Process for purifying biodiesel

Abstract

The present invention describes a process for purifying biodiesel without using a filter aid, in which purification of the biodiesel takes place by a sequence of washing operations after the reaction section, with stirring that is sufficiently vigorous to assist in the transformation of the molecules of esterified steryl glycosides, in order to convert them to a chemical form that can be removed by the process.

Claims

1. A process for purifying biodiesel, comprising the following steps: a) operations of washing of a stream of biodiesel followed by decanting; and b) filtration of a light phase resulting from a decanting operation, wherein the filtration is carried out in the absence of filter aids; and wherein a first washing operation uses dilute glycerol, and has a residence time from 2 to 5 minutes.

2. The process for purifying biodiesel according to claim 1, further comprising addition of a stream of dilute acid to the stream of biodiesel.

3. The process for purifying biodiesel according to claim 2, wherein dilute hydrochloric acid is used in the stream of dilute acid.

4. The process for purifying biodiesel according to claim 1, wherein the washing operation is carried out with stirring above 700 rpm and at a temperature in the range from 50 C. to 60 C.

5. The process for purifying biodiesel according to claim 4, wherein the washing operation is carried out with stirring above 800 rpm.

6. The process for purifying biodiesel according to claim 2, wherein the step of addition of acid is carried out before a first washing operation only.

7. The process for purifying biodiesel according to claim 1, wherein the dilute glycerol is produced in the actual plant of the biodiesel production process.

8. The process for purifying biodiesel according to claim 1 characterized in that a light phase resulting from a decanting operations is cooled to a temperature in the range between 20 C. and 40 C. before it enters a further washing operation.

9. The process for purifying biodiesel according to claim 1, wherein a washing operation includes mixing an incoming stream with fresh water in an amount in the range between 2% and 6% of the weight of the light stream, and for a residence time in the range between 15 and 25 minutes.

10. The process for purifying biodiesel according to claim 1, wherein, before filtration of the light phase resulting from decanting, the light phase undergoes a process of drying and subsequent cooling to a temperature in the range from 15 C. to 25 C., and remains in this condition for a residence time between 3 and 14 hours.

11. The process for purifying biodiesel according to claim 1, wherein the filtration is carried out after the decanting operation and before any further additives are added to the light phase resulting from the decanting operation.

12. A process for purifying biodiesel, comprising the following steps: a) addition of a stream of dilute acid to a stream of biodiesel; b) an operation of washing of the stream of biodiesel followed by a first decanting operation, and further taking the light phase resulting from the first decanting operation and performing further washing and decanting operations; c) collecting dense phases resulting from the decanting operations, and recycling at least one dense phase to one of the washing operations; d) drying of the light phase resulting a final decanting operation; e) cooling of the light phase resulting from the drying step; f) filtration of the light phase resulting from the cooling step, in the absence of filter aids.

13. The process for purifying biodiesel according to claim 12, further comprising incorporation of additives to the product stream generated in the filtration.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The detailed description presented hereunder refers to the appended figures, in which:

(2) FIG. 1 shows a proposed configuration for a, called Process A.

(3) FIG. 2 shows another proposed configuration for a process, called Process B.

(4) FIG. 3 shows an assessment of the configuration of Process A, as presented in Example 1 of the disclosure.

(5) FIG. 4 shows an assessment of the configuration of Process B, as presented in Example 2 of the disclosure.

DETAILED DESCRIPTION OF THE INVENTION

(6) The present disclosure relates to a process for purifying biodiesel. It can use a sequence of washing operations after the reaction section, including cold washing operations and, in one of the embodiments, it also uses washing with a stream of glycerol, which may be formed during the process. The washed product formed is then decanted. Stirring is preferably sufficiently intensive (above 700 rpm, preferably above 800 rpm) to assist in the transformation of the molecules of esterified steryl glycosides, in order to convert them to a chemical form that can be removed by the process.

