MODIFICATION OF ZEOLITES

Abstract: A method for the modification of the framework structure of a zeolite comprises treating the zeolite with a solution in an organic solvent of a compound of an element capable of structural remplacement of aluminium in the framework, the aluminium-replacing element being selected from, for example, boron, tin, silicon, titanium, germanium, gallium, phosphorus, beryllium and magnesium preferably in the form of their halides or organometallic compounds. Typical compounds are BCl3, BBr3, SnCl4, SnBr4, SnI4, SiCl4, SiI4, TiCl4, GeCl4, GaCl4, PCl5, BeCl2, MgCl2 and beryllium diphenyl. In a preferred embodiment the zeolite is reacted with silicon tetrachloride in carbon tetrachloride under reflux. However, the reaction time can be reduced by utilizing a solvent which has a molecular size which prevents it entering the channels of the zeolite, one such solvent being tetraethoxysilane.

Description: Modification of Zeolites This invention relates to a process for the chemical modification of zeolite structures. Zeolites are crystalline hydrated aluminium silicates which have the general chemical formula: M 2/n°- A1 2 0 3- ~ S1 V y H 2° where M is a cation of valency n and x is greater than or equal to 2.0. Structurally they have a porous framework based on an extended three-dimensional framework of SiO, and &1Q, tetrahedra linked together through common oxygen atoms. A large number of natural and synthetic zeolites are known but only a comparative few of these have found application as catalysts in the chemical industry. However, the important catalysts faujasite (in the form of the synthetic zeolites X and Y), mordeπite and ZSM-5 (Trade Mark) are used in substantial quantity: for example, more than 100,000 tons per year in 1970 were consumed in petroleum cracking. It is synthetic faujasite (as zeolite Y) which is principally used for this purpose. However, as synthesised, the value of x in the above formula for zeolite Y is approximately 5.0 and the resulting framework is not sufficently stable to withstand the high temperatures (800 C) involved in the regenerator unit of cracking plants where coke is burnt off. (By "coke" is meant the deposits of carbon and low hydrogen content hydrocarbons that build up in petroleum cracking). To improve the thermal stability of the zeolite, the Si0 2 /Al 2 0« ratio has to be increased. Several methods have been proposed but, principally for reasons of cost, the preferred methods ar_ based on the following chemical process: Naγ exchange calcine 500°C H _ y with ~ Eζ ~~ under steam that is, the hydrogen (H ) form is made by calcination of the ammonium (NH,) exchanged form in the presence of steam at high temperatures. This results in some of the aluminium atoms leaving the framework and being deposited in the channel network as extra-framework aluminium. The vacancies are filled by atoms of silicon diffusing from other parts of the crystallites. Obviously the net result is the production of a partially crystalline material along with some amorphous material and the introduction of some mesopores into the system. The resulting material, however, is an excellent selective catalyst. The other methods which can be used to increase the silicon to aluminium ratio are (a) extraction of aluminium by EDTA (ethylenediaminetetraacetic acid) (b) acid treatment and (c) use of silicon tetrachloride vapour. EP-A-82211 describes the use of an aqueous solution of a fluorosilicate to replace aluminium with silicon in the framework. The use of the SiCl, vapour, as described for example in EP-A-62123 and EP-A-72397, has some useful effects. The vacancies in the framework, produced by the extraction of aluminium, are healed by silicon atoms from the tetrachloride, and, the aluminium removed from the framework is converted to its volatile trichloride effecting