Field of the invention

[0001] The present invention relates to a continuous flow process for the preparation of sugar esters. The invention further relates to a system to prepare sugar esters.

Background art

[0002] Sugar esters are an interesting class of surfactants with wide application for example in pharmaceuticals, cosmetics, polymer synthesis, latex, paints, inks, drilling fluids, detergents and food. By varying the nature of the sugar and the length of the fatty chain, sugar esters have a broad ranging hydrophilic-lipophilic balance and thus have a wide range of functional properties.

[0003] Sugar esters can be synthesized by esterification of sugars (or sugar alcohols) with acids. The synthesis of sugar esters can be carried out either chemically or enzymatically.

[0004] The chemical synthesis of sugar esters has a number of drawbacks. The synthesis has for example a low selectivity and results in a mixture of sugar esters with different degrees of esterification. Furthermore, the high temperature necessary for such chemical reaction may cause discoloration of the final products.

[0005] Enzymatic synthesis of sugar esters has the advantage of being performed under mild conditions. Furthermore, the enzymatic synthesis of sugar esters has the advantage to be more specific than the chemical synthesis of sugar esters. A major problem of enzymatic synthesis of sugar esters is however the low solubility of the sugars in organic solvents. Enzymatic synthesis therefore requires vigorous stirring to reduce the solubility problems and limits the synthesis to batch processes. Furthermore, as the esterification reaction is a reversible reaction, the reaction products such as water should preferentially be removed to avoid hydrolysis.

[0006] Therefore, there is a need for an improved process for the preparation of sugar esters.

Summary of the invention

[0007] It is an object of the present invention to provide a process for the preparation of one or more sugar esters avoiding the drawbacks of the prior art.

[0008] It is another object of the present invention to provide a process to selectively prepare a particular sugar ester.

[0009] It is another object of the present invention to provide a continuous flow process for the preparation of one or more sugar esters.

[0010] It is a further object of the present invention to provide a process for the preparation of one or more sugar esters having a high yield.

[0011] It is still a further object of the present invention to provide a process for the preparation of one or more sugar esters allowing in-line purification.

[0012] It is still a further object of the present invention to provide a process for the preparation of one or more sugar esters requiring a limited reaction time. [0013] It is a further object of the present invention to provide a process for the preparation of one or more sugar esters that is not suffering from the presence of water liberated in the esterification reaction.

[0014] It is also an object of the present invention to provide a process for the preparation of one or more sugar esters allowing scale-up.

[0015] It is another object of the present invention to provide a system for the continuous production of sugar esters.

[0016] According to a first aspect of the present invention, a continuous flow process for the preparation of one or more sugar esters is provided. The process comprises the steps of

providing at least one inlet flow comprising a carbohydrate, a carboxylic acid and an organic solvent;

introducing the at least one inlet flow to flow through a reaction zone comprising at least one enzyme to provide a product flow comprising one or more sugar esters;

(re)introducing a part of the product flow comprising one or more sugar esters obtainable from the reaction zone to flow through the reaction zone.

[0017] The product flow obtainable from the reaction zone comprises one or more sugar esters as reaction product. In preferred processes according to the present invention, the product flow comprises or consists of a particular sugar ester.

[0018] The process according to the present invention allow to selectively prepare a particular sugar ester, for example a particular sugar ester with a specific degree of esterification.

[0019] As mentioned above, the solubility of the carbohydrate in an organic solvent is a major problem in the enzymatic synthesis of sugar esters. Carbohydrates are soluble in water but have no or a limited solubility in an organic solvent. Carboxylic acids on the other hand are soluble in an organic solvent but have no or a limited solubility in water. Surprisingly, it has been found that by introducing or reintroducing a part of the product flow (i.e. the flow comprising one or more sugar esters) to flow through the reaction zone, the solubility problems are drastically reduced. By introducing or reintroducing a part of the product flow sugar ester can be synthesized in a continuous flow process.

