A process for the production of dipentaerythritol

Abstract

The present invention relates to a process for producing dipentaerythritol from pentaerythritol in the presence of sulfolane and a heterogeneous polyacid catalyst supported on a carrier comprising a compound selected from the group consisting of: SnO2, mesoporous silica, and zeolite.

Description

[0001] A PROCESS FOR THE PRODUCTION OF DIPENTAERYTHRITOL

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a process for producing dipentaerythritol from pentaerythritol in the presence of sulfolane and a heterogeneous polyacid catalyst supported on a carrier comprising a compound selected from the group consisting of: SnC>2, mesoporous silica, and zeolite.

[0004] BACKGROUND OF THE INVENTION

[0005] Dipentaerythritol is an important chemical compound used in various applications, such as coatings, lubricants, radiation curing, adhesives, plasticizers, and cosmetics. Due to its high functionality, with six primary hydroxyl groups, dipentaerythritol has the ability to enhance the drying and hardness in coatings, and improve the properties of various products, making it a valuable compound in industrial applications. The industrial production of dipentaerythritol is currently a byproduct of pentaerythritol production (from formaldehyde and acetaldehyde in the presence of sodium hydroxide, undergoing a Cannizzaro reaction, also producing sodium formate as a byproduct) and the yields were low. Although recent advancements have focused on increasing the yield of dipentaerythritol by optimizing reaction conditions and using specific catalysts, dipentaerythritol yields only reaches up to 10%.

[0006] There are some patent documents, like JPH07258139, JP3814642, JPH07188086, JP2005015379, JP2005015380, CN101531573 and JP3368958, disclosing routes to dipentaerythritol using different types of heterogenous catalysts. A scientific paper: Okuhara et al., “Catalytic dehydration of pentaerythritol to dipentaerythritol over heteropoly compounds”, Applied Catalysis A: General, 2003, vol.253, pages 29-32, has proposed the selective dimerization of the polyol with the use of heteropolyacids H3PW12O40 and H4SiWi204o / Si02 at 170 °C for 24 h. The conversions of pentaerythritol were respectively 81.6% and 57%, and the dipentaerythritol yield were respectively 22.7% and 22.8%. Even though the yield of dipentaerythritol is improved compared to other prior art, the selectivity and conversion of pentaerythritol to dipentaerythritol is still unsatisfactory, causing the above disclosed processes to be too costly to be competitive.

[0007] There is accordingly a need for an improved process for producing dipentaerythritol were pentaerythritol conversion and dipentaerythritol selectivity and yield is balanced and optimized and the loss of reactants is kept to a minimum.

[0008] SUMMARY OF THE INVENTION

[0009] The Applicant has observed that the nature of the carrier on which a heteropolyacid catalyst is supported plays a very important role. By modifying the pore-size distribution of a support, the yield of dipentaerythritol from pentaerythritol could significantly be improved. The choice of solvent, supported catalyst, catalyst loading, reaction temperature, and reaction time, has a great impact on the yield and the selectivity of dipentaerythritol.

[0010] The Applicant further found out that the selectivity for dipentaerythritol is very high for sulfolane, and that sulfolane as a solvent generates less side reactions compared to other solvents like water, and diethyl carbonate. Sulfolane turned out to be a the stable solvent, generating the best results regarding both conversion and dipentaerythritol selectivity.

[0011] The applicant has surprisingly found that a heteropolyacid catalyst supported on a carrier comprising a compound selected from the group consisting of: SnO2, mesoporous silica, and zeolite, has the ability to efficiently catalyze the production of di pentaerythritol from pentaerythritol in the presence of sulfolane and balancing a high pentaerythritol conversion with a high dipentaerythritol selectivity. The present invention therefore refers, in a first aspect, to a process for producing dipentaerythritol from pentaerythritol in the presence of sulfolane and a heterogeneous polyacid catalyst supported on a carrier comprising a compound selected from the group consisting of: SnC>2, mesoporous silica, and zeolite.

