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Graham-Fridjonsson NaCN Production Feasibility Study

Graham-Fridjonsson NaCN Production Feasibility StudyLiterature Review, Process Selection, Mass and Energy Balances Presented to The School of Mechanical and Chemical Engineering:Dr. Einar Fridjonsson, PhDPrepared byDesign Group 2Chanel Bernardo 21131417Callum Biggs 20498066Wei Cui 21250612Pauline Ho 21108549Vincent Lim 20859448

Table of ContentsTable of Contents1List of figures1List of tables21.Introduction32.Literature Review42.1Literature Sources42.2Gas Treatment42.3Primary Reaction Pathway42.3.1Andrussow Process42.3.2BMA Process (Degussa or Blausare-Methan-Ammoniak Process)42.3.3Shawinigan Process (or Flouhmic Process)52.3.4Formamide Process52.4Quenching52.5Ammonia Recovery62.5.1Fertiliser Production62.5.2Ion Exchange62.6HCN-NaCN Conversion72.6.1Articles72.7Storage82.8Waste Management82.8.1Cyanide Waste82.8.2HCN Absorber Off-Gas93.Process Selection103.1Selection Method103.2Batch versus Continuous113.3Ammonia Recovery123.4Waste Management133.5Quencher134.Mass & Energy Balance165.Project Management175.1Team Allocation175.2Gantt Chart175.3Timeline175.4Resource Graph175.5Network Diagram175.6Critical Path Assessment176.Conclusion187.Appendices19Appendix A Literature Review Data197.1Primary Reaction Pathway197.2Quenching227.3Recycle & Waste Treatment277.4HCN-NaCN Conversion337.5Storage438. References49

List of FiguresFigure 1 Internal and external constraints placed on the design space (Sinnott 2005)10Figure 2 Iterative design process (Sinnott 2005)10Figure 3 The onion model for process design. The inner layers must be designed before the outer layers can be determined (Smith 2005).11Figure 4 BMA (left) and Andrussow (right) reactor geometries (Brennan 2012)22Figure 5 Temperature decay curves at typical quenching conditions (Pylilo 2012)22Figure 6 Typical quenching processes (top) (Pylilo 2012)and heat exchanger transfer line (bottom) (Moulijn et al. 2013)23Figure 7 PFD for Andrussow Process (IntratecSolutions)25Figure 8 Hydrogen cyanide processes global distribution (Evonik)26Figure 9 Evolution of accumulated number of ammonia separation patents (Mendivil et al. 2005)28Figure 10 Median lethal dose toxicity measurement guideline based on European Union (Towler and Sinnott 2008)28Figure 11 Selected international quality guidelines for cyanide in groundwater (Dzombak et al. 2006)30Figure 12 Cyanide treatment technology summary (reference?)31Figure 13 NaCN/NaOH solubility chart (Aigueperse and Guerin 1966)37Figure 14 NaCN-NaOH-H2O 25C system37Figure 15 NaCN-NaOH-H2O 35C system38Figure 16 NaCN-NaOH-H2O 55C system38

List of TablesTable 1 Design factors for batch and continuous processes11Table 2 Ammonia recovery considerations12Table 3 Achievable cyanide treatment level (Dzombak et al. 2006)13Table 4 Quencher considerations13Table 5 Typical reactor off-gas compositions (Maxwell 2007)19Table 6 Reactor summary19Table 7 Comparison of methods to produce hydrogen cyanide20Table 8 Summary and selection of quencher unit (Cross and Hesketh 1995, BCS_Inc 2008, Brennan and Hoadley 2003)24Table 9 Quench water requirements (Brennan and Hoadley 2003)25Table 10 Summary of various ammonia recoveries from inventors27Table 11 Comparison of hydrogen gas separation methods (Shenoy 1980, Nguyen 2012, Phair and Badwal 2006)28Table 12 Toxicity data for selected chemicals (Towler and Sinnott 2008)29Table 13 Selected international quality guidelines for cyanides in soil (Dzombak et al. 2006)32Table 14 HCN liquid least-squares parameters to fit Ln(P(torr))=A+B/T+CT2 (Appleton and Van Hook 1982)33Table 15 Vapour pressure of HCN Ln P=C1+C2+C3LnT+C4TC5 in Pa (Green and Perry 2007)33Table 16 Single temperature or unspecified temperature values for KH for HCN (Ma et al. 2010)33Table 17 Temperature dependence of KH values of HCN as reported in literature (Ma et al. 2010)34Table 18 Flammability limits, important temperatures and heats of phase change for hydrogen cyanide (Green and Perry 2007)35Table 19 Physical properties of NaCN36Table 20 Summary of existing patent literature of ?39

Introduction

Literature Review

Literature SourcesWhilst a patent does not have to have commercial viability in order to be granted (Heines, 2008), they can still be considered to be a viable source of information given that the experimental conditions match the proposed process conditions (Towler and Sinnott, 2008b) and the processes in question are relatively well established (Sinnott, 2005). However, even if a patent is to be applied in a design, it cannot be assumed to work without checking or testing (Horsley and Engineers, 1998).

Gas TreatmentThe feed of natural gas pipeline to the proposed plant location in Kwinana originates in Dampier (Kimber, 2006). The mole fraction of the feed stream is listed in Appendix #. Appendix # lists the maximum fraction of impurities that coming into the reactor, data which was taken from the work of Caton et al. (2015). Analysis of the feed stream in Appendix # in light of these maximum allowed impurities identifies the necessity of gas pre-treatment for the proposed NaCN production facility. Failure to do so could lead to yields reducing, equipment damage, and costing increasing (Trusov, 2001, Shimekit and Mukhtar, 2012).

Nitrogen TreatmentIn order to avoid carbon dioxide generation and reduce ammonia decomposition (Delagrange and Schuurman, 2007), the ratio of NH3/CH4 should between 1.08 and 1.085 (reference).Keeping nitrogen in the reactor feed has several benefits. The selectivity and yields of hydrogen cyanide can be improved as nitrogen will inhibit the decomposition of ammonia (Delagrange & Schuurman 2007). Furthermore, nitrogen is an inert gas so that no side reaction will occur in the system. For these reasons, nitrogen will not be removed as long as satisfy the pipeline composition specification of natural gas (Shimekit & Mukhtar 2012).

Ethane TreatmentEthane will exert negative effect on the content of hydrogen cyanide in the production gas (Trusov 2001). Moreover, carbon black, the by-product from the hydrogen cyanide synthesis, do occur disturbances when using types of natural gas which contains only a few percentage of ethane (Voigt et al., 1981). Thus, ethane has to be removed before reaction.There are four methods to remove ethane from natural gas (Mokhatab et al., 2006, Tobin et al., 2006).

Refrigeration ProcessRefrigeration is the simplest and most direct process for NGL recovery (Mokhatab et al. 2006). When natural gas was cooled or pressurised, the ethane will become liquid so that it can be separated (1914). It can separate ethane efficiently, while the energy consuming is extremely high (Ikoku, 1992).

