The present invention provides a process for producing alcohol.

In the recent years , there has been a growing interest in the use of alcohols, in particular bio- alcohols as an environmentally friendly fuel or fuel blending feedstock. Bio-alcohols, such as b±o-ethanol, and bio-butanol, are typically produced by a fermentation process. In the fermentation process, sugars and other fermentable carbohydrates are converted into alcohols and carbon dioxide using a suitable microbiological organism. The alcohol is subsequently isolated from the fermentation broth.

Typical fermentation processes are characterised by their end-product inhibition. The production of the desired alcohol ceases, when the alcohol concentration in the fermentation broth reaches levels, which are toxic to the microbiological organism. Typically, in an ethanol fermentation, the ethanol concentration becomes toxic to the microbiological organism at concentration of 12vol% and higher. In case of butanol fermentation, butanol concentrations as low as 2vol% may already result in an fermentation environment, which is toxic to the microbiological organism.

In order to maintain the alcohol concentrations below the toxic levels, the alcohol is removed from the fermentation broth.

In US 20070031954, a process for producing and recovering light alcohols from for instance fermentations broths is disclosed. In US 20070031954, a dilute mixture of ethanol and water comprising up to 20 wt% of ethanol is separated using a pervaporation membrane separation processes . The obtained permeate comprised in between 15 and 70 wt% of ethanol. In order to increase the ethanol content in the permeate, the permeate is subsequently subjected to a dephlegmation and second membrane separation process .

The membrane process of US 20070031954 cannot produce a high purity ethanol permeate without requiring subsequent purification of the permeate. In US 4442210, a process for the production of fermentation ethanol is described, wherein the ethanol is recovered from a fermentation mixture using a crystalline zeolite, such as ZSM-5.

In US 6603048, a process to separate 1,3- propanediol, glycerol, or a mixture thereof from a biological mixture is described. In US 6603048, 1,3- propanediol and/or glycerol is absorbed from the biological mixture using zeolite structures such as MFI, MEL, BEA, MOR, FAU, LTL, GME, FER, MAZ, OFF, AFI, AEL and AET.

In M.T.Holtzapple, R. F. Brown, Conceptual design for a process to recover volatile solutes from aqueous solutions using silicalite, Sep. Technol . , vol 4, 1994, p213, a process for removing various alcohols from diluted aqueous alcohol solutions is described. In

Holtzapple, a hydrophobic silicalite zeolite is used to concentrate an 1 wt% aqueous solution is contacted with the zeolite to separate the alcohol from the solution. The obtained alcohol product still comprised 76, 66 and 50 wt% water for starting solutions of 1 wt% ethanol, 1- propanol, and 1-butanol, respectively. Maximum adsorption capacities for the mentioned alcohols described to be 0.09, 0.11 and 0.12 gram of ethanol, 1-propanol, and 1- butanol, respectively, per gram of zeolite.

A disadvantage of using zeolites, such as described in US 4442210, US 6603048 and Holtzapple, is that although most silicalite zeolites are hydrophobic, these silicalite zeolites have been shown to take up as much as 50 wt% of water. As a result, the ethanol, butanol or other product obtained after desorption from the zeolite, comprises significant amounts of water and needs to undergo further purification steps. In addition, the zeolite inventory required to absorb sufficient ethanol from the fermentation mixture is increased due to water co-absorption.

There is a need in the art for a separation process, which can isolate alcohols from dilute aqueous mixtures efficiently and selectively.

It has now been found that it is possible to selectively isolate alcohols from dilute aqueous mixtures using a zeolitic imidazolate framework material (ZIF) as absorbent.

