SE424195B - Process for the removal of nitrogen impurities from a hydrocarbon mixture - Google Patents

Abstract

The invention relates to a process for the removal of nitrogen impurities from a liquid hydrocarbon mixture. In the process according to the invention an aqueous acid and the mixture of hydrocarbons are introduced into a small mixer. The acid concentration of the said solution can be between 0.01 and 5 vol-%. The mixer is used to form an emulsion of hydrocarbons in the aqueous acid solution by operating it for no more than 2 seconds. The emulsion is transferred from the mixer to a decanter, and the purified hydrocarbons are extracted.

Description

_79oe49s-6 form gasolines, with an organic or inorganic acid. However, the nitrogen compounds are only partially removed by this acid treatment and therefore nitrogen compounds are still formed when the hydrocarbon batch is subjected to cracking and these compounds must be removed before the reforming is carried out. In addition, the working conditions in the acid treatment of the hydrocarbon batch before cracking are not suitable for application to the cracked products.

The cracked products actually contain unsaturated hydrocarbons, which can polymerize if subjected to an acid treatment under the conditions proposed for the acid treatment before cracking. The polymerization of these unsaturated hydrocarbons depends on the acid concentration of the solution and on the contact time between the batch and the acid solution.

The conditions in the acid treatment of the batch before cracking are an acid concentration of from 85 to 100% and contact times included between 5 minutes and 2 hours; under these conditions, the unsaturated hydrocarbons present in the batch will polymerize.

It has been proposed to directly treat the cracked products with an acid solution, especially a sulfuric acid solution, but under specific conditions in terms of acid concentration and contact time.

Thus, in The Science of Petroleum, Vol.III, page 1775, it has been proposed to use a water-sulfuric acid solution with an acid concentration between 40 and 98% with contact times such that the lower the acid concentration, the longer the contact time.

However, the polymerization of the unsaturated hydrocarbons can not be completely avoided, even if the acid concentration is as low as 40%.

To reduce the contact time and consequently the polymerization rate, it has been proposed to use more concentrated sulfuric acid solutions but in accordance with special methods for contacting the batch with the sulfuric acid solution.

As special contacting devices, there may be mixed batteries in which the batch and the concentrated sulfuric acid solution move in countercurrent, or a contacting column with a special contact bed described in U.S. Pat. No. 2,999,807. According to the process described in this U.S. patent, an aqueous sulfur solution is used. with an acid concentration of at least 65% plus contact times in the column between 3 and 25 seconds. The feature of the column is in a contact bed made of an inert material, which may be ceramic, coke or glass with a hydrophilic surface, so that it is easily wetted by sulfuric acid, which is thereby retained on the surface to form a large contact area. However, this process does not avoid the formation of a considerable amount of polymerized products.

An object of the present invention is to eliminate these disadvantages.

Another object of the present invention is an improved process for removing nitrogen impurities from a liquid hydrocarbon mixture by contacting it with an aqueous solution of an inorganic or organic acid, said method enabling the reduction of the basic content. nitrogen compound to less than one ppm.

A further object of the invention is an improved process for removing nitrogen impurities from a liquid hydrocarbon mixture containing unsaturated hydrocarbons by contacting the mixture with an aqueous solution of an inorganic or organic acid, the process enabling the formation of polymerized products to be avoided.

The process of the present invention for removing nitrogen impurities from a liquid hydrocarbon mixture by means of an organic or organic acid comprises the steps of: I - continuously introducing the acid into a low volume mixer, the acid being used in the form of a dilute aqueous solution with an acid concentration between about 0.01 and about 5% by volume, and wherein the volume ratio between the amount of dilute aqueous-acid solution and the amount of hydrocarbons is between about 0.075 and about 5, - to continuously introduce the hydrocarbons into the mixer, - to form in the mixer an emulsion of the hydrocarbons in said water-acid solution by mixing for a period not exceeding about 2 seconds, said dilute water-acid solution extracting the bulk of the nitrogen impurities, - withdrawing the obtained emulsion to a decantation zone, in which the emulsion is broken and, - from said decanting zone recover the hydrocarbons containing not more than about 2 ppm basic nitrogen impurities.

