WO2013095204A1

WO2013095204A1 - Method for preparing fuels from lignocellulosic feedstock

Info

Publication number: WO2013095204A1
Application number: PCT/SE2011/000237
Authority: WO
Inventors: Anders OSTMAN
Original assignee: Skandinavisk Kemiinformation Ab
Priority date: 2011-12-21
Filing date: 2011-12-21
Publication date: 2013-06-27
Also published as: FI20145686A; FI127169B

Abstract

The present invention refers to a method to produce fuels for combustion engines from ligno-cellulose-containing material. The distinguishing features are the following steps: separation of lignin from ligno-cellulose-containing material, whereby a liquid lignin-containing phase and a solid phase of cellulose-containing material (cellulose and hemicellulose) is produced, hydrolysis of the cellulose-containing material, fermentation of the hydrolysate from the cellulose-containing material to ethanol, precipitation and processing of the lignin from the liquid lignin-containing phase, and catalytic pyrolysis or depolymerisation of the processed lignin in the first sub- stream to gasoline and diesel-like products.

Description

Method for Preparing Fuels from Lignocellulosic Feedstock

Technical Area

The following invention envisages a method of producing ethanol from lignocel- lulose material.

State of art

It has proved difficult to produce ethanol from lignocellulose or in lignocellulosic materials as cellulose is found in wood, straw and several similar raw materials. According to SE-C2-527-646 ethanol has been produced by using conventional pulp technology where lignin is separated from the cellulose which can then quite easily be hydrolyzed and be fermented into ethanol. To make the process cost-effective, lignin in black liquor is processed via what is known as black-liquor gasification into a synthesis gas from which methanol, DME (dimethyl ether) and/or, for example, Fischer-Tropsch products can be produced.

The processing of lignin in black liquor thus means that the value of lignin is increased from a fuel value to a transportation fuel value and the sum of the products (from the gasification line and the ethanol line) can even pay for the introductory pulp cooking. The cited reference comprises a process combination with a transfer of material and energy between the sub-processes.

Tests have shown that this process combination results in the ethanol line having a very simple structure and that inherent energy and by-product problems can be resolved by transfers to the other sub-processes. At the same time, however, ongoing work with black-liquor gasification has shown that it involves increasingly higher investment costs for this line. Further, a resistance from the pulp industry as regards giving up the conventional soda recovery boiler for producing cellulose (pulp) has been noted. The pulp industry states inter alia that the efficiency of the soda recovery boilers is continuously increased and that lack of experience with black liquor gasification results in less reliability which could result in less accessibility for the whole pulp process.

To avoid the uncertainties which are assumed to be involved in black-liquor gasification and to maintain the soda recovery boiler's function in a pulp mill, ethanol production from the solid cellulose fraction can be combined with two sub-processes which convert the liquid lignin phase to transportation fuels without black-liquor gasification. In this process combination, a part of the lignin is precipitated from the black liquor after which it is subjected to catalytic pyrolysis or depolymerizing. Object of the invention

One object of this invention is to demonstrate a method of producing fuels for combustion engines from material containing ligno-cellulose.

Brief description of the invention The invention demonstrates a method to produce fuels for combustion engines from ligno-cellulosic materials which is characterized by dissolving lignin from the lig- no-cellulosic materials, whereby a liquid lignin-containing phase and a solid phase of cellulose-containing material (cellulose and hemicellulose) is obtained, hydrolysis of the material containing cellulose, fermentation of the hydrolysate from the material con- taining cellulose to ethanol, precipitation and processing of lignin from the liquid lignin- containing phase and catalytic pyrolysis or depolymerizing of the processed lignin to products similar to gasoline and diesel.

According to a preferred embodiment the dissolving of the lignin from the lig- no-cellulose-containing material, the hydrolysis and fermentation of the cellulose- containing material, the separation and processing of lignin and the catalytic pyrolysis or depolymerizing are physically connected with each other through continuous flows of material and exchange of energy and utility streams, such as steam and water, and possibly electric power.

