AU2010278595A1

AU2010278595A1 - Method for extracting lignite wax

Info

Publication number: AU2010278595A1
Application number: AU2010278595A
Authority: AU
Inventors: Junjie Gu; Chengcai Song; Lijun Zhang
Original assignee: ENN Science and Technology Development Co Ltd
Current assignee: ENN Science and Technology Development Co Ltd
Priority date: 2009-07-27
Filing date: 2010-07-27
Publication date: 2012-03-08
Anticipated expiration: 2030-07-27
Also published as: AU2010278595B2; CN101967396A; CN101967396B; WO2011011972A1

Abstract

Method for extracting lignite wax is provided, which includes the following steps: a) coal powder is treated in subcritical or supercritical fluid in the presence of a catalyst so as to obtain semi-coke containing lignite wax; b) a solvent which is capable of dissolving lignite wax is used to leach the lignite wax from semi-coke. Optionally, hydrogen can be added in step a).

Description

A Process For Extracting Montan Wax Background Montan wax is a kind of valuable mineral product existed in lignite, and is a kind of mixture comprising wax, resin and asphalt. The properties of Montan wax mainly depend on the raw material, solvent and leaching condition used. With the increase of asphalt content, the color of Montan wax varies from brown to black. The Montan wax typically has a melt point of 75 860 and a density (measured at 200 ) of 0.98 - 1.03g/cm 3 . The main components of Montan wax are as follows : wax ester comprised of Cl6 - C34 acid and C24, C26 or C30 alcohol ; long chain fatty acid (C16 -C35) ; aliphatic alcohol (C20 - C34) and alkanes (C23 - C33). The main components in the resin are resin acid, small amount of sterol and terpenes material. The asphalt are mainly polymeric, esterified oxygen-containing resin acid. Due to its big hardness, high melt point and stable chemistry property, the Montan wax is widely used in the fields of papermaking, printing, spinning, precise casting, and chemical industry concerned with products for daily use. Now, Montan wax is mainly extracted from lignite by using solvents such as benzene, toluene, mineral spirit, or the like. But the Montan wax reserves in China are of relative shortage and the content of Montan wax is relative low. Some Montan wax reserves are going to be depleted after many years' exploration. Montan wax is also contained in some other kind of coal, but its content is relative low, and its extracting cost will be large. So, in its current industrial production, Montan wax is still extracted from lignite. In foreign countries, a process for extracting Montan wax is: the raw material lignite is first dried to reduce its water content to 15 20% by passing the lignite through a titled rotating cylinder drier, then the lignite is ground to a particle size of less than 1.3 mm, and was dried again. Then the coal powders are fed into a continuous leacher and are leached by toluene solvent under 820. The wax-containing leaching liquor thus obtained is fed into an evaporator and is fractioned under 125 - 1300. The distilled toluene is used circularly, and the remaining crude wax liquid is cooled and shaped, obtaining crude Montan wax. The crude Montan wax contains 7 - 1Owt% asphalt and 18 - 20wt% resin. The main component of the leacher is rotatable transportation belt which equipped with several hoppers for receiving coal. During the transmission of hoppers, the toluene solvent is sprayed into the hoppers and leaches the coal loaded in the hoppers. The wax-containing leaching liquor, is discharged from the sieve plate 2 located in the bottom of leacher, and then fed into distillation system and other auxiliary systems to separate the wax from the solvent. In China, a process for extracting Montan wax is: the lignite is first ground to a particle size of 3-10 mm, then is dried to reduce its water content to about 20%, then the lignite is contained in a leacher, and to which an amount of pure benzene (as much as 8 times of the weight of lignite) is added. The residence time of lignite in this leacher is about 2 to 4 hours. To enhance the operation conditions and to improve the leaching efficiency as well as to shorten the leaching time, the leaching is carried out under a slightly increased pressure than