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  
       [0001]     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  
       [0002]     Vegetable oils are a possible alternative for replacing energy of fossil origin by renewable raw materials.  
         [0003]     Transesterification of vegetable oils (rapeseed oil) to give diesel fuels is a known process. For fuel applications, the esters require their own specification.  
         [0004]     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 C 17  and C 18  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.  
         [0005]     There are only a few publications concerning the isomerization of normal &gt;C 10  paraffins (n-alkanes) with longer chains. Weitkamp, J., Jacobs, P. A., and Martens J. A. have investigated the hydroisomerization of C 10 -C 16  n-alkanes using platinum and palladium on zeolite Y and HZSM-5 in the articles: Isomerization and Hydrocracking of C 9  through C 16  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.  
         [0006]     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  
       [0007]     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.  
         [0008]     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.  
         [0009]     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  
       [0010]     Middle distillate refers to a mixture of hydrocarbons boiling at a temperature ranging between 150 and 400° C.  
         [0011]     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.  
         [0012]     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.  
                         
 
         [0013]     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:  
                         
 
         [0014]     In the hydrogenation step, commercially available desulphurization catalysts for middle distillates, typically NiMo/Al 2 O 3  or CoMo/Al 2 O 3  catalysts, may be used.  
         [0015]     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/Al 2 O 3 , Pt/ZSM-22 and 23/Al 2 O 3 . A metal of the group VIII of the periodic table of the elements may be added to the catalyst.  
         [0016]     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   &gt;30           hydrogen feed, l/l   about 900   ≧150                      
 
         [0017]     In the isomerization step, the parameters are:  
                                                                 recommended   range                                    LHSV, h −1     about 1   &lt;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                  
 
         [0018]     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.  
         [0019]     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.  
         [0020]     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  
       [0021]     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.  
         [0000]     Feedstock  
         [0022]     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/m 3             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 
 
         [0023]     TOFA vas hydrogenated using a normal desulphurization catalyst for middle distillates, NiMo/Al 2 O 3 . 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/m 3     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   &gt;74       n-Paraffins   p-%   GC-MS   82.0       i-Paraffins   p-%   GC-MS   0.6                  
 
         [0024]     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.  
         [0000]     Isomerization  
         [0025]     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.  
         [0026]     The catalysts were produced using normal processes for producing catalysts. Production methods are also presented in the above Finnish patents.  
         [0027]     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 H 2 /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 (&lt;C 5 ), % by weight   1   3   0   1   0   10       Gasoline (C 5  &lt; 174° C.), % by   7   17   3   7   3   30       weight       Middle distillate (&gt;174° C.),   92   80   97   92   97   60       % by weight       (n-C 17  + n-C 18 ) 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-C 17 +n-C 18 ) conversion in % by weight is calculated from the equation:  
       Conversion   =     100   *     [     1   -     (         product   ⁢     :     ⁢           ⁢   n   ⁢     -     ⁢     C     17   ⁢                 +     n   ⁢     -     ⁢     C   18             feed   ⁢     :     ⁢           ⁢   n   ⁢     -     ⁢     C     17   ⁢                 +     n   ⁢     -     ⁢     C   18           )       ]           
 
         [0028]     Isomerization selectivity of the middle distillate fraction in % by weight is calculated from the equation:  
       Selectivity   =     100   *     (               isomers   ⁢           ⁢   of   ⁢           ⁢   the   ⁢           ⁢   middle   ⁢           ⁢   distillate   ⁢           ⁢   in   ⁢           ⁢   the   ⁢           ⁢   product     -               isomers   ⁢           ⁢   of   ⁢           ⁢   the   ⁢           ⁢   middle   ⁢           ⁢   distillate   ⁢           ⁢   in   ⁢           ⁢   the   ⁢           ⁢   feed           conversion     )           
 
         [0029]     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.  
         [0030]     However, all catalysts of eventually very different types described above still isomerize hydrogenated TOFA.  
         [0000]     Hydrogenated and Isomerized TOFA  
         [0031]     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/m 3     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   &gt;74   &gt;74       n-Paraffins   p-%   GC-MS   82.0   13       i-Paraffins   p-%   GC-MS   0.6   73                  
 
         [0032]     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.  
         [0033]     The largest volumes applicable for the middle distillates thus produced from vegetable oils would naturally be those of biocomponents for diesel fuels.  
       EXAMPLE 2  
       [0034]     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 Al 2 O 3  was added as the support, whereas platinum (about 0.5% by weight) was added by impregnation using an aqueous Pt(NH 3 ) 4 Cl 2  solution.  
                                 TABLE 5                           Analyses of the catalysts                SiO 2 /Al 2 O 3  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                  
 
         [0035]     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.                      
 
         [0036]     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   &lt;1.0   2.1   5.0       (&lt;nC 5 ), % by weight       Gasoline (nC 5  &lt; 174° C.),   1.5   3.9   2.6   9.6   16.0       % by weight       Middle distillate (&gt;174° C.),   97.5   95.0   97.4   88.3   79.0       % by weight       (n-C 17  + n-C 18 ) 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                  
 
         [0037]     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 &gt;90% by weight.  
       EXAMPLE 3  
       [0038]     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 (&lt;nC 5 ),   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       (nC 5  &lt;       174° C.),       % by weight       Middle   95.3   96.9   97.5   89.0   93.1   95.0       distillate       (&gt;174° C.),       % by weight       (n-C 17  +   54.9   33.1   20.1   92.2   80.3   63.4       n-C 18 )       conversion,       % by weight       Isomerization   78.3   78.1   76.2   74.3   77.8   78.9       selectivity       of the middle       distillate       fraction, %       by weight                  
 
         [0039]     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.