Process for producing pulp and at least one organic liquid or liquefiable material of value with offgas recycling

Abstract

The present invention relates to an integrated process for producing pulp and at least one organic liquid or liquefiable material of value, wherein a) a lignocellulose-comprising starting material is provided and subjected to digestion with an aqueous-alkaline treatment medium, b) a cellulose-enriched fraction and a cellulose-depleted black liquor are isolated from the digested material, c) the black liquor is subjected to a treatment to give at least one organic liquid or liquefiable material of value and at least one offgas stream, d) at least one of the offgas streams obtained in step c) is recycled to the process for producing pulp and utilized.

1 . An integrated process for producing pulp and at least one organic liquid or liquefiable material of value, wherein
 a) a lignocellulose-comprising starting material is provided and subjected to digestion with an aqueous-alkaline treatment medium,   b) a cellulose-enriched fraction and a cellulose-depleted black liquor are isolated from the digested material,   c) the black liquor is subjected to a treatment to give at least one organic liquid or liquefiable material of value and at least one offgas stream,   d) at least one of the offgas streams obtained in step c) is recycled to the process for producing pulp and utilized.   
     
     
         2 . The process according to  claim 1 , wherein the treatment medium used in step a) comprises NaOH and at least one sulfur-comprising compound, preferably Na 2 S and/or NaHS, in an aqueous medium. 
     
     
         3 . The process according to either of the preceding claims, wherein the isolation of the cellulose-enriched fraction and the cellulose-depleted black liquor in step b) is effected by filtration, centrifugation, extraction, precipitation, distillation, stripping or a combination thereof. 
     
     
         4 . The process according to any of the preceding claims, wherein, in step b), a black liquor comprising at least one component selected from
 lignin;   hemicellulose;   optionally cellulose;   optionally organic components other than lignin, hemicellulose and cellulose;   optionally inorganic constituents from the lignocellulose-comprising starting material;   inorganic digestion chemicals;   and mixtures thereof   is isolated from the digested material.   
     
     
         5 . The process according to any of the preceding claims, wherein at least part of the compounds other than lignin is firstly removed from the black liquor in step c) to give a lignin-enriched fraction. 
     
     
         6 . The process according to any of the preceding claims, wherein the black liquor or a lignin-enriched fraction obtained therefrom is subjected to a decomposition for the treatment in step c) and the decomposed material obtained is optionally subjected to a dealkylation. 
     
     
         7 . The process according to  claim 6 , wherein the black liquor or the lignin-enriched fraction obtained therefrom is subjected to a pyrolysis to effect decomposition and the unvaporizable components obtained under the pyrolysis conditions are used for obtaining the offgas stream. 
     
     
         8 . The process according to either  claim 6  or  7 , wherein the black liquor or the lignin-enriched fraction obtained therefrom is subjected to pyrolysis to effect decomposition and the decomposition product obtained is subjected to a separation, resulting in a fraction depleted in organic liquid or liquefiable materials of value, which fraction is used at least partly as offgas stream. 
     
     
         9 . The process according to any of  claims 6  to  8 , wherein the black liquor or a lignin-enriched fraction obtained therefrom is subjected to a decomposition for the treatment in step c) and the decomposed material obtained is subjected to a dealkylation, a discharge is taken from the dealkylation zone and subjected to a separation to give at least one organic liquid or liquefiable material of value and at least one stream enriched in components which are more volatile than the organic material of value and the latter stream is at least partly used as offgas stream. 
     
     
         10 . The process according to any of the preceding claims, wherein a synthesis gas produced in the process is at least partly used as offgas stream. 
     
     
         11 . The process according to any of the preceding claims, wherein, in step c):
 c 1 ) at least part of the compounds other than lignin is optionally removed from the black liquor to give a lignin-enriched fraction,   c 2 ) the black liquor or the lignin-enriched fraction obtained in step c 1 ) is subjected to a decomposition,   c 3 ) the decomposed material obtained in step c 2 ) is optionally separated into at least one aromatics-enriched fraction C 1 ) and at least one aromatics-depleted fraction C 2 ),   c 4 ) the decomposition product from step c 2 ) or the aromatics-enriched fraction C 1 ) from step c 3 ) is fed into a dealkylation zone and reacted in the presence of hydrogen and/or water vapor,   c 5 ) a discharge is taken off from the dealkylation zone and subjected to a separation, with at least one organic liquid or liquefiable material of value and at least one stream enriched in components which are more volatile than the organic material of value being obtained.   
     
