ITRM960487A1 - PROCESS AND ADDITIVE TO INCREASE THE YIELD IN THERMAL CONVERSION OPERATIONS IN OIL PLANTS - Google Patents

Abstract

A method and composition of additive to increase yield in medium distillates or to obtain a TAR with a higher level of stability in thermal conversion operations, in particular in Visbreaking, in petroleum plants used to refine crude products with a high paraffin content, where a catechol derivative-based additive is continuously added during the process.

Description

DESCRIPTION of the industrial invention entitled: "PROCEDURE AND ADDITIVE TO INCREASE THE YIELD IN THERMAL CONVERSION OPERATIONS IN PETROLEUM PLANTS"

DESCRIPTION

The present invention relates to a process and an additive composition to be used in a thermal conversion operation in petroleum plants starting from a feed formed by a residue of crude oil with a high content of paraffinic components.

In oil plants, thermal conversion processes are carried out to split the larger molecules of hydrocarbons, particularly hydrocarbons having a boiling temperature above 350 ° C, into smaller molecules of hydrocarbons with a lower boiling point. The conversion processes transform the heavy residues obtained in the petroleum refining industry into more easily marketable products consisting of intermediate or light cuts.

The conversion operation can follow different and distinct technologies consequently with different technical names such as Visbreaking, Coking, Hydrocracking, Thermal Cracking.

In particular, Visbreaking (VSB) has acquired a certain importance in Europe and in the industrial countries due to the contraction of the fuel oil market and the expansion of the consumption of middle distillates, in particular diesel for transport.

The VSB plant is schematically constituted by the following parts: a train of exchangers into which the feed charge enters for preheating, then a furnace in which the actual thermal cracking takes place, then a fractionation column from the bottom of which it exits the residue (TAR) that passes through the exchangers, releasing part of its heat to the charge. It is also possible to provide a "soaker" between the oven and the fractionation column.

The operating conditions of such a thermal cracking plant are briefly the following: a charge consisting of a residue of primary distillation or vacuum is introduced into the furnace which operates at temperatures of 420-500 ° C (in case of presence or absence of "soaker") at pressures between 3 and 20 bar.

The charge thus treated goes to a fractionation column from which light distillates (3 to 10% by weight approximately) middle distillates (15-20% by weight) and a residue (TAR 65-75% by weight of the charge) are obtained .

The plants are sized in such a way as to allow residence times at the cracking temperature such as to carry out the conversions required by the process.

The term "conversion yield" refers to the percentage of light and medium distillates (gas, petrol, diesel) with respect to the total charge. The products thus obtained from the fractionation column have the following final destinations:

a) gas and LPG usually enter the refinery network;

b) gasolines (generally high octane) go to the gasoline "pool" after hydrogenation and desulphurization;

c) unstable gas oils, showing a marked tendency to polymerization, are used as far as possible, after any hydrogenation, as components of finished gas oils or as fluxes; And

d) the residue (TAR) present in a higher rate is unstable due to the presence of unsaturated compounds and cracking by-products (coke and asphaltenes) and is transformed into fuel oil.

The VSB process is managed with the aim of obtaining a maximum transformation into medium and light distillates to meet the needs of the market.

It should be noted that a conversion increase equal to 1% of the charge treated is to be considered extremely satisfactory in terms of economic yield.

The limiting factor in obtaining high conversions is the need to obtain a residue (TAR) with qualitative characteristics such as to comply with the specifications imposed by the markets for the resulting fuel oil.

The quality of the TAR is evaluated with reference to specifications relating to the following parameters: stability, percentage of asphaltenes, viscosity.

In fact, increasing the cracking temperature in the VSB process could certainly obtain a greater conversion into light middle distillates, but this would produce a much more unstable TAR which would require a greater addition of flux (generally gas oil) for its transformation into fuel.

The stability of diesel fuel and TAR is measured by the tendency towards separation over time of the polymeric or asphaltenic components that separate from the paraffinic components.

In fact, the composition of these distillation products includes a paraffinic, and therefore aliphatic, portion and an asphaltenic, and therefore essentially aromatic, portion. Given that by definition asphaltenes are macromolecular aggregates of the naphthenic type with a reduced hydrogen content, insoluble in N-hexane, i.e. in paraffins, it is clearly understood that over time there is a tendency to separate the two types of components from each other. . In this regard, it is also noted that the ratio between the paraffinic and the naphthenic portion is clearly influenced by the origin of the crude oil that is treated in the plant.

Furthermore, the percentage of asphaltenic components is another parameter that is controlled in determining the quality of the fuel oil produced.