[0020] Preferably, between 2 vol% and 70 vol% of the product flow obtainable from the reaction zone is (re)introduced to the reaction zone, i.e. to flow through the reaction zone. More preferably, between 5 vol% and 70 vol%, between 20 vol% and 70 vol%, between 20 vol% and 60 vol%, for example 30 vol%, 40 vol%, 50 vol% or 60 vol% of the product flow obtainable from the reaction zone is (re)introduced to flow through the reaction zone.

[0021] The term“(re)introduce” incorporates both“introducing” and“reintroducing”, whereby the term“introducing a flow” refers to leading or bringing in a flow for the first time while the term “reintroducing a flow” refers to leading or binging in a flow again. In particular, the wording “(re)introducing a part of the product flow obtainable from the reaction zone to flow through the reaction zone” refers to introducing a part of the product flow obtainable from the reaction zone to flow through the reaction zone for the first time or to introducing a part of the product flow obtainable from the reaction zone to flow again through the reaction zone.

[0022] A reaction zone comprises at least one enzyme, preferably at least one immobilized enzyme. It can be preferred that the reaction zone comprises more than one enzyme, for example more than one immobilized enzyme.

[0023] The reaction zone is preferably situated in a reaction chamber, for example in a flow channel or a vessel. It is clear that a reaction chamber, such as a flow channel or a vessel may comprise a plurality of reaction zones.

[0024] Furthermore, a system for the preparation of a sugar ester according to the present invention may comprise one reaction chamber or a plurality of reaction chambers, each reaction chamber comprising one or a plurality of reaction zones.

[0025] The process according to the present invention comprises the introduction of at least one inlet flow to the reaction zone comprising at least one enzyme to flow through this reaction zone. In preferred processes, one inlet flow is introduced to the reaction zone to flow through the reaction zone. Alternatively, more than one inlet flow, for example two inlet flows or three inlet flows are introduced to the reaction zone to flow through the reaction zone.

[0026] The inlet flow or inlet flows is/are for example introduced to the reaction zone by pumping the inlet flow or inlet flows to a reaction chamber and by pumping the inlet flow or inlet flows through a reaction zone of the reaction chamber. Preferably, the inlet flow or inlet flows is/are continuously introduced to the reaction chamber, for example continuously pumped to the reaction chamber to flow through the reaction zone.

[0027] A part of the product flow (i.e. the flow comprising one or more sugar ester) is for example (re)introduced to the reaction zone by pumping a part of the product flow to the reaction chamber and by pumping this part of the product flow through the reaction zone. Preferably, the product flow is continuously (re)introduced, for example continuously pumped to the reaction chamber to flow through the reaction zone.

[0028] In preferred embodiments an inlet flow comprising a carbohydrate, a carboxylic acid and an organic solvent is introduced to the reaction chamber to flow through the reaction zone. The inlet flow is for example obtained by mixing a first flow of carbohydrate in an organic solvent and a second flow of a carboxylic acid in an organic solvent for example by a static mixer.

[0029] Preferably, the product flow obtainable from the reaction zone is divided in a first flow part and a second flow part, for example by means of a flow splitter. The first flow part of the product flow is preferably (re)introduced to flow through the reaction zone whereas the second flow part of the product flow is preferably delivered to an outlet channel. The first flow part comprises for example between 2 vol% and 70 vol% of the product flow, for example between 5 vol% and 70 vol% of the product flow. In preferred examples the first flow part comprises between 20 vol% and 60 vol%, for example 40 vol%, 50 vol% or 60 vol% of the product flow.

[0030] Preferred enzymes comprise hydrolases, in particular hydrolases suitable to synthesize esters as for example lipases, proteases, esterases, glycosidases, cutinases and amidases. [0031] Preferably, the enzymes are immobilized. Any type of immobilized enzymes known in the art can be considered. Examples comprise enzymes immobilized by adsorption on a carrier material, enzymes covalently bond to a carrier material, enzymes entrapped in a carrier. The carrier material may comprise a polymer support such as polyacrylic, polystyrene, polyacrylamide or nylon based material. The carrier material may also comprise inorganic material as for example carbon based material, silica based material, zirconia based material or alumina based material.