Accordingly, the present invention provides a process for producing an alcohol, which process comprises: fermenting a fermentable hydrocarbonaceous compound in the presence of a microbiological organism, thereby forming an aqueous alcohol- comprising solution; absorbing at least part of the alcohol from the aqueous alcohol-comprising solution by contacting at least part of the aqueous alcohol-comprising solution with the ZIF absorbent to obtain an aqueous alcohol-depleted solution and an alcohol- comprising ZIF absorbent; and desorbing the alcohol from the alcohol-comprising ZIF absorbent to obtain an alcohol product. Reference herein to a ZIF is to a material comprising, essentially consisting of or consisting of zeolitic imidazolate framework. Preparation and characterisation of ZlFs have been extensively described in the literature, for instance by Yaghi et al . (Yaghi et.al, Proceedings of the National Academy of Sciences, volume 103, no. 27, 2006, pl0186-10191, Yaghi et al, Nature materials, volume 6, July, 2007, p501-505 and

Yaghi et al . , Science, volume 319, no. 5865, 2008, p939- 943) . At least 35 ZIFs, including ZIF termed ZIF-I to -12 and -20 to -23, have been synthesized as crystals by copolymerization of either Zn(II) (ZIF-I to -4, -6 to -8, and -10 to -11) or Co(II) (ZIF-9 and -12) with imidazolate-type links, new ZIF types include structures wherein one or more of the carbon atoms of a benzimidazolate linker have been replaced by nitrogen atoms, giving ZIF-20 and -21 (purinate linker) , ZIF-22 (5-azabenzimidazolate linker) and ZIF 23 (4- azabenzimidazolate linker) . These ZIF materials are disclosed in detail in WO2007/101241, which is hereby incorporated by reference. The ZIF crystal structures are based on the topologies of seven distinct aluminosilicate zeolites: tetrahedral Si or Al atoms and the bridging O atoms are replaced with transition metal ions and imidazolate linkers, respectively. It will be appreciated by the skilled person that a ZIF is not a zeolite, on the contrary they are materials belong to the Metallic Organic Framework family of materials.

ZIFs are typically hydrophobic and they are stable in water, alkaline environments and organic solvents. The ZIFs have a high porosity and good thermal stability, e.g. characterisation of ZIF-8 and -11 has demonstrated a permanent porosity (Langmuir surface area: 2IF-S= 1,947 mVg, ZIF-Il= 1,676 m ² /g} and a thermal stability up to 55O ⁰ C.

The ZIFs have a high internal volume, typically in the range of from 0.5 to 1.6 ml/g ZIF. For comparison, typical zeolites have an upper inner volume limit of approximately 0.3 ml/g zeolite. Reference herein to absorbed is to both the absorption and adsorption of material .

In the process according to the invention an alcohol is produced by fermenting a fermentable hydrocarbonaceous compound in the presence of a microbiological organism. Typically, such fermenting processes comprise providing an aqueous slurry of the microbiological organism, i.e. a mixture comprising water and the microbiological organism. This slurry is also referred to a fermenting broth or fermenting mixture , The fermentable hydrocarbonaceous compound is added to fermenting mixture and converted or consumed by the microbiological organism, also referred to microbiological fermentation. At least one of the fermentation products is an alcohol . In case, the fermentable hydrocarbonaceous compound was obtained from renewable sources, the obtained alcohol may also referred to as bio-alcohol.

The obtained alcohol dissolves in the water to form an aqueous alcohol-comprising mixture. This mixture then forms the liquid part of the fermentation mixture. The fermentation process is characterised by its end-product inhibition. As a result, the microbiological organism produces less of the desired alcohol as the alcohol concentration increases . When the alcohol concentration in the fermentation mixture reaches a level, above a certain toxic alcohol concentration, the alcohol production by microbiological organism reduces drastically or even ceases. Reference herein to toxic alcohol concentration is to an alcohol concentration at which the microbiological organism stops or essentially stops producing the desired alcohol. Typically, in an ethanol fermentation the ethanol concentration becomes toxic to the microbiological organism at ethanol concentrations of I6vol% and higher, based on the total liquid volume of the fermentation mixture. In case of butanol fermentation, butanol concentrations as low as 2vol%, based on the total liquid volume of the fermentation mixture. Therefore, preferably, the alcohol concentration in the aqueous alcohol-comprising solution, i.e. the liquid part of the fermentation mixture, should be maintained below the toxic alcohol concentration. It will be appreciated that the exact toxic concentration depends on the type of alcohol produced and the microbiological organism used. These toxic concentrations are well known in the art. Preferably, the alcohol concentration in the aqueous alcohol-comprising solution is maintained at a concentration below 90% of the toxic concentration, even more preferably below 75% of the toxic concentration. In the process according to the present invention, the alcohol is removed from the fermentation mixture. By removing the alcohol from the fermentation mixture it is possible continuously or semi- continuously produce alcohol, while the alcohol concentration in the fermentation mixture is maintained below toxic levels .

