Abstract:
A method for agglomerating fine particles, involves reacting urea, urea/formaldehyde condensate, a strong inorganic acid, preferably sulfuric acid, and at least one polyfunctional compound chosen from the group consisting of hydroxycarboxylic acids, dicarboxylic acids, and polyols (containing at least two hydroxy groups) in the presence of particles to be agglomerated to form a fine particle agglomerate. Optionally, molasses, p-toluene sulfonic acid, xylene sulfonic acid or resorcinol can be added to the binder solution.

Description:
BACKGROUND OF THE INVENTION  
       Field of the Invention  
         [0001]    Various methods are known for agglomerating fine particles into physical forms such as briquettes and pellets. Carbonaceous materials such as coal can be agglomerated to form briquettes and pellets which are useful in residential and industrial heating applications. Generally speaking, briquettes and pellets can be made by agglomerating fine particles using various binder systems. The briquettes and pellets can be made by mixing the binder and particles, and then extruding or pelletizing the mix.  
           [0002]    Binders which are known for “cold” curing processes (i.e., those not requiring heat above room temperature to cure the binder) include bitumen starch and resin combinations, binders based on polyvinyl alcohol/calcium oxide (GB2138442), polyvinyl alcohol/molasses (ep135784), polyvinyl alcohol/calcium carbonate (EP135785), molasses and lime, molasses and phosphoric acid (GB2187754), binders based on sulfite lye (EP127351), and phenol-formaldehyde resins (EP241156). However, these binder systems are undesirable in some respects. Generally, briquettes and pellets made from such binders show poor water and crush resistance.  
           [0003]    Briquettes made using bitumen must be heated in order to make smokeless briquettes. Briquettes made from either molasses or starch-based binder systems need to be heated in order to become weather resistant. These heating requirements undermine some of the economic advantages of cold briquerring. Phenolic-based binder systems need so-called green strength additives in order to give initial strength to the agglomerated material, before the binder system fully cures. These additives add expense to the manufacture of briquettes.  
           [0004]    U.S. Pat. No. 5,244,473 discloses a method of agglomerating particles using a phenol-aldehyde resin, polyisocyanate, and a catalyst. The resulting briquettes can be cured at room temperature or at elevated temperature. The key disadvantage to this process is the cost of the raw materials.  
           [0005]    Accordingly, there is a need for a new lower cost method for agglomerating fine particles, particularly carbonaceous materials, to form briquettes and pellets which show improved water and crush resistance, require short cold cure times and do not require green strength additives.  
           [0006]    This need is met by the present invention which is a method for agglomerating fine particles, comprising reacting urea, urea/formaldehyde condensate, a strong inorganic acid, preferably sulfuric acid, and, at lease one polyfunctional compound chosen from the group consisting of hydroxycarboxylic acids, dicarboxylic acids, and polyols (containing at least two hydroxy groups) in the presence of particles to be agglomerated to form a fine particle agglomerate. Optionally, molasses, p-toluene sulfonic acid, xylene sulfonic acid or resorcinol can be added to the binder solution. In a preferred embodiment, the particles to be agglomerated are particles of a carbonaceous material such as coal.  
         DETAILED DESCRIPTION OF THE INVENTION  
         [0007]    Generally, the various materials from which the agglomerates are made can be mixed together at the same time, in any order.  
           [0008]    In a preferred embodiment, however, the first step of the present method is the preparation of two solutions from which the binder is made. The first solution is an aqueous-based solution containing form 12-30 wt % of at least one compound selected from the group consisting of hydroxycarboxylic acids, dicarboxylic acids, and polyols, 15-25 wt % of urea, 2-10 wt % of sulfuric acid, 0-2 wt % of xylene sulfonic acid or p-toluene sulfonic acid, 0-75 wt % molasses, and 0-2.5 wt % resorcinol. Advantageously, the dicarboxylic acid and/or hydroxycarboxylic source can be the by-products from cyclohexane oxidation as practiced in the manufacture of adipic acid and caprolactam. Polyols can be obtained from the waste streams of glycol manufacture. Suitable dicarboxylic acids are those which show good water solubility. These include adipic acid, succinic acid, and glutaric acid. Suitable hydroxycarboxylic acids include hydroxycaproic acid and hydroxyvaleric acid. The carboxylic acid groups of the dicarboxylic acids and hydroxycarboxylic acids may be in the form of their corresponding esters or salts. Suitable polyols include, but are not limited to, glycerol, ethylene glycol and polyvinylalcohol.  
