Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Particular raw cellulosic materials
Patent
1996-01-26
1998-09-08
Czaja, Donald E.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Particular raw cellulosic materials
162 10, 162150, 162165, 162166, 162189, 241 15, D21C 300, D21C 500
Patent
active
058040358
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATION
Priority is claimed to International Application Number PCT/DE95/00360 having international filing date Mar. 14, 1995 and corresponding German priority application No. P 44 08 788.8, filed Mar. 15, 1994.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
Not applicable
BACKGROUND OF THE INVENTION
The present invention is related to recycling systems, and in particular to a process
A known recovery process is specified in DE 42 24 629 A1. During this process, the residues of derived timber products are exposed to steam at high temperatures between 120.degree. and 180.degree. C. and the consequential high pressures (2-11 bar). The derived timber products are subjected to a pretreatment in the course of which the material is crushed and any metal components are removed. Chips produced according to this method are rebonded with modified urea binders. However, the chips suffer not only from the high temperatures but are also mechanically damaged, i.e. shortened, during the previous crushing of the starting material. Another disadvantage of this method is that it is very difficult to separate coating materials and other undesired components from the chips after the steam treatment because the starting material has been so thoroughly crushed.
Another process for the recovery of chips from derived timber products is described in DE-AS 1 201 045. This procedure involves excess pressured steam to which the residues of the derived timber products are exposed. This process is preferably performed in a steam chamber at a pressure between 1 and 5 atmospheres above atmospheric pressure. The process duration varies between 0.5 and 4 hours. However, the processed materials are not fully disintegrated, which means that subsequent crushing is required. The chips are considerably damaged by the high temperature and the pressure and turn brown. Chip board with acceptable properties can only be produced of the recovered chips if fresh chips are added. Due to the degree of damage and their brown color, it is recommended to use the recovered chips preferably in the middle layer of chip board.
Another method is the boiling of chip board bonded with urea formaldehyde resins and medium density wood fiber board in large quantities of water to disintegrate them. However, this procedure is very energy consuming and cost intensive. The increased energy consumption is, in particular, due to the fact that such large quantities of water must be heated. The chips are boiled out, which has a negative impact on their characteristics. The swellability of the chips is increased due to removal of timber particles, while the technological qualities of the chips are reduced. The binder is removed from the chips, which means that it cannot enhance the rebonding of the recovered chips. Additional considerable problems occurring in connection with this method are the disposal of the produced waste water and the drying of the soaked chips or fibers.
DE 42 01 201A1 furthermore specifies a method for the recycling of derived timber products and wood-containing waste. This method is based on a special mechanical treatment of the derived timber product residues, which are subsequently processed into new semifinished or finished products.
SUMMARY OF THE INVENTION
The purpose of the proposed invention is the introduction of an environmentally friendly and economically feasible method to recover chips and fibers from derived timber products. As an additional objective, this method is designed to yield high-quality chip and fiber material (secondary chips/fibers). This
In accordance with the present invention, a process for recovering fibers from residues of derived timber materials bonded with binders that can be hydrolyzed or chemically disintegrated, comprises the steps of: impregnating the materials with a saturating or impregnating solution and allowing the materials to swell until the materials have absorbed at least 50% of their own weight in impregnating solution, thereby becoming impregna
Boehme Christian
Michanickl Andreas
Czaja Donald E.
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
Leavitt Steven B.
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