Asphaltenes take on particular importance as the paraffin content in the batch increases. This is due to the fact that the cracking of long paraiphine molecules leads to a subsequent cyclization of the radicals formed and to a consequent generation of asphaltenes. In fact, it has been seen in practice that from the cracking of paraffin fillers residues are obtained with a percentage of asphaltenes higher than the filler and not justified by the concentration effect due to the extraction of light distillates.

Viscosity is another parameter that directly affects the conversion yield of the plant as a lower viscosity of the residue requires smaller quantities of flux to achieve the required commercial viscosity specifications.

The viscosity variation depends not only on the extraction of light products, but also on the ability to polymerize that the radicals formed during cracking have. This capacity is greater the more the charge is rich in paraffins.

The polymers formed directly affect viscosity by increasing it and requiring more flux to reach specifications. This entails a reduction in net yield with the same viscosity.

In the patent 1,211,979 of the same Applicant, a process and a composition for increasing the thermal conversion yield have been proposed, in which an additive based on alkylsuccinimides is added continuously during the process, particularly a VSB process. The addition of additive makes it possible to increase the conversion yield either in the form of an increase in the fraction of middle distillates or in the form of a better quality of the TAR obtained.

The process described in the aforementioned patent has provided good results for a process charge having a prevalent aliquot in naphthenic hydrocarbons. However, when the filler contains a prevalent aliquot of paraffinic hydrocarbons, the process of patent 1,211,979 gives unsatisfactory results.

It has now been surprisingly found, and this forms the object of the present invention, that a significant increase in the yield of oil conversion plants with particular reference to the processing of residues deriving from crude oils with a high paraffin content, is achievable by means of a process which in one of its stages it provides for the continuous addition of an additive as defined in the following of the present description.

The present invention therefore satisfactorily completes the general technology described in the aforementioned patent 1,211,979, extending it to the entire field of crude petroleum products, defined both as paraffinic crude oils and as naphthenic crude oils.

As a residue of crude oil with a high content of paraffinic components, we mean a residue deriving from a crude oil with a low sulfur content not exceeding 1% by weight, a pour point of not less than -5 ° C and a TBP distillation product not exceeding 50% by weight at 350 ° C. In this regard, it should be noted that it is not necessary that the three parameters indicated above all satisfy the prescribed condition, but it is sufficient that two of the parameters satisfy the condition for the process and the additive of the present invention to provide effective results.

It is important to note that also in the case of the present invention, the "increase in yield" can be understood both as an increase in conversion into medium and light distillates, and as an improvement in the quality of the TAR.

However, in the present invention it is appropriate to distinguish the quality of the TAR intended as stability and asphaltenes content from the quality intended as viscosity.

In fact, the additive of the present invention has shown: a) at the same temperature of the furnace to produce an increase in yield by reducing the viscosity of the TAR, accompanied by a higher quality of the TAR understood as stability and asphaltenes content, while b) a following an increase in the temperature of the oven, to produce an increase in yield by reduction of viscosity accompanied by a further increase in the conversion yield of the middle distillates.

The continuous additivation can take place in the feed on the charge upstream of the furnace, on the quench, on the bottom of the fractionating column, or in the outlet from the bottom of the column, preferably on the charge upstream of the furnace.

Preferably, in the process of the present invention, reference parameters of the quality of the TAR are determined at the outlet of the fractionation column of the thermal conversion plant to determine the quantity of additive to be added. A new check of the new reference parameters of the quality of the TAR is carried out when the system is fully operational with the added quantity of additive and possibly, with an increase in the temperature of the furnace of the thermal conversion system, up to initial value the reference parameters of the quality of the TAR, if it is intended to obtain an increase in the percentage of middle distillate.

The object of the invention is therefore a process for increasing the yield in a thermal conversion operation in oil plants, starting from a charge formed by a residue deriving from crude oil with a high content of paraffinic components having a low sulfur content not exceeding 1% by weight and, or a pour point of not less than -5 ° C and, or a TBP distillation product of not more than 50% by weight at 350 ° C, where

an additive is continuously added to the conversion plant, in a proportion of 100 to 1000 ppm with respect to the system charge, said additive comprising

one or more active ingredients in a proportion of 5 to 95% by weight with respect to the total weight of said additive e

known solvents per se,

in which said active ingredients are chosen from the group which includes:

a) sterically hindered phenols,

b) catechol derivatives

c) bisphenols.

The present invention also relates to an additive for use in the process described above in which said additive has the composition indicated above.

The additive to be used in the present invention, combined with known solvents, is essentially formed by one or more active ingredients. Among such active ingredients, the catechol derivatives are preferred. Among these, 4-tert-butyl-catechol and pyrocatechin are mentioned in particular.

Among the active ingredients of the phenolic type, those in which at least one tert-butyl substituent group is in an ortho position with respect to the hydroxyl of the phenolic group are preferred. Among these are mentioned in particular 2,6-di-tert-butyl-phenol, 2,6-di-tert-butyl-4-methylphenol and 2,4-dimethyl-6-tert-butylphenol.

