GB2122637A

GB2122637A - Process for improving the quality of gasoline

Info

Publication number: GB2122637A
Application number: GB08317250A
Authority: GB
Inventors: Erp Willibrord Adelbert Van; Jacques Pierre Lucien
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1982-06-28
Filing date: 1983-06-24
Publication date: 1984-01-18
Also published as: ES8403960A1; GB8317250D0; ES523592A0; IT1170157B; AU554301B2; NZ204691A; IT8321787A0; FR2537152A1; AU1620983A; FR2537152B1; CA1203496A; GB2122637B

Abstract

The quality of a gasoline obtained by catalytic cracking is improved by contacting the gasoline with a crystalline metal silicate which after one hour's calcination in air at 500 DEG C, has the following properties: a) thermally stable up to a temperature of at least 600 DEG C, b) an X-ray powder diffraction pattern in which the strongest lines are the four lines mentioned in Table A. <IMAGE> c) in the formula which represents the composition of the silicate expressed in moles of the oxides and which, in addition to SiO2, includes both Fe2O3 and Al2O3, the SiO2/Fe2O3 molar ratio is 25-90 and the SiO2/Al2O3 molar ratio is 250-1200.

Description

SPECIFICATION Process for improving the quality of gasoline The invention relates to a process for improving the quality of gasoline obtained by catalytic cracking.

Gasoline obtained by catalytic cracking has a high olefins content. This is the reason why the gasoline displays a strong tendency to form gum. Gasoline obtained by catalytic cracking also has a relatively low aromatics content. This is the reason why the gasoline has a relatively low octane number.

In view of the above-mentioned properties the quality of gasoline obtained by catalytic cracking must be improved, before it becomes eligible for use as motor gasoline. Such quality improvement may be carried out by catalytic reforming, in which, among other things, the olefins content will fall and the aromatics content will rise. A serious drawback connected with the catalytic reforming of gasoline obtained by catalytic cracking is this gasoline's high content of sulphur compounds and nitrogen compounds. Since the presence of sulphur and nitrogen compounds in the feed has a highly unfavourable effect on the performance of catalysts suitable for use in reforming, extreme removal of said compounds from the feed is needed before the latter can be subjected to catalytic reforming. This requires a catalytic hydrotreatment under extra severe conditions.Although the above-mentioned twostep process, in which gasoline is first subjected to a catalytic hydrotreatment under extra severe conditions and subsequently to catalytic reforming, results in a considerable quality improvement of the gasoline obtained by catalytic cracking, there is an urgent need for a process which leads to the desired end in a single step.

Recently new crystalline metal silicates having a special structure have been synthesized, which silicates show catalytic activity in the conversion of non-aromatic organic compounds, such as olefins, into aromatic hydrocarbons. The catalytic performance of these silicates is quite unsusceptible to the presence of sulphur and nitrogen compounds in the feed. The crystalline metal silicates concerned are characterized in that after one hour's calcination in air at 5000C they have the following properties: a) thermally stable up to a temperature of at least 6000 C, b) an X-ray powder diffraction pattern in which the strongest lines are the four lines mentioned in Table A.

TABLE A d(A) 11.1 +0.2 10.0 *0.2 3.84 + 0.07 3.72 + 0.06 c) in the formula which represents the composition of the silicate expressed in moles of the oxides and which in addition to SiO2, includes either Awl203 or Fe203, the SiO2/AI203 or the SiO2/Fe203, molar ratio is higher than 10.

In the present patent application a crystalline silicate having a thermal stability of at least tOC should be taken to be a silicate whose X-ray powder diffraction pattern, upon heating to a temperature of tOC, remains substantially unchanged.