Leon Oil AbsorptionLean oil absorption is the oldest and least efficient process to recover NGLs (Mokhatab et al. 2006). It is a mature technology but this method can only absorb from C3-C7+. In other words, this method cannot separate methane and ethane effectively (Kohl & Nielsen 1997).

Membrane SeparationGas permeation membranes are usually made with vitreous polymers that exhibit good diffusional selectivity (Mokhatab et al. 2006). In order to separate effectively, the membrane must be very permeable with respect to the contamination to be separated and it also must be relatively impermeable to methane (Katz, 1959).

AdsorptionThis process is generally reverted by applying heat to the adsorbent and adsorb phase. If the heat applied is sufficient, the ethane will leave the adsorbent internal surface and pores. To complete regeneration, the adsorbent is once again cooled to its initial temperature (Triebe et al., 1996). Suitable adsorbent materials include materials based on silica, silica gel, alumina or silica-alumina. Among them, silica gel is declining in favor of continuous process such as cryogenic condensation and absorption (Kohl & Nielsen 1997). Furthermore, Zeolite type adsorbents are preferred (Dolan and Wyatt, 2013).

Carbon Dioxide TreatmentAn important gas purification technology is removing carbon dioxide (Shimekit & Mukhtar 2012). The process of CO2 may cause operational problems, pipeline and equipment corrosion and effect the purity of HCN and NaCN (Allison et al., 2010, Nagelvoort and Robertson, 1999). Five methods for removing CO2 are applied in industry (Halim, 2015), which can be listed:1. Membrane2. Adsorption3. Cryogenic separation4. Physical absorption5. Chemical absorption

MembraneSome gas molecules permeate faster through a membrane because of the differences in physical or chemical properties of gas. For producing an impure CO2 product, membranes suffer from both the cost of compression and heat exchange. No commercial applications of membranes, however, for recovery CO2 from flue gases (Mofarahi, 2008).

AdsorptionCO2 can be separated from natural gas based on physical attraction between the gas components and active sites on the solid (Mofarahi et al. 2008). Suitable adsorbent materials include materials based on silica, silica gel, alumina or silica-alumina (Kohl & Nielsen 1997). Furthermore, Furthermore, Zeolite type adsorbents are preferred (Dolan & Wyatt 2013).

Cryogenic SeparationThrough condensing CO2 at cryogenic temperature (56.61, 5.18 bar), it can be separated from other gases. It is normally used for purification of high concentrations of CO2 while amount of energy is needed if the concentration is low (Mofarahi et al. 2008).

Physical SeparationDue to Henrys Law, CO2 can be physically absorbed in a solvent, but no chemical reaction will occur during the process. This technology is favoured for the gases which contain low concentration of inert gases or under high pressure (Mofarahi et al. 2008).

Chemical AbsorptionUnlike previous one, chemical reaction will occur during the absorption. Chemical solvents are likely to be preferred for gases with low concentrations of CO2 in the flue gas (Halim et al. 2015). Furthermore, amine solvents are good choice for capturing CO2.

Primary Reaction PathwayThe reactor for which hydrogen cyanide is synthesised is dependent on the reaction that is taking place. The following reactions are presented by (Maxwell, 2005):1. Andrussow Process2. BMA Process3. Shawinigan Process4. Formamide Process5. Methanol Process6. SOHIO ProcessThe SOHIO and Methanol processes will not be discussed here, due to the commercial unviability and technological immaturity of the processes (Stanford Research Institute International, 2000, Maxwell, 2005). Supplementary information on the advantages, disadvantages, reaction information and current operating plants for all of the processes are presented in Appendix #, # and #.

Andrussow ProcessThe Andrussow Process consists of the exothermic reaction between methane and ammonia in the presence of oxygen (Evonik Industries AG, 2014), conducted over a platinum-rhodium catalyst gauze (Hickman et al., 1993):

The reactor off-gas must be immediately quenched after the reaction to reduce the probability of HCN decomposition (Brennan, 2012a). Due to the exothermic nature of the reaction, the reaction becomes self-sustaining, and costs associated with the reactor are low in comparison to other processes, thus making this process dominant in industry (Ponton, 1998). However, the presence of multiple side reactions reduces the selectivity for hydrogen cyanide, thus reducing the yield, and increases the need for further separation units downstream (Hazair et al., 1999). As with reactions that will be discussed below, the risk also exists that hydrogen cyanide will behave explosively in the reactor if in contact with excess ammonia, and not quenched sufficiently (Ponton, 1998), making this process potential dangerous. BMA Process (Degussa or Blausare-Methan-Ammoniak Process)Another common production method of hydrogen cyanide is the BMA Process (Owen and Parekh, 1998). This synthesis is similar to the Andrussow, however, the reaction occurs in the absence of air, and is highly endothermic (Mendivil, 2003):

The literature states that the catalyst for this reaction is platinum with a rhodium supporter (Maxwell, 2005), that is lined within the tubular reactor (Brennan and Hoadley, 2003). There is also some suggestion for the use of an Al2O3-ThO2 catalyst, with a promoter of H2S or CS2, by Kotake et al. (1958). However, this catalyst system may be ineffective, as methane is required to be in large excess, which may result in coke formation and deactivation of the catalyst (Kotake et al., 1958).There are three reactor types that may be used for the BMA reaction tubular, monolithic membrane and dual membrane (Hazair et al., 1999). The tubular configuration will be discussed here, as there is limited literature pertaining to the alternative reactors for industrial use. The tubular reactor consists of a series of tubes mounted in a furnace chamber, which provides the heating required to counteract the endothermic nature of the reaction (Brennan and Hoadley, 2003). Multiple reactor units are required for this reaction, thus making the design complex and expensive (Maxwell, 2005). However, the reaction produces hydrogen cyanide in high yield, as well as hydrogen gas, which can be used in the furnace (Maxwell, 2005). Shawinigan Process (or Flouhmic Process)The Shawinigan method forms hydrogen cyanide from hydrocarbon gases (methane, propane or butane) and ammonia, with no catalyst (Maxwell, 2005, Mendivil, 2003) and in the absence of oxygen (The Lummus Company, 1961). The reaction using propane is stated below (Maxwell, 2005):

At present, there is a plant in Australia that operates with this method (Maxwell, 2005), and the process appears desirable due to the many advantages (Appendix #). However, in comparison to BMA and Andrussow, this synthesis is not as commercially dominant, and attracts higher operating costs if the cost of electricity in the plant location is high (Maxwell, 2005). Formamide ProcessThe Formamide Process was conceived in 2001 and follows three reaction steps to obtain hydrogen cyanide (Maxwell, 2005, Weissermel and Arpe, 2008):1. Methyl Formate synthesis

2. Formamide synthesis

3. HCN formation

The reaction occurs in a tubular reactor that is packed with an appropriate catalyst (Maxwell, 2005) (Appendix # for catalyst systems). Although the selectivity for HCN is high and the operating conditions are less energy intensive than the dominant processes (Maxwell, 2005), the reactor configuration for this synthesis is still being optimised, and this method has limited used in industry (Maxwell, 2005).

