WO2010065872A1

WO2010065872A1 - Biomass conversion using solid base catalyst

Info

Publication number: WO2010065872A1
Application number: PCT/US2009/066803
Authority: WO
Inventors: Paul O'connor; Steve Yanik; Robert Bartek
Original assignee: Kior Inc
Current assignee: Inaeris Technologies LLC
Priority date: 2008-12-05
Filing date: 2009-12-04
Publication date: 2010-06-10
Anticipated expiration: 2011-06-05

Abstract

A process is disclosed for the catalytic conversion of solid biomass. The process comprises heating the solid particulate biomass in the presence of a solid base catalyst. The catalytic reaction may be carried out in a cyclone reactor, a fluid bed reactor, or an ablative reactor. Alumina and doped alumina are particularly suitable solid base catalysts.

Description

BIOMASS CONVERSION USING SOLID BASE CATALYST

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates generally to the conversion of biomass to a bio-oil in the presence of a solid base catalyst, and more particularly to the conversion of a solid biomass material comprising ligno-cellulose.

2. Description of the Related Art

[0002] Solid base catalyzed processes have been proposed for a variety of chemical reactions of organic compounds. Most commonly solid base catalysts have been proposed for isomerization of olefins, hydrogenation reactions and de-hydrogenation reactions. It has also been suggested that solid base catalysts can be used for addition reactions and cyclization reactions.

[0003J Researchers at Sumitomo Chemical Company Limited have focused on solid base catalysts comprising alumina. For example, US Patent 4,71 1,873 to Suzukamo et al. discloses a process for preparing an alumina catalyst doped with alkali metals. The alkali metals serve to amplify the basic properties of the catalyst.

[0004] US Patent 4,987,1 14 to Suzukamo et al. discloses a method for preparing an alumina catalyst doped with earth alkaline metals.

[0005] US Patent 5,097,088 to Fukao et al. discloses a process for preparing an alkyl- substituted hydrocarbon. The process comprises reacting an alkylaromatic hydrocarbon with an olefin in the presence of a solid base catalyst. The solid base is an alumina doped with both an alkali metal and an earth alkaline metal.

[0006] US Patent 7,341 ,973 to Flego et al. discloses a solid base catalyst consisting of an amorphous material obtained from a silica or alumina gel containing an alkaline, earth alkaline or transition metal. The catalyst is shown to be useful in double bond migration reactions. [0007] Solid acid catalysts, in particular acidic zeolites, are used in catalytic cracking of mineral oil fractions. Specifically H-ZSM-5 is the catalyst of choice for fluid catalytic cracking (FCC) processes.

[0008] Building on the FCC experience, several researchers have focused on the use of solid acid catalysts, such as ZSM-5, for the upgrading of bio-oils obtained in the pyrolysis of biomass. See, for example, Home et al., "Upgrading of biomass-derived pyrolytic vapours over zeolite ZSM-5 catalyst: effect of catalyst dilution on product yields", Fuel 75 (1996), pp 1043- 1050, and other papers from these authors.

[0009] This approach has two important disadvantages. It requires a two-step process pyrolysis to form a bio-oil, and upgrading of the bio-oil Moreover, the bio-oil is thermally unstable and forms copious amounts of coke in the upgrading reaction. Even after upgrading the quality of the bio-oil is poor.

[0010] Thus, there is a particular need for a catalyst that can be used during the pyrolysis itself. The catalyst preferably is inexpensive, easily separable from the reaction products, and stable enough to withstand high temperatures as may be needed to removed deposited coke in a regeneration step.

BRIEF SUMMARY OF THE INVENTION

[001 1 ] The present invention addresses these problems by providing a process for converting a solid paniculate biomass to a bio-oil, said process comprising the step of heating the solid particulate biomass in the presence of a solid particulate basic catalyst.

[0012] Another aspect of the invention comprises a method for pretreating the solid biomass prior to the conversion in the presence of the solid base catalyst.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0013] The following is a description of certain embodiments of the invention, given by way of example only.

[0014] The use of solid base catalysts in the catalytic pyrolysis of solid biomass material offers a number of advantages. [0015] Firstly, the catalyst can be used during the pyrolysis step itself. The resulting bio- oil is of better quality than that obtained with non-catalytic processes or processes using an acid catalyst. The resulting bio-oil, in certain cases, is of good enough quality that it can be blended with mineral oil fractions, such as vacuum gas oil (VGO) without requiring further upgrading. Even if the bio-oil requires upgrading before further processing, the use of a solid catalyst during the pyrolysis step produces a bio-oil that can be more easily, and more cheaply, upgraded.

[0016] Secondly, being a solid, the catalyst can be readily separated from the liquid and gaseous reaction products. This offers a major advantage as compared to prior art processes in which the biomass is soaked with a solution of an alkali and/or earth alkaline metal.

