Abstract:
A fixed-bed catalyst is used for treating waste plastics to produce hydrocarbon fractions, gasoline and diesel oil. The catalyst comprises a silica carrier and active components having the formula of A a  B b  Al c  M d  Na e  Ca f  Fe g  O x . In the formula, A represents potassium, barium, phosphorus, vanadium, chromium, rare earth elements or their mixture. B represents elements of tungsten, molybdenum, nickel, germanium and platinum series. This catalyst has very high selectivity and activity and can be used for reaction at a relatively low temperature, thereby reducing energy consumption, and ensuring good yield of product. The mixed hydrocarbons generated by catalytic reaction using this catalyst may comprise more than 30 percent of aromatics and cyclanes in content.

Description:
FIELD OF THE INVENTION 
     This invention relates to a catalyst used for treatment of waste plastics to obtain hydrocarbon fractions, gasoline and diesel oil, particularly to a fixed bed catalyst. 
     BACKGROUND OF THE INVENTION 
     With the rapid development of plastic industry, plastic products are getting more and more important in our daily life and in the industrial production. Hence, more wastes from plastics are generated in accompanying with the abundant applications of plastics. Because the waste plastics can hardly be decomposed by themselves under natural condition, the waste plastics have polluted our survival environment seriously. Therefore, it has become a key problem for us to solve the pollution caused by the waste plastics, and to recover and re-utilize the waste plastics by processes of deharmfulness treatment and resource utilization. 
     So far, various methods have been proposed for treating waste plastics. Generally, a catalyst will be used for catalyzing thermal cracking of the waste plastics. For example, a method of treating waste plastics is described in U.S. Pat. No. 4,851,601, which includes disintegration of waste plastics, thermal cracking of the waste plastics in the reactor, and further catalytic cracking of vapor products by ZSM-5 catalyst with a medium-sized pore diameter. The product is then separated by a conventional technology. Another method known from JP-A-5-345894 is that waste plastics are thermally cracked at 200°-700° C., and then the product is catalytically cracked at 230°-650° C. 
     At present, most catalysts used to treat waste plastics are molecular sieve type, such as the above mentioned ZSM-5. When the catalysts are used in the above mentioned technologies to treat the waste plastics, there are certain disadvantages, such as the high temperature required for treatment, high energy-consumption, bad stability against oxidation for products, high cost and complicated manufacturing process for the catalysts, etc. Moreover, the pretreatment of cleaning and drying is needed, and serious carbonization occurs in the inner part of the reactor. 
     SUMMARY OF THE INVENTION 
     The present invention is aimed to solve the problems mentioned above and provide a catalyst which is of low-cost, simple operation, good product stability against oxidation and lower reaction temperature. 
     In accordance with this invention, a fixed-bed catalyst used for treating waster plastics comprises a carrier and a mixture of active components having the following formula: 
     
         A.sub.a B.sub.b Al.sub.c M.sub.d Na.sub.e Ca.sub.f Fe.sub.g O.sub.x 
    
     Wherein A is selected from the group consisting of potassium, barium, phosphorus, vanadium, chromium, rare earth elements and their mixture; B selected from the group consisting of molybdenum, tungsten, nickel, germanium and platinum series; wherein a is from 25 to 26.35 percent by weight, b from 36 to 37.05 percent by weight; c from 7.2 to 9 percent by weight, d from 1.14 to 1.55 percent by weight, e from 1.75 to 2.15 percent by weight, f from 2.40 to 2.80 percent by weight, g from 2.42 to 3.2 percent by weight, and wherein x is a sum of oxygen needed to the chemical bonding valences of said components in the catalyst, The carrier is a silica carrier. The content of the silica carrier in the catalyst has a range of 17 to 22% by weight. 
     A manufacturing and preparing method for this catalyst may be similar to those normal methods of any catalyst manufacturing, but has its own distinctive features. All components in the present catalyst is blended into a quasi thin silica powder at a ratio of less than 1:0.1. Then, the mixture is made into a slurry with Na 2  SiO 3 , and through a double roller machine to form pellets of diameter (Φ) about 6 mm and length 6 mm (Φ6 mm×6 mm). Then, the pellets are roasted under a temperature of 400° C.-800° C. to obtain the final product of catalyst. The roasting process is continuous without any pause during the roasting. The formation process of every element component of the catalyst is to be finished below 400° C. Therefore, the temperature increase should be controlled when it is approaching 400° C., that is, to keep the temperature between 300° C. to 400° C. for 20 to 30 minutes. The roasting and final formation are respectively conducted between the temperature from 400° C. to 800° C. A mass production can be carried out in a small concrete rotary kiln, with the complete period to be controlled within 4 to 5 hours. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The catalyst of this invention includes a silica carrier and a mixture of active components having the formula: 
     
