**1. Introduction**

The development of new process technologies using lignocellulosic feedstock as a carbon source for the production of fuels and chemicals is, currently, one of the main drivers of society to move towards a more sustainable future [1]. Second-generation biofuel plants are already a reality at a commercial scale and, to become truly sustainable and circular, industry is also increasingly viewing the production of chemicals from renewable resources as an attractive area for investment.

Biofuels and biochemicals can be produced in single product processes; however, their production in an integrated biorefinery is seen as a more e fficient and interesting approach to solve economic challenges related to biomass conversion processes since, currently, the cost of single biobased production processes, in many cases, still exceeds the cost of petrochemical production [2]. One of the main reasons for these high costs is the recalcitrant nature of biomass that, therefore requires a two-step

processing to obtain sugars for fermentation as follows: a pretreatment step to fractionate the material and solubilize especially hemicellulose sugars, and a subsequent hydrolysis step to recover glucose from cellulose. Pretreatment, in particular, is an energy intensive step and significantly contributes to the final cost of the process [3].

Itaconic acid stands out as one of the most relevant among the variety of chemicals that can be produced from lignocellulosic biomass, since it is a platform chemical with extensive applications in di fferent fields. Some of the main interests around itaconic acid arise from its potential to substitute petrochemically produced acrylic acid. However, it can also be used to produce biodegradable polymers, paints, varnishes, and di fferent organic compounds. Moreover, itaconic acid and its derivatives support the synthesis of a wide range of innovative polymers through crosslinking, with applications in special hydrogels for water decontamination, drug delivery, nanohydrogels for food applications, coatings, and elastomers [4].

Currently, itaconic acid is produced industrially from aerobic fungal fermentation using pure glucose as a carbon source, which is not the cheapest or the most sustainable substrate option. Moreover, although the production is done by fermentation, at present, the cost to produce itaconic acid is high and has been a bottleneck preventing its application in di fferent sectors [5]. With a market in expansion due to the increased number of potential applications (its market was worth USD 126.4 million in 2014 and with an expected growth rate of 60% it is predicted to reach around USD 204.6 million by 2023 [6]), the establishment of a more sustainable and cost-competitive process for the production of itaconic acid from renewable feedstock has been strongly encouraged. The present study aims to contribute with new knowledge to advance this area by using industrially produced bleached cellulose pulp as a feedstock for itaconic acid production.

Bleached cellulose pulp, which is the material used for paper manufacturing, is one of the most abundant raw materials worldwide. With a huge volume of production, and a weak demand from the paper industry in the last years, the stocks of bleached cellulose pulp have been extremely high and are posing a major problem for the entire pulp market, according to industry experts [7]. To overcome this problem, di fferent alternative uses for the pulp have been explored with the aim of promoting innovation and new business opportunities [8], including the production of biofuels, nanocellulose, and biocomposites.

Recently, attempts have been done to produce itaconic acid from di fferent types of biomass including beech wood [9], corn stover [10], wheat cha ff [11], rice husks [12], and corn cobs [13]. A comprehensive examination of the itaconic acid production from these di fferent feedstocks clearly demonstrates an important impact of biomass pretreatment steps, presence of inhibitor compounds, and fermentation conditions on itaconic acid yield and on the feasibility of the process in general.

This paper is the first study on the use of bleached cellulose pulp for the production of itaconic acid. In this study, the composition of cellulose pulp, as well as its degradation by enzymes and fermentability were some of the points explored to evaluate its feasibility for application in the production of itaconic acid. Then, e fforts were done to select process conditions able to result in an improved bioconversion e fficiency. Sterilization of the cellulose pulp hydrolysate through di fferent techniques, medium composition in terms of carbon-to-nitrogen ratio (C:N ratio) and initial glucose concentration, and oxygen availability were evaluated and discussed in detail. At the end, the process conditions that maximize the production of itaconic acid were selected and the results were compared with literature data from other feedstocks to conclude on the potential of this new bioprocess.