     
         12 . The process according to  claim 11 , wherein the decomposition of the black liquor or a lignin-enriched fraction obtained therefrom in step c 2 ) comprises a pyrolysis. 
     
     
         13 . The process according to  claim 12 , wherein, in step c 3 ), the separation into at least one aromatics-enriched fraction C 1 ) and at least one aromatics-depleted fraction C 2 ) comprises an absorption. 
     
     
         14 . The process according to  claim 11 , wherein, in step c 2 ), the black liquor or a lignin-enriched fraction obtained therefrom is subjected to a decomposition in the liquid phase. 
     
     
         15 . The process according to  claim 14 , wherein, in step c 3 ), the separation into at least one aromatics-enriched fraction C 1 ) and at least one aromatics-depleted fraction C 2 ) comprises an extraction and/or a distillation. 
     
     
         16 . The process according to  claim 15 , wherein the separation into at least one aromatics-enriched fraction C 1 ) and at least one aromatics-depleted fraction C 2 ) in step c 3 ) comprises the following substeps:
 c 31 ) extraction of the decomposition product obtained in step c 2 ) to give an aromatics-enriched extract and an aromatics-depleted residue,   c 32 ) optionally separation of the extract into an extractant-enriched and aromatics-depleted fraction and an aromatics-enriched and extractant-depleted fraction,   c 33 ) introduction of the aromatics-enriched extract obtained in step c 31 ) or the aromatics-enriched fraction obtained in step c 32 ) into step c 4 ).   
     
     
         17 . The process according to any of  claims 11  to  16 , wherein the aromatics-depleted fraction C 2 ) isolated in step c 3 ) is at least partly used for producing synthesis gas. 
     
     
         18 . The process according to any of  claims 11  to  17 , wherein the reaction in step c 4 ) comprises a hydrodealkylation or a steam dealkylation or a mixed form derived therefrom. 
     
     
         19 . The process according to any of  claims 11  to  18 , wherein the temperature in the dealkylation zone is in the range from 400 to 900° C., preferably from 500 to 800° C. 
     
     
         20 . The process according to any of  claims 11  to  19 , wherein the absolute pressure in the dealkylation zone is in the range from 1 to 100 bar, particularly preferably from 1 to 20 bar. 
     
     
         21 . The process according to any of  claims 11  to  20 , wherein the discharge from the dealkylation zone in step c 5 ) is subjected to a separation to give the following three streams:
 E 1 ) a stream enriched in single-ring aromatics which are unalkylated or have a low degree of alkylation, 
 E 2 ) a stream enriched in aromatics which are not dealkylated or have a low degree of dealkylation, 
 E 3 ) a stream enriched in by-products which are more volatile than E 1 ) and E 2 ). 
 
     
     
         22 . The process according to any of the preceding claims, wherein the separation of the discharge from the dealkylation zone in step c 5 ) comprises an absorption. 
     
     
         23 . The process according to  claim 22 , wherein the separation of the discharge from the dealkylation zone in step c 5 ) comprises the following substeps:
 c 51 ) contacting of the discharge from the dealkylation zone with an absorption medium to give an aromatics-enriched absorbate and a gas stream E 3 ) depleted in aromatics,   c 52 ) separation of the absorbate into a stream E 1 ) enriched in single-ring aromatics which are unalkylated or have a low degree of alkylation, a stream E 2 ) which is enriched in aromatics which are not dealkylated or have a low degree of dealkylation and optionally a stream comprising the absorption medium,   c 53 ) recycling if present, of the stream comprising the absorption medium to step c 51 ),   c 54 ) optionally recycling of at least part of the stream E 2 ) to the dealkylation zone of step c 4 ).   
     
     
         24 . The process according to any of  claims 21  to  23 , wherein the stream E 3 ) obtained in step c 5 ) is at least partly used for obtaining the offgas stream. 
     
     
         25 . The process according to any of  claims 21  to  24 , wherein the stream E 3 ) obtained in step c 5 ) is at least partly used for producing synthesis gas. 
     
     
         26 . The process according to any of the preceding claims, wherein a synthesis gas-comprising stream or a hydrogen-enriched stream produced from the synthesis gas is at least partly used for obtaining the offgas stream.