Abstract: Described in a process for producing bis(2-hydroxyethyl) terephthalate (BHET) in liquid form by depolymerization of polyethylene terephthalate (PET), wherein BHET obtained from depolymerization by glycolysis with monoethylene glycol (MEG) is purified and subsequently crystallized by cooling to obtain BHET in crystalline form impregnated with a solvent. The BHET is then melted down to obtain a solution of BHET in the solvent. The solvent content in the resulting BHET solution is adjusted, if necessary, to a value such that the BHET is in a liquid form at a temperature of less than or equal to 90° C. and greater than or equal to 70° C. This provides a BHET in liquid form that is stable for a long time within the above temperature range, which can be stored, transported, and fed to the polycondensation reactor for PET production.

Abstract: A process for depolymerizing a polyethylene terephthalate (PET) by glycolysis with ethylene glycol (EG) is described. Also described is a plant for carrying out the process. The PET is first mixed in the solid state with EG at a temperature of 60-120° C. to form a heterogeneous mixture with an EG:PET weight ratio of 0.1-3.0, and is then pressed to squeeze out an aliquot of EG. The compressed mixture is fed to a reactor, where the mixture is heated and kept under mixing at a temperature of 170-270° C., with an EG:PET weight ratio of 0.1-4.0, to glycolize the PET and obtain a glycolyzed product containing bis(2-hydroxyethyl) terephthalate and/or oligomers thereof. The process is advantageous in treating waste PET as such and reducing the EG to PET ratio necessary for glycolysis that allows the reaction to be carried out at relatively high temperatures of 230° C. and above to expedite the process.

Abstract: Process for purifying bis(2-hydroxyethyl)terephthalate (BHET) obtained from depolymerization of a polyethylene terephthalate (PET) waste, the process comprising: treating said solution with at least one oxidizing agent at a temperature of from 30° C. to 100° C., preferably from 50° C. to 90° C., to obtain an oxidized solution; treating the oxidized solution with at least one adsorbing agent to obtain a purified oxidized solution; separating the at least one adsorbing agent from the purified oxidized solution to obtain a purified BHET solution. This process is particularly effective for eliminating organic dyes and other low molecular weight organic contaminants, so as to achieve a high purity degree of the recovered BHET.

Abstract: Process and apparatus for completely recovering the reusable components of an abrasive slurry used in slicing crystalline materials of silicon, quartz or ceramics when it becomes exhausted and enriched with undesired waste matter. The process consists of an initial centrifuge separation of the exhausted slurry as such and of a wet size-sorting treatment of the fraction containing the abrasive grains obtained from the centrifuge, carried out in a battery of hydrocyclones or centrifuges connected in series. The section for the recovery and purification of the abrasive grains comprises a multifunctional apparatus that performs all the required operations within a single pressure vessel.

Abstract: Process for the re-use of silicon powder recovered from band saws and other silicon mechanical operations, as feed material to prepare the crucible charges for casting of polycrystalline-multicrystalline silicon ingots usable for photovoltaic applications. The process is multisteps in which most of the operations are carried out under inert atmosphere.

Abstract: Process for completely recovering the reusable components of an abrasive slurry used in slicing crystalline materials of silicon, quartz or ceramics when it becomes exhausted and enriched with undesired waste matter. The process consists of an initial centrifuge separation of the exhausted slurry as such and of a wet size-sorting treatment of the fraction containing the abrasive grains obtained from the centrifuge, carried out in a battery of hydrocyclones or centrifuges connected in series. The section for the recovery and purification of the abrasive grains comprises a multifunctional apparatus that performs all the required operations within a single pressure vessel. The process enables the complete recovery of the reusable abrasive grains contained in the exhausted slurry as well as of the suspending or cutting liquid of the abrasive slurry, in order to reuse both components in the manufacturing process.

Abstract: A method of separating, recovering and reusing components of an exhausted slurry used in slicing silicon wafers from a silicon ingot. In the method, the solid particles and lubricating fluid of the exhausted slurry are separated without decreasing the viscosity of the exhausted slurry. The separated lubricating fluid may be collected and reused in the preparation of a fresh slurry. Additionally, the silicon particulate and metal slicing wire particulate are dissolved and separated from the abrasive grains. The abrasive grains are separated into spent abrasive grains and unspent abrasive grains. The separated unspent abrasive grains are suitable for reuse in the preparation of a fresh slurry.

Abstract: A method of separating, recovering and reusing components of an exhausted slurry used in slicing silicon wafers from a silicon ingot. In the method, the solid particles and lubricating fluid of the exhausted slurry are separated without decreasing the viscosity of the exhausted slurry. The separated lubricating fluid may be collected and reused in the preparation of a fresh slurry. Additionally, the silicon particulate and metal slicing wire particulate are dissolved and separated from the abrasive grains. The abrasive grains are separated into spent abrasive grains and unspent abrasive grains. The separated unspent abrasive grains are suitable for reuse in the preparation of a fresh slurry.

Abstract: A method of separating, recovering and reusing components of an exhausted slurry used in slicing silicon wafers from a silicon ingot. In the method, the viscosity of the exhausted slurry is reduced and the lubricating fluid component of the slurry is separated from solids and collected, the collected lubricating fluid component being suitable for reuse in the preparation of a fresh slurry without any additional separation steps being necessary. Additionally, the separated solids may be collected and further separated into an unspent abrasive grain component, which is suitable for reused in the preparation of a fresh slurry, and a waste product containing silicon particulate and spent abrasive grains.