As bisphenols to be used as active ingredient in the additive of the present invention, 4,4'-methylenebis (2,6-diterz.butylphenol), 4,4'-thiobis (6-tert.butyl-m) can be named in particular. cresol), 2,2'-methylene-bis (4-methyl-6-nonylphenol), 2,2'-methylene-bis (4-methyl-6-tert-butylphenol).

In the choice of the active ingredients to be used in the additive, the catechol derivatives must be present, while the phenols and bisphenols can be used alternatively or simultaneously. Under this condition, the proportions of the above active ingredients can be any.

As a further active ingredient in the additive, alkylsuccinimides of the type used in the process described in patent no. 2,211,979 mentioned above. However, the addition of succinimides is not essential to the effects of the present invention. By such alkylsuccinimides we mean those having a nitrogen content of 1 to 8% and a total basicity number of 20-200 mg / KOH / g and possibly containing atoms of an element selected from the class formed by boron and phosphorus. The alkylsuccinimides can be added up to a proportion of 30% by weight with respect to the total weight of the additive.

In particular, this proportion can be limited to less than 5% by weight.

The proportion of active ingredients with respect to the total weight of the additive amounts to a percentage of 5 to 95% by weight, so that the proportion of solvents is between 95 and 5%.

Metal deactivators may also optionally be included in the additive in a proportion by weight not exceeding 5% of the total weight of the active ingredients in the additive.

Here are some examples of experimental tests on a Visbreaking plant. The known additive is an additive as described in patent no. 1.211.979 comprising as active ingredients succinimides and phenolic antioxidants in the ratio 3: 1.

The additive according to the invention does not comprise succinimides and as active ingredients it includes sterically hindered phenols with tert-butyl groups in the ortho position, catechol derivatives and bisphenols.

Example 1

To compare the effect produced by the action of an additive according to patent 1,211,979 and an additive according to the present invention, with respect to a situation without additives, the residue from VSB (crude AMNA) is added at 100 ° C and stored in muffle, in a closed container at 200 ° C for 24 hours for a dosage of 150 ppm of additive.

The viscosity at time zero (TO) and the viscosity after a time of 24 hours are measured respectively for a test without additive (S.A.), an additive according to patent 1,221,979 (A.V.) and an additive according to the invention (A.N.) . The results are reported in Table 1, with the viscosity indicated in centipoise. Viscosity was determined by Brookfield (TL 6-speed 60) at 100 ° C.

Table 1

As can be seen, the test without additive produces an increase in viscosity of the residue. The test with the known additive produces an increase in viscosity not very far from the viscosity without additive, while the use of the additive according to the invention produces a net decrease in the viscosity increase. In this test the asphaltenes and stability were not analyzed.

Example 2

A highly paraffinic residue is treated in a Visbreaking plant with Soaker. The charge includes 85% of paraffinic residues and 15% of asphaltenic residues from a vacuum fractionation tower. A comparison test is carried out between a condition in the absence of additives (B1) and with the addition of a known additive (A.V.) according to patent 1,211,979.

The results are shown in Table 2.

Table 2

As can be seen, the percentage of isoviscosity yield, ie with the same viscosity of the product TAR, does not show a significant difference when using the known additive with a paraffinic residue.

Example 3

In a plant such as the one described in example 2 and using the same charge and with a residence time of about 20% less depending on the flow rate, a comparison test is carried out without additives (B2) and respectively using an additive according to present invention (A.N.). The results are reported in the following table 3.

Table 3

It can be observed that in this case the isoviscosity yield increased by about 20% compared to the blank B2 test, without additives.

This demonstrates that the additive according to the invention has surprisingly higher effects in the same conditions of use than an additive according to patent no. 1,211,979, in the case of paraffin filler.

Example 4

A mixed charge AMNA-SARIR 60: 40 of a highly paraffinic nature is treated in a Visbreaking plant with Soaker. A comparison test without additive (B3) and with additive according to the present invention (A.N) is carried out. The additive was metered upstream of the cracking oven. The two tests are carried out with the same oven temperature.

The results are reported in Table 4 Table 4

Δ isoviscos yield. = 1.1%

Δ asphaltenes = 1.8% (-16.5%)

Δ viscosity = 23 cPs 100 ° C = (-10%)

The result of the tests shows in the case of the present invention an improvement in the yield at isoviscosity (+ 1.1%) due to a reduction in viscosity of the residue (-10%) and at the same time a reduction in asphaltenes (-16.5 %) in the residual which translates into an improvement in the quality of the TAR.