[0012] DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention relates, in a first aspect, to a process for producing dipentaerythritol from pentaerythritol, wherein said method comprises the steps of: a) feeding a reactor with pentaerythritol, sulfolane and a heteropolyacid catalyst supported on a carrier comprising a compound selected from the group consisting of: SnC>2, mesoporous silica, and zeolite, forming a reaction solution, b) heating said reaction solution to a temperature in the range of 150 - 250°C, at a pressure in the range of 0.5 - 5 bar, for a time period of 30 - 600 minutes under continuous stirring to obtain dipentaerythritol, and then c) separating said obtained dipentaerythritol from the reaction solution.

[0014] Surprisingly, the Applicant has indeed found out that this process enables a catalytic dimerization of pentaerythritol with a high conversion of pentaerythritol in combination with a high selectivity of dipentaerythritol, resulting in a high dipentaerythritol yield.

[0015] Within the framework of the present description and in the subsequent claims, except where otherwise indicated, all the numerical entities expressing amounts, parameters, percentages, and so forth, are to be understood as being preceded in all instances by the term "about". As used herein, the term “about” will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which it is used. As used herein when referring to a measurable value such as an amount, a temporal duration, and the like, the term “about” is meant to encompass variations of ±20% or ±10%, including ±5%, ±1%, and ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods. Also, all ranges of numerical entities include all the possible combinations of the maximum and minimum values and include all the possible intermediate ranges, in addition to those specifically indicated herein below.

[0016] Unless defined otherwise, all technical and scientific terms used herein generally have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0017] As used herein, the articles “a” and “an” refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, “a heteropolyacid catalyst” means one heteropolyacid catalyst or more than one heteropolyacid catalyst.

[0018] The present invention may present in one or more of the above aspects one or more of the characteristics disclosed hereinafter.

[0019] The process according to the present invention comprises the steps of: a) feeding a reactor with pentaerythritol, sulfolane and a heteropolyacid catalyst supported on a carrier selected from the group consisting of: SnO2, mesoporous silica, and zeolite, forming a reaction solution, b) heating said reaction solution to a temperature in the range of 150 - 250°C, at a pressure in the range of 0.5 - 5 bar, for a time period of 30 - 600 minutes under continuous stirring to obtain dipentaerythritol, and then c) separating said obtained dipentaerythritol from the reaction solution.

[0020] The weight ratio of pentaerythritol, sulfolane and catalyst is suitably 1 : 0.5 - 4 : 0.1 - 1 , and in a preferred embodiment of the present invention the weight ratio is 1 : 2 : 0.5. The heteropolyacid catalyst of the present invention is suitably selected from the group consisting of H3PW12O40, HaSiW^O^, H^SiW^C o] and combinations thereof. Preferably the heteropolyacid catalyst is H3PW120 o.

[0021] The heteropolyacid catalyst of the present invention is preferably applied on a carrier in an amount of 20-30 wt%, most preferably in an amount of 30 wt%, based on the weight of the carrier. Said carrier is preferably SnO2, and most preferably a nanoporous SnC>2, with an average pore size in the range of 5 - 10 nm.

[0022] In one embodiment of the present invention the carrier is doped with V2O5. A suitable amount of V2O5 is 0.5 - 4.5 wt%, based on the weight of the carrier. Preferably the carrier is doped with 1 wt% of V2O5, based on the weight of the carrier.

[0023] The dipentaerythritol obtained in the process according to the invention, is preferably separated from the reaction solution by fractional crystallization.

[0024] The heteropolyacid catalyst of the present invention is preferably prepared by a method comprising the following steps: a) impregnating the heteropolyacid catalyst on the carrier by use of incipient wetness impregnation, b) drying the heteropolyacid catalyst carrier composition for at least 2 hours at 110 °C, and c) calcinating the dried heteropolyacid catalyst carrier composition for at least 4 hours at 250°C.

[0025] This method is illustrated in Figure 1 (a).