atmospheric pressure, so that the boiling point of benzene solvent can reach 900. After leaching, the materials are filtered, the filtrate is fed into evaporator and is evaporated by steam heating. Benzene (which has relative low boiling point, for example, its atmospheric boiling point is 800) and water volatilize in the form of vapor and enter the oil-water separator via the condenser at the top of evaporator. The Montan wax is obtained at the bottom of evaporator. The main problems of the Montan wax extracting process in the prior art are: (1) the raw material source is limited to lignite raw coal; (2) the lignite must be dried prior to leaching, so as to reduce its 3 water content to below 20%; (3) the particle size of lignite is relative big, sometimes more than 600 microns; or, the bulk coal with a size of 3-10 mm is used, which can not be sufficiently leached; (4) benzene and toluene are strongly toxic materials and will do harm to operator or make pollution to surroundings (5) after the Montan wax has been extracted, a significant amount of solvent will remained in the residues. The solvent remained in the residues may not only result in solvent loss, but also limit the application of Montan wax product. Chinese Patent CN101029255 introduced a method for extracting Montan wax with a mixture of alcohol and hexane, wherein the particle size of coal grain is 0.6 - 20 mm, the leaching mode is the batch-wise leaching occurred in leacher, and the volume ratio of solid to liquid ranges from 1:1 to 1:4, and the solution obtained after leaching is subjected to solvent recovery, the resulted product is Montan wax. Though this patent uses less toxic solvent, it still requires lignite containing a certain amount of Montan wax as the raw material, so it still can not eliminate the limitation to raw material. Furthermore, this patent requires the separated extractant be re-mixed in a certain ratio, which not only increase the complexity of this process, but also increase the energy cost, the 4 investment of equipments and labor cost. Summary of the invention The invention provide a process for extracting Montan wax from coal, in particular, the invention relates to a process for extracting Montan wax by treating coal with sub-critical or super-critical fluid and then leaching out the Montan wax by solvent. The process comprises the following steps: a) treating coal powders in a sub-critical fluid or super-critical fluid under the action of catalyst, obtaining semi-coke containing Montan wax; and, b) leaching out said Montan wax from said semi-coke with a solvent capable of dissolving said Montan wax. In the invention, hydrogen can additionally be introduced into step a). Thus, the invention also provides a process for extracting Montan wax, comprising the following steps: a) treating coal powders in a sub-critical fluid or super-critical fluid under the action of catalyst and hydrogen, obtaining semi-coke containing Montan wax; and, b) leaching out said Montan wax from said semi-coke with a solvent capable of dissolving said Montan wax. Detailed description of the invention In the invention, before the step a), one can mix coal powders 5 with water by any means known in the art to prepare aqueous coal slurry. Wherein the coal can selected from bituminous coal, anthracite, lignite or mixture thereof. It should be especially noted that, those coal, which can not be treated by conventional solvent leaching process due to their low Montan wax content, is also suitable for being the raw material of the present invention. The coal powders can has the particle size of less than 300 microns, preferably 60 - 150 microns. Based on the total weight of the aqueous coal slurry, the coal powders content (i.e., the concentration of the aqueous coal slurry), can be in the range from 8 wt% to 68 wt%, preferably from 25 wt% to 45 wt%. A certain amount catalyst can be added into the aqueous coal slurry. The catalyst is selected from alkali metal oxide or alkaline earth metal oxide, alkali metal hydroxide or alkaline earth metal hydroxide, alkali metal salt or alkaline earth metal salt, or a mixture thereof. For example, the catalyst is selected from K 2 0, Na 2 0, CaO, MgO, KOH, NaOH, Ca(OH) 2 , Mg(OH) 2 , K 2