The alcohol is removed from the fermentation mixture by contacting at least part of the aqueous alcohol- comprising solution with a ZIF absorbent. As a result, at least part of the alcohol is absorbed in the ZIF absorbent and consequently isolated and removed from the aqueous mixture. An aqueous alcohol-depleted solution and an alcohol- comprising ZIF absorbent are obtained.

The alcohol-comprising ZIF absorbent is subsequently- treated to desorb the alcohol and to obtain an alcohol product .

Prior to treating the alcohol-comprising ZIF absorbent to desorb the alcohol, the alcohol-comprising ZIF absorbent is separated from the aqueous alcohol- depleted solution and/or aqueous alcohol-comprising solution.

The alcohol product preferably comprises less than 5 vol% or water, more preferably less than 2 vol% water, even more preferably less than 0.5 vol% water, based on the total liquid volume of the alcohol product . Due to the above-mentioned hydrophobic nature of the ZIFs, they are especially suitable for separating water-alcohol mixtures, as the water uptake of the ZIF is minimal.

Water is essentially excluded from the interior volume of the ZIF due to the polar nature of water. The maximum water uptake of a ZIF is typically in the order of 0,40 wt%. For comparison, known Metallic Organic Frameworks (MOF) , which have structural dimensions similar to the

ZIFs discussed hereinbefore have been shown to be able to absorb up to 40 wt% of water. Silicalite zeolites, e.g. ZSM-5 as frequently used in prior art processes, are among the most hydrophobic zeolites. However, silicalite zeolites, have been shown to take up as much as 50 wt% of water, as shown in M.T.Holtzapple, R. F. Brown, Conceptual design for a process to recover volatile solutes from aqueous solutions using silicalite, Sep. Technol . , vol 4, 1994, p213. The alcohol product will comprise predominantly the desired alcohol. However, it may further comprise other alcohols or hydrocarbonaceous products, which are produced by the microbiological organism.

Although, the ZIF adsorbent does not significantly adsorb water, some water may be present as a small part of the aqueous alcohol-comprising solution remains in the inter particle space and on the outer surface of the ZIF absorbent. This water is loosely bound as the water is in principle excluded from the inner volume of the ZIF and can be early removed drying the alcohol-comprising ZIF adsorbent at low temperatures. Depending on the size and structure of the ZIF absorbent, which may e.g. be applied in the form of pellets or particles, the water loosely bound water may be removed at temperatures as low as 1O ⁰ C e.g. under a vacuum pressure. However, typically temperatures around 5O ⁰ C may be used. At such temperatures the loosely bound water is removed, together with any loosely bound alcohol. In order to obtain a high alcohol purity, it is preferred to first treat the alcohol-comprising ZIF absorbent to remove the loosely bound water .

The aqueous alcohol-comprising mixture is contacted with the ZIF absorbent for such a period that at least part of the alcohol in the aqueous alcohol-comprising mixture is be absorbed by the ZIF absorbent. Preferably, the aqueous alcohol-comprising mixture is contacted with ZIF absorbent for a period long enough to allow at least part of the alcohol to be absorbed but no longer than the time necessary to reach the equilibrium concentration of the alcohol in the aqueous alcohol-comprising mixture. Reference herein to the equilibrium concentration is to the concentration of the alcohol in the aqueous alcohol- comprising mixture at which no further decrease of the concentration of the alcohol in the aqueous alcohol- comprising mixture is observed in time. The obtained alcohol product can be used directly as biofuel, fuel-blending component or as feed to a fuel cell.