QuenchingThe quench unit operation is implemented to rapidly cool the reactor gas. The heat must be removed to prevent fouling and subsequent reactions taking place (Pylilo, 2012). Literature shows, the type of quencher employed is not dictated by production process. The auto ignition temperature for HCN is 538oC (Orica, 2014) while NH3 becomes unstable at 426oC (AirProducts, 1999). Quenching to 300oC (Gail et al., 2011) in less than a second (Chatelain, 1955) inhibits decomposition and avoids ignition of NH3 resulting in cleaner products with reduced environmental impact (Lior, 2004). Sundstrom and DeMichiell (1971) investigated plasma chemical processes and found no quenching method is superior as all exhibited similar cooling rates (106 oR/second). Predominantly, industrial quenching is done directly with water spray towers or indirectly in waste heat boilers (WHB) for heat recovery (Santoleri et al., 2000, Brennan, 2012a, Caton et al., 2015). Pylilo (2012) investigates chemical quenching with light hydrocarbons. Cooling takes place through dilution of product streams and hydrocarbon cracking. A valuable hydrocarbon product is produced as a form of heat recovery. Hunt and Steinmeyer (2000) suggests using waste streams from the absorber, cooled product gas or reactants as quench fluid to minimise waste (Pylilo, 2012), however using product gas encourages HCN and NH3 decomposition.Direct quenching through contacting the process stream with air (Danielson, 1973), acidic solution to neutralise NH3 (Hunt and Steinmeyer, 2000), a cold surface (Santoleri et al., 2000) with high heat capacity such as ceramic elements (Santoleri et al., 2000, Pylilo, 2012) or a heat pipe coated in alumina where pressure differential drives cooling (Slaten, 2010, Reay et al., 2013) is alternatives. A venturi scrubber, reverse heat scrubber (Hunt and Steinmeyer, 2000), a packed or plate tower, draft cooling, shell and tube exchanger (Danielson, 1973, Coulson and Richardson, 2005), and a submerged tank is infrequently seen as operational (Santoleri et al., 2000) but can be used (see Appendix 3.1 further discussion and schematics).Industrially, a WHB is followed by an economiser with BFW (Mtetwa, 2014), second WHB or a water tower ensuring the stream leaves at 90oC (Caton et al., 2015). It is possible to quench with an aqueous solution directly from 1100oC to the desired temperature (Kent, 2013) or use externally cooled water recirculation in the tower (Hunt and Steinmeyer, 2000). Industry also uses liquid spray towers with water or oil and a transfer-line-exchanger (figure 3.1.3) to generate high pressure steam (Moulijn et al., 2013). Quartz, alumina or carbon steel is the materials proposed as high temperatures can be tolerated, steel is preferred as its cheaper (Pylilo, 2012, Gail et al., 2011). Green and Perry (2007) states the performance of a quencher is governed by flash temperature; stability and appropriate heat transfer characteristics and needs to be considered in the design phase.

Ammonia RecoveryThe presences of NH3 in the process after quenching can result in either explosive interactions with produced HCN (Ponton, 1998), or due to its alkaline nature, self-polymerisation and decomposition of HCN (Ullmann, 2007). If the latter self-polymerization was allowed to occur, the exothermic nature of the reaction could result in a runway process, resulting in explosive pressure production (Flynn and Theodore, 2002, Gause and Montgomery, 1960). Hoffmann et al. (2001) states that unit operations are only required to prevent the aforementioned interactions at ammonia levels above several hundred ppm, below this simple small scale scrubbing or absorbing/adsorbing operations could suffice. Table # details the multitude of patents regarding the elimination of the ammonia that was reviewed. Of these technologies, both Sulphuric Acid and Ammonium Phosphate treatment are of particular relevance to the production of NaCN and as seen in Figure # are the most intensively studied and documented.

Fertiliser ProductionSulphuric Acid, H2SO4 could be introduced to react with the unreacted NH3 to form Ammonium Sulphate, (NH4)2SO4, the fertiliser. The by-product fertiliser could be sold, yet expensive crystallisation process is needed (EPA, 2000, Mendivil, 2003):

This method does not allow the recycle of the unreacted ammonia, as the chemical process is expensive to employ (Radke and Kotheimer, 1955). In addition, dilute H2SO4 is recommended in the literature (typically 99.9%). (Dzombak et al., 2006) In fact, EPA (1990) claimed that CSBP managed to reduce the CN- concentration to 50ppm by heating the combustion tank up to 100C on the existing NaCN plant, after the treated effluent pass through a cooling tower airstream. (EPA, 1990)

HCN Absorber Off-GasH2, N2 and minor unreacted CH4 gas will present in the off-gas streamline after HCN absorption occurs (Caton et al., 2015). There are 3 common methods employed to separate the gases (Seader and Henley, 2006): Pressure Swing Adsorption (PSA) - in which the selective gas will be adsorbed by the molecular adsorbing bed, Cryogenic distillation (Phair and Badwal, 2006) by utilising the difference in gas boiling point and freezing gas mixture as well as Membrane separation (Phair and Badwal, 2006)The pros and cons for each process are detailed in Table #. Since the recovered H2 gas is highly purified, it could be used either as a feed for other processes (Caton et al., 2015) or to use for energy source through combustion (Ballard, 2011). Brennan (2003) stated that due to BMA process produce more H2 as a byproduct than is consumed as H2 within ammonia in cyanide production compared to Andrussow, its possible to produce sufficient NH3 to self-supply the reactant. The off-gas stream which contains about 95wt% of N2 can then be vent out via the flue gas stream for flare emission. (EPA, 1990)

Process Selection

Selection MethodIn the design of any chemical process, the variety of possible operations at each stage create a large solution space of all possible solutions (Hoffmann et al., 2001). The subspace of plausible designs is exists within the inflexible external constraints and flexible internal constraints placed on the design (Sinnott, 2005).

Figure 1 Internal and external constraints placed on the design space (Sinnott, 2005)

Figure 2 Iterative design process (Sinnott, 2005)The creation of a plausible design involves an iterative process, detailed in Error! Reference source not found., where a possible design is generated from the collection of data, physical properties and methods, and then compared to the original objective. This objective, is the requirement placed on the design in order to produce a satisfied customer (Towler and Sinnott, 2008b). This method, presented by Sinnott (2005) has been combined with the onion model (depicted in Error! Reference source not found.) of process design, as presented by Smith (2005) to create structure method in which a viable NaCN production facility can be designed. Not depicted in the hybrid process is the determination of Batch vs. Continuous process utilization.Figure 3 The onion model for process design. The inner layers must be designed before the outer layers can be determined (Smith, 2005).

It is stressed by Sinnott (2005) that a wise engineer will prefer tried and true technology (i.e. matured technology), over new, novel untested technology. This is particularly applicable to the proposed production of NaCN, given that is falls into the second category of process designs presented by Sinnott (2005), one in which a new production capacity to meet growing demand is required. It is suggest in this case that repetition of existing design with only minor design changes is the best course of action.

Batch versus ContinuousThere exists an overabundance of literature guiding the utilization of batch or continuous processes in the context of process synthesis, in the following table are the aspects to be considered in the decision of batch or continuous process.