CO

3 , Na 2

CO

3 , or a mixture thereof. The adding amount of catalyst can account for 3-30% by weight of the coal powders, preferably 5-10 wt%. The aqueous coal slurry as formulated above can be fed into a reactor by a fluid transportation device such as a pump, so as to carry out step a). At the same time, water in condition of high 6 temperature and high pressure can be fed into this reactor, so as to adjust the weight ratio of coal to water in this reactor, for example, the weight ratio of coal to water can range from 1:1 to 1:20, preferably 1:1-1:5. Alternatively, the aqueous coal slurry can first be mixed with the water in condition of high temperature and high pressure, and then the mixture thus obtained is fed into reactor. The water in the reactor is brought to a sub-critical state or super-critical state, wherein the sub-critical water state is defined as the following state: a temperature of 120 - 3740 and a pressure of 10-22 MPa (the pressures herein are all absolute pressure), whereas the super-critical water state is defined as the following state: a temperature of 374 -6500and a pressure of 22.1-30 MPa. Preferably, the temperature and pressure of the water in the reactor are 300-5000 and 15-25 MPa, respectively. After reaching reaction conditions, the reaction is conducted for 1-30 min, preferably 5-10 min. After the reaction is completed, the reaction mixture is separated in any traditional separation means, obtaining solid product, gas product and light tar. Wherein the solid product is said semi-coke, which contains Montan wax, and the solid product can be leached by using de-ionic water at ambient temperature and atmospheric pressure to dissolve out the catalyst contained therein. The small amount of phenolics contained in the coal, and the methane-rich gas produced during the treatment 7 of coal, are mixed with and dissolved in the sub-critical or super-critical fluid and are taken away by the fluid. The phenolics can be recovered and sold as product, and the methane-rich gas can be further purified and then be used as fuel gas. In this technical field, above process, which extracts the phenolics and methane-rich gas from coal by using sub-critical fluid or super-critical fluid and remains the Montan wax-containing semi-coke, is called the "stripping" process of coal. Moreover, the inventor also found that, by selecting the specific type and/or composition of the catalyst, one can control the "stripping degree" of the coal, and control in turn the amount and purity of the Montan wax extracted in subsequent step b). The main components of the semi-coke are carbon, ash and volatile component. The semi-coke is characterized by its black color, high porosity and low mechanic strength. Compared with coal, the high porosity character of semi-coke will increase its contact surface area with solvent. This is very desirable for the solvent leaching process. The ingredients contained in the coal will occur to complex reaction upon the treatment of sub-critical fluid or super-critical fluid, producing wax component. This will be favour of the increase of wax yield and wax quality. It should be noted that, the fluid used in step a) can not be limited to water. Other fluid, such 8 as alcohols or carbon dioxide, can also be used. For the specific temperature and pressure of the selected fluid, the skilled in the art will judge whether they will fall within the temperature and pressure range corresponding to its sub-critical or super-critical state or not by using its critical temperature and critical pressure and common technical practice. For example, if a fluid has a temperature above its critical temperature and a pressure above its critical pressure, then this fluid is on its super-critical state. But for the definition to sub-critical state, it is somewhat more complex. Even for the same fluid, the temperature and pressure ranges corresponding to its sub-critical state will vary from references to references. For the sake of clarity, if the specific temperature and pressure ranges corresponding to the sub-critical state have been given herein, these ranges will control; if these ranges are not given, then the definition to sub-critical state follows the principle below: if the fluid has a temperature above its atmospheric boiling point but below its critical temperature and a pressure under which the fluid remains in liquid state, then this fluid is on its sub-critical state. In step b), the Montan wax can be leached out from said semi-coke by using a solvent capable of dissolving said Montan wax as leaching solvent. This leaching step can be carried out in a leacher. The solvent employed can be any kind of solvent used in the art, 9 including but not limiting to: an aqueous solution of alcohol, a mixture of alcohol and hydrocarbon solvent, ketone solvent or ether solvent, or the like; Wherein the hydrocarbon solvent can be selected from benzene, toluene, n-hexane, cyclohexane, mineral spirit or a mixture thereof. The mixture of various solvents can also be used. Preferably, the alcohol is selected from methanol, ethanol, iso-propanol, propylene glycol or a mixture thereof. When a mixture of alcohol and hydrocarbon solvent is used, the volume content of alcohol in this mixture may be 30-99%. When the aqueous solution of alcohol is used, the volume content of alcohol in this aqueous solution may be 30-99 %. The leaching condition in step b ) comprises a temperature of 65-2000 and a pressure of 0.1-I MPa. The leaching step can be conducted in batch-wise or continuously. In the batch-wise leaching process, the semi-coke is immersed into leaching solvent, and after a certain period a solid/liquid separation operation is made. The remained solid after recovering solvent from liquid phase, is the crude Montan wax, which can be further purified to obtain refined Montan wax. In the continuous leaching process, the semi-coke with a certain particle size, can be fed by a hopper to a delivering device in a