CH237790A - Process for the production of high alpha and low pentosan pulps - Google Patents

Description

  

  Process for the production of high alpha and low pentosan pulps. It is known for the production of cellulose .cellulosehalti suitable for further chemical processing, in particular for the production of viscose spinning solutions.

  b To pretreat raw materials with acids and then subject them to a conventional pulp digestion process.

   These known hydrolysis processes make it possible to obtain pulps with a high alpha content from a wide variety of cellulose-containing raw materials. This is made possible by the fact that the pentosans can be almost completely dissolved out by the acid pretreatment.



  In the production of cellulose, the procedure is now that the digestion liquid is thickened and evaporated; excess water is returned and used for further new digestions.

    If you want to use the well-known hydrolysis process in a pulp factory, you will get into difficulties because the pre-hydrolysed, highly water-containing cellulose raw material dilutes the digestion liquids so that you cannot get by with the number of evaporators available.

   It is therefore necessary to further restrict the digestion liquid by installing additional evaporators.



  It has now surprisingly been found that further narrowing can be avoided and the dehydration of the pre-cyclized raw material can be carried out in an advantageous manner if the excess hydrolysis liquid is removed by squeezing.

   It is only through this method of operation that the prehydrolysis process becomes economical. to design and bring the Laugehaus.halt into the CTlei.ch weight. A wide variety of types of Abpressvorrichtunb n can be used for pressing. For example, roller presses are well suited to remove the excess liquid.



  The. Operation according to the invention can be used for a wide variety of cellulosic raw materials, both for pre-hydrolyzed wood carved, z. Use eg pine and beech wood chips, as well as pre-hydrolysed straw, potato leaves or reeds or other annual plants. After the pre-hydrolysing acid has been drained off, the acid is removed by washing with a subsequent alkaline digestion.

   If an acidic digestion is carried out, it is not always necessary to wash out the Ilydrolysic acid.



  The prehydrolysis can be carried out under the usual known conditions. There are usually organic acids such as hydrochloric acid, sulfuric acid or phosphoric acid, different concentration used. Organic acids, such as formic acid or acetic acid, can also be used. The digestion of the acid pre-treated, cellulose-containing raw material can then take place by any desired digestion process.

   Both acidic digestion processes, for example the sulfite process, or alkaline digestion processes, such as the soda or sulfate process, can be used. It is advantageous to use an alkaline digestion process, since this method of working produces cellulose which is particularly suitable for the production of synthetic fiber cellulose.



  The acid concentration used for the pre-hydrolysis must be selected differently depending on the working conditions. When working under atmospheric pressure, higher acid concentrations are required than when working under increased pressure. When using sulfuric acid, for example, concentrations of about 1-35% sulfuric acid can be used.

   It is particularly useful to purify under increased pressure and to use dilute sulfuric acid or hydrochloric acid below 1%.



       Execution example: 850 kg air-dry straw (corresponding to 750 kg atro) are mixed with 7000 liters of water and 19, <B> 2 </B> 5 liters of technical sulfuric acid (D 1.84, sulfuric acid concentration 0.48 percent by weight) Heated as quickly as possible to 130 in an acid-proof, sealed container and left at this temperature for 3 hours.

   After the pressure has been released, the pretreated straw is separated from the hydrolic acid, washed out with water and pressed down to a water retention of around <B> 60% </B>. The pressed, moist straw is subjected to boiling in a lye which contains L) 0% effective alkali (calculated as NaOH), based on absolutely dry, pre-hydrolysed material.

   The cooking liquor contains <B> 80% </B> of the effective alkali as NaOI1 and 20% as wet in addition to 15 Na-CO., And 3-47o 'Na-, SO ,. The cooking is carried out with a liquor ratio of 1: 4.9 at 160-165 I maximum temperature.



  The yields for pre-hydrolysis are 65% and for alkaline boiling -1: 0%. so that for finished bleached cellulose, assuming a bleaching loss of '-)' ö, there is a yield of 24%, based on the material originally used.



  The pulp obtained has an alpha web width of 94 'and a wood content of 3%. The ash content is 19% and the degree of polymerisation is 730.

 

Claims (1)

PATENT CLAIM Process for the production of cellulose from hobein alpha and low pentosan content from cellulosic raw materials by I1ei; soot-dissolving the Pent: Osane with dilute acids and an additional disintegration of cellulose, which means that the pre-hydrolyzed raw material is freed from hot liquid by pressing it off before the pulp is disintegrated. 1TXTER CLAIM: Procedure. according to claim, characterized. class an alkaline digestion is used and the raw material treated with acid is freed from acid by washing out with water before it is pressed.