Reactive Distillation Column Design for Tetraethoxysilane (TEOS) Production: Economic and Environmental Aspects

Self Cite

The silicon industry is a source of various types of products, including materials for the implementation of renewable energy systems, with a comparatively lower environmental impact than conventional fossil energy sources and high added value byproducts. In this context, the exploitation of the different byproducts generated in the production of polycrystalline silicon (polysilicon) offers opportunities to increase the economics of the polycrystalline silicon production process. In this work, a silicon based refinery is conceptually designed using surrogate models for the major units to evaluate the portfolio of products. Although the main product is polysilicon, there are a number of products that might be obtained in the process to improve its profitability, such as tetraethoxysilane (at different purities) as well as chlorosilanes, including SiH 4 , SiH 2 Cl 2 , and SiH 3 Cl. Next, an economic evaluation of the facility is carried out to determine its economic feasibility. The results show that the refinery produces tetraethoxysilane and chlorosilanes in addition to the production of polysilicon. The proposed design reduces the cost for polycrystalline silicon to 6.86 $/kg, compared to a cost of 8.93 $/kg of polycrystalline silicon if the plant does not generate high value-added byproducts, both values below the commercial price of polycrystalline silicon, which is estimated at 10 $/kg. Therefore, the refinery is not only capable of meeting the market share requirements, but in a way that the generation of different high added value byproducts increases the plant profit compared to that of the net income earned by traditional polysilicon monoproduct plants.

Section: Methodsmentioning

confidence: 99%

Optimal Portfolio of Products in a Polycrystalline Silicon Refinery

Ramírez‐Márquez

Hernández

Martı́n

et al. 2020

Self Cite

“…Although reactive distillation columns (RDCs) are extremely advantageous in the separations of quaternary reversible reactions with the most favorable ranking of relative volatilities (which features the lightest and heaviest products and the two reactants in between), they are generally disadvantageous in the separations of quaternary reversible reactions with the most unfavorable ranking of relative volatilities (MURRV) (which features, on the other hand, the lightest and heaviest reactants and the two products in between). − It is mainly due to the unfavorable thermodynamic properties of such kinds of reacting mixtures that cause a single RDC unable to perform efficiently the reaction operation and separation operation required. As a result, a multiple-column system involving an RDC, followed by one or two conventional distillation columns (CDCs), usually must be adopted, which incurs inevitably considerable capital investment and operating cost. − The practice reminds us of not only the inherent limitations of the RDC but also the great potential of seeking process intensification in the separations of quaternary reversible reactions with the MURRV.…”

Section: Introductionmentioning

confidence: 99%

Reactive Double Dividing-Wall Distillation Columns: Structure and Performance

Zang

Zhang

Huang

et al. 2020

The separations of quaternary reversible reactions with the most unfavorable ranking of relative volatilities (i.e., the two reactants are the lightest and heaviest components and the two products in between) require a reactive distillation column, followed by one or two conventional distillation columns. The multiple-column structure reflects not only a high energy intensity in the reaction operation and separation operation involved but also a great potential of process intensification in process development. With reference to a two-column system involving a reactive distillation column with an external recycle and a conventional distillation column (ER-RDC + CDC), a kind of reactive double dividing-wall distillation column (R-DDWDC) is derived via careful coordination and mass and thermal coupling between the ER-RDC and CDC. Closely dependent upon the magnitude of the reaction thermal effect, the left dividing wall is located either at the top or at the bottom. In addition to allowing the mass and thermal coupling between the ER-RDC and CDC, it facilitates primarily the reaction operation in the reactive section. The right dividing wall is located at the middle to fully strengthen the mass and thermal coupling not only between the ER-RDC and CDC but also between the separation operations included. The derived R-DDWDC features essentially the greatest degree of process intensification and becomes consequently the most thermodynamically efficient scheme in the separations of quaternary reversible reactions with the most unfavorable ranking of relative volatilities. The derived R-DDWDC is evaluated in terms of two examples, involving, respectively, the separations of ideal exothermic and endothermic quaternary reversible reactions with the most unfavorable ranking of relative volatilities. The derived R-DDWDC is found to be much more energy efficient than the ER-RDC + CDC, the reactive single dividing-wall distillation column, and those R-DDWDCs with different configurations. These outcomes demonstrate that the derived R-DDWDC is a much competitive alternative for the separations of quaternary reversible reactions with the most unfavorable ranking of relative volatilities. They also highlight the feasibility and effectiveness of the proposed strategy for process synthesis and design, that is, when the reaction processed is exothermic, the optimum R-DDWDC must come from one of R-DDWDC2 and R-DDWDC4; otherwise, the R-DDWDC4 remains to be the only possibility.

“…With its moderately reactive Si–OR bonds, tetraethyl orthosilicate or tetraethoxysilane (TEOS) is a useful ingredient in the synthesis of various silicon compounds, such as zeolite membranes, bifunctional mesoporous organosilica, and silicon-nanotube-based batteries. − In particular, through sol–gel processes, TEOS-based insulators, binders, and crosslinking agents are used in diverse industries. , Currently, TEOS is commercially produced from metallurgical silicon (Si mg ) as the raw material. − The synthesis process is well-established, but Si mg production from silica-containing sources requires a high-temperature (1900 °C) carbon thermal-reduction process, which draws an extremely large electricity supply. , Consequently, the conventional synthesis is costly to operate and generates high CO 2 emissions.…”

Section: Introductionmentioning

confidence: 99%

Impact of the Water Removal Method on Tetraethyl Orthosilicate Direct Synthesis: Experiment and Process Assessment

Nguyễn

Fukaya

Choi

et al. 2019

A direct synthesis pathway of tetraethyl orthosilicate from silica and ethanol was recently proposed. Although this pathway has many advantages over the conventional one producing tetraethoxysilane (TEOS) from metallurgical silicon, its potential can be further increased by the effective removal of its byproducts. This study investigates the removal of the water byproduct, which reduces the TEOS product yield and enhances the loss of raw materials. Several inorganic dehydrating agents were examined under different conditions, on the basis of which a suitable TEOS synthesis process using the selected dehydrating agent was designed and its optimal conditions were determined. The feasibility of the designed process was evaluated in comparison with our previously reported process using a molecular sieve as a water adsorbent and the conventional process. The evaluation results confirmed that the CaO process is more economically competitive and environmentally friendlier, reducing 24% production cost and 40% greenhouse gas emissions of the conventional process.