LiBr Research Articles

Photoredox-Catalyzed Decarboxylative Bromination, Chlorination and Thiocyanation Using Inorganic Salts.

Decarboxylative halogenation reactions of alkyl carboxylic acids are highly valuable reactions for the synthesis of structurally diverse alkyl halides. However, many reported protocols rely on stoichiometric strong oxidants or highly electrophilic halogenating agents. Herein, we describe visible-light photoredox-catalyzed decarboxylative halogenation reactions of N-hydroxyphthalimide-activated carboxylic acids that avoid stoichiometric oxidants and use inexpensive inorganic halide salts as the halogenating agents. Bromination with lithium bromide proceeds under simple, transition-metal-free conditions using an organic photoredox catalyst and no other additives, whereas dual photoredox-copper catalysis is required for chlorination with lithium chloride. The mild conditions display excellent functional-group tolerance, which is demonstrated through the transformation of a diverse range of structurally complex carboxylic acid containing natural products into the corresponding alkyl bromides and chlorides. In addition, we show the generality of the dual photoredox-copper-catalyzed decarboxylative functionalization with inorganic salts by extension to thiocyanation with potassium thiocyanide, which was applied to the synthesis of complex alkyl thiocyanates.

First Law Optimization and Review of Double and Triple-Effect Parallel Flow Vapor Absorption Refrigeration Systems

Parallel flow double and triple-effect vapor absorption cooling systems (VACS) are trying to meet the challenges of vapor compression cooling systems due to their better performance. Therefore, the present study deals with the review, thermodynamic analysis, and optimization of operating parameters for both double and triple-effect VACS. Lithium bromide water was selected as the working fluid, while liquified petroleum gas (LPG) and compressed natural gas (CNG) were taken as the source of energy to drive both the VACS. Detailed First Law analysis, i.e., coefficient of performance (COP), was examined along with the optimization of operating parameters (such as salt concentration and operating generators temperature at different pressure levels) and the volume flow rate of the gases. Optimization was carried out for maximum COP of the VACS using an iterative technique. Our results show that the COP of the triple-effect system was approximately 32% higher than the double effect, while 15–20% less consumption of the gases (LPG and CNG) was observed. The most optimum stage for the operation of triple-effect VACS was reached at Te = 4 °C and Tc = Ta = 30 °C, Tg = 180 °C, Tc4 = 104 °C, Tc3 = 66 °C, Z1 = 0.5, and Z2 = 0.45.

Effect of rhombus mesh on 3D falling film flow characteristics over microchannel flat tube for LiBr (Lithium bromide) absorber

Effect of rhombus mesh on 3D falling film flow characteristics over microchannel flat tube for LiBr (Lithium bromide) absorber

Enhancing energy efficiency and sustainability in ejector expansion transcritical CO2 and lithium bromide water vapour absorption refrigeration systems

Enhancing energy efficiency and sustainability in ejector expansion transcritical CO2 and lithium bromide water vapour absorption refrigeration systems

Preparation of aerogels from corn stalks and research on their properties and gelation behavior

Corn straw is a kind of agricultural biomass waste produced by the corn crop. It is a question of how to make effective use of this waste resource. Biomass aerogel is a good adsorbent which can be used to deal with water pollution. The direct use of non-component separated maize straw as the raw material in this paper can effectively reduce the experimental cost, simplify the experimental procedures and make efficient use of maize straw compared to traditional cellulosic raw materials. The inorganic salt lithium bromide (LiBr) solution was used as the solvent, and the environmentally friendly corn stover whole component aerogels (CA) with excellent performance were prepared by solvent replacement and freeze-drying. The optimum process for the preparation of aerogels was obtained using a single factor test method: 1:200, 150 ℃, 40 min, 70 wt% LiBr. The full-component aerogels from maize straw contained cellulose, hemicellulose and lignin, which indicated that the maize straw was effectively utilised. CA has a three-dimensional network pore structure, mainly composed of micropores and mesoporous pores. It has ultra-low density (9 mg/cm3) and excellent adsorption capacity for methylene blue and soybean oil (123.59 mg/g, 103.58 g/g). At the same time, the Rheolaser Master Microrheological (RMM) analyzer of French Formulaction Company was used to investigate the changes in solution gel process. The mean azimuth shift (MSD) curve of the sample was measured by optical microrheometer. The elastic factor (EI), macroscopic viscosity factor (MVI), solid-liquid equilibrium point (SLB), and photon free path (I*) values of the samples were calculated to explore the microstructure and rheological characteristics of the samples during the gel process. The gel behaviour and processes have been explored based on the analysis of these parameters. Potential applications of whole-component aerogels from corn stalks include building insulation, thermal insulation, light-blocking materials, and packaging materials.