removal from the system. However, problems associated with the vapour phase process are (a) the cost of the silicon tetrachloride, (b) the high temperature required, and, (c) the potential danger of collapse of the structure of the framework unless the temperature is strictly controlled. EP-A-210018 describes another process for the modification of zeolite framework structures which involves treatment of the zeolite with a molten salt medium which contains a reactive component which has a "radius ratio" of less than 0.6, the "radius ratio" being defined as the ratio of the crystal ionic radius of the central atom of the reactive component to that of the the 2- oxygen anion 0 . The method is applicable to porous crystalline minerals which have pores large enough to sorb normal hexane. Examples of the components which have the required radius ratio are: the trichlorides of aluminium, boron, iron, phosphorus and gallium, and the tetrachlorides of titanium and 4+ tin, the Si ion being also mentioned. The method may be used to insert aluminium into high silicon zeolite frameworks or otherwise alter the framework without substantial alteration of its structure. An object of the present invention is to provide an improved method for * the modification of zeolite framework structures. According to the present invention there is provided a method for the modification of the framework structure of a zeolite comprising treating the zeolite with a solution in an organic solvent of a compound of an element capable of structural replacement of aluminium in the framework. The compound is preferably a metal halide of the aluminium- replacing element, examples being: BC1~, BBr,, S Q 1_., SnBr 4 , Snl^, SICl^ . Sil 4 _ TiC__ 4 _ GeCl 4 , GaCl 4 , PCl e , BeCl 2 CI, and MgCl„. However, organometallic compounds of the selected element may also be suitable, for example, beryllium diphenyl. The zeolite may be, for example, Erionite, Beta, ZSM-5, ZSM-11 (Trade Marks), Mordenite, Chabazite, and Offretite. -4- The selection of the solvent is not critical. Solvents, and solvent mixtures, of small molecular size, such as carbon tetrachloride and ethanol, are suitable but the reaction may be accelerated by the use of a solvent of a molecular size which is too large to enter the channels of the zeolite, one particularly preferred solvent for this purpose being tetraethoxysilane [C 2 H 5 0) 4 Sil. The temperature of the treatment is not of critical importance but would normally be carried out at the reflux temperature of the solvent in order to minimise the treatment time. The method of the invention may include a pretreatment step in which the zeolite is treated with acid to effect a desired degree of dealumination, prior to treatment with the solvent solution compound of the aluminium-replacing element. Since the degree of dealumination with acid is restricted only by the need to maintain the integrity of the zeolitic structure, the use of the acid pretreatment step enables the production of zeolites with very high silicon to aluminium ratios. As well as increasing the thermal stability of the zeolite increase of the silicon to aluminium ratio improves the Bronsted activity of the OH groups which remain in the dealuminated framework. The invention will now be described, by way of illustration, in the following Examples. EXAMPLE 1 About 1 gram of Na_ zeolite was calcined in a muffle furnace at 600 G for a few hours. The zeolite was then cooled to 80-100 C in a desiccator and 25ml of carbon tetrachloride (CC1 4 ) was then added with continuous stirring to form a slurry. various amounts (0.10 to 0.77ml) of silicon tetrachloride (SiCl 4 ) were added to several separate samples of the slurry which were then refluxed at a fixed temperature (58-59°C; 76-77°C) for a period of three hours. The final slurry was then centrifuged to separate