GB2535797B - Process for removal of water and light organics from pyrolysis oil - Google Patents

Description

PROCESS FOR REMOVAL OF WATER AND LIGHT ORGANICS FROM PYROLYSIS OIL

Field Of The Invention

The present invention relates to an integrated process for converting biomass pyrolysis oil into products that will be more useful for transportation fuels as well as industrial Chemicals.

Background To The Invention ln recent years, thermochemical utilisation of biomass in the energy sector has attracted renewed interest worldwide. The reason being, while the output of the other renewable energy sources is primarily electricity, biomass is able to produce liquid, gaseous, or solids of variable energy contents that can be used for energy or Chemicals' production. Pyrolysis oii is a free flowing liquid product produced from biomass fast pyrolysis. ln the fast pyrolysis process, biomass is rapidly heated to 500-550°C in the absence of oxygen, with short residence time (a few seconds or less), and rapidly quenched to produce a condensate which is known as pyrolysis oil, bio-oil or bio-crude. Pyrolysis oil has been recognised as renewable feedstock for the production of transportation fuels and various other green applications.

Pyrolysis oil as a fuel has many environmental advantages when compared to fóssil fuels. Upon combustion, pyrolysis oil produces half of the NOX, negligible quantities of SOX emissions and is moreover CO2 neutral when compared with fóssil fuels. However, the large-scale production of liquid fuels from pyrolysis oil was limited because of its high acidity and thermal instability. Furthermore, pyrolysis oil has high water content (25-30%), high oxygen content (40-50%), presents immiscibility with fóssil fuels, phase separation and increased viscosity during prolonged storage (aging).

Pyrolysis oil is a, compositionally complex mixture and contains various kinds of oxygen-containing organics (e.g. acids, aldehydes, aicohols, phenols, phenolic derivatives, sugars, and others with multiple functional groups). These oxygen containing organic compounds make pyrolysis oil unstable, corrosive, and incompatible with conventional fuel and directly affect its commerciai applications. Therefore, it is necessary to upgrade the raw pyrolysis oiis before they can be used as a viable renewable fuel.

Currently there are no commerciai technologies that will produce fungible renewable fuels from pyrolysis oil. Novel technologies need to be developed that can generate sufficient renewable fuel volumes to replace or to blend with the current petroleum sources. Therefore, new methods and processes for upgrading pyrolysis oils obtained by pyrolysis of lignocellulosic biomass are required.

Distillation techniques have been used in order to remove water and acid organic compounds from pyrolysis oil, although polymerization and aging reactions take place thus deteriorating properties ofthe oil and reducing its stability. Reduced pressure reactive distillation or vacuum reactive distillation is proposed in order to separate light molecules and water from pyrolysis oil thus mitigating the effects of atmospheric distillation. Similar work was carried out (US 2014/0256965 A1) using methanol as azeotropic agent thus reducing acidity on the product, although no stability data or testing distillation with various alcohols is presented.

It is an object of the current invention to disclose a process which seeks to address the above problems.

Summary Of The Invention

According to the invention, pyrolysis fuels and methods for improving the quality of the produced pyrolysis oils are provided. ln accordance with exemplary embodiment, a method for stabilizing the pyrolysis oil is provided. The method also includes usage of various types of stabilizing agents to stabilize the pyrolysis oil. ln accordance with another exemplary embodiment, a method which includes a process to dewater the stabilized pyrolysis oil at reduced temperature and pressures using vacuum distillation is provided. The method also includes a process to produce a vacuum heavy fraction (VHF) and vacuum light fraction (VLF). ln accordance with another exemplary embodiment, a process to recover, recycle and reuse the stabilising agent is disclosed. The method also includes an exemplary embodiment utilising recycled stabilising agent to stabilise the pyrolysis oil.

Furthermore, the foregoing and other desirable features and characteristics will be more clearly comprehended from the summary and detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

Brief Description Of The Drawings

The invention is now described with respect to the accompanying drawings, which show by way of example only, an embodiment of the process. ln the drawings: FIG.1 shows a schematic of the integrated process; FIG.2 shows vacuum distillation curves with liquid recoveries at 5 kPa for pyrolysis oil blended with C1 to C4 alcohol addition; FIG.3 shows the effect of alcohol addition on the liquid recovery from pyrolysis oil vacuum distillation under 5 kPa; FIG.4 shows the effect of addition of C1 to C4 alcohols addition and recovered distillates on the stabiiisation of pyrolysis oil; FIG.5 illustrates the effect of addition of ethanol and recovered distillates on the stabiiisation of pyrolysis oil; FIG.6 illustrates the effect of the aging time over the VHF at different temperatures; and FIG. 7 shows a ternary phase diagram for VHF-based emulsions; FIG. 8 illustrates the acetic acid and ethanol recovery in the recovered distillates on the stabilisation of pyrolysis oil.

