Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Defibration by projection or explosion
Reexamination Certificate
2000-09-11
2002-07-09
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Defibration by projection or explosion
C422S198000, C422S233000, C162S018000
Reexamination Certificate
active
06416621
ABSTRACT:
The invention relates to a process, an apparatus and a pressure reactor for the treatment of solids with pressurised liquid gases, in liquid ammonia.
A process of the type is described, for example, in the WO 96/3 04 11. With the known processes polysaccharides are brought into contact with pressurised liquid ammonia. During the subsequent pressure release the volume available to the polysaccharide/liquid ammonia system is enlarged explosion-like whilst reducing the pressure by at least 5 bar. By doing so an increased accessibility and reactivity of the treated polysaccharides can be obtained.
To obtain an as high as possible yield of treated solids in a short time, such processes are preferably carried out continuously. However, with the continuous process suitable steps must be taken to feed the solid into the pressure tank.
From the DE-27 14 993 a process is known for feeding fibrous lignose cellulose raw material into a pressurised tank. Here the raw material, before entering the pressure tank, is pre-compacted to a density of at least 0,72 g/cm3 and is then fed into the tank by a conveying screw. The pre-compacted raw material then acts as a plug which on passing the inlet opening of the pressure tank seals same off, so that the pressure in the tank can be maintained. As a result thereof it is possible to continuously feed cellulose to the tank.
However, this continuous process requires a great amount of apparatus on the feeding side. In addition, due to the high pressure that must be exerted on the cellulose to compact it, a disadvantageous change of the inherent properties of the cellulose is produced.
Furthermore, the known method requires a dwell time (approx. 4 minutes) of the cellulose in the pressure tank, which is unnecessarily long especially for the treatment with pressurised liquid ammonia, in particular under high pressure, since as is known, liquid ammonia diffuses into solids within a few seconds up to one minute and in doing so is uniformly distributed.
Moreover, a reliable and adequate sealing off of the apparatus when working with liquid ammonia under pressures of up to 40 bar, in particular at the lead-through of the drive shafts for the pressure tank and for the screw conveyor in the outlet part underneath the pressure tank, is problematical. The sealing off of the pressure reactor to the outside takes place, as indicated above, by the to be treated material itself. This may possibly be satisfactory in the case of very moist, plastically deformable solids, such as for example wood chips. With cellulose, guar splits, i.e. hard, small lentil-shaped seeds, as well as with minerals, e.g. zeolites or silicates, as solid, a sealing is, however, hardly possible.
Finally, the smallest possible size of the apparatus for carrying out the known process lies at a through-put of approximately 400 tons per year, which is much too large for specific fields of application.
From the U.S. Pat. No. 5,171,592 a process is known, with which the to be treated biomass is pressed by means of a solids pump against a large valve so as to compact the material and press out the enclosed air before the valve is opened to feed the biomass into the reactor. The reactor is provided with finger-like teeth on the inside wall of the reactor and on a rotating tool. The teeth have a hole for dosing liquid ammonia into the reactor. The reactor outlet is provided with a valve through which the ammonia-treated biomass can escape explosion-like into a collecting tank. The apparatus for carrying out the process is, therefore, relatively complex and not suitable for processes that are carried out under high pressure, seeing that rotating machine parts are located in the high-pressure area, which causes increased wear and susceptibility to problems of the known apparatus.
It is, therefore, the object of the present invention to indicate a process with which the described disadvantages of the state of the art are avoided, and with which at the same time the treated solid is obtained practically continuously. It is a further object of the invention to make available an apparatus suitable for carrying out the process and a respective pressure reactor, which stand out by a high availability and low maintenance costs.
These objects are achieved by the process for the treatment of solids with pressurised liquid gases, in particular liquid ammonia, according to claim 1, by the apparatus according to claim 10 and by the pressure reactor according to claim 45 or the process according to claim 55.
According to same, with the process according to the invention the to be treated solid is fed into a pressure reactor at atmospheric pressure, subsequent to which the pressurised liquid gas is fed to the pressure reactor and after a pre-set dwell time the resultant liquid gas/solid mixture is expanded explosion-like into an expansion tank, wherein at least two reactors are operated in a time-staggered manner.
With the process according to the invention it is possible to feed a pressurised liquid gas into a solid present in any form, and to treat it with the pressurised liquid gas for a pre-set time, without a drop in pressure occurring and without the to be treated solid itself being used for sealing functions so as to maintain the pressure. For this reason, at the start of the process the to be treated solid need not be compacted so heavily that its structure or morphology changes or is adversely affected. Accordingly, a rapid and uniform diffusion of the pressurised liquid gas in the to be treated solid is ensured.
At the start of the process according to the invention, in particular after a preceding preparation in the sense of a splitting up or comminuting, the to be treated solid can be pre-compacted to a desired bulk density or to a specific compacting degree. In this way the yield of treated solid per unit of space and time can be adapted to the requirements in question, for example with regard to the size of the apparatus. In this connection it must be borne in mind, however, that the compacting pressure is kept so low that no change in the inherent properties of the solid occurs.
The process according to the invention can be used for the treatment of cellulose, starch, gelatine, guar or wood chips and in general of polysaccharide-containing materials, but also for the treatment of minerals such as silicates and zeolites as well as of thermoplastic polymers. Because of its particularly good diffusion properties, ammonia has proved eminently suitable for use as liquid gas.
By the cyclic operation of at least two pressure reactors, a quasi-continuous treatment of the solid can be obtained, so that starting material can be made available practically uninterruptedly for further processing.
Preferably, the gas released during the explosion-like pressure release is recovered. The recovered gas can subsequently be fed back to the process in liquid form. This permits a particularly economic mode of operation, as in total only a small part of the used gas, which for example escapes into the atmosphere by unavoidable diffusion or evaporation, need be replaced.
The solid can be fed into the pressure reactor with the aid of dosing screws. By using this known, technically perfected conveying means, the process according to the invention can be implemented particularly reliably.
Alternatively, the solid can also be fed into the pressure reactor by a pneumatically operating conveying device. By this measure a particularly quick and specific feeding of the to be treated solid can be achieved.
Preferably, the to be treated solid is actively mixed with the liquid gas in the pressure reactor. This has the advantage that the liquid gas penetrates even more deeply into the solid and distributes itself even more homogeneously in same. Furthermore, by this additional measure the dwell time of the mixture liquid gas/solid in the reactor can be reduced and accordingly the throughput per pressure reactor can be increased. This measure is particularly expedient when the liquid gas has only moderately good diffusion properties or w
Chin Peter
Darby & Darby
Hug Eric
Rhodia Acetow GmbH
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