         A.sub.a B.sub.b Al.sub.c M.sub.d Na.sub.e Ca.sub.f Fe.sub.g O.sub.x 
    
     The components of the catalyst related to this invention are taken from the following raw materials. The component A uses the oxides of potassium, barium, phosphorus, vanadium, chromium, and rare earth elements. The component B uses the oxides of molybdenum, tungsten, nickel, germanium and platinum group elements. The component Al uses Al 2  O 3 . The component M uses WO or (NH 4 ) 2  WO 4 . The component Na uses Na 2  SiO 3 , NaNO 3  NaOH or other sodium compounds. The component Ca uses CaCO 3 . The component Fe uses Fe 3  O 4 . A silica gel can be used as the silica carrier in the catalyst. 
     When the catalyst of this invention is being prepared, the raw materials for the components A and B can use all kinds of the oxides mentioned above respectively, or use one raw material containing all of the oxides mentioned above. The present inventor has discovered that a useful material is a tail-ore product of gold ores containing the oxides of potassium, barium, phosphorus, vanadium chromium and rare-earth elements, and the oxides of molybdenum, tungsten, nickel, germanium and platinum group elements. It is further found that the catalyst manufactured from the tail-ore product of gold ores possesses satisfactory performance. Therefore, it is a further advantage for this invention to make use of the waste materials causing pollution to the environment and achieve the aim of the environmental protection. When the catalyst of this invention is being prepared by the tail-ore product of gold ore, the contents of the various components of the tail-ore vary with the different natural conditions of the gold ores. Thus, it is necessary to adjust their amounts in accordance with analytical data. 
     According to this invention, the tail-ore product of gold ores is the optimal raw material for components A and B. However, any product having the listed elements should be equally acceptable as stated above. 
     When the waste plastics of polypropylene (PP), polyethylene (PE) and polystyrene (PS) are cracked into hydrocarbons by use of the catalyst of this invention, a mixture of various hydrocarbon fractions is obtained, which comprises 25 to 35% of alkane, 45 to 55% alkene, 10 to 15% of cyclanes and 15 to 23% of aromatics. The distribution of hydrocarbon fractions is relatively ideal, from which many chemical products can be obtained by proper methods of separation. Gasoline and diesel oil products can be obtained by rectification to separate the two fractions directly. 
     When the waste plastics are treated with the catalyst of this invention, the raw material PP, PE and PS are put into the reactor directly without any cleaning treatment. The reaction temperature needed is 150° C. lower than those using the catalysts of other technologies. Also, during the whole process of catalytic cracking, the yield of lean gas decreases, which increases the yield of the mixed hydrocarbon fractions by 3%. The ratio of catalyst to raw material treated is 1.5% by weight. 
     When the catalyst of this invention used in a fixed-bed reactor, the temperature of reaction ranges from 280° C. to 480° C., where the optimal temperature ranges from 280° C. to 415° C. The pressure of the reaction system ranges from 0.01 to 0.04 MPa, where the optimal reaction pressure is 0.025 MPa. 
     When the catalyst of this invention is used to decompose the waste plastics, a mixture of liquid fractions with the distribution of hydrocarbons mentioned above can be obtained by one-step process. When the mixed hydrocarbon fractions are put into the storage tank, the rectification can be proceeded directly to obtain gasoline and diesel oil and further processed by extraction, reaction, and fractionating so that other chemical products, such as benzene, toluene, xylene, butane and butadiene, etc., can be obtained. 
    