Table 1 Design factors for batch and continuous processesBatch(Sinnott, 2005, Towler and Sinnott, 2008b, Albright, 2008) Production rate is greater than 5 x 106 kg/h A range of products or product specifications Severe fouling Short catalyst life New product Uncertain design Processes with difficulty in scale up Integrity of the product is paramount Production rate can be very flexible and suffers no turn down issues when operating at low output

Continuous(Sinnott, 2005) Production rate is greater than 5 x 106 kg/h Single product No severe fouling Good catalyst life Proven processes design Established market

Gas Treatment

Ethane treatment

Table 2 Ethane treatment considerationsAspectsChoicesReasons

EconomyLean oil absorption Cheap raw material, doog for mass production (Mokhatab et al. 2006)

Energy EfficiencySolid bed adsorption The operation temperature and pressure of natural gas is similar with feed natural gas

SafetySolid bed adsorption High degree of automation (Tobin et al. 2006)

Product QualitySolid bed adsorption Separate efficiently Easy to start up (Tobin et al. 2006)

MaturityLean oil absorption The oldest process(Mokhatab et al. 2006)

Environmental SustainabilityMembrane Less environment impact (Mokhatab et al. 2006)

According to Table 3, solid bed adsorption is the best method to remove C2H6 from natural gas because of energy efficiency, safety and product quality. Furthermore, Zeolite 13X can be selected because it is one of the preferred adsorbents (Dolan & Wyatt 2013).

Carbon dioxide treatment

Table 3 Carbon dioxide treatment consdierationsAspectsChoicesReasons

EconomyChemical absorption Show the greatest promise of implementation for thermal power plants(Mokhatab et al. 2006)

Energy EfficiencyAdsorption Low energy requirements(Shimekit & Mukhtar 2012) Highly energy intensive for regeneration of cryogenic separation (Ali et al. 2014)

SafetyAdsorption Relative moderate conditions, no high pressure or low temperature (Cavenati et al. 2005; Mofarahi et al. 2008; Shimekit & Mukhtar 2012; Medeiros et al. 2013; Alias et al. 2014)

Product QualityAdsorption Nearly all the carbon dioxide can be captured(Cavenati et al. 2005)

MaturityChemical absorption Widely used technology for efficient (50-100%) removal of carbon dioxide (Medeiros et al. 2013)

Environmental SustainabilityMembrane Less environment impact(Mokhatab et al. 2006) No physical or chemical solvents

From table 2 and table 4, because of the high quality of CO2 specification in purified natural gas, adsorption is the best method for CO2 capture. A bunch of adsorbents have been applied in industries widely (Rufford, 2012). Among the adsorbents, activated carbon and zeolites are the commercially available adsorbents mostly studied for CO2 capture (Liu, 2011). Whats more, Zeolite 13X performs good results in separating CO2 and CH4 as the CO2 was removed completely in the zeolite layer (Cavenati et al., 2005). Thus, Zeolite 13X can be used in removing CO2.

Primary Reaction PathwayThe literature review has identified many methods of hydrogen cyanide synthesis and their reactors. However, as the alternative processes has a lack of industrial application, the BMA and Andrussow Processes will be considered for process selection.

Table 4 Primary reaction pathway considerationsAspectsChoiceReason

EconomyAndrussow The Andrussow Process has a lower CAPEX then the BMA Process, as the reactor design is less complicated (Maxwell, 2007) Additional heating is required for the BMA process, increasing the OPEX for this reaction (Brennan and Hoadley, 2003)

Energy EfficiencyAndrussow The Andrussow Process becomes self-sustaining at high temperatures (Ponton, 1998) There is a requirement for heating for the BMA reaction (Maxwell, 2007) to counteract the endothermic nature of the reaction

SafetyBMA More side reactions exist in the Andrussow Process (Brennan, 2012a) However, the safety for each reaction is comparable

Product QualityBMA The BMA Process has reactor off gas composition higher in HCN (Appendix 7.1.1) The BMA Process produces high purity hydrogen gas, which can be sold or used for heating purposes (Maxwell, 2007).

MaturityAndrussow The Andrussow Process was established in the 1933 (Maxwell, 2007) The BMA process was established in 1949, with improvements being made in the mid 1990s (Maxwell, 2007) The majority of hydrogen cyanide production occurs via the Andrussow Process (Appendix 7.2.6)

Environmental SustainabilityBMA High purity hydrogen gas in the BMA reactor off gas, can be sold or used for heating other unit operations (Maxwell, 2007) Andrussow off-gas produces carbon dioxide and carbon monoxide, which are environmentally undesirable (appendix 7.1.1)

The above table shows that BMA and Andrussow both excel in certain aspects; however, as the client has specified the BMA Process, this will be the final choice for the reaction pathway.

Quencher The literature review has identified several of methods of quenching; due to the lack of industrial application the selection process will focus on WHB and spray towers (ST). From the literature review Table 3.1 and Table 3.2 was constructed. For elaboration on the content see Appendix 3.2.

Table 5 Quencher considerationsAspectsChoiceReasons

EconomyST ST has a lower CAPEX and OPEX BMA process produces less gas hence steam generation not viable. ST less area hence lower footprint than WHB ST does not require BFW which is expensive

Energy EfficiencyWHB 60-70% heat recovery

SafetyST Decomposition and auto ignition of HCN and NH3 needs to be considered. ST cooling is more efficient hence less chance of runaway reactions

Product QualityST BMA process needs water addition, hence product quality not adversely affected Excessive dilution results in difficult separation WHB does not affect product quality

Maturity-Both options are most commonly used in tandem and hence will have the same technical maturity score.

EnvironmentalST BFW is not required as in a WHB Lower quality water is requires less processing Less CAPEX/OPEX required for utilising generated steam

SustainabilityWHB If feed has impurities plugging occur in ST and impurities in quench water can increase fouling. Shut down is required every 6 months for maintenance. WHB can operate 2 years before shut down is required Dilution in ST causes 10% of water removed from the quench feed

Table 3.2 shows the spray tower is preferred for our process primarily due to the low production rate of our plant making steam generation uneconomical. (Brennan and Hoadley, 2003) confirmed for a plant of 18,000 ton/yr. the WHB was an economic burden. It was decided the ammonia removal will further cool the product stream during the neutralisation to 90oC (McKetta, 1987).

Ammonia RecoveryThorough considerations have been taken and decision is chose to add H2SO4 to separate ammonia from the product stream for fertiliser production, mainly due to more cost-effective, more energy efficient, safer to operate, and more importantly the industry maturity as clarified in table 1.