[0032] Particularly preferred examples comprise enzymes immobilized on beads, for example polymeric beads such as (poly)acrylic beads.

[0033] Other preferred examples comprise enzymes entrapped in a carrier such as a gel.

[0034] Alternatively, lyophilized powders can be chosen as substrate for the enzyme. However, in case, a filter is preferably positioned at the inlet and/or at the outlet of the reaction zone to prevent the circulation of the enzymes.

[0035] The concentration of the enzymes is preferably at least 1wt% and more preferably at least 2 wt%, for example at least 4 wt%.

[0036] The reaction zone comprising the (immobilized) enzyme preferably allows the inlet flow to flow over the reaction zone comprising the (immobilized) enzyme at a reasonable flow rate. The flow rate ranges for example between 0.4 ml/minute and 2 ml/minute. The residence time in the reaction zone ranges preferably between 20 minutes and 120 minutes.

[0037] As mentioned above the inlet flow comprises at least one carbohydrate, at least one carboxylic acid and at least one solvent. Possibly, the inlet flow comprises more than one carbohydrate, more than one carboxylic acid and/or more than one solvent.

[0038] As carbohydrates any carbohydrate suitable for the preparation of sugar esters can be considered. Preferred carbohydrates comprise sugars and sugar alcohols. Oligosaccharides and polysaccharides can - although less preferred - be considered as well.

[0039] Preferred sugars comprise monosaccharides such as glucose, galactose, fructose, mannose, altrose and xylose or disaccharides such as sucrose, lactose, maltose, trehalose. Preferred sugar alcohols comprise sorbitol and mannitol.

[0040] As carboxylic acid any carboxylic acid suitable for the preparation of sugar esters can be considered. Examples of carboxylic acids comprise (un)saturated (mono)carboxylic acids and fatty acids. Preferred carboxylic acids comprise acids and fatty acids such as acetic acid, butyric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, stearic acid and (L-)proline.

[0041] As solvent any organic solvent can be considered. Preferred solvents comprise acetone, t- butanol and isopropanol.

[0042] The process according to the present invention may further comprise one or more in-line purification steps. Any purification step known in the art can be considered. Preferred examples of purification steps comprise evaporation of the solvent and/or washing of the product flow.

[0043] The process according to the present invention allows to prepare monoesters.

[0044] Compared to other processes for the preparation of sugar esters known in the art, the process according to the present invention is less affected to the presence of water. The water generated during the reaction is pushed forward in the continuous process. If needed the water can be removed.

[0045] According a second aspect of the present invention, a system for the continuous preparation of at least one sugar ester is provided. The system comprises

a reaction zone comprising at least one enzyme;

a first channel in fluid communication with a first end of the reaction zone for introducing an inlet flow comprising a carbohydrate, a carboxylic acid and an organic solvent to flow through the reaction zone;

a second channel in fluid communication with a second end of the reaction zone for providing a product flow;

a device in fluid communication with the second channel to divide the product flow in a first flow part and a second flow part;

a third channel in fluid communication with the device to divide the product flow to (re)introduce the first flow part to flow through the reaction zone;

a fourth channel in fluid communication with the device to divide the product flow to deliver the second flow part.

[0046] The system preferably comprises one reaction zone although systems comprising more than one reaction zone can be considered as well.

[0047] A reaction zone comprises at least one enzyme, for example at least one immobilized enzyme. A reaction zone may comprise more than one enzyme, for example more than one immobilized enzyme.

[0048] A reaction zone is for example situated in a reaction chamber, for example a flow channel or a vessel. It is clear that a reaction chamber may comprise a plurality of reaction zones.

[0049] Furthermore, the system according to the present invention may comprise a plurality of reaction chambers, each reaction chamber comprising one or more reaction zones.

[0050] The system may comprise one first channel in fluid communication with a first end of the reaction zone, for example to introduce one inlet flow to flow through the reaction zone. Alternatively, the system may comprise multiple first channels (for example two or three first channels) to introduce multiple inlet flows to one reaction zone or to multiple reaction zones.