    
     Further explanation to this invention, the catalyst and preparation method, will be given with reference to the following examples: 
     EXAMPLE 1 
     100 grams of the tail ore mentioned above is pulverized together with a mixture of 7 grams of Al 2  O 3 , 4 grams of MoS 2 , 2.5 grams of NaNO 3 , 2.4 grams of CaCO 3 , 2.42 grams of Fe 3  O 4  into a powder of 80-120 μm in size, and then blended with 30 grams of quasi thin alumina powder. Then, the mixture obtained is mixed with 30 grams of silica gel to form a slurry with the addition of water. From the slurry, pellets of Φ6 mm×6 mm are formed through a double roller machine. Then, the pellets are treated for about 25 minutes at 400° C. and roasted for 3 hours at 650° C. to obtain the catalyst for this invention. 
     The catalyst obtained comprises A a  consisting of K of 0.035-1, B a  of 0.01-0.05, P of 0.01-0.05, Cr of 0.001-0.005, and R.E. of 0.01-0.7, wherein the optimal value is K of 0.08, Ba of 0.015, P of 0.025, Cr of 0.001, and R.E. of 0.3; B b  consisting of Mo of 0.02-1, W of 0.1-2.5, Ni of 0.01-0.04, Ge of 0.01-2, and Ru, Rh, Pd, Os, Ir, Pt of 0.01-0.02, wherein the optimal value is Mo of 0.075, W of 1.8, Ni of 0.025, Ge of 1.3, and Ru, Rh, Pd, Os, Ir, Pt of 0.01; and Al c  of 7; MOS 2d  of 4; Na e  of 3.5; Ca f  of 2.4; Fe g  of 2.42; O x  of the required amount. 
     EXAMPLE 2 
     140 grams of the tail-ore mentioned above is pulverized together with a mixture of 10 grams of Al 2  O 3 , 5 grams of MoS 2 , 5 grams of NaNO 3 , 4 grams of CaCO 3 , 2.42 grams of Fe 3  O 4  into a powder of 80-120 μm in size, and blended with 30 grams of quasi thin alumina powder. Then, the mixture obtained is mixed with 60 grams of silica gel to form a slurry with the addition of water. Pellets of Φ6 mm×6 mm are formed by the double roller machine. Then, the pellets are treated for about 25 minutes at 400° C. and roasted for 3 hours at 650° C. to obtain the catalyst of this invention. 
     The catalyst obtained comprises A a  consisting of K of 0.035-1, Ba of 0.01-0.05, P of 0.01-0.05, Cr of 0.001-0.005, and R.E. of 0.01-0.7, wherein the optimal value is K of 0.08, Ba of 0.015, P of 0.025, Cr of 0.001, and R.E. of 0.3; B b  consisting of Mo of 0.02-1, W of 0.1-2.5, Ni of 0.01-0.04, Ge of 0.01-2, and Ru, Rh, Pd, Os, Ir, Pt of 0.01-0.02, wherein the optimal value is Mo of 0.075, W of 1.8, Ni of 0.025, Ge of 1.3, and Ru, Rh, Pd, Os, Ir, Pt of 0.01; and Al c  of 10; MoS 2d  of 5; Na e  of 5; Ca f  of 4; Fe g  of 2.42; O x  of the required amount. 
     EXAMPLE 3 
     140 grams of the tail-ore mentioned above is pulverized together with a mixture of 15 grams of Al 2  O 3 , 7 grams of MoS 2 , 7 grams of NaNO 3 , 5.5 grams of CaCO 3 , 2.42 grams of Fe 3  O 4  into a powder of 80-120 μm in size, and blended with 30 grams of quasi thin alumina powder. Then, the mixture obtained is mixed with 75 grams of silica gel to form a slurry with the addition of water. Pellets of Φ6 mm×6 mm are formed by the double roller machine. Then, the pellets are treated for about 25 minutes at 400° C. and roasted for 3 hours at 650° C. to obtain the catalyst of this invention. 
     The catalyst obtained comprises A a  consisting of K of 0.035-1, Ba of 0.01-0.05, P of 0.01-0.05, Cr of 0.001-0.005, and R.E. of 0.01-0.7, wherein the optimal value is K of 0.08, Ba of 0.015, P of 0.025, Cr of 0.001, and R.E. of 0.3; B b  consisting of Mo of 0.02-1, W of 0.1-2.5, Ni of 0.01-0.04, Ge of 0.01-2, and Ru, Rh, Pd, Os, It, Pt of 0.01-0.02, wherein the optimal value is Mo of 0.075, W of 1.8, Ni of 0.025, Ge of 1.3, and Ru, Rh, Pd, Os, Ir, Pt of 0.01; and Al c  of 15; MOS 2d  of 7, Na e  of 7; Ca f  of 5.5; Fe g  of 2.42; O x  of the required amount. 
     APPLICATION EXAMPLE 1 
     15 grams of the catalyst obtained from example 1 is added to a 3-liter rector, and 1000 g. of uncleaned agricultural plastic films are added by several batches. The temperature is raised to 400±°40° C. 30-40 grams of gas product and 820-840 grams of liquid product are obtained by means of a 2-stage condensation system and the composition of the obtained liquid product is shown in table 1 below: 
     