Table 6 Ammonia recovery considerationsAspectsChoicesReason

EconomyFertiliser Production Cheaper to design a production for fertiliser production Elimination of solid impurities due to the polymerisation of HCN present in recycle stream would increase the operating cost. (Benderly, 2002) Ion Exchange Method is Licensed by Dupont which means increased cost (Mendivil, 2003)

Energy EfficiencyFertiliser Production Ion Exchange would not be as effective in BMA Process as less unreacted NH3 could be recycled back to the reactor due to high yield compared relatively to Andrussow Process (see yield table) (Mendivil et al., 2005) NH4H2PO4 considered to be poor adsorbent for NH3 (Miller, 1978)

SafetyFertiliser Production Unreacted HCN will present in the ammonia ion exchange method stream which would cause polymerisation and might Block the pipeline due to the formation of tarry and gummy materials. (Kotheimer, 1955)

Product QualityIon Exchange Recycled ammonia would have more recovery value than fertiliser as fertiliser is cheap and not in demand (Miller, 1978)

MaturityFertiliser Production Degussa Plants in the United State is has been using fertiliser production method (EPA, 2000) NH3 is not recovered at any of the 3 centralised NaCN plants in Australia(Brennan and Hoadley, 2003)

Environmental SustainabilityIon Exchange Fertiliser production could consider as waste generation (Mendivil, 2003)

When it comes to cost analysis, burning the separated ammonia together with other gases in the flaring stream can be considered as it greatly reduce the process cost and unwanted waste fertiliser could be avoided. However, the primary drawback of this cost-effective measure is the generation of oxides of N2 which are extremely toxic, and one of the primary anthropogenic sources for air pollutants (Flagan and Seinfeld, 1988).

HCN-NaCN ConversionA significant factor which influences the choice of HCN to NANC conversion is the lack of CO2 in the feed stream, due to the implementation of the BMA reactor (Pesce, 2000), in a 96-97% pure product can be obtained by direct contacting of BMA product gases with a 50 w/w% solution of NaOH (Pesce, 2000)AspectsChoicesReason

CAPEXDirect NaOH Contacting Direct contacting could occur in a simple absorption column (Pesce, 2000), compared to either r a simulated moving bed setup or merry-go-round setup of multiple columns required for an ion exchange process (Zagorodni, 2006)

OPEXIon Exchange Exchange resins can be reused with minimal degradation (Say et al., 2004) Cost of Ca(OH)2 is 1/10 of NaOH (Ray and Rajchel, 2001)

Energy EfficiencyDirect NaOH Contacting Direct contacting would only require energy to pump and contact the liquid and vapour streams, as opposed to the energy to create a counter current simulated moving bed or an automated merry-go-round system (Zagorodni, 2006)

SafetyIon Exchange Ion exchange could theoretically only involve the use of NaCl as a reagent, compared to NaOH, which is far more toxic (Green and Perry, 2007)

Product QualityDirect Contacting By ensuring that the final solution is alkaline (via NaOH in solution), the product will be more stable (Gail et al., 2011)

MaturityDirect Contacting Refer to Appendice

Environmental SustainabilityIon Exchange The reduced used of caustic reagents would reduce the possible impact on the environment

From the above table, the clear choice is the use of a direct NaOH contacting tower. This choice was primarily influenced by the choice of reactor implemented, which was determined initially by the hybrid onion model used.

Storage

Waste ManagementThere are 3 selections needed to be justified in the waste management, as follow:

Cyanide Waste TreatmentBoth chemical and thermal treatment could effectively lower the cyanide concentration, where chemical chlorination would be much cheaper to install than the incineration method (Dzombak et al., 2006).Even though the chemical method makes it more cost-effective in term of CAPEX, however consideration of expensive chemicals injection should not be forgotten as it will contribute to OPEX, include the SO2 injection to perform de-chlorination to protect aquatic life from toxic effect of chlorine (EPA, 2000). Moreover, another major environmental consideration should be included for selection judgement, by the fact that thermal treatment is much more effective when it comes to reduce the cyanide concentration. Furthermore, technology maturity for this method is verified by the CSBP Kwinana NaCN plant (EPA, 1990).

Table 7 Achievable cyanide treatment level (Dzombak et al., 2006)Chemical TreatmentThermal Treatment

0.2mg/L (roughly 200ppm after density conversion) 1500C5, atmospheric pressure10No catalyst required2, 5Fluidised bed reactor, heated by carbon electrodes2

Formamide380 430C, reduced pressures2 Phosphate of Fe or Al, with promoter of Mg, Ca, Zn or Mn2Tubular2or fluidised bed reactor9

Methanol350 500C, 1 bar8Oxide catalyst containing Fe, Sb, P, V2Vapour phase, fluidised bed reactor2

SOHIO400 510C, 0.35 2.07 bar7Mixed metal oxides6Fluidised bed catalytic reactor2

1. (Hickman et al., 1993), 2. (Maxwell, 2007) 3. (Koch et al., 2000) 4. (Brennan, 2012a) 5. (Mendivil, 2003) 6. (Cespi et al., 2014) 7. (Midwest Research Institute, 1993) 8. (Sasaki et al., 1998) 9. (Mattmann et al., 2002) 10. (The Lummus Company, 1961) 11. (Kotake et al., 1958) 12. (Brennan and Hoadley, 2003) 13. (Gail et al., 2011)

Comparison of hydrogen cyanide production processes

Table 13 Comparison of methods to produce hydrogen cyanideProcess and reaction/sAdvantagesDisadvantagesCurrent plants1, 2, 9

Andrussow

Low reactor costs (maintenance and procurement)1 Dominant method for HCN production, large knowledge base1 Medium to high purity product2 Long catalyst life2 Self-sustaining at temperatures about 1000C4 due to combustion reactions9 Many side reactions reduce efficiency3 (side reactions are oxidation of CH4 and NH3)11

Japan (Mitsubishi Gas), France (Butachemie, Elf-Atochem), United States (Dupont, Rohm and Haas, Novartis, Cyanco), United Kingdom (ICI)

BMA

Higher HCN yields in comparison with Andrussow1 High purity hydrogen by-product can be used in other operating units5 Complex reactor design1 High costs associated with reactor design and maintanence1 High heating needed to counteract endothermic reaction1United States (Degussa),Switzerland (Lonza)

Shawinigan

No catalyst needed6 Low concentration of ammonia in off gas reduces recovery units required1 Able to process reactants of varying purity, as there is no catalyst to deactivate10 High HCN concentration in off gas12 Not suited for locations with high electricity costs1Some plants in Australia, Spain and South Africa

FormamideMethyl Formate synthesis

Formamide synthesis

HCN formation

Useful if cost carbon monoxide low1 If fluidised bed reactor use, less equipment damage and more economical7 High selectivity for HCN1

Limited use in industry Reactor configuration still being optimised1Germany (BASF)

Methanol

Lower operating temperatures in comparison to Andrussow and BMA Limited use in industry High costs of obtaining carbon source1-

SOHIO

Lower operating temperatures in comparison to Andrussow and BMA Synthesis aim is not HCN (by-product) Low yield of HCN1 Multiple reaction steps required Technically immature8-

1. (Maxwell, 2007) 2. (Gail et al., 2011) 3. (Brennan, 2012a) 4. (Pirie, 1958) 5. (Owen and Parekh, 1998) 6. (Mendivil, 2003) 7. (Mattmann et al., 2002) 8. (Stanford Research Institute International, 2000) 9. (Midwest Research Institute, 1993) 10. (McKetta, 1987) 11. (Ponton, 1998) 12. (The Lummus Company, 1961)