[0026] In a preferred embodiment of the present invention the heteropolyacid catalyst is supported on a carrier comprising nano-powder. Said nano-powder is suitably prepared by a method comprising the following steps: a) diluting SnCh -2H2O in distilled water, b) adding HCI, c) agitating until approximately pH 1, d) adding V2O3 to an amount approximately equimolar to SnCh, e) agitating the solution through sonification at room temperature for at least 10 minutes, f) neutralizing the solution to approximately pH 9 using an alkali metal hydroxide, g) agitating the solution for at least 30 minutes at a temperature in the range 35 -65°C, h) separating the obtained carrier particles from the diluent and soluble byproducts, i) washing the carrier particles with water and acetone, j) drying the particles at 90°C and, h) calcinating the particles at a temperature in the range 400 - 500°C for 15 - 45 minutes.

[0027] This method is illustrated in Figure 1 (b).

[0028] In one embodiment of the present invention the nano-powder particles obtained according to the described method are coated on a carrier, after being washed in step i) and before being dried in step j).

[0029] In one embodiment of the invention pentaerythritol and sulfolane are suitably preheated to at least 50°C allowing the pentaerythritol to dissolve in the sulfolane.

[0030] In another embodiment of the invention the reactor is preferably provided with a sensor selected from the group consisting of: a pressure sensor, a temperature sensor and a CO2 sensor. The pentaerythritol to dipentaerythritol reaction is suitably allowed to endure for 30 - 600 minutes and is preferably interrupted before pressure is starting to increase or before an increase in forming of CO2 is detected. This can be detected by an increase in the exotherm reaction. Data from a selection of above mentioned sensors can be used together with an analysis of the obtained results for statistical guidance of the process, this in order to over time adjust the process parameters for optimizing the results. It has during experimentation been found that, once the maximum yield of dipentaerythritol has been reached, carbon dioxide will form from undesired decomposition of pentaerythritol and / or dipentaerythritol. Once this undesired reaction starts CO2 will form and the pressure in the reactor will increase. This point in time can, within the scope of the invention happen any time between 30 minutes and 600 minutes, suitably between 30 minutes and 360 minutes or possibly even within the range 45 minutes - 180 minutes, all depending on selection of catalyst, carrier, reactant / solvent / catalyst ratio, within the scope of the invention. Unreacted pentaerythritol can be recovered once separated from the obtained dipentaerythritol. This is disclosed in more detail later in this description.

[0031] In one embodiment of the present invention the obtained dipentaerythritol is separated from the reaction solution, after first having separated the catalyst by means of filtration and or precipitation, through means of: a) evaporating part of the solvent from the reaction solution until the dipentaerythritol reach saturation and crystallize, b) separating the dipentaerythritol crystals by means of filtration, c) feeding the remaining reaction solution comprising solvent and unreacted pentaerythritol together with the evaporated solvent and separated catalyst to a unit where next batch is prepared, and d) washing the obtained dipentaerythritol crystals with water.

[0032] Preferably, the solvent is sulfolane evaporated at a temperature in the range 100 - 250°C and a pressure in the range 10 - 500 mbar.

[0033] The dipentaerythritol crystals are suitably separated from the reaction solution by means of a centrifuge. The obtained dipentaerythritol crystals are then preferably washed with water at a temperature below 35°C. In one embodiment of the process of the invention obtained dipentaerythritol is extracted by adjusting the sulfolane / dipentaerythritol ratio and temperature to initiate crystallization of only the dipentaerythritol while the catalyst nanoparticles remains in suspension. In other words, let the nano-particles act as crystal seeding, separating them from the mother liquor, dissolving the crystalized dipentaerythritol in warm water, separating the freed catalyst particles from the solution and recrystallizing the dipentaerythritol. This alternative separation method is preferably used in a batch process. Temperature and concentration dependence is important for the separation process. The process window becomes larger the more di pentaerythritol and the less pentaerythritol is present in the solution.

[0034] Figure 2 illustrates an embodiment of process layout for the production of dipentaerythritol according to the present invention.