It is preferred that dissolution of lignin takes place through sulphate cooking, sulphite cooking, soda cooking or modifications of these with use of oxygen-containing gas and/or anthraquinone and that the solid phase of cellulose-containing material is de- watered to 10-70% dry matter and then subjected to hydrolysis in one or more steps and is ultimately fermented to ethanol in a combined hydrolysis and fermentation step (what is known as SSF, Simultaneous Saccharification and Fermentation).

According to another preferred embodiment, the solid phase of the cellulose- containing material is dewatered to 5%-30% and is led directly to a combined hydrolysis and fermentation step (SSF).

From the liquid lignin-containing phase, lignin is partially precipitated and is processed to transportation fuels via two established process steps which are described more in detail below.

Further preferred embodiments are apparent from claims 6-10. Brief description of the figure

The enclosed figure shows the process combination of the present method.

Detailed description of the invention

The present invention comprises a process combination where an alternative to black liquor gasification is to process lignin in a part of the black liquor in what is designated as a "catalytic depolymerisation" of lignin to hydrocarbon fractions similar to gasoline and diesel.

The primary processing of the lignin involves a precipitation of the lignin by means of a reduction of pH with the aid of carbon dioxide and a separation/de watering of the solid lignin. The precipitation of solid lignin is an established technique which, for instance, is described in Irmventias (and later Metsos) "Lignoboost" process. This technique is described in several cases on Innventias' and Metsos' homepages and for which inter alia a patent application was filed as PTC/SE2005/001301, could be an alternative for processing solid lignin. According to the present invention, however, simpler proce- dures for the precipitation using carbon-dioxide and separation may be considered. According to the invention the same requirements as regards, for example, low ash content as in the "Lignoboost" process, do not apply. That is to say, the up-grading does not have to be as extensive.

The "catalytic depolymerisation" is a process which has been demonstrated using several raw materials up to the capacity of tons/hour. The process is described in popular form inter alia on a homepage by BTL Bionic (You Tube). It corresponds to conventional thermic pyrolysis of carbon-containing raw materials with oxygen and hydrogen content, for example raw materials of wood, certain plastic materials and residual oils, but where the reaction temperature is considerably lower and a catalyst is used ins- tead. In reality the term "catalyst" is dubious as it - even if it remains unchanged after the reaction - can scarcely be separated and used again in the residual product where it is to be found.

The catalyst seems to be similar to the catalysts used in hydrocracking but it is doped in the catalytic depolymerisation with alkaline metals and/or alkaline-earth met- als. The actual composition is secret but the catalyst is commercially available via special agreements.

In the catalytic depolymerisation the catalyst is mixed with the material and the mixture is heated to temperatures where first water vapor is removed and then hydrocar- bon fractions are evaporated. The residue is made up of something which could most easily be compared to coke residue and in this the catalyst is found.

In this particular context the black liquor is divided into two parts after the cellulose separation (modified pulp cooking = an alkaline cooking without sulphur, known as soda cooking). One part is lead off to the recovery boiler to produce the necessary amount of energy and from the other part the remaining lignin is separated. The separated - and processed - lignin then undergoes catalytic depolymerisation which produces a flammable gas, fractions similar to gasoline and diesel as well as a carbon-containing solid residue which can be used as fuel.

The cellulose is sent for ethanol production where the cellulose is first hydro- lyzed enzymatically and then fermented to ethanol in what is known as SSF fermentation (Simultaneous Saccharification and Fermentation).

The process combinations make it possible to effectively produce liquid fuels from ligno-cellulose-containing raw materials such as wood. The products are solely fuels. Therefore no consideration needs to be taken of side-markets. In addition, minimal amounts of rest products and waste streams are produced which in the separate sub- processes has proved to involve significant costs for i.a. environmental protection measures.

The annexed figure illustrates the interaction of the sub-processes. The carbon dioxide from the ethanol fermentation is used to precipitate lignin from black liquor. (This process is the same as that used in the "Lignoboost" process). The precipitated lignin is dewatered to suitable dry matter content for the catalytic depolymerisation after which catalyst is added and the temperature is raised until the reaction commences.

The gas from the catalytic depolymerisation is used as fuel in the lime kiln which is contained in the chemical cycle for cooking. Residues from the up-grading of ethanol, i.e. the fusel oil and what is known as "heads", are also led to the lime kiln as fuel.

