WO2010136838A1

WO2010136838A1 - Method for processing crude glycerol waste streams

Info

Publication number: WO2010136838A1
Application number: PCT/IB2009/005775
Authority: WO
Inventors: Geert F. Versteeg; Piet Ijben; K. Klepacov; Sjaak Van Loo
Original assignee: The Gtbe Company Nv
Priority date: 2009-05-29
Filing date: 2009-05-29
Publication date: 2010-12-02
Also published as: EP2435546A1

Abstract

A method for processing crude glycerol waste streams including applying a concentrated acid to the waste stream, at pH 4, preferably in two stages, the first at pH about 7 & second between 0 and 7, preferably 4.

Description

METHOD FOR PROCESSING CRUDE GLYCEROL WASTE STREAMS

TECHNICAL FIELD OF THE INVENTON

The present invention relates to a method for processing crude glycerol waste streams.

More particularly, the present invention relates to a method for processing crude glycerol waste streams from biodiesel production plants.

BACKGROUND ART

Crude glycerol waste streams originating from biodiesel production have become a major concern in most industrialized countries. The European Union defined the program of replacing 2% of the consumption of liquid fuels by 2005 and 5.75% by 2010 with biofuels, where biodiesel is one of the key components.

Accordingly, the biodiesel production capacity is increasing rapidly. Based on the EU program only, it is expected that by 2010, 9 million tons of biodiesel and consequently 1.8 million tons of crude glycerol will be produced in Europe. This quantity should be seen against current - delicately balanced - supply/demand of 300,000 tons per year. Hence, it is expected that the economic processing of crude glycerol waste streams shall become more and more, important, and in particular the performance and effectiveness of such processes shall be of critical importance.

In general crude glycerol from transesterification process consists of glycerol (±50 wt%), methanol (±15 wt%), water (±7 wt%), catalyst, free fatty acids (FFA), methyl esters of higher fatty acids and further components. Though substantially different compositions can also be encountered. Depending on the catalyst (acid or caustic) used, the free fatty acids are present as free fatty acids or in the form of alkali soaps.

COWRRMATfON COPy In general crude glycerol from transesterification process or glycerides hydrolysis is generally not suitable for further utilization due to the mentioned impurities present in this glycerol. Crude glycerol can be purified to various grades. There are many processes for crude glycerol evaluation depending on the required glycerol purity.

Prior patent references on glycerol purification involve the distillation process (US 2,215,189; US 4,655,897; US 6,288,287), obtaining purified glycerol with the aid of ion-exchangers (CS 244 273; GB 690,008), ultrafiltration and nanofiltration using membranes (CZ 284 042; DE 43 25 786; US 5,527,974) of filter materials as alumina (US 4,990,695). Another way of glycerol purification utilize the chemical precipitation with different flocculants and separation of insoluble precipitates from glycerol solution (CZ 282 917; GB 650,438; US 2,381 ,055, US 2,487,611) and this process can be combined with additional purification like distillation or ion-exchange to reach a high glycerol purity grade.

For most glycerol recovery processes, like recovery by distillation, the present FFA (free fatty acids) and salts in crude glycerol are causing problems in downstream unit operations and have to be removed first.

A known technique (Kocsisova, T. and Cvengros, J., G-phase from methyl ester production - splitting and refining, Petroleum & Coal 48(2), 2006, 1-5) is the application of a diluted mineral acid, applied at a temperature of 60 ⁰C, to the crude glycerol to a pH between 4.5 and 2.5. The dilute mineral acid decomposes the alkali potassium soaps to free fatty acids (FFA). As a result, different phases are formed which are separated by filtration at 60 ⁰C (free fatty acids (FFA) and glycerol) or after cooling (salts).

The process of glycerol purification using hydrochloric acid and removing the formed salts from glycerol solution is described in the patent SK 284 543. The glycerol phase from transesterification process is acidulated with the acid, after the water and methanol are removed, the low alcohol is mixed with glycerol solution and the salts are separated from the solution because of the decreased solubility of salts present in the glycerol solution. Patent GB 647,884 describes the process of purifying alcoholic glycerol solution having a high content of soaps which includes the step of splitting the soaps and extracting the resultant free fatty acids and esters with selective solvent.

Another patent (GB 1 ,479,880) claims a process for purifying an aqueous solution of glycerol containing cationic impurities, which comprises adding methanol and sulphuric acid to the aqueous solution to precipitate the impurities as insoluble sulfates, removing the precipitate from the solution, removing the methanol and thereby forming a purified aqueous solution of glycerol.