[0035] Pentaerythritol, sulfolane and a heteropolyacid catalyst on particle carrier is loaded into a premixing / preheating vessel 1 where the content is preheated to at least 50°C before being feed into the reactor 2 via the mix feed line 11. The reactor 2 is provided with means for heating and agitation. The agitation is here an important part to mention as a sufficient shear force is needed for obtaining an adequate mass transport and also for keeping catalyst in suspension. The content of the reactor is heated to 230°C and the pentaerythritol is allowed to in part react into dipentaerythritol under ambient pressure. The reactor 2 is further provided with a temperature sensor. After 30 minutes - 8 hours of synthesis, the temperature will start to rise caused by an exotherm reaction where pentaerythritol start to decompose forming carbon dioxide. For this purpose the reactor 2 may further be provided with CO2 detectors and / or pressure sensors. This shows that undesired side reactions have started and that further synthesis will cause loss of pentaerythritol to side reactions rather than dipentaerythritol. Lowering the temperature in the reactor 2 though cooling at a point just before CO2 starts to form has shown to radically reduce the undesired side reactions. Even though a pressure increase or detection of CO2 is by far the best indicator of undesired side-reaction it is indeed a bit late as undesired degradation of pentaerythritol has already commenced. Such measurement data may however be acceptable at start-up, where the measurements may be used for statistical process guidance, improving the process and reducing undesired side reaction. This concept is particularly useful in semi-batch wise or continuous processes. The reaction is preferably interrupted at this point and the content of the reactor is emptied via reaction solution feed line 21 to a catalyst separation unit 3, where catalyst is separated either through precipitation, where the catalyst particles are allowed to settle at the bottom of catalyst separation unit 3, or through filtration from the reaction solution. The catalyst is then collected in a catalyst collection vessel 3a. The collected catalyst is then to be reused for the next batch and is thus fed back to the premixing / preheating vessel 1 via a catalyst return feed line 31.

[0036] In one embodiment of the invention it is possible to use a fixed bed catalyst in the reactor 2. In case of a fixed bed, the catalyst need not to be premixed with solvent and pentaerythritol in premixing / preheating vessel 1. Neither will it be necessary to separate the catalyst from the reaction solution, whereby the catalyst separation unit 3, the catalyst collection vessel 3a, and the catalyst return feed line 31 can be omitted. The reaction solution feed line 21 will in this case connect directly to a reaction solution sans catalyst feed line 31.

[0037] Once the reaction solution is free from catalyst, it is suitably fed via a reaction solution sans catalyst feed line 31 to at least one distillation unit 4a-b, where the solvent sulfolane is evaporated under reduced pressure <15 mbar at 150°C - 250°C allowing the dipentaerythritol to crystalize to be able to be separated from the reaction solution. Water formed during the dimerization in the reactor 2, is also preferably separated off in the distillation unit 4a-b. Said water is easily separated from the sulfolane due to the large difference in boiling point. The unreacted pentaerythritol will remain dissolved in remaining sulfolane. The evaporated sulfolane, sans water, is preferably collected through solvent collection feed lines 41 to a solvent collection vessel 5. The collected sulfolane is preferably returned to the premixing / preheating vessel 1 for further use with other effluents from the process. The reaction solution containing crystalized dipentaerythritol will then preferably be feed to a centrifuge 6, where sulfolane and pentaerythritol are separated from the crystalized dipentaerythritol and collected in a unit 6a. The pentaerythritol / sulfolane mixture is preferably returned to the premixing / preheating vessel 1 via a mother liquor return line 61 in order to be used for a new production batch once refurbished with new pentaerythritol and some sulfolane. The collected dipentaerythritol is preferably feed to a washing unit 7a-b via a purification feed line 62. The dipentaerythritol crystals are preferably washed with water in the washing unit 7a-b. Here it is possible to use on or more centrifuges. The purified dipentaerythritol is obtained through the outlet 72 and can then be dried. The wash water from outlet 71 contains amounts of sulfolane, pentaerythritol and dipentaerythritol. The obtained wash water can be submitted to further separation where pentaerythritol and sulfone can be returned to the premixing / preheating vessel 1 and the dipentaerythritol can be joined with the dipentaerythritol obtained through outlet 72.