continuous leaching equipment, then a leaching solvent is sprayed on the semi-coke powders to carry out leaching operation. The 10 leachate drops into a tank of the leacher via the orifices in the delivering device. The residual semi-coke is removed by filtration, and the water potentially carried by the solvent, can be removed by oil/water separation, the separated water can be recycled to a slurrying step for reuse. The separated oil phase product can be subjected to a flash, distillation operation or the like, so as to remove the solvent from it. Then the oil phase product is dried to obtain dry Montan wax product. The removed solvent can also be recovered for reuse. After the Montan wax has been leached out, the remained lignite can be sold as up-graded lignite product, because its purity is much increased. Alternatively, in some cases, a step of pre-treating said semi-coke can be optionally added between step a ) and step b, this step pre-treats said semi-coke under the addition of water, hydrogen, carbon dioxide, or the like, or the combination thereof, so as to improve the leaching yield in step b). Above-mentioned is the first embodiment according to the invention. The invention can also be carried out in other manner. For example, in the step a), a certain amount of hydrogen can be introduced into the reactor to modify the coal, so as to further increase the Montan wax content in the coal, thus formed the second i1 embodiment according to the invention. In this second embodiment according to the invention, many process parameters, such as the type of coal, the particle size of coal powders, the weight ratio of water to coal, the catalyst and its adding amount, the state of super-critical water, reaction temperature, pressure, etc., can be selected in the same manner as described in the first embodiment according to the invention, and in step a) the hydrogen gas is introduced into system by using gas compressor to let the partial pressure of hydrogen in the system reach I - 5MPa. The invention has significant advantages compared with traditional process. Firstly, instead of being directly leached by solvent, the lignite powders are firstly treated by a sub-critical fluid or super-critical fluid and are converted into porous semi-coke. By doing so, the contact area between raw materials and solvent is greatly increased and thus the leaching yield is improved. Based on above reasons, the raw material used in the invention can not be limited to lignite alone, instead, any coal which contains Montan wax component, especially the coals which can not be used by conventional process due to their low Montan wax content, even the residue coke obtained in the gasification of some kind of coal such as bituminous coal, can also be used. So the source of raw materials is enlarged and the cost is reduced. Secondly, the solvent used in the 12 invention has wide source and is cheaper than traditional solvent. The solvent used in the invention is of little toxicity and will neither do harm to operator nor pollute environment due to its diffusion into surrounding air, so it can be regarded as environment-friendly solvent. Thirdly, the amount and/or purity of the extracted Montan wax can be controlled by controlling the type and/or composition of said catalyst, and by doing so, the work load for purifying the crude Montan wax in subsequent steps can be reduced. Fourthly, the invention can also co-produce methane-rich gas, small amount of phenolics and up-graded lignite, these by-products can be sold as commodity, so the economic benefit of the invention can further be increased. Brief description of figure Fig 1 is the schematic drawing of the embodiment of the invention. Examples Referring to Fig 1, the invention will be illustrated by following non-limiting examples. Comparative example I Lignite is used as raw coal. The lignite powders ground and sieved to a particle size of 60 - 150 microns, are slurried to prepare 13 an aqueous coal slurry containing 30wt% coal. This aqueous coal slurry is fed into a reactor after mixing with sub-critical water or super-critical water. No catalyst is added to the reactor, and the coal is treated in the reactor under the temperature and pressure listed in Table 1, producing a mixed gas containing methane, a mixture of water and combustive oil component, and a combustive solid component. The gas, liquid and solid phases are separated in separator. Then the resulted solid material is cooled, obtaining semi-coke. The semi-coke thus obtained is ground and sieved, then enters coal silos, and is fed via a coal hopper to the delivering device in the leacher. Then an ethanol-water mixed solvent with a temperature of 100], which comprising 50 vol% ethanol, is sprayed from the upper portion of the leacher onto the semi-coke powders. The leachate drops into a tank located in the lower portion of the leacher via the orifices in the delivering belt. To maintain the solvent in liquid phase, the pressure in the leacher is 0.1 5MPa. The liquid outlet of the tank located in the lower portion of the leacher is opened every 20 min. The leachate flows through a filter to filter out small amount of semi-coke solid entrained in the leachate, then enters a liquid separator to conduct oil/water separation. An upper wax-containing liquid phase obtained by oil/water separation enters a flash drum to 14 recover solvent. The recovered solvent can return to the leacher for reuse. The leaching residue left in the flash drum, which still has a certain amount of solvent, is fed into wax drier to be dried, obtaining Montan wax product. An aqueous phase obtained as the lower layer in oil/water separator is subjected to further treatments such as desalination and then be recovered for reuse. Example I Lignite is used as raw coal. The lignite powders ground and sieved to a particle size of 60 - 150 microns are slurried to prepare an aqueous coal slurry containing 30wt% coal, and to this aqueous coal slurry a catalyst K 2

