Process for the manufacture of diesel range hydro-carbons

Abstract

The invention relates to chemical industry and is directed to the production of middle distillate from vegetable oils. In the first step of the production method, the fatty acids or triglycerides of said vegetable oils are hydrogenated to give n-paraffins, and in the second step, the n-paraffins are catalytically converted to paraffins with branched chains. Using this process having two steps, a high-quality middle distillate useful as a component of diesel fuels without any particular specifications may be produced.

Description

FIELD OF THE INVENTION

The invention relates to the chemical industry and is directed to the production of middle distillate from vegetable oils. The product may for instance be used as a diesel fuel.

BACKGROUND OF THE INVENTION

Vegetable oils are a possible alternative for replacing energy of fossil origin by renewable raw materials.

Transesterification of vegetable oils (rapeseed oil) to give diesel fuels is a known process. For fuel applications, the esters require their own specification.

According to patent U.S. Pat. No. 4,992,605, fatty acids or triglycerides of fatty acids may be hydrogenated using conventional desulphurization catalysts (Co/Mo/alumina, or NiMO/alumina), resulting in diesel fuels as products with superior ignition properties. The feed stock fatty acid may be the TOFA fraction (TOFA=Tall Oil Fatty Acid) that may be distilled from tall oil. According to the examples of this document, said triglycerides may be derived from the following plants: rape, sunflower, or palm. The diesel fraction obtained by hydrogenation mainly consists of straight chain C₁₇ and C₁₈ paraffins which are known to have a high cetane number but also extremely poor low temperature properties. Thus, any amounts of such products mixed for instance into diesel fuels are necessarily low.

There are only a few publications concerning the isomerization of normal >C₁₀ paraffins (n-alkanes) with longer chains. Weitkamp, J., Jacobs, P. A., and Martens J. A. have investigated the hydroisomerization of C₁₀-C₁₆ n-alkanes using platinum and palladium on zeolite Y and HZSM-5 in the articles: Isomerization and Hydrocracking of C₉ through C₁₆ n-alkanes on Pt/HZSM-5 Zeolite (Applied Catalysis, 8, 1983). Said catalysts are very acidic, and accordingly, as a result of the high cracking activity thereof, hydrocarbons are cracked to give shorter, less valuable products.

For the isomerization of n-alkanes with long chains, various zeolites and molecular sieves generally added with a metal of Group VIII, normally platinum, as the hydrogenating component have been suggested, see for instance the documents FI 72435, 73367, and 89073.

GENERAL DESCRIPTION OF THE INVENTION

Now, a process according to Claim 1 for producing a middle distillate has been invented. Preferred embodiments of the invention are presented in other Claims.

In this process, fatty acids, or triglycerides of a vegetable oil are hydrogenated to give n-paraffins, followed by the conversion of said n-paraffins to paraffins with branched chains.

With said two-step process according to the present invention, a high quality middle distillate may be produced from vegetable oils, and further, this middle distillate may be used as a component in diesel fuels without modifying existing specifications.

DETAILED DESCRIPTION OF THE INVENTION

Middle distillate refers to a mixture of hydrocarbons boiling at a temperature ranging between 150 and 400° C.

In the process of the invention, a vegetable oil is used as the starting material. It may for instance comprise rapeseed oil, tall oil, sunflower oil, mustard oil, palm oil, or soybean oil.

A typical triglyceride molecule of rapeseed oil, and products obtained therefrom by hydrogenation are presented below. No cracking of the triglyceride structure is necessary for the hydrogenation of the TOFA fraction. Fatty acid molecules may be directly hydrogenated to n-paraffins, the acid groups then reacting to give water.

In the first step, the feed is hydrogenated to give n-paraffins as shown above. In the second step, the n-paraffins are isomerized using a suitable catalyst to give molecular structures retaining the favourable properties (such as high cetane number), associated, however, with the significant improvement of the low temperature properties. This requires that the overall total carbon number is preserved, and methyl branches are formed on the carbon chain at optimum sites for the cetane number. An example for the hydrogenation and isomerization of a TOFA molecule is shown below with the following equations, respectively:

In the hydrogenation step, commercially available desulphurization catalysts for middle distillates, typically NiMo/Al₂O₃ or CoMo/Al₂O₃ catalysts, may be used.