[0038] The above described process and equipment set-up can be either be a semi- continuous or semi-batchwise process. It is indeed possible to control the reaction, as indicated above, in the reactor 2, by controlling the temperature and introducing the cooling. In one embodiment of the present invention the reactor 2 can be designed as a flow reactor which has a continuous feed of reactant and solvent and where the dipentaerythritol obtained is extracted continuously in a process set-up very similar to the above described process. The reactor 2 may in a continuous process have two or more temperature zones or even be divided into two or more reactors in series allowing for better control of the temperature profile.

[0039] The process described according to the embodiments above, regardless of whether it is batch-wise, semi-batch wise or continuous, is adventurously provided with extraction / purification stages in the mother liquor return line 61 in ll order to separate any dipentaerythritol and side reactions not caught in the centrifuge 6.

[0040] The dipentaerythritol obtained from the outlet 72 may be submitted to further purification and re-crystallization as is common practice in the art. It is for example known that minor portions of side reaction products having a molecular weight higher than the molecular weight of pentaerythritol will be separated off in the centrifuge 6 together with the dipentaerythritol. Recrystallization of the dipentaerythritol is sometimes also used in order to obtain uniform size of the crystals.

[0041] In one embodiment of the present invention the process is continuous and it is possible to balance the ratio between solvent and the obtained dipentaerythritol in the reactor 2 so that, by lowering the temperature in a stage before the centrifuge 6, the dipentaerythritol starts to crystallize. In such a process it is preferable to utilize a fixed bed catalyst in the reactor 2, due to a high likelihood of interference between crystallization of dipentaerythritol and precipitation of nano - micro meter scale catalyst particles.

[0042] The present invention is further explained with reference to enclosed embodiment Examples, which are to be construed as illustrative and not limiting in any way.

[0043] EXAMPLES

[0044] In Examples 1-14 dipentaerythritol is produced from pentaerythritol in the presence of sulfolane and different heteropolyacid catalysts. Examples 1-6 are comparative examples and Examples 7-14 illustrate embodiments of the present invention. The results of the experimental reactions are presented in Table 1.

[0045] Chemicals and reagents used in the Examples

[0046] All of the following chemicals and materials were of analytical grade, namely pentaerythritol (PE, >99%, Sigma-Aldrich), dipentaerythritol (DPE, >99%, Sigma Aldrich), 1-Trimethylsilylinnidazole (TMSI, >98%, Sigma-Aldrich), N,N-bis- trimethylsilyl-trifluoroacetamide (>98.5%, Sigma-Aldrich), Pyridine (99%, Sigma- Aldrich), n-Eicosane (C20H42, >99%, Sigma-Aldrich), Sulfolane (99%, Sigma- Aldrich), phosphotungstic acid (H3PW12O40, >99.5%, Sigma-Aldrich), phosphotungstic acid (FhSiW^C o, >99.5%, Sigma-Aldrich), Y-AI2O3 (Puralox SCCa 150 / 200, Sasol), Silica (SiC>2, >99.0%, catalyst support, Alfa Aesar), Silica SBA16 (>99.0%, Sigma-Aldrich), TiO2 (High surface area, 99.99%, Sigma- Aldrich), tin (IV) oxide (nano-SnO2, 99.99%, Sigma Aldrich), nanopowder tin (IV) oxide (SnO2, >99.5%, Sigma-Aldrich), Tin (II) chloride dihydrate (SnCU-2H2O, Sigma-Aldrich, 98%), vanadium (V) oxide (V2O5, Sigma-Aldrich, >99.6%) and hydrochloric acid (HCI, ACROS ORGANICS, 37%).