An investigation into the use of the above-mentioned crystalline iron or aluminium silicates as catalysts for improving the quality of gasoline obtained by catalytic cracking has shown that although some reduction in olefins content and some increase in aromatic content do occur, these changes are insufficient for the purpose of the desired quality improvement. It has further been found that the catalysts have insufficient activity and stability.However, continued research has revealed that crystalline metal silicates having the special structure of the iron or aluminium silicates mentioned hereinbefore when used as catalysts for improving the quality of gasoline obtained by catalytic cracking, display excellent performance if they comprise both iron and aluminium and if, in addition, these metals are present in the silicate in such quantities that in the formula which represents the composition of the silicate expressed in moles of the oxides, the SiO2/Fe203 molar ratio is 25-90 and the SiO2/AI203 molar ratio is 250-1200. Compared with the crystalline iron or aluminium silicates the abovementioned iron-aluminium silicates have considerably better activity and stability and provide a gasoline having a considerably lower olefins content and a considerably higher octane number.

The present patent application therefore relates to a process for improving the quality of gasoline obtained by catalytic cracking, in which the gasoline is contacted with a crystalline metal silicate which, after one hour's calcination in air at 5000C has the properties mentioned above under a) and b) as well as the property that in the formula which represents the composition of the silicate expressed in moles of the oxides and which in addition to SiO2, include both Fe2O3 and Awl203, the SiO2/Fe203 molar ratio is 25-90 and the SiO2/AI203 molar ratio is 250-1200.

In the process according to the invention the starting material is a gasoline obtained by catalytic cracking. Such gasolines may very suitably be prepared by the application of catalytic cracking to heavy hydrocarbon oils, such as atmospheric gas oils, vacuum gas oils, deasphalted vacuum residues and mixtures thereof. The feed used by preference is a gas oil. Catalytic cracking on a commercial scale is usually carried out in a continuous process using an arrangement which consists substantially of a vertically disposed cracking reactor and a catalyst regenerator. Hot, regenerated catalyst coming from the regenerator is suspended in the oil to be cracked and the mixture is passed through the cracking reactor in an upward direction. The deactivated catalyst is separated from the cracked product and, following stripping, transported to the regenerator.The cracked product is separated into a light fraction having a high content of C3 and C4 olefins, a gasoline fraction and several heavy fractions, such as light cycle oil, a middle cycle oil, a heavy cycle oil and a slurry oil.

The crystalline metal silicates used as catalysts in the process according to the invention are defined, among other things, by the X-ray powder diffraction pattern which they show after one hour's calcination in air at 5000 C. In this pattern the strongest lines should be the four lines mentioned in Table A. The complete X-ray powder diffraction pattern of a typical example of a crystalline metal silicate used in the process according to the invention, is presented in Table B.

TABLE B d(A) Rel. int. d(A) Rel. int.

11.1 100 3.84 (D) 57 10.0 (D) 70 3.72 (D) 31 8.93 1 3.63 16 7.99 1 3.47 1 7.42 2 3.43 5 6.68 7 3.34 2 6.35 11 3.30 5 5.97 17 3.25 1 5.70 7 3.05 8 5.56 10 2.98 11 5.35 2 2.96 3 4.98 (D) 6 2.86 2 4.60 4 2.73 2 4.35 5 2.60 2 4.25 7 2.48 3 4.07 2 2.40 2 4.00 4 (D) = doublet The crystalline metal silicates may be prepared starting from an aqueous mixture comprising the following compounds: one or more compounds of an alkali metal (M), one or more organic nitrogen compounds (RN) which include an organic cation or from which an organic cation is formed during the preparation of the silicate, one or more silicon compounds, one or more compounds comprising iron in a trivalent form and one or more aluminium compounds.

The preparation is carried out by maintaining the mixture at an elevated temperature until the silicate has formed and subsequently separating the silicate crystals from the mother liquor and washing, drying and calcining the crystals. In the aqueous mixture from which the silicates are prepared the various compounds should be present in the following molar ratios, expressed -- with the exception of the organic nitrogen compounds -- in moles of the oxides: M20 : Si02 = 0.01--0.35, RN: siO2 = 0.02-1.0, Ski02 : Fe203 = 25-270, Si02 :Al203 = 250-2400, and H20 : SiO2 = 5-65.