[0051] The system may comprise one second channel in fluid communication with a second end of the reaction zone, for example to provide one product flow, i.e. a flow comprising one or more sugar esters. Alternatively, the system may comprise multiple second channels (for example two or three second channels) to provide one or multiple product flows.

[0052] The device to divide the product flow in a first flow part and a second flow part comprises for example a flow splitter.

[0053] The device to divide the product flow divides the product flow at least in a first flow part and a second flow part. Possibly, the device to divide the product flow divides the flow in more than two flow parts, for example in three or four flow parts. [0054] At least part of the product flow, for example the first flow part of the product flow, is (re)introduced to the reaction zone.

[0055] The system may comprise one third channel in fluid communication with the device to divide the product flow to (re)introduce part of the product flow to the reaction zone. Alternatively, the system comprises multiple third channels (for example two or three third channels) to (re)introduce part of the product flow to a reaction zone or to multiple reaction zones.

[0056] The system may comprise one fourth channel in fluid communication with the device to divide the product flow to deliver part of the product flow. Alternatively, the system comprises multiple fourth channels (for example two or three fourth channels) to deliver the product flow. The fourth channel or channels correspond for example with an outlet channel or with outlet channels.

Brief description of the drawings

[0057] The present invention will be discussed in more detail below, with reference to the attached drawings, in which:

- Fig. 1 shows a schematic illustration of a system for the continuous preparation of a sugar ester according to the present invention.

Description of embodiments

[0058] The present invention will be described with respect to particular embodiments and with reference to certain drawings, but the invention is not limited thereto but only by the claims. The drawings are only schematic and are non-limiting. The size of some of the elements in the drawing may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

[0059] When referring to the endpoints of a range, the endpoints values of the range are included.

[0060] When describing the invention, the terms used are construed in accordance with the following definitions, unless indicated otherwise.

[0061] When describing the invention, the terms used are construed in accordance with the following definitions, unless indicated otherwise.

[0062] The terms‘first’,‘second’ and the like used in the description as well as in the claims, are used to distinguish between similar elements and not necessarily describe a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0063] The term‘and/or’ when listing two or more items, means that any one of the listed items can by employed by itself or that any combination of two or more of the listed items can be employed.

[0064] Figure 1 is an illustration of a system 100 for the continuous preparation of a sugar ester according to the present invention. A flow 101 of reactant A and a flow 102 of reactant B are mixed by a mixer 103, for example a static mixer or any other mixing system to provide a flow 104. Reactant A comprises for example a saccharide in a solvent. Reactant B comprises for example a carboxylic acid in a solvent. Flow 104 is introduced by a first channel 104’ to reaction chamber 105 to flow through reaction zone 106. The reaction zone 106 comprises at least one immobilized enzyme 107. The product flow 108 leaving the reaction zone is discharged by a second channel 108’ and is divided in a first flow part 109 and a second flow part 1 10 by flow junction 1 1 1 . The first flow part 109 of the product flow 108 is introduced or reintroduced to the first channel 104’ by third channel 109’ and is introduced or reintroduced to the reaction chamber 105 to flow through reaction zone 106. Alternatively (not shown), the first flow part 109 of the product flow 108 is introduced directly to reaction chamber 105 to flow through reaction zone 106. The second flow part 1 10 is discharged by a fourth channel 1 10’ and is collected in recipient 1 12. Possibly, the system 100 comprises a purification step (not shown) to purify the product flow and/or the first flow part 109 of the product flow and/or the second flow part 1 10 of the product flow.