           [0009]    The second solution is a condensation product of the reaction of urea and formaldehyde(hereinafter defined as “urea/formaldehyde condensate”). This second solution is an aqueous solution of methylol ureas containing free formaldehyde. Such solutions are commercially available from, for example, Borden Chemicals. The ratio of formaldehyde to urea can be from 5:1 to 3:1, and generally, the solution contains about 80% solids.  
           [0010]    In a preferred embodiment, the agglomeration method of the present invention includes introducing into a mechanical mixer the two binder solutions discussed above and the fine particles to be agglomerated. For the manufacture of heating briquettes or pellets, the fine particles to be agglomerated will be carbonaceous materials such as anthracite, bituminous coal, coking coal, thermal coal, sub-bituminous coal, peat, wool, coke, petroleum coke and blends thereof. The binder will generally constitute 2-12 wt % of the total ingredients. Industrial briquettes will contain 2-5 wt % of binder, while residential briquettes will contain from 7-12 wt % binder. Generally speaking, the lower the amount of binder, the worse strength of the briquette. Pellets will contain 1-9 wt % of binder. Pellets for domestic heating will contain 5-9 wt % binder. For industrial heating, lower percentages are preferred.  
           [0011]    Generally speaking the ratio of the first to second binder solution should be from 60:40 to 75:25.  
           [0012]    When manufacturing briquettes or pellets for heating purposes using carbonaceous materials, it is important to adjust the amount of water in the carbonaceous material and the size of the particles in order to achieve optimum manufacturing performance. For the manufacture of industrial pellets, where a “pellet mill” will be used, it is preferred to use carbonaceous materials having 14-20 wt % water and a particle size less than 3 millimeters. For the manufacture of domestic briquettes, the carbonaceous material should be dried and crushed before introduction into the mechanical mixer. It is preferred that the water content be from 1-4 wt % and the particle size be less than about 3 millimeters.  
           [0013]    The two binder precursor solutions and the fine particles are placed in a mechanical mixer. High intensity mixers generally result in better blending. After the material is mixed, it is placed in a briquette “roller press” for making briquettes or into a “pellet mill” for making pellets. After the material exits the pellet mill or briquette roller, it is placed on a conveyer for approximately 20 minutes to allow the binder system to harden, resulting in the formation of a briquette or pellet having the desired size and shape.  
           [0014]    The use of the binder system of the present invention causes the briquettes to have better water and crush resistance than they would have absent the dicarboxylic acid, hydroxycarboxylic acid, and/or polyol. Additionally, the binder system allows for relatively short cure times at cure temperatures which do not necessitate the need for an oven.  
           [0015]    The present agglomeration can be used to agglomerate other fine particles such as mineral fines and wood particles.  
           [0016]    The present invention is illustrated by the following nonlimiting examples. In all examples, the Welsh “Coedbach” Anthracite coal and the low sulphur petroleum coke had a moisture content of 2% and a size of 0-3 mm. The Bituminous coal had a moisture content of 15-18% and a size of less than 500 microns. 
       
    
    
     EXAMPLE 1  
       [0017]    This example shows the use of a binder system using a dicarboxylic acid, glutaric acid. A first solution (A) consisting of 7.29% glutaric acid, 65.59% water, 1.24% resorcinol, 18.37% urea, 5.98% sulfuric acid (77%), and 1.53% xylene sulfonic acid was prepared. A second solution (B)consisting of 100% urea-formaldehyde condensate was prepared. The two solutions were mixed together in a ratio of 65:35 (A:B) in the absence of coal and a firm gel set in 22 seconds with an exotherm of 58 degree C. Three agglomerations were performed using this component (A and B) binder system.  
         [0018]    15.0 grams of Welsh “Coedbach” Anthracite 35.0 grams of low sulphur petroleum coke, 6.5 grams of solution A, and 3.5 grams of solution B were mixed together by hand, then pressed into a cylindrical shape (a “slug”) using a hydraulic press. The slug set to a hard rigid form.  
         [0019]    1500 grams of Welsh “Coedbach” Anthracite, 3500 grams of low sulphur petroleum coke, 325 grams of solution A and 175 grams of solution B were mixed with a high intensity mechanical mixer for 30 seconds and then passed in a double roll briquette press to “pillow shaped briquettes” weighing approximately 32 grams. The resulting briquettes hardened into a rigid form.  