Thermodynamic and economic analysis of a multi-energy complementary distributed CCHP system coupled with solar thermochemistry and active energy storage regulation process

The combination of distributed energy systems (DES) and solar energy is considered a vital measure to save the usage of fossil energy. A new distributed combined cooling, heating and power (CCHP) system integrated with solar thermochemistry (STC) and energy storage (ES) units is proposed. The methane steam reforming (MSR) reaction is driven by solar energy to produce hydrogen-rich syngas, which is fed with high-efficiency solid oxide fuel cell (SOFC) – micro gas turbine (MGT) to produce electricity. The residual heat of the flue gas drives a double effect lithium bromide unit for cooling and a heat exchanger for heating, while a parabolic trough collector (PTC) is used to supplement cooling and heating supply. Under different weather conditions and user load demands, simulation analysis of the matching between system outputs and user loads is conducted, and the thermodynamic and economic performance are analyzed. The results show that through active energy storage regulation, the new system outputs can meet the hourly user loads with a matching degree of 1. The total exergy efficiencies of the system on typical summer, transition and winter days are 69.93%, 62.03%, and 52.28%, respectively, and the specific CO2 emission rates are 152.57 g/kWh, 191.75 g/kWh, and 234.16 g/kWh, respectively, indicating that the system has higher exergy efficiency and is more environmentally friendly under strong solar radiation. Economic analysis indicates that the capital investment cost is 779.34 k$, and the revenue begins in the 9-th year.

Evaluation of water + imidazolium ionic liquids as working pairs in absorption refrigeration cycles

Ionic Liquids (ILs) have been proposed as alternative absorption media for water in absorption refrigeration cycles to replace the currently used lithium bromide, which suffers from problems like crystallization and corrosiveness. This work investigates the use of imidazolium based ionic liquids as water absorbents in absorption refrigeration cycles. A predictive procedure is followed for calculating the parameters that mostly affect the performance of the cycle, that is the Vapor-Liquid Equilibrium (VLE) of the working pair and its heat capacity: UNIFAC is employed for the VLE calculations while a new predictive method has been developed for the heat capacity of the ILs. The effect of the alkyl chain length of the cation and the type of the anion that compose the IL is investigated, and it is shown that ILs consisting of imidazolium cation with short alkyl chain and the anions [Cl] and [DMP] exhibit the best performance in terms of Coefficient of Performance (COP) and circulation ratio (f). Comparison with the conventional LiBr absorbent indicates that the best ILs exhibit higher COP values but higher f ratios as well. Also, double cycle configurations are studied revealing the major effect of the supplied heat temperature on COP, even for the higher temperatures, compared to the single effect one. Finally, it is shown that there is a clear correlation between the COP of the refrigeration cycle and the product of the circulation ratio and the specific heat capacity of the strong solution, which is proposed in this work as a new reliable index for screening different ILs as absorbents, without the necessity of solving the mass and energy balances of the cycle.

Catalytic Conversion of Chitin Biomass to 5-Hydroxymethylfurfural in Lithium Bromide Molten Salt Hydrates

Catalytic Conversion of Chitin Biomass to 5-Hydroxymethylfurfural in Lithium Bromide Molten Salt Hydrates

Highly Stable Hybrid Electrolyte Lithium-Air Batteries Based on Weakly Acidic Lithium Bromide Catholyte

Hybrid lithium-air battery (HLAB) have garnered significant attention from researchers due to their relatively low overpotential, stable cyclability, and reversibility. In this paper, we investigate an HLAB system that uses a catholyte of lithium bromide solution in a weak acid state to enhance the stability of Li1−xAlxGe2−x(PO4)3 (LAGP) and improve its cycle life. The electrochemical performance of the optimized LiBr electrolyte exhibited stability after 443 cycles (1772 h) in ambient air (RH = 15%). Additionally, an improvement of >20% in coulombic efficiency was observed at a discharge specific capacity of 10736 mAh·g−1 compared to HLABs using LiOH electrolyte. This study provides insights into the protection of LAGP membranes in HLAB and the inhibition of reaction product precipitation.

