Method for separating alcohol mixture with high water content by using liquid-liquid extraction method

Abstract

The invention relates to a method for separating alcohol mixtures with high water content using naphtha as an extraction solvent. Specifically, the present invention relates to a process for the production of biofuels, said process comprising or consisting of a step of liquid-liquid extraction of a mixture of C2-C3 / C2-C4 alcohols from a mixture of C2-C3 / C2-C4 alcohols and water with an extraction solvent, where the extraction solvent is naphtha.

Description

Technical Field

[0001] The present invention relates to a process for separating alcohol mixtures having a high water content. Background Art

[0002] While water-alcohol separation is a well-known and studied problem in the literature, the separation of alcohol mixtures from water (i.e., when multiple alcohols are simultaneously present in an aqueous solution) presents a more challenging problem due to its complexity. The difficulty lies in identifying a solvent or solvent mixture that can simultaneously extract all of the alcohols, separating them from the bulk water in which they are dissolved, while minimizing the energy requirements of the process.

[0003] Ethylene glycol is one of the most widely used solvents in extractive water-alcohol distillation. Its high boiling point and high hydrophilicity make it an excellent dehydrating agent. The solution typically used to promote the dehydration of alcohol streams can be summarized as follows: an added solvent (i.e., ethylene glycol) is added to an extractive distillation column along with the water-alcohol mixture to be separated. This column fractionates the alcohol stream obtained as an overhead product from the water-glycol stream recovered from the bottom of the column. The water-glycol stream must be further fractionated in a downstream distillation column to regenerate the solvent before being recycled to the extractive distillation column. Extractive distillation using ethylene glycol as a solvent typically requires a non-negligible heat load to be supplied to the reboiler of the solvent regeneration column.

[0004] In fact, although the chemical-physical properties of ethylene glycol make it particularly suitable as a dehydrating agent, its high boiling point is the reason for the high temperatures reached during the regeneration process, a fact that reduces the energy requirements of the process itself (i.e. the heat load of the bottom reboiler and the related operating temperature).

[0005] As an alternative to extractive distillation, liquid-liquid extraction using toluene, isooctane, or other hydrocarbons as solvents has been reported in the literature. However, these proposed solutions involve mixing trace amounts of water and ethanol. Therefore, they are inflexible regarding the distribution of alcohols in the feedstock and are unsuitable for separating alcohol mixtures, particularly those diluted in water.

[0006] Various known processes provide alcohols, particularly mixtures of C2-C3 alcohols in water, as products or by-products. One example is the glycerol hydrogenation process to produce propanol described in co-pending patent application No. 102021000016859, filed on June 28, 2021.

[0007] Propanol is particularly recommended as a biofuel. In terms of ignition quality and calorific value, propanol has the same favorable characteristics as ethanol, but has a higher energy density (+12%), lower volatility, and a lower latent heat of vaporization (-8%). In principle, glycerol is a good source of propanol.

[0008] Propanol can also be produced using noble metal-based catalysts modified with dopants and promoters, particularly metal oxides (Groups 4-7) (Shinmi, Y., Koso, S., Kubota, T., Nakagawa, Y., Tomishige, K., Modification of Rh / SiO2 catalyst for the Hydrogenolysis of Glycerol in Water, Appl. Catal. B Environ. 2010, 94(3–4), 318–326).

[0009] These processes produce mixed propanols that contain significant amounts of water, which can be as high as 50% by weight, and therefore cannot be advantageously used as biofuels.

[0010] Therefore, there is a need to provide a simple and cost-effective method for separating substantially anhydrous propanol mixtures. Summary of the Invention

[0011] The present invention is based on the discovery that treating a mixture of C2-C4 alcohols and water with naphtha produces a substantially anhydrous naphtha enriched in C2-C3 alcohols, which can itself be used as a fuel.

[0012] The term "naphtha" refers herein to "petroleum naphtha", ie the fraction of crude oil comprising mainly (in volume %) linear and cyclic aliphatic hydrocarbons boiling in the range of 125°C to 240°C, inclusive.

[0013] Therefore, the present invention relates to:

[0014] 1. A method for producing biofuel, comprising or consisting of the step of liquid-liquid extraction of a mixture of C2-C3 alcohols from a mixture of C2-C3 alcohols and water using an extraction solvent, wherein the extraction solvent is naphtha.