the solid and liquid phases. Three successive portions of CC1 4 (approximately 15ml) followed by three successive portions of ethanol (approximately 15ml) were employed during the solid/liquid separation stage. The product was dried on a water bath and treated with sodium chloride solution (1-5M) repeatedly to convert the zeolite to the pure sodium form. The product was then well washed with distilled deionised water (boiled and cooled out of contact with air) until free of chloride, dried at 100 C and calcined at 600 C for one hour. The calcined zeolite was allowed to cool and treated with sodium chloride solution (1-5M at pH 8-9) repeatedly. The final product was well washed until chloride-free, filtered and dried at 100°C. Analysis of the dealuminated samples was as follows: (a) Dealuminated samples were calcined at 600 C to obtain the dry weight and the residues dissolved to determine the aluminium content by EDTA titration. 22 (b) Sodium was determined by Na tracer method. (c) Silicon was estimated by difference. (d) Collapse temperature was determined by differential thermal analysis using a Du Pont 990 Thermal Analyser (in nitrogen). The results are reported in Table I below. TABLE I Sample sιcι 4 Ee lux Al Na Al Collapse No. added(ml) T°C mmol/g mmol/g /u.c* T°C CSO.10/58 0.10 58-59 2.95 2.92 49.3 1012 CSO.20/58 0.20 58-59 2.97 2.89 50.1 1014 CSO.33/58 0.33 58-59 2.79 2.83 46.8 1023 CSO. 0/58 0.40 58-59 2.84 2.86 47.5 1015 CSO.77/58 0.77 58-59 2.86 2.82 47.3 993 CSO.10/76 0.10 76-77 2.98 2.94 49.5 984 CSO.27/76 0.27 76-77 2.78 2.72 45.8 1009 CSO.33/76 0.33 76-77 2.71 2.61 45.3 1021 CSO.77/76 0.77 76-77 2.74 2.64 44.8 1007 Starting Material, Na_Y 3.28 3.11 56.1 933 * based on total Al present - 192 Al sites in unit cell (u.c.) EXAMPLE 2 The same procedure as described in Example 1 was used except that 15ml of CCl, and 0.3ml SiCl 4 were refluxed with Na_Y zeolite with different water content at 59°C for 20 minutes. The results are given in Table II below. TABLE II Sample Water Al Na Al Collapse No. content :/u. ,c. mmol/g mmol/g /u.c. T°C CS (1) 11 2.96 2.89 49.9 1002 CS (2) 30 2.90 2.91 48.4 1015 CS (3) 23 2.90 2.89 48.7 1013 CS (4) 39 2.90 3.01 48.1 1008 0.3 CSH 245 2.47 2.38 39.8 998 EXAMPLE 3 Using the procedure described in Example 1 above ' , 20ml of CCl, and 10ml SiCl, were refluxed with zeolites with different 4 4 cationic forms at 58-60 C for one hour. The results are given in Table III below. TABLE III Sample Cationic Al Na /other Al Coll. No . form mmol/g ; cation mmol/g /u.c . T°C LiY 600* Li 3.01 2.66 49.0 1001 NaY 600 Na 2.70 2.64 44.5 1030 KY 600 K 2.89 2.71 47.1 1015 ** CsY 600 Cs ,Na 3.12 3.11 52.4 996 BaY 600 Ba ,Na 3.09 2.32 50.0 982 ** 2LaY 600 La , Na 2.84 1.71/0.66 52.0 956 ** CeY 600 Ce ,Na 2.91 1.77/0.69 53.7 978 * zeolite Y calcined at 600°C ** + 16 Na in small cages. EXAMPLE 4 Using the same procedure as is described in Example 1, 30ml of SiCl1 4 , wwaass rreefflluuxxeedd wwiitthh NNaaYY_ zzeeoolliittee aatt 557 " C and samples were withdrawn after 30, 60 and 90 minutes. The results are reported in Table IV below. TABLE IV Sample Seflux Al Na Al Collapse No. Time (min) mmol/g mmol/g /u.c. τ°c S0.50/57 30 2.31 2.24 37.5 1031 SI.0/57 60 2.33 2.20 37.0 - SI. /57 90 2.32 2.25 37.3 1041 SS0.5/1.5 30 2.16 1.93 33.2 1070 Samples SO.50/57, SI.0/57 and SI.5/57 were mixed with 15ml SiCl 4 and refluxed at 57 C for 30 minutes to produce sample SS0.5/1.5. EXAMPLE 5 Using the procedure described in Example 1, 15ml of SiCl 4 were refluxed with zeolite produced from Example 1 (Sample Nos. CSO.10/58 + CS0.20/58 -i- CSO.10/76) at 57°C for 30 minutes. Four cycles were carried out. The results are given in Table V below. TABLE V Sample Reflux Al Na Al Collapse No. Cycle mmol/g mmol/g /u.c. τ°c S 1 2.09 2.04 33.4 1056 SS 2 2.00 1.81 30.6 1063 SSS 3 1.83 1.66 27.8 1078 SSSS 4 1.81 1.62 27.4 