[0017] Thirdly, the solid base catalyst is thermally stable. It is inevitable that coke is formed during the pyrolysis of solid biomass material. The coke is deposited onto the catalyst particles. The preferred method of removing the coke is burning it off in a regenerator. A typical regenerator temperature is in the range of 600 to 700 DC. For economic reasons it is important that the catalyst be able to withstand these temperatures, so that the catalyst can be re-used in the process after regeneration.

[0018] Fourthly, many of the solid base catalysts are inexpensive. For example, alumina- based solid catalysts are considerably less expensive than the solid acid zeolites. It will be understood that the skilled person may forego the cost advantage and use a more expensive solid base catalyst, such as a basic zeolite or a hydrotalcite, in order to optimize another process parameter, such as conversion yield or coke yield. Importantly, though, the use of solid base catalysts offers the option of using relatively inexpensive materials.

[0019] In its most general aspect, the invention provides a process for converting a solid particulate biomass to a bio-oil, said process comprising the step of heating the solid particulate biomass in the presence of a solid particulate basic catalyst. The step of heating the solid paniculate biomass in the presence of a solid particulate basic catalyst will be referred to herein as the "pyrolysis step".

[0020] The pyrolysis step may be carried out in any of a number of reactors. Suitable examples include cyclone reactors, fluid bed reactors, and ablative reactors. It is possible, and often preferable, to give the catalyst particles a secondary role as heat carrier particles. That is, the catalyst particles are preheated, prior to contacting them with the solid biomass particles, so that the catalyst particles provide at least part of the heat for the endothermic pyrolysis reaction. Suitably, the catalyst particles may be pre-heated in the regenerator, using the heat developed by burning off the coke deposits.

[0021 ] Depending on the catalyst/feed ratio and the temperature of the catalyst particles entering the reactor, it may be necessary or desirable to provide a second heat carrier material. This second heat carrier material may be an inert material, such as sand.

[0022] It is also possible to conduct an incomplete regeneration of the catalyst particles, so that the hot catalyst particles still contain a small amount of coke, e.g. 1 -3 wt%. The coke increases the heat capacity of the catalyst particles, and acts as a reducing agent to the biomass. The presence of coke on the catalyst tends to improve the quality of the bio-oil produced in the reaction.

[0023] Operating the regenerator with sub-stoechiometric amounts of oxygen produces significant amounts of carbon monoxide (CO). Carbon monoxide provides another inexpensive reducing agent for the biomass.

[0024] In cyclone reactors the catalyst particles and the solid biomass particles are taken up in a vortex of carrier gas. Due to the centrifugal forces present in the vortex, solid material becomes automatically separated from the gaseous and vaporized reaction products.

[0025] It may be desirable to provide a filter for screening small solid particles and liquid droplets from the gas stream leaving the cyclone. US Patent 7,202,389 to Brem, the disclosures of which are incorporated herein by reference, discloses a cyclone reactor provided with a rotating filter. The reactor of this reference is particularly suitable for the pyrolysis step of the process of the present invention.

[0026] In ablative reactors, the heat required for the endothermic reaction is provided by contact of the solid particulate biomass material with a hot surface, generally the reactor wall. US Patent 7,438,785 to Meier et al., the disclosures of which are incorporated herein by reference, discloses an ablative reactor in which biomass material is pressed against a hot plate under pressures of 5 to 80 bars. The reactor disclosed in this reference is particularly suitable for the pyrolysis step of the process of the present invention.

[0027] There are two main classes of fluidized bed reactors. In "stationary" or "non- circulating" fluidized bed reactors the fluidized particles that make up the reactor bed stay in the reactor. In circulating fluidized bed reactors the particles that make up the fluidized bed leave the reactor, to be recycled back into the reactor for example after passing through a regenerator.

[0028] US Patent 5,728,271 to Piskorz et al., the disclosures of which are incorporated herein by reference, discloses a stationary fluidized bed reactor. The reactor bed is heated indirectly, allowing for a relatively long residence time of more than 2 seconds. The reactor disclosed in this reference is particularly suitable for the pyrolysis step of the process of the present invention.

[0029] Circulating fluidized bed reactors are well known in fluid catalytic cracking (FCC) of mineral oil fractions. It has been found that FCC reactors are particularly suitable for the pyrolysis step of the process of the present invention.

[0030] Any solid base is in principle suitable as a solid base catalyst in the process of the present invention. Suitable examples include silica; alumina; layered hydroxy oxide; hydrotalcite; a hydrotalcite-like material; an anionic clay; a cationic clay; a metal oxide; a metal hydroxide; a metal carbonate; a basic zeolite, alumino phosphates; or a combination thereof.