In the preparation of the silicates the base mixture started from may very suitably be a mixture which as a nitrogen compound comprises a quaternary alkylammonium compound, such as a tetrapropylammonium compound. Preference is given to the use of an amine as an organic nitrogen compound and in particular to n-butylamine. Further, in the preparation of the silicates preference is given to the use of a base mixture which, as an alkali metal compound comprises a sodium compound and as a silicon compound amorphous silica.

The silicates prepared as described hereinbefore comprise alkali metal ions. By using suitable exchange methods these may be replaced by other cations, such as hydrogen ions or ammonium ions.

The crystalline silicates used in the process according to the invention preferably have an alkali metal content of less than 0.05 /Ow.

The process according to the invention may very suitably be carried out by passing the feed in an upward or downward direction through a vertically arranged reactor containing a fixed or a moving bed of the crystalline metal silicate. Suitable conditions for carrying out the process according to the invention are a temperature of 300--600"C, a pressure of 1-50 bar and a space velocity of 0.1-1 0 kg . kg~' . h-t. The process is preferably carried out under the following conditions: a temperature of 400--5000C, a pressure of 2.5-25 bar and a space velocity of 0.2-3 kg . kg-l . h-1. The process may be carried out in the presence of hydrogen, if desired.

In the process according to the invention the formation of aromatics is accompanied with cracking. As a result of this cracking the C4 product fraction contains a considerable proportion of C3 and C4 olefins. The investigation has revealed that the recirculation of the C4 product fraction leads to considerable improvement of the catalyst's selectivity and stability, whilst the excellent quality of the gasoline is maintained. Therefore, in the process according to the invention at least part of the C4 product fraction is preferably recirculated.

Depending upon the degrees of thoroughness with which the separation between the light fraction and the gasoline fraction of the catalytically cracked product is carried out, the separated gasoline may contain larger or smaller proportions of C3 and C4 olefins. The investigation has revealed that in the process according to the invention an increase in the C3 and/or C4 olefins content of the feed results in enhanced selectivity of the quality improvement. An increase in the C3 and/or C4 olefins content of the feed may be achieved in various ways. In the first place one may carry out the separation between the light fraction and the gasoline fraction of the cracked product less thoroughly and thus allow a considerable portion of the olefins usually present in the light fraction to go into the gasoline fraction.

Another option is separating the gasoline from the catalytically cracked product and subsequently adding additional C3 and/or C4 olefins. For this purpose preference is given to the use of C3 and/or C4 olefins which can be separated from the light fraction of a product obtained by catalytic cracking. In view of its favourable effect on selectivity and quality improvement the process according to the invention is preferably applied to a gasoline obtained by catalytic cracking which has an increased C3 and/or C4 olefins content.

The invention is now elucidated with the aid of the following example.

EXAMPLE Four crystalline silicates (silicates 1-4) were prepared by heating mixtures of NaOH, Fe(NO3)3 and/or Naval02, amorphous silica containing 100 ppmw aluminium and C4HgNH2 or (C3H7)4NOH in water in an autoclave under autogenous pressure, with stirring, at 1 500C. In the preparation of silicates 1-3 the mixtures were heated for 24 hours. In the preparation of silicate 4 the mixture was heated for 1 20 hours.After cooling of the reaction mixtures the silicates formed were filtered off, washed with water until the pH of the wash water was about 8 and dried at 1 200C. After one hour's calcination in air at 5000 C, silicates 1-4 had the following properties: a) thermally stable up to a temperature of at least 8000 C, b) an X-ray powder diffraction pattern substantially corresponding with that mentioned in Table B, and c) values of the SiO2/Fe203 and SiO2/AI203 molar ratios as mentioned in Table C.

TABLE C Silicate No. Si02/Fe2O3 SiO2/Al203 1 - 250 2 108 1900 3 127 600 4 79 1000 The molar composition of the aqueous mixtures from which silicates 1 4 were prepared may be represented as follows: v Na2O . w (C3H)4NOH . x C4H9NH2. y Al2O3 . z Fe203. 25 SiO2. 450 H20, where v, w, x, y and z have the values mentioned in Table D.

