Towards carbon neutrality of calcium carbide-based acetylene production with sustainable biomass resources

Acetylene is produced from the reaction between calcium carbide(CaC_(2))and water,while the production of CaC_(2) generates significant amount of carbon dioxide not only because it is an energy-intensive process but also the raw material for CaC_(2) synthesis is from coal.Here,a comprehensive biomass-to-acetylene process was constructed that integrated several units including biomass pyrolysis,oxygen-thermal CaC_(2) fabrication and calcium looping.For comparison,a coal-to-acetylene process was also established by using coal as feedstock.The carbon efficiency,energy efficiency and environmental impacts of the bio-based calcium carbide acetylene(BCCA)and coal-based calcium carbide acetylene(CCCA)processes were systematically analyzed.Moreover,the environmental impacts were further evaluated by applying thermal integration at system level and energy substitution in CaC_(2) furnace.Even though the BCCA process showed lower carbon efficiency and energy efficiency than that of the CCCA process,life cycle assessment demonstrated the BCCA(1.873 kgCO_(2eq) kg-prod^(-1))a lower carbon footprint process which is 0.366 kgCO_(2eq) kg-prod^(-1) lower compared to the CCCA process.With sustainable energy(biomass power)substitution in CaC_(2) furnace,an even lower GWP value of 1.377 kgCO_(2eq) kg-prod^(-1) can be achieved in BCCA process.This work performed a systematic analysis on integrating biomass into industrial acetylene production,and revealed the positive role of biomass as raw material(carbon)and energy supplier.

Development of calcium coke for CaC2 production using calcium carbide slag and coking coal

A type of calcium coke was developed for use in the oxy-thermal process of calcium carbide production.The calcium coke was prepared by the co-pyrolysis of coking coal and calcium carbide slag, which is a solid waste generated from the chlor-alkali industry.The characteristics of the calcium cokes under different conditions were analyzed experimentally and theoretically.The results show that the thermal strength of calcium coke increased with the increase in the coking coal proportion, and the waterproof property of calcium coke also increased with increased carbonation time.The calcium coke can increase the contact area of calcium and carbon in the calcium carbide production process.Furthermore, the pore structure of the calcium coke can enhance the diffusion of gas inside the furnace, thus improving the efficiency of the oxy-thermal technology.

Life cycle assessment of HFC-134a production by calcium carbide acetylene route in China

HFC-134a is a widely used environment-friendly refrigerant.At present,China is the largest producer of HFC-134a in the world.The production of HFC-134a in China mainly adopts the calcium carbide acetylene route.However,the production route has high resource and energy consumption and large waste emission,and few of the studies addressed on the environmental performance of its production process.This study quantified the environmental performance of HFC-134a production by calcium carbide route via carrying out a life cycle assessment(LCA)using the CML 2001 method.And uncertainty analysis by Monte-Carlo simulation was also carried out.The results showed that electricity had the most impact on the environment,followed by steam,hydrogen fluoride and chlorine,and the impact of direct CO_(2) emissions in calcium carbide production stage on the global warming effect also could not be ignored.Therefore,the clean energy(e.g.,wind,solar,biomass,and natural gas)was used to replace coal-based electricity and coal-fired steam in this study,showing considerable environmental benefits.At the same time,the use of advanced production technologies could also improve environmental benefits,and the environmental impact of the global warming category could be reduced by 4.1%via using CO_(2) capture and purification technology.The Chinese database of HFC-134a production established in this study provides convenience for the relevant study of scholars.For the production of HFC-134a,this study helps to better identify the specific environmental hotspots and proposes useful ways to improve the environmental benefits.

Non-isothermal kinetics and characteristics of calcium carbide nitridation reaction with calcium-based additives

The nitridation reaction of calcium carbide and N_(2) at high temperatures is the key step in the production of lime-nitrogen.However,the challenges faced by this process,such as high energy consumption and poor product quality,are mainly attributed to the lack of profound understanding of the reaction.This study aimed to improve this process by investigating the non-isothermal kinetics and reaction characteristics of calcium carbide nitridation reaction at different heating rates(10,15,20,and 30℃·min^(-1))using thermogravimetric analysis.The kinetic equation for the nitridation reaction of additive-free calcium carbide sample was obtained by combining model-free methods and model-fitting method.The effect of different calcium-based additives(CaCl_(2) and CaF_(2))on the reaction was also investigated.The results showed that the calcium-based additives significantly reduced reaction temperature and activation energy E_(a) by about 40% with CaF_(2) and by 55%-60% with CaCl_(2).The reaction model f(α)was also changed from contracting volume(R3)to 3-D diffusion models with D3 for CaCl_(2) and D4 for CaF_(2).This study provides valuable information on the mechanism and kinetics of calcium carbide nitridation reaction and new insights into the improvement of the lime-nitrogen process using calcium-based additives.

