Patent Application
20060009549
1. Field of the Invention
This invention generally relates to silane treatment operations, and in particular, relates to a low-VOC silanol additive for use in various industrial applications.
2. Description of the Related Art
Silane is commonly used as a treating agent for various materials to impart certain desired properties to the material. Silane compounds have been used extensively as a coupling agent to enhance the adhesion between organic polymers and an inorganic substrate such as glass or metal. Silanes are also used to treat the surfaces of inorganic additives such as silica for use in a reinforced polymer system. Other commercial applications of silane include uses in the textile industry as an antimicrobial treatment agent for fibers, in surface chemistry, ink formulations, and production of silicone rubber. Silane has also been used in coating glass fibers and surfaces or in cross-linked polyethylene pipes to help improve polymer high temperatures and chemical resistance. Certain forms of silane can also be used as a sizing agent for cellulose fibers to increase the water durability of the fibers as described in U.S. Pat. No. 6,676,745, which is hereby incorporated by reference.
In many of these applications, it is generally recognized that silane hydrolysis is required for interactions to occur between silane and various materials. In a typical silane treatment process, silanes are added to a mixture and hydrolyzed to form silanols, which are compounds containing one or more Si—OH groups. The silanols can directly bond to the treated surface or undergo self-condensation reactions to give compounds containing the siloxane (Si—O—Si) linkage. However, the silane hydrolysis process can be slow due to low reactivity of silane and the amount of silane hydrolyzed can be affected by various processing conditions. Moreover, silane hydrolysis reaction typically releases one or more volatile organic compounds (VOCs) such as alcohol, which in turn requires proper on-site emission control. Consequently, the efficiency and effectiveness of large-scale industrial silane treatment processes are often less than optimal due in large part to the varying amount and rate at which silanol is formed during silane hydrolysis and concerns of excessive emission of VOC by-products.
In certain manufacturing applications where silane is added to a fiber slurry as a sizing agent for the cellulose fibers, a large amount of the silane may not hydrolyze and react with cellulose fibers quickly enough, resulting in un-reacted silane getting lost in the machine effluent, which in turn reduces the efficiency of the treatment process. Moreover, when silane is mixed with industrial scale aqueous solutions, large amounts of VOC by-products are released during silane hydrolysis and the emission of such by-products needs to be properly controlled on-site, which adds to the complication and cost of the silane treatment process.
Hence from the foregoing, it will be appreciated that there is a need for a more efficient, effective, and environmental friendly large-scale silane treatment process for various industrial applications. To this end, there is a particular need for a more efficient and cost-effective method of controlling and managing VOC by-products resulting from the formation of silanol from silane.
In one aspect, the preferred embodiments of the present invention provide a method of producing a silanol additive having a low-VOC content. The method comprises providing a silane-containing compound and a catalyst; transferring a pre-determined amount of each of the silane-containing compound and the catalyst to a mixing container; mixing the silane-containing compound and the catalyst with water in the mixing container; hydrolyzing the silane-containing compound under pre-determined processing conditions with the aid of the catalyst, thereby forming a mixture comprising silanol and one or more volatile organic compounds (VOCs), and removing at least a substantial portion of the VOCs from the solution so as to form a low-VOC silanol additive. In one embodiment, the method further includes transferring the silanol additive to a container.
In one embodiment, the low-VOC silanol additive comprises about 90% or greater by weight silanol. In another embodiment, removing at least a substantial portion of the VOCs from the mixture comprises removing about 50% or more by weight of the VOCs in the mixture. The VOCs removed are preferably selected from the group consisting of alcohols, amines, and mixtures thereof. In one embodiment, the VOCs removed are selected from the group consisting of ethanol, methanol, propanol, butanol, known isomers thereof, and mixtures thereof. In some embodiments, a wipe film separator is used to remove the VOCs from the mixture. Preferably, the mixture is introduced into the wipe film separator at a flow rate of about 1 lb/min or higher and at a temperature of about 40-60° C. under vacuum and the separator has a surface area of about 0.5 m2-10 m2. Preferably, the removed VOCs are placed in a waste container for off-site disposal.