TABLE D Silicate No. v w x y z 1 1 9 - 0.066 2 2.5 - 10 0.003 0.20 3 1 - 10 0.036 0.20 4 1 - 10 0.036 0.33 From silicates 1-4 were prepared silicates 5-8, respectively, by boiling silicates 1 4 with a 1.0 molar NH4NO3 solution, washing with water, boiling again with a 1.0 molar NH4NOa solution, washing drying at 1 200C and calcining at 5000C.

Silicates 5-8 were tested in six experiments (Experiments 1-6) as catalysts for improving the quality of gasoline obtained by catalytic cracking. The experiments were carried out in a reactor containing a fixed catalyst bed. All the experiments were carried out at a temperature of 4500 C, a pressure of 5 bar and a space velocity of 0.5 kg . kg-l . h-'. In Experiments 5 and 6 the CJ product fraction was recirculated at a C4~/gasoline molar ratio of 10:1.

Experiments 1-5 were applied to a gasoline 1. Experiment 6 was applied to a gasoline 2 which had been obtained by mixing 93.0 pbw of gasoline 1 with 7.0 pbw of a mixture of butenes. Gasoline 1 has the following properties: Composition in %w: C4- 4.7 aromatics 24.2 naphthenes 13.6 paraffins + olefins 57.5 olefins/paraffins weight ratio approx. 50/50 sulphur content, %w 0.14 nitrogen content, ppmw 60 final boiling point, C 244 ozone number, mmole/g* 4.0 MON-O** 80.4 * The ozone number is a measure of the olefins content of the gasoline. According as the gasoline contains fewer olefins, the ozone number will be lower.

**MON-O is the motor octane number without the addition of lead.

The results of Experiments 1-6, are given in Tables E-G. The parameters activity, selectivity, stability and selectivity of the operation given in the Tables are defined as follows: (%w C5+ non-aromatics present in feed) - (%w C5+ non-aromatics present in product) Activity = x 100 (%w C5+ non-aromatics present in feed) (%w aromatics present in product) - (%w aromatics present in feed) Selectivity = ---- x 100 (%w C5+ non-aromatics present in feed) - (%w C5+ non-aromatics present in product) Instability = decrease in activity from run hour 100 to run hour 350.

increase in %w aromatics Selectivity of the operation = decrease in %w C5+ fraction Of Experiment 1-6 only Experiments 4-6 are experiments according to the invention. Experiments 1-3 fall outside the scope of the invention. They have been included in the patent application for comparison.

TABLEE Experiment No. - 1 2 3 4 Silicate No. - 5 6 7 8 Feed gasoline No. 1 1 1 1 1 Aromatics present in feed or total product, resp., %w 24.2 36.8 41.0 43.3 46.7 C5+ present in feed or total product, resp., %w 95.3 79.8 82.0 79.8 74.9 Activity averaged over 350 hours, %w - 39.5 42.3 48.8 60.3 Selectivity averaged over 350 hours, %w - 44.8 55.8 55.2 52.5 Instability, %w - 65 38 39 33 MON-O of feed or liquid product, resp. 80.4 83.2 83.2 84.8 87.4 Ozone number of feed or liquid product, resp. mmole/g 4.0 2.0 1.1 0.6 0.3 TABLE F Experiment No. - 4 5 Silicate No. - 8 8 Feed gasoline No. 1 1 1 C4 recirculation - no yes Aromatics present in feed or total product, resp., %w 24.2 46.7 48.5 C5+ present in feed or total product, resp., %w 95.3 74.9 77.1 Activity averaged over 350 hours, %w - 60.3 59.8 Selectivity averaged over 350 hours, %w - 52.5 57.2 Instability, %w - 33 27 MON-O of feed or liquid product, resp. 80.4 87.4 87.3 Ozone number of feed or liquid product, resp. mmole/g 4.0 0.3 0.4 TABLE G Experiment No. - 5 - 6 Silicate No. - 8 - 8 Feed gasoline No. 1 1 2 2 C4 recirculation - yes - yes Aromatics present in feed or total product, resp., %w 24.2 48.5 22.2 47.0 C6+ present in feed or total product, resp., %w 95.3 77.1 88.6 76.8 Increase of aromatics, %w 24.3 24.8 Decrease of C5+, O/oW 18.2 11.8 Selectivity of operation 1.3 2.1 MON-O of feed or total product, resp., 80.4 87.3 80.3 87.2 Ozone number of feed or total product, resp. mmole/g 4.0 0.4 4.2 0.3 Referring to the results mentioned in Tables E-G the following may be remarked.