Calcium Carbide:From Elemental Carbon to Isotope-Economic Synthesis of^(13)C_(2)-Labeled Heterocycles

^(13)C-Carbon is the most available source of carbon-13.It is a relatively inexpensive solid material,which can be easily converted to calcium carbide-^(13)C_(2).In current work,Ca^(13)C_(2)was used for in situ generation of^(13)C_(2)-acetylene in 1,3-dipolar cycloaddition and[4+2]cycloaddition reaction.For the first time,1H-1,2,3-triazoles-4,5-^(13)C_(2)and isoxazoles-4,5-^(13)C_(2)were synthesized using calcium carbide-^(13)C_(2).A Diels-Alder type cycloaddition of 3,6-di(pyridin-2-yl)-1,2,4,5-tetrazine and Ca^(13)C_(2)was investigated,and the best way for the synthesis of 3,6-di(pyridin-2-yl)pyridazine-4,5-^(13)C_(2)was proposed for the first time.Here we perform a detailled description of NMR spectra of^(13)C_(2)-labeled triazoles,isoxazoles and 3,6-di(pyridin-2-yl)pyridazine.

CO_(2) mineralization of carbide slag for the production of light calcium carbonates

The production of polyvinyl chloride by calcium carbide method is a typical chemical process with high coal consumption,leading to massive flue gas and carbide slag emissions.Currently,the carbide slag with high CaO content is usually stacked in residue field,easily draining away with the rain and corroding the soil.In this work,we coupled the treatment of flue gas and carbide slag to propose a facile CO_(2)mineralization route to prepare light calcium carbonate.And the route feasibility was comprehensively evaluated via experiments and simulation.Through experimental investigation,the Ca^(2+) leaching and mineralization reaction parameters were determined.Based on the experiment,a process was built and optimized through Aspen Plus,and the energy was integrated to obtain the overall process energy and material consumption.Finally,the net CO_(2)emission reduction rate of the entire process through the life-cycle assessment method was analyzed.Moreover,the relationship between the parameters and the CO_(2)emission life-cycle assessment was established.The final optimization results showed that the mineralization process required 1154.69 kW·h·(t CO_(2))^(-1) of energy(including heat energy of 979.32 kW·h·(t CO_(2))^(-1) and electrical energy of 175.37 kW·h·(t CO_(2))^(-1)),and the net CO_(2)emission reduction rate was 35.8%.The light CaCO_(3)product can be sold as a high value-added product.According to preliminary economic analysis,the profit of mineralizing can reach more than 2,100 CNY·(t CO_(2))^(-1).

One-Pot Three-Component Synthesis of 2-Methyl-3-aminobenzofurans Using Calcium Carbide as a Concise Solid Alkyne Source

A one-pot three-component method for the synthesis of 2-methyl-3-aminobenzofurans using calcium carbide as a concise solid alkyne source,and salicylaldehydes and secondary amines as starting materials is described.This protocol has salient feature of the use of inexpensive,abundant and easy-to-handle alkyne source,avoiding the use of inflammable and explosive acetylene gas as an original alkyne source.In addition,step economy,satisfactory yield,and simple work-up procedure are also advantages of this route.

Effect of potassium carbonate on catalytic synthesis of calcium carbide at moderate temperature

Calcium carbide was successfully synthesized by carbothermal reduction of lime with coke at 1973 K for 1.5 h.The effect of potassium carbonate as additive on the composition and morphology of the product was investi-gated using X-ray diffraction and scanning electron microscope.Addition of potassium carbonate increased the yield of calcium carbide.The sample in the presence of potassium carbonate generated acetylene gas of 168.3 L/kg,which was 10%higher than that in the absence of potassium carbonate.This result confirmed the catalytic effect of potassium carbonate on the synthesis of calcium carbide.A possible mechanism of the above effects was that the additive,which was melted at the reduction temperature,dissolved CaO and so promoted the contact between CaO and carbon,which was essential for the solid-solid reaction to form calcium carbide.

Calcium carbide and its recent advances in biomass conversion

Calcium carbide(CaC_(2))is a sustainable source of acetylene which plays an important role in organic synthesis due to its active triple bonds and terminal protons.Solid CaC_(2) has several advantages over acetylene gas such as easy handling,convenient storage and transportation.The CaC_(2) is considered as a safer and more convenient source of acetylene.The chemistry of the CaC_(2) is not confined to its use as a source of acetylene and its applications are not limited to the known reactions of acetylene.With the CaC_(2) chemistry being actively developing recently,it may eventually lead to the development of new transformations of alkyne chemistry.Herein,this mini review is focused on the synthesis and application of the CaC_(2) in biomass transformations.