Effect of lithium bromide doping on structural, dielectric, and transport properties of methylcellulose-based solid polymer electrolyte films

Effect of lithium bromide doping on structural, dielectric, and transport properties of methylcellulose-based solid polymer electrolyte films

Waste Heat Recycling Absorption Refrigeration Circulation System

To maximize energy use, this paper designs a lithium bromide absorption refrigeration system that is used to recycle and use low-temperature energy and industrial residual heat. Firstly, the mathematical model of the system is established using the lithium bromide aqueous solution status equation and the equation of the state of water and steam to obtain the state parameters in the thermodynamic calculation process of the system. Secondly, according to the principle of mass economy, energy saving, and heat transfer, the thermodynamic parameters of each process of the system are obtained to assist the design of the system. Finally, the influence of some key parameters on the system is simulated and analyzed to obtain the optimal parameters which can make the system recovery efficiency the highest. The simulation results show that the system conceived in this article can efficiently recycle waste gas and achieve the purpose of refrigeration. Therefore, it has a certain value of popularization.

Effect of lignin and released acid on the gelation and aerogel fabrication of whole biomass in the lithium bromide molten salt hydrate system

Effect of lignin and released acid on the gelation and aerogel fabrication of whole biomass in the lithium bromide molten salt hydrate system

Control Strategy Based on Artificial Intelligence for a Double-Stage Absorption Heat Transformer

Thermal energy recovery systems have different candidates to mitigate CO2 emissions as recommended by the UN in its list of SDGs. One of these promising systems is thermal absorption transformers, which generally use lithium-water bromide as the working fluid. A Double Stage Heat Transformer (DSHT) is a thermal machine that allows the recovery of thermal energy at a higher temperature than it is supplied through the effect of steam absorption in a concentrated solution of lithium bromide. There are very precise thermodynamic models which allow us to calculate all the possible operating conditions of the DSHT. To perform the control of these systems, the use of Artificial Intelligence (AI) is proposed with two computational techniques—Fuzzy Logic (FL) and Artificial Neural Network (ANN)—to calculate in real-time the set of variables that maximize the product’s Gross Temperature Lift (GTL) and Coefficient of Performance (COP) in a DSHT. The values for Coefficient of Determination (R2), Mean Square Error Root (MRSE), and Mean Error Bias (MBE) for the two types of computational techniques were analyzed and compared with the purpose of identifying which of them may be more accurate to calculate the operating conditions (temperatures, pressures, concentration and flows) with the highest COP for an interval of the value of the temperature absorption entered by the user. The result of the analysis of the evaluated techniques concluded that the control strategy of a DSHT in real-time will be based on the precise calculation of the refrigerant flow in the second evaporator with a Neural Network of 30 neurons, 300 weights and 40 bias, as it is more accurate than the Fuzzy Logic technique. The goodness-of-fit for two computational techniques was evaluated as having an R2 higher than 0.98 for the provided data. Future AI controllers must be based on evaporator flow values with evaporator power at 3.9−04 kg/KJ.

Simulation of heat transfer and effectiveness in a helical heat exchanger made from thermally enhanced polymer material for use in absorption cooling