The treatment to desorb the alcohol from the alcohol-comprising ZIF absorbent by any suitable treatment known in the art, such treatments include a temperature treatment, a treatment with a sweep gas and/or vacuum, solvent extraction or elution. Suitable solvents or elution media may for instance include hydrocarbons such as pentane. Preferably, the ZIF absorbent and absorbed alcohol are recovered by heating the alcohol-comprising ZIF absorbent to a temperature in the range of from 20 to 500 ⁰ C, preferably the ZIF absorbent is heated to a temperature in the range of from 40 to 25O ⁰ C. It will be appreciated that the exact choice of temperature depends on the type of ZIF and on the properties of the absorbed alcohol. It was found that ZIF-8 releases 1-butanol when subjected to a temperature of 50 ⁰ C, more preferably 80 ⁰ C, even more preferably, in the range of from 100 to 130 ⁰ C, where typical silicalite zeolites need to be re-activated at significantly higher temperatures before a substantial release of 1-butanol is observed. Recovery using a temperature treatment may take place in air, under an inert atmosphere such as nitrogen or vacuum, or in contact with a sweep gas, Subsequent to obtaining the alcohol product, the ZIF absorbent may be reused, optionally following a reactivation. The ZIF absorbent may be contacted with the mixture in any form or shape. Typically, the 2IF absorbent is in the form of particles. The particles can have any form suitable for the planned use. Preferably, is the particles are pellet, tablet or bar shaped. In the context of the present invention, the term particle preferably refers to any solid body that extends to at least 0,2 mm in at least one direction in space. No other restrictions apply, i.e., the body may take any conceivable shape and may extend in any direction by any length so long as it preferably extends to at least 0.2 mm in one direction. In a more preferred embodiment, the shaped bodies do not extend to more than 50 mm and not to less than 0,2 mm in all directions. In a further preferred embodiment, the shaped bodies do not extend to more than 1 mm and not to less than 16 mm in all directions, preferably not extend to more than 1,5 mm and not to less than 5 mm. Optionally, the 2IF absorbent particles may comprise a binder material. Alternatively, the ZIF absorbent may also be supported, e.g. on known supports like metal or inorganic supports or in pouches.

In the process according to the invention, the aqueous alcohol comprising mixture may be contacted with the 2IF absorbent by directly mixing the ZIF absorbent with the fermentation mixture. Although the fermentation mixture comprises other components besides the aqueous alcohol comprising mixture, such as the microbiological organism, sugars and other nutrients, it was found that these compounds do not significantly influence the absorption behaviour of the ZIF absorbent. No significant absorption of glucose was measured. This is in line with expectations as the heat of solvation for glucose in water is very high, which makes it undesirable for the polar glucose to enter the hydrophobic ZIF absorbent, In addition, the glucose molecule is too big to enter the pores of the ZIF adsorbent.

Preferably, the aqueous alcohol-comprising solution first separated from the fermentation mixture prior to contacting the ZIF absorbent. This is done by removing at least part of the microbiological organism prior contacting the aqueous alcohol-comprising solution with the ZIF absorbent. The at least part of the microbiological organism may be removed by any means known in the art for separation liquid/solid mixtures, preferably by filtration. Alternatively, it is possible to use an immobilized microbiological organism. Any microbiological organism separated from the aqueous alcohol-comprising mixture may be redirected to the fermentation mixture Preferably, the aqueous alcohol- comprising solution is contacted with the ZIF absorbent by passing the aqueous alcohol-comprising solution through at least one ZIF absorbent-comprising absorption bed. For instance one or more packed beds or filter beds comprising the ZIF are provided and the liquid mixture is contacted with the ZIF by flowing the liquid mixture over or through the beds .

