Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
1998-06-02
2001-06-05
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S030000, C536S032000
Reexamination Certificate
active
06242595
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for the recovery from a reaction mixture of cellulose carbamate produced by conversion of cellulose with excess urea in an inert organic liquid reaction carrier.
2. Description of the Related Art
U.S. Pat. No. 5,378,827 discloses a multi-step process for the production of cellulose carbamate in which the cellulose is mixed with aqueous urea solution, the water portion of the mixture is exchanged for an organic reaction carrier, the conversion to the carbamate is carried out under formation or addition of an inert vaporous or gaseous medium which is led off from the reaction zone, a part of the organic reaction carrier is separated mechanically from the conversion mixture, the remaining mixture is added with aqueous urea solution, the remaining organic reaction carrier removed by distillation, the aqueous cellulose carbamate-containing mixture cooled by lowering its pressure, and the cellulose carbamate separated on a band filter from the aqueous urea solution and washed with water. The financial expense for the separation of the cellulose carbamate and the recovery of urea and reaction carrier is considerable.
According to DE-A 44 17 140, the organic reaction carrier can also be washed out with methanol or ethanol and recovered from the washing filtrate by extraction with water. The remaining extraction mixture can be separated by rectification in alcohol and aqueous urea solution. A disadvantage is that in addition to the reaction carrier, another auxiliary material must be used, namely, alcohol.
In the process of the EP Patent 97 685, the whole organic reaction carrier is separated from the reaction mixture through vacuum distillation and the remaining mixture washed with water. Because of the voluminous nature of the cellulose carbamate, there remains a considerable amount of organic reaction carrier in the cellulose carbamate after the distillation. Also, biuret, the by-product formed, is washed out only with difficulty.
SUMMARY OF THE INVENTION
The present invention comprises a process for the recovery from a reaction mixture of cellulose carbamate produced by conversion of cellulose with excess urea in an inert organic liquid reaction carrier. The process is more economical than those of the prior art. An advantage of the invention is that one can obtain water-wet cellulose carbamate that is practically free from excess urea, biuret, and organic reaction carrier.
The process comprises treating the cellulose carbamate reaction mixture with water under heat, separating the liquid phase from this mixture as much as possible on a filter, washing the cellulose carbamate remaining on the filter with water, which is then optionally pre-dried and/or dried and recovered, and recovering the organic reaction carrier by phase separation from the combined liquids for further use.
The foregoing merely summarizes certain aspects of the invention and is not intended, nor should it be construed, as limiting the invention in any manner. The invention is described in full detail below.
REFERENCES:
patent: 5378827 (1995-01-01), Keunecke
patent: 44 17 140 A1 (1995-11-01), None
patent: 0 097 685 (1986-06-01), None
Geist Gary
Lurgi Zimmer Aktiengesellschaft
McDonnell & Boehnen Hulbert & Berghoff
White Everett
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