Heat exchangers in absorption chillers are usually made of copper material. However, prob-lems of corrosion are usually encountered, especially in the solution heat exchanger. In this study a numerical investigation of the heat transfer effectiveness in a double pipe helical heat exchanger made from a thermally enhanced polymer material was conducted. The material consists of a Liquid crystal polymer (LCP), (Vectra A950) as the matrix material, while carbon fibre is the filler material. The resulting composite has a carbon fibre weight fraction of 74%. The heat exchanger was modelled as a counter flow solution heat exchanger to be used in a lithium bromide – water absorption chiller of 3 kW capacity. The numerical software ANSYS fluent (version 14.5) was used for the modelling and simulation. Thermal and mechanical properties of the thermally enhanced polymer were used in the modelling and simulation. The viscous laminar model was used, while employing a second order upwind solution method. Results indicate that the heat exchanger was able to perform the required duty by reducing the strong solution temperature from 90oC at inlet to 57oC at outlet, while increasing the weak solution temperature from 40oC at inlet to 67oC at outlet. The effectiveness of the heat ex-changer was 77.4%. Results were numerically compared to a corresponding heat exchanger of same geometry and flow conditions, made of copper. It was observed that the polymer heat exchanger attained 89.2% effectiveness of the copper heat exchanger.

SELECTION OF THE OPTIMAL HEATING COOLANT FOR ARM DEPENDING ON THE TECHNICAL CONDITIONS OF THE OIL AND GAS ENTERPRISE

Generation of cold is great demand process for many enterprises of the oil and gas industry. With large capacities of the enterprise, deeper cooling of heat carriers is required in chemical and petrochemical industries, metallurgy, compressor stations, etc. In administrative buildings and workshops located on the sites, it is required to create comfortable conditions in the buildings for the people who are there. In this regard, the demand for refrigeration units is increasing. Until recently, steam compression refrigerating machines were the market leader in refrigeration units. However, their main disadvantage is the high consumption of electricity, and often the process of generating cold has become too expensive.Relatively recently, steam compression refrigerating machines (chillers) have been replaced by absorption refrigerating machines (ARM). Their main and key feature is that they generate cold without consuming a single kilowatt of electrical energy, since the process of generating cold is based on the thermophysical properties of low-boiling solutions of lithium bromide or ammonia.

Ion/Water Network Structural Dynamics in Highly Concentrated Lithium Chloride and Lithium Bromide Solutions Probed with Ultrafast Infrared Spectroscopy

The structural dynamics of highly concentrated LiCl and LiBr aqueous solutions were observed from 1-4 to 1-16 water molecules per ion pair using ultrafast polarization-selective pump-probe (PSPP) experiments on the OD stretch of dilute HOD. At these high salt concentrations, an extended ion/water network exists with complex structural dynamics. Population decays from PSPP experiments highlight two distinct water components. From the frequency-dependent amplitudes of the decays, the spectra of hydroxyls bound to halides and to water oxygens are obtained, which are not observable in the FT-IR spectra. PSPP experiments also measure frequency-dependent water orientational relaxation. At short times, wobbling dynamics within a restricted angular cone occurs. At high concentrations, the cone angles are dependent on frequency (hydrogen bond strength), but at higher water concentrations (>10 waters per ion pair), there is no frequency dependence. The average cone angle increases as the ion concentration decreases. The slow time constant for complete HOD orientational relaxation is independent of concentration but slower in LiCl than in LiBr. Comparison to structural MD simulations of LiCl from the literature indicates that the loss of the cone angle wavelength dependence and the increase in the cone angles as the concentration decreases occur as the prevalence of large ion/water clusters gives way to contact ion pairs.

Design and experimental analysis of a shell and tube vapor generator for solar thermal vapor absorption refrigeration

The generator is a crucial component of absorption refrigeration system as it provides a major input to the system. The overall performance of the absorption system mainly depends on vapor generation rate in a generator. Various studies are available in the literature on LiBr-H2O vapor absorption refrigeration systems. However, all these studies are focused on the performance of high-capacity commercial systems. Further, detailed analysis and feasibility of generator designs is not well explored though it is an important component of the system. Thus, present novel study is aimed to provide the idea about generator design and performance for a low-capacity system useful for residential applications. The objective of the present work is to investigate the shell and tube heat exchanger as a vapor generator for a vapor absorption refrigeration system experimentally. A LiBr-H2O vapor absorption refrigeration system requires water separation from LiBr in the vapor generator. The vapor generation depends on the saturation temperature and pressure. In this study, a shell and tube heat exchanger is designed for a vapor absorption refrigeration system of 0.5 ton of refrigeration. The experimental investigations are carried out at different operating conditions to evaluate the unit's performance and define its suitability for low-capacity absorption refrigeration system. Considering the output temperature of hot water from the solar thermal collector (80 –90 ℃) and pressure restrictions on the vapor generation process due to the crystallization of lithium bromide, the presented heat exchanger design is evaluated for pressure ranging between −0.90 bar and −0.65 bar. The experimental evaluation revealed that the heat exchanger is the most effective when the inlet temperature is 80 ℃ at a flow rate of 3 L per minute, and the initial pressure is −0.65 bar, while it is least effective for −0.90 bar. Further, vapor generation is greatest at −0.90 bar and lowest at −0.65 bar. The given configuration is suitable for an absorption system of cooling capacity 0.16 to 0.3 TR, as it can supply the vapor at the required flow rate at a given saturation temperature and pressure suitable for the de-absorption of water from LiBr.