Upon the saturation or partial saturation of the ZIF absorbent, it is preferred to periodically regenerate the at least one ZIF absorbent-comprising absorption bed by treating at least one ZIF absorbent-comprising absorption bed to desorb alcohol in the absence of the aqueous alcohol-comprising solution. Methods for desorbing alcohols from the ZIF absorbent have been described herein above .

In order to allow for a continuous production of the alcohol it is preferred to use two or more absorption beds, whereby one bed. is contacted with the aqueous alcohol-comprising solution, while the other bed is regenerated by desorbing the alcohol. By alternately passing the aqueous alcohol-comprising solution is through at least two ZIF absorbent-comprising absorption beds, to absorb alcohol in at least one bed, while another bed is treated to desorb alcohol from the ZIF absorbent it is possible to continuously produce alcohol. An equally preferable alternative is to contact the fermentation mixture or the aqueous alcohol-comprising solution with a membrane comprising the ZIF absorbent, for instance under pervaporation conditions . The membrane may essentially consist of ZIF absorbent, however it is preferred that the membrane is a composite membrane comprising a layer of ZIF absorbent supported by a polymeric, inorganic or metal support. Alternatively, the ZIF absorbent is dispersed in an inorganic or polymeric membrane material . The ZIF absorbent material may for instance be incorporated in a silica membrane using a silica solution comprising both the ZIF absorbent as well as silica. Preferably, the ZIF absorbent is dispersed in a polymeric membrane material, such as a silicon rubber (PDMS) , polyimide, polysulphone, or polyethersulphone type polymer. Preferably, a rubbery polymer is used to enhance interaction between the ZIP and the polymer matrix by reducing the formation of voids at the ZIF/polymer interface. It is preferred to use a hydrophobic polymer material, more preferably a rubbery hydrophobic material such as PDMS. The ZIF absorbent may be incorporated in any form or structure, such as a particle or a crystal. Preferably, the ZIF absorbent structure has an average diameter of no more than the thickness of the polymeric membrane layer, typically the membrane thickness is about 500 nm. More preferably, no more than half of the thickness of the polymeric membrane layer. Even more preferably, in the range of from 1 to 100 nm. It will be appreciated that when choosing a polymeric membrane material, the stability of such a polymeric membrane material is taken into consideration in the presence of either water or any other compound in the fermentation mixture is considered.

The obtained aqueous alcohol-depleted mixture may be redirected to the fermentation mixture

The fermenting process may be any fermenting process comprising the use of a suitable microbiological agent to produce a desired alcohol. Examples of such processes include for instance an ABE (Acetone, Butanol, Ethanol) fermentation and ethanol fermentation. The exact fermentation conditions will depend on the specific fermentation process chosen and will be clear to the person skilled in the art. The fermentable hydrocarbonaceous compound may be any hydrocarbonaceous compound that may be fermented to produce an alcohol. Preferably, the hydrocarbonaceous compound is a fermentable carbohydrate, such as glucose and other sugars .

The alcohol may be any alcohol that can be produced by microbiological fermentation process. Preferably, the alcohol is a mono-alcohol, a di-alcohol or tri-alcohol. Reference herein to a mono-alcohol, a di-alcohol or tri- alcohol is to an alcohol comprising one, two or three functional -OH groups, respectively. The alcohol may be a linear or branched alcohol. Typically the alcohol will comprises in the range of from 1 to 12 carbon atoms, preferably 2 to 8. Preferably, the alcohol is one or more alcohols selected from the group of ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol, or 1,3- dipropanol. Preferably, the alcohol is a mono-alcohol, in particular ethanol, 1-propanol, 2-propanol, 1-butanol, 2- butanol, isobutanol, more preferably 1-butanol, 2- butanol, isobutanol.

It will be appreciated that if there are two or more alcohols in the aqueous alcohol-comprising mixture, it is possible that two or more compounds are absorbed by the ZIF absorbent and isolated from the aqueous alcohol- comprising mixture.

