WO2009145691A1

WO2009145691A1 - Production of 1,2-propanediol

Info

Publication number: WO2009145691A1
Application number: PCT/SE2009/000260
Authority: WO
Inventors: Dalvi V. Pramod; Juha Lehtonen; Neil Cruise
Original assignee: Perstorp Specialty Chemicals AB
Current assignee: Perstorp Specialty Chemicals AB
Priority date: 2008-05-30
Filing date: 2009-05-20
Publication date: 2009-12-03
Anticipated expiration: 2010-11-30

Abstract

This invention relates to a process for producing 1,2 -propanediol by hydrogenolysis of glycerol in the presence of a supported metal catalyst and hydrogen. Glycerol having a water content of less than 3 % by weight and hydrogen are introduced into a reactor and reacted in the presence of a copper-based catalyst at a pressure of 20-150 bar and a temperature of 150-4000°C. Water formed in the reaction is removed from the reactor to keep the water content in the obtained reaction solution at less than 5 % by weight.

Description

PRODUCTION OF 1,2-PROPANEDIOL

This invention relates to a process for producing 1,2-propanediol by hydrogenolysis of glycerol, where water formed in the reaction is removed to keep a low water content in the obtained reaction solution.

In recent years fatty acid methyl esters derived from vegetable oils and animal fats has become important as diesel fuel extenders known as biodiesel. In the production of biodiesel almost 10 % crude glycerol is formed as a byproduct. The production costs for biodiesel are very high compared to diesel and therefore there is an interest in converting glycerol to consumer products with higher value than glycerol to increase the profitability of biodiesel production plants.

One profitable way to utilize glycerol from biodiesel production is conversion to propylene glycol, i.e.1,2-propanediol. 1,2-propanediol is a major commercial product that is used in a wide variety of applications such as cosmetic and personal healthcare products, unsaturated polyester resins, antifreezes, liquid detergents, pharmaceuticals, food, flavours and fragrances, paints and animal food.

A commercial used way to produce 1,2-propanediol is by hydration of propylene oxide derived from propylene by either the chlorohydrin process or the hydroperoxide process.

OH ? + OH

H- /⁰X

H

Propylene oxide 1,2-propanediol

This petroleum-based 1,2-propanediol production is however not environmental friendly. There are several ways to produce 1,2-propanediol from renewable feedstocks. One of those production routes is hydrogenolysis of glycerol.

Glycerol 1,2-propanediol

In the presence of metallic catalysts and hydrogen, glycerol can be hydrogenated to 1,2-propanediol, 1,3-propanediol or ethylene glycol.

There are several publications and "patent documents on the hydrogenation of glycerol to form 1,2-propanediol. For instance the US Patents 5,276,181 and 5,214,219 describe a method of hydrogenating glycerol using copper and zinc catalyst as well as sulfided ruthenium catalyst at a pressure of 150 bar. The published International application WO 2005/095536 describes a process for converting glycerol to propylene glycol where the glycerol-containing feed stock contains 50 % or less by weight water, preferably 5-15 % by weight water. Another published International application WO 2007/053705 also describes a process for converting glycerol to propylene glycol but through a gas phase reaction. The published International application WO 2007/099161 discloses a process for preparation of 1,2-propanediol, in which a glycerol-containing stream, in particular a stream obtained on an industrial scale in the preparation of biodiesel, is subjected to a hydrogenation at a pressure of 100-325 bar.

A common disadvantage in prior art is the use of high pressures which requires expensive equipment that increases the capital cost of the process. Another drawback is dilute solutions of glycerol. Typically solutions with 10-30 % by weight of glycerol has mainly been used which are then further diluted by water formed in the reaction. This reduces the average space-time yield of the reaction, which increases the energy consumption and in turn decreases the process profitability. There are some patents and applications, for instance WO 2007/099161, disclosing a process for producing 1,2-propanediol where water is removed from the glycerol before the reaction, but none of the 1,2-propanediol producing processes reported in literature involves any decreasing of the water content in the reaction solution during the reaction.

The object of the present invention is to provide a process for producing 1,2- propanediol by hydrogenolysis of glycerol with increased profitability and which process offers increased stability and prolonged life time of the catalyst.