[0015] The present invention also relates to:

[0016] 2) The method according to 1), wherein the mixture of C2-C3 alcohols consists of ethanol, n-propanol and isopropanol;

[0017] 3) The process according to 1) or 2), wherein the water content of the mixture of C2-C3 alcohol and water is up to 50% by weight;

[0018] 4) The process according to any one of 1) to 3), wherein the naphtha is selected from the group consisting of reformed naphtha (RC3 and RC2), alkylated naphtha, isomerized naphtha, FCC naphtha and light cracked naphtha (LCN);

[0019] 5) The process according to any one of 1) to 3), wherein the naphtha has an aromatics-olefins / paraffins weight ratio of 0.5 to 4, preferably 0.6 to 3.8;

[0020] 6) The process according to any one of 1) to 5), wherein the recovery of the C2-C3 alcohol is higher than 95% by weight, preferably higher than 99% by weight;

[0021] 7) The process according to any one of 1) to 6), wherein the weight ratio of the extraction solvent to the feed water-alcohol mixture is 2:1 to 10:1, preferably 4:1 to 8:1;

[0022] 8) The process according to any one of 1) to 7), wherein the process is carried out at ambient pressure and ambient temperature;

[0023] 9) The process according to any one of 1) to 8), wherein the process is carried out in a liquid-liquid separator, wherein the extraction solvent is fed to the lower part and the mixture of C2-C3 alcohol and water is fed to the upper part, and wherein the extraction mixture of naphtha and C2-C3 alcohol is removed in the upper part and the separated water is removed in the lower part. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A simplified diagram illustrating the process of the present invention in a preferred embodiment is shown. DETAILED DESCRIPTION

[0025] The present invention is directed to the separation of a mixture of short-chain primary alcohols (mainly C2-C4 primary alcohols, preferably C2-C3 primary alcohols) containing a high water content (up to about 50% by weight) using an extractant selected from naphtha.

[0026] The present invention relates to a method for producing biofuel, which comprises or consists of the step of liquid-liquid extraction of a mixture of C2-C4 alcohols or a mixture of C2-C3 alcohols from a mixture of C2-C3 / C2-C4 alcohols and water (hereinafter also referred to as "water-alcohol mixture") using an extraction solvent, wherein the extraction solvent is naphtha.

[0027] For the purposes of the present invention, the term "comprising" refers to a process in which the characterization step consists of a liquid-liquid extraction, but it may also include other steps, such as pretreatment of the mixture of C2-C3 / C2-C4 alcohols in water, or the final addition of additives to the organic mixture forming the extract.

[0028] For the purposes of the present invention, the term "consisting of" refers to a process which does not comprise further post-treatment of the extract, ie, wherein the extract containing naphtha and C2-C3 / C2-C4 alcohols is used as biofuel.

[0029] Different types of mineral naphtha can be used as the extraction solvent.

[0030] In Italy, the physical and chemical properties of gasoline and naphtha are governed by regulations issued by CUNA (Commissione tecnica di UNificazione nell'Autoveicolo - Technical Commission for Unification in Motor Vehicles). The most important properties are anti-knock performance (expressed by octane number) and volatility. Because automotive gasoline contains hydrocarbons with 4 to 8 carbon atoms, its boiling point ranges from 35°C to 210°C. Top-grade gasoline is considered primary gasoline. Other refining processes, such as catalytic cracking, thermal and catalytic reforming, polymerization, alkylation, and isomerization, are then used to produce products such as reformed naphtha, alkylated naphtha, and isomerized naphtha.

[0031] The term "naphtha" as used in this patent application may be synonymous with "crude oil", "fuel oil" or "diesel" (semi-thick naphtha), "kerosene" or "diesel" (light naphtha with a cetane number of 40 to 75).

[0032] In the oil refining industry, various types of naphtha are usually blended in different percentages to obtain the desired products (e.g. RON95 gasoline) for use in the automotive sector.

[0033] The present invention allows obtaining an extract containing a mixture of alcohols as an octane booster, which can be used directly in a mixture of final products having better engine performance (e.g., octane rating) than the starting naphtha. Taking into account that the production capacity (kt / y) of the different naphthas is unique to each refinery, the process of the present invention is applicable to the following naphthas: reformed naphtha (RC3 and RC2), alkylated naphtha, isomerized naphtha, FCC naphtha, and light cracked naphtha (LCN).

[0034] Table 1 below shows the compositions of some naphthas that can be used as extraction solvents for C2-C3 / C2-C4 alcohols according to the present invention.

[0035] Table 1: Figure 1 The composition and molecular weight (MW) of the liquid-liquid extraction solvent are shown

[0036]

[0037] The mixture of C2-C3 alcohols includes ethanol, n-propanol and isopropanol as main components.