Preferably, the aqueous alcohol-comprising solution is contacted with the ZIF absorbent at a temperature in the range of from 0 to 500 ⁰ C. Typically, however, the mixture will be contacted with the ZIF absorbent at temperatures in the range of from 1 to 300 ⁰ C, preferably from ambient temperatures to 200 ⁰ C, more preferably ambient to 5O ⁰ C. Typically, the aqueous alcohol- comprising solution is contacted with the ZIF at the temperature at which the fermentation process is operated.

The aqueous alcohol-comprising solution may be contacted with the ZIF absorbent at any pressure, preferably, in the range of from 0.1 to 200 bar, more preferably of from 1 to 50 bar. It is preferred that the pH of the aqueous alcohol- comprising solution is above pH 3. Without whishing to be bound to any theory it is presently believed that some acids may react directly with the ZIF absorbent or interact with other compounds in the mixture resulting in an irreversible modification of the ZIF absorbent.

Preferably, if an acid is present the pH of the mixture is at least 3, more preferably 3.5, or higher. Preferably, if an acid is present this is an acid comprising non or weakly co-ordinating anion{s) . Preferably, the mixture does not comprise an acid. Due to the stability of the ZIF absorbent in alkaline environments, the mixture may have a pH as high as 15. Preferably, the mixture has a pH of in the range of from 3.5 to 11, more preferably 5.5 to 10.

The ZIF may be any suitable ZIF, preferably the ZIF is ZIF-I, ZIF-2, ZIF-3, ZIF-4, ZIF-5, ZIF-6, ZIF-7, ZIF-8, ZIF-9, ZIF-IO, ZIF-Il, ZIF-12, ZIF 14, ZIF-20, ZIF-21, ZIF-22, ZIF-23, ZIF-60, ZIF-61, ZIF 62, ZIF-63, ZIF-64, ZIF-65, ZIF-66, ZIF-67, ZIF-68, ZIF-69, ZIF-70, ZIF-71, ZIF-72, ZIF-73, ZIF-74, ZIF-75, ZIF-76, or a mixture of one or more thereof. More preferably, the ZIF is ZIF-8, ZIF-10, ZIF-Il, ZIF-12, ZIF-20, ZIF-21, ZIF-65, ZIF-67, ZIF-68, ZIF-70, ZIF-71, ZIF-76 or a mixture of one or more thereof . These preferred ZIFs combine a good thermal and chemical resistance properties with a large internal volume, i.e. the framework will accommodate a sphere having a diameter of over 10 Angstrom. Even more preferably, ZIF-8, as this is commercially available. It will be appreciated that the internal volume of a ZIF may affect its separation properties. For instance a large internal volume allows for a high absorption capacity, whereas using a ZIF with a lower internal volume may result in an even higher selectivity.

In another aspect the invention relates to the use of ZIF absorbent to absorb alcohols from a fermentation mixture or the liquid part of a fermentation mixture. Example 1 : Separation of diluted aqueous alcohol solutions.

ZIF-8 (2-methylimidazole zinc, BASOLITE Z1200 ex Aldrich) was evacuated {< 1 mbar) at 200 ⁰ C for 16-20 hours prior to contacting it with the aqueous alcohol solution to remove any residual solvents.

Diluted aqueous alcohol solutions were prepared by- mixing the alcohol with demineralised water. In each experiment the evacuated ZIF- 8 was immersed in the diluted aqueous alcohol solution for 24 hours at ambient temperature.

Subsequently, the solution together with the ZiF-8 was filtrated over a P4 glass filter. The liquid filtrate was collected.