[0047] Catalysts preparation

[0048] Prior to the experiments of producing dipentaerythritol through pentaerythritol dimerization, the different heteropolyacid supported catalysts to be used in the process were synthesized. The synthesis procedure is illustrated in Figure 1 (a). The catalysts were prepared using solutions of phosphotungstic acid (HPW) and silicotungstic acid (HSiW). Supported catalysts based on heteropolyacids were prepared using several commercially available supports, SiO2, y-AI2O3, SBA16, TiO2, SnO2. The heteropolyacid catalysts were prepared by incipient wetness impregnation of supports and subsequently dried at 100°C overnight to obtain 20 wt% heteropolyacid catalysts on support (e.g. 20% HsPW^C TiCh). Prior to use as catalyst, these catalysts were calcined in air at 250°C for 6h.

[0049] A modified synthesis procedure of nano-powder SnO2 supports is presented in Figure 1 (b). In this step, pure and doped SnO2 with V2O5 nano-powders were synthesized via sol-gel method using different V2O5 ratios (1 , 5, and 10 wt.%). The preparation of SnO2-based nano-powders containing (0, 1 , 5 and 10 wt%) of V2O5 by sol gel technique explores the use of tin chloride dihydrate (SnCI2’2H2O) that is put in a beaker, and then, diluted water hydrochloric acid is added until the solution pH ~ 1 and is kept under stirring. Then, an aqueous acidic V2O5 solution for the doping process is added with different ratios and after that ammonia solution is dropped to the previous solution during stirring until the pH of the mixture is raised to 9 to convert tin chloride into tin hydroxide. The solution becomes white milky, while the solution is continued stirring at a temperature of 50 °C for 1 h in a glass beaker using a magnetic stirrer. White powders are precipitated when centrifuged at 4000 rpm for 20 min and washed many times using distilled / deionized water to remove the ammonia ions and ammonium chloride; then, it allowed to obtain pure precipitate. A final washing step is done by acetone that allows a faster drying for the powder and the precipitate is dried at 90 °C. The Sn(OH)4 is dehydrated directly to form SnO2 powder, and then, the nano-powders are calcinated at 450 °C for 10 min. Later on, these new supports were utilized to prepare heteropolyacid supported catalyst involved typically steps as described-above in Figure 1 (a).

[0050] Procedure for dimerization of pentaerythritol

[0051] All experiments of pentaerythritol dimerization were performed in a 10 mL glass vial. The vial has a screw cap which tightens by means of threads cast into the top of the vial. The vial was filled with pentaerythritol, various amounts of solvent namely sulfolane, and the screened catalysts (loading dependent on acidity). A range of temperatures (150 - 230°C), reaction times (0.5 - 6 h), catalyst loading (0.1 - 0.5 g), and a variety of reactant / solvent ratios were tested to identify their respective effect and to tune the reaction toward the desired outcome. To draw valid conclusions, the reaction was followed over time by sampling every 1 h, except for higher catalytic loading the sampling was reduced to every 30 minutes or less. The vial was heated to desired reaction temperature and stirring was fixed for all experiments at 200 rpm to avoid external diffusion limitations. The time zero was set once the desired reaction temperate was reached. Changes to the conditions were tested individually, to be certain the effect each change had on the overall reaction. After the reaction, a part of the homogenized solids formed was pretreated, prior to GC-MS analysis, using silylation method. In this study, 25 mg of resultant solid was sampled into a 2 mL vial and treated in two steps as follows. 0.3 mL of TMSI and 0.6 mL of pyridine were added to the solid sample. The vial is capped and heated for 0.5 h at 120°C until completely dissolved. A 0.1 mL aliquot of the resulted solution was added to a vial with 0.1 mL N,N-bis-trimethylsilyl-trifluoroacetamide, 0.7 mL pyridine and 0.1 mL of 10000 ppm n-Eicosane (as internal standard). The mixture was then heated for 0.25 h at 120 °C. In most cases the silylation of hydroxyl groups is a fast reaction proceeding at moderate temperature to prevent further pentaerythritol dimerization. This procedure also allows the excellent selectivity for the silylation of primary (dipentaerythritol) hydroxyl groups in polyols groups. The resulting silylated compounds were analyzed using a GC-MS.