CO

3 is added in an amount of 5wt% relative to the weight of coal powders. This aqueous coal slurry is fed into a reactor after mixing with sub-critical water or super-critical water. The coal is treated in the reactor under the temperature and pressure listed in Table 1, producing a mixed gas containing methane, a mixture of water and combustive oil component, and a combustive solid component. The gas, liquid and solid phases are separated in separator. Then the resulted solid material is cooled, obtaining semi-coke. The subsequent leaching step and the process parameters therein are same with that in comparative example 1. Example 2 15 The steps in this example are basically same with that in example 1, except that the pure K 2

CO

3 is replaced with a mixture of

K

2

CO

3 and Na 2

CO

3

(K

2

CO

3 :Na 2

CO

3 =1:1, weight ratio ) , and the total amount of catalyst is still 5wt% relative to the weight of coal powders. Example 3 The type of coal, the catalyst, other process conditions and parameters in this example are same with those in example 1, except that an ethanol-cyclohexane mixed solvent comprising 35 vol% ethanol is used as the extracting solvent. Example 4 Lignite is used as raw coal. The lignite powders ground and sieved to a particle size of 60 - 150 microns are slurried to prepare an aqueous coal slurry containing 30wt% coal, and to this aqueous coal slurry a catalyst K 2

CO

3 is added in an amount of 5wt% relative to the weight of coal powders. This aqueous coal slurry is fed into a reactor after mixing with sub-critical water or super-critical water, at the same time, hydrogen gas is introduced into system by using gas compressor to let the partial pressure of hydrogen in the system reach 5MPa. Other process steps and parameters are same with those in example 1. Comparative example 2 16 By using the same solvent and leaching conditions with those in example 1, the lignite powders are directly leached according to step b), without conducting step a) Comparative example 3 By using the same solvent and leaching conditions with those in example 3, the lignite powders are directly leached according to step b), without conducting step a) Example 5 Bituminous coal is used as raw coal. The processing method and process parameters are same with those in example 3. Comparative example 4 By using the same solvent and leaching conditions with those in example 5, the bituminous coal powders are directly leached according to step b), without conducting step a ) Example 6 A step is added between step a ) and step b ) in example 1, this step pre-treats said semi-coke under the addition of hydrogen. This pre-treating step is a distinct step from step a) and step b), as it occurs after the separator shown in Fig 1 but before the step b). This pre-treating step comprises: hydrogen is introduced into fix-bed reactor in a ratio of 1000 m 3 hydrogen per ton semi-coke, the temperature is heated to 4000 and maintained at this value for 5 min, 17 then the temperature is decreased, then solid obtained in reaction is subjected to step b) described in example 1. The process conditions and results of all examples and comparative examples above-mentioned are shown in Table 1. From the data in Table 1 it can be seen that, for the same lignite, if the Montan wax is extracted according to traditional solvent leaching method without conducting step a ) , the wax yield is only 1.45% and 1.78% (see comparative example 2 and comparative example 3), but when step a) is used, the wax yield can reach 2.28% and 3.51% (see example land example 3). When hydrogen is introduced into step a ) , the wax yield is further increased, see example 4. When the bituminous coal is used as raw coal, if it is directly leached by solvent without any pre-treatment, nearly no materials conforming to the characters of Montan wax can be detected, see the comparative example 4. In contrast, after being treated in step a), the wax yield can reach 1.75%, see example 5. In example 6, a step of pre-treating semi-coke with hydrogen is inserted between step a) and step b). As one can find from the results, this can further increase the wax yield compared with example 1 in which only step a) and step b) are carried out in the same conditions. By comparing example I with comparative example 1, it can be seen that the wax yield obtained in the presence of catalyst is obviously !8 higher than that obtained in the absence of catalyst, when other conditions are same. By comparing example 2 with example 1, it can be seen that the wax yield obtained when using a mixture of two kind of carbonate as catalyst is obviously higher than that obtained when using single carbonate as catalyst. Moreover, it can be visually seen that, the color of the Montan wax obtained in example 2 is more close to the color of pure Montan wax compared with that obtained in example 1, thus the Montan wax obtained in example 2 has a higher purity. The "wax yield" used herein means the weight percent of obtained Montan wax relative to the raw coal. 19 0 - U .2 .2 .~ .~9b Fl F Fl~~l Lj

