1. Introduction

Security supply of energy and raw materials together with economically healthy and environmentally friendly production processes are decisive factors for sustainable development of future chemical industry. Substitution of bio-based feedstocks for the fossil-based is a potential paradigm for sustainable chemical production. In addition, designing sustainable bio-based chemical production processes can positively contribute to sustainable development.

The sustainability of the chemical process is determined by three integrated elements: input raw material, synthesis process and output product. To be sustainable, the input feedstock needs to be renewable and available. The sustainability of synthesis process and output product needs to be assessed considering not only production cost but also environmental problems and health and safety hazards. The sustainability of chemical process cannot be guaranteed, unless the sustainability of these elements is evaluated. Nevertheless, such integrated assessment has not been addressed in almost all guidelines of process design and evaluation, e.g., [1-3].

Biomass has been considered as sustainable resource. The concept of utilizing biomass for chemical production has received many attentions. The economic and environmental assessment has been performed to provide some forecasts about the potential of bio-based chemicals [4, 5]. However, to solve complicated issues related to utilizing bio-based feedstock for chemical production such as resource availability and production process feasibility, a more comprehensive approach is needed.

In this study, I developed a structural framework to support design and assessment of bio-based chemical process for sustainability. It addresses the important issues of bio-based chemical production: designing sustainable production process, evaluating and selecting sustainable input bio-based feedstock and output products.

2. Structural framework supporting design and evaluation of bio-based chemical process

Figure 1 shows the schematic framework supporting design and assessment of bio-based chemical process. It consists of six main stages. At the first stage, the environmental problems caused by running processes are defined. Market demand, company and local conditions are checked to define desired function of output chemical and available bio-based raw materials as well. At the second stage, alternative chemicals are generated and synthesis routes are investigated based on literature, patent and available information. At the third stage, alternative processes producing alternative chemicals are designed with the aid of computer-aided process engineering tools. The running fossil-based process is examined if it can be modified to switch to using bio-based feedstock in replacement of fossil-based. At the fourth stage, evaluation of bio-based chemical alternatives is performed by assuming a representative bio-based feedstock. At this stage, production cost, CO2 emission and fossil energy consumption are evaluated, since they are the main criteria determining the success of bio-based chemicals versus the fossil-based in the commercial market. The social criteria such as health and safety hazards can also be assessed to find potentially safer processes. At the fifth stage, the potential feedstock alternatives are generated considering feedstock criteria including renewability, availability and collectability and economic criteria represented by investment and transportation costs. At the last stage, the investigated potential bio-based feedstocks together with the process alternatives are further evaluated. Since the plantation of bio-based feedstocks caused many environmental problems, different environmental criteria are assessed at this stage such as CO2 emission, fossil energy consumption, eutrophication, acidification and ozone depletion. While the evaluation boundary of the fourth stage consists of only the process converting bio-based feedstock to the target chemical, the last stage includes not only the conversion but also the plantation and collection stages of bio-based feedstock. The processes that cannot satisfy desired environmental performance are eliminated. Among the satisfying processes, the most sustainable is selected if it gives good performances toward economic and social criteria. Pareto optimum curve is applied when the processes have trade-off results of economic and social criteria.

3. Case study on design of bio-based chemical process

The applicability of developed framework is demonstrated through a case study on design of bioethanol based chemical process. Before the complete case study, I focus on the design of separation system, which has strong influence on the sustainability of the whole process, performing a separate case study on MAA purification.

3.1. Case study on MAA purification

The case study on extraction of MAA (Methyl Methacrylic acid) from water and acetic acid in the production process of MMA (Methyl Methacrylate) is considered.

To extract MAA, three feasible alternative solvents are selected based on patents: heptane, xylene and mixture of MMA and xylene. Due to the differences of split fractions, boiling points and the possibilities of forming azeotropic mixtures between solvents and process substances, feasible extraction processes are designed and modeled individually.

The alternative processes are designed and evaluated considering three indicators: production cost represented by Net Present Value (NPV), CO2 emission calculated based on CED (Cumulative Energy demand) [6] and safety hazards evaluated by applying EHS method [7]. The evaluation result shows that Heptane and (MMA + Xylene) processes are rather comparative to each other for all evaluation indicators. Xylene process has the worst performances toward these evaluation objectives. Applying weighting method (multiplying weighting factors 0.5, 0.3, 0.2 to production cost, safety hazard and CO2 emission indicators, respectively), the most suitable process is selected. Among the process alternatives, Heptane process is the best process for purification of MAA.

With the case study on MAA purification, method of designing separation process included in the developed framework was clearly illustrated.

3.2. Case study on bio-chemical production

Three kinds of high volume chemicals are accounted in this case study: ethyl acetate, acetic acid and ethylene.

Generation of synthesis routes and design of alternative synthesis processes

Possible synthesis routes of the chemicals considered are investigated based on literatures. Based on these synthesis routes, bio-based alternative processes are designed and examined for the potential of substituting for the fossil-based processes.