In the isomerization step, all isomerizing molecular sieves, and zeolites may be used as catalysts. Isomerization catalysts with lowest cracking activities are most suitable, e.g. Pt/SAPO-11/Al₂O₃, Pt/ZSM-22 and 23/Al₂O₃. A metal of the group VIII of the periodic table of the elements may be added to the catalyst.

In the hydrogenation step, the parameters are:

	recommended	range
	LHSV, h−1	about 1.5	0.5-5
	temperature, ° C.	about 390	330-450
	pressure, bar	about 50	>30
	hydrogen feed, l/l	about 900	≧150

In the isomerization step, the parameters are:

	recommended	range
LHSV, h−1	about 1	<10
temperature, ° C.	about 330	200-500
pressure, bar	about 70	normally pressurized to stabilize the
		catalyst
hydrogen feed, l/l	about 1000	normally in hydrogen to stabilize the
		catalyst

The middle distillate produced as described above may be used in various products, e.g. as an agent improving the cetane number of a diesel fuel (“super component”) without any particular specifications. Superior low temperature properties allow the use in winter, and further, permit large mixing ratios.

The product may be free of aromatics, thus making it excellently suitable for applications causing exposure to solvent vapours, or requiring burning of the product inside buildings. Such applications include solvents free of aromatics, and lamp kerosene.

No diesel fuels having acceptable low temperature properties are obtained by hydrogenation from vegetable oils. On the other hand, it is not possible to use only isomerization in case of olefins containing oxygen. Using the process of the invention, diesel fuels may be provided with a combination of properties otherwise hardly found simultaneously. The isomerization may be carried out without proceeding to far to detrimentally reduce the cetane number.

EXAMPLE 1

In the following, an example for conversion of vegetable oils to give high-quality middle distillate starting from the fatty acid fraction of tall oil (TOFA) is presented.

Feedstock

The feedstock comprised of TOFA having properties shown in Table 1 below.

TABLE 1
Tall Oil Fatty Acid 2 (TOFA 2)
Typical analysis
Acid number           194
Saponification number 195
Resin acids           1.9%
Unsaponified          2.4%
Iodine number (Wijs)  152
Colour °G             4 . . . 5
Density (20° C.)      0.91 kg/m3
Refractive index nD20 1.471
Fatty acid composition, % (typical)
16:0                  0.4
17:0 ai               0.6
18:0                  1.1
18:1 (9)              30.2
18:1 (11)             1.1
18:2 (5, 9)           1.0
18:2 (9, 12)          41.7
19:1 (9) ai           0.6
18:3 (5.9.12)         9.0
19:2 (5, 9) ai        0.3
19:2 (9, 12) ai       0.3
18:3 (9, 12 . . . 15) 0.6
20:0                  0.4
18:2 Conjugated       5.5
18:3 Conjugated       2.1
20:2 (11.14)          0.2
20:3 (5.11.14)        1.1
20:3 (7.11.14)        0.2
Others                3.6
                      100.0

Hydrogenation

TOFA vas hydrogenated using a normal desulphurization catalyst for middle distillates, NiMo/Al₂O₃. The aqueous phase was separated from the product with a separation funnel, the proportion of said phase being about 10% by weight. Analyses of the liquid hydrocarbon are presented in Table 2.

TABLE 2
Analyses of the hydrogenated TOFA product
	Method
Analysis	ASTM	Hydrogenized TOFA
Density 50° C.	kg/m3	D4052	771.6
Sulphur	mg/kg	D4294	0
Br index	—	D2710	64
Turbidity point	° C.	D2500	25
Distillation	TA/° C.	D86	285
	5 ml/° C.		298
	10 ml/° C.		301
	30 ml/° C.		304
	50 ml/° C.		304
	70 ml/° C.		306
	90 ml/° C.		312
	95 ml/° C.		341
	TL/° C.		347
Water	mg/kg	D1744	9.3
Acid number TAN	mg KOH/g	D974	0.05
Cetane number	—	D643	>74
n-Paraffins	p-%	GC-MS	82.0
i-Paraffins	p-%	GC-MS	0.6

The low acid number shows the considerable hydrogenization of the acid groups. The turbidity point of the product is very high, and accordingly, the product may be used as a diesel component only in minor proportions.