TABLE E Silicate 5 (aluminium silicate is not suitable as catalyst for the present purpose, since this silicate has a very low average activity, a low average selectivity and a very low stability and, in addition, it provides a gasoline with a moderate octane number and a very high olefins content.

Silicate 6 (iron silicate) is not very suitable as catalyst for the present purpose, since this silicate has a very low average activity and, in addition provides a gasoline with a moderate octane number and a high olefins content.

Silicate 7 (iron-aluminium silicate, outside the scope of the invention) is not very suitable as catalyst for the present purpose, since this silicate has a low average activity and, in addition, provides a gasoline with a moderate octane number and a relatively high olefins content.

Silicate 8 (iron-aluminium silicate according to the invention) is excellently suitable as catalyst for the present purpose. The silicate has a very high average activity, a high average selectivity and a very high stability. In addition, the silicate provides a gasoline with a very high octane number and a very low olefins content.

TABLE F Recirculation of the C4 product fraction results in a higher average selectivity and a higher stability whilst the very high average activity and very high product quality are maintained.

TABLE G When a gasoline with a higher butenes content is used as the feed, then, at a comparable increase in aromatics content, a much smaller loss of C5+ is attained, in other words a higher selectivity of the quality improvement. Meanwhile the very high product quality is maintained.

Claims

1. A process for improving the quality of a gasoline obtained by catalytic cracking, characterized in that the gasoline is contacted with a crystalline metal silicate which, after one hour's calcination in air at 5000C, has the following properties: a) thermally stable up to a temperature of at least 6000 C, b) an X-ray powder diffraction pattern in which the strongest lines are the four lines mentioned in Table A.

TABLE A d(A)

11.2 +0.2

10.0 +0.2

3.84 + 0.07

3.72 + 0.06 c) in the formula which represents the composition of the silicate expressed in moles of the oxides and which, in addition to SiO2, includes both Fe2O3 and A12O3, the SiO2/Fe2O3 molar ratio is 25-90 and the SiO2/Al2O3 molar ratio is 2501200.

2. A process as claimed in claim 1, characterized in that the crystalline metal silicate has an alkali metal content of less than 0.05 %w.

3. A process as claimed in claim 1 or 2, characterized in that it is carried out at a temperature of 300-6000C a pressure of 1-50 bar and a space velocity of 0.1-1.0 kg. kg-l . h-1.

4. A process as claimed in any one of claims 1-3, characterized in that at least part of the C4product fraction is recirculated.

5. A process as claimed in any one of claims 1-4, characterized in that it is applied to a gasoline obtained by catalytic cracking which has an increased C3 and/or C4 olefins content.

6. A process as claimed in claim 5, characterized in that the increase of the olefins content of the gasoline has come about by carrying out the separation between the C4 fraction and the gasoline fraction of the cracked product in such a manner that at least part of the olefins which as a rule are withdrawn together with the C4- fraction, go into the gasoline fraction.

7. A process as claimed in claim 5, characterized in that the increase of the olefins content of the gasoline has come about by adding C3 and/or C4 olefins from an external source.

8. A process for improving the quality of a gasoline obtained by catalytic cracking, as claimed in claim 1, and substantially as described hereinbefore with reference to Experiments 4-6 of the example.

9. Gasoline of improved quality obtained according to a process as described in claim 8.