Claims

1. A process for extracting Montan wax, comprising the following steps: a) treating coal powders in a sub-critical fluid or super-critical fluid under the action of catalyst, obtaining semi-coke containing Montan wax; and, b) leaching out said Montan wax from said semi-coke with a solvent capable of dissolving said Montan wax.

2. A process for extracting Montan wax, comprising the following steps: a) treating coal powders in a sub-critical fluid or super-critical fluid under the action of catalyst and hydrogen, obtaining semi-coke containing Montan wax; and, b) leaching out said Montan wax from said semi-coke with a solvent capable of dissolving said Montan wax.

3. The process according to claim I or 2, wherein the super-critical fluid means that a fluid has a temperature above its critical temperature and a pressure above its critical pressure ;and wherein the sub-critical fluid means a fluid has a temperature above its atmospheric boiling point but below its critical temperature and a pressure under which the fluid 21 is remained in liquid state.

4. The process according to claim I or 2, wherein the solvent in step b) is an aqueous solution of alcohol, a mixture of alcohol and hydrocarbon solvent, ketone solvent or ether solvent.

5. The process according to claim 4, wherein said alcohol is selected from methanol, ethanol, iso-propanol, propylene glycol or a mixture thereof; and said hydrocarbon solvent is selected from n-hexane, cyclohexane, mineral spirit or a mixture thereof.

6. The process according to claim I or 2, wherein said fluid is selected from water, alcohol or carbon dioxide.

7. The process according to claim I or 2, wherein the catalyst in step a) is selected from alkali metal oxide or alkaline earth metal oxide, alkali metal hydroxide or alkaline earth metal hydroxide, or, alkali metal salt or alkaline earth metal salt.

8. The process according to claim I or 2, wherein said coal is selected from bituminous coal, anthracite or lignite.

9. The process according to claim 1 or 2, wherein the reaction conditions in step a) comprise a temperature of 300-5000, a pressure of 15-25MPa, a reaction time of 1-30 min, an adding amount of catalyst accounting for 3-30wt% of the 22 coal powders and a weight ratio of coal to water from 1:1 to 1:20; and the leaching conditions in step b) comprise a temperature of 65-200 0 and a pressure of 0.1-1MPa.

10. The process according to claim I or 2, wherein at least one pre-treating step is added between step a ) and step b ) , which pre-treating said semi-coke under the addition of water, hydrogen, carbon dioxide, or the like, or the combination thereof.

11. The process according to claim I or 2, wherein the amount and/or purity of the Montan wax leached out in step b) is controlled by controlling the type and/or composition of said catalyst in step a). 23