Isomerization

The zeolite ZSM-22 was prepared at the Åbo Akademie. The molecular sieves SAPO-11 were produced by the Indian National Chemical Laboratory (NCL) according to the documents U.S. Pat. No. 4,440,871 and U.S. Pat. No. 5,158,665. Also the ferrierite was produced by the NCL. Alumina, and platinum were added to the zeolites and molecular sieves as the support, and as the hydrogenating component, respectively.

The catalysts were produced using normal processes for producing catalysts. Production methods are also presented in the above Finnish patents.

The finished catalyst was ground and sieved to a suitable particle size for testing. The catalysts were loaded to a tubular reactor and reduced in a hydrogen stream at a temperature varying between 350 and 450° C. for an hour. The catalyst was cooled to 150° C. prior to pressurizing, and starting the feed of the hydrogenized TOFO. The test conditions were as follows: temperature, from 250 to 400° C.; hydrogen pressure, 50 bar; feed rate, WHSV=3 l/h; and hydrogen stream H₂/HC=500 l/l. The results are shown in Table 3.

TABLE 3
The product distribution in hydrogenated
and isomerized TOFA for various catalysts
			Pt/
	Pt/ZSM-22	Pt/SAPO-11	ferrierite
Gases (<C5), % by weight	1	3	0	1	0	10
Gasoline (C5 < 174° C.), % by	7	17	3	7	3	30
weight
Middle distillate (>174° C.),	92	80	97	92	97	60
% by weight
(n-C17 + n-C18) conversion,	39	90	38	79	8	68
% by weight
Isomerization selectivity of	65	63	78	75	40	18
the middle distillate fraction,
% by weight

(n-C₁₇+n-C₁₈) conversion in % by weight is calculated from the equation: $\mathrm{Conversion}=100*\left[1-\left(\frac{\mathrm{product}\text{:}n\text{-}{C}_{17}+n\text{-}{C}_{18}}{\mathrm{feed}\text{:}n\text{-}{C}_{17}+n\text{-}{C}_{18}}\right)\right]$

Isomerization selectivity of the middle distillate fraction in % by weight is calculated from the equation: $\mathrm{Selectivity}=100*\left(\frac{\begin{array}{c}\mathrm{isomers}\mathrm{of}\mathrm{the}\mathrm{middle}\mathrm{distillate}\mathrm{in}\mathrm{the}\mathrm{product}-\\ \mathrm{isomers}\mathrm{of}\mathrm{the}\mathrm{middle}\mathrm{distillate}\mathrm{in}\mathrm{the}\mathrm{feed}\end{array}}{\mathrm{conversion}}\right)$

As may be seen from Table 3, the selectivity of the isomerization depends on the type of the catalyst rather than on conversion. More acidic zeolites such as ZSM-22 and the ferrierite crack more effiently, and accordingly, the selectivities thereof are lower.

However, all catalysts of eventually very different types described above still isomerize hydrogenated TOFA.

Hydrogenated and Isomerized TOFA

The properties of hydrogenated and isomerized TOFA are presented in Table 4 below.