Both the filtrate and the original aqueous alcohol solution were analyzed with GC/FID. The quantity of alcohol absorbed by the ZIF was calculated from the reduction of the alcohol GC peak area. Table 1 gives an overview of the prepared aqueous solutions and the obtained reduction of the alcohol concentration. It will be clear that all tested alcohols can be selectively removed from the aqueous solution. The best results were obtained with alcohols comprising 2 to more carbon atoms. More than 90 wt% of C5+ alcohols were removed from the solution by contact with the ZIF

Table 1

* based on the weight of the total solution ** based on the initial concentration

Example 2 ^■ . Recovery of l-butanol from ZIF-8

The filter residue obtained in Example IE was dried by evacuation at ambient temperature for 10 minutes and subsequently analyzed with TDA-GC/MS (Thermal Desorption Analysis, coupled with GC/MS) .

This revealed that all (>99 wt%) of the absorbed matter, i.e. l-butanol and water, can be removed at 50 ⁰ C and that its purity is >99%. l-butanol of such purity may for instance be used directly for biofuel application. Further TDA-GC/MS analysis at temperatures above 100 ⁰ C did not detect additional matter being desorbed.

From this experiment it can be concluded that 1- butanol is selectively absorbed over water with a selectivity over 100, whereby the selectivity is defined a the ratio of the absorbed amount (wt%)of l-butanol over the absorbed amount (wt%) of water.

Similar experiments were performed using a zeolite ZSM-5 absorbent. These experiments showed a l-butanol over water selectivity of less than 0.5, approximately 0.1 grams of l-butanol and 0.3 grams of water were absorbed per gram of zeolite . This is comparable to M.T.Holtzapple, R. F. Brown, Conceptual design for a process to recover volatile solutes from aqueous solutions using silicalite, Sep. Technol . , vol 4, 1994, p213, where an 1- butanol over water selectivity of 1 is reported. Example 3 : Absorption of alcohol by ZIF-8.

From the results obtained in Example 1, the amount of alcohol absorbed per amount of ZIF-8 was determined in order to give an indication of the absorption capacity of ZIF-8, The results are shown in Table 2. It will be clear that ZIF-8 can selectively absorb high weight percentages of alcohols. It should be noted that it was not the aim to determine the maximum absorption capacity for each alcohol. For example, it is expected that in case of experiments IH and II, i.e. 1-pentanol and 1-octanol, the maximum absorption capacity is significantly higher than the absorption reported in Table 2 as very dilute solution were used. Similar absorption experiments using a zeolite ZSM-5 absorbent, showed a maximum 1-butanol absorption, which was almost 4 times lower than the absorption found for ZIF-8.

Table 2.

* based on the dry weight of the ZIF

Example 4 : Separation of diluted solutions

In Experiment 1, a relatively high concentration of alcohol was used. To determine the effect of concentration on the separation ability of the ZIF several solutions were prepared of l~butanol in demineralised water. Pre-treated ZIF- 8 was immersed in the prepared solution in a quantity such that the equilibrium concentration was lowered from 3.6 to approximately 0.5. Table 3 shows the wt% of 1-butanol in ZIF- 8 at each equilibrium concentration.

Table 3

* based on the dry weight of the ZIF ** saturated

It can be concluded that saturation concentration of 1-butanol in ZIF-8 was already reached at an equilibrium concentration of 0.6%, as the amount of 1-butanol absorbed did not further significantly increase at higher equilibrium concentrations. The amount of 1-butanol absorbed is approximately 30%wt. Thus, ZIF-8 is able to absorb approximately 0.3 gram of 1-butanol per gram of dry product at 1-butanol levels in water of 0.6 wt% and above . This is about three times as much as achieved with typical silicalite zeolites known in the art. Example 6 : Regeneration of ZIF

A ZIF-8 sample was pre-treated as described under Example 1. A methane sorption isotherm was recorded at

20 ⁰ C in the pressure range of 0 to 55 bar. Subsequently, the ZIF-8 was immersed in a solution of ethanol in demineralised water (the same as was used in example IB) following the procedure of Example 1. Following the ethanol absorption the ZIF-8 sample was evacuated at a temperature of 200 ⁰ C to remove the ethanol and again the methane sorption isotherm was recorded at 20 ⁰ C in the pressure range of 0 to 55 bar. No loss of absorption volume was observed.

