Class 8 - Class 8 Chemical Reactors and Separations Reactor...

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Unformatted text preview: Class 8 Chemical Reactors and Separations Reactor Separation Unit Operations Feed Impure Product Product Co-products Idealized Reactor/Separations Unit Operations Typical Catalytic Reactor Design (reactor looks like a shell/tube heat exchanger) (catalyst is packed in tubes; tube length and diameter important) (heat transfer fluid runs through shell) (gas or liquid) (need separations operations to meet specification) (typically something like a Dowtherm TM ) (T adjusted via heat Exchange System) Heat Exchange Reactor Use of Diluent External Heat Exchange Hot/Cold Shot Continuous Reactor Configurations For Solids Pusher Kiln Solids Gas Solids Gas Rotary Moving Bed Transport Flow Solids Solids Gas Gas Fluidized Bed Gas Solids Invention, Development, and Commercialization of the Rapid Carbothermal Reduction (RCR) Process Class 8a Chemical Reactors for Solids Business Objective The Dow Chemical Company intended to be the low cost producer in the world of high quality non-oxide ceramic powders Classification of Non-oxides Nitrides Carbides Silicides Sulfides Phosphides Borides AlN, Si 3 N 4 , TiN, ZrN WC, SiC, B 4 C , TiC TiB 2 , LaB 6 , ZrB 2 MoSi 2 , TaSi 2 MoS 2 , CdS BP Nonoxide Ceramics Carbothermal Reduction Precursor Preparation Reaction SiO 2 + 3C SiC + 2CO 2B 2 O 3 + 7C B 4 C + 6CO Excess C or B 2 O 3 Removal SiC/C + O 2 SiC + CO 2 B 4 C/B 2 O 3 + 3H 2 O B 4 C + 2H 3 BO 3 Ultrafine Milling Acid Leaching Size Classification C B 2 O 3 , SiO 2 CO Air H 2 O CO 2 H 3 BO 3 HF, HCl Oversize Waste Acid Sol’n SiC, B 4 C SiC/C, B 4 C/B 2 O 3 Commercial Acheson Process for SiC Electric Arc Furnace Process for B 4 C Traditional Boron Carbide Powders Medium Grade Fine Grade 5 10 15 20 25 30 35 2 4 6 8 10 Final Particle Size (µm) Total Cost SiC ($/kg) Estimates of SiC Powder Cost with Comminution of Acheson SiC Grain Laser Synthesized B 4 C High-Performance Advanced Ceramics Applications Requirements • Submicron Sized Particles • Low Degree of Agglomeration • High Purity • Cost/Performance Advantages Technical Objective Develop a continuous process for producing submicron ceramic powders with properties similar to laser product, but at a substantially reduced cost Strategy to Meet Program Objectives • Direct synthesis of submicron powders • Use carbothermal reduction chemistry High purity, low cost raw materials Develop continuous reactor technology B 4 C, TiB 2 : ∆ G vs. Temperature (P = 0.1 MPa) (kJ/mol) Enthalpy Considerations 3C + SiO 2 SiC* + 2CO 7C + 2B 2 O 3 B 4 C* + 6CO 1515 o C 1561 o C + 14,688 + 29,901 ∆ H (kJ/kg*) @ ∆ G = 0 Induction Heated Laboratory Reactor Reaction Completed in seconds (Rapid Intrinsic Kinetics) C/B 2 O 3 Boron Carbide Products from Carbon Black/Boric Acid Precursors Reaction Characteristics...
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This note was uploaded on 11/14/2011 for the course CHEN 4520 taught by Professor Wiemer during the Fall '11 term at Colorado.

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Class 8 - Class 8 Chemical Reactors and Separations Reactor...

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