TABLE 4
Properties of hydrogenated and isomerized TOFA
			Hydroge-
			nated and
	Method	Hydrogenated	isomerized
Analysis	ASTM	TOFA	TOFA
Density 50° C.	kg/m3	D4052	771.6	769.7
Sulphur	mg/kg	D4294	0	0
Br index	—	D2710	64	200
Turbidity point	° C.	D2500	25	−12
Solidification point	° C.	D97		−12
Filterability	° C.	EN116		−11
Distillation	TA/° C.	D86	285	122
	5 ml/° C.		298	268
	10 ml/° C.		301	280
	30 ml/° C.		304	295
	50 ml/° C.		304	297
	70 ml/° C.		306	299
	90 ml/° C.		312	304
	95 ml/° C.		341	314
	TL/° C.		347	342
Cetane number	—	D643	>74	>74
n-Paraffins	p-%	GC-MS	82.0	13
i-Paraffins	p-%	GC-MS	0.6	73

The properties of hydrogenated and isomerized TOFA are excellent. It was possible to considerably improve the low temperature properties using isomerization, without simultaneously lowering the cetane number. The product is well suited as a component for diesel oil without limitations to the mixing ratio. It is also very suitable for solvents.

The largest volumes applicable for the middle distillates thus produced from vegetable oils would naturally be those of biocomponents for diesel fuels.

EXAMPLE 2

The catalysts were produced from the molecular sieve SAPO-11 synthetized at the NCL, in India. SAPO-11 A, and SAPO-11 B were crystallized according to the documents U.S. Pat. No. 4,440,871, and U.S. Pat. No. 5,158,665, respectively. 35% of Al₂O₃ was added as the support, whereas platinum (about 0.5% by weight) was added by impregnation using an aqueous Pt(NH₃)₄Cl₂ solution.

TABLE 5
Analyses of the catalysts
	SiO2/Al2O3 ratio in the	Pt content,
Catalyst	molecular sieve	% by weight	Pt dispersion
SAPO-11 A	0.35	0.50	50
SAPO-11 B	0.45	0.47	85

Hydrogenated TOFA feed was isomerized using above catalysts under following conditions:

Pressure    50 bar
WHSV        3−1
H/HC        about 600 l/l
Temperature 340, 360, 370° C.

The results are presented in Table 6.

TABLE 6
The product distribution in hydrogenated and isomerized
TOFA for the catalysts SAPO-11 A, and B
	SAPO-11A	SAPO-11A	SAPO-11B	SAPO-11B	SAPO-11B
Property	340° C.	360° C.	340° C.	360° C.	370° C.
Gases	1.0	1.1	<1.0	2.1	5.0
(<nC5), % by weight
Gasoline (nC5 < 174° C.),	1.5	3.9	2.6	9.6	16.0
% by weight
Middle distillate (>174° C.),	97.5	95.0	97.4	88.3	79.0
% by weight
(n-C17 + n-C18) conversion,	20.1	63.4	48.4	93.3	95.7
% by weight
Isomerization selectivity of the	76.2	78.9	81.4	73.3	63.9
middle distillate fraction,
% by weight

As may be seen from the results shown in the table, the isomerization selectivity of the middle distillate is considerably reduced once the conversion level is increased to >90% by weight.

EXAMPLE 3

A higher conversion level may be obtained by reducing the feed rate (WHSV). Isomerizations of the hydrogenated TOFA were carried out with the catalyst SAPO-11A using three WHSV values, or 1, 2 and 3 h−1. Other conditions are as in example 2. The results are presented in Table 7.

TABLE 7
Influence of WHSV on the isomerization
of TOFA using SAPO-11A
	340° C.	340° C.	340° C.	360° C.	360° C.	360° C.
Property	1 h-l	2 h-l	3 h-l	1 h-l	2 h-l	3 h-l
Gases (<nC5),	2.1	1.1	1.0	2.3	3.1	1.1
% by weight
Gasoline	2.7	2.1	1.5	8.7	3.9	3.9
(nC5 <
174° C.),
% by weight
Middle	95.3	96.9	97.5	89.0	93.1	95.0
distillate
(>174° C.),
% by weight
(n-C17 +	54.9	33.1	20.1	92.2	80.3	63.4
n-C18)
conversion,
% by weight
Isomerization	78.3	78.1	76.2	74.3	77.8	78.9
selectivity
of the middle
distillate
fraction, %
by weight

As from the results of Table 7 may be seen, a higher conversion level is obtained both by elevating the temperature, and lowering the WHSV value. The selectivity is clearly reduced only when the conversion level exceeds the limit value of 90% by weight.