[0031 ] Because of its relatively low cost and high thermal stability, alumina is a specifically preferred solid base material for use in the catalyst for the process of the present invention. Alumina is sufficiently basic to be used as-is. The basic characteristics of alumina can be enhanced by doping alumina with an alkali metal, an earth alkaline metal, or a combination thereof. Silica by itself is not catalytic, but can be made into a solid base catalyst by doping with an alkali metal and/or an earth alkaline metal.

[0032] Doping of alumina or silica may be accomplished with any of a number of processes known in the art. Examples include the processes disclosed in Patent 4,71 1 ,873 to Suzukamo et al.; US Patent 4,987,1 14 to Suzukamo et al.; US Patent 5,097,088 to Fukao et al.; and US Patent 7,341 ,973 to Flego et al., the disclosures of each of which being incorporated herein by reference.

[0033] The solid base catalyst preferably has a particle size in the range of from 20 μm to 2000 μm, preferably from 30 μm to 800 μm. For use in a fluidized bed the particles preferably have a spherical shape.

[0034] Prior to the pyrolysis step, the solid particulate biomass material may be pretreated with an alkaline material. The alkaline material may be the same material as the solid base catalyst, or may be a different material. Preferably the alkaline material is different from the solid base catalyst.

[0035] Examples of suitable alkaline materials include alkali metals and earth alkaline metals, in particular Na, K, or a combination thereof. Suitably, the Na or K may be in the form of its carbonate or its hydroxide.

[0036] The pretreatment may comprise subjecting the solid particulate biomass to impregnation with a solution containing the alkaline material, or to mechanical treatment in the presence of the alkaline material. Suitable examples of mechanical treatment include milling, grinding, kneading, or a combination thereof.

[0037] Any solid biomass material is suitable for use in the present invention. Preferred are biomass materials comprising cellulose, in particular ligno-cellulosic materials.

[0038] For ethical and economic reasons it is preferred to use biomass materials that cannot themselves be used as food, and do not compete with food harvests for arable acreage. Preferred sources of biomass include aquatic plants, such as algae; energy crops such as switch grass and fast-growing trees (willow, poplar, eucalyptus); agricultural wastes (straw, com stover; bagasse); and forestry wastes (bark, branches, saw dust, wood chips).

Claims

WHAT IS CLAMED IS:

1. A process for converting a solid particulate biomass to a bio-oil, said process comprising the step of heating said solid particulate biomass in the presence of a solid particulate base catalyst.

2. The process of claim 1 which comprises heating said solid particulate biomass in a reactor selected from the group consisting of cyclone reactors, stationary fluidized bed reactors, circulating fluidized bed reactors, ablative reactors, and combinations thereof.

3. The process of claim 1 wherein said solid particulate solid base catalyst comprises silica; alumina; layered hydroxy oxide; hydrotalcite; a hydrotalcite-like material; an anionic clay; a cationic clay; a metal oxide; a metal hydroxide; a metal carbonate; a basic zeolite, or a combination thereof.

4. The process of anyone of the preceding claims wherein said paniculate solid base catalyst comprises alumina.

5. The process of claim 4 wherein said alumina comprises an alkali metal; an earth alkaline metal; or a combination thereof.

6. The process of anyone of the preceding claims wherein said paniculate solid base catalyst functions as a heat carrier material.

7. The process of anyone of the preceding claims wherein said particulate solid base catalyst comprises spherical particles.

8. The process of claim 7 wherein said spherical particles have a mean particle size in the range of from 20 μm to 2,000 μm, preferably from 30 μm to 800 μm.

9. The process of anyone of the preceding claims comprising the use of a circulating fluid bed reactor.

10. The process of anyone of claims 1 to 8 comprising the use of a cyclone reactor.

1 1. The process of claim 10 wherein said cyclone reactor is provided with a filter for separating vapors and solids.

12. The process of claim 1 1 wherein said filter is a rotating filter.

13. The process of anyone of claims 1 to 8 comprising the use of an ablative reactor.

14. The process of anyone of the preceding claims wherein said solid particulate biomass is pretreated with an alkaline material prior to the step of heating said solid particulate biomass material in the presence of a particulate solid base catalyst.

15. The process of claim 14 wherein said alkaline material comprises an alkali metal or an earth alkaline metal.

16. The process of claim 15 wherein said alkaline material comprises Na, K, or a combination thereof.

17. The process of claim 16 wherein said alkaline material comprises sodium carbonate, sodium hydroxide, potassium carbonate, potassium hydroxide, or a combination thereof.

18. The process of anyone of claims 14 - 17 wherein said pretreatment comprises subjecting said solid particulate biomass to impregnation with a solution containing said alkaline material.

19. The process of anyone of claims 14 - 17 wherein said pretreatment comprises subjecting said solid particulate biomass to mechanical treatment in the presence of said alkaline material.

20. The process of claim 18 wherein said mechanical treatment comprises milling, grinding, kneading, or a combination thereof.