The present invention relates to a process for producing 1,2-propanediol by hydrogenolysis of glycerol in the presence of a supported metal catalyst and hydrogen. Glycerol having a water content of less than 3 % by weight, such as 0.5 % by weight and hydrogen are introduced into a reactor and reacted in the presence of a copper-based catalyst at a pressure of 20-150 bar, preferably 30-100 bar and a temperature of 150-400°C, preferably 200-300⁰C, whereby water formed in the reaction is removed from the reactor to keep the water content in the obtained reaction solution at less than 5 % by weight, such as 1.5 % by weight.

In this way, by removing water from the reaction solution during the reaction, the object of the invention is achieved. The stoichiometric amount of water that is formed in the hydrogenolysis τeaction of glycerol to 1,2-propanediol is partly adsorbed on the catalyst surface resulting in inhibition of the main reaction. Water also seems to enhance decomposition of the catalyst structure resulting in decreased stability of the catalyst. By keeping the water content in the reaction solution low the catalyst can work efficiently for a longer period of time. This is a major advantage of the current process over the processes of prior art. An increased profitability for the process of invention is reached by a decreased energy demand due to relatively low pressures and more concentrated solutions.

In a preferred embodiment of the present invention the water formed in the reaction is removed from the reactor by a counter current flow of hydrogen. Most of the water is assumed to be formed in the upper end of the catalyst bed and is removed by hydrogen before it flows any further. The initial activity of the catalyst is impart increased by the water removal resulting in improved conversion and yield.

In a further embodiment of the invention the reactor contains two or more catalyst beds and the water is removed between the beds by a hydrogen gas flow passed through the reaction solution. In this set up hydrogen and liquid are flowing co- currently in the catalyst bed.

In another preferred embodiment of the present invention the water formed in the reaction is removed by a method combining the two embodiments mentioned above. In this embodiment the reactor contains two or more catalyst beds and the water is removed both by a counter current flow of hydrogen and between the beds by a hydrogen gas flow passed through the reaction solution.

In embodiments where the reactor contains two or more catalyst beds, the beds can be placed either in one or in separate τeactor vessels.

In a preferred embodiment of the invention hydrogen is separated from the water and re-circulated into the reactor. The separation can be carried out in a flash vessel. Recycling of hydrogen is advantageous while it increases the overall yield of the reaction.

In a further embodiment of the invention an inert gas, such as nitrogen, can be used together with or instead of the hydrogen as a stripping gas and be passed through the reaction solution to remove some of the water formed in the process.

High selectivity and conversion is obtained using a copper-based catalyst, where the copper content was 30-65 % or preferably 37-45 % by weight as CuO. Catalysts containing higher content of copper showed higher selectivity for 1,2-propanediol. The copper-based catalyst used in the process of the present invention may additionally comprise manganese and/or zinc. Catalysts suitable for use in the process of the present invention may also contain other metals from Group VIII and/or VIB of the periodic table. The catalyst is suitably supported on aluminium oxide bodies in the form of pellets. Other forms of catalyst appropriate for packed catalyst bed may also be used, e.g. tablets, extrudates or the like.

The obtained product 1,2-propanediol is purified by distillation or by evaporation, separating excess hydrogen, water, unreacted glycerol and by-products from the desired product. In a preferred embodiment of the invention unreacted glycerol is separated from the reaction product, purified and re-circulated into the reactor. Recycling of glycerol is advantageous while it increases the overall yield of the reaction.

Glycerol obtained as a by-product from a biodiesel production using a heterogeneous catalyst is advantageously used in embodiments of the present invention. This glycerol has a higher purity than glycerol obtained from the traditional technology to produce biodiesel with homogeneous base catalysts which requires a complicated separation of reaction products and a neutralization step. The feedstock of glycerol and hydrogen used in the process may however contain impurities. The minimum glycerol concentration of the glycerol feed stream is 95 % by weight and the minimum hydrogen concentration of the fresh hydrogen stream fed to the process is 80 mol-%.

Important parameters that influence the selectivity for 1,2-propanediol in the hydrogenolysis of glycerol are selection of catalyst, activation of the catalyst and reaction conditions. Selecting correct catalyst activation conditions is also important from another perspective. It was found that when activation was done under continuous hydrogen flow at 140 - 25O⁰C, preferably at 180 - 22O⁰C, the harmful effect of water was suppressed.

The process of the present invention is illustrated in figures 1-3. The invention is however not restricted to the embodiments described below, there are also other ways to carry out the invention without deviating from the scope of the appended claims. Only the main parts of the process are shown in these figures. The process also contains other equipments necessary to operate the process, e.g. pumps, compressors and heat exchangers.