Novel solar-driven low temperature district heating and cooling system based on distributed half-effect absorption heat pumps with lithium bromide

Utilizing solar energy for space heating and cooling would contribute to achieving the goal of China's carbon emission peak by 2030. However, solar energy is featured by low energy density and intermittent energy output, and it mismatches with the continuous demand of high energy density in the Chinese Northern cities. For the solar-driven district heating and cooling system, both time and space mismatches between supply and demand are two key problems to be solved. To solve the two problems, a novel solar-driven low temperature district heating and cooling system based on distributed half-effect absorption heat pumps with lithium bromide is proposed, and it is analyzed by using thermodynamics and economics. Results show that the proposed novel solar-driven low temperature district heating and cooling system can achieve annual system coefficient of performance about 8.52, annual system product exergy efficiency about 36.7%, and cost-effectively heat transmission distance about 24.5 km. Compared with the conventional heating and cooling systems, the proposed novel solar-driven low temperature district heating and cooling system can reduce heating cost, cooling cost and annual carbon emission by about 27.14 ¥/GJ, 12.12 ¥/GJ and 23 kg per floor area, and it energy conversion and transfer process is advanced.

Flame‐retardant, flexible, and breathable smart humidity sensing fabrics based on hydrogels for respiratory monitoring and non‐contact sensing

AbstractSmart sensing fabrics are becoming increasingly attractive in the emerging wearable areas of medical and military so far. Here, for the first time, we present a smart humidity sensing fabric (SHSF) based on a moisture‐sensitive polyacrylamide hydrogel for respiratory monitoring and non‐contact sensing. Fabricated by in situ cross‐linking of the hydrogel precursors on the fibers of the fabric, the flexible SHSF shows excellent sensitivity, outstanding flame retardance, air permeability, water retention capacity, and stability after treatment with lithium bromide solution. Specifically, its conductance increases more than 311 times as humidity increased from 11% to 98%. Besides, the humidity sensor features good repeatability and the ability to work normally under folding due to its flexible nature. As a clothing material, hydrogel–fabric composite exhibits 4.3 times the burning time compared to cotton fabric, illustrating better flame retardance. The SHSF is used to monitor human breathing and non‐contact finger approaching in real time, demonstrating its flexibility in practical applications. This work provides strategies for preparing high‐performance, flame‐retardant SHSF for emerging wearable electronic devices.

Process design and technoeconomic analysis for zero liquid discharge desalination via LiBr absorption chiller integrated HDH-MEE-MVR system

A novel multipurpose seawater desalination process is presented that integrates a Lithium Bromide (LiBr) absorption chiller, humidification-dehumidification (HDH), multi-effect evaporator, and mechanical vapor recompression (MVR) to improve the energy effectiveness of conventional desalination processes. The proposed process uses the LiBr absorption chiller cycle to preheat the seawater prior to the steam generation in the multi-effect evaporators while the MVR system activates the LiBr cycle. The integration of HDH further allows to recover the excess water in the process stream and concentrates the brine effluent for zero liquid discharge processing. A stand-alone HDH desalination is comparatively studied with the integrated system to quantify their respective performances over several metrics. Technoeconomic analysis is also performed to assess the economic feasibility and a sensitivity analysis is carried out to observe the effects of changing process variables on the overall performance of these systems. The results show that the proposed process design achieves several times higher gain-output ratio compared to a conventional HDH system of equal capacity, with a levelized water production cost of $8.4/m3 and 6 kW of cooling capacity that can be used for air conditioning.