(7) In the context of the present disclosure, feed means the stream produced in a reaction section of the overall plant. The feed (so-called unspecified biodiesel) consists of a mixture of compounds rich in esters, preferably methyl esters, obtained from oils of vegetable origin (preferably soya oil and palm oil), and also contains various other substances in small amounts.

(8) In general outline, the process for purifying biodiesel described by the present disclosure comprises the following steps:

(9) a) addition of dilute acid 1 to a stream of biodiesel 2 (i.e. unspecified biodiesel);

(10) b) operations of washing of the stream of biodiesel 2, as exemplified by operations 3a and 3b and 3c of FIG. 1, or operations 3d and 3e of FIG. 2, followed by decanting as exemplified by operations 4a and 4b and 4c of FIG. 1, or 4d and 4e of FIG. 2;

(11) c) separation of the dense phase 5 resulting from decanting 4a, 4b, 4c, 4d, 4e;

(12) d) drying 8 of the light phase resulting from decanting 4c, 4e;

(13) e) cooling 9 of the light phase;

(14) f) filtration 10 of the light phase;

(15) g) optional incorporation of additives 11 in the stream generated in filtration 10 to produce the specified biodiesel 12,

(16) where the dense phase 5 generated after decanting from some steps, exemplified by operations 4b, 4c, 4e in FIGS. 1 and 2, is recycled to a washing step, exemplified by operations 3a, 3b, 3d in FIGS. 1 and 2, and filtration 10 is carried out in the absence of filter aids.

(17) In a first example variant of the process (Process A, which is shown in FIG. 1), a stream of (unspecified) biodiesel 2 to be purified is received from the reaction section of a plant and enters a washing vessel 3a. As discussed below, washing vessel 3a, is able to receive the dense phase 5 generated after decanting 4b downstream of a further washing vessel 3b.

(18) In this first washing step performed in first washing vessel 3a, a stream containing dilute acid 1, preferably hydrochloric acid, is added to neutralize any residual catalyst arising from the upstream biodiesel production process, and to assist in the purification of the biodiesel produced. In some embodiments, the residence time in this washing vessel 3a can be from 5 to 15 minutes. In some embodiments, a temperature from 50 C. to 60 C. can be desirable. In some embodiments, stirring above 700 rpm can be desirable, more preferably above 800 rpm.

(19) After the first washing step in washing vessel 3a, the mixture proceeds to a (first) decanter 4a, where two new phases are separated from the incoming mixture. The light (i.e. less denser) phase of the two phases produced by the first decanter 4a proceeds to a (second) washing vessel 3b. The heavy (i.e. denser) phase produced by the first decanter 4a forms a stream 5 that leaves the process.

(20) In this example, the second washing vessel 3b also receives the heavy (i.e. denser) phase generated after a third decanting step performed in third decanting vessel 4c downstream of a third washing vessel 3c, as discussed below. A second washing step is performed in the second washing vessel 3b. In some embodiments, it is desirable for the conditions in the second washing vessel 3b to be identical to those applied in washing vessel 3a, only differing by the absence of addition of acid and the use of washing water.

(21) After washing vessel 3b, the mixture proceeds to a new, i.e. second, decanting vessel 4b. The second decanting vessel 4b splits the mixture into new light (i.e. less dense) and heavy (i.e. more dense) phases. The new light phase leaves from the second decanting vessel 4b, and proceeds to third washing vessel 3c. In some embodiments, it is desirable for this stream to be cooled to a temperature in the range between 20 C. and 40 C. before it enters the third washing vessel 3c. As mentioned above, the heavy phase from the second decanting vessel 4b is recycled upstream, and provided as an input to the first washing vessel 3a.

(22) In a third washing step performed in washing vessel 3c, the in coming light stream is mixed with an amount of fresh water 6. In some embodiments, the amount of water is in the range between 2% and 6% of the weight of the light stream. In some embodiments intensive stirring (above 700 rpm, more preferably above 800 rpm) is applied. In some embodiments, residence time in the vessel is in range between 15 and 25 minutes.