Typical reactor configurations for BMA and Andrussow Processes

Figure 5 BMA (left) and Andrussow (right) reactor geometries (Brennan, 2012a)Quenching

Figure 6 Temperature decay curves at typical quenching conditions (Pylilo, 2012)Temperature decay correlations for typical quenching

Quencher diagrams

Figure 7 Typical quenching processes (top) (Pylilo, 2012)and heat exchanger transfer line (bottom) (Moulijn et al., 2013)

Further explanations on quenchingQuenching is essentially a type of heat exchanger under the category of direct contact. The difference between a normal heat exchanger and a quencher comes down to the time in which cooling is done. Cooling mechanisms looked at can be shell and tube, double, pipe, plate , agitated vessels and fired heaters (Coulson and Richardson, 2005). However, majority of the usual heat exchanger types is not considered for the range of cooling the HCN requires (Zoldak, 1989). The only possible option is a shell and tube heat exchanger which in industry is referred to as a waste heat boiler for the purposes of rapid cooling and heat recovery. Direct contact is usually done through spray chambers or spray, plate and packed columns and when the fluids are compatible and heavy fouling (Coulson and Richardson, 2005). The design of the quencher is analogous to that for gas absorption (Coulson and Richardson, 2005). Heat pipes is an emerging form of quenching but lacks industrial application (Reay et al., 2013)

Further explanations on types of quenchingDirect water cooling can be advantageous over indirect boilers such as bayonet heat exchangers or a WHB because of the lower capital costs, operational costs and maintenance requirements (Mular et al., 2002, Sundstrom and DeMichiell, 1971, Cross and Hesketh, 1995). Direct contact requires lower quality water feed hence can be cheaper (Brennan and Hoadley, 2003). The offset from steam generation is what makes WHB viable in most situations (Brennan, 2012a), however BMA has a lower volume product gas hence makes this benefit less attractive (Seddon, 2006).WHB recover 60-70%(Santoleri et al., 2000) of heat and H2 can be burned to provide heating for feed streams. If excessive dilution takes place separation will be more difficult than the WHB (Pylilo, 2012), however this dilution might be beneficial downstream as the BMA process produce a more concentrated product stream (Brennan, 2012a). Dilution results in 10% top up required as some of the water saturates the product stream gas (Santoleri et al., 2000, Brennan and Hoadley, 2003) See table 3.2.2.Spray towers can handle fouling fluids however needs replacing every 6 months due to water impurities while a WHB can potentially operate for 2 years before needing to be shut down (Caton et al., 2015) are prone to fouling since impurities might cause plugging however it is better suited to handle heavy fouling fluids. Direct Quenching is more efficient at cooling than WHB (Coulson and Richardson, 2005), runaway reactions are a risk in the quench operation (Green and Perry, 2007) hence the faster the temperature is reduced below 300 (Gail et al., 2011) the safer the process. Weightings were made on the basis of the above discussion. For clarification, waste disposal and environment had the same scores because a spray tower needs regular shutdowns but this can be avoided if the construction material can handle fouling. A waste heat boiler needs BFW which requires extensive processing to be of high quality so both options have drawbacks.

Quencher unit specifications

Table 14 Summary and selection of quencher unit (Cross and Hesketh, 1995, BCS_Inc, 2008, Brennan and Hoadley, 2003)TypeMass transferCorrosive PotentialDevelops a wet plumeInstallation Space requiredHeat RecoveryOperation and MaintenanceOperator trainingRelative Capital cost

WHBNoNo*NoSmallYesModerate to highHighHigh2

HEXNoNo*NoModerateMinimalModerate to highLowModerate

QuencherYesYes**Yes1SmallNoModerate to highLow to moderateModerate

* minimum corrosion if temperatures are kept above dew point ** can be handled by design and material of construction1 can be handled by reheat 2 offset by payback from steam produced.Table 15 Quench water requirements (Brennan and Hoadley, 2003)

NOTE:

Rough estimate:

Miscellaneous quencher data

Figure 8 PFD for Andrussow Process (IntratecSolutions)

Figure 9 Hydrogen cyanide processes global distribution (Evonik)

Recycle & Waste Treatment

Ammonia Recovery Inventions

Table 16 Summary of various ammonia recoveries from inventorsPatent Topics & InventorsIndustry TechnologyProcessDescription

Process for the separation of NH3 from a gaseous mixture containing HCN and NH3 (Miller, 1978)

Ion ExchangeHNO3 use of ammonium nitrate, NH4NO3 solutionIt can effectively separate ammonia from HCN solution due to the fact that nitric acid, HNH3 is volatile as to ensure HCN is in acidic environment to prevent the formation of Azulmic acid.

Improved Process Ammonia Recovery (Benderly, 2002)AdsorptionASD system is introduced (Adsorption, Stripping and Dissociation)It is basically a process of monitoring the Nickel concentration as polymerisation of HCN could occur due to the formation of Nickel-Cyano complexes through corrosion of process equipment.

Process for the production of Hydrogen Cyanide (Voigt et al., 1982)Ion ExchangeAbsorption by zeoliteNH3 can be selectively absorbed onto zeolites through ion exchange, and then flushed off with reactor gases.

Production of Hydrogen Cyanide(Radke and Kotheimer, 1955)AdsorptionSilica Gel as adsorbentSome HCN would be adsorbed initially but ammonia would preferred to be adsorbed as reaction time goesDesorption of ammonia is quite rapid by passing air through the heated column

Method of recovering Ammonia (Amakawa et al., 2008)DistillationDistillation Apparatus made with different alloys contentDistillation comes in contact with solution made with alloys of molybdenum, nickel and chromiumProduction of nitrile as side reaction

Process forRecovering Ammoniafrom a gaseousmixture containingNH3 and HCNIon ExchangeAbsorption by Ammonium Hydrogen PhosphateFormation of Diammonium Hydrogen Phosphate through the ion exchange between ammonia and ammonium phosphate

Figure 10 Evolution of accumulated number of ammonia separation patents (Mendivil et al., 2005)

Hydrogen Separation

Table 17 Comparison of hydrogen gas separation methods (Shenoy, 1980, Nguyen, 2012, Phair and Badwal, 2006)TechnologyDescriptionAdvantagesDisadvantages

PSAMolecular adsorbing beds adsorb non hydrogen gas in high pressure conditionHigh Purity of gas ProducedMature Technology hence widely usedHigh EnergyRequirement for adsorbent regeneration

Cryogenic DistillationUtilise difference in gas boiling point by freezing gas mixtureVery high purity gases can be achievedEfficient for large gas productionVery High Energy Requirement for RefrigerationHigh cost

MembraneSupply enriched gas mixture to one side of membrane to create potential gradient for mass transferMore cost-effectiveLess energy needed

Cannot achieve high degree of separationMultiple stages are neededNot very widely used as not as developed

7.3.3 Toxicity Data

Figure 11 Median lethal dose toxicity measurement guideline based on European Union (Towler and Sinnott, 2008b)

Table 18 Toxicity data for selected chemicals (Towler and Sinnott, 2008b)

