TechnoEconomic Design for the Addition of PHB Production to a Sugar Mill - Assignment Example

PROC 1025 Design Project 2016 Techno‐Economic Design for the Addition of PHB Production to a Sugar Mill Name/Student Number: Tutor: Date: Introduction Poly 3‐hydroxybutyric acid (PHB) is a bio-derived polyesters that is biodegradable. Some sugar mill by-products have nutrients that can be used as culture media for the micro-organisms that can be used in the commercial production of PHB. This paper focuses on the additional design and integration of a PHB production plant to utilize molasses produced by Victoria Sugar Mill in Ingham, located North of Queensland to produce PHB in a more economical way. The work includes a review of technologies available, development of a flow sheet, mass and energy balances, equipment design, process flow diagrams, environmental impact studies and initial techno-economic evaluations. Based on the techno-economic evaluations, recommendations have been made on the type of sugar mill products that can be utilized in the PHB production process, the production rate of PHB, as well as the bacteria to be used in the process. Other issues discussed include the layout and utility sharing arrangements between the PHB process and the sugar mill, and the discussion and analysis of the potential for PHB production in North Queensland based on the economic, environmental, and sustainability criteria. Background Every year, the amount of non-biodegradable plastics produced from petro-chemical elements increase in our environment. This contribute to environmental pollution and degradation, posing danger to many living organisms. Some of the by-products and waste-water effluents released from sugar crushing mills also contribute to environmental pollution. Over years, an interest on the production of bacterial polyesters has grown. The PHB polymer is mainly made of carbon assimilation and is used by the micro-organisms for storage of energy to be metabolized in the absence of other energy sources (Petrasovits, et al., 2007). Different bacterial types, such as Azotobacter vinelandii, Bacillus megaterium, Bacillus subtilis, Bacillus sphaericus, Ralstonia eutrophus, Alcaligenes latus and Methylobacterium rhodesianum can be used in the production of PHB in response to physiological stress (conditions of limited nutrients) using sugar and molasses. These micro-organisms use carbohydrates through fermentation to produce PHB whose chemical formula is as shown below. The production process of PHB starts with sunlight. Carbon dioxide is converted to carbohydrates, which is the primary raw material for the manufacture of PHB, through photosynthesis via sugar molecules (Koller, et al., 2010). The materials include glucose, molasses, lactose and sugar beets. The sugar is broken down to C2 building blocks in the metabolism. The C2 building blocks are then converted into C4 monomers, and finally, polymerization of PHB takes place. Below is a diagram showing the bio-synthesis process of PHB. PHB find applications in medicine, pharmacology, and packaging in food industries etc. (Yang, et al., 2013). Design for the PHB Production Below is the process flow diagram for the production of PHB. Figure 1: PHB production process from molasses PHB Production Process Sterilization - At this point, the process materials are introduced into a fermenter. Molasses is a sugar-rich by-product of sugar manufacturing and have been widely used as a source of carbon in industrial fermentations because of its abundance and relatively low cost. In the sterilization phase, the nutrient broth is mixed in the fermenter, together with the micro-organisms, to set off the conversion process of changing the feedstock to PHBs. Fermentation Process - During this process, bacterial agents act as bio-factories, converting the materials into PHB in an environment that is aerobic. Fermentation achieves up to 90% content of biomass. Micro-organism Setting – The materials are in liquid state and the bacteria are suspended in the liquid. Separation of the cells from the solution takes place at this point. After the cells are separated, they are allowed to pass on to the PHB extraction phase. PHB extraction phase – In this phase, a solvent is added to the cells. The cells usually react to the non-toxic ethanol production by-product solvent by bursting. This leaves the PHB absorbed by the solvent. Cell particles that do not dissolve remain suspended in the solvent. The dissolved PHB and the solvent are filtered to separate them from the cell debris. From here, the mixture of the dissolved PHB and the solvent then move on to the crystallization and purification phases while the cell debris is removed off the batch (Sathiyanarayanan, et al., 2013). Crystallization/ Purification – After filtration, PHB is separated from the solvent. During the purification step, the solvent that has been removed is recycled. After achieving a high level of PHB purity, the product is dried using steam, and then packaged for different applications (Grothea, et al., 1999). Layout and utility sharing arrangements between the PHB process and the sugar mill Figure 2 below shows the arrangement of PHB process integrated in the sugar mill. Figure 2: Integrating PHB production in the Sugar Mill Production Rate of PHB The sugar mill produces 165t/h of raw sugar and 33t/h of molasses. Molasses is composed of 45.8% sucrose, 10% glucose and 9.5% fructose. If all the nutrients in the molasses are utilized as carbon source for the production of PHB, the quantity of molasses that will be utilized will be: Sucrose: (0.458 x 33) = 15.114 tonnes/hr The conversion rate of sucrose to PHB is about 19%. PHB production from sucrose = (0.19 x 15.114) = 2.87 tonnes of PHB Glucose: (0.1 x 33) = 3.3 tonnes/hr The conversion rate of glucose to PHB is about 24%. PHB production from glucose = (0.24 x 3.3) = 0.792 tonnes of PHB Fructose: (0.095 x 33) = 3.135 tonnes/hr The conversion rate of fructose to PHB is about 16%. PHB