(23) On leaving the washing vessel 3c, the mixture proceeds to a third decanting step in a third decanter 4c. Once again, the decanter 4c produces two phases, a light (i.e. less dense) phase and a heavy (i.e. more dense) phase. As mentioned above receives the heavy phase generated by the third decanting step in third decanter 4c is recycled upstream to be an input to the second washing vessel 3b.

(24) The light phase undergoes a process of drying in a dryer 8 and then a step of cooling in a cooler 9. In some embodiments the cooling is to a temperature in the range from 15 C. to 25 C., and the contents of the cooler 9 may remain in the vessel in this condition for a residence time between 3 and 14 hours, preferably between 3 and 6 hours.

(25) After the cooling step, the stream proceeds to a filtration step performed in a filtration device 10, which is implement without the use of a filter aid (e.g. such as diatomaceous earth). As explained above in the purification of biodiesel the removal of water soluble contaminants is traditionally accomplished by water-washing the biodiesel. Another process of biodiesel purification traditionally involves the use of an adsorbent filter-air such as magnesium silicate, and in the case of polar impurities it is usual to use a diatomaceous filter, but such filter aids are not used in the process of the present disclosure. The output of the filtration step is a product that meets the specifications for biodiesel (so-called specified biodiesel) 12 usually after incorporation of additives 11, according to the Brazilian regulatory authority (Agncia Nacional de Petrleo, Gs Natural e BiocombustveisNational Agency for Petroleum, Natural Gas and BiofuelsANP).

(26) In a second example variant of the process (Process B, which is shown in FIG. 2), a stream 7 containing glycerol and water is also supplied for the first washing step performed in a first washing vessel 3d. Also supplied is a heavy (i.e. denser) phase generated after a second decanting step in a second decanter 4e downstream of second washing step performed in a second washing vessel 3e, which is discussed further below. The stream of glycerol 7 may be obtained by the union of the heavy (i.e. denser) phase obtained in the reaction section of the overall plant with the dense phase generated at the first washing step performed in first washing vessel 4d (discussed in more detail below), which can be rectified to remove the alcohol used in the production of biodiesel, and can be recycled to transesterification reactors, for example.

(27) Therefore the light phase 2 received from the reaction section enters the first washing vessel 3d, where it will be able to receive the heavy (i.e. denser) phase generated after the second decanting step performed the second decanting vessel 4e downstream of the second washing step performed in the second washing vessel 3e, and receive the glycerol stream 7. In some embodiments, the glycerol stream 7 is preferably in the form of 50 wt % of a bottom stream of a methanol rectification tower, of a conventional biodiesel production. The methanol rectification tower is used in conventional biodiesel production to recover the glycerine and the excess of methanol used in the transesterification reaction.

(28) In this first washing step performed in first washing vessel 3d, a stream containing dilute acid 1, preferably hydrochloric acid, is added to neutralize the residual catalyst arising from the biodiesel production process and to assist in purification of the resultant biodiesel. In some embodiments, the residence time in the first washing vessel 3d is preferably from 2 to 5 minutes. In some embodiments, a temperature in the range between 50 C. and 60 C. is desirable. In some embodiments, stirring above 700 rpm is desirable, more preferably above 800 rpm.

(29) After the first washing step performed in the first washing vessel 3d, the mixture proceeds to the first decanting step performed in first decanting vessel 4d. The first decanting vessel 4d produces two phases as output streams, a light (i.e. less dense) phase and heavy (i.e. more dense) phase. The heavy phase forms a stream 5 that leaves the process.