Example 7 : ZIF stability in acid environment. Solutions of HCl in demineralised water were prepared. A sample of ZIF-8 was pre-treated as described in Example 1 and subsequently immersed in the HCl solutions. It was found that ZIF-8 was structurally unstable in a 1 M (raole/1, pH 0) solution of HCl. However, the ZIF-8 remained stable in a solution of 0.001 M HCl (pH 3} . Example 8 : Water adsorption.

The water adsorption of several materials was tested. Prior to the exposure to water all materials were pre-treated in a nitrogen atmosphere for 90 min at 150°C.

Water adsorption was determined using continuous adsorption/desorption process . Adsorption was measured by contacting the sample material under atmospheric pressure with a nitrogen stream comprising water vapour at a water partial pressure of 2000Pa for a time period of 90 minutes . The temperature during adsorption was maintained at 30 ⁰ C. Regeneration took place at a temperature of 100 ⁰ C for a time period of 90 minutes under a nitrogen atmosphere at atmospheric pressure. The adsorption desorption cycle was repeated 100 times. Water uptake was determined using Thermal Gravimetrical Analysis (TGA) , the TGA results were corrected for buoyancy differences.

The following materials were tested: MOF-5, MOF-177, Cu-BTC, Fe(III)-BTC, MIL-53, and ZIF-8. The results are reported in Table 4. It will be clear that the ZIF material in particular ZIF-8, show an exceptionally low water uptake. It was further observed that MOf-5, MOF-177 and Cϋ-BTC were not stable in water. It was found that not all water could be desorbed and part of the water was irreversibly adsorbed. A separate experiment determining the water uptake of a ZSM 5 zeolite adsorbent, based on the absorption of water from an 1% 1-butanol in water solution using TGA-MS as analysis method, showed a maximum water uptake as high as 50 wt%.

Table 4.

BDC: Benzene-1, 4-dicarboxylic acid or terephtalic acid

BTC: Benzene-1, 3, 5 -tricarboxylic acid or trimesic acid

BTB: Benzene 1, 3 , 5-tribenzoate

1 : ex Sigma Aldrich

2 : prepared in-house

3 : below detection limit

4: adsorption partially irreversible

Example 9 : 1-Butanol fermentation with continuous product removal by adsorption to ZIP-8 (calculated)

A modelled experiment was performed to simulate a process for procuring alcohol according to the invention. The modelled experiment simulates a process for producing 1-butanol by fermentation with continuous 1-butanol absorption using a ZIF-8 absorbent. In the modelled experiment a fermenter unit is provided and two parallel aligned absorption columns comprising ZIF-8 particles. Additionally, a filter unit is provided to filter the effluent from the fertnenter unit prior to entering one of the absorption columns. The filter removes the microbial cells, which are recycled back to the fermenter. Instead of a filter it is also possible to use immobilized cells.

The absorption columns are filled with ZIF-8 granules of 30-80-mesh size. At a given time-point, one column is in absorption mode and another column is in regeneration mode. After adsorption, the 1-butanol free liquid part of the fermentation mixture is recycled back to the fermenter. Upon breakthrough {more than 10% of the 1-butanol provided to the absorber is not absorbed) the first column is taken to regeneration mode and the other column is switched to absorption mode operation. In the experiment, fermenter volume is continuously withdrawn from the fermenter unit and provided, via the filter unit, to the absorption column in absorption mode. The 1-butanol concentration in the fermenter is maintained at l%wt to prevent 1-butanol inhibition. Absorption calculations were performed for 1-butanol production rate of Ig and 15g of 1-butanol per litre of fermenter volume per hour. The results are shown in Table 5.

Table 5

*fermenter volume ** ZIF-8

For an isobutanol fermentation process column sizes are 114 g ZIF-8 and 1710 g ZIF-8 per litre of fermenter volume for productivities of 1 and 15 g/l/h, respectively.