production from fructose = (0.16 x 3.135) = 0.502 tonnes of PHB Expected production rate of PHB based on the molasses production rate from the sugar mill = (2.87 + 0.792 + 0.502) = 4.164 tonnes/hr. Environmental Impact Study of PHB Production Bio-based polyesters have a potentially low environmental impact because of the ability to undergo bio-degradation. PHBs are completely degraded to carbon dioxide and water in the environment. It has been known that water and carbon dioxide are the primary requirements by green plants to produce carbohydrates through the process of photosynthesis. This demonstrates the fact that PHBs are embedded into the environmental carbon cycle, as opposed to petro-chemical based polyesters (Singh, et al., 2013). This creates renewable carbon-dioxide, reduces the carbon footprint and also reduces the landfill crisis contributed by the petro-chemical-based plastics. Contrary to the above stated environmental benefits, PHBs have some controversial environmental impacts. First, CO2 is a greenhouse gas. Emissions of the gas into the environment contribute to the already existing problem of greenhouse gas emissions. The total input energy required in the production of PHB is higher compared to the energy required in the production of polystyrene and petrochemical polymers. According to Harding, et al., (2007), The common contributions of PHB production are high energy and water requirements. This has the implication that PHB production limit the opportunities for reduction of emission. Initial Techno-economic Evaluations Until this date, production of PHB through bio-technology require a lot more energy compared to petrochemical plastics (Gouda, et al., 2001). There are several advantages of integrating PHB production in a sugar mill: The sugar mill provides the energy required to run the production process of PHB. The by-products of the sugar mill provides the raw materials. A side production process of ethanol can be integrated in the sugar mills to provide extraction solvent. On hourly basis, Victoria sugar mill crushes 1100 tonnes of sugar. This produces 165 tonnes of raw sugar and 4.164 tonnes of PHB per hour. Making up the balance, after a period of eight months over which the mill operates, 23,985 tonnes of PHB can be produced in one season. Beginning from the canes, it would require about 3kg of sucrose to produce a kilogram of PHB, as well as 3.24 kWh of electrical energy and 39.5 kg of steam. The demand of electrical energy is met by generating electrical power through high pressure steam from burning of bagasse. Burning of bagasse also provides low-pressure steam required for heating. Compared to other PHB production processes, there is an economic advantage of integrating PHB production in a sugar mill. According to Eyerer, et al., (2010), a kilogram of PHB is sold at $10 - $20. It costs about $5.85 to make a kilogram of PHB using sucrose. The price of PHB made from sucrose as the carbon source, and supply of energy from fossil fuel would be $2.65 per kg (Eyerer, et al., 2010). This limit would be approached depending on how prices of sucrose change. Sucrose accounts for about 29% of the cost if taxes are not considered. Usually, the carbon substrate accounts for about 50% of the cost used in PHB production. Figure 3 below shows the mass and energy balance scheme for an annual production of 23, 985 tonnes of PHB. Figure 3: Mass and energy balance scheme for the production of PHB. Potential for PHB production in North Queensland There are several sugar mill companies located in North Queensland. The sugar industry in Australia is valued at between $1.5 and $2.5 Billion per annum (A.El-sayed, et al., 2009). According to the data presented, production of PHB using bio-technological method can be economically viable environmentally sustainable when integrated in a sugar mill. This provides a greater opportunity to integrate the production of PHB into the sugar mills. This will increase the use of bio-plastic and reduce the environmental impact of petro-chemical plastic. Other Considerations The type of bacteria most preferred for use in the production of PHB are Ralstonia eutreopha and Alcaligenes latus because of its ability to produce PHB in large amounts using molasses from sugar industries (Dua, et al., 2012). To increase the productivity of PHB, it is necessary to increase cell density and reduce culture time, and also consider the PHB content. Culture batches with very high cell density increases the production of PHB and reduces the cost of waste water treatment and downstream processing. The most popular culture system is the fed-batch culture, which attains a higher cell density as well as higher PHB content (LA, et al., 2012). However, besides increased susceptibility to contamination and more complicated operation, fed-batch cultivation depends on high cell-density accumulation causing low rates of growth before induction, which sometimes lengthens the time required for PHB production (Ramadas, et al., 2009). On the other hand, in batch cultivation, micro-organisms are inoculated in a bio-reactor under some pre-determined conditions of pH, temperature, aeration, etc. to go through growth phases. The microbial cells are collected after fermentation. The fermenter is cleaned and sterilized before another batch is added. An advantage of the batch culture over the Fed-Batch culture is that a batch culture can be used for a variety of fermentation reactions daily and can be sterilized to minimize the risk of contamination or strain mutation (Kalia, 2016). On the other hand, batch culture has the disadvantage of extended idle time and higher labour costs. According to A.El-sayed, et al., (2009), organic sources of nitrogen are recommended as they give a higher PHB production compared to inorganic sources of nitrogen. Each of the bacterial strain has its own C/N ratio required for maximum growth. A C/N ratio of about 12.57 is recommended to achieve the highest growth of PHB. References Read More