Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
2000-05-31
2003-06-17
Wilson, James O. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S033000, C536S034000, C536S059000, C536S062000, C536S124000, C536S127000, C514S057000
Reexamination Certificate
active
06579977
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This application is a 371 of PCT/DE98/03504, filed Nov. 27, 1998.
The invention relates to a process for producing biosorbents by phosphorylation of cellulose-containing materials with phosphoric acid or ammonium phosphate in the presence of urea. The invention further relates to biosorbents with particularly good application properties. Biosorbents of this type are employed in particular for removing heavy metals from aqueous solutions.
2. The Prior Art
DE 42 39 749 C2 discloses a process for producing phosphorylated wood. Powdered wood with a particle size of from 0.05 to 3 mm is stirred with phosphoric acid, water and urea to form a paste and partially dried at about 80° C. for about 1 hour. The reaction mixture obtained in this way is heated at about 170° C. for about 70 min, then washed with hot water until the washing liquid appears colorless, and dried. In an alternative embodiment of the process, the use of ammonium phosphate in place of phosphoric acid is also described. It is necessary subsequently to remove phosphate residues and colored impurities from the resulting reaction product or crude product. The purification stages are very time-consuming and have disadvantageous effects on the costs of the final product. According to the purification process described in DE 42 39 749, the crude product must be washed with hot water until the washing liquid appears colorless. The product then obtained is washed with sodium hydroxide solution and finally again washed until the filtrate is colorless, and dried. A further disadvantage of this process is the very large expenditure on phosphoric acid or phosphate and urea. The reaction at 170° C. within the stated duration is very energy-consuming and leads to the formation of intensely dark-colored impurities and decomposition products of wood constituents, which must subsequently be washed out again. In addition, the high phosphorus content in the sorbent, which is desired to achieve a satisfactory sorption capacity, makes it necessary to use a large excess of phosphoric acid or phosphate and urea. Heavy pollution of the washing water during the purification of the crude product is therefore to be expected, resulting in high disposal costs.
DE-A 23 57 696 describes a process in which inter alia cellulose-containing material is mixed with phosphoric acid in the ratio by weight of phosphoric acid to organic material of from 0.25:1 to 2.0:1, and the mixture is roasted at temperatures of from 160 to 600° C. and subsequently washed with water and dried to give a powder.
The disadvantage of this process is, in particular, a low yield of adsorbent. In addition, only inadequate sorption results are achieved with this adsorbent. As is known, cellulose is relatively quickly degraded by strong acids. Addition of phosphoric acid on its own leads to unwanted side reactions which are the cause of the aforementioned disadvantages. WO 95/02452 discloses a process for producing sorbents from polysaccharide-containing raw materials in which modifying agents or mixtures of these agents are added to the latter, and a thermal treatment is carried out at temperatures of up to 600° C. According to the examples, a mixture of orthophosphoric acid, dimethylformamide and urea can serve as modifying agent. The mixture is boiled with the cellulose-containing material at 150° C. for two hours. The mixture is then filtered, the solid residue is washed with distilled water until the liquid phase is neutral, and the residue is dried and comminuted.
However, carrying out the phosphorylation in dimethylformamide proves to be a disadvantage because of the complexity of the removal and recycling of this solvent, which is known not to be without problems. In addition, this process requires the use of relatively large amounts of urea. The sorbents produced in this way and based on cellulose-containing raw materials such as sugar beet pulp and fungal mycelia have unfavorable mechanical properties which preclude use in the adsorber columns which are known to be very efficient. In addition, the products show sorption performances which do not exceed those of phosphorylated celluloses in either capacity or durability. RU-2096082 C1 moreover discloses that the phosphorylated crude product must be subjected to an elaborate purification. Despite the elaborate purification operations in the known processes, the resulting biosorbents are not free of soluble phosphorus-containing impurities. These are organic polymeric phosphates which cannot be removed completely by washing processes. These by-products can be detected in the final product only with difficulty. They can be flocculated out of their solution for example by making strongly acidic, and give the known phosphate reaction with ammonium molybdate and nitric acid only after boiling for a lengthy period. Because of their structure, these by-products are good complexing agents and moreover impair sorption of heavy metals to the biosorbent. A further disadvantage of the known generic biosorbents is their low mechanical stability. At high flow rates there may be compaction of the sorbent packing, which may lead to complete blockage of the exchange or purification process.
Owing to the low mechanical stability of the biosorbents, they become sponge-like after the purification, and the surface of the particles is covered with fine fibers which, when the biosorbents are used as intended in exchanger columns, are abraded off and washed away even with low mechanical stress. This results in the solutions to be purified becoming cloudy and, moreover, constituents to be adsorbed are discharged with the fiber components which are also washed away. This is a considerable qualitative deficiency of the known biosorbents.
SUMMARY OF THE INVENTION
The invention was based on the object of improving the known processes for producing biosorbents based on cellulose-containing materials by phosphorylation with phosphoric acid or ammonium phosphate in the presence of urea so that the expense of purifying the resulting crude products can be considerably reduced, the formation of unwanted soluble organic polymeric phosphates as by-products is prevented, and biosorbents with increased mechanical strength are obtained.
It is further intended to obtain biosorbents which are distinguished by very good application properties, in particular are suitable for use in adsorber columns and require little expense to produce.
The object is achieved according to the process of the present invention. In addition biosorbents with particularly good application properties are part of the present invention.
In a first embodiment of the inventive procedure, it is necessary for elemental sulfur to be added to the reaction mixture or to one of the reaction components before the start of the reaction in order to suppress almost completely the formation of soluble organic polymeric phosphates as by-products and in order to achieve biosorbents with greater mechanical strength, in particular for use thereof as packing in columns for exchange or extraction processes.
In another embodiment of the inventive procedure, without addition of sulfur, biosorbents are distinguished in particular by good sorption performances. If necessary, it is also possible according to a further embodiment of this procedure to add elemental sulfur to the reaction components or to the reaction mixture before the start of the reaction. The elemental sulfur can be mixed either with the cellulose-containing material or with the phosphorylating agent, phosphoric acid or ammonium phosphate, or with the urea, or be added to the reaction mixture. On use of phosphoric acid, the sulfur can also be dispersed in the phosphoric acid. It is essential that the addition of the elemental sulfur takes place before the required reaction temperature is reached. If the reaction or synthesis mixture is dried before the reaction under vacuum, the elemental sulfur can also be added to the synthesis mixture after completion of the drying process. The amounts of
Camacho Juan
Fieseler Christine
Ikier Hendrik
Lange Ekkehard
Pieschel Friedemann
Collard & Roe P.C.
EISU Innovative Gesellschaft fur Technik und Umweltschutz mbH
White Everett
Wilson James O.
LandOfFree
Biosorbents and process for producing the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Biosorbents and process for producing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Biosorbents and process for producing the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3097705