The process of the invention is applicable to a wide range of liquid hydrocarbon mixtures and especially to hydrocarbons having a boiling point between about 50 and about 300 ° C. The process according to the invention is particularly applicable to liquid hydrocarbon mixtures obtained from direct-run distillates (primary distillates or distillates obtained by fractional distillation process) and in particular to liquid hydrocarbon mixtures containing unsaturated hydrocarbons boiling in the gasoline terminus and of heavier hydrocarbons.

The liquid hydrocarbon mixtures obtained from direct-run distillates or distillates from fractional distillation usually consist of kerosene or crystal oils with a boiling point between 150 and 29000 and between 150 and 20,000 respectively. These hydrocarbon mixtures contain from 20 to 50 ppm nitrogen compounds including from about 10 to about 17 ppm basic nitrogen compounds and thus they are not suitable for being subjected to hydrogenation treatment in the presence of noble metal catalyst.

The liquid hydrocarbon mixtures obtained by thermal or catalytic cracking of heavier hydrocarbons contain unsaturated hydrocarbons and have a boiling point included in the gasoline range. These liquid hydrocarbon mixtures generally contain from 50 to 60 ppm nitrogen compounds including from about 30 to about 50 ppm basic nitrogen compounds and are thus not suitable for catalytic reforming.

When these hydrocarbon mixtures are treated according to the process of the invention, the content of basic nitrogen compound in the batch is reduced to less than 2 ppm; The residue of the nitrogen compounds is then removed by a hydrogenation treatment under working conditions similar to those of desulphurisation to finally reach a nitrogen compound content of less than 0.5 ppm. According to the prior art, such liquid hydrocarbon mixtures must be treated with concentrated aqueous solutions of sulfuric acid; usually 40-98%, and for a period that can vary between 3 and 50 seconds.

The applicant has unexpectedly found that these liquid hydrocarbon mixtures can be treated with highly dilute aqueous solution of an inorganic or organic acid for an extremely short period of time, less than 2 seconds, as long as an emulsion of the hydrocarbon batch to be treated in the aqueous acid solution is formed in the mixer.

The applicant has now found that the nitrogen compounds can be easily removed from the above-described hydrocarbon mixtures by treating these mixtures with an aqueous solution of an inorganic or organic acid having an acid concentration which can be as low as 0.01% by volume. which is usually included between 0.01 and 2.5% by volume, and with extremely short contact times, which do not exceed 2 seconds or even 1 second. When hydrocarbon mixtures containing unsaturated hydrocarbons are treated in accordance with the operating conditions of the invention, it has been noted that polymerized products are substantially not formed. The content of polymerized products is determined according to the ASTM D 381 method.

To carry out the acid treatment according to the invention, an inorganic acid as well as an organic acid can be used. Examples of suitable acids which may be mentioned are H01, HBr, HF, HI, sulfuric acid, phosphoric acid, boric acid, fluorosulfuric acid, trifluoroacetic acid, trichloroacetic acid, formic acid, alkanesulfonic acids and alkylbenzenesulfonic acids. However, sulfuric acid is generally used due to its ease of storage and handling.

The amount of dilute acid solution to be used with respect to the amount of hydrocarbons to be treated to carry out the process of the invention can vary widely. The volume ratio between the amount of hydrochloric acid solution and the amount of hydrocarbons is between 0.075 and 5 and usually between 0.3 and 2.

Among the mixers which can be used in the process according to the invention, centrifugal pumps and static mixers can be mentioned in particular.

Such mixers enable the formation of an emulsion of the hydrocarbons in the dilute acid solution in a very short time. In addition, said emulsion can be withdrawn substantially immediately after its formation. As a result, the contact times between the liquids to be treated are sufficiently short and the formation of significant amounts of polymerized products is avoided.

It has been unexpectedly noted that substantially complete removal of the basic nitrogen compounds from the hydrocarbon mixtures can be carried out by means of the mixers described above using such a slightly concentrated hydrochloric acid solution.

According to an embodiment of the process of the invention, the water-acid solution and the hydrocarbon mixture are introduced simultaneously into the suction side of a centrifugal pump. The emulsion formed inside the pump is then sent into a decanter, where the breakage of the emulsion is achieved substantially immediately. The purified or clarified hydrocarbon mixture is then recovered at the top of the decanter.