In certain embodiments, the silane-containing compound is selected from the group consisting of n-octylethoxysilane, n-octylethoxysilane, silanes, alkoxylsilanes, alkylalkoxysilanes, halide organosilanes, carboxylated organosilanes, epoxyalkoxylsilanes, silicone emulsions, and mixtures thereof. In one embodiment, the catalyst is selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, acetic acid, formic acid, citric acid, phosphoric acid, sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium hydroxide, magnesium hydroxide, beryllium hydroxide, and mixtures thereof. In one embodiment, the catalyst aids in the hydrolysis of the silane in a manner such that the hydrolysis reaction time is about one fifth of the reaction time of an equivalent hydrolysis reaction without the aid of the catalyst. In another embodiment, the catalyst aids in the hydrolysis of the silane in a manner such that no more than about silane 5% of the silane in the silane-containing compound silane remains unhydrolyzed in the mixture. In yet another embodiment, providing the silane-containing compound and catalyst comprises batching the compound and catalyst in separate bulk storage containers. In yet another embodiment, the storage containers for the silane-containing compound and the catalyst are connected in line with the mixing container such that the silane-containing compound and the catalyst can be directly transferred from the respective storage containers to the mixing container. Preferably, the pre-determined amount of silane-containing compound transferred to the mixing container comprises about 0.1%-75% by weight of the total of the silane-containing compound, catalyst and water in the mixing container. The pre-determined amount of catalyst transferred preferably comprises about 0.01%-20% by weight of the total weight of the silane-containing compound, catalyst, and water in the mixing container.
In certain embodiments, the method further comprises adding the low-VOC silanol additive to a treatment process, such as a process for treating a substrate. In one embodiment, the low-VOC silanol solution can be used as an additive in a manufacturing process selected from the group consisting of fiber cement manufacturing, textile manufacturing, photographic paper manufacturing, building products manufacturing, ink manufacturing, mineral material processing and modification, and pressure sensitive tape adhesive manufacturing. The low-VOC silanol additive can be added to a process for treating celluloses fibers to increase the hydrophobicity of the fibers. The low VOC silanol additive would therefore have utility as a sizing or a hydrophobic agent for cellulose containing materials including but not limited to fabrics, textiles, paper, paperboard, wood, wood composites, and cementitious composites containing cellulose. The low-VOC silanol additive can be added to a process for treating an inorganic substrate to modify one or more properties of the substrate, such as the external and/or internal surfaces (e.g. voids or pores) of the substrate to make the substrate more hydrophobic. The low-VOC silanol additive can also be added to a process for treating textile fibers to apply an antimicrobial agent to the fibers. The low-VOC silanol additive can be added to a process for manufacturing pressure sensitive adhesives. The low-VOC silanol additive can also be added to a fiber cement slurry for treating the fibers and other ingredients such as cement and ground silica in the slurry to make the formed fiber-cement article more water resistant.
In another aspect, the preferred embodiments of the present invention provide a method of producing a silanol solution having a low-VOC content. The method comprises providing a silane-containing compound and a catalyst; transferring a pre-determined amount of each of the silane-containing compound and the catalyst to a mixing tank; mixing the silane-containing compound and the catalyst together with water in the mixing tank using a mechanical mixer; mixing the silane-containing compound and the catalyst together with water in the mixing tank using a mechanical mixer; hydrolyzing the silane-containing compound with the aid of said catalyst, thereby forming a mixture comprising silanol and one or more volatile organic compounds (VOCs). Preferably, the mixture has a volume of about 1 gallon or more. The method further includes removing at least a substantial portion of the VOCs from the mixture so as to form a low-VOC silanol solution and adding the low-VOC silanol solution to a treatment process. In one embodiment, the mixing tank is a 55-gallon tank. In another embodiment, a separator is used to remove the ethanol from the mixture. In yet another embodiment, the silane-containing compounds and catalyst are batched in separate storage tanks. Preferably, the mixing tank is interconnected with the separator in a manner such that the mixture comprising silanol and VOCs can be transferred to the separator at a pre-selected rate. Preferably, the VOCs are removed by the separator and stored in a waste storage container. In one embodiment, the separator is in fluid communication with the waste storage container such that removed VOCs can be directly transferred to the waste storage container from the separator.