[0038] Examples of typical compositions of water-alcohol mixtures to be subjected to the process of the invention are shown below:

[0039]

[0040] A solvent selected from those shown in Table 1 was fed from below to a liquid-liquid extraction column ( Figure 1 In the column, the solvent is brought into contact with the water-C2-C3 / C2-C4 alcohol feed to be separated, which is introduced into the upper part of the separator. This device allows the aqueous phase ( Figure 1 The raffinate in the organic phase ( Figure 1 The organic phase, containing the solvent (naphtha), in which almost all of the alcohol in the mixture is dissolved, is removed from the upper part of the separator, while the aqueous phase, consisting of water with traces of alcohol and added solvent, is removed from the lower part. The organic phase forms a ready-to-market biofuel mixture.

[0041] The weight ratio of the solvent to the water-alcohol mixture is 2:1 to 10:1, preferably 4:1 to 8:1.

[0042] Tables 2 and 3 show the results of liquid-liquid extraction using two different solvent / water-alcohol mixture weight ratios (S / Mix ratios) according to the present invention. The data in Table 2 represent an S / Mix ratio of 4, while the data in Table 3 represent an S / Mix ratio of 8.

[0043] Table 2: When considering changes in naphtha composition, Figure 1 Performance of the flow diagram shown. The S / Mix ratio entering the extractor is 4 [kg / kg]. The residual water content (H2O) is calculated for the alcohol alone.

[0044]

[0045] Table 3: When considering the change of naphtha composition, Figure 1 Performance of the flow diagram shown. The S / Mix ratio entering the extractor is 8 [kg / kg]. The residual water content (H2O) is calculated for the alcohol alone.

[0046]

[0047] In Tables 2 and 3 above, the "Bio / fossil" ratio is the weight percent of propanol + ethanol in the extract relative to the weight percent of naphtha in the extract.

[0048] As can be seen from the data reported in the table, the best results are achieved with naphthas having an aromatics-olefins / paraffins weight ratio of 0.5 to 4, preferably 0.6 to 3.8. In this case, the process of the invention allows C2-C3 alcohol recoveries of greater than 95% by weight to be achieved. When using naphthas having an aromatics-olefins / paraffins ratio of less than 0.5, in particular less than 0.1, C2-C3 alcohol recoveries of greater than 95% by weight can only be achieved with an S / Mix ratio of greater than 7.

[0049] The method of the present invention can achieve several advantages.

[0050] The process of the invention, consisting of a single operation, has the advantage of facilitating the separation between the aqueous and organic phases at negligible energy costs, with the exchange of substances occurring exclusively in the liquid phase. Consequently, the subsequent, expensive step of regenerating the solvent itself is avoided, significantly simplifying the process flow, which in this case comprises a single extraction column.

Claims

1. A method for producing biofuel, comprising or consisting of the step of liquid-liquid extraction of a mixture of C2-C3 alcohols or a mixture of C2-C4 alcohols from a mixture of C2-C3 / C2-C4 alcohols and water using an extraction solvent, wherein the extraction solvent is naphtha.

2. The method of claim 1, wherein the mixture of C2-C3 alcohols consists of ethanol, n-propanol and isopropanol.

3. The process according to claim 1 or 2, wherein the water content in the mixture of C2-C3 alcohol and water is up to 50% by weight.

4. The process according to any one of claims 1 to 3, wherein the naphtha is selected from the group consisting of reformed naphtha (RC3 and RC2), alkylated naphtha, isomerized naphtha, FCC naphtha and light cracked naphtha (LCN).

5. The process according to any one of claims 1 to 3, wherein the naphtha has an aromatics-olefins / paraffins weight ratio of 0.5 to 4, preferably 0.6 to 3.

8.

6. The process according to any one of claims 1 to 5, wherein the recovery of the C2-C3 alcohol is higher than 95% by weight, preferably higher than 99% by weight.

7. The process according to any one of claims 1 to 6, wherein the weight ratio of the extraction solvent to the water-alcohol mixture feed is 2:1 to 10:1, preferably 4:1 to 8:

1.

8. The process according to any one of claims 1 to 7, wherein the process is carried out at ambient temperature and ambient pressure.

9. The process according to any one of claims 1 to 8, wherein the process is carried out in a liquid-liquid separator, wherein the extraction solvent is fed to the lower part and the mixture of C2-C3 / C2-C4 alcohol and water is fed to the upper part, and wherein the extraction mixture of naphtha and C2-C3 / C2-C4 alcohol is removed in the upper part and the separated water is removed in the lower part.

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