Developing trimethyl borate production process from ulexite ore

Boron is an industrially important element and the largest boron reserve in the world is located in Turkey on the basis of B2O3. The most important boron ores in Turkey are colemanite, tincal and ulexite. Colemanite is used in the production of boric acid, and tincal is used in the production of basic boron compounds such as borax and sodium pentaborate. Certain grade of ulexite ore is exported without being utilized any production process. Trimethyl borate, which has many uses in the industry, is not produced in our country, which is rich in boron mines, and is still imported from abroad. Trimethyl borate the chemical structure B(OCH3)3 is an orthoborate and is also called as methyl borate. TMB is mostly used in the production of alkali metal borohydride compounds which has significant hydrogen storage properties. Additionally, it is utilized as a fire retardant in the cotton weaving industry, as a lubricant in hydraulic fluids and as a crosslinker in polymeric materials. Within the scope of this thesis, a new alternative production process has been developed to produce trimethyl borate from ulexite together with methanol in CO2 medium. Using carbon dioxide is advantageous instead of mineral acid in terms of process. Thanks to this study, CO2 was kept as stable compounds by mineral carbonization method and TMB production was realized. For this purpose, firstly, pure ulexite and calcined ulexite obtained from Bigadiç Eti Mine were dissolved with methanol and CO2. In the dissolution process, reaction temperature, reaction time, particle size, solid-liquid ratio, reaction pressure and calcination temperature were selected as parameters and optimum working conditions were determined by utilizing the Taguchi method. In the experiments carried out under optimum operating conditions, the dissolve ratio of B2O3 for ulexite and calcined ulexite were determined as 92.94% and 94.72%, respectively. The dissolution kinetics of ulexite mineral with CO2 in methanol medium was investigated. By using experimental data, graphical and statistical methods, it has been determined that the reaction kinetics was found to fit Avrami model equation. The activation energy was found to be 21.47 kJ/mol. Experiments were carried out reactor by utilizing optimum dissolution working conditions for both ulexite and calcined ulexite and the liquid solution taken from the reactor was distillated to form trimethyl borate azeotrope. The effects of boron/methanol molar ratio, propionic acid/sodium molar ratio, boron/calcium sulfate ratio and boron/calcium chloride ratio on distillate yield were investigated. In distillation, different dosage of propionic acid was utilized in order to enhance both dissolution ratio and yield of trimethyl borate. In experiments using propionic acid and 40/200 solid liquid ratio, yield of TMB and dissolution rate of B2O3 were found to be 82,78% and 97,80% respectively. In order to increase product yield, water was removed from reaction medium. CaCl2 and CaSO4 were selected as the desiccant and when the CaCl2 was used, the yield of TMB was estimated at about %99,65 and approximately 74%wt of TMB was obtained. The pervaporation method was used in the purification of trimethyl borate from trimethyl borate azeotrope. In this part, both the synthetically prepared trimethyl borate-methanol azeotrope and approximately containing 74%wt of TMB which was obtained in distillation were used. Hydrophilic pervaporation membranes were prepared by utilizing polyvinyl pyrrolidine (PVP), hydroxyethyl cellulose (HEC) and chitosan polymers. TMB-methanol azeotrope separation was performed by using PVP-HEC and PVP-Kitosan which was prepared at different blend ratios. Four of the prepared mixture membranes were selected and crosslinked in order to investigate the effect of crosslinking. All of the prepared membranes were characterized by utilizing FTIR, XRD, SEM, TGA and contact angle analysis. In pervaporation process, trimethyl borate was obtained with a purity of %95.81 and 97.71 when PVP-Kitosan-2 and PVP HEC-2 membrane were used respectively.