Figure 12 Selected international quality guidelines for cyanide in groundwater (Dzombak et al., 2006)

Figure 13 Cyanide treatment technology summary (reference?)Table 19 Selected international quality guidelines for cyanides in soil (Dzombak et al., 2006)

7.4 HCN-NaCN Conversion

7.4.1 Hydrogen cyanide physiochemical data

7.4.1.1 Vapour pressure data

Table 20 HCN liquid least-squares parameters to fit Ln(P(torr))=A+B/T+CT2 (Appleton and Van Hook, 1982)RefNo. of pointsTemperature rangeKb (RMS Error)ABC

27259-2947 x 10-317.99320.063-3389.1617.3

3c10260-2993 x 10-420.19870.109-3687.2515.2-4.1067 x 10-3 (0.19 x 10-3)

Present Work40260-2971.1 x 10-319.77770.239-3624.2833.1-3.4169 x 10-3 (0.43 x 10-3)

Table 21 Vapour pressure of HCN Ln P=C1+C2+C3LnT+C4TC5 in Pa (Green and Perry, 2007)CAS No.C1C2C3C4C5Temperature rangeKPressure at temperature range Pa

74-90-836.75-3927.1-2.124538948 x 10-176259.83 456.652.95E+4 5.35E+6

7.4.1.2 Henrys Law Constants

Table 22 Single temperature or unspecified temperature values for KH for HCN (Ma et al., 2010)KH, M/atmt, oCpHCN, ppmvReferenceComments

13.318138 0008Based on the lowest concentration data in this tabulation

9.325197 0009Value extrapolated from above data

8.8-9.6--10Secondary compilation, no sources are cited

7.5--11Stated to be effective constant at pH 4, no sources cited

8.72510012Value given in atm/mol fraction, extrapolated to infinite dilution

8.2-8.82510012,13As for previous entry, data from (12), interpreted by authors of (13)

8.8-15013As for previous entry, this paper has different values in a table than in text, tabulated values are given here; this result is for a pure cyanide solution

8.4-9.8-2190-415013As for previous entry, results for a cyanide bearing synthetic leaching solution

10.5-11.6-2020-303013As for previous entry, results for a cyanide based actual zinc leaching solution

13.7--1Ref1 cites this as from ref14, we were unable to locate this in ref 14.

1225-15Secondary source, cites Edwards et al. (1978) that contains no primary data

12.2202-4016Electronically published MS thesis

12.825318-37617

9.4--18Review, primary source not given

11.93082519As interpreted in (16)

7.6252120Static measurement of headspace by GC. Author suggests that static techniques produce lower KH values

Table 23 Temperature dependence of KH values of HCN as reported in literature (Ma et al., 2010)KH, M/atmt, oCpHCN, ppmvReferenceComments

7.56419 75021Most previous treatments assume that ref 21 has also measured results at 18C. In fact, these authors merely take that datum from the International Critical Tables8, based on their three experimental temperatures we derive the following linear eq: ln(KH(M/atm))= (6023.6 (682.9)/T-15.817(1.922,r2 =0.9873

3.085.549 38021r2 drops to 0.8362 if KH value of 13.3 at 18 oC is added to these three points

1.3100113 96021

20-958400-64 60022Primary data not givent=20-95 range was studied for C=0.01-0.5 M to estimate range of gas concentrationConservatively assumed 0.5 M at 20 oC and 0.01 M at 95 oC

10-70

10-14025No primary data, cited as peronal communication

14.380.8-36(Ma et al., 2010)24 Measurements used in triplicate

7.4.1.3 Dissociation constant of HCN and CN- (Ma et al., 2010)Dissociation constant allows for the concentration of undissociated HCN to be computed.

7.4.1.4 Hydrogen cyanide flammability data and important temperatures

Table 24 Flammability limits, important temperatures and heats of phase change for hydrogen cyanide (Green and Perry, 2007)LFLLFLratingUFLUFLratingFlash point oCFlash pointratingAuto ignitionTemperature oCAuto ignitionrating

6.001141.0011-18.006537.8511

Melting pointCHeat of fusion cal/molBoiling point at 1 atm CHeat of vaporisation cal/mol

-13.2200925.76027

7.4.2 Hydrogen cyanide physiochemical data

7.4.2.1 Chemical reactions (Pesce, 2000) Thermal Decomposition occurs from 600-1050oC in He and from 1050-1225oC in N2 The pH of a solution of NaCN should maintained above 9 to avoid formation of nitrogen trichloride At lower pH aqueous solutions react with chlorine to form cyanogen chloride Solutions are slightly hydrolysed at room temperature according to the following NaCN + H2O NaOH + HCN Above 50oC an aqueous solution of NaCN will undergo irreversible hydrolysis, NaCN + 2H2O NH3 + HCOONa If heat of reaction is not removed the increased temperature accelerates the decomposition and can create high pressure in a closed vessel (reference the other stuff) In presence of a trace of iron or nickel oxide, rapid oxidation occurs when cyanide is heated in air, 2NaCN + O2 + 2NaCNO2NaCNO + 1.5 O2 Na2CO3 + N2 + CO2

7.4.2.2 Sodium cyanide physical data

Table 25 Physical properties of NaCNPropertyValueReferences

Molecular Weight (g/Mol)49.015(Pesce, 2000)

Melting Point (oC)562(Pesce, 2000, Gail et al., 2011, Green and Perry, 2007)

561.7 (98 wt %)

563.7

Boiling Point (oC)1530

1500 10oC

1496

Density of Solutions (g/mL)at 25oC10% NaCN 1.04720% NaCN 109830% NaCN 1.15(Pesce, 2000)

Vapour Pressure (kPa)800oC 0.1013

1360oC 41.8

Heat Capacity, (J/gK)

298.15-345.15K 1.4(Pesce, 2000, Gail et al., 2011)

273.1K 1.667

288K 1.7950

298.6K 1.402

Heat of Fusion J/g179(Pesce, 2000, Gail et al., 2011)

314

Heat of Formation (J/mol)Hform-89.9 x 103(Pesce, 2000)

Heat of Vaporization (J/g)Hvap,3041(Pesce, 2000, Gail et al., 2011)

3185

Heat of Solution (J/mol)200 mol H2O, Hsoln,-1547(Pesce, 2000)

Hydrolysis Constant Kh, 25oC2.51 x 10-5

AppearanceWhite, Granular or crystalline Solid(Fingas, 2001)

OdourFaint, almond-like odor

Odour Threshold0.2-5 ppm as HCN

Reaction with H2OSinks and mixes

Viscosity4 cP

Index of Refraction1.452

Solubility10oC 480000 ppm

35oC 820000 ppm

Specific Heat Capacity

7.4.2.3 NaCN/NaOH solubility chart

Figure 14 NaCN/NaOH solubility chart (Aigueperse and Guerin, 1966)7.4.2.4 NaCN/NaOH/H2O isotherms (Oliver and Johnsen, 1954)

Figure 15 NaCN-NaOH-H2O 25C system

Figure 16 NaCN-NaOH-H2O 35C system

Figure 17 NaCN-NaOH-H2O 55C system

7.4.3 Existing patent literature

Table 26 Summary of existing patent literature of ?Inventor, YearRelevant IndustryAbsorber TechnologyNotes