         [0020]    500 grams of Bituminous coal, 82 grams of solution A, and 44 grams of solution B were mixed in a high intensity mechanical mixer for 30 seconds, then pressed in a die pellet mill to form cylindrical shaped pellets weighing approximately 5 grams. The pellets hardened into a rigid form.  
       EXAMPLE 2  
       [0021]    This example shows the use of a binder system using monoethylene glycol. A first solution (C) consisting of 64.80% monoethylene glycol, 6.48% water, 1.43% resorcinol, 18.73% urea, 7.26% sulfuric acid (77%), and 1.30% xylene sulfonic acid was prepared. A second solution (D) consisting of 100% urea-formaldehyde condensate was prepared. The two solutions were mixed together in a ratio of 65:35 (C:D) in the absence of coal and a firm gel set in 78 seconds with an exotherm of 53 degree C. Three agglomerations were performed using this 2 component (C and D) binder system.  
         [0022]    15.0 grams of Welsh “Coedbach” Anthracite, 35.0 grams of low sulphur petroleum coke, 6.5 grams of solution C, and 3.5 grams of solution D were mixed by hand, then pressed into a cylindrical shape (a “slug”) using a small hydraulic press. The slug set to a hard rigid form in 18 minutes.  
         [0023]    1500 grams of Welsh “Coedbach” Anthracite, 3500 grams of low sulphur petroleum coke, 325 grams of solution C and 175 grams of solution D were mixed with a high intensity mechanical mixer for 30 seconds and the pressed in a double roll briquette press to form “pillow shaped briquettes” weighing approximately 32 grams. The resulting briquettes hardened into a rigid form.  
         [0024]    5000 grams of Bituminous coal, 82 grams of solution C, and 44 grams of solution D were mixed in a high intensity mechanical mixer for 30 seconds, then pressed in a die pellet mill to form cylindrical shaped pellets weighing approximately 5 grams. The pellets hardened into a rigid form.  
       EXAMPLE 3  
       [0025]    This example shows the use of a binder system using a polyol, glycerol. A first solution (E) consisting of 64.80% glycerol, 6.48% water, 1.43% resorcinol, 18.73% urea, 7.26% sulfuric acid (77%), and 1.30% xylene sulfonic acid was prepared. A second solution (F) consisting of 100% urea-formaldehyde condensate was prepared. The two solutions were mixed in a ratio of 65:35 (E:F) in the absence of coal and a firm gel set in 37 seconds with an exotherm of 66 degrees C. Three agglomerations were performed using this 2 component (E and F) binder system.  
         [0026]    15.0 grams of Welsh “Coedbach” Anthracite, 35.0 grams of low sulphur petroleum coke, 6.5 grams of solution E, and 3.5 grams of solution F were mixed by hand, then pressed into a cylindrical shape (a “slug”) using a small hydraulic press. The slug set to a hard rigid form in 6 minutes.  
         [0027]    1500 grams of Welsh “Coedbach” Anthracite, 3500 grams of low sulphur petroleum coke, 325 grams of solution E and 175 grams of solution F were mixed with a high intensity mechanical mixer for 30 seconds and then passed in a double roll briquette press to form “pillow shaped briquettes” weighing approximately 32 grams. The resulting briquette hardened into a rigid form reaching a crush strength of 80 kg in 20 minutes and 150 kg in 24 hours.  
         [0028]    5000 grams of Bituminous coal, 82 grams of solution E, and 44 grams of solution F were mixed in a high intensity mechanical mixer for 30 seconds, then pressed in a die pellet mill to form cylindrical shaped pellets weighing approximately 5 grams. The pellets hardened into a rigid form.  
       EXAMPLE 4  
       [0029]    This example shows the use of a binder system using a hydroxycarboxylic acid and a dicarboxylic acid. A first solution (G) consisting of 73.33% adipic acid waste stream, 1.25% resorcinol, 18.40% urea, 6.00% sulfuric acid (77%), and 1.02% xylene sulfonic acid. The adipic acid waste stream contained approximately 10% hydroxycaproic acid, 30% hydroxyvaleric acid, 10% hydroxybutyric acid, 20% adipic acid, 5% succinic acid, and 5% glutaric acid, with the balance consisting of water and minor components was prepared. A second solution (H) consisting of 100% urea-formaldehyde condensate was prepared. The two solutions were mixed together in a ratio of 65:35 (G:H) in the absence of coal and a firm gel set in 30 seconds with an exotherm of 65 degrees C. Three agglomerations were performed using this 2 component (G and H) binder system.  