Detailed Description Of Embodiments Of The Invention

Compared to fóssil fuels, pyrolysis oil is not chemically stable overtime. Many of the wide range of functional groups present in pyrolysis oil are reactive even at room temperature. The lack of Chemical stability during storage results in polymerization which leads to an increase in the molar mass of the pyrolysis oil and consequently changes in its physical properties. Pyrolysis oil has a high oxygen content in the form of water and oxygenated functional groups that results in a similar elemental composition to that of the biomass from which it has been derived. The high oxygen content leads to a lower heating value (LHV) which is similar to that of biomass and half that of hydrocarbon fuels. It also makes pyrolysis oil immiscible with conventional hydrocarbon fuels. The functional groups primarily carboxylic acids, sugars, phenolics, hydroxyaldehydes, and hydroxyketones cause pyrolysis oil to be chemically unstable. The high acidity and subsequent corrosiveness of pyrolysis oil is due to its considerable carboxylic acid and phenolic content.

The lack of Chemical stability appears in the form of self-polymerisation of pyrolysis oil during storage and processing. Polymerisation of double bonds, etherification and esterification between hydroxyl, carbonyl, and carboxyl groups with production of water as a by-product are the major Chemical reactions observed in the pyrolysis oil. Polymerisation must be prevented as much as possible during processing, as the polymerisation products lead to reactor plugging, catalyst poisoning and coke formation.

The above drawbacks prevent pyrolysis oil from being suitable for direct use as a transportation fuel, thereby emphasizing the necessity of developing a process suitable for pyrolysis oil upgrading.

Accordingly, it is desirable to provide a method and integrated process for processing the pyrolysis oil to high value commodities and also to be usable as a feedstock for numerous upgrading applications. Further it is desirable to reuse and recycle the solvents used in the process. ln the proposed integrated process, a vacuum distillation technique is used for all distillation purposes. Vacuum and atmospheric distillations are simple, and widely used separation techniques in petrochemical refinery.

However, due to the aging and polymerization of biomass pyrolysis oil, conventional distillation techniques have been limited to the separation of the pyrolysis oil. ln order to mitigate these limitations, a method is proposed, in a preferred embodiment, to add a stabilising agent to the pyrolysis oil and subsequently the stabilised pyrolysis oil is processed through vacuum distillation. The proposed stabilising agent or altematively or additionally the use of reactive alcohol entrainers assists in subsequent distillation to dewater the pyrolysis oil at lower temperature and with reduced pressure by forming an azeotropic mixture with molecular bound water. Also the stabilising agent helps to separate the light molecules and water from the stabilised biomass pyrolysis oil.

The preferred embodiments of the invention are described by way of example only. Modifications of these embodiments, further embodiments and modifications thereof will be apparent to the skilled person and as such are within the scope of the invention.

According to the invention, there is provided an integrated process for producing a liquid biofuel mixture, a stabilised pyrolysis oil, dewatered pyrolysis oil, a vacuum light fraction (VLF) and a vacuum heavy fraction (VHF) through vacuum distillation, said process comprising: selecting a pyrolysis oil derived from pyrolysis of biomass, and particularly lignocellulosic biomass, mixing the pyrolysis oil with an alcohol component, the alcohol component being selected from Ci to C4 alcohol the concentration of the alcohol being 5-100% w/w , or in a further preferred embodiment, a mixture of two or more different Ci to C4 alcohols, the mixture including from 3 - 50%w/w, preferably 5-50% w/w of the alcohol, vacuum distilling the distillation mixture, the distillation process being performed under a vacuum at 1-10kpa, at a distillation temperature of from 4O-95°c and at a vapour temperature of from 35-50°c.

The added alcohol is preferably ethanol, methanol a mixture of two or more Ci to C4 alcohols or industrial methylated spirit (IMS) to produce a distillation mixture.

The alcohol is chosen for its reactivity in esterification of both the light acids and the heavy organic molecules, as well as for its capability in forming azeotropes with the water phase so that the water phase will be entrained in the subsequent distillation to separate the water, alcohol and light acid esters from the heavy organic phase. A process is also disclosed in which the alcohol serves as a stabilizing agent reducing the rate of polymerization of the heavy organic fraction. A process is also disclosed including the optional steps of distilling the distillation mixture with added stabilizing agent (alcohol etc.), together with water and light organic compounds from biomass pyrolysis oil mixture under a vacuum (1.5 kPa -5.0 kPa) distillation process; obtaining a vacuum light fraction (VLF) initially at vapour temperature (35-50°C) and pyrolysis oil mixture temperature around 40-95°C; obtaining a vacuum heavy fraction (VHF) with a recovery of > 55 % mass fraction at a pyrolysis oil temperature around 40-95°C.

