Gasification has emerged as a prominent technique to convert biomass, coal, plastic, and municipals wastes sludge (generated from agriculture, industrial, and domestics, urban centers) into energy in the form of gaseous products. However, co-gasification of these materials has many advantages, such as desired product yield and uninterrupted feedstock supply as well as the sustainable utilization and disposal of these wastes. Numerous reviews have been documented based on the gasification of individual materials of biomass and coal, nevertheless, very few reviews have been reported on the process of co-gasification. In co-gasification, the effect of parameters becomes very important when dealing with the co-gasification of different mixed materials. The objective of this review to study the effect of temperature, blending ratio, and equivalence ratio (ER) on catalytic co-gasification of biomass-coal, biomass-plastic, biomass-sewage sludge, and mixed plastic blends. In addition, the effects of these parameters on gaseous products, heating values, tar formation, and gasification performance have been analyzed. It is also important to specify the ranges of parameters for the feed combinations in catalytic co-gasification that will provide a guideline for researchers and commercial enterprises to investigate co-gasification. For temperature from 650 to 750 °C found good for hydrogen rich syngas production. Whereas, the ratio of biomass 50% or above and ER of 0.20 and 0.25 were found good for higher hydrogen and lower CO₂ and tar production. Moreover, the current issues are related to technology, operational problems, policy requirements and route map for commercial success of co-gasification technology have been highlighted.

Graphical Abstract

Temperature is one of the most crucial parameters considered in the gasification process that influences the devolatilization process at all stages of gasification and its product gas composition. The conversion of biomass into gaseous products increases with an increase in the temperature due to the high volatile matter of biomass that enhances the solid to gas conversion at high temperature. The conversion of solid into the gaseous products also occurred in second phase due to the char gasification, methane reforming, and Boudouard reaction in gasification. Methane reforming, water gas shift reaction, and tar cracking were enhanced with the increase in temperature that increases the H₂ and CO content in the product gas. On the other hand, at lower temperatures, methane formation occurred which increased the CH₄ content in the product gas. Furthermore, tar cracking and reforming are endothermic reactions and enhance the gas yield at high temperature. The effect of temperature in discrete biomass gasification has been studied by many researchers. The effect of temperature on different blended feedstocks in gasification is also important due to the presence of different hydrogen, carbon, and oxygen ratios (H/C and O/C) of two or more materials gasified at the same time in a gasifier. It is also important to consider the effect of catalysts used in the co-gasification of blended feedstock on the temperature of the gasification process.

Effect of temperature on H₂ concentration (vol%) from co-gasification of (a) biomass-coal, (b) biomass-plastic, (c) biomass-sewage sludge, and (d) miscellaneous feedstock.

Enhanced Efficiency: Identifying and understanding the key process parameters in catalytic co-gasification can lead to improved efficiency in the conversion of biomass and other feedstocks into syngas. Optimizing these parameters can result in higher gas yields and better energy conversion rates.

Reduced Environmental Impact: By optimizing process parameters, catalytic co-gasification can potentially reduce the environmental impact of gasification processes. This includes lower emissions of greenhouse gases and pollutants compared to traditional fossil fuel combustion methods.

Increased Resource Utilization: Catalytic co-gasification allows for the simultaneous conversion of multiple feedstocks, including biomass and waste materials. By optimizing process parameters, it becomes possible to effectively utilize a wider range of feedstocks, thereby reducing waste and maximizing resource utilization.

Flexibility and Versatility: Understanding the influence of process parameters enables the design of catalytic co-gasification systems that are more flexible and versatile. This flexibility allows for the adaptation of the process to different feedstock compositions and operating conditions, enhancing its applicability across various industries and regions.

Effect of biomass blending ratio on H₂ concentration (vol%)from co-gasification of (a) biomass-coal, (b) biomass-plastic, (c) biomass-sewage sludge, and (d) miscellaneous feedstock.

Industry Demand: Determine the demand within industries related to catalytic co-gasification, such as energy production, chemical manufacturing, and environmental engineering. Look into trends, policies, and initiatives that drive the need for efficient and sustainable gasification processes.

Research Interest: Investigate the current level of research interest in catalytic co-gasification. Explore recent publications, conference proceedings, and funding opportunities in this field to gauge the interest and investment in understanding process parameters.

Technological Advancements: Assess the pace of technological advancements in catalytic co-gasification and related areas. Identify any emerging technologies or innovations that could benefit from a comprehensive review of process parameters.

Competitive Landscape: Analyze existing literature and publications on catalytic co-gasification to understand the competitive landscape. Identify gaps or areas where existing reviews may be lacking, and position your critical review to address these gaps effectively.

Effect of equivalence ratio (ER) on the gaseous composition from co-gasification of (a) biomass-coal, (b) biomass-plastic, (c) biomass-sewage sludge, and (d) miscellaneous feedstock.