(30) The light phase produced in the first decanting step leaves the first decanting vessel 4d and proceeds to a second washing vessel 3e. In some embodiments, for a second washing step performed in second washing vessel 3e, it is desirable for the conditions to be identical to those applied in the first washing vessel 3d, only differing by the absence of addition of acid. In this second washing step performed in the second washing vessel 3e, the light phase stream received from the first decanting vessel 4d is mixed with an amount of fresh water 6. In some embodiments the amount of water is in the range between 2% and 6% of the weight of the light phase stream. In some embodiments it is desirable to have with intensive stirring (above 700 rpm, more preferably above 800 rpm). In some embodiments it is desirable for the residence time in the second washing vessel 3e to be in the range from 2 to 5 minutes.

(31) On leaving the second washing vessel 3e, the mixture proceeds to a second decanting step in in second decanting vessel 4e. In the second decanting vessel 4e separation of the mixture into two phases is performed. As mentioned above, the heavy (i.e. denser) phase is recycled upstream and used as an input to the first washing vessel 3d.

(32) The light (i.e. less dense) phase obtained from the second decanting vessel 4e undergoes a process of drying in a dryer 8 and cooling in a cooler 9. In some embodiments the cooling is to a temperature in the range from 15 C. to 25 C. In some embodiments, the mixture remains in the cooling vessel 9 for a residence time between 3 and 14 hours, preferably between 3 and 6 hours. From the cooler 9, the mixture proceeds to a filtration step at a filter 10. The filtration step is preferably performed without the use of filter aid. The resulting product, output from the filter 10 meets the specifications for biodiesel 12, usually after incorporation of additives 11, according to the Brazilian regulatory authority (ANP).

(33) In this second example variant, an amount of water is used that is less than that used in the technology from Crown Technologies. Also, the stream 7 with dilute glycerol, when produced in the plant itself and added to the process, brings economies in the amount of water used and minimizes the number of process steps.

(34) In a further refining section (i.e. steps carried out after drying of the biodiesel, i.e. after the cooling and filtration steps, and after the additives are added), the stream of dry biodiesel can be cooled to a temperature in the range from 15 C. to 25 C., as discussed above. The stream can remain in a vessel in this condition for a residence time between 3 and 14 hours, preferably between 3 and 6 hours. From there it can proceed to a pre-filtration step, preferably in bag filters. After this pre-filtration, the stream of biodiesel may be cooled again to a temperature in the range from 15 C. to 25 C. The stream can remain in a vessel in this condition for a residence time between 4 and 14 hours. From there it may proceed to filtration on a filter of the high-flow pleated polypropylene cartridge type (with absolute degree of filtration of 10 m). That can be followed by filtration on a high-efficiency cartridge filter consisting of cellulose and inorganic filter aids (with absolute degree of filtration of 1 m, in some embodiments). Alternatively, the stream of dry biodiesel may only be cooled to a temperature in the range between 25 C. and 50 C., and then proceed to a step of pre-filtration in bag filters and to a filtration step in a filter of the high-flow pleated polypropylene cartridge type, followed by filtration in a high-efficiency cartridge filter consisting of cellulose and inorganic filter aids.

(35) In plants that use the technology from Crown Technologies, it is more feasible to implement Process A, without the need to recycle the glycerol, since the glycerols generated in these units already meet the specification for light glycerol, and therefore, despite being a product with commercial value, it may not be effective for removing impurities from the stream tested.

(36) The description that follows is based on preferred embodiments of the invention. As will be obvious to person skilled in the art, the invention is not limited to these particular embodiments.

EXAMPLES

(37) To illustrate the greater efficiency of the process disclosed here, sequential batch reactions were carried out using recycling of the dense phases to simulate countercurrent washing and, when applicable, partial recycling of the dilute glycerol.