Evaluation of alternative bio-based chemicals

Sugarcane is selected as the representative bio-based feedstock to produce bioethanol and bioethanol derivatives supplied to the process alternatives. To succeed in the commercial market, the bio-based chemicals must not only bring more environmental benefits but also be more economic attractive than the fossil-based. Thus, three kinds of indicators are considered to select the most appropriate chemical: production cost, CO2 emission and fossil energy consumption.

The evaluation results show that all process alternatives producing the chemicals considered help reduce marked amount of CO2 emission. Among the chemicals considered, bio-based ethyl acetate is the most attractive as it helps reduce marked amount of fossil energy consumption and save lot of production cost.

Generation of alternative bio-based feedstocks

To generate the alternative bio-based feedstocks, it is necessary to consider economic and feedstock criteria. The economic criteria are represented by investment cost of process alternatives and transportation cost of bio-based feedstocks. The feedstock criteria are represented by renewability, availability and collectability. The local conditions have strong influence on the performance evaluated at this stage. This fact is illustrated by the case study which is described in detail in the next chapter.

Evaluation of potential feedstocks and processes

In addition to production cost, different categories of environmental impacts such as fossil energy consumption, eutrophication, global warming, ozone depletion, acidification and photooxidant formation are considered, because the plantation of biomass has caused many environmental problems. The evaluation results of these categories are normalized before being summed up to give the total environmental index. The inherent safety index is considered to assess the potential hazards of the process alternatives by applying ISI method [8]. The higher the indexes are, the worse the performances of the process alternatives are.

Based on the evaluation results, the most sustainable process together with input bio-based feedstock which possesses desired environmental performance and the lowest inherent safety index and production cost is selected for producing the selected chemical.

4. Case study on impacts of local conditions on bio-based chemical process design

The local conditions strongly influence the criteria that need to be considered in the stage of generation of bio-based feedstock alternatives. In this chapter, the availability, distribution and transportation of biomass are considered in the local conditions of Vietnam.

Different kinds of bio-based feedstocks (sugarcane, corn, cassava, corn stove, rice straw and rice husk) and different scales of production are accounted to highlight the impact of local conditions on the design of bio-based chemical process. Two scenarios of producing target bio-based chemical are developed: 1) Centralized plant: bio-based feedstock is collected to the centralized gathering plant, and all amount of target chemical is produced at that plant, 2) Distributed plant: bio-based resource is collected to the multiple plants distributed close to the available resource. The production scale of distributed plant is divided by the determined productivity of target chemical to the number of distributed plants.

The evaluation result clearly shows that within the centralized plant scenario, the collection cost is markedly high with the increase of production scale when bio-based feedstock is widely distributed. In distributed plant scenario, the collection cost dramatically decreases while the investment cost increases. The distribution, available amount and the transportation distance of bio-based feedstock are the main factors determining the collection cost of raw material. Thus, they strongly influence the economic performance of bio-based chemical process, especially the processes utilizing large amount of input raw material. Directly, the local conditions have strong impact on the selection of bio-based feedstock, production scale, synthesis process and its plant set-up.

5. Developed framework under IDEF0 representation

From the performance of the case studies above, the developed framework is improved and modified by adding more necessary information to clarify input and output, supporting resources and the constraints that need to be considered during the performance of each stage.

Under IDEF0 (Integration DEFinition language 0), the framework supporting design of bio-based chemical process is described in more detail as shown in Fig.2. There are 6 main activities included in the main level activity. The activities A2 to A5 are performed under the management of activity A1 and with the support resources provided by activity A6. Each activity is described in detail by being decomposed into some sub-layer activities. The top side arrows show the constraints controlling the performance of the activities such as external (e.g., market demand and governmental laws), internal (e.g., company policies and capacity) and technical constraints (e.g., conditions and performances of running processes). The left and right side arrows are the input and output of each activity, respectively. The bottom side arrows are the mechanisms, necessary tool and information supporting the performance of each activity.

Output from activity A2 are the chemical alternatives that meet the market demand and satisfy the conditions of company's situation. Within activity A3, all possible feedstocks are investigated and checked for feasibility respect to local conditions. The process alternatives producing target chemicals are designed by performing activity A4. Besides investigating new synthesis routes, the fossil-based process is also examined if it can be modified to use bio-based resource for producing target chemical. The alternative processes are evaluated within activity A5. Suitable evaluation models which include considered indicators and evaluation methods are developed. As the final targets, sustainable synthesis process, output chemical and input bio-based feedstock are produced after the activity A5.

6. Conclusion and outlook

6.1 Conclusion

・A novel framework supporting design of bio-based chemical process was developed. It addressed the important issues related to utilization of bio-based feedstock for chemical production.

・Using the flowchart diagram, the necessary stages included in the framework are clearly displayed, supporting designers to fulfill the tasks of design and assessment of bio-based chemical process for sustainability. The framework is modeled by IDEF0 in more detail, facilitating more effective communication and discussion among designers.