1073 Starting material dealuminated zeolite 49.6 Table VI reports the results of infra-red characterisation studies and Table VII the results of X-ray diffraction studies, confirming the increase of the Si/Al ratio of the zeolite Y framewor . ΓABLE VI Sample Al/u.c. Asymmetric Symmetric Double Sings No. (cm ) (cm ) (cm ) NaY 56 .1 1015 s 790 m 582 CS (1) 50, .1 1023 s 793 m 584 m CS (4) 48, .1 1030 s 793 m 585 m CSO.33/58 46. .8 1030 s 798 m 588 CSO.33/76 45. .3 1030 s 8C0 m 588 m S 33, .4 1042 s 805 m. 593 m SS 30. ,6 1045 s 810 m 597 m SSSS 27. ,4 1050 s 810 m 597 m s = strong m = medium TABLE VII Sample Lattice Constant Al/u.c. No. a +0.06 A o— NaY 24 .59 56.1 SO.50/57 24 .68 37.5 SI.0/57 24 .48 37.0 SI.5/57 24 .48 37.3 SS0.5/1 .5 24 .41 33.2 S 24 .41 33.4 SS 24 .41 30.6 SSS 24 .38 27.8 SSSS 24 .38 27.4 CSO.33/57 24 .53 46.8 CSO.77/57 24 .53 47.3 EXAMPLE 6 Table VIII below reports the products (in sodium form) resulting from the dealumination of sodium Y zeolites by SiCl 4 in the solvent tetraethoxysilane [(C 2 H.0 4 Si_ (TES). The methods used were as follows: Method A (Sample STES NaY) About 1 gram of sodium Y zeolite [Z_(H)_ was calcined at 600 C and allowed to cool in a desiccator. 25ml of TES were added to the zeolite followed by 1ml of SiCl, . The mixture was refluxed for one hour. Method B (Sample STES DY) The method was as described under Method A above but sodium Y zeolite [ZY(D)_ was used. Method C (Samples STES DY 0.5; STES DYl; STES DY2 and STES DY18B) About 19 grams of sodium If zeolite (ZY[D_) was calcined at 600 C and allowed to cool in a desiccator. 45 ml of SiCl 4 were added to the zeolite with constant stirring for 1-2 minutes follwed by 70ml of TES. The resultant slurry was refluxed for 18 hours. Zeolite slurry samples were withdrawn after 30 minutes, one hour, two hour and 18 hour intervals. From the results reported in Table VIII below, particularly the results of Method C, it can be seen that dealumination is substantially complete within the first 30 minutes of reaction time. These samples all showed very good crystallinity; as good as the starting sodium Y zeolite. TABLE VIII Sample Beflux H 2 0 Al 2 Λ NTa Si/Al No. T°C % mmol l ~ mmol/g ratio 1STES NaY 110- 116 22.76 3.02 3.17 2.87 1STES DY 103 22.92 3.02 3.07 2.88 STES DY 0.5 80 21.15 2.28 2.07 4.43 STES DY 1 78 21.28 2.28 2.09 4.41 STES DY 2 78 20.89 2.46 2.05 4.05 STES DY 18B 78 21.32 2.28 2.07 4.41 TABLE : viii (continued) Sample Al/u. >c. Collapse Lattice 0 No. τ°c Constant A 1STES NaY 49.6 991 - 1STES DY 49.5 999 - STES DY 0.5 35.4 1052 24, .34 STES DY 1 35.5 1052 24. .36 STES DY 2 38.0 1050 - STES DY 18B 35.5 1010 24. ,36 • EXAMPLE 7 Table IX reports the product (in sodium form) resulting from the dealumination of sodium Y zeolite by a SiCl 4 /CCl 4 / C„H-0H solvent mixture. About one gram of sodium Y zeolite [56Al/u.c, ZY(H)] was calcined at 600 C for a few hours and allowed to cool in a desiccator. 12.5ml of CC1 4 were added to the zeolite followed by 1ml of SiCl.. The mixture was refluxed at 56 C for 30 minutes when 12.5ml of ethanol were Introduced. Hefluxing at 63 C was continued for a further 30 minutes. TABLE IX Sample No. 1 CSEtNaY Beflux 56/63°C H 2 0 22.12% Al 2.94mmol/g 22 Na 2.97mmol/g Si/Al ratio 3.04 Al/u.c. 47.5 Collapse 994°C EXAMPLE 8 Table X below reports the products (in sodium form) resulting from the dealumination of sodium Y zeolites by SiCl 4 /ethanol solutions. TABLE X Sample Seflux H 2 0 Al 22 Na Si/Al No. T°C % mmol/g mmol/g ratio SEtDY 0.5 70 22.41 2.72 2.68 3.39 SEtDY 1 70 22.46 2.71 2.69 3.40 S0.5EtDY 0.5 70 22.21 2.60 2.60 3.62 S0.5EtDY 1 70 22.47 2.62 2.48 3.58 5S5EtDY 78.9 21.73 2.76 2.78 3.35 lOSlOEtDY 78.3 22.09 2.81 2.79 3.25 !CSEt5NaY 75.2 22.34 2.79 2.65 3.29 SEtNaY 57/74 19.79 2.81 2.80 3.39 ISEtNaY 57/74 23.24 2.88 2.87 3.07 SEtG 57/74 21.31 2.65 2.49 3.60 TABLE X (continued) Sample Al/u.c. Collapse No. τ°c SEtDY 0.5 43.7 1014 SEtDY 1 43.6 1019 S0.5EtDY 0.5 41.6 1027 S0.5EtDY 1 41.9 1028 5S5EtDY 44.1 1017 lOSlOEtDY 45.2 1007 lCSEt5NaY 44.8 1006 SEtNaY 43.7 990 ISEtNaY 47.2 1001 SEtG 41.7 1030 EXAMPLE 9 Method (i) (Samples SEtDY 0.5 and SEtDY 1) About 5 grams of the sodium form " zeolite (approximately 56 Al/u.c; ZY[D]) was calcined at 600 C for a few hours and allowed to cool in a desiccator. 