Figure 1 schematically shows one embodiment of the present invention, where the reactor is divided into two beds and operated in co-current mode and water is stripped by hydrogen or hydrogen rich gas between the beds.

Figure 2 schematically shows another embodiment of the invention, where the reactor contains one catalyst bed and is operated in counter-current mode of liquid and gas flows.

Figure 3 schematically shows a third embodiment of the invention, where the reactor is divided into two beds and a counter-current operation mode is combined with water stripping by hydrogen between the two catalyst beds.

Below follows a more detailed description of the preferred embodiments of the process.

Figure 1

Liquid glycerol (2) is fed to the first catalyst bed (31) of the reactor (30) together with hydrogen rich gas (10) recycled from a gas/water separation unit (40). Optionally some fresh hydrogen may be fed to the first catalyst bed. The main part of fresh hydrogen (1) is fed to a stripping zone after the first catalyst bed. From this zone gaseous mixture (4) of hydrogen, water and inert material is removed from the reactor and the liquid effluent (11) from the first catalyst bed (31) is passed on to the next zone of the reactor, where it is mixed with recycled hydrogen rich gas (9) before entering the second catalyst bed (32).

The product mixture (3) of gas and liquid is taken out at the bottom of the reactor (30) and passed on to a separation unit (50), where hydrogen and other light gases are separated. The separation is carried out either by flashing, evaporation or distillation. The gas stream (13) from the separation unit (50) is either incinerated or is used as fuel gas (14). Optionally a part of this hydrogen rich steam (17) can be recycled in the process.

After the separation step the liquid product, 1,2-propanediol (12), is purified (60), usually by distillation. If there is some glycerol left in the product mixture, this glycerol may be separated (60) and recycled back (16) into the reactor (30).

The gaseous mixture (4) of hydrogen, water and inert material removed from the reactor after the first catalyst bed (31) is passed on to a separation unit (40), where water (5) is separated either by evaporation or by flashing and sent to e.g. waste water treatment. The main part of hydrogen rich gas (6) is fed into the reactor (7) and a smaller part (8) is removed from the process.

In case the reactor contains more than two catalyst beds there are water stripping zones after each catalyst bed, except the last one, and hydrogen is added prior to each catalyst bed. The catalyst beds can be placed in either one or several pressurized reaction vessels.

Figured

Liquid glycerol (2) is fed to the upper end of the catalyst bed (31) of the reactor (30) and fresh hydrogen gas (1) is fed to the bottom of the catalyst bed (31). Optionally some hydrogen rich gas may be recycled (7) from a gas/water separation unit (40).

The product mixture (3) of gas and liquid is taken out at the bottom of the reactor (30) and passed on to a separation unit (50), where hydrogen and other light gases are separated. The separation is carried out either by flashing, evaporation or distillation. The gas stream (13) from the separation unit (50) is either incinerated or is used as fuel gas (14). Optionally a hydrogen rich part of this steam (17) can be recycled in the process. After the separation step the liquid product, 1,2-propanediol (12), is purified (60), usually by distillation. If there is some glycerol left in the product mixture, this glycerol may be separated (60) and recycled back (16) into the reactor (30).

A gaseous mixture (18) of hydrogen, water and inert material from the top of the reactor (30) is passed on to a separation unit (40), where water (5) is separated either by evaporation or by flashing and sent to e.g. waste water treatment. The gas stream (6) from this separation unit (40) is either incinerated or is used as fuel gas (8). Optionally a part of this steam (7) is recycled back into the reactor (30).

In case the reactor contains more than one catalyst bed, hydrogen can be added prior to each catalyst bed, while still applying the counter-current flow principle of liquid and gas. The catalyst beds can be placed in either one or several pressurized reaction vessels.

Figure 3

Liquid glycerol (2) is fed to the first catalyst bed (31) of the reactor (30) and hydrogen rich gas (10) recycled from a gas/water separation unit (40) is fed to the bottom of the second catalyst bed (32). Optionally some fresh hydrogen may be fed to the bottom of the second catalyst bed (32).

The main part of fresh hydrogen (1) is fed to a stripping zone above the second catalyst bed (32). Liquid effluent (11) from the first catalyst bed (31) passes this zone on its way to the second catalyst bed (32) and gaseous mixture (4) of hydrogen, water and inert material is removed from the reactor via this zone.

Above the stripping zone is another zone where recycled hydrogen rich gas (9) is fed to the bottom of the first catalyst bed (31) and flows upward through the first catalyst bed (31).