・With the performance of the concrete case studies, the applicability of the developed framework was verified. The framework provides practical business model for further research and development of bio-based and thus sustainable chemical industry.

6.2 Outlook

The following points should be considered in the future research:

・Process integration and multi-product integration

・Assessment of land use impact and water use impact

・Rigorous assessment of social issues: job creation, change of local status, etc.

Fig.1 Framework of design of bio-based chemical process

Fig.2 Illustration of developed framework by IDEF0 model

本論文は、「Structured framework supporting design of bio-based chemical process toward sustainability(和訳:持続性に向けたバイオマス原料による化学プロセス設計支援の構造化フレームワーク)」と題し、再生可能なバイオマス資源を原料とする持続性を考慮した化学プロセスの設計手法の構築を目的とした研究であり、全6章より構成されている。

第1章は緒言であり、本研究の背景および目的を述べている。化石資源である石油を原料とする化学産業において再生可能なバイオマス資源を原料とする製品が研究開発されている中で、持続性を考慮するためには、経済性だけではなく、環境性と社会性の3指標の統合的な評価が必要であることを述べている。また、特定のバイオマス資源から特定の製品合成法が提案されている中で、企業や社会の制約のもとで相互依存している資源、製品、プロセスを、同時に評価し、選択することの必要性を述べている。さらに、そのための手法論が欠如していることを述べている。これらの背景を受け、持続性を考慮した化学プロセス設計を支援する構造化されたフレームワークを構築することを本論文の目的として示している。

第2章では、バイオマス資源を原料とする化学プロセス設計を支援する構造化フレームワークをフローチャートとして提示している。構造化フレームワークは6段階の手順で構成されており、第1段階では、現在のプロセスにおける問題点、企業や社会の制約、製品に求められる機能などを規定し、第2段階では、製品とその合成ルートの代替案を生成し、第3段階では、第2段階で生成された合成ルートによる化学プロセスを設計し、第4から第6段階では、それぞれ、製品、資源、プロセスの評価を実施し、選択を行う。評価におけるシステム境界や評価指標の選定、具体的な評価手法についても議論している。

第3章では、2つのケーススタディによって、第2章で提案したフレームワークの適用可能性の検証を行っている。まず、化学プロセスの中で持続性への影響が大きい分離プロセスを対象として抽出溶剤とプロセスの選定を行い、提案したフレームワークによる支援が可能であり、3指標の統合的な評価によって適切なプロセスが選定できることを示している。次に、バイオエタノールを出発原料とする化学製品製造を例として、資源、製品、プロセスの選択について実際に代替案を生成し、プロセス案を設計し、プロセスシミュレータを用いた評価を行っている。プロセス内の化学物質やプロセス条件から安全性を評価していること、バイオエタノール製造のためのバイオマス資源による3指標の変化も評価し、持続性に適した資源、製品、プロセスを示していることに特徴がある。

第4章では、第3章で行ったバイオエタノールを原料とするプロセスのケースについて、地域の制約を考慮したケーススタディの結果を示している。地域によって得られるバイオマス資源の種類や量、輸送システムに制約があり、ベトナムの条件を参考データとして用いながら、利用可能なバイオマス資源ごとに、プラントの規模や配置について経済性評価を行っている。サトウキビを原料とした場合では小規模プラントを分散させる方が望ましく、稲わらを原料とした場合では、原料を集約した大規模プラントが望ましいことを示し、地域の制約を考慮すると、稲わらを原料とすることが最適であることを明らかにしている。このケーススタディによって、提案したフレームワークによって地域の制約を考慮することが可能であることを示している。

第5章では、第2章で提案した構造化フレームワークによる支援を実践可能とするために、機能モデリング手法IDEF0によるアクティビティモデルを構築している。第3章および第4章でのケーススタディから、持続性を考慮した化学プロセス設計のアクティビティ構造を分析し、各アクティビティについて考慮すべき企業内制約、地域や法制などの外部制約、技術的制約、用いるべきツールや評価手法、出力すべき結果などを明示し、フレームワークによる化学プロセス設計の実践を可能としている。

第6章は終章であり、本論文で構築した構造化フレームワークが、持続性を考慮した化学プロセス設計の実践的な支援を可能とすると結論づけている。加えて、提案されたフレームワークに関わる今後の研究課題についても述べられている。

以上要するに本論文は、再生可能なバイオマス資源を原料とする化学製品製造における資源、製品、プロセスを決定するという設計問題について、経済性、環境性、社会性の3指標を統合的に評価しながら意思決定を可能とする構造化されたフレームワークを提案し、ケーススタディによってその有効性を示している。この成果は、化石資源である石油を原料とする化学産業を再生可能なバイオマス資源を原料とする持続的な産業に転換することを具現化するために極めて有用であり、プロセスシステム工学、ライフサイクル工学および化学システム工学に大きく貢献するものである。

よって本論文は博士(工学)の学位請求論文として合格と認められる。