Claims

1. Process for the manufacture of diesel range hydrocarbons wherein a feed is hydrotreated in a hydrotreating step and isomerised in an isomerisation step, characterized in that the feed comprises fresh feed containing at least 20% by weight of triglyceride C12-C16 fatty acids or C12-C16 fatty acid esters or C12-C16 fatty acids or combinations of thereof and the total feed contains 50-20000 w-ppm sulphur calculated as elemental sulphur.

2. Process according to claim 1, characterized in that the fresh feed contains at least 30% by weight and preferably at least 40% by weight of triglyceride C12-C16 fatty acids or other fatty acid esters or combinations of thereof.

3. Process according to claim 1, characterized in that the fresh feed contains more than 5% by weight of free fatty acids.

4. Process according to claim 1, characterised in that the feed contains less than 10 w-ppm alkaline and alkaline earth metals, calculated as elemental alkaline and alkaline earth metals, less than 10 w-ppm other metals, calculated as elemental metals and less than 30 w-ppm phosphorus, calculated as elemental phosphorus.

5. Process according to claim 1, characterized in that the feed comprises less than 20 wt-% of fresh feed and additionally at least one diluting agent.

6. Process according to claim 5, characterized in that the diluting agent is diluting agent is selected from hydrocarbons and recycled products of the process or mixtures thereof and the diluting agent/fresh feed-ratio is 5-30:1, preferably 10-30:1 and most preferably 12-25:1.

7. Process according to claim 1, characterized in that the feed contains 1000-8000 w-ppm and preferably 2000-5000 w-ppm of sulphur calculated as elemental sulphur.

8. Process according to claim 1, characterized in that at least one inorganic or organic sulphur compound or a refinery gas and/or liquid stream containing sulphur compounds is added to the feed.

9. Process according to claim 1, characterized in that the fresh feed is of biological origin selected from plant oils/fats, animal fats/oils, fish fats/oils, fats contained in plants bred by means of gene manipulation, recycled fats of the food industry and mixtures thereof.

10. Process according to claim 1, characterized in that the fresh feed is selected from rapeseed oil, colza oil, canola oil, tall oil, sunflower oil, soybean oil, hempseed oil, olive oil, linseed oil, mustard oil, palm oil, peanut oil, castor oil, coconut oil, lard, tallow, train oil or fats contained in milk or mixtures thereof.

11. Process according to claim 1, characterized in that the fresh feed comprises feed of biological origin and a hydrocarbon/hydrocarbons.

12. Process according to claim 1, characterized in that in the hydrotreatment step a catalyst bed system is used comprising one or more catalyst beds.

13. Process according to claim 1, characterized in that in the hydrotreating step, the pressure varies in the range of 2-15 MPa, preferably in the range of 3-10 MPa, the temperature varying between 200 and 400° C., preferably between 250 and 350° C., and most preferably between 280 and 345° C.

14. Process according to claim 1, characterized in that in the isomerisation step, the pressure varies in the range of 2-15 MPa, preferably in the range of 3-10 MPa, the temperature varying between 200 and 500° C., preferably between 280 and 400° C.

15. Process according to claim 1, characterized in that the hydrotreatment is carried out in the presence of a hydrogenation catalyst, said hydrogenation catalyst containing a metal from the Group VIII and/or VIB of the Periodic System.

16. Process according to claim 15, characterized in that the hydrotreating catalyst is a supported Pd, Pt, Ni, NiMo or a CoMo catalyst, the support being alumina and/or silica.

17. Process according to claim 1, characterized in that an isomerisation catalyst containing molecular sieve is used in the isomerisation step.

18. Process according to claim 17, characterized in that isomerisation catalyst comprises a metal from the Element Group VIII.

19. Process according to claim 17, characterized in that the isomerisation catalyst contains Al2O3 or SiO2.

20. Process according to claim 17, characterized in that the isomerisation catalyst contains SAPO-11 or SAPO-41 or ZSM-22 or ZSM-23 or ferrierite and Pt or Pd or Ni and Al2O3 or SiO2.