[0052] Data processing

[0053] The pentaerythritol conversion, product yield and selectivity were calculated according to equations 1-3, respectively:

[0054] PE Conversion 100 (Eq. 1)

[0055] Yield (wt.%)= n xcmoie orproduet) v7mole of initial PE

[0056] Selectivity ( 100 (Eq. 3) where n is theoretical mole of PE converted into the corresponding polyols.

[0057] In Examples 1-14 dipentaerythritol was produced from pentaerythritol according to the procedure disclosed in the earlier paragraph: “Procedure for dimerization of pentaerythritol” in the presence of sulfolane and different heteropolyacid catalysts according to Table 1. The reaction conditions, catalyst load and the results regarding conversion of pentaerythritol, yield and selectivity of dipentaerythritol are all presented below in Table 1.

[0058] Table 1 Pentaerythritol conversion, dipentaerythritol yield and selectivity over heteropolyacid catalysts. Reaction conditions: glass vial reactor, pentaerythritol / sulfolane / catalyst: 0.5g / 1g / 0.25g, 200°C, 200 rpm. Ex Catalyst Pentaerythritol Dipentaerythritol Dipentaerythritol Reaction time

[0059] Conversion (%) Yield (%) Selectivity (%) (min)

[0060] Comparative examples

[0061] 1 Unsupported 90.5 2.4 2.6 120

[0062] H3PWI204O

[0063] 2 Unsupported 98.5 0.0 0.0 120

[0064] H3SiWi204o

[0065] 3 20%H3PWI2O4045.1 6.1 13.5 120

[0066] / ZrO2

[0067] 4 20%H3PWI2O4010.1 2.2 21.8 120

[0068] / TiO2

[0069] 5 20%H3PWI2O4074.2 23.0 31.0 120

[0070] / y-Al2O3

[0071] 6 20%H3PW12O4021.5 20.8 96.5 120

[0072] / SiO2

[0073] Examples of the invention

[0074] 7 20%H3PWI2O4041 24 59 120

[0075] / SnO2

[0076] 8 20%H3PWI2O4069 29 42 120

[0077] / SBA16

[0078] 9 30%H3PWI2O4045 27 61 120

[0079] / SnO2

[0080] 10 30%H3PWI2O4038 35 94 120

[0081] / 1 %V2O5-SnO2

[0082] 11 30%H3PWI2O4046 40 87 180

[0083] / SnO2

[0084] 12 30%H3PW12O4049 47 96 180

[0085] / 1 %V2O5-SnO2

[0086] 13 30%H3PW12O4051 43 84 240

[0087] / SnO2

[0088] 14 30%H3PW12O4050 50 97 240

[0089] / 1 %V2O5-SnO2

[0090] Successful processing of a pentaerythritol catalytic reaction step often involves optimizing of reaction conditions to increase dipentaerythritol yield and selectivity, as well as carefully control of catalyst deactivation and recovery to allow for the recycling and reuse of expensive catalysts. From the above result, catalytic activities can be compared. The remarkable feature of the catalytic system of the present invention may be seen in this Table 1 , where the pentaerythritol conversion, dipentaerythritol yield, and selectivity are illustrated. All supports were catalytic inactive under operating conditions. The results indicate that HaSiW^O^ was the most active of the two catalysts, where almost all the pentaerythritol was converted at 200°C for 120 min. Previously disclosed reference, Okuhara et al. suggested the selective dimerization of the pentaerythritol in a sealed reactor over SiO2 supported polyacids, namely 15 % FhSiW^C o / SiO2 and 20% HsPW^C SiC ?. The best results disclosure in that reference performed without solvent at 170°C for 24 h and converted, respectively, 72.9 % of pentaerythritol for 26.0 % of dipentaerythritol selectivity and 81.6 of pentaerythritol for 27.8 % dipentaerythritol selectivity. While the results disclosed in Table 1 , use sulfolane as a solvent, and reach a much higher dipentaerythritol selectivity. The supported catalysts are more selective and reach higher dipentaerythritol yield for a maximal pentaerythritol conversion.