Fareid (2012)Cyanide ProductionDirect Neutralization - Absorption Column HCN is passed through cold water absorber initially, with free off gases being used for fuel CO present in HCN feed is managed by catalytic conversion of NH3 + H2 into HNCO, to prevent Na2CO3 formation in neutralization HCN gas is directly contacted

Allison et al. (2014)Cyanide ProductionDirect Neutralization CSTR Reactor Contacting impure HCN gas with NaOH Management of polymerization due to CO2 content by controlling residence time in CSTR reactor Ideal contacting times, temperatures and pressures discussed Expected feed conditions also discussed Flowsheet detailed Bench scale tests detailed

Deckers et al. (2006)Cyanide ProductionDirect Neutralisation Absorption Column Treatment of HCN gas from dehydration of formamide Production of up to 98% pure cyanide salts Details of NaOH concentration and the feed stream conditions are given Regular monitoring of hydroxide levels during absorption is considered ideal Comparison to existing methods for treatment of HCN from dehydration of formamide is given Bench scale tests detailed

Rogers and Green (2005)Cyanide ProductionDirect Neutralisation Absorption Column NaOH should be kept in excess to prevent polymerisation and decomposition of NaCN and HCN Bench scale tests detailed

Thorpe and Fleming (2005)Hydrometallurgical waste CN- recoveryIon Exchange Strong Base Anion

IX applied to CN- Patent is for the production of Ca(CN)2, which occurs via contacting with Ca(OH)2 Provides detailed information on the IX behaviour of multiple resins and elution solutions with CN- in various states Bench scale tests detailed PFDs given

Dreisinger (2001)Hydrometallurgical waste CN- recoverySolvent Extraction Cyanide recovery in gold industry can occur through the AVR, SART and MNR process Requires the use of NaOH solution for the strip List of possible commercial solvents given, mostly organophosphorous compounds Issue of effect of ammonia in feed not addressed Bench scale tests detailed PFDs detailed

Ray and Rajchel (2001)Cyanide ProductionIon Exchange Anion and CationSimulated Moving Bed Discusses the use of both Anion or Cation Ion Exchangers, in a one or two step process NaCl is used as eluant Can result in the production of CuCl2 as a useful by product Anion Exchangers are the preferred IX technology Expected feed conditions not detailed, leaves many things broad Bench scale testing is detailed PFDs detailed

Day et al. (2000)Cyanide ProductionDirect Neutralization Absorber Column Market share of NaCN production DuPont: 25% of NaCN Degussa: 20% of NaCN ICI: 15% NaCN Most producers contact pure HCN with pure NaOH, important to ensure the purity of both Transportation of NaCN in concentrated solution form reduces crystallization expense and but increases transportation costs Bench scale testing is detailed PFDs detailed

Hecht et al. (1990)Cyanide ProductionDirect Neutralization Absorber Column Gaseous HCN contacted with fine droplets of NaOH Aim is to enhance crystallization of final product Details ideal feed conditions, including the ideal feed ratios of NaOH and HCN Crystallization is enhanced by the injection of HCN into the vessel via fluidized nozzles

Coltrinari (1987)Hydrometallurgical waste CN- recoveryIon Exchange Weak Base Anion Packed Bed Treatment of solution containing 10-2500 mg/L CN- in free or complexed form Ion Exchanging of complexed cyanide, not free cyanide Elution with Ca(OH)2 Regeneration with H2SO4 Proposed feed conditions and resins are given Contains proposed simplistic PFD Flowsheet detailed PFDs given

Crits (1981)Hydrometallurgical waste CN- recoveryIon Exchange AnionPacked Bed IX of weak CN- solutions, both complexed and free Elution with NaCl Details possible resins to be used Resins can be regenerated by a weak alkaline solution, which would be required anyway to prevent polymerization of the final NaCN product Minimal CN- in waste Academic references supplied Bench scale experiments detailed

Fries (1976)Hydrometallurgical waste CN- recoveryIon Exchange Anion and CationPacked Bed CN- must be complexed with Cu before contacting Bench scale tests are discussed Suitable resins are detailed Alkaline regeneration is required

Friedrich et al. (1971)Cyanide ProductionDirect Neutralization Absorber Column Contacting of pure HCN gases with aqueous NaOH or KOH Details feed stream conditions Provides PFD

Aigueperse and Guerin (1966)Cyanide ProductionDirect Neutralisation Absorption Column Reacting with 30-35% NaOH until free OH has been lowered to 0.3-0.1% to prevent polymerization NaCN solution of 28-33% produced NaCN solubility table is provided

Byron (1959)Cyanide Production Production of 96% NaCN HCN solution undergoes quick intermitant contacting with solution of NaOH/NaCN, with NaOH being the minor proportion NaCN, NaOH solution should remain between 50 oC and 35 oC as to prevent the polymerization and hydration of NaCN respectively NACN solution should contain at least 0.2 % w/w NaOH so that it remains stable Neutralisation can occur in multiple steps, 2 is considered ideal Contact between NaOH and polymerized HCN will result in a violent reaction and a large increase in gas volume PFD detailed

Oliver (1955)Cyanide ProductionDirect Neutralisation Absorption Column Contains several ternary phase diagrams for NaOH-NaCN-H2O Simplistic PFD

Mcminn (1955)Cyanide Production Direct Neutralisation Absorption Column Production of anhydrous alkali metal cyanides Feed flowrates and conditions discussed for neutralisation States the neutralization reaction is slightly exothermic Simplistic PFD

7.4.4 Ion Exchange Resins

AuthorResinCapacityAdsorbed IonsEluate

Goldblatt (1956)Amberlite IRA-4001% H2SO4

Ning et al. (2013)Metal Loaded Zeolites

Silva et al. (2003)Imac HP555sCN0.05 M H2SO4

Silva et al. (2003)Amberlite IRA-420CN0.05 M H2SO4

Say et al. (2004)Molecular Recognition5.41 mg/LCN-NaOH

7.5 Storage(I STOPPED EDITING HERE PAULINE)Storage selection for specific fluidsFluidTemperaturePressureMaterialTypeCommentsReferences

NH3 (liquid)1 ] -33oC

2] ambient

3] 0oC1.1 bar

16-18bar

3-5 barHigh strength steelDouble wall full containment is preferred in a cylindrical insulated tank with flat bottom and domed roof, 50,000t [1]

Semi-refrigerated sphere or cylindrical, 1500t [2] and 2500t [3]All insulated to avoid radiated heating. Inert gases for pressure control. Horizontal pressurised tank is a safety hazard if leakages occur. Alternatives are difficult to construct and more expensive.

Stress corrosion cracking is a problem in tanks, 0.2% water added during transportation to avoid it Brennan, lele, appl

HCN5oCatmSteelMonelHastelloy

Steel is cheaper so preferred Liquid phase and not corrosive

Recirculation is requiredWould not usually store as it goes straight to absorption.

Water content < 3%

Prevent decomposition and polymerization by addition of