METHOD OF PRODUCING LIGNIN WITH REDUCED AMOUNT OF ODOROUS SUBSTANCES

Abstract

The present invention relates to a method of producing lignin with reduced amount of guaiacoland etylguaiacol in order to reduce the content of odorous substances by subjecting the ligninto a heating processing order to remove guaiacol.

Claims

1. Method for treatment of lignin in order to reduce the amount of guaiacol and etylguaiacol in the lignin to provide a lignin with less odour in which said lignin is heated to a temperature above 60 degrees Celsius characterized in that said lignin being subjected to the heat treatment has a dry content of at least 50% w/w.

2. Method for treatment of lignin according to claim 1 characterised in that the heat treatment is performed for at least 5 minutes, more preferably at least 10 minutes and most preferably at least 30 minutes.

3. Method for treatment of lignin according to claim 1 characterised in that said lignin is heated to a temperature of 60 to 160 degrees Celsius, more preferably to a temperature within the range of 70 to 145 degrees Celsius and most preferably within the range of 80 to 130 degrees Celsius.

4. Method for treatment of lignin according to claim 1, characterized in that the lignin during heat treatment is in the shape of a particulate material having an average equivalent spherical diameter (ESD) of less than 10 mm, more preferably less than 5 mm and most preferably less than 1 mm.

5. Method for treatment of lignin according to claim 1 characterized in that said lignin have a dry content of 60 to 90% w/w when starting the heat treatment and a dry content of at least 90 percent, more preferably at least 95 percent and most preferably being essentially dry having a dry content of 98 to 100 percent % w/w after the heat treatment.

6. Method for the treatment of lignin according to claim 1 characterized in that said lignin is heated by a gas.

7. Method for the treatment of lignin according to claim 6 characterized in that said lignin is present as particulate matter and heated by the heating gas used as a carrier gas in a ring flow heater.

8. Method for the treatment of lignin according to claim 6 characterized in that said lignin is present as particulate matter and mixed by the heating gas in a bed such as a bubbling bed or a fluidized bed.

9. Method for the treatment of lignin according to claim 1 characterized in that said lignin is heated in an oven, by drum heaters, tray heaters, rotary heaters, heated screw, flash heaters, IR-radiation or by steam heating.

10. Method for the treatment of lignin according to claim 1 characterized in that said lignin is heated in an environment of an essentially inert gas.

11. Method for the treatment of lignin according to claim 1 characterized in that said lignin is treated by an alcohol and/or a carboxylic acid in addition to the heat treatment.

12. Method for the treatment of lignin according to claim 1 characterized in that said lignin is heated at a temperature above 60 degrees Celsius, more preferably above 70 degrees and most preferably above 80 degrees until the content of guaiacol or etylguaiacol in the lignin has been reduced by at least 60 percent, preferably at least 75 percent and most preferably at least 90 percent, the concentration being calculated from a peak area of a respective peak in a chromatogram.

13. Method for the treatment of lignin according to claim 1 characterized in that said lignin is heated at a temperature above 60 degrees Celsius, more preferably above 70 degrees and most preferably above 80 degrees until the content of guaiacol or etylguaiacol in the lignin has been reduced to less than 5 mg/kg, more preferably less than 1 mg/kg and most preferably 0.5 mg/kg, the concentration being calculated from a peak area of a respective peak in a chromatogram.

14. Method for the treatment of lignin according to claim 1 characterized in that the lignin originates from woody biomass.

15. A method according to claim 1 wherein the lignin is obtained from a process comprising the steps of: i. precipitating lignin by acidifying black liquor obtained from the alkaline chemical pulping process; ii. dewatering and/or filtrating the obtained lignin to provide a first filter cake; iii. re-suspending the lignin; iv. adjusting the pH of the obtained suspension in step c) to a pH lower than 6; v. dewatering and/or filtrating the acidic suspension from step d) to provide a second filter cake; and vi. washing and dewatering the second filter cake; whereby the lignin containing starting material is obtained.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 discloses a ring flow heater for heat treatment of lignin in order to reduce odorous substances