A gaseous mixture (18) of hydrogen, water and inert material from the top of the reactor (30) is combined with the gaseous flow (4) from the stripping zone and passed on to a separation unit (40), where water (5) is separated either by evaporation or by flashing and sent to e.g. waste water treatment. The hydrogen rich gas stream (6) from this separation unit (40) is either incinerated or is used as fuel gas (8). Optionally a part of this steam (7) is recycled back to the reactor (30).

In case the reactor contains more than two catalyst beds there are a hydrogen feed zone and a water stripping zone after each catalyst bed, except the last one. The catalyst beds can be placed in either one or several pressurized reaction vessels.

Example 1

This example demonstrates the effect of removal of water formed in the reaction.

A catalyst in an amount of 10 % by weight was loaded into a 1 litre Parr type autoclave reactor. The catalyst used is a commercially available catalyst in the form of pellets comprising CuO, Al₂O₃ and MnO₂ in amounts of 56 %, 34 % and 10 % by weight. First the catalyst was activated by a continuous hydrogen flow at a temperature of 200⁰C for a period of 3 hours. There after glycerol was charged to the reactor, the temperature was increased to 210°C and the inlet hydrogen flow was controlled to maintain a constant hydrogen pressure of 44-49 bars in the reactor. The reaction was allowed to proceed for 16 hours under these conditions. Following the first experiment a second experiment was carried out in the same way but with an outlet gas flow from the reactor. A continuous hydrogen flow of 11 g/h was led through the reactor during the reaction, stripping water away from the reactor. In this way water was continuously removed from the reaction.

The results of the experiment, shown in table 1 below, indicate that higher conversion of glycerol and higher yield of 1,2-propanediol are obtained when water is continuously removed during the reaction.

Table 1 Effect of water removal during the reaction

Experiment Water removed Conversion (%) Yield (%) during reaction

First No 62.2 34.1

Second Yes 66.4 37.2

Example 2

This example demonstrates how the stability of the catalyst is affected by water formed in the reaction.

Each of the experiments carried out in example 1 was repeated three times in a row without changing the catalyst. First the experiment without water removal was repeated three times and then, after a catalyst reload, the experiment with continuous water removal was carried out and repeated three times. This was done in order to investigate the stability of the catalyst and to see whether the water removal had any effects on the stability of the catalyst. The reaction conditions were the same as for the experiments in example 1.

The results of the experiments, shown in table 2 below, indicate that the stability of the catalyst and thereby the life time of the catalyst is improved when water is continuously removed during the reaction. Table 2 Effect of water removal on catalyst life time

Claims

1. A process for producing 1,2-propanediol by hydrogenolysis of glycerol in the presence of a supported metal catalyst and hydrogen, characterized in that glycerol having a water content of less than 3 % by weight, such as 0.5 % by weight and hydrogen are introduced into a reactor and reacted in the presence of a copper-based catalyst at a pressure of 20-150 bar, preferably 30-100 bar and a temperature of 150-400⁰C, preferably 200-300⁰C, whereby water formed in the reaction is removed from the reactor to keep the water content in the obtained reaction solution at less than 5 % by weight, such as 1.5 % by weight.

2. A process according to claim 1, characterized in that the water formed in the reaction is removed from the reactor by a counter current flow of hydrogen.

3. A process according to claim 1, characterized in that theτeactor contains two or more catalyst beds and that water is removed between the beds by a hydrogen gas flow passed through the reaction solution.

4. A process according to claim 1, characterized in that the reactor contains two or more catalyst beds and water is removed both by a counter current flow of hydrogen and between the beds by a hydrogen gas flow passed through the reaction solution.

5. A process according to claim 2, 3 or 4, characterized in that hydrogen is separated from the water and re-circulated into the reactor.

6. A process according to anyone of the claims 1-5, characterized in that also an inert gas, such as nitrogen, is passed through the reaction solution.

7. A process according to anyone of the claims 1-6, characterized in that the catalyst additionally comprises manganese and/or zinc.

8. A process according to anyone of the claims 1-7, characterized in that the catalyst is supported on aluminium oxide bodies in form of tablets, pellets or the like.

9. A process according to anyone of the claims 1-8, characterized in that unreacted glycerol is separated from obtained reaction product, purified and re-circulated into the reactor.

10. A process according to anyone of the claims 1-9, characterized in that the 1,2- propanediol obtained is purified by distillation or evaporation.