Claims (22)

CLAIMS I. Process for increasing the yield in a thermal conversion operation in oil plants, starting from a feed formed by a residue deriving from crude oil with a high content of paraffinic components having a low sulfur content not exceeding 1% by weight and , or a pour point of not less than -5 ° C and, or a TBP distillation product of not more than 50% by weight at 350 ° C, characterized by the fact of continuously add an additive in the conversion plant, in a proportion of 100 to 1000 ppm with respect to the system charge, said additive comprising one or more active ingredients in a proportion of 5 to 95% by weight with respect to the total weight of said additive e known solvents per se, in which said active ingredients are chosen from the group which includes: a) spherically hindered phenols, b) catechol derivatives c) bisphenols. 2. Process according to claim 1, wherein said active principles comprise said catechol derivatives b) alone, or together with said sterically hindered phenols a), or together with said bisphenols c), or together with both. 3. Process according to claim 1, wherein said sterically hindered phenols a) have at least one substituent tert-butyl group in at least an ortho position with respect to the hydroxyl. 4. Process according to claim 3, wherein said phenols a) are selected from the group comprising 2.6-di-tert-butyl-phenol, 2.6-di-tert-butyl-4-methyl-phenol, 2,4-dimethyl-6-tert-butyl-phenol. 5. Process according to claim 1, wherein said catechol derivatives are selected from 4-tert-butyl-catechol, and pyrocatechin. 6. Process according to claim 1, wherein said bisphenols are selected from the group comprising 4,4 '-methylene-bis (2,6-diterz.butylphenol), 4,4' -thio-bis (6-tert.butyl). cresol), 2,2'-methylene-bis (4-methyl-6nonylphenol), 2,2'-methylene-bis (4-methyl-6-tert-butylphenol). 7. Process according to any of the preceding claims, wherein said additive further comprises as a further active ingredient one or more alkyl-succinimides having a nitrogen content of 1 to 8% and a total basicity number of 20 to 200 mg KOH / g, in a proportion by weight of up to 30% with respect to the total weight of said active ingredients in said additive. 8. Process according to claim 7, wherein said succinimides contain boron or phosphorus atoms. 9. Process according to claim 8 or 9, wherein the proportion by weight of said succinimides is less than 5% by weight with respect to the total weight of said active ingredients in said additive. 10. Process according to any of the preceding claims, wherein said additive further comprises metal deactivators in a proportion by weight not exceeding 5% of the total weight of said active ingredients in said additive. 11. Process according to any of the preceding claims, wherein said thermal conversion operation is a Visbreaking operation in a plant essentially comprising a furnace and a fractionating column, and in which said additive is continuously added to the furnace charge and, or at the exit of the furnace and, or at the bottom of the column and, or at the exit from the bottom of the column. 12. Process according to claim 11, wherein said additive is added to the furnace charge. 13. Additive for use in a process as defined in any of the preceding claims, comprising one or more active ingredients in a proportion of 5 to 95% by weight with respect to the total weight of said additive e known solvents per se, in which said active ingredients are chosen from the group which includes: a) sterically hindered phenols, b) catechol derivatives c) bisphenols. 14. Additive according to claim 13, wherein said active principles comprise said catechol derivatives b) alone, or together with said sterically hindered phenols a), or together with said bisphenols c), or together with both. 15. Additive according to claim 13, wherein said sterically hindered phenols a) have at least one substituent tert-butyl group in at least an ortho position with respect to the hydroxyl. 16. Additive according to claim 15, wherein said phenols a) are selected from the group comprising 2.6-di-tert-butyl-phenol, 2.6-di-tert-butyl-4-methyl-phenol, 2,4-dimethyl-6-tert-butyl-phenol. 17. Additive according to claim 13, wherein said catechol derivatives are selected from 4-tert-butyl-catechol, and pyrocatechin. 18. Additive according to claim 13, wherein said bisphenols are selected from the group comprising 4,4'-methylene-bis (2,6-diterz.butylphenol), 4,4'-thiobis (6-tert.butyl-m.cresol), 2,2'-methylene-bis (4-methyl-6-nonylphenol), 2,2'-methylene-bis (4-methyl-6-tert-butylphenol). 19. Additive according to any of claims 13 to 18, wherein said additive further comprises as a further active principle one or more alkyl-succinimides having a nitrogen content of 1 to 8% and a total basicity number of 20 to 200 mg KOH / g, in a proportion by weight of up to 30% with respect to the total weight of said active ingredients in said additive. 20. Additive according to claim 19, wherein said succinimides contain boron or phosphorus atoms. 21. Additive according to claim 19 or 20, wherein the proportion by weight of said succinimides is less than 5% by weight with respect to the total weight of said active ingredients in said additive. Additive according to any of claims 13 to 21, wherein said additive further comprises metal deactivators in a proportion by weight not exceeding 5% of the total weight of said active ingredients in said additive,