                       TABLE 1______________________________________  component          A (g)______________________________________  n-alkane          9.88  iso-alkane          11.80  Σ alkene          47.57  n-alkene          17.14  iso-alkene          30.43  cyclanes          9.47  aromatics          21.28______________________________________ 
    
     APPLICATION EXAMPLE 2 
     The catalyst obtained from example 2 is used, and the other processing conditions are the same. The composition of the obtained liquid product is presented in table 2 below: 
     
                       TABLE 2______________________________________  component          B (g)______________________________________  n-alkane          27.73  iso-alkane          10.98  Σ alkene          41.68  n-alkene          18.16  iso-alkene          23.52  cyclanes          10.29  aromatics          9.32______________________________________ 
    
     APPLICATION EXAMPLE 3 
     The catalyst obtained from example 3 is used, and the other processing conditions are the same. The composition of the obtained liquid product is presented in table 3 below: 
     
                       TABLE 3______________________________________  component          C (g)______________________________________  n-alkane          16.68  iso-alkane          10.34  Σ alkene          55.32  n-alkene          16.53  iso-alkene          38.79  cyclanes          6.66  aromatics          11.00______________________________________ 
    
     APPLICATION EXAMPLE 4 
     The result in table 4 is obtained with the adjustment of reaction conditions indicated in table 4. In the application of Examples 1-3, in addition to the changes of hydrocarbon composition caused by the catalyst, the following parameters of overall efficiency, product yield and varying range of temperature, etc., have the same correlation as shown in Table 4. 
     
                       TABLE 4______________________________________Items          A         B         C______________________________________Amount of feed (Ton)          5         5         5Catalyst       Example 1 Example 2 Example 3Reaction time (hr.)          11        8         9Temp. of liquid phase (°C.)          337-389   341-384   315-376Temp. range (°C.)          52        43        61Temp. of vapor phase (°C.)          91-124    89-110    83-131Temp. range (°C.)          33        21        48Temp. of top part (°C.)          210-267   231-273   209-275Temp. range (°C.)          57        42        66Yield (%)      84.3      81.6      76.8______________________________________ 
    
     In sum, the advantages of the catalyst of this invention are low loss of lean gas, high average yield, long operation period, abundant resources of raw materials, low cost, and simple process, and satisfactory quality of products.