It is an object of the invention to suggest a method for processing crude glycerol waste streams, which will assist in overcoming these problems.

SUMMARY OF INVENTON

According to the invention, a method for processing crude glycerol waste streams includes the step of applying a concentrated acid to a crude glycerol waste stream.

Also according to the invention, a method for processing crude glycerol waste streams includes the step of applying an acid to a crude glycerol waste streams in two stages, namely a first pH-stage and a second pH-stage.

Yet further according to the invention, a method for processing crude glycerol waste streams includes the step of applying a highly concentrated acid to a crude glycerol waste stream in two stages, namely a first pH-stage having a pH of about 7 and a second pH-stage having a pH between 2 and 6.

Yet further according to the invention, there is provided an arrangement for processing crude glycerol waste streams, which includes

(a) crude glycerol waste stream processing means for processing a crude glycerol waste stream;

(b) acid adding means for applying a highly concentrated acid to the crude glycerol waste stream in one or two stages, namely a first pH-stage having a pH of about 7 and a second pH-stage having a pH between 2 and 6, or applying the said acid to the crude glycerol waste stream directly to second pH-stage having a pH between 2 and 6. The crude glycerol waste streams may originate from biodiesel production plants.

The concentrated acid may be a highly concentrated acid, with a concentration in the order of 30 to 100 wt%. preferably above 50 wt%.

The two stages may have different pH-values.

The pH of the first pH-stage may be higher than the pH of the second pH-stage.

The pH of the first pH-stage may be about 7.

The pH of the second pH-stage may vary from 2 - 6, but preferably 4.

Salts and liquid phase may be formed in the first pH stage.

The salts formed in the first pH-stage may be separated from the liquid phase by means of gravity, in for example mixer-settler.

Methanol may be added in the first pH-stage to simplify the separation.

More acid may be added to decrease the pH of the first pH-stage to obtain the second pH-stage.

Alkaline soaps may decompose to free fatty acids (FFA) to form a first phase and do not mix with polar glycerol and water forming a second phase, thereby creating two separate liquid layers of phases in the second pH-stage.

Methanol may be added to the second pH-stage.

The separation may be simplified utilising a simple mixer/settler process.

The second phase may include besides glycerol also methanol and water.

The methanol and water may be separated from the glycerol in the second phase with the aid of well known standard separation processes, for example distillation.

The concentrated acid may include concentrated sulphuric acid.

The salt yield may be increased by lowering the water content of the crude glycerol waste stream.

DETAILED DESCRIPTON OF INVENTON A method for processing crude glycerol waste streams from biodiesel production plants, in accordance with the invention, includes the step of applying a highly concentrated acid to a crude glycerol waste stream in one or two stages, namely a first pH-stage having a pH of about 7 and a second pH-stage having a pH between 2 and 6, or applying the said acid to the crude glycerol waste stream directly to second pH-stage having a pH between 2 and 6.

In the case of a caustic catalyst (for example KOH) the application of acid (for example H₂SO₄) till a pH of around 7 results in the formation of the salt K₂SO₄, which is an easy way to separate solid.

Thereafter more acid is added till a pH varying from 2 till 6, preferably to pH of 4. Now, also the alkaline soaps decompose to free fatty acids which do not mix with the polar glycerol and water and create a separate liquid layer. The separation of the different phases at pH-value 2 - 6 is not as easy as the separation at pH = 7. By adding methanol, the separation is simplified and can be executed by a simple mixer/settler process (instead of a more complicated and more expensive filtration or centrifuge process). The desalinated glycerol phase consists besides glycerol mainly of methanol and water. Methanol and water can be separated from the glycerol with the aid of well known standard separation processes, like for example distillation.

Important parameters of the presented invention are;

(a) The acid is applied in one or two distinct stages, namely a. step 1: pH-value A (pH equals approximately 7); and b. step 2: pH-value B (pH range from 2 to 6) or the acid is applied directly to pH-value B;

(b) At the first pH-value the formed salts can easily be separated from the liquid phase by gravity, in for example a mixer-settler. If needed, the separation can be further simplified by the addition of methanol;

(c) At the second pH-value the separation of the different phases (FFA, glycerol and salts) can be simplified by the addition of methanol. The separation at a pH-value B can therefore also be executed with a simple separation process like for example a mixer-settler;

(d) A concentrated acid, with a concentration in the order of 30 to 100 wt%, preferably above 50 wt%, in stead of a diluted acid, is applied, for increasing the salt yield.

