Preparation of TMTHF

Abstract

A process for the preparation of 2,2,5,5-tetramethyltetrahydrofuran (TMTHF) includes contacting a TMTHF precursor with a solid catalyst, where the TMTHF precursor is 2,5-dimethylhexane-2,5-diol and/or 2,5-dimethyl-4-hexen-2-ol, and where the solid catalyst is a beta zeolite. TMTHF produced by the process may be used as a solvent.

Claims

1. A process for the preparation of 2,2,5,5-tetramethyltetrahydrofuran (TMTHF) comprises: contacting a TMTHF precursor with a solid catalyst, wherein the TMTHF precursor is 2,5-dimethylhexane-2,5-diol and/or 2,5-dimethyl-4-hexen-2-ol, wherein the process results in TMTHF containing less than 6% of unreacted precursor or side products, wherein the solid catalyst has a Si/Al ratio of 150:1 or lower in respect of the amount of Si, and wherein the solid catalyst is a beta zeolite selected from the group consisting of HCZB 25, HCZB 21, HCZB 30, HBEA 25, HCZB 150, HBEA 150, or combinations thereof.

2. The process according to claim 1, wherein the solid catalyst is beta-zeolite HCZB 25 and/or HBEA 25.

3. The process according to claim 1, wherein contacting of the TMTHF precursor with a solid catalyst is carried out continuously in a flow reactor packed with the solid catalyst.

4. The process according to claim 1, wherein contacting of the TMTHF precursor with a solid catalyst is carried out in a batch reactor.

5. The process according to claim 1, which is carried out at a temperature in the range of 50 to 200 C.

6. The process according to claim 5, which is carried out at a temperature in the range of 85 to 200 C.

7. The process according to claim 6, which is solvent free.

8. The process according to claim 1, wherein the TMTHF precursor is bio-based.

9. The process of claim 1, wherein the yield of TMTHF from 2,5-dimethylhexane-2,5-diol and/or 2,5-dimethyl-4-hexen-2-ol is greater than 95%.

10. The process according to claim 1, wherein the solid catalyst has a Si/Al ratio of 30:1 or lower in respect of the amount of Si.

11. The process according to claim 5, which is carried out at a temperature in the range of 100 to 175 C.

12. A process for the preparation of 2,2,5,5-tetramethyltetrahydrofuran (TMTHF) comprises: contacting a TMTHF precursor with a solid catalyst, wherein the TMTHF precursor is 2,5-dimethylhexane-2,5-diol and/or 2,5-dimethyl-4-hexen-2-ol, and wherein the solid catalyst is a beta zeolite selected from the group consisting of HCZB 25, HCZB 21, HCZB 30, HBEA 25, or combinations thereof, wherein the solid catalyst has a Si/Al ratio of 30:1 or lower in respect of the amount of Si, and wherein the yield of TMTHF from 2,5-dimethylhexane-2,5-diol and/or 2,5-dimethyl-4-hexen-2-ol is greater than 95%.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The invention may be illustrated by the following reaction scheme:

(2) ##STR00002##

(3) When 2,5-dimethylhexane-2,5-diol is contacted with a beta zeolite catalyst it is believed that 2,5-dimethyl-4-hexen-2-ol is produced as an intermediate before TMTHF is formed. The intermediate product may therefore be used instead or in combination with 2,5-dimethylhexane-2,5-diol.

(4) Zeolites are microporous crystalline silica-alumina composites. The presence of aluminium atoms in the framework results in an overall negative charge on the surface of the material. Metal counterions such as Ca.sup.2+ or Mg.sup.2+ are present in the pores and they can be exchanged with protons to produce an acidic surface. Zeolites are prepared using templating agents, the nature of which determines the size of the pores. Beta-zeolites are prepared using tetraethylammonium cations as the templating agent while ZSM-5 zeolites are prepared using tetrapropylammonium cations as the templating agent. Adjusting the Si/Al ratio effects the acidity of the material: higher Si/Al ratios reduce the number of active sites within the catalyst but increase the number of stronger acid sites and the surface hydrophobicity.

(5) Zeolites are very cheap and are the most used catalysts in the petrochemical industry along with sulfuric acid. Zeolites are much more robust than Nafion-H, being able to take temperatures of over 1000 C. Zeolites can be reactivated simply by calcination to remove organic material from the pores.

(6) Yields of 95% up to even 100% were obtained using beta-zeolites as a catalyst in a process according to the current invention. Other catalysts reported in the literature and/or tested by the current inventors were not as effective as beta-zeolites for the production of TMTHF. For example, ZSM-5 zeolite (Si/Al ratio 80:1) was much less effective with a yield of only 28%. In general, all other catalysts produced TMTHF in lower yields and with a high amount of a side product and some unreacted diol in the reaction mixture.

(7) Preferably the beta zeolite has a Si/Al ratio of 150:1 or lower in respect of the amount of Si. Beta-zeolites with these Si/Al ratios have been found to perform excellently, producing TMTHF in yields of 95% and more.

(8) More preferably, the beta zeolite catalyst has a Si/Al ratio of 30:1 or lower in respect of the amount of Si. Beta-zeolites with these Si/Al ratios (30:1 or lower, e.g. between 21-30) have been found to perform excellently, producing TMTHF in yields close to 100%.