[0091] Examples 9-14, show the difference between 30%H3PWi2C>40 catalysts supported on SnC>2 and supported on V2O5 doped SnC>2. Compared to none-doped SnC>2, 1% V2O5 doped SnC>2 showed significant improvement in all aspect including pentaerythritol conversion, dipentaerythritol selectivity and dipentaerythritol yield, under same operating conditions.

Claims

CLAIMS1. A process for producing dipentaerythritol from pentaerythritol, wherein said process comprises the steps of: a) feeding a reactor with pentaerythritol, sulfolane and a heteropolyacid catalyst supported on a carrier comprising a compound selected from the group consisting of: SnC>2, mesoporous silica, and zeolite, forming a reaction solution, b) heating said reaction solution to a temperature in the range of 150 - 250°C, at a pressure in the range of 0.5 - 5 bar, for a time period of 30 - 600 minutes under continuous stirring to obtain dipentaerythritol, and then c) separating said obtained dipentaerythritol from the reaction solution.

2. A process according to claim 1 , wherein the weight ratio of pentaerythritol, sulfolane and catalyst is 1 : 0.5 - 4 : 0.1 - 1.

3. A process according to claim 1 or 2, wherein the weight ratio of pentaerythritol, sulfolane and catalyst is 1 : 2 : 0.5.

4. A process according to any of claims 1-3, wherein the heteropolyacid catalyst is selected from the group consisting of H3PW12O40, F SiW^C o, H4[SiWi2C>4o] and combinations thereof.

5. A process according to any of claims 1-4, wherein the heteropolyacid catalyst is FhPW^C o-6. A process according to any of claims 1-5, wherein the amount of heteropolyacid catalyst is 20-30 wt%, based on the weight of the carrier.

7. A process according to any of claims 1-6, wherein the amount of heteropolyacid catalyst is 30 wt%, based on the weight of the carrier.

8. A process according to any of claims 1-7, wherein said carrier is SnO2.

9. A process according to any of claims 1-8, wherein said carrier is nanoporous SnC>2.

10. A process according to any of claims 1-9, wherein said carrier has an average pore size in the range of 5 - 10 nm.

11. A process according to any of claims 1-10, wherein said carrier is doped with V2O5.

12. A process according to any of claims 1-11 , wherein said carrier is doped with 0.5 - 4.5 wt% of V2O5, based on the weight of the carrier.

13. A process according to any of claims 1-12, wherein said carrier is doped with 1 wt% of V2O5, based on the weight of the carrier.

14. A process according to any of claims 1-13, wherein the dipentaerythritol is separated from the reaction solution by fractional crystallization.

15. A process according to any of claims 1-14, wherein said heteropolyacid catalyst is prepared by a method comprising the following steps: a) impregnating the heteropolyacid catalyst on the carrier by use of incipient wetness impregnation, b) drying the heteropolyacid catalyst carrier composition for at least 2 hours at 110 °C, and c) calcinating the dried heteropolyacid catalyst carrier composition for atleast 4 hours at 250°C.

16. A process according to any of claims 1-15, wherein said carrier comprises nano-powder prepared by a method comprising the following steps: a) diluting SnCh -2H2O in distilled water, b) adding HCI, c) agitating until approximately pH 1 , d) adding V2O5 to an amount approximately equimolar to SnCh, e) agitating the solution through sonification at room temperature for at least 10 minutes, f) neutralizing the solution to approximately pH 9 using an alkali metal hydroxide, g) agitating the solution for at least 30 minutes at a temperature in the range 35 -65°C, h) separating the obtained nano-powder particles from the diluent and soluble by-products, i) washing the nano-powder particles with water and acetone, j) drying the particles at 90°C and, h) calcinating the particles at a temperature in the range 400 - 500°C for 15 - 45 minutes.

17. A process according to claim 16, wherein said nano-powder particles are coated on a carrier, after being washed in step i) and before being dried in step j).

Images