Process for preparing at least one low molecular weight aromatic material of value from a lignin-comprising starting material

Abstract

The present invention relates to a process for preparing low molecular weight aromatic materials of value from a lignin-comprising starting material produced from biomass.

1 . A process for preparing an aromatics composition having a high content of single-ring aromatics which are unalkylated or have a low degree of alkylation from a lignin-comprising starting material, wherein
 a) a lignin-comprising starting material is provided,   b) the lignin-comprising starting material is subjected to a pyrolysis to give a pyrolysis gas stream,   c) the pyrolysis gas stream is, essentially without a material component being separated off, fed into a dealkylation zone and reacted in the presence of hydrogen and/or water vapor,   d) a discharge is taken from the dealkylation zone and subjected to a separation to obtain the aromatics composition.   
     
     
         2 . The process according to  claim 1 , wherein a lignin-comprising starting material comprising at least 10% by weight, preferably at least 15% by weight, based on the dry mass of the material, of lignin is provided in step a). 
     
     
         3 . The process according to either of the preceding claims, wherein a lignocellulose material from wood and/or plant fibers is used for providing the lignin-comprising starting material in step a). 
     
     
         4 . The process according to any of the preceding claims, wherein a lignin-comprising stream from the digestion of a lignocellulose material for producing cellulose (pulp) is used for providing the lignin-comprising starting material in step a). 
     
     
         5 . The process according to  claim 4 , wherein a lignin-comprising stream from the digestion of a lignocellulose material by means of an alkaline treatment medium, preferably a black liquor, in particular a black liquor from kraft digestion (sulfate digestion), is used for providing the lignin-comprising starting material in step a). 
     
     
         6 . The process according to  claim 5 , wherein, to provide the lignin-comprising starting material in step a), a black liquor is acidified so that at least part of the lignin comprised precipitates and the precipitated lignin is isolated by filtration. 
     
     
         7 . The process according to any of the preceding claims, wherein the pyrolysis gas stream obtained in step b) comprises substituted aromatics and/or polycyclic aromatics. 
     
     
         8 . The process according to any of the preceding claims, wherein essentially none of the components comprised in the pyrolysis gas stream obtained in step b) are condensed out from this stream before it enters the dealkylation zone. 
     
     
         9 . The process according to any of the preceding claims, wherein the temperature of the pyrolysis gas stream after leaving the pyrolysis zone and before entering the dealkylation zone is never more than 200° C. below, particularly preferably never more than 100° C. below, the exit temperature from the pyrolysis zone. 
     
     
         10 . The process according to any of the preceding claims, wherein the reaction in step c) comprises a hydrodealkylation or a steam dealkylation or a mixed form thereof. 
     
     
         11 . The process according to any of the preceding claims, wherein the temperature in the dealkylation zone is in the range from 400 to 900° C., preferably from 500 to 800° C. 
     
     
         12 . The process according to any of the preceding claims, wherein the absolute pressure in the dealkylation zone is in the range from 1 to 100 bar, particularly preferably from 1 to 20 bar, in particular from 1 to 10 bar. 
     
     
         13 . The process according to any of the preceding claims, wherein the discharge from the dealkylation zone is subjected in step d) to a separation to give the following three streams:
 D 1 ) a stream enriched in single-ring aromatics which are unalkylated or have a low degree of alkylation,   D 2 ) a stream enriched in aromatics which are not dealkylated or have a low degree of dealkylation,   D 3 ) a stream enriched in by-products which are more volatile than D 1 ) and D 2 ).   
     
     
         14 . The process according to any of the preceding claims, wherein the separation of the discharge from the dealkylation zone in step d) comprises an absorption. 
     
     
         15 . The process according to  claim 14 , wherein the separation of the discharge from the dealkylation zone in step d) comprises the following substeps:
 d 1 ) contacting of the discharge from the dealkylation zone obtained in step c) with an absorption medium to give an aromatics-enriched absorbate and a gas stream D 3 ) which is depleted in aromatics,   d 2 ) separation of the absorbate into a stream comprising the absorption medium, a stream D 1 ) enriched in single-ring aromatics which are unalkylated or have a low degree of alkylation and a stream D 2 ) enriched in aromatics which are not dealkylated or have a low degree of dealkylation,   d 3 ) recycling of the stream comprising the absorption medium to step d 1 ),   d 4 ) optionally recycling of at least part of the stream D 2 ) to the dealkylation zone of step c).   
     
     
         16 . The process according to any of  claims 13  to  15 , wherein at least part of the stream D 3 ) obtained in step d) is used for producing synthesis gas. 
     
     
         17 . The process according to  claim 16 , wherein the stream obtained in step d) is at least partly subjected to reforming and/or converting. 
     
     
         18 . The process according to either  claim 16  or  17 , wherein a stream comprising synthesis gas or a hydrogen-enriched stream produced from the synthesis gas is fed into the pyrolysis in step b) and/or the dealkylation in step c).