DETAILED DESCRIPTION OF THE DRAWINGS

[0038] In FIG. 1 is disclosed a heat treatment system 1 for heating of lignin in the shape of a particulate matter. The heat treatment system is connected to a lignin supply conduit 2 which delivers lignin to a lignin feeder 3 connected to a ring flow heater 4. The flow of lignin particles in the FIGURE is represented by block arrows having continuous lines. The ring flow heater 4 is a conduit in which the lignin is transported and mixed by a carrier gas in order to dry the lignin. Hence, the ring flow heater 4 is provided with a blower 5 and a heater 6 in order to heat the carrier gas and provide for transport of the lignin by inducing a movement of the carrier gas withdrawing lignin. The carrier gas is mixed with lignin from the feeder 3 so as to provide a combined flow of lignin and carrier gas. The combined flow of lignin and carrier gas is generally represented by block arrows having dashed lines. The ring flow heater 4 is further connected to a collector 7 by a collector inlet conduit 8 and a collector return conduit 9 where a flow of carrier gas is returned to the ring flow heater 4. A flow of carrier gas without particles is generally designated by solid arrows. The collector 7 is further provided with a filter 10 at the top of the collector 7 close to the inlet of the collector return conduit 9. The collector return conduit 9 is provided with an upper outlet conduit 11 where carrier gas may be exhausted. The filter 10 is intended to separate the gas from lignin particles. The collector 7 further comprises a lower outlet conduit 13 and a discharge device 12 located close to the lower outlet conduit 13. The lignin particles will thus be collected in the outlet stream through the lower outlet conduit 13. The mixed stream of carrier gas and lignin in the ring flow heater 4 is preferably selectively directed to the collector 7 by passing a separator 14 such that a portion of the lignin particles will be directed to the collector 7. If there are larger or heavier particles, e.g. particles with a rather high wet content, present in the ring flow heater 4, they will be guided through a return conduit 15 back to the feeder 3. The heat treatment system 1 also comprises a carrier gas supply conduit 16 in order to replace and compensate for carrier gas exhausted through the upper outlet conduit 11.

[0039] When the heat treatment system 1 is in use, lignin is fed to the ring flow heater 4 from the lignin feeder 3. The feeder 3 may be any kind of feeding device suitably used for feeding the lignin substance to the ring flow heater. The feeder 3 could be provided with some kind of crusher or mill in order to disintegrate the lignin to a desired size if that not has been made before the lignin enters the feeder. It is also possible that a crusher or disintegrator could be located inside the ring flow heater 4. The ring flow heater 4 could for example be provided with an arrangement close to the feeder and inlet which allows larger particles or pieces of lignin, which not are carried away with the carrier gas, to be separated and guided to a crusher or disintegrator before being recirculated to the ring flow heater. The return flow of lignin in the return conduit 15 may be directed such that it will pass through the crusher or disintegrator again or bypass these features.

[0040] From the feeder 3 the lignin is fed into the ring flow heater 4 where the lignin is mixed with a carrier gas. The carrier gas could be air, flue gas or any desired gas. If there is access to a flue gas it could advantageously be used since the flue gas is a rather inert, hot gas which thus may be used to heat the lignin while also being rather inert and undesired chain reaction in the lignin could be reduced.

[0041] The ring flow heater 4 herein disclosed is schematically described and comprises a blower 5 for inducing a circulation of the carrier gas and a heater 6 for heating the carrier gas and the lignin particles. These features may not be needed if for example the gas is induced at high pressure and thus causes a circulation in the ring flow heater 4 when entering the heat treatment system 1. A heater may not be necessary neither if the carrier gas entering the system is hot enough.

[0042] The flow of carrier gas and lignin will pass the separator 14 which is designed to divide a flow of the carrier gas and lignin particles such that lignin which has been heated enough will be guided to the collector 7 and the other particles will continue to be heated in the ring flow heater 4. This could for example be achieved by a cyclone which thus will separate particles depending on size, shape and density and thus may produce a stream of lighter, and thus drier, particles to the collector 7 and allow the more dense particles to continue in the ring flow drier 4.

[0043] The separator 14 may be any kind of separator and could also just be a simple valve allowing a batch of lignin to flow through the ring flow 4 heater for a certain time or until a certain criteria is achieved, e.g. until a certain temperature or dryness has been reached.

[0044] The lignin which is directed to the collector 7 will be collected through the lower outlet 13. The mixed stream of smaller lignin particles and carrier gas will flow upwards where the lignin particles will be trapped in the filter while the gas will leave through the upper outlet 11 and somewhat larger particles may flow downwards. In order to collect lignin particles from the filter it may be back flushed and the lignin will thus fall down and may be collected via the lower outlet.

[0045] The heat treatment system 1 may include further equipment such as sensors, e.g. for measuring temperatures and humidity, and control units in order to control parameters in dependence of measured values. Hence, the above system only gives a schematic view of how a heat treatment system for reducing odours may be designed. As previously mentioned, there is a multitude of different ways of heating the lignin in order to reduce odours and the above system is only one example of how this may be achieved.