Preparation of CaO-containing carbon pellets from coking coal and calcium oxide:Effects of temperature,pore distribution and carbon structure on compressive strength in pyrolysis furnace

CaO-containing carbon pellets(CCCP)were successfully prepared from well-mixed coking coal(CC)and calcium oxide(CaO)and roasted at different pyrolysis temperatures.The effects of temperature,pore distribution,and carbon structure on the compressive strength of CCCP was investigated in a pyrolysis furnace(350-750℃).The results showed that as the roasting temperature increased,the compressive strength also increased and furthermore,structural defects and imperfections in the carbon crystallites were gradually eliminated to form more organized char structures,thus forming high-ordered CC.Notably,the CCCP preheated at 750℃exhibited the highest compressive strength.A positive relationship between the compressive strength and pore-size homogeneity was established.A linear relationship between the com-pressive strength of the CCCP and the average stack height of CC was observed.Additionally,a four-stage caking mechanism was developed.

Losses of Urea-Nitrogen Applied to Maize Grown on a Calcareous Fluvo-Aquic Soil in North China Plain

Field experiments were conducted in a maize (Zea mays L.)field of a calcareous fluvo-aquic soil in North China Plain for studying the fate and ammonia loss of urea-N applied at seedling stage,as well as the effectiveness of coated calcium carbide(CCC) in reducing N loss and in improving the yield efficiency of urea.Results show that:(1) For the surface-broadcast treatment ammonia volatilization (measured with micro-meteorological technique)took place quickly,reached the peak 20-26hr after application,and then declined gradually;the cumulative ammonia loss approached the maximum 188hr after application (30% of the N applied),and increased only to 32% 284 hr after application;the latter accounted for 71% of the total loss (45% of applied N).(2) In the case of point placement at a depth of 5-10 cm,ammonia loss 188hr after application was only 12% of the N applied,accounting for 40% of the total loss.(3) There was no difference in total loss between the application depths of 6cm and 10 cm,the loss of them was 30% and 29%,respectively.(4) Total loss of N applied at lower rate (40kg N/ha)with point deep placement at 6cm depth was found only 4% of the N applied,it rose up to 30% when the rate of application increased to 80kg N/ ha.(5) The nitrification inhibitor,CCC,seemed to enhance N loss of urea rather than reduce it,and did not show any benefit effect in improving the yield efficiency of urea,which is presumably due to the high potential of ammonia volatilization in the soil and climatic conditions under investigation.

Resource utilization of solid waste carbide slag:a brief review of application technologies in various scenes

China is the largest producer and consumer of calcium carbide in the world.The calcium carbide industry is an indispensable industry to support the basic life of people.The huge production capacity of calcium carbide is accompanied by a large number of solid waste carbide slag.Due to the immature treatment technology of carbide slag,a large number of carbide slag are stacked on-site,resulting in land occupation,air-drying,easy take-off ash,and pollution of the environment and water resources.In China,calcium carbide is mainly used to produce acetylene and further utilized,80%of which is used to produce polyvinyl chloride(PVC).A large amount of carbide slag is not used,while only a small part is used in the traditional building materials industry,flue gas desulfurization,sewage treatment,etc.,however,the economic benefits are poor.Therefore,converting the solid waste carbide slag produced by the calcium carbide industry into high value-added CaCO3,CaCl2,CaSO4 whiskers,etc.has become a potential way to expand the development field of the calcium carbide industry and is environmentally friendly.This paper focuses on summarizing the traditional and emerging high value-added utiliza-tion technologies of carbide slag,and then introduces the application research of carbide slag in carbon emission reduction.Finally,the defects of these technologies are summarized and further research directions are prospected.This study provides basic guidance for the diversified development of efficient resource utilization of carbide slag.Graphical abstract Diversified development of calcium carbide industry,resource utilization of solid waste carbide slag and its application of carbon emission reduction have been fully reviewed.

Reaction kinetics of CaC2 formation from powder and compressed feeds

The production of CaC2 from coke/lime powders and compressed powder pellets are low cost and fast processes. A number of studies have reported the reaction kinetics of these reactions but they are still not well understood and the proposed kinetic models are not comparable due to differences in the reaction conditions. Therefore the reaction behavior of CaO/C powders （0.074 mm） and cubes （5 mm × 5 mm × （4.6-5.1） mm） compressed from a mixture of powders have been studied using thermal gravimetric analysis （TGA） at 1700- 1850 ℃. Kinetic models were obtained from the TGA data using isoconversional and model-fitting methods. The reaction rates for the compressed feeds were lower than those for the powder feeds. This is due to the reduced surface area of the compressed samples which inhibits heat transfer from the surrounding environment （or the heating source） to the sample. The compression pressure had little influence on the reaction rate. The reaction kinetics of both the powder and the compressed feeds can be described by the contracting volume modelf（α） = 3（1 -α）^2/3, where a is the conversion rate of reactant. The apparent activation energy and pre-exponential factor of the powder feed were estimated to 346-354 kJ·mol^-1 and 5.9 x 10^7 min^-1, respectively, whereas those of the compressed feed were 305-327 kJ·mol^-1 and 3.6 ×10^6 min^-1, respectively.