In yet another aspect, the preferred embodiments of the present invention provide a method of manufacturing a fiber reinforced cement composite material. The method comprises providing a silanol additive that is substantially VOC-free; adding the silanol additive to a fiber cement slurry comprising cellulose fibers, said silanol additive treats the fibers in a manner that increases the hydrophobicity of the fibers; forming the fiber cement slurry into a fiber cement article of a pre-selected shape and size; and curing the fiber cement article to form the fiber cement composite material. In one embodiment, the silanol additive comprises about 5% by weight of the dry weight of the cellulose fibers. In another embodiment, silanol in the silanol additive has a hydrophilic and a hydrophobic functional group, such that the hydrophilic functional group bonds to hydroxyl groups on the cellulose fiber surface and the hydrophobic functional group repels water therefrom. In some embodiments, the fiber cement article of a pre-selected shape and size is formed by the Hatschek process. In certain other embodiments, the fiber cement article is formed by an extrusion, molding, or casting process.
In yet another aspect, the preferred embodiments of the present invention provide a method of treating a hydrophilic surface to increase the water-repellency of the surface. The method comprises providing a solution comprising silanol and applying the solution to the surface under conditions such that the silanol reacts with hydrophilic functional groups on the surface so as to tie up the hydrophilic functional groups, resulting in the hydrophilic surface having increased hydrophobicity. In one embodiment, the hydrophilic surface comprises a surface of a cellulose fiber. In another embodiment, the silanol solution is provided by reacting silane with water to form an aqueous solution comprising silanol and ethanol and removing at least a substantial portion of the ethanol from the aqueous solution.
In yet another aspect, the preferred embodiments of the present invention provide a solution comprising about 50% or greater of silanol by weight. In one embodiment, the solution comprises a silanol compound which includes a hydrophobic and a hydrophilic functional group, the hydrophilic group is adapted to bond to hydrophilic surfaces to cause the surface to become more hydrophobic. In one embodiment, the solution is an aqueous solution. In another embodiment, the solution is substantially alcohol-free. In yet another embodiment, the solution comprises no greater than about 5% silane by weight.
Preferred embodiments of the present invention provide a silanol additive having a low-VOC content which can be used in various industrial applications.
The silane-containing compound may include, but is not limited to, n-octylethoxysilane, n-octylmethoxysilane, silanes, alkoxylsilanes, alkylalkoxysilanes, halide organosilanes, carboxylated organosilanes, epoxyalkoxylsilane, silicone emulsions, and mixtures thereof. The catalyst can be an acid or a base that is capable of catalyzing a hydrolysis reaction between silane and water. The catalyst may include, but is not limited to, sulfuric acid, hydrochloric acid, nitric acid, acetic acid, formic acid, citric acid, phosphoric acid, sodium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, beryllium hydroxide, and calcium hydroxide. The water is preferably fresh tap water or deionized water.
As also shown in
In Step 130 of the process 100 illustrated in
In one embodiment, the VOC by-products are primarily alcohols such as ethanol. The alcohol is evaporated from the film of the separator and removed by vacuum at about 50-300 mbars. Preferably, the total alcohol removal from the reaction mixture is more than 50%, more preferably about 90% -99.9% by weight of the alcohol originally present in the mixture. The remaining substantially alcohol-free silanol solution is subsequently removed from the bottom of the separator at a flow rate of about 0.7 lb/minute. In one embodiment, the silanol solution has a VOC-content of preferably less than about 5% by weight, more preferably less about 1% by weight. In another embodiment, the silanol solution has about 50% or greater of silanol by weight.
As
In certain embodiments, the silanol solution having a low-VOC content is used as an additive in a cellulose fiber treatment process, in which the silanol acts as a sizing agent that improves the hydrophobicity of the fibers. The low-VOC silanol additive can also be applied to the fibers at hydropulper, raw stock chests, or refined stock chests in the treatment of cellulose fibers. The low-VOC silanol additive can also be batched with other ingredients, which may include treated or engineered cellulose fibers and other ingredients. Additionally, the low-VOC silanol additive can also be used to coat a formed fiber-cement products that is in either greensheet form or autoclaved.