Advantageously, the process includes the step of adding a stabilizing component the stabilizing component comprising one or more components selected from hydroxyl-ketone compounds, acetone, glycol, glycerol. This process obtains higher yields of the fractions with lower production of side-products. A process is disclosed which also includes the further step of separating the alcohol and other light organic Chemical compounds from water by atmospheric distillation or further preferably membrane separation. A process is disclosed which also includes the step of re-using the alcohol and light organic compounds to stabilise the raw pyrolysis oii which reduces manufacturing costs overall.

The vacuum light fraction can contain about 80 % mass fraction of water and total acid number (TAN) measured as KOH of around 10-40 mg /g of sample dependent upon the added alcohol amount (range of 1 % -50 % mass fraction of the initial reactive mixture).

Typically, the vacuum heavy fraction has water content and acetic acid below 1 % mass fraction, TAN higher than 200 mg /g of sample and elemental composition (mass fraction of dry material): 54-57 % C, 6-7 % H and 35-39 % O. Advantageously, the VHF has a heating value of greater than 20 MJ/kg.

Preferably, the process includes the step in which the vacuum distillation of stabilized pyrolysis oil is carried out at 5kPa, and from 4O-95°C, further preferably 65°C and a vapour temperature of from 35 - 50°C. A process is disclosed which includes the step in which the atmospheric distillation of vacuum light fraction produces up to 25 % mass fraction of a light distillate with water content below 20 %w/w and TAN below 5 mg KOH /g at vapour temperature below 85°C. A process is disclosed which includes subsequent stabilisation of the vacuum heavy fraction using organic additives such as alcohols, toluene, tetralin, surfactants or their mixture or catalytic processes such as hydro-processing, decarboxylation, decarbonylation or a combination of these reactions. Further advantageously, the vacuum heavy fraction is stabilized using alcohol concentration between 15 % and 67 % mass fraction.

Preferably, the vacuum heavy fraction is stabilized using a non-ionic surfactant, a non-ionic block-copolymer, fatty-acid methyl ester (FAME), cooking oil or a combination thereof.

In FIG.1 is illustrates a schematic of the integrated process which can be used to firstly separate out the fractions from biomass-derived pyrolysis oil, and secondly to illustrate further processing of the light fraction obtained from the process.

Beginning with pyrolysis oil, this is firstly stabilised to ameliorate any effects of the subsequent heating and distillation process. The distillation is then carried out, often at reduced (below atmospheric) pressure to produce two major fractions designated as a Vacuum Light Fraction (VLF) and a Vacuum Heavy Fraction (VHF).

Further processing of the VLF yields three main further components. The first component can be used as the stabilising agent for the distillation of a further batch of pyrolysis oil. The second component is water and the third an atmospheric heavy fraction; which on further separation can yield Chemicals for use elsewhere in industry, or be upgraded to petroleum fuel substitutes.

EXPERIMENTAL DATA

Distillation curves

The data ofthe distillation curves given in Fig.2 were obtained at 5.0 kPa from room temperature (ca. 20 °C) to ca. 100 °C for oil bath temperature. Liquid samples were collected at variable intervals of time (20-40 minutes). The calculation of liquid recovery data was based on pyrolysis oil instead of pyrolysis oil plus ethanol and the alcohol concentration (ca. 3 - 8 % mass fraction) was calculated in order to keep a constant concentration of OH group. A large fraction of liquid recovery (35-40 % mass) was obtained, particularly for the mixtures containing methanol, ethanol and iso-propanol (i.e. boiling points (BPs) between 60 and 85 °C). Note that butanol, whose BP is above 100 °C, showed lower liquid recovery.

The data ofthe distillation curves in Figure 3 were obtained at 5.0 kPa from room temperature (ca. 20 °C) to ca. 190-210 °C for the oil bath temperature. Liquid samples were collected at variable intervals of time (10-30 minutes). Note that the calculation of liquid recovery data was based on pyrolysis oil instead of pyrolysis oil plus ethanol.

Larger liquid recovery was obtained with increasing ethanol concentration in the pyrolysis oii in comparison to lower concentrations. However this is beyond what is to be expected purely with extra mass from ethanol taken into account. Therefore such increase on liquid recovery was observed in ethanol free basis calculation. Additionally, importantly, much of the recovery was achieved at a lower temperature than conventional distillation, with the result that the risk of adverse reactions taking place due to the heating is minimised. Moreover the energy required to obtain the iight fraction is reduced due to said lower temperatures.