(e) Glycerol treated with the process according to present invention can be used in acid catalyzed etherification reaction as a starting material for alkyl glycerol ethers production for example glycerol tert-butyl ethers, glycerol ethyl ethers etc., hence if using for etherification reaction, it does not need to be neutralized and can be used for further use directly at the pH-value B (not additional salts formed via neutralization).

EXAMPLES

Concentrated sulphuric acid (Example 1 and 2) or 40 wt% sulphuric acid (Example 3 and 4) respectively are applied to two different crude glycerol waste streams.

One glycerol waste stream contains less water and free fatty acids (FFA). At pH = 7.0 (first pH-value) both tables show that only the salt potassium sulphate is formed. After removing the formed salts more sulphuric acid is added till the second pH-value (pH = 4.0) besides salts also free fatty acids are formed. Both tables also show that by adding sulphuric acid directly till pH = 4.0, both potassium sulphate and free fatty acids are formed. The highest yield of salt formation is achieved by applying concentrated acid.

In case of diluted acid the salt apparently dissolves partly in the present water. The pH-value influences the ease of phase separation. At pH = 4.0 the different phases cannot be separated by gravity. However, at pH = 7.0 the different phases can be separated by gravity. The results are based on the calculation using amount of the dry salt amount after washing with methanol as a reference value to calculate the amount of glycerol phase loss.

Example 1: Application of concentrated sulphuric acid to crude glycerol

Example 2: Application of concentrated sulphuric acid to crude glycerol (with lower FFA and water content)

Example 4: Application of 40 wt% sulphuric acid to crude glycerol (with lower FFA and water content)

Claims

CLAIMS:

1. A method for processing crude glycerol waste streams characterised in that it includes the step of applying a concentrated acid to the waste stream;

2. A method according to claim 1 characterised in that the pH value, after acid application, is between 0 and 7, preferably 4;

3. A method according to claim 1 characterised in that the pH value, after acid application, is between 2 and 6, preferably 4;

4. A method according to claim 1 characterised in that the acid is applied in two stages, namely a first pH stage and a second pH stage;

5. A method according to claim 4 characterised in that the first pH stage has a pH of about 7 and the second pH stage has a pH of between 0 and 7, preferably 4;

6. A method according to claim 4 characterised in that the first pH stage has a pH of about 7 and the second pH stage has a pH of between 2 and 6, preferably 4;

7. A method according to any of the above claims characterised in that the salt yield can be increased by applying concentrated acid with a concentration in the order of 30 to 100 wt%, preferably above 50 wt%, instead of diluted acid;

8. A method according to any of the above claims characterised in that the salt yield can be increased by lowering the water content of the crude glycerol waste stream;

9. A method according to any of the above claims characterised in that the glycerol obtained from the crude glycerol waste stream via the process according to the present invention can be used for alkyl glycerol ethers production (for example glycerol ethyl ethers, glycerol terf-butyl ethers) without additional neutralization;

10. A method according to any of the above claims characterised in that the crude glycerol streams originate from biodiesel production plant(s);

11. A method according to any of the above claims characterised in that the concentrated acid is highly concentrated acid, preferably sulphuric acid with a concentration in the order of 30 to 100 wt%, preferably above 50 wt%;

12. A method according to any of the above claims characterised in that salts formed in the first pH stage are separated from the liquid phase by means of gravity, preferably a mixer-settler;

13. A method according to any of the above mentioned claims characterised by adding methanol to the first stage in order to simplify the separation and/or to the second pH stage;

14. A method according to any of the above claims characterised in that more acid is added to decrease the pH of the first pH stage to obtain the second pH stage;

15. A method according to any of the above claims characterised in that alkaline soaps decompose to free fatty acids (FFA) to form a first phase which does not mix with polar glycerol and water forming a second phase, thereby creating two separate liquid layers of phases in the second pH stage;

16. Apparatus for carrying out the process of any of the above claims characterised in a crude glycerol waste stream processing means, means for adding a concentrated acid to the waste stream in one or two stages, namely a first pH stage of about 7 and a second pH stage of pH about 0 to 7, or means for applying concentrated acid to the waste stream directly to the second pH stage having a pH of about 0 to 7.

17. Apparatus for carrying out the process of any of the above claims characterised in a crude glycerol waste stream processing means, means for adding a concentrated acid to the waste stream in one or two stages, namely a first pH stage of about 7 and a second pH stage of pH about 0 to 7, or means for applying concentrated acid to the waste stream directly to the second pH stage having a pH of about 2 to 6.