Examples

Example 1

[0065] In the system illustrated in Figure 1 , 80 mM glucose and an equimolar amount of lauric acid are suspended in an organic solvent, for example, but not limiting, acetone, t-butanol or isopropanol. t-Butanol offers the highest conversions. However as handling of t-butanol is difficult due to crystallization at room temperature, acetone is preferred as organic solvent due to the easier handling and its acceptance as a food additive. Increasing the ratio of acid to sugar has shown to accelerate the reaction. Using said conditions, no acetal formation was observed with acetone as the solvent. The water content is checked by Karl Fischer titration and preferably kept below 0.05 % at the start of the reaction. If required, solvents are dried over activated molecular sieves and stored in an exicator. The immobilized enzymes were packed in the reactor in such a way that the flow of the reactants is still possible (approximately 80 % of the reaction vessel is allocated to the immobilized enzyme beads). The temperature of the reaction chamber is thermostatically controlled. The temperature ranges preferably between 40 C and 70 °C, thereby avoiding caramelization of the sugars and denaturation of the enzymes. Increasing temperatures has also shown to deactivate the enzyme. The product is obtained predominantly as a monoester and the progress up until 120 minutes is verified by HPLC-MS. A complete conversions was reached with recirculation of the product stream to increase solubility of the carbohydrate. In this example, based on HPLC-MS calculations, a one pass recirculation was shown to improve the conversion upto 95 %.

[0066] The product flow can be purified for example by evaporating the solvent and by removing the residual acid with a solvent, for example by using a (warm) alkane solution. A preferred washing method comprises 2 to 4 washings with warm heptane.

[0067] The obtained products can show a purity upto 99 % making further preparative chromatography steps unnecessary. [0068] The temperature of the reaction chamber is thermostatically controlled. The temperature ranges preferably between 40 °C and 70 °C, thereby avoiding caramelization of the sugars and denaturation of the enzymes. Increasing temperatures has also shown to deactivate the enzyme. The product is obtained predominantly as a monoester and the progress up until 120 minutes is verified by HPLC-MS. A complete conversion was reached with recirculation of the product stream to increase solubility of the carbohydrate. In this example, based on HPLC-MS calculations, a one pass recirculation was shown to improve the conversion upto 95 %.

Example 2

[0069] In the second example a sugar ester was prepared according to the procedure of the first Example, however starting from 40 mM fructose instead of glucose.

Example 3

[0070] In the third example a sugar ester was prepared according to the procedure of the first Example, however starting from 40 mM sucrose instead of glucose.

Example 4

[0071] In the fourth example a sugar ester was prepared according to the procedure of the first Example, however starting from 40 mM mannose instead of glucose.

Example 5

[0072] In the fifth example a sugar ester was prepared according to the procedure of the first Example, however starting from 40 mM altrose instead of glucose.

Example 6

[0073] In the sixth example a sugar ester was prepared according to the procedure of the first Example, however starting from 40 mM lactose instead of glucose.

Example 7

[0074] In the seventh example a sugar ester was prepared according to the procedure of the first Example, however starting from 40 mM maltose instead of glucose.

Example 8

[0075] In the eight example a sugar ester was prepared according to the procedure of the first Example, however starting from 40 mM galactose instead of glucose.

Example 9

[0076] In the ninth example a sugar ester was prepared according to the procedure of the first Example, however starting from 40 mM dicarboxylic azelaic acid instead of lauric acid. Example 10

[0077] In the tenth example a sugar ester was prepared according to the procedure of the first Example, however starting from 40 mM stearic acid instead of lauric acid. Example 11

[0078] In the eleventh example a sugar ester was prepared according to the procedure of the first Example, however starting from 40 mM L-proline instead of lauric acid.

[0079] The above-mentioned examples are summarized in Table 1.

Table 1

Handling of enzymes

[0080] The enzymes used in the examples are kept in a dry and cool place and are immobilized onto acrylic beads. The highest conversions were reached with the Candida Antartica Lipase B. Lipozyme RM, Lipozyme TL IM Lipozyme 435 showed for Example 1 in an ascending order increasing conversions at otherwise constant conditions. The activity can be determined by means of a spectrophotometer. Activities of 5000 U/min are expected. The temperature should be kept below 70 °C to keep the activity constant and to avoid denaturation of the enzymes. The enzyme loaded in the reaction vessel can be reutilized, prior to the required flushing of the reactor with the solvent to be used.