(9) Preferably the beta zeolite is beta-zeolite HCZB 25 and/or HBEA 25. A process according to the invention in which these particular beta zeolites were used as a catalyst produced TMTHF in a yield of 99-100%.

(10) The TMTHF precursor may be in the liquid or gas phase. Preferably, contacting of the TMTHF precursor with a beta zeolite catalyst is carried out in a flow reactor packed with the beta zeolite catalyst. In such a reactor, liquid and gas phase reactions using a solid state catalyst are easily performed. Alternatively, contacting of the TMTHF precursor with a beta zeolite catalyst is carried out in a batch reactor.

(11) Preferably the process is carried out at a temperature in the range of 50-200 C.

(12) More preferably the process is carried out at a temperature in the range of 85-200 C. At a temperature of about 85 C., the 2,5-dimethylhexane-2,5-diol melts, and a solvent is not necessary for executing the process according to the invention. Most preferably the process is carried out at a temperature in the range of 100-175 C.

(13) Preferably, the process is solvent free. Many of the aforementioned prior art methods required the use of a solvent, which is a disadvantage. Solvents need to be removed from the reaction product later, and increase the production costs.

(14) The TMTHF precursor may be fully or partially petroleum derived. For example, 2,5-dimethyl-2,5-hexanediol can be produced according to the method of U.S. Pat. No. 6,956,141 B 1.

(15) Preferably, the TMTHF precursor is bio-based. This is advantageous for the environment, as the use of solvents which have been sourced from biomass leads to no net increase in the levels of atmospheric CO.sub.2, establishing a closed carbon cycle.

(16) A TMTHF precursor obtained from fermentative biomass treatment processes can be used to make the TMTHF of the current invention. However, fermentative production of chemicals is expensive and susceptible to infection. To prevent infection, antibiotics can be used, although residual antibiotics in biorefinery side-streams can hinder their use as secondary feedstocks as the use of antibiotics can spread antibiotics resistance in microorganisms. It is another objective of the invention to overcome these disadvantages.

(17) Thereto, preferably, the TMTHF precursor is obtained by a process which comprises chemocatalytic treatment of biomass. As such, chemocatalytic treatment of biomass is a more robust method of producing price sensitive chemicals such as solvents than the fermentative production.

(18) Preferably, the TMTHF precursor is obtained from hydroxymethylfurfural (HMF). HMF is a bio-platform molecule produced by chemocatalytic treatment of biomass. HMF can be converted to 2,5-hexanedione (see Sacia et al. in Green Chem. 2015, 17, p 2393, and Ren et al. in Green Chem. 2016, 18, p 3075). 2,5-hexanedione can be methylated at the carbonyl groups to produce 2,5-dimethyl-2,5-hexanediol.

(19) The invention also provides for the use of a beta zeolite catalyst for the preparation of TMTHF, and the use of TMTHF prepared by a process according to the invention as solvent, e.g. in a process for the polymerization of vinyl monomers.

(20) The present invention will be explained in more detail by reference to the following examples, but the invention should not be construed as being limited thereto.

EXAMPLES

(21) Testing of several catalysts was performed as follows. 2,5-dimethylhexan-2,5-diol (5 g), a white solid, was added to a 25 ml round-bottomed flask and heated to 105 C. At 85 C. the solid melts to a clear liquid. Upon reaching the desired temperature, 50 mg catalyst was added and the mixture was stirred for 1.5 hours. Yields and conversions were obtained by NMR and GC-FID of the organic phase. Results are summarized in table 1. Table 1 further includes catalyst results reported in the literature.

(22) As can be seen yields of up from 95% were obtained using beta zeolites as a catalyst. Thus, beta zeolites outperform all other catalysts. Notably, yields are much higher than for another type of zeolite, ZSM-5. Moreover, even the 94% yield of Nafion-H is improved upon. Beta-zeolites HCZB 25 and HBEA 25 even performed excellently with a yield of 99-100%.

(23) TABLE-US-00001 TABLE 1 Yields of TMTHF from 2,5-dimethylhexan- 2,5-diol using different catalysts Catalyst Yield Conditions (reference) Beta-zeolite HCZB 25 100.0 As described above Beta-zeolite HCZB 21 99.0 As described above Beta-zeolite HBEA 25 99.0 As described above Beta-zeolite HCZB 21 98.8 As described above Beta-zeolite HCZB 30 98.0 As described above Beta-zeolite HBEA 150 97.1 As described above Beta-zeolite HCZB 150 95.2 As described above Nafion-H 94.0 2 hrs, 130 C. (Olah et al.) KSF 3 84.0 As described above Pentaethoxyphosphorane 78.0 450 hrs, RT, DCM as solvent (Denney et al.) DMSO, 75.0 75 hrs, 20 C., benzene as solvent Chlorotrimethylsilane (Vlad & Ungur) Al doped 65.0 175 C. (Kotkar et al.) Montmorillonite DMSO 52.0 17 hrs, 162 C., DMSO as solvent (Gillis & Beck) Carbonic acid 40.0 3 hrs, 14.6 Mpa CO2 as solvent (Yamaguchi et al.) ZSM-5 80 28.2 As described above SZ 0.0 As described above