20 ml of SiCl, were added to 4 the zeolite and stirred for 5 minutes. Five successive portions of CC1 4 of approximately 20ml were added to the zeolite slurry and the CC1 4 was discarded after centrifuging the slurry. 80ml of ethanol were then added and refluxed for one hour. Approximately 50ml of the slurry was withdrawn after 30 minutes and the rest after one hour. Method (ii) (Samples S0.5EtDY0.5 and S0.5EtDY 1) The method was the same as Method (i) above except that the contact time of the zeolite and SiCl, was increased to 15 minutes. Method (iii) (Sample 5S5EtDY) About 5 grams of sodium _ zeolite (ZY[D]) was calcined at 600°C for a few hours and cooled in a desiccator. 5ml of SiCl, were added to the zeolite and stirred for 5 minutes. 4 50ml of ethanol were then added to the slurry and refluxed for one hour. Method (iv) (Sample lOSlOEtDY) The method was the same as Method (iii) above except that 10ml of SiCl, were used and the SiCl.-zeolite contact time was 4 4 - increased to 10 minutes. Method (v) (Sample !CSEt5NaY) About one gram of sodium _ zeolite (ZY[H]) was calcined at 600 C for a few hours and allowed to cool in a desiccator. About 1ml of SiCl, was added to the zeolite and stirred for 5 minutes. 25ml of ethanol were then added to the slurry and refluxed for one hour. Method (vi) (Sample SEtNaY) About one gram of sodium Y_ zeolite (ZY[H]) was calcined at 600 C for a few hours and allowed to cool in a desiccator. About 15ml of SiCl 4 were added to the zeolite and refluxed for 30 minutes. The zeolite slurry was then centrifiged to separate the solid and liquid phases. The zeolite was washed with three successive 10ml portions of CCl,. About 25ml of ethanol were added to the zeolite and refluxed for 15 minutes. Me hod (vii) (Sample lSEtNaY) The method was the same as Method (vi) except that 1ml of SIC1 4 and 14ml of CC1 4 were used in the first refux. Method (viii) (Sample SEtG) The method was the same as Method (vi) except that 10 grams of sodium Y zeolite (ZY.GD, 80ml of SiCl 4 and 100ml of ethanol were used. EXAMPLE 10 Table XI below reports the products resulting from the dealumination of sodium Y_ zeolites followed by treatment with various mixtures including SiCl, as a component. TABLE XI o 22 Sample Temperature C H 2 0 Al Na Si/Al No. Preheat Eeflux % mmol/g mmol/g ratio Method I - CSH SEBIES CS4 100 59 2 244..3300 2 2..9900 3 3..0011 2 2..9977 CSH48 100 59 2 244..7733 2 2..4422 2 2..4477 3 3..8800 CSH40 100 59 2 244..7744 2 2..2211 2 2..2200 4 4..3311 CSH32 100 59 2 233..7733 1 1..9977 1 1..9988 5 5..0088 CSH24 100 59 2 244..9966 1 1..5566 1 1..5566 6 6..6644 CSH16 100 59 2 233..9999 1 1..2222 1 1..2233 9 9..0000 Method II - HCS SEBIES HCS32 100 59 18.67 2.11 2.12 5.05 HCS16 100 59 17.52 1.25 1.27 9.61 Method III - STES SEBIES STES NaY 300 71 21.78 2.96 3.05 3.02 STES H48 300 71 21.58 2.66 2.76 3.53 STES H40 300 69 20.24 2.44 2.51 4.07 STES H32 120 69 16.64 2.19 2.21 4.97 STES H24 120 67 17.27 1.74 1.88 6.52 STES HI6 120 69 16.05 1.38 1.45 8.74 TABLE XI (continued) Sample Al/u.c. Collapse No. τ°c Method I - CSH SEBIES CS4 48.4 1008 CSH48 40.0 1021 CSH40 36.2 1031 CSH32 31.6 1023 CSH24 25.1 981 CSH16 19.2 990 Method II - HCS SEBIES HCS32 31.7 1021 HCS16 18.1 1014 Method III - STES SEBIES STES NaY 47.8 993 STES H48 42.4 1001 STES H40 37.9 1013 STES H32 32.2 991 STES H24 25.5 949 STES H16 19.7 931 The dealuminated zeolite is made by treatment of sodium Y zeolite with hydrochloric