In certain other embodiments, the silanol additive having a low-VOC and/or alcohol content is incorporated in a fiber cement formulation. Preferably, the silanol additive is between about 0.05%-10% by weight, more preferably about 5%, of the fibers in the formulation. Preferably, the silanol additive is between about 0.01%-2% by weight, more preferably about 0.3%, of the total formulation. In fiber cement technology, the silanol additive can be used in processes including, but is not limited to, Hatschek, extrusion, mazza, casting, twin wire, and fourdrinier forming. The silanol additive can also be used as an additive in other fiber and wood technologies such as medium density fiberboard (MDF), particle board, oriented strain board (OSB), or any other wood composites. The silanol additive may also be used as an additive in formulations related to concrete, bricks and other building/construction materials. The low-VOC silane may also be used to modify the inorganic mineral raw materials including but not limited to sand, ground silica, clays, calcium silicate, calcium silicate hydrate, calcium carbonate, perlite, volcanic ash, bottom ash, fly ash, blast furnace slag, diatomaceous earth, amorphous silica, rice hull ash, glasses, ceramics and mixtures thereof or other silicate or aluminosilicates minerals known to be used in cement composites or as fillers in plastics.
As also shown in
Advantageously, the system 200 allows a low-VOC silanol solution to be prepared in batches and stored for future use. The scale of manufacturing is such that the equipment and processes are set up to produce large volumes of low-VOC silanol in batches or in a continuous process. In one embodiment, the silane storage tank has a volume of about 55 gallons, the catalyst storage tank has a volume of about 1 gallon, the mixing tank has a volume of about 50 gallons, the waste storage tank and silanol product tank each has a volume of about 55 gallons. The silanol additive can be produced in batches ranging in volume from 10 to 40 gallons, however larger quantities of low-VOC silanol may be produced by scaling up the process disclosed herein. Moreover, the removed VOCs are captured in closed containers that can be disposed off-site, reprocessed to reclaim the VOC constituents, (typically amines or alcohols such as ethanol, methanol, propyl alcohol, butanol or isomers thereof), or burned as fuel. Capturing VOC emissions in this manner greatly reduces the environmental impact of using silanes on a commercial scale and may enable certain processes to better comply with local air quality regulations.
Table 1 provides a comparison of certain physical properties of fiber cement articles incorporating fibers treated with the silanol additive, conventional silane, as well as fibers that are untreated. As shown in Table 1, fiber cement articles treated with the silanol additive and silane show significantly reduced water permeability, wicking, and moisture movement as compared to an equivalent article incorporating fibers without any treatment. Table 1 also shows that samples incorporating silanol treated fibers show greater freeze thaw MOE retention percentage as compared to an equivalent fiber cement article incorporating silane treated fibers.
Table 1: Property comparison of fiber cement articles reinforced with fibers treated with silanol, silane, and fibers that are untreated.
Silane is commonly used as an additive for various surface treatment applications. The silane treatment process typically involves hydrolyzing silane in water to form silanol, which is a compound containing one or more Si—OH groups. The silane hydrolysis reaction is known to release VOCs such as ethanol as a by product. VOC emissions from silane treatment processes have been a general environmental concern and must be properly controlled and managed. Typically, special permits and equipment have to be obtained for silane treatment operations to properly dispose of the VOC on site. The preferred embodiments of the present invention provide a low-VOC silanol additive that can be used in various industrial silane treatment processes so that VOC emission is less of a concern at the manufacturing site. Moreover, in conventional silane treatment processes, silane is added to a solution and then hydrolyzed before reacting with a substrate surface. Because silane hydrolysis has a relatively slow reaction rate, large quantities of silane often remain unreacted and result in poor manufacturing efficiency and losses. This is particularly a problem in the manufacture of fiber cement articles or other composites containing cellulose fiber that are manufactured using slurry dewatering processes such as the Hatcheck process or Fourdrinier process. Advantageously, the silanol additive of the preferred embodiments can be added to an aqueous slurry to directly react with organic and inorganic fillers, fibers, cement, or other materials in the slurry. This speeds up and improves the efficiency of the silane treatment process in that the silane hydrolysis reaction is already complete.
The preferred embodiments of the silanol additive and methods of manufacturing as described above have applicability in a wide range of industries, including but not limited to, the manufacturing of building products, concrete, textiles, inks, paints, coatings, paper, adhesives, pulp and paper fibers, vegetable fibers, wood, and wood composite products. The embodiments illustrated and described above are provided as examples of certain preferred embodiments of the present invention. Various changes and modifications can be made from the embodiments presented herein by those skilled in the art without departure from the spirit and scope of this invention.