The addition of 5 % mass fraction ethanol significantly improved the ability of raw pyrolysis oil to be distilled, and the ability was further improved when ethanol addition was increased to 50 % mass fraction. The alcohol utilised can additionally or altematively be methanol or mixture of ethanol and methanol such as industrial methylated spirits (IMS). Furthermore, any light alcohol (C1-C4), glycol, hydroxyl-ketone compounds and mixture thereof can be used.

The distillation curve shows clearly the formation of an azeotrope, and the entrainment of the water component of the original pyrolysis oil. This restricts the use to alcohols that have boiling points at atmospheric pressure <100 °C, and have the ability to act as entrainers for water.

Recovery of light distillates from vacuum light fraction

Two types distillations were carried out at atmospheric pressure from room temperature to 102 °C using two different distillation columns (ca. 16 cm and 32 cm). The results are shown in Table 1. Compared with the short column, the longer distillation column (ca. 32 cm), which was additionally filled with glass beads, showed remarkable improvement of separation of small molecules from remaining water. Hence the VLF distillation was significantly improved at temperatures below 90°C with an increase in the recovery of light organics and a reduced water content.

On the other hand TAN numbers of the organic sample fractions at temperatures above 100°C increased mostly due to the accumuiation of e.g. acetic acid in the sample fractions. Highest TAN numbers were observed at temperatures above 100°C, which also coincides with the boiling point of acetic acid i.e. 118 °C.

Table 1 Recovery of light distillates from vacuum light fraction by atmospheric distillation.

In a typical distillation process, as described above, a vacuum light fraction produces a light distillate in a quantity up to 25 % mass fraction having a water content below 20% mass fraction and a TAN below 5mg KOH/g sample at a vapour temperature below 85°C and especially below 83°C. The light distillate comprises alcohols, methyl acetate, ethyl acetate which can be used as stabilising agents to stabilise pyrolysis oil. FIG. 8 illustrates the acetic acid and ethanol recovery in the recovered distillates on the stabilisation of pyrolysis oil High ethanol concentrations are observed in the first batch of liquid recovery, which is to be expected because of the low boiling point of the ethanol. Also, a high concentration of acetic acid was observed in the last batch of recovered liquid: this is also expected because of the high boiling point of acetic acid. In addition to ethanol

and acetic acid, water is also obtained in all the recovered samples. From this figure, it can be assumed the stabilizing agent can be recovered and recycled back to stabilise the pyrolysis oil. Additionally, light Chemicals are separated and purified and used as a market solvents and industrial Chemicals. ln a non-illustrated embodiment, membrane separation is used in place of the distillation step.

Stabilising biomass pyrolysis oil and vacuum heavy fraction

The effects of addition of alcohol (methanol, ethanol, isopropanol and butanol) on the stabiiisation of biomass pyrolysis oil were investigated and the results are shown Fig.4.

The mixture of pyrolysis oil blended with ethanol showed a marked stability. The poor effect of the other alcohols over the pyrolysis oil stability is a consequence of either the loss of the alcohol because of its lower boiling point and concentration (methanol) or weak affinity with pyrolysis oil (iso-propanol and butanol) because of phase separation over a long period at 80°C.

The effects of addition of alcohol (for example: ethanol) and recovered distillates on the stabilization of biomass pyrolysis oil have been investigated and the results are shown FIG.5. Compared with the raw pyrolysis oil, the addition of 5% mass of ethanol significantly increased the stability of pyrolysis oil, and resulted in no increase of viscosity during aging test at 80°C. The addition of 5% mass of the distillates recovered before 90°C, using a large distillation column showed the same effect as ethanol. This demonstrates that the addition of alcohol can stabilize the pyrolysis oil, improve the distillation ability and with the alcohol being recycled in the process.

Fig.6 displays the dependence of the viscosity with the aging time. Note that the VHF is relatively stable for period of up to seven months at temperatures between 4-25 °C. At temperature of 40 °C the VHF viscosity drastically increased as a consequence of the condensation reactions.

Characterísation o f Vacuum Heavy Fraction

Table 2 shows the properties of several typical vacuum heavy fractions generated under different vacuum distillation conditions. Under different vacuum distillation conditions, VHF yield varies between 60 to 65%w/w, but elemental analysis results showed that the VHFs have very similar elemental composition. On the other hand, high distillation temperature generated a VHF with high viscosity. The resulting VHF has a water content of less than 1%w/w and a total TAN value higher than 200mg KOH/g sample. A typical heating value achieved for the VHF is greater than 20MJ/kg.