         [0030]    15.0 grams of Welsh “Coedbach” Anthracite, 35.0 grams of low sulphur petroleum coke, 6.5 grams of solution G, and 3.5 grams of solution H were mixed by hand, then pressed into a cylindrical shape (a “slug”) using a small hydraulic press. The slug set to a hard rigid form in 10 minutes.  
         [0031]    1500 grams of Welsh “Coedbach” Anthracite, 3500 grams of low sulphur petroleum coke, 325 grams of solution G and 175 grams of solution H were mixed with a high intensity mechanical mixer for 3 seconds and then pressed in a double roll briquette press to form “pillow shaped briquettes” weighing 32 grams. The resulting briquettes hardened into a rigid form reaching a crush strength of 60 kg in 20 minutes and 100 kg in 24 hours.  
         [0032]    5000 grams of Bituminous coal, 82 grams of solution G, and 44 grams of solution H were mixed in a high intensity mechanical mixer for 30 seconds, then pressed in a die pellet mill to form cylindrical shaped pellets weighing approximately 5 grams. The pellets hardened into a rigid form.  
       EXAMPLE 5  
       [0033]    This example shows the use of a binder system using a dicarboxylic acid. A first solution (I) consisting of a 36.44% citric acid, 36.44% water, 1.24% resorcinol, 18.37% urea, 5.08% sulfuric acid (77%), and 1.00% xylene sulfonic acid was prepared. A second solution (J) consisting of urea-formaldehyde condensate was prepared. The two solutions were mixed together in a ratio of 65:35 (I:J) in the absence of coal and a firm gel set in 22 seconds with an exotherm of 58 degrees C. Three agglomerations were performed using this 2 component (I and J) binder system.  
         [0034]    15.0 grams of Welsh “Coedbach” Anthracite, 35.0 grams of low sulphur petroleum coke, 6.5 grams of solution I, and 3.5 grams of solution J were mixed by hand, then pressed into a cylindrical shape (a “slug”) using a small hydraulic press. The slug set to a hard rigid form.  
         [0035]    1500 grams Solutions I and J from Example 17 were used. 1500 grams of Welsh “Coedbach” Anthracite, 3500 grams of low sulphur petroleum coke, 325 grams of solution I and 175 grams of solution J were mixed with a high intensity mechanical mixer for 30 seconds and then passed in a double roll briquette press to form “pillow shaped briquettes” weighing approximately 32 grams. The resulting briquettes hardened into a rigid form.  
         [0036]    5000 grams Bituminous coal, 82 grams of solution I, and 44 grams of solution J were mixed in a high intensity mechanical mixer for 30 seconds, then pressed in a die pellet mill to form cylindrical shaped pellets weighing approximately 5 grams. The pellets hardened into a rigid form.  
       EXAMPLE 6  
       [0037]    This example shows the use of a binder system using a polyol. A first solution (K) consisting of 6.21% polyvinyl alcohol, 65.93% water, 0.92% resorcinol, 18.44% urea, 7.20% sulfuric acid (77%), and 1.53% sulfonic acid was prepared. A second solution (L) consisting of 100% urea-formaldehyde condensate was prepared. The two solutions were mixed together in a ratio of 65:35 (K:L) in the absence of coal and a firm gel set in 33 seconds with an exotherm of 55 degrees C. Three agglomerations were performed using this 2 component (K and L) binder system.  
         [0038]    15.0 grams of Welsh “Coedbach” Anthracite, 35.0 grams of low sulphur petroleum coke, 6.5 grams of solution K, and 3.5 grams of solution L were mixed together by hand, then pressed into a cylindrical shape (a “slug”) using a hydraulic press. The slug set to a hard rigid form in 5 minutes.  
         [0039]    1500 grams of Welsh “Coedbach” Anthracite, 3500 grams of low sulphur petroleum coke, 325 grams of solution K and 175 grams of solution L were mixed with a high intensity mechanical mixer for 30 seconds and then pressed in a double roll briquette press to form “pillow shaped briquettes” weighing approximately 32 grams. The resulting briquettes hardened into a rigid form reaching a crush strength of 80 kg in 20 minutes and 150 kg in 24 hours.  
         [0040]    5000 grams of Bituminous coal, 82 grams of solution K, and 44 grams of solution L were mixed in a high intensity mechanical mixer for 30 seconds, then pressed in a die pellet mill to form cylindrical pellets weighing approximately 5 grams. The pellets hardened into a rigid form.