acid. Dealumination does not occur when the pH of the acid is greater than 2.30, while complete dealumination occurs at pH less than 0.46. It appears that four hydrogen atoms are required to remove one aluminium atom. This acid dealumination results in a structure which is less crystalline than the initial zeolite (due to accumulated defects In the structure ) and is not thermally stable. However, treatment with SiCl 4 -containing mixtures allows insertion of silicon into the zeolite matrix and gives a product of reasonable thermal stability. The treatment with SiCl 4 was by three different methods. Method I - CSH SEBIES About 0.5 gram of dealuminated Y_ zeolite (by HC1 treatment) in sodium form was dehydrated in an oven at 100 C for a few hours and then allowed to cool in a desiccator. The zeolite was then mixed with 15ml of CC1 4 followed by 0.30ml of SiCl, and refluxed for 30 minutes. Method II - HCS SEBIES The procedure was the same as Method I above except that 10ml of CC1 4 and 5ml of SIC1 4 were used. Method III - STES SEBIES About one gram of dealuminated Y_ zeolite (by HC1 treatment) in sodium form (as used in Methods I and II above) was dehydated in an oven at two temperatures (120 C and 300 C) for a few hours and then allowed to cool In a desiccator. The zeolite was then mixed with 3ml of SiCl, with constant stirring for 5 minutes. 20ml of TES was added to the slurry and refluxed for one hour. The highly dealuminated samples (those with fewer than 32 atoms of aluminium per unit cell) had poor crystallinity.

Claims: CLAIMS 1. A method for the modification of the framework structure of a zeolite, comprising treating the zeolite with a solution in an organic solvent of a compound of an element capable of structural replacement of aluminium in the framework. 2. A method as claimed in claim 1, in which the aluminium-replacing element is selected from boron, tin, silicon, titanium, germanium, gallium, phosphorus, beryllium aluminium and magnesium. 3. A method as claimed in claim 1 or claim 2, in which the said compound is selected from the halides of the aluminium- replacing element. 4. A method as claimed in claim 3, in which the halide is selected from BC1- , BBr 3 , SnCl 4 , SnBr 4 , Snl 4 , SiCl 4 ) , sιι 4 , TiCl 4 , GeCl 4 . , GaCl 4 . , PCI 5 , BeCl 2 A1C1 3 and MgC . 5. A method as claimed in claim 4, in which the halide is silicon tetrachloride. 6. A method as claimed in claim 1 or claim 2, in which the said compound Is an organometallic compound. 7. A method as claimed in claim 6, In which the organometallic compound Is beryllium diphenyl. 8. A method as claimed in any preceding claim, in which the organic solvent is carbon tetrachloride or ethanol or a mixture thereof. 9. A method as claimed in any of claims 1 to 7, in which the solvent is an organic liquid having molecules which are too large to enter the channels of the zeolite. 10. A method as claimed in claim 9, in which the solvent is tetraethoxysilane. 11. A method as claimed in any preceding claim, in which the zeolite Is selected from Erionite, Beta, ZSM-5, ZSM-11, Mbrdenite, Chabazite, and Offretite. 12. A method as claimed in any preceding claim, in which the treatment carried out under solvent reflux conditions. 13. A method as claimed in any preceding claim, in which the zeolite is pretreated with acid to remove aluminium therefrom. 14. A method of thermally cracking petroleum hydrocarbons characterised in that said cracking is conducted in the presence of a modified zeolite, said zeolite being the product of a process as claimed in any of the preceding claims.

Inventors: LEE EDWARD FOOK TIN, REES LOVAT VICTOR CHARLES, LEE, EDWARD, FOOK, TIN, REES, LOVAT, VICTOR, CHARLES
Applicants: RESEARCH CORP, RESEARCH CORPORATION LIMITED
Application year: 1987
Main classification: C01B33
IPC codes: B01J29, C01B35, C01B39, C10G11