Example 1Process A

(38) The process configuration assessed consists of a purification section for biodiesel derived from soya oil, containing three steps of water washing in countercurrent. The oil used for producing the biodiesel was supplied by the Usina de Biodiesel de Montes Claros [Montes Claros Biodiesel Plant], after undergoing the industrial-scale pretreatment steps. In this configuration, the dense phase resulting from second decanting vessel 4b is used in the first washing step performed in vessel 3a and the dense phase resulting from the third decanting vessel 4c is used in the second washing step performed in washing vessel 3b, whereas only pure water 6 is employed in the third washing step performed in vessel 3c. In the first washing vessel 3a, the temperature is in the range from 50 C. to 60 C., with continuous, intensive stirring (above 800 rpm) throughout this step, with a residence time between 5 and 15 minutes. In the second washing vessel 3b, the conditions of the first washing vessel are repeated, apart from absence of the acid. The third washing vessel 3c uses 4% of water relative to the weight of light phase resulting from second decanting vessel 4b, and intensive stirring (above 800 rpm) continues for a residence time between 15 and 25 minutes, at a temperature in the range from 20 C. to 40 C. The light stream generated in the third decanting vessel 4c proceeds to a step of drying 8 and cooling 9, remaining at a temperature in the range between 15 C. and 25 C. for 5 hours before undergoing the filtration step 10 in the absence of a filter aid.

(39) In all, four sequential batches were carried out, using recycling of the dense phases to simulate countercurrent washing. The results are presented in FIG. 3. It can be seen that the values of contamination of all the products are below what is stipulated in the specification E (maximum impurities of 24 mg/kg of biodiesel, represented by the dotted line in the diagram). Furthermore, on progressing to equilibrium of the composition of the recycling streams, the contamination values decrease.

Example 2Process B

(40) The process configuration assessed consists of a purification section for biodiesel derived from food-grade soya oil, containing two steps of water washing in countercurrent. In this configuration, dilute glycerol 7, received from the bottom of a methanol tower used in the production of the biodiesel, is mixed with the aqueous phase resulting from second decanting vessel 4e, and the mixture is used in the first washing step performed in washing vessel 3d, whereas only pure water 6 is used in the second washing step performed in washing vessel 3e. In the first washing vessel 3d, the temperature is in the range from 50 C. to 60 C., with continuous, intensive stirring (above 800 rpm) throughout this step, which takes between 2 and 5 min. The second washing step performed in the second washing vessel 3e uses 3% of water relative to the weight of light phase resulting from washing 3d, and intensive stirring (above 800 rpm) continues for a time of between 2 and 5 minutes, and with a temperature in the range from 50 C. to 60 C. The light stream generated in the second decanting vessel 4e proceeds to a step of drying 8 and cooling 9, remaining at a temperature between 15 C. and 25 C. for 5 hours before being filtered without using a filter aid.

(41) In all, eight sequential batches were carried out, using recycling of the dense phases to simulate countercurrent washing and partial recycling of the dilute glycerol. The first batch used only water in first washing vessel 3d, as the first streams of dilute glycerol 7 and dense phase 5 had not yet been generated. Besides this, it was considered to be unnecessary to determine the total contamination of the products from batches 3 and 4, since these batches had not reached equilibrium. The results starting from the fifth and up to the eighth batches, together with the second as reference of the initial, non-equilibrium state, are presented in FIG. 4. All the products from this sequence had contamination values below the limit E (maximum impurities of 24 mg/kg of biodiesel, represented by the dotted line in the diagram) required by the specification of the Brazilian regulatory authority (ANP) for B100, confirming that the process configuration, in the conditions employed, reduces the concentration of impurities to acceptable values. Despite the small variations in the contamination result, the mean value and standard deviation were 10.5 mg/kg and 3.2 mg/kg respectively, which means it is safe to state that the concentration of impurities meets the requirement (max. 24 mg/kg).

(42) The description made thus far of the subject matter of the present invention must only be regarded as a possible embodiment or possible embodiments, and any particular features introduced therein are only to be understood as something that has been written to facilitate understanding. Modification of the above-described apparatuses and methods, combinations between different variations as practicable, and variations of aspects of the invention that are obvious to those of skill in the art are intended to be within the spirit and scope of the claims.