Table 2. Properties of Vacuum Heavy Fraction (VHF) produced under different distillations

Table 3 shows the properties of different vacuum heavy fractions made from different biomass (clean wood and wheat straw). Stable and clean VHFs have been produced from pyrolysis oil obtained from different biomasses, such as clean wood and wheat straw. Different fluidising agents, sand and olivine do not show any influence on the VHF, but the VHF obtained from wheat straw pyrolysis oil had much lower oxygen content, higher viscosity and higher conradson carbon content.

Table 3. Physical and Chemical properties of different VHFs from different biomass feedstock

The vacuum heavy fraction can be stabilised through the addition of organic additives such as alcohols, toluene, tetralin, surfactants or mixture thereof or by catalytic processes such as hydro-processing, decarboxylation, decarbonylation or a combination of these reactions. Furthermore, the vacuum heavy fraction can be stabilized using a non-ionic surfactant, a non-ionic block-copolymer, fatty-acid methyl ester (FAME), cooking oil or a combination thereof.

Following its manufacture, the vacuum heavy fraction can be used as raw material for resin production. The vacuum heavy fraction can also be used to produce an emulsified fuel with diesel. Additionally the vacuum heavy fraction can be upgraded to transportation fuel through a catalytic process that reduces oxygen content up to 80 % mass fraction based on oxygen concentration of the untreated vacuum heavy fraction.

Emulsifícation ofthe Vacuum Heavy Fraction FIG7 illustrates that VHF can be emulsified in a mixture of ethanol and toluene. It is also possible to produce VHF-based emulsion free of water with VHF concentration comparable to VHF in pyrolysis oil.

Note that the use of diesel-containing emulsion requires large concentrations of ethanol to get a single phase.

On the other hand high alcohol concentrations within the range shown on Figure 7 enhance the fluidity of vacuum heavy fraction.

The preferred embodiments of the invention have been described by way of example only. Modifications of these embodiments, further embodiments and modifications thereof will be apparent to the skilled person and as such are within scope of the invention.

Claims (14)

1. A process for producing a vacuum light fraction (VLF) and a vacuum heavy fraction (VHF) through vacuum distillation of liquid bio-fuel mixture or stabilized pyrolysis oil comprising the steps of; selecting a liquid bio fuel mixture or stabilised pyrolysis oil, adding an alcohol component thereto, the alcohol component being selected from a Ci to C4 alcohol to produce a distillation mixture, the concentration of the alcohol being from 5-100% w/w, and wherein the mixture includes from 3-50% w/w of the alcohol, - vacuum distilling the distillation mixture - the distillation process being performed under a vacuum at 1 to 10 kPa, at a distillation temperature of from 4O-95°C and at a vapour temperature of from 35-50°C.

2. A process according to Claim 1, wherein the mixture includes from -5-50%.

3. A process according to Claim 1 or Claim 2, wherein the pressure is 5kPa.

4. A process according to Claims 1 -3, wherein the temperature is 65°C.

5. A process according to claims 1-4, wherein a liquid bio-fuel mixture produces a VHF having a water content and acetic acid content below 1 % mass fraction, a total acidity number (TAN) higher than 200 mg KOH/g per sample and elemental composition: 54-57 % mass fraction C, 6-7 % mass fraction H and 35-39 % mass fraction O.

6. A process according to claim 5, wherein the VHF has a heating value of greater than 20 MJ/kg

7. A process according to any preceding claim wherein the mixture includes 3-8% w/w of the alcohol.

8. A process according to any preceding claim, wherein the process includes a further step of adding a stabilising component, the stabilising component comprising one or more components selected from hydroxyl-ketone compounds, acetone, glycol, glycerol.

9. A process according to any preceding claim, wherein the alcohol is ethanol.

10. A process according to claims 1-8, wherein the alcohol is methanol.

11. A process according to claim 1 wherein a mixture of two or more different Ci to C4 alcohols is selected.

12. A process according to claim 11, wherein the mixture comprises industrial methylated spirits.

13. A method of recycling and reusing a stabilizing agent comprising the steps of: carrying out a process in accordance with Claims 1-12 including the further step of separating the alcohol or stabilizing agent and other light organic Chemical compounds and water from VLF atmospheric distillation or membrane separation.

14. A process according to claim 13, wherein the atmospheric distillation of vacuum light fraction produces up to 25 % mass fraction of a light distillate with water content below 20 % mass fraction and TAN below 5 mg KOH/g at vapour temperature below 85°C.