Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With regeneration – reclamation – reuse – recycling or...
Patent
1996-06-21
1998-03-24
Hastings, Karen M.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With regeneration, reclamation, reuse, recycling or...
162 16, 162 301, 423325, D21C 1100
Patent
active
057308381
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a process for extracting pure, coarse grain silicic acid crystals from silicic acid-containing spent lye in cellulose production, in particular the processing of annual plants.
BACKGROUND OF THE INVENTION
A method by which silicic acid is separated from a pre-concentrated waste liquor by means of exposure to CO.sub.2 is known, as disclosed in DE-A1-3208200 or U.S. Pat. No. 2,504,356. Furthermore, EP-A-0431337 discloses a method by which the spent lye of cellulose digestion of annual plants is exposed to CO.sub.2 to slowly lower the pH, whereby the silicic acid is precipitated and most of the lignin remains in the solution during the lowering of the pH to about 10.2. According to the process disclosed in EP-A-0431337, the lignin separation is suppressed by limiting the pH lowering, and the silicic acid is precipitated at a relatively slow rate. By inoculating the spent lye with precipitated silicic acid, the extraction is improved, but cost of equipment is expensive.
In order to rapidly attain a high degree of desilification it is necessary to lower the pH value further. At pH values below 10, however, more lignin is precipitated. Although this facilitates sedimentation and coarsening of the silicic acid grain in a desirable manner, return of the precipitated silicic acid to the precipitation device leads to an undesirable enrichment in the desilification steps, thereby hindering the precipitation of the silicic acid. Therefore, further lowering of the pH would make it possible to accelerate the extraction, except that the lignin content of the spent lye for depletion of silicic acid is increased such that silicic acid can no longer be removed. For example, the dissolved silicic acid contents in rice straw are approximately 10% SiO.sub.2 dry substance, with 100 g/l dry substance of the spent lye being thus dissolved at 10 g/l SiO.sub.2. When the pH value is lowered, up to 5 g/l of lignin can however be precipitated, causing a high proportion of organic material to be contained in the produced sludge.
It is therefore desirable to produce a coarse-grain silicic acid in the form of a saleable product by a process in which the lignin remains in the spent lye to increase useful fuel output in the lye combustion furnace.
SUMMARY OF THE INVENTION
It is the object of the present invention to obtain pure, coarse grain silicic acid by a stable process and to return the co-precipitated lignin into the liquification and subsequent combustion phases.
It is the object of the present invention that alkalized spent lye from cellulose production is inoculated with coarse-grain silicic acid, the pH value is then lowered preferably to about 9, the sludge produced as the pH value is lowered is separated during its sedimentation into coarse grain and fine grain silicic acid with a small amount of lignin and into lignin-containing, silicic acid depleted spent lye, and the coarse grain silicic acid is separated from the lignin in a washing device and the seaprated lignin is mixed into the lignin-containing spent lye.
It is an object of the present invention that part of the coarse-grain silicic acid is fed back into the first silicic acid precipitation step for inoculating and that withdrawal of the excess silicic acid takes place discontinuously.
It is an object of the present invention that the lignin-containing, in particular coarse grain silicic acid is fed back into the desilification cycle after washing, preferably by means of a partial flow of the desilified spent lye, if necessary with the addition of carbonates or hydroxides and a separation of the lignine.
It is an object of the present invention that the silicic acid obtained in the overflow of the washing phase is introduced directly into the spent lye to be desilicified in the alkalizing container or in a dissolving container upstream of same.
It is an object of the present invention that the pH value of the spent lye in the individual precipitation steps is equal to approximately the pH value of a relative silic
REFERENCES:
patent: 4331507 (1982-05-01), Roberts
patent: 4504356 (1985-03-01), Mulder et al.
Austrian Energy & Environment SGP/Waagner-BIRO GmbH
Hastings Karen M.
LandOfFree
Process for extracting pure, coarse grain silicic acid crystals does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for extracting pure, coarse grain silicic acid crystals , we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for extracting pure, coarse grain silicic acid crystals will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2285953