Other types of mixers may be used to form an emulsion of the contact liquids; however, these other types of mixers, for example a vessel equipped with a turbo disperser or a pulsed extraction column, have various disadvantages. For example, the contact time is usually too long or the emulsion formed is not sufficiently homogeneous; as a result, the amount of polymerized products is too high or the extraction of the basic nitrogen compounds is not sufficiently complete.

The following examples are given for the purpose of better illustrating the invention without limiting it.

Example 1 At the suction side of a centrifugal pump, at the same time: 7 a hydrocarbon mixture was introduced, the characteristics of which are given in Table I below, with a total nitrogen content of. 61.5 ppm including 43.3 ppm basic nitrogen.

The content of polymerized products in this batch was measured according to the ASEEM ID 381 method and was 1 mg per 1000 ml of hydrocarbon. - a dilute sulfuric acid solution with an acid concentration of 0,2 vol-ß webell I Characteristics. Kit nestilletiøn Asthma D 86 Initial point _ 54 ° c end point 2o5 ° c specific weight 15/4 ° c 0.793 Composition Paraffins (vol. W 27.5 Olefins (vol.%) 35.0 Naphthenes (v01. Ffä) 5.5 Aromatic compounds (vol.%) 36, 0 7 7906498-6 The volume ratio between the dilute acid solution and the hydrocarbon mixture was 1/1.

The rotation speed of the pump was 1450 rpm.

Inside the centrifugal pump, both liquids were mixed intimately and an emulsion of the hydrocarbon mixture in the selected acid solution was formed. The Cens trifugal pump sent this emulsion to a decanter, in which breaking of the emulsion was achieved substantially immediately with the formation of two phases: a phase containing the purified hydrocarbons located at the top of the decanter and an aqueous phase at the bottom of the decanter.

The contact time between the two liquids was estimated by the time required to pass through the centrifugal pump, i.e. to 1 second.

The phase containing the hydrocarbons was analyzed to determine the nitrogen compound content.

The following results were obtained - total nitrogen compound content: 8 ppm - content of basic nitrogen compounds: 0.8 ppm - content of polymerized products: 15 mg / 1000 ml hydrocarbon.

Then a batch containing 75% by volume of naphtha and 25% by volume of the purified hydrocarbon mixture was prepared. I This batch was subjected to a sulfur sulfur treatment under the following conditions: - conventional desulfurization catalyst: 400 ml _- fi z partial pressure 12,5 kb / cmz n - total pressure = 25 kb / cmz - temperature: 305,4 ° C - space hourly rate: 4 hr'1 - Hz / Hc = 150 N1 / 1.

No trace of nitrogen compounds was detected in the desulfurized hydrocarbon mixture.

For comparative purposes, a batch was prepared containing 75% by volume of naphtha and 25% by volume of the hydrocarbon mixture not subjected to the acid treatment.

This batch was subjected to a desulfurization treatment under the same conditions as those described above. .f "190e498-6 After desulfurization the batch had a nitrogen content of. 5 ppm. This content was too high and this batch was not suitable for catalytic reforming.

Example gel 2 * The procedure described in Example 1 was repeated but using other hydrocarbon mixtures (the characteristics of which are given in Table II below), other acid concentrations and other volume ratios of the diluent. the acid solution and the hydrocarbon mixture.

The working conditions and results are given in Table III below.

Table II Theorem Characteristics. 7 2,1 2,2 2,5 2,4- Distillation ASTM D 86 Iniiiell punkæ fi c) 56 51 62 55 siuipunki (° c) 171 160 200 172 specific gravity 15/4 ° c 0.776 0.757 0.702 0.777 Composition in "Paraffins ( v01. 73) 51.5 49 55 54 olefins (v01.%) 56 45.6 54 - 54 Martens: (v01. 71) 2.5 5.5 2 2 Aromatic compounds (v01. 78 50 5.9 51 i 9. units (v ,, 1ym_%) (rpm) (ppm) 2.1 5 5591 4911 2.2 e 55.5 44.9 2.5 7 45.5 10.1 2.4 7 57.5 55.6 '2.1 15 0.5 0.12 1.2 10.5 2.1 12 0.25 0.12 1.6 11.4 2.2 12 0.5 0.05 1.0 10.6 2.2 17 0 .5 0.29 0.7 8 2.3 15 0125 0125 118 999 2.4 15 0.5 0.12 1.4 10.6 07906498-6 For comparative purposes, batch 2.2 was subjected to a pure water treatment.

