5:1 89 2.9 27.8 9 1:0.2 1.8:1 89 2.7 26.8 10 1:0.2 2.5:1 87 2.5 25.5 11 1:0.2 2.6:1 86 2.3 24.5

(26) As seen from Table 2, when the polar solvent:extract ratio in the mixture in the pretreatment step is less than 1.4:1, the resulted product does not meet the requirements for the PCA extract content according to the IP-346 method and is more than 3.0%/o (Example 7). When the polar solvent:extract ratio in the additional treatment step is more than 2.5:1 (Example 11) the extraction selectivity of polycyclic aromatic hydrocarbons reduces.

EXAMPLES 12-16

(27) The method was carried out according to Example 2. The weight ratio of polar solvent and extract in the pretreatment step was varied within the range of 0.07-0.4:1. The process of preparation and additional treatment of the extract was carried out according to Example 2 of the description.

(28) The total weight ratio of polar extract and extract in the pretreatment step and additional treatment step is 1.9:1. In Example 12 the polar solvent was fully mixed with the extract, the flotation of impurities did not occur. The formation of an intermediate layer in an extraction column is noticeable. The results of treating the extract with polar solvents are given in Table 3.

(29) TABLE-US-00003 TABLE 3 Polar solvent/extract The Polar ratio in Yield of non- presence of solvent/extract additional carcinogenic intermediate PCA Content of ratio in treatment in aromatic layer in the extract aromatic Example pretreatment column process oil, % column content, % carbon C.sub.a 12 0.07:1 1.83:1 89 Yes 3.1 28.0 13 0.1:1 1.8:1 89 No 2.9 27.4 14 0.2:1 1.7:1 89 No 2.8 27 2 15 0.3:1 1.6:1 87 No 2.8 26.8 16 0.4:1 1.5:1 86 No 3.1 26.0

(30) According to Examples 12-16 it is apparent when the polar solvent and extract ratio reduces below 0.1:1 in the pretreatment step (Example 12) no coagulation and flotation of contaminations take place, consequently contaminations come to the extraction column, an intermediate layer appears in the column deteriorating the extraction process. When the polar solvent and extract ratio increases above 3.0:1 in the pretreatment step the selectivity of the process (the content of aromatic carbon decreases, the content of PCA extract rises), the yield of final product and the quality thereof (Example 16) reduce.

EXAMPLE 17

Comparative

(31) The process of refining the extract is carried out according to Example 2 of the description. As a selective solvent dimethyl sulphoxide having a water content of 2% wt. was used. The results of refining the extract with polar solvents are given in Table 4.

EXAMPLE 18

(32) The process of refining the extract is carried out according to Example 2 of the description. As a selective solvent a mixture consisting of dimethyl sulphoxide (85% wt), N-methylpyrrolidone (13%) and water 2% wt was used. The results of refining the extract with polar solvents are given in Table 4.

(33) TABLE-US-00004 TABLE 4 Polar solvent/extract Yield of non- Composition of ratio in carcinogenic Content of polar solvent additional aromatic PCA extract aromatic Example DMSO/NMP treatment process oil, % content, % carbon C.sub.a, % 17 98/0/2 1.8/1 90 3.5 28.2 18 85/13/2 1.8/1 89 2.8 27.5

(34) When the dimethyl sulphoxide:N-methylpyrrolidone ratio is more than 1:0.5 the density difference of the selective solvent and extract a driving motive for the extraction process in a column extractor decreases, as the flow rate and, therefore, the agitating intensity reduce. The process selectivity decreases, as N-methylpyrrolidone has a higher dissolvability than dimethyl sulphoxide, and lower selective dissolubility to polycyclic aromatic hydrocarbons, therefore, the product yield decreases, the content of aromatic carbon lowers and, consequently, the compatibility with rubbers reduces. When the content of N-methylpyrrolidone is lower than 10%, the refining process compared to the prototype does not improve (Example 3).

(35) The weight ratio of the polar solvent and the extract in the additional treatment step is in the range of from 1.5 to 2.5:1. When the ratio of polar solvent and extract is lower than 1.5:1, refining from polycyclic aromatic hydrocarbons is more than 3.0% according to the IP-346 and the produced refined petroleum does not meet the requirements of the REACH European Union Directive. When the polar solvent and extract ratio is more than 2.5:1, the content of aromatic carbon according to the ASTM D 2140 declines, above that the energy demands for regeneration of solvents from an extraction solution rise and the capacity of the extraction column declines.

(36) The weight ratio of the polar solvent and the extract in the step of pretreatment is in the range of from 0.1 to 0.3:1. When the ratio of polar solvent and extract is lower than 0.1:1, no coagulation of impurities takes place as a consequence of forming a homogenous solution and the absence of a two-phase system. When the polar solvent and extract ratio is more than 0.3:1, the energy demands for regeneration of solvents increase.

(37) Thus, proposed is a new more efficient method for producing non-carcinogenic aromatic process oil having a content of PCA extract of less than 3.0% according to the IP-346 and a content of aromatic carbon according to the ASTM D 2140 of at least 25% suitable for use in mixtures with rubbers and RTA if reducing the energy demands of the refining process.

(38) The purpose of preventing getting mechanical contaminations into the column improving the plant capacity for producing a non-carcinogenic aromatic process oil is achieved.

(39) Introducing a pretreatment step and using a mixture of dimethyl sulphoxide and N-methylpyrrolidone allow lowering the polar solvent:extract ratio compared to the prototype method declining thereby the energy demands in the step of regenerating, stripping the solvent, improving the performance of the extraction step without complicating and appreciating the column contact devices, increasing the time of continuous operation of the column without cleaning the column contact devices and pump equipment declining thereby the specific production unit expenses, as well as expenditures for cleaning, washing and repairing the equipment.

(40) Also the method allows reducing the energy demands in the step of drying a solvent by reducing the reflux ratio and residence time of the solvent in the rectification column, as for extraction a solvent having a water content of more than 1% may be used.

(41) For ones skilled in the art other embodiments of the invention may be apparent without changing the substance thereof as it is disclosed in the present description. Accordingly, the invention should be regarded as limited in the scope only to the following claims.