The stillage from the evaporation of the ethanol is mixed with the black liquor and evaporated before it is lead to the recovery boiler.

The amount of black liquor which enters the recovery boiler is determined by the steam requirements needed for the alkaline cooking, the evaporation of black liquor/ stillage and the ethanol line's steam requirements. In modern pulp mills, electricity is generated by back-pressure turbines why even the electricity requirements are sometimes included in the recovery boiler's fuel requirements.

Finally the solid residue from the catalytic depolymerisation can be used in the lime kiln.

With these material and energy exchanges between the sub-processes a total process combination can be achieved where minimal amounts of residues are produced and where the products completely are made up of liquid fuels; ethanol, gasoline and diesel fractions.

The alkaline cooking of wood raw materials via soda cooking has been demonstrated in large scale in an existing pulp mills. The cellulose from this cooking was used for a qualitative verification of the ethanol production and the ethanol line has been built up and tested in week-long runs in pilot scale. The "Lignoboost" process has similarly been demonstrated on a large scale up to a lignin product which as regards the quality by far exceeds the requirements in the proposed process combinations. The catalytic depolymerisation has been run in small scale with a number of raw materials of the hydrocarbon and carbohydrate type.

Claims

1. A method to produce fuels for combustion engines from ligno-cellulose- containing material, characterized by

separation of lignin from ligno-cellulose-containing material, whereby a liquid lignin-containing phase and a solid phase of cellulose-containing material (cellulose and hemicellulose) is produced,

hydrolysis of the cellulose-containing material,

fermentation of the hydrolysate from the cellulose-containing material to ethanol,

separation of the lignin-containing phase into a first and a second sub-stream, precipitation and processing of lignin from the first sub-stream,

catalytic pyrolysis or depolymerisation of the processed lignin in the first sub- stream to gasoline- and diesel-like products, and

transferring the second sub-stream is to conventional combustion in a soda recovery boiler.

2. Method according to claim 1, characterized in that the separation of lignin is done by means of sulphate cooking, sulphite cooking, soda cooking or modifications of these with the use of oxygen-containing gas and anthraquinone.

3. Method according to claim 1 and 2, characterized in that

the separation of the lignin from the ligno-cellulose-containing material, the hydrolysis and fermentation of the cellulose-containing material, the separation and the processing of the lignin and the catalytic pyrolysis or depolymerisation are physically connected with each other through continuous material streams and exchange of energy and utility streams, such as steam and water,

by-products from the catalytic pyrolysis are used as fuel to produce energy required for the alkaline separation as well as further steam production,

steam required for all sub-processes is produced by combustion in the recovery boiler and from flue gases from the lime kiln, and

steam is mainly consumed in the cooking process, the evaporation of the lignin phase as well as in the ethanol production.

4. Method according to one or more of claims 1-3, characterized in that the solid phase of the cellulose-containing material is dewatered to 10-70% dry substance and is then subjected to hydrolysis in one or several steps in order to finally be subjected to fermentation to ethanol in a combined hydrolysis and fermentation step.

5. Method according to one or more of claims 1-4, characterized in that the solid phase of cellulose containing material is dewatered to 5-30% and is then transferred directly to a combined hydrolyses and fermentation step.

6. Method according to one or more of claims 1-5, characterized in that the carbon-dioxide which has formed during fermentation is fully or partially used in the separation of lignin from that part of the liquid lignin phase which is transferred to precipitation and processing of the lignin.

7. Method according to one or more of claims 1-6, characterized in that the separated lignin is processed to at least 50% dry substance content and is led to a catalytic pyrolysis or depolymerisation.

8. Method according to one or more of claims 1-7, characterized in that the ethanol produced is processed to fuel quality as well as products similar to gasoline and diesel from the catalytic pyrolysis are separated and processed to fuel qualities.

9. Method according to one or more of claims 1-8, characterized in that

by-products from the ethanol fermentation are either completely or partially transferred to the recovery boiler for combustion together with liquid lignin product, and by-products from the processing of the ethanol to fuel quality are completely or partially used as fuel for producing necessary energy for the alkaline separations as well as remaining steam production.