In the treated product, 55.5 ppm basic nitrogen compound was detected.

For comparative purposes, batch 2.2 was treated in accordance with the embodiment described above but with a dilute sulfuric acid solution with an acid concentration of. 25 volym-Va. The volume ratio of the dilute acid solution to the hydrocarbon mixture was 0.5.

The content of polymerized product was determined. the treated hydrocarbon mixture according to the ASTM D 581 method and a value of 80 mg / 1000 ml was determined, which is too high.

Example 5 At the suction side of a centrifugal point, at the same time: - a hydrocarbon mixture was introduced, the characteristics of which are those given in Table IV below, with a total nitrogen compound content of. 55.7 ppm including 59.2 ppm basic. nitrogen compounds. The content of polymerized product was determined according to the ASTM D 581 method and was 5 mg / 100 ml. a dilute hydrochloric acid solution with an acid content of. 0.5 vol-ß Table IV Characteristics Batch Distillation ASEM D 86 Inieieii pwukt 55 ° c mp 175 ° c specific weight 15/4 ° c 0.782 Composition Paraffins (vol.%) 54 Olefins (vol. 'Ss 56 Aromatic compounds (vol. 3%) 50 The volume ratio between the dilute acid solution and the hydrocarbon mixture was 2/1.

The rotation speed of the pump was 1450 rpm.

Both liquids were intimately mixed inside the centrifugal pump and an emulsion of the hydrocarbon mixture in the dilute acid solution was formed. The centrifugal pump sent this emulsion to a decanter, in which 7906498-6 m breaking of the emulsion was achieved almost immediately with the formation of two. phases.

The contact time between the two. the liquids were estimated by the time required to flow through the centrifugal pump, i.e. to 1 second.

The nitrogen content of the phase containing the hydrocarbon mixture was as follows: Total nitrogen content: 8.6 ppm Content of basic nitrogen: 0.9 ppm 7 Content of polymerized product according to ASTM D 581: 15 mg / 1000 ml The run was continued as described in Example 1 and the desulfurized phase did not contain any trace of nitrogen compounds.

Example g At the inlet to a static mixer with a diameter of 4 cm and a length of 75 cm was introduced at the same time: - a hydrocarbon mixture, the characteristics of which are given in Table V below, with a total nitrogen compound content of. 54.4 ppm including 45.4 ppm basic nitrogen compounds, at a rate of 0.85 mš / hour.

The content of polymerized products according to ASTM D 581 was 8 mg / 1000 ml. a dilute sulfuric acid solution with an acid concentration of. 0.5 volume- 9% via a speed possibly 1.7 m5 / win.

Table V 'Characteristics Batch Distillation ASTM D 86 Initial point 6o ° c sinvpvnkv 1s4 ° c specific gravity 15/4 ° c 0.767 Composition Pnrefrins (voi. Vu) 52 olefins (v01.%) 56 Naphthenes (vol.%) 2 Aromatic I compounds (vol. 71) 50 n 2906498-6 The contact time in the static mixer was about 1 second.

Both liquids were mixed intimately in the static mixer and an emulsion of the hydrocarbon mixture in the dilute acid solution was formed.

The emulsion was then sent to a decanter, in which the refraction of the emulsion was achieved substantially immediately with the formation of two phases as indicated in Example 1.

The nitrogen compound content of the phase containing the hydrocarbon mixture was as follows: Total nitrogen compound content: 10.5 ppm Content of basic nitrogen compounds: 1.4 ppm Content. polymerized product according to ASTM I) 581: 17 mg / 1000 ml.

The run was continued as described in Example 1 and the desulfurized batch did not contain any trace of nitrogen compound.

Example Q At the suction side of a centrifugal pump, at the same time: a hydrocarbon mixture was introduced, the characteristics of which are given in Table VI below, with a total nitrogen compound content of. 23 ppm including 12 ppm 'basic nitrogen compounds. p - a dilute sulfuric acid solution with an acid concentration of. 0.2 volym-7š.

Table vI Characteristic batch nestillation Asm ll es Initial point 1so ° c final weight 261 ° c specific gravity 15/4 ° C o, a2o Composition Paraffins (vel.%) Ao Olefins (vol.%) Traces Aromatic compounds (vol. 76) The volume ratio between the dilute acid solution and the hydrocarbon mixture was 1/1.

The rotation speed of the pump was 1450 rpm. Both liquids were intimately mixed inside the centrifugal pump and an emulsion of the hydrocarbon mixture in the dilute acid solution was formed.

The centrifugal pump sent this emulsion to a decanter, in which breaking of the emulsion was achieved substantially immediately with the formation of two phases as indicated in Example 1.

The contact time between the two liquids was estimated by it. to flow through the pump the required time, ie 1 second.

The nitrogen compound content of the phase containing the hydrocarbon mixture was as follows: 6 ppm Content basic. nitrogen compounds: 0.5 ppm.

Total nitrogen compound content: This purified batch was then subjected to a hydrodesulfurization treatment under the conditions described in Example 1.

In the desulfurized hydrocarbon mixture, no trace of nitrogen compounds was detected.

Claims (9)

, ~ 13 7906498-6 Patent claims A process for removing nitrogen impurities from a liquid hydrocarbon mixture by means of an inorganic or organic acid, characterized in that it comprises the steps of: - continuously introducing the acid into a low volume mixer, the acid being used in the form of a dilute aqueous solution with a acid concentration between about 0.01 and about 5% by volume, and wherein the volume ratio between the amount of dilute hydrochloric acid solution and the amount of hydrocarbons is between about 0.075 and about 5, - to continuously introduce the hydrocarbons into the mixer, - to form in the mixer an emulsion of the hydrocarbons in said hydrochloric acid solution by mixing for a period of time not exceeding 2 seconds, said dilute hydrochloric acid solution _extracting the major part of the nitrogen impurities, _ - extracting the resulting emulsion into a decantation zone in which the emulsion is broken, and d - recovering hydrocarbons from the decantation zone more than about 2 ppm basic nitrogen pollutants. 2. 2. A process according to claim 1, characterized in that the liquid hydrocarbon mixture comprises hydrocarbons having a boiling point between * about 50 and about 50,000. 3. Process according to claims 1 and 2, characterized in that the hydrocarbon mixture is a direct run distillate. 4. A process according to claims 1 and 2, characterized in that the hydrocarbon mixture is obtained by thermal or catalytic cracking of heavier hydrocarbons. 5. A process according to claim 4, characterized in that the hydrocarbon mixture contains unsaturated hydrocarbons and has a boiling point in the gasoline range. 6. A process according to any one of claims 1-5, characterized in that the hydrocarbon mixture is treated by means of an aqueous solution of an acid selected from the group comprising hydrochloric acid, hydrobromic acid, hydrofluoric acid, iodobutyric acid, sulfuric acid, phosphoric acid, hydrochloric acid, fluorine sulfuric acid, trifluoroacetic acid, trichloroacetic acid, formic acid, alkunsulfonic acids and alkylbenzenesulfonic acids. -, ”f ~ 79o649s-e lll- A method according to any one of claims 1-6, characterized in that the aqueous solution has an acid concentration between about 0.01 and 2.5 volume-ß A process according to any one of claims 1-7, characterized in that the volume ratio between the amount of hydrochloric acid solution and the amount of new hydrocarbons is between about 0.3 and about 2. 9. A method according to any one of claims 1-8, characterized in that the low volume mixer is selected from the group comprising centrifugal pumps and static mixers. This invention relates to a process for removing nitrogen contaminants from a liquid hydrocarbon mixture, which process comprises introducing into a low volume mixer a water-acid solution having an acid concentration between 0.01 and 5 volume-76, and the hydrocarbon mixture, in the mixer, 7906498-6. forming an emulsion of the hydrocarbons in the hydrochloric acid solution by mixing for a period of time not exceeding 2 